diff --git a/AGENTS.md b/AGENTS.md
index 168db54..cc4ad04 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -12,16 +12,21 @@ BTRC Hub / タグ広場 is a split Rails API and React frontend repository.
 ## Stack
 
 - Backend: Ruby `3.2.2` from `backend/.ruby-version`, Rails `~> 8.0.2`.
-- Backend dependencies include `mysql2`, `sqlite3`, `rspec-rails`, `factory_bot_rails`, `rack-cors`, `jwt`, `discard`, `gollum`, `whenever`, `aws-sdk-s3`, `brakeman`, and `rubocop-rails-omakase`.
+- Backend dependencies include `mysql2`, `sqlite3`, `rspec-rails`,
+  `factory_bot_rails`, `rack-cors`, `jwt`, `discard`, `gollum`, `whenever`,
+  `aws-sdk-s3`, `brakeman`, and `rubocop-rails-omakase`.
 - Frontend: React `^19.1.0`, TypeScript `~5.8.3`, Vite `^6.3.5`.
-- Frontend data/UI dependencies include Axios, TanStack Query, Tailwind CSS, Framer Motion, Radix UI components, lucide-react, MDX/Markdown tooling, and Zustand.
+- Frontend data/UI dependencies include Axios, TanStack Query, Tailwind CSS,
+  Framer Motion, Radix UI components, lucide-react, MDX/Markdown tooling, and
+  Zustand.
 
 ## Main directories
 
 - `backend/app/controllers`: Rails API controllers.
 - `backend/app/models`: Active Record models.
 - `backend/app/representations`: API response representation classes.
-- `backend/app/services`: domain services such as version recording, wiki commit, YouTube sync, and similarity calculation.
+- `backend/app/services`: domain services such as version recording,
+  wiki commit, YouTube sync, and similarity calculation.
 - `backend/config/routes.rb`: API routes.
 - `backend/db/migrate`: migrations.
 - `backend/db/schema.rb`: current schema snapshot.
@@ -84,52 +89,210 @@ cd frontend
 npm run dev
 npm run build
 npm run lint
+npm run test
+npm run test:run
 npm run preview
 ```
 
-`npm run build` runs `tsc -b && vite build`, then `postbuild` runs `node scripts/generate-sitemap.js`.
+`npm run build` runs `tsc -b && vite build`, then `postbuild` runs
+`node scripts/generate-sitemap.js`.
 
-Do not write or report `npm test` as a repository command unless a `test` script is added to `frontend/package.json`.
+`npm run test` runs Vitest in watch mode. Use `npm run test:run` for a non-watch frontend test run.
 
 ## Coding style
 
 - Prefer precise, minimal changes.
 - Do not flatter or over-explain.
 - Explain risks directly.
-- Prefer single quotes for strings unless interpolation or escaping makes double quotes better.
+- Prefer single quotes for strings unless interpolation or escaping makes
+  double quotes better.
 - Ruby: never put a space before method-call parentheses.
+- Ruby: `render` 系メソッド呼び出しでは、keyword 引数付きでも括弧を書かない。
+- Ruby: never put a line break immediately before `)`.
 - Ruby: do not use `%w` or `%i`.
-- TypeScript and Python: use GNU-style spacing before parentheses where syntactically valid.
+- In Ruby, when an `if` condition is split across multiple lines and combines
+  clauses with `&&` or `||`, wrap the whole condition in parentheses.
+- Ruby hashes are not blocks; keep `}` on the same line as the final pair.
+- Ruby hashes keep the first pair on the same line as `{` unless line length
+  requires a break.
+- Short Ruby hashes may stay visually compact across two lines with the first
+  pair kept on the opening line and aligned continuation pairs below it.
+- Ruby blocks use separate `{ ... }` rules from hashes, with 2-space body
+  indentation.
+- For arrays, never put whitespace or a line break immediately before `]`.
+- Keep the first element on the same line as `[` by default.
+- If an array would exceed the line limit, break after `[` and indent
+  elements by 4 spaces.
+- TypeScript and Python: use GNU-style spacing before parentheses where
+  syntactically valid.
+- Never write Ruby, TypeScript, or TSX lines longer than 99 characters.
+- Aim to keep Ruby, TypeScript, and TSX lines within 79 characters where practical.
+- TypeScript and TSX use 4-space logical indentation.
+- In TypeScript and TSX only, replace every leading run of 8 spaces with a tab.
+- Tabs are only for leading indentation, never for spaces after non-space text.
+- TypeScript and TSX imports may stay on one line if they remain within the
+  line limit; do not expand short type-only imports mechanically.
+- In TypeScript and TSX, when a function takes one destructured object
+  argument plus an inline type, prefer this shape when it fits locally:
+
+```ts
+const helper = (
+    { value, flag }: { value: string
+		       flag:  boolean },
+): Result => {
+  // ...
+}
+```
+
+- In TypeScript and TSX, put `switch` case block braces on their own lines
+  when a case needs a lexical block:
+
+```ts
+case 'yes':
+case 'no':
+  {
+    const expected = valueFor (item)
+    return expected == null || expected === answer
+  }
+```
+
+- In TypeScript and TSX, use `value == null` and `value != null` as the
+  default nullish checks. Do not use `=== null`, `=== undefined`,
+  `!== null`, or `!== undefined`.
+- If code appears to need a distinction between `null` and `undefined`, treat
+  that as a design smell and revise the logic to avoid the distinction.
+  External library APIs that explicitly require distinguishing the two are the
+  only exception.
+- In TypeScript and TSX, keep short arrays on one line when they fit under the
+  line limit; break arrays only when readability or line length requires it.
+- In TypeScript and TSX, when a ternary expression is split across multiple
+  lines, align `?` and `:` with the condition expression. Do not indent `?` and
+  `:` one extra level under the condition.
+
+```ts
+const value =
+    condition
+    ? consequent
+    : alternate
+```
+
+- In TypeScript and TSX, keep short ternary expressions on one line when they
+  fit cleanly under the line limit.
+- In TypeScript and TSX, prefer ternary expressions for simple conditional
+  value selection. Do not replace a clear ternary with `if` statements, and do
+  not introduce immediately invoked functions just to avoid or reformat a
+  ternary expression.
+- In TypeScript and TSX, do not write `let` followed by later `if` assignments
+  when the value can be expressed as a single `const` initializer. Prefer
+  `const` because it prevents accidental later reassignment.
+- When fixing formatting, change formatting only. Do not change expression
+  structure, control flow, or variable mutability unless the requested style
+  explicitly requires it.
 - Do not add production dependencies without explicit approval.
+- Do not create, modify, or run tests unless the user explicitly asks for
+  test work. When the user asks for tests, keep working and rerun them until
+  they pass or the remaining failure is clearly blocked.
 
 ## Backend rules
 
-- Inspect existing routes, controllers, models, services, and specs before editing backend behavior.
-- For API behavior changes, add or update request specs under `backend/spec/requests`.
-- Prefer RSpec for new backend tests; existing minitest files under `backend/test` do not make minitest the default for new coverage.
+- Inspect existing routes, controllers, models, services, and specs before
+  editing backend behavior.
+- For API behavior changes, add or update request specs under
+  `backend/spec/requests` only when the user explicitly asks for tests.
+- Prefer RSpec for new backend tests; existing minitest files under
+  `backend/test` do not make minitest the default for new coverage.
 - Do not weaken authentication, BAN user checks, or IP BAN checks.
-- Preserve the `X-Transfer-Code` user identification flow unless the task explicitly changes authentication.
-- Be careful with version tables, `version_no`, optimistic concurrency, wiki revisions, and restore/diff behavior.
+- Preserve the `X-Transfer-Code` user identification flow unless the task
+  explicitly changes authentication.
+- Be careful with version tables, `version_no`, optimistic concurrency,
+  wiki revisions, and restore/diff behavior.
 - Be careful with tag names, tag normalization, implications, similarities, and discard behavior.
+- Be sensitive to N+1 queries; avoid introducing them and proactively fix
+  existing N+1 issues in the code path being edited.
 - Keep migration files and `backend/db/schema.rb` consistent when changing schema.
 
 ## Frontend rules
 
 - Use `frontend/src/lib/api.ts` for API calls so headers and camelCase conversion stay consistent.
-- Add or reuse TanStack Query keys through `frontend/src/lib/queryKeys.ts`; avoid ad hoc query key arrays.
+- Add or reuse TanStack Query keys through `frontend/src/lib/queryKeys.ts`;
+  avoid ad hoc query key arrays.
 - Encode URL path-segment values with `encodeURIComponent`.
 - React hooks must be called unconditionally.
-- Keep page-level code under `frontend/src/pages` and shared UI/feature code under `frontend/src/components` unless existing patterns point elsewhere.
+- Keep page-level code under `frontend/src/pages` and shared UI/feature code
+  under `frontend/src/components` unless existing patterns point elsewhere.
 - Match existing Tailwind, component, and import alias conventions.
+- In TypeScript and TSX, prefer direct comparison operators such as `===` and
+  `!==` over negating a comparison like `!(a === b)`.
+- In TypeScript and TSX, prefer `++i` or `--i` over `i += 1` or `i -= 1` for
+  simple unit-step counter updates.
+- For user-facing Japanese text, prefer modern kana usage and natural current
+  phrasing over historical spellings or awkward literal wording.
+- For user-facing Japanese ellipses, prefer `……` over ASCII `...`.
+
+### Frontend TSX style
+
+- Preserve the local TSX formatting style.
+- Do not normalize TSX to common Prettier-style React formatting unless
+  explicitly asked.
+- Prefer `const` arrow functions for TypeScript/TSX component and helper declarations.
+- Put two blank lines before and after top-level `const` function
+  declarations, unless imports, exports, or file boundaries make that awkward.
+- In TSX, indent with 4-space logical indentation.
+- A leading tab is exactly equivalent to 8 leading spaces.
+- Keep a tag's closing marker on the same line as the final prop when the tag
+  spans multiple lines.
+- Do not put `/>` or `>` on its own line unless the existing surrounding code
+  does so.
+- Keep JSX closing parentheses in the existing compact style, for example
+  `</div>)` rather than moving `)` onto a separate line.
+- Do not add braces around `if`, `else`, or `for` bodies when the body is a
+  single physical line.
+- Always add braces around `if`, `else`, or `for` bodies when the body spans
+  two or more physical lines, even if it is one statement.
+- Do not use a leading semicolon for expression statements such as
+  `;([...]).forEach(...)`; rewrite the expression to avoid ASI hazards
+  explicitly, for example with `void`.
+
+Preferred:
+
+```tsx
+const PostFormTagsArea: FC<Props> = ({ tags, setTags, errors, ...rest }) => {
+  return (
+      <TextArea
+	  {...rest}
+	  ref={ref}
+	  value={tags}
+	  invalid={errors && errors.length > 0}
+	  onChange={ev => setTags (ev.target.value)}/>)
+}
+```
+
+Avoid:
+
+```tsx
+function PostFormTagsArea ({ tags, setTags }: Props) {
+  return (
+    <TextArea
+      value={tags}
+      onChange={ev => setTags (ev.target.value)}
+    />
+  )
+}
+```
 
 ## Codex workflow
 
 - First inspect existing patterns; do not invent new architecture when a local convention exists.
 - Keep changes scoped to the requested issue.
-- Do not scan or summarize dependency/generated/runtime directories such as `node_modules`, `dist`, `tmp`, `log`, and `storage` unless explicitly needed.
-- Before touching wiki, tag, versioning, BAN, IP BAN, or authentication behavior, inspect the related request specs and service objects.
-- If frontend code changes, run the existing frontend verification commands that apply: `npm run build` and `npm run lint`.
-- If backend code changes, run the relevant RSpec command; for broad backend changes, run `bundle exec rspec`.
+- Do not scan or summarize dependency/generated/runtime directories such as
+  `node_modules`, `dist`, `tmp`, `log`, and `storage` unless explicitly needed.
+- Before touching wiki, tag, versioning, BAN, IP BAN, or authentication
+  behavior, inspect the related request specs and service objects.
+- If frontend code changes, run only non-test verification commands that
+  apply, such as `npm run build` and `npm run lint`. Run `npm run test:run`
+  only when the user explicitly asks for tests.
+- If backend code changes, do not run RSpec unless the user explicitly asks
+  for tests.
 - If a verification command cannot be run or fails, report the exact command and failure.
 
 ## Completion criteria
@@ -137,7 +300,8 @@ Do not write or report `npm test` as a repository command unless a `test` script
 A task is complete only when:
 
 - implementation is complete,
-- relevant verification commands pass, or failures are clearly explained,
+- relevant non-test verification commands pass, or failures are clearly
+  explained,
 - unrelated files are not changed,
 - migrations and schema are consistent when schema changes are made,
 - user-facing behavior is documented when needed.
diff --git a/backend/AGENTS.md b/backend/AGENTS.md
index 33d1b1f..2953f22 100644
--- a/backend/AGENTS.md
+++ b/backend/AGENTS.md
@@ -4,7 +4,9 @@
 
 These rules apply to work under `backend/`.
 
-This is a Rails API app using Active Record, RSpec, request specs, service objects, representation classes, and version tables for post/tag/wiki history.
+This is a Rails API app using Active Record, RSpec, request specs,
+service objects, representation classes, and version tables for post/tag/wiki
+history.
 
 ## Commands
 
@@ -45,37 +47,72 @@ bundle exec rspec
 
 If a command cannot be run or fails, report the exact command and failure.
 
+Do not create, modify, or run tests unless the user explicitly asks for test
+work. When the user asks for tests, keep working and rerun them until they
+pass or the remaining failure is clearly blocked.
+
 ## Rails structure
 
 - `app/controllers`: API controllers.
 - `app/models`: Active Record models and concerns.
 - `app/representations`: JSON response shaping.
-- `app/services`: domain services such as version recorders, wiki commit, YouTube sync, and similarity calculation.
+- `app/services`: domain services such as version recorders, wiki commit,
+  YouTube sync, and similarity calculation.
 - `config/routes.rb`: public API routes.
 - `db/migrate`: migrations.
 - `db/schema.rb`: schema snapshot.
 - `lib/tasks`: custom Rake tasks.
 - `spec`: RSpec tests.
 
-Before changing behavior, inspect the matching route, controller, model, service, representation, and spec.
+Before changing behavior, inspect the matching route, controller, model,
+service, representation, and spec.
 
 ## Ruby style
 
 - Prefer precise, minimal changes.
 - Use single quotes unless interpolation or escaping makes double quotes better.
 - Do not put a space before Ruby method-call parentheses.
+- For `render`-family method calls, omit parentheses even when passing
+  keyword arguments.
+- Never put a line break immediately before `)` in Ruby.
 - Do not use `%w` or `%i` in new Ruby code.
+- Never write a Ruby line longer than 99 characters.
+- Aim to keep Ruby lines within 79 characters where practical.
+- For small Ruby method definitions that take keyword arguments, match the
+  local no-parentheses style when nearby code uses it.
+- When an `if` condition is split across multiple lines and combines clauses
+  with `&&` or `||`, wrap the whole condition in parentheses.
+- Treat Ruby hash `{ ... }` style and Ruby block `{ ... }` style as separate
+  rules.
+- Do not format Ruby hashes like Ruby blocks.
+- For Ruby hashes, keep the closing `}` on the same line as the final pair.
+- Keep the first pair on the same line as `{` by default.
+- Short Ruby hashes may stay visually compact across two lines with the first
+  pair kept on the opening line and aligned continuation pairs below it.
+- If the hash would exceed the line limit, break after `{` and indent pairs
+  by 4 spaces.
+- Put one logical pair per line when the expression would otherwise become
+  dense.
+- For Ruby arrays, never put whitespace or a line break immediately before `]`.
+- Keep the first element on the same line as `[` by default.
+- If an array would exceed the line limit, break after `[` and indent
+  elements by 4 spaces.
+- For Ruby blocks, use 2-space indentation for the block body.
 - Keep comments short and useful; avoid narrating obvious code.
 - Do not add production dependencies without approval.
 
 ## Authentication and authorization
 
-- Authentication is handled through the `X-Transfer-Code` header in `ApplicationController#authenticate_user`.
+- Authentication is handled through the `X-Transfer-Code` header in
+  `ApplicationController#authenticate_user`.
 - `current_user` is set by looking up `User.inheritance_code`.
-- Do not bypass or weaken the `X-Transfer-Code` flow unless the task explicitly changes authentication.
-- Unauthenticated write actions should return `:unauthorized` consistently with existing controllers.
+- Do not bypass or weaken the `X-Transfer-Code` flow unless the task
+  explicitly changes authentication.
+- Unauthenticated write actions should return `:unauthorized` consistently
+  with existing controllers.
 - Role checks use `User` enum roles: `guest`, `member`, and `admin`.
-- Use `current_user.gte_member?` for member-or-admin write permissions where existing controllers do so.
+- Use `current_user.gte_member?` for member-or-admin write permissions where
+  existing controllers do so.
 - Use `current_user.admin?` only for admin-only paths, such as tag child relationship changes.
 - Do not replace role checks with looser presence checks.
 
@@ -88,7 +125,9 @@ Before changing behavior, inspect the matching route, controller, model, service
 - User and IP bans use `banned_at`, not a boolean `banned` column.
 - `User#banned?` and `IpAddress#banned?` check `banned_at.present?`.
 - Do not weaken BAN or IP BAN behavior.
-- If changing request authentication or controller before actions, add or update request specs covering banned users and banned IP addresses.
+- If changing request authentication or controller before actions, add or
+  update request specs covering banned users and banned IP addresses only when
+  the user explicitly asks for tests.
 
 ## RSpec
 
@@ -99,49 +138,88 @@ Before changing behavior, inspect the matching route, controller, model, service
 - Put Rake task coverage under `spec/tasks`.
 - `spec/rails_helper.rb` loads `spec/support/**/*.rb`.
 - Request specs include `AuthHelper` and `JsonHelper`.
-- `AuthHelper#sign_in_as(user)` stubs `ApplicationController#current_user`; use it when matching existing request spec style.
-- Add or update request specs for API behavior changes, especially status codes, permissions, response shape, and version conflict behavior.
+- `AuthHelper#sign_in_as(user)` stubs
+  `ApplicationController#current_user`; use it when matching existing
+  request spec style.
+- Add or update request specs for API behavior changes only when the user
+  explicitly asks for tests, especially status codes, permissions, response
+  shape, and version conflict behavior.
 
 ## Migrations
 
 - Keep migrations and `db/schema.rb` consistent.
 - Use reversible migrations where practical; otherwise define explicit `up` and `down`.
-- For data backfills inside migrations, follow the existing pattern of defining migration-local `ActiveRecord::Base` classes with `self.table_name`.
+- For data backfills inside migrations, follow the existing pattern of
+  defining migration-local `ActiveRecord::Base` classes with
+  `self.table_name`.
 - Preserve existing indexes, foreign keys, check constraints, and null constraints.
 - Be careful with MySQL-specific options already present in migrations, such as `after:`.
-- Do not edit old migrations just to change current behavior unless explicitly requested; add a new migration.
+- Do not edit old migrations just to change current behavior unless
+  explicitly requested; add a new migration.
 
 ## Version tables
 
 - Versioned records include posts, tags, nico tags, and wiki pages.
-- Current records have `version_no`; version tables have positive `version_no` with unique indexes scoped to the parent record.
+- Current records have `version_no`; version tables have positive
+  `version_no` with unique indexes scoped to the parent record.
 - Version event types are `create`, `update`, `discard`, and `restore`.
 - Version rows are readonly through the `VersionRecord` concern.
-- Use the existing recorder services instead of manually inserting version rows in application code:
+- Use the existing recorder services instead of manually inserting version
+  rows in application code:
   - `PostVersionRecorder`
   - `TagVersionRecorder`
   - `NicoTagVersionRecorder`
   - `WikiVersionRecorder`
   - `TagVersioning`
-- `VersionRecorder` locks the current record, validates sequence consistency, skips unchanged update snapshots, creates the next version row, and updates the record `version_no`.
+- `VersionRecorder` locks the current record, validates sequence consistency,
+  skips unchanged update snapshots, creates the next version row, and updates
+  the record `version_no`.
 - Do not update versioned records without considering whether a version snapshot must be created.
-- For optimistic concurrency paths, preserve `base_version_no`, `force`, and `merge` semantics and cover conflicts in request specs.
+- For optimistic concurrency paths, preserve `base_version_no`, `force`, and
+  `merge` semantics. Cover conflicts in request specs only when the user
+  explicitly asks for tests.
 
 ## Domain cautions
 
-- Posts have tag snapshots, parent post implications, original-created ranges, viewed state, and version conflict behavior.
-- Tags have canonical names, aliases through `TagName`, categories, parent implications, discard behavior, and version snapshots.
-- Nico tags have separate relation/version behavior; do not treat them like normal editable tags without checking existing code.
-- Wiki pages involve page content, revisions/history, version rows, title/tag-name behavior, and diff/restore paths.
-- Materials, theatres, and comments have user and permission checks; inspect the controller before changing them.
+- Posts have tag snapshots, parent post implications, original-created ranges,
+  viewed state, and version conflict behavior.
+- Tags have canonical names, aliases through `TagName`, categories, parent
+  implications, discard behavior, and version snapshots.
+- Nico tags have separate relation/version behavior; do not treat them like
+  normal editable tags without checking existing code.
+- Wiki pages involve page content, revisions/history, version rows,
+  title/tag-name behavior, and diff/restore paths.
+- Materials, theatres, and comments have user and permission checks; inspect
+  the controller before changing them.
 
 ## API responses
 
 - Use representation classes under `app/representations` when existing endpoints do.
-- Keep response keys consistent with existing JSON contracts; frontend code expects camelCase conversion client-side, while Rails params and JSON keys are generally snake_case.
-- Preserve existing HTTP status conventions: `:unauthorized` for no user, `:forbidden` for insufficient role or banned user, `:not_found` for missing records, and `:unprocessable_entity` for validation failures.
+- Keep response keys consistent with existing JSON contracts.
+- Frontend code expects camelCase conversion client-side, while Rails params
+  and JSON keys are generally snake_case.
+- Preserve existing HTTP status conventions:
+  `:unauthorized` for no user, `:forbidden` for insufficient role or banned
+  user, `:not_found` for missing records, and `:unprocessable_entity` for
+  validation failures.
+- For diagnostic or internal helper JSON, prefer a deliberately light response
+  shape over full representation classes when callers only need identifiers,
+  labels, URLs, or weights.
+
+## Active Record performance
+
+- When a controller action serializes nested associations, preload the
+  associations it will touch instead of allowing N+1 queries.
+- Be sensitive to N+1 queries in all backend work.
+- Avoid introducing N+1 queries, and proactively fix existing N+1 issues when
+  you find them in the code path you are editing.
+- When an association may already be preloaded, prefer loaded-association
+  checks that reuse the preloaded data without losing the efficient database
+  path.
 
 ## Files to avoid in routine work
 
-- Do not inspect or edit `tmp/`, `log/`, `storage/`, `vendor/`, or dependency directories unless explicitly needed.
-- Do not modify generated schema or migration output without the corresponding migration when schema changes are made.
+- Do not inspect or edit `tmp/`, `log/`, `storage/`, `vendor/`, or dependency
+  directories unless explicitly needed.
+- Do not modify generated schema or migration output without the corresponding
+  migration when schema changes are made.
diff --git a/backend/Gemfile b/backend/Gemfile
index 2d0a90c..7b44641 100644
--- a/backend/Gemfile
+++ b/backend/Gemfile
@@ -69,3 +69,5 @@ gem 'discard'
 gem "rspec-rails", "~> 8.0", :groups => [:development, :test]
 
 gem 'aws-sdk-s3', require: false
+
+gem 'rails-i18n', '~> 8.0.0'
diff --git a/backend/Gemfile.lock b/backend/Gemfile.lock
index f9dc02c..555f867 100644
--- a/backend/Gemfile.lock
+++ b/backend/Gemfile.lock
@@ -306,6 +306,9 @@ GEM
     rails-html-sanitizer (1.6.2)
       loofah (~> 2.21)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
+    rails-i18n (8.0.2)
+      i18n (>= 0.7, < 2)
+      railties (>= 8.0.0, < 9)
     railties (8.0.2)
       actionpack (= 8.0.2)
       activesupport (= 8.0.2)
@@ -477,6 +480,7 @@ DEPENDENCIES
   puma (>= 5.0)
   rack-cors
   rails (~> 8.0.2)
+  rails-i18n (~> 8.0.0)
   rspec-rails (~> 8.0)
   rubocop-rails-omakase
   sprockets-rails
diff --git a/backend/app/controllers/application_controller.rb b/backend/app/controllers/application_controller.rb
index 4f3d6ed..42adc75 100644
--- a/backend/app/controllers/application_controller.rb
+++ b/backend/app/controllers/application_controller.rb
@@ -1,4 +1,7 @@
 class ApplicationController < ActionController::API
+  rescue_from ActiveRecord::RecordInvalid, with: :render_record_invalid
+  rescue_from ActiveRecord::RecordNotUnique, with: :render_record_not_unique
+
   before_action :reject_banned_ip_address!
   before_action :authenticate_user
   before_action :reject_banned_user!
@@ -25,6 +28,27 @@ class ApplicationController < ActionController::API
     end
   end
 
+  def render_bad_request message = 'リクエストが不正です．'
+    render json: { type: 'bad_request',
+                   message:,
+                   errors: { },
+                   base_errors: [message] },
+           status: :bad_request
+  end
+
+  def render_unprocessable_entity message = '入力を確認してください．', field: nil
+    render_validation_error(fields: field ? { field => [message] } : { },
+                            base: field ? [] : [message])
+  end
+
+  def render_record_invalid error
+    render_validation_error error.record
+  end
+
+  def render_record_not_unique _error = nil
+    render_validation_error base: ['すでに存在してゐます．']
+  end
+
   def reject_banned_ip_address!
     ip_address = IpAddress.find_by(ip_address: IPAddr.new(request.remote_ip).hton)
     return unless ip_address&.banned?
@@ -37,4 +61,28 @@ class ApplicationController < ActionController::API
 
     head :forbidden
   end
+
+  def render_validation_error record = nil, fields: { }, base: [], status: :unprocessable_entity
+    errors = { }
+
+    if record
+      record.errors.each do |error|
+        errors[error.attribute] ||= []
+        errors[error.attribute] << error.message
+      end
+    end
+
+    fields.each do |attr, messages|
+      errors[attr.to_sym] ||= []
+      errors[attr.to_sym].concat(Array(messages))
+    end
+
+    base_errors = Array(base) + Array(errors.delete(:base))
+
+    render json: { type: 'validation_error',
+                   message: '入力内容を確認してください．',
+                   errors:,
+                   base_errors: },
+           status:
+  end
 end
diff --git a/backend/app/controllers/deerjikists_controller.rb b/backend/app/controllers/deerjikists_controller.rb
index dff9d82..9302370 100644
--- a/backend/app/controllers/deerjikists_controller.rb
+++ b/backend/app/controllers/deerjikists_controller.rb
@@ -2,7 +2,8 @@ class DeerjikistsController < ApplicationController
   def show
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
-    return head :bad_request if platform.blank? || code.blank?
+    return render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if code.blank?
 
     deerjikist = Deerjikist
                  .joins(:tag)
@@ -22,7 +23,9 @@ class DeerjikistsController < ApplicationController
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     tag_id = params[:tag_id].to_i
-    return head :bad_request if platform.blank? || code.blank? || tag_id <= 0
+    return render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if code.blank?
+    return render_bad_request('tag_id が不正です．') if tag_id <= 0
 
     deerjikist = Deerjikist.find_or_initialize_by(platform:, code:).tap do |d|
       d.tag_id = tag_id
@@ -38,7 +41,8 @@ class DeerjikistsController < ApplicationController
 
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
-    return head :bad_request if platform.blank? || code.blank?
+    return render_bad_request('platform は必須です．') if platform.blank?
+    return render_bad_request('code は必須です．') if code.blank?
 
     Deerjikist.find([platform, code]).destroy!
 
diff --git a/backend/app/controllers/gekanator_games_controller.rb b/backend/app/controllers/gekanator_games_controller.rb
new file mode 100644
index 0000000..ad3aebf
--- /dev/null
+++ b/backend/app/controllers/gekanator_games_controller.rb
@@ -0,0 +1,272 @@
+class GekanatorGamesController < ApplicationController
+  def create
+    return head :unauthorized unless current_user
+
+    guessed_post_id = params.require(:guessed_post_id)
+    correct_post_id = params[:correct_post_id].presence
+    answers = params.require(:answers).as_json
+
+    game = GekanatorGame.new(
+        user: current_user,
+        guessed_post_id:,
+        correct_post_id:,
+        won: correct_post_id.present? && guessed_post_id.to_i == correct_post_id.to_i,
+        question_count: answers.length,
+        answers:)
+
+    if game.invalid?
+      render json: { errors: game.errors.full_messages }, status: :unprocessable_entity
+      return
+    end
+
+    learned_example_count = 0
+
+    ActiveRecord::Base.transaction do
+      game.save!
+      learned_example_count = learn_answers_from_game!(game)
+    end
+
+    render json: {
+      id: game.id,
+      learned_example_count:
+    }, status: :created
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
+  end
+
+  def extra_questions
+    game = find_owned_game
+    return if performed?
+
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .where(kind: 'post_similarity', source: 'user_suggested')
+        .to_a
+
+    selected =
+        prioritized_extra_questions(
+            questions,
+            post_id: game.correct_post_id,
+            user: current_user,
+            limit: 6)
+
+    render json: {
+      questions: selected.map { |question| extra_question_json(question) }
+    }
+  end
+
+  def extra_question_answers
+    game = find_owned_game
+    return if performed?
+
+    answer_params = params.require(:answers)
+    if !answer_params.is_a?(Array)
+      return render_validation_error fields: { answers: ['配列で指定してください．'] }
+    end
+
+    answers = answer_params.map { |answer|
+      {
+        question_id: answer.require(:question_id).to_i,
+        answer: answer.require(:answer)
+      }
+    }
+    questions = GekanatorQuestion.where(id: answers.map { _1[:question_id] })
+    question_by_id = questions.index_by(&:id)
+    if questions.length != answers.length
+      return render_validation_error fields: { answers: ['質問が見つかりません．'] }
+    end
+    if questions.any? { |question| question.status != 'accepted' || question.kind != 'post_similarity' }
+      return render_validation_error fields: { answers: ['質問が不正です．'] }
+    end
+
+    ActiveRecord::Base.transaction do
+      answers.each do |item|
+        question = question_by_id[item[:question_id]]
+        example =
+            GekanatorQuestionExample.find_or_initialize_by(
+                gekanator_question: question,
+                post: game.correct_post,
+                user: current_user)
+        example.record_answer!(
+            answer: item[:answer],
+            source: 'post_game_extra',
+            gekanator_game: game)
+        example.save!
+      end
+    end
+
+    render json: { count: answers.length }, status: :created
+  end
+
+  private
+
+  def extra_question_json question
+    {
+      id: question.id,
+      text: question.text,
+      source: question.source,
+      priority_weight: question.priority_weight
+    }
+  end
+
+  def prioritized_extra_questions questions, post_id:, user:, limit:
+    answered_question_ids =
+        GekanatorQuestionExample
+        .where(user:, gekanator_question_id: questions.map(&:id))
+        .distinct
+        .pluck(:gekanator_question_id)
+    unanswered, answered =
+        questions.partition { |question| !answered_question_ids.include?(question.id) }
+    selected = weighted_sample_questions(unanswered, post_id:, limit:)
+    return selected if selected.length >= limit
+
+    selected + weighted_sample_questions(
+        answered.reject { |question| selected.any? { _1.id == question.id } },
+        post_id:,
+        limit: limit - selected.length)
+  end
+
+  def weighted_sample_questions questions, post_id:, limit:
+    remaining = questions.uniq(&:id)
+    selected = []
+
+    while selected.length < limit && remaining.any?
+      weighted =
+          remaining.map { |question|
+            [question, selection_weight_for(question, post_id: post_id)]
+          }
+      total_weight = weighted.sum { |_question, weight| weight }
+      break if total_weight <= 0
+
+      target = rand * total_weight
+      cumulative = 0.0
+      chosen =
+          weighted.find do |_question, weight|
+            cumulative += weight
+            cumulative >= target
+          end&.first || weighted.first.first
+
+      selected << chosen
+      remaining.reject! { |question| question.id == chosen.id }
+    end
+
+    selected
+  end
+
+  def selection_weight_for question, post_id:
+    sample_count =
+        question.gekanator_question_examples.sum { |example|
+          next 0 unless example.post_id == post_id
+
+          example.sample_count.presence || 1
+        }
+
+    question.priority_weight.to_f / (1.0 + sample_count * 0.15)
+  end
+
+  def find_owned_game
+    return head :unauthorized unless current_user
+
+    game = GekanatorGame.find_by(id: params[:id])
+    return head :not_found unless game
+    if !current_user.admin? && game.user_id != current_user.id
+      return head :not_found
+    end
+
+    game
+  end
+
+  def learn_answers_from_game! game
+    correct_post = game.correct_post
+    return 0 if correct_post.blank?
+
+    accepted_questions =
+        GekanatorQuestion
+        .accepted
+        .index_by { |question| public_question_id_for(question) }
+    learned_count = 0
+
+    Array(game.answers).each do |answer|
+      answer_value = answer['answer'].to_s
+      next if answer_value.blank? || answer_value == 'unknown'
+
+      question_id = game_answer_question_id(answer)
+      next if question_id.blank?
+
+      question = accepted_questions[question_id.to_s]
+      next unless learnable_game_answer_question?(question)
+
+      example =
+          GekanatorQuestionExample.find_or_initialize_by(
+              gekanator_question: question,
+              post: correct_post,
+              user: current_user)
+      example.record_answer!(
+          answer: answer_value,
+          source: 'post_game_answer',
+          gekanator_game: game)
+      example.save!
+      learned_count += 1
+    end
+
+    learned_count
+  end
+
+  def public_question_id_for question
+    condition = normalize_condition(question.condition)
+
+    case condition[:type]
+    when 'tag'
+      "tag:#{condition[:key]}"
+    when 'source'
+      "source:#{condition[:host]}"
+    when 'original-year'
+      "original-year:#{condition[:year]}"
+    when 'original-month'
+      "original-month:#{condition[:month]}"
+    when 'original-month-day'
+      "original-month-day:#{condition[:monthDay] || condition[:month_day]}"
+    when 'title-length-at-least'
+      "title:length-at-least:#{condition[:length]}"
+    when 'title-length-greater-than'
+      "title:length-at-least:#{condition[:length].to_i + 1}"
+    when 'title-has-ascii'
+      'title:ascii'
+    when 'title-contains'
+      "title:contains:#{condition[:text]}"
+    when 'post-similarity'
+      "post-similarity:#{question.id}"
+    else
+      "catalog:#{question.id}"
+    end
+  end
+
+  def normalize_condition condition
+    json = condition.deep_dup.as_json
+
+    if json['type'] == 'original-month-day' && json['monthDay'].blank?
+      json['monthDay'] = json.delete('month_day')
+    end
+
+    json.deep_symbolize_keys
+  end
+
+  def learnable_game_answer_question? question
+    return false if question.nil?
+    return true if question.kind == 'post_similarity'
+    return false unless question.kind == 'tag'
+
+    condition = normalize_condition(question.condition)
+    key = condition[:key].to_s
+    !key.start_with?('nico:')
+  end
+
+  def game_answer_question_id answer
+    answer['question_id'] ||
+      answer[:question_id] ||
+      answer['questionId'] ||
+      answer[:questionId]
+  end
+end
diff --git a/backend/app/controllers/gekanator_posts_controller.rb b/backend/app/controllers/gekanator_posts_controller.rb
new file mode 100644
index 0000000..a176354
--- /dev/null
+++ b/backend/app/controllers/gekanator_posts_controller.rb
@@ -0,0 +1,71 @@
+class GekanatorPostsController < ApplicationController
+  def index
+    posts =
+        Post
+        .preload(:post_similarities, tags: :tag_name)
+        .with_attached_thumbnail
+        .order(Arel.sql(
+            'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE, ' \
+            'posts.original_created_from, posts.created_at) DESC, posts.id DESC'))
+        .to_a
+
+    active_tags_by_post_id =
+        posts.each_with_object({ }) do |post, h|
+          h[post.id] = post.tags.reject(&:deprecated?)
+        end
+
+    render json: {
+      posts: posts.map { |post|
+        post_json(post,
+                  active_tags_by_post_id:)
+      }
+    }
+  end
+
+  private
+
+  def post_json post, active_tags_by_post_id:
+    {
+      id: post.id,
+      url: post.url,
+      title: post.title,
+      thumbnail: thumbnail_url(post),
+      thumbnail_base: post.thumbnail_base,
+      original_created_from: post.original_created_from,
+      original_created_before: post.original_created_before,
+      post_similarity_edges: post_similarity_edges_json(
+          post,
+          active_tags_by_post_id:),
+      tags: active_tags_by_post_id.fetch(post.id, []).map { |tag| tag_json(tag) }
+    }
+  end
+
+  def post_similarity_edges_json post, active_tags_by_post_id:
+    post
+        .post_similarities
+        .filter_map do |similarity|
+          next unless active_tags_by_post_id.key?(similarity.target_post_id)
+
+          {
+            target_post_id: similarity.target_post_id,
+            cos: similarity.cos.to_f
+          }
+        end
+  end
+
+  def tag_json tag
+    {
+      id: tag.id,
+      name: tag.name,
+      category: tag.category
+    }
+  end
+
+  def thumbnail_url post
+    return nil unless post.thumbnail.attached?
+
+    rails_storage_proxy_url(post.thumbnail, only_path: false)
+  rescue
+    nil
+  end
+end
diff --git a/backend/app/controllers/gekanator_question_suggestions_controller.rb b/backend/app/controllers/gekanator_question_suggestions_controller.rb
new file mode 100644
index 0000000..a73bfca
--- /dev/null
+++ b/backend/app/controllers/gekanator_question_suggestions_controller.rb
@@ -0,0 +1,95 @@
+class GekanatorQuestionSuggestionsController < ApplicationController
+  def create
+    return head :unauthorized unless current_user
+
+    game = GekanatorGame.find_by(id: params.require(:gekanator_game_id))
+    return head :not_found unless game
+    if !current_user.admin? && game.user_id != current_user.id
+      return head :not_found
+    end
+
+    existing_question_id = params[:existing_question_id].presence
+    if existing_question_id
+      question = GekanatorQuestion.accepted.find_by(id: existing_question_id)
+      return head :not_found unless question
+      unless learnable_existing_question?(question)
+        return render_validation_error fields: { existing_question_id: ['質問が不正です．'] }
+      end
+
+      example =
+          GekanatorQuestionExample.find_or_initialize_by(
+              gekanator_question: question,
+              post: game.correct_post,
+              user: current_user)
+      example.record_answer!(
+          answer: params.require(:answer),
+          source: 'post_game_extra',
+          gekanator_game: game)
+
+      if example.save
+        render json: {
+          id: question.id,
+          count: game.question_suggestions.count
+        }, status: :created
+      else
+        render_validation_error example
+      end
+      return
+    end
+
+    suggestion = GekanatorQuestionSuggestion.new(
+        gekanator_game: game,
+        user: current_user,
+        question_text: params.require(:question_text),
+        answer: params.require(:answer))
+
+    if suggestion.valid?
+      ActiveRecord::Base.transaction do
+        suggestion.save!
+        Gekanator::QuestionSuggestionPromoter.call(
+            suggestion: suggestion,
+            user: current_user)
+      end
+
+      render json: {
+        id: suggestion.id,
+        count: game.question_suggestions.count
+      }, status: :created
+    else
+      render_validation_error suggestion
+    end
+  end
+
+  def ai_convert
+    return head :not_found unless current_user&.admin?
+
+    suggestion = GekanatorQuestionSuggestion.find_by(id: params[:id])
+    return head :not_found unless suggestion
+    if Gekanator::AiRunBudget.exceeded_after_next_run?
+      suggestion.gekanator_ai_runs.create!(
+          model: 'budget_guard',
+          status: 'blocked_budget',
+          input_tokens: 0,
+          output_tokens: 0,
+          estimated_cost_jpy: 0)
+      return head :payment_required
+    end
+
+    Gekanator::QuestionSuggestionAiConverter.call(
+        suggestion: suggestion,
+        user: current_user)
+    head :no_content
+  rescue NotImplementedError
+    head :not_implemented
+  end
+
+  private
+
+  def learnable_existing_question? question
+    return true if question.kind == 'post_similarity'
+    return false unless question.kind == 'tag'
+
+    key = question.condition.as_json['key'].to_s
+    !key.start_with?('nico:')
+  end
+end
diff --git a/backend/app/controllers/gekanator_questions_controller.rb b/backend/app/controllers/gekanator_questions_controller.rb
new file mode 100644
index 0000000..cc08a21
--- /dev/null
+++ b/backend/app/controllers/gekanator_questions_controller.rb
@@ -0,0 +1,147 @@
+class GekanatorQuestionsController < ApplicationController
+  def index
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .order(priority_weight: :desc, id: :asc)
+        .to_a
+    deprecated_tag_keys = deprecated_tag_keys_for(questions)
+
+    render json: {
+      questions: questions.filter_map { |question|
+        json = question_json(question)
+        next if hidden_question?(json[:condition], deprecated_tag_keys)
+
+        json
+      }
+    }
+  end
+
+  private
+
+  def question_json question
+    condition = condition_json(question.condition).deep_symbolize_keys
+    json = {
+      record_id: question.id,
+      id: question_id_for(question, condition),
+      text: question_text_for(question, condition),
+      kind: question.kind,
+      condition: condition,
+      source: question.source,
+      priority_weight: question.priority_weight
+    }
+    if question.kind == 'post_similarity' || question.kind == 'tag'
+      json[:example_answers] = example_answers_json(question)
+    end
+    json
+  end
+
+  def question_id_for question, condition
+    case condition[:type]
+    when 'tag'
+      "tag:#{ condition[:key] }"
+    when 'source'
+      "source:#{ condition[:host] }"
+    when 'original-year'
+      "original-year:#{ condition[:year] }"
+    when 'original-month'
+      "original-month:#{ condition[:month] }"
+    when 'original-month-day'
+      "original-month-day:#{ condition[:monthDay] || condition[:month_day] }"
+    when 'title-length-at-least'
+      "title:length-at-least:#{ condition[:length] }"
+    when 'title-length-greater-than'
+      "title:length-at-least:#{ condition[:length].to_i + 1 }"
+    when 'title-has-ascii'
+      'title:ascii'
+    when 'title-contains'
+      "title:contains:#{ condition[:text] }"
+    when 'post-similarity'
+      "post-similarity:#{ question.id }"
+    else
+      "catalog:#{ question.id }"
+    end
+  end
+
+  def condition_json condition
+    json = condition.deep_dup.as_json
+
+    if json['type'] == 'original-month-day' && json['monthDay'].blank?
+      json['monthDay'] = json.delete('month_day')
+    end
+
+    if json['type'] == 'title-length-greater-than'
+      json['type'] = 'title-length-at-least'
+      json['length'] = json['length'].to_i + 1
+    end
+
+    json
+  end
+
+  def question_text_for question, condition
+    return question.text unless question.kind == 'title'
+
+    case condition[:type]
+    when 'title-length-at-least'
+      "タイトルは #{ condition[:length] } 文字以上?"
+    when 'title-contains'
+      "題名に「#{ condition[:text] }」が含まれる?"
+    else
+      question.text
+    end
+  end
+
+  def example_answers_json question
+    question
+        .gekanator_question_examples
+        .group_by(&:post_id)
+        .transform_values { |examples| aggregate_answer(examples) }
+  end
+
+  def aggregate_answer examples
+    examples
+        .group_by(&:answer)
+        .map { |answer, grouped| [answer, grouped.sum(&:weight), grouped.max_by(&:updated_at)&.updated_at] }
+        .sort_by { |(_answer, weight, updated_at)| [-weight, -(updated_at&.to_f || 0)] }
+        .first
+        &.first
+  end
+
+  def deprecated_tag_keys_for questions
+    tag_keys = questions.filter_map { |question|
+      condition = condition_json(question.condition)
+      next unless condition['type'] == 'tag'
+
+      condition['key'].to_s.presence
+    }.uniq
+    return {} if tag_keys.empty?
+
+    categories = []
+    names = []
+    tag_keys.each do |key|
+      category, name = parse_tag_key(key)
+      categories << category
+      names << name
+    end
+
+    Tag
+        .joins(:tag_name)
+        .where(category: categories.uniq)
+        .where(tag_names: { name: names.uniq })
+        .where.not(deprecated_at: nil)
+        .pluck('tags.category', 'tag_names.name')
+        .each_with_object({ }) do |(category, name), h|
+          h["#{ category }:#{ name }"] = true
+        end
+  end
+
+  def hidden_question? condition, deprecated_tag_keys
+    condition[:type] == 'tag' && deprecated_tag_keys[condition[:key].to_s]
+  end
+
+  def parse_tag_key key
+    parts = key.to_s.split(':')
+    [parts.first.to_s, parts.drop(1).join(':')]
+  end
+end
diff --git a/backend/app/controllers/materials_controller.rb b/backend/app/controllers/materials_controller.rb
index d61a4b3..2a86b77 100644
--- a/backend/app/controllers/materials_controller.rb
+++ b/backend/app/controllers/materials_controller.rb
@@ -40,7 +40,11 @@ class MaterialsController < ApplicationController
     tag_name_raw = params[:tag].to_s.strip
     file = params[:file]
     url = params[:url].to_s.strip.presence
-    return head :bad_request if tag_name_raw.blank? || (file.blank? && url.blank?)
+    return render_unprocessable_entity('タグは必須です．', field: :tag) if tag_name_raw.blank?
+    if file.blank? && url.blank?
+      return render_validation_error fields: { file: ['ファイルまたは URL は必須です．'],
+                                               url: ['ファイルまたは URL は必須です．'] }
+    end
 
     tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
     tag = tag_name.tag
@@ -54,7 +58,7 @@ class MaterialsController < ApplicationController
     if material.save
       render json: MaterialRepr.base(material, host: request.base_url), status: :created
     else
-      render json: { errors: material.errors.full_messages }, status: :unprocessable_entity
+      render_validation_error material
     end
   end
 
@@ -68,7 +72,11 @@ class MaterialsController < ApplicationController
     tag_name_raw = params[:tag].to_s.strip
     file = params[:file]
     url = params[:url].to_s.strip.presence
-    return head :bad_request if tag_name_raw.blank? || (file.blank? && url.blank?)
+    return render_unprocessable_entity('タグは必須です．', field: :tag) if tag_name_raw.blank?
+    if file.blank? && url.blank?
+      return render_validation_error fields: { file: ['ファイルまたは URL は必須です．'],
+                                               url: ['ファイルまたは URL は必須です．'] }
+    end
 
     tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
     tag = tag_name.tag
@@ -84,7 +92,7 @@ class MaterialsController < ApplicationController
     if material.save
       render json: MaterialRepr.base(material, host: request.base_url)
     else
-      render json: { errors: material.errors.full_messages }, status: :unprocessable_entity
+      render_validation_error material
     end
   end
 
diff --git a/backend/app/controllers/nico_tags_controller.rb b/backend/app/controllers/nico_tags_controller.rb
index 087c592..ce63840 100644
--- a/backend/app/controllers/nico_tags_controller.rb
+++ b/backend/app/controllers/nico_tags_controller.rb
@@ -1,26 +1,69 @@
 class NicoTagsController < ApplicationController
   def index
-    limit = (params[:limit] || 20).to_i
-    cursor = params[:cursor].presence
+    name = params[:name].presence
+    linked_tag = params[:linked_tag].presence
+    link_status = params[:link_status].presence
+    order = params[:order].to_s.split(':', 2).map(&:strip)
+    order[0] = 'updated_at' unless order[0].in?(['name', 'created_at', 'updated_at'])
+    unless order[1].in?(['asc', 'desc'])
+      order[1] = order[0] == 'name' ? 'asc' : 'desc'
+    end
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
+
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    post_tag_max_sql =
+        PostTag
+        .select('tag_id, MAX(created_at) AS max_created_at')
+        .group('tag_id')
+        .to_sql
 
     q = Tag.nico_tags
+           .joins(:tag_name)
+           .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
+                  'ON post_tag_max.tag_id = tags.id')
            .includes(:tag_name, tag_name: :wiki_page, linked_tags: { tag_name: :wiki_page })
-           .order(updated_at: :desc)
-    q = q.where('tags.updated_at < ?', Time.iso8601(cursor)) if cursor
-
-    tags = q.limit(limit + 1).to_a
-
-    next_cursor = nil
-    if tags.size > limit
-      next_cursor = tags.last.updated_at.iso8601(6)
-      tags = tags.first(limit)
+    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
+    if linked_tag
+      linked_tag_ids =
+        Tag
+        .joins(:tag_name)
+        .where('tag_names.name LIKE ?', "%#{ linked_tag }%")
+        .pluck(:id)
+      linked_nico_tag_ids = NicoTagRelation.where(tag_id: linked_tag_ids).pluck(:nico_tag_id)
+      q = q.where(id: linked_nico_tag_ids)
+    end
+    if link_status.in?(['linked', 'unlinked'])
+      exists_sql =
+          'EXISTS (SELECT 1 FROM nico_tag_relations ' \
+          'WHERE nico_tag_relations.nico_tag_id = tags.id)'
+      q = link_status == 'linked' ? q.where(exists_sql) : q.where("NOT #{ exists_sql }")
     end
 
+    count = q.count
+    sort_sql =
+        case order[0]
+        when 'name'
+          'tag_names.name'
+        when 'updated_at'
+          'post_tag_max.max_created_at'
+        else
+          "tags.#{ order[0] }"
+        end
+    tags = q.reselect('tags.*',
+                      Arel.sql('post_tag_max.max_created_at AS recent_post_tag_created_at'))
+            .order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
+            .limit(limit)
+            .offset((page - 1) * limit)
+            .to_a
+
     render json: { tags: tags.map { |tag|
-      TagRepr.base(tag).merge(linked_tags: tag.linked_tags.map { |lt|
-        TagRepr.base(lt)
-      })
-    }, next_cursor: }
+      TagRepr.base(tag).merge(
+          recent_post_tag_created_at: tag.recent_post_tag_created_at,
+          linked_tags: tag.linked_tags.map { |lt| TagRepr.base(lt) })
+    }, count: }
   end
 
   def update
@@ -30,14 +73,18 @@ class NicoTagsController < ApplicationController
     id = params[:id].to_i
 
     tag = Tag.find(id)
-    return head :bad_request unless tag.nico?
+    return render_bad_request('ニコニコ・タグを指定してください．') unless tag.nico?
 
     linked_tag_names = params[:tags].to_s.split
-    linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
-                                                        with_no_deerjikist: false)
-    return head :bad_request if linked_tags.any? { |t| t.nico? }
+    linked_tags = nil
 
     ApplicationRecord.transaction do
+      linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
+                                                          with_no_deerjikist: false)
+      if linked_tags.any? { |t| t.nico? }
+        raise Tag::NicoTagNormalisationError
+      end
+
       TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
 
       tag.linked_tags = linked_tags
@@ -47,5 +94,21 @@ class NicoTagsController < ApplicationController
     end
 
     render json: tag.linked_tags.map { |t| TagRepr.base(t) }, status: :ok
+  rescue Tag::NicoTagNormalisationError
+    render_validation_error fields: { tags: ['ニコニコ・タグ同士は連携できません．'] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_nico_tag_form_record_invalid e.record
+  end
+
+  private
+
+  def render_nico_tag_form_record_invalid record
+    if record.is_a?(TagName) || record.is_a?(Tag)
+      render_validation_error fields: { tags: record.errors.full_messages.map { |message|
+        "タグ名 “#{ record.name }”: #{ message }"
+      } }
+    else
+      render_validation_error record
+    end
   end
 end
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 000577b..068795a 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -44,7 +44,8 @@ class PostsController < ApplicationController
         filtered_posts
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
-        .preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+        .preload(:uploaded_user, :parents, :children,
+                 tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -95,22 +96,36 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts
-           .preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
-           .order('RAND()')
-           .first
+    post = filtered_posts.preload(:uploaded_user, :parents, :children,
+                                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+                         .with_attached_thumbnail
+                         .order('RAND()')
+                         .first
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
   end
 
   def show
-    post = Post.includes(tags: [:deerjikists, :materials, { tag_name: :wiki_page }]).find_by(id: params[:id])
+    post =
+        Post
+        .includes(:uploaded_user, :parents, :children,
+                  tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+        .with_attached_thumbnail
+        .find_by(id: params[:id])
     return head :not_found unless post
 
-    render json: PostRepr.base(post, current_user)
-                         .merge(tags: build_tag_tree_for(post),
-                                related: PostRepr.many(post.related(limit: 20)))
+    parent_posts = post.parents.with_attached_thumbnail.order(:id).to_a
+    child_posts = post.children.with_attached_thumbnail.order(:id).to_a
+    sibling_posts = sibling_posts_by_parent(parent_posts.map(&:id))
+    related = post.related(limit: 20).to_a
+
+    render json: PostRepr.detail(post, current_user,
+                                 parent_posts:,
+                                 child_posts:,
+                                 sibling_posts:,
+                                 related:)
+                         .merge(tags: build_tag_tree_for(post))
   end
 
   def create
@@ -133,10 +148,11 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.save!
 
-      Tag.normalise_tags!(tag_names, with_sections: true) => { tags:, sections: }
+      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
+          { tags:, sections: }
       TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
-      tags = Tag.expand_parent_tags(tags)
+      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
       sync_post_tags!(post, tags, sections)
 
       sync_parent_posts!(post, parent_post_ids)
@@ -149,11 +165,13 @@ class PostsController < ApplicationController
     post.reload
     render json: PostRepr.base(post), status: :created
   rescue Tag::NicoTagNormalisationError
-    head :bad_request
+    render_validation_error fields: { tags: 'ニコニコ・タグは直接指定できません．' }
+  rescue Tag::DeprecatedTagNormalisationError
+    render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue ArgumentError => e
-    render json: { errors: [e.message] }, status: :unprocessable_entity
+    render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
-    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
+    render_post_form_record_invalid e.record
   end
 
   def viewed
@@ -176,10 +194,10 @@ class PostsController < ApplicationController
 
     force = bool?(:force)
     merge = bool?(:merge)
-    return head :bad_request if force && merge
+    return render_bad_request('force と merge は同時に指定できません．') if force && merge
 
     base_version_no = parse_base_version_no
-    return head :bad_request if !(force) && !(base_version_no)
+    return render_bad_request('base_version_no は必須です．') if !(force) && !(base_version_no)
 
     title = params[:title].presence
     tag_names = params[:tags].to_s.split
@@ -239,11 +257,13 @@ class PostsController < ApplicationController
     json['tags'] = build_tag_tree_for(post)
     render json:, status: :ok
   rescue Tag::NicoTagNormalisationError
-    head :bad_request
+    render_validation_error fields: { tags: ['ニコニコ・タグは直接指定できません．'] }
+  rescue Tag::DeprecatedTagNormalisationError
+    render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue ArgumentError => e
-    render json: { errors: [e.message] }, status: :unprocessable_entity
+    render_validation_error fields: { parent_post_ids: [e.message] }
   rescue ActiveRecord::RecordInvalid => e
-    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
+    render_post_form_record_invalid e.record
   end
 
   def changes
@@ -370,7 +390,7 @@ class PostsController < ApplicationController
   end
 
   def build_tag_tree_for post
-    tags = post.tags.to_a
+    tags = post.tags.reject(&:deprecated?).to_a
     tag_ids = tags.map(&:id)
 
     implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
@@ -385,6 +405,11 @@ class PostsController < ApplicationController
     root_ids = tag_ids - child_ids
 
     tags_by_id = tags.index_by(&:id)
+    sections_by_tag_id =
+        PostTagSection
+        .where(post_id: post.id, tag_id: tag_ids)
+        .order(:begin_ms)
+        .group_by(&:tag_id)
 
     memo = { }
 
@@ -392,11 +417,11 @@ class PostsController < ApplicationController
       tag = tags_by_id[tag_id]
       return nil unless tag
 
-      sections = PostTagSection.where(post_id: post.id, tag_id:)
-                 .as_json(only: [:begin_ms, :end_ms])
+      sections = sections_by_tag_id.fetch(tag_id, [])
+                                   .as_json(only: [:begin_ms, :end_ms])
 
       if path.include?(tag_id)
-        return TagRepr.base(tag).merge(children: [], sections:)
+        return TagRepr.inline(tag).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -408,12 +433,26 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.base(tag).merge(children:, sections:)
+      memo[tag_id] = TagRepr.inline(tag).merge(children:, sections:)
     end
 
     root_ids.filter_map { |id| build_node.call(id, []) }
   end
 
+  def sibling_posts_by_parent parent_post_ids
+    return { } if parent_post_ids.blank?
+
+    implications =
+        PostImplication
+        .where(parent_post_id: parent_post_ids)
+        .includes(post: { thumbnail_attachment: :blob })
+        .order(:parent_post_id, :post_id)
+
+    implications.group_by(&:parent_post_id).transform_values { |items|
+      items.map(&:post)
+    }
+  end
+
   def parse_parent_post_ids
     raise ArgumentError, 'parent_post_ids は必須です．' unless params.key?(:parent_post_ids)
 
@@ -427,7 +466,7 @@ class PostsController < ApplicationController
 
   def sync_parent_posts! post, parent_post_ids
     if parent_post_ids.include?(post.id)
-      post.errors.add(:base, '自分自身を親投稿にはできません．')
+      post.errors.add :parent_post_ids, '自分自身を親投稿にはできません．'
       raise ActiveRecord::RecordInvalid, post
     end
 
@@ -435,7 +474,8 @@ class PostsController < ApplicationController
     missing_ids = parent_post_ids - existing_ids
 
     if missing_ids.present?
-      post.errors.add(:base, "存在しない親投稿 ID があります: #{ missing_ids.join(' ') }")
+      post.errors.add :parent_post_ids,
+                      "存在しない親投稿 Id. があります: #{ missing_ids.join(' ') }"
       raise ActiveRecord::RecordInvalid, post
     end
 
@@ -486,6 +526,7 @@ class PostsController < ApplicationController
         .kept
         .joins(tag: :tag_name)
         .merge(Tag.not_nico)
+        .merge(Tag.where(deprecated_at: nil))
         .includes(:sections, tag: :tag_name)
         .order('tag_names.name')
         .map do |post_tag|
@@ -527,10 +568,11 @@ class PostsController < ApplicationController
   end
 
   def incoming_tag_names_for_snapshot raw_tag_names
-    Tag.normalise_tags!(raw_tag_names, with_tagme: false, with_sections: true) =>
+    Tag.normalise_tags!(raw_tag_names, with_tagme: false, deny_deprecated: true,
+                                        with_sections: true) =>
         { tags:, sections: }
 
-    Tag.expand_parent_tags(tags).uniq(&:id).map { |tag|
+    Tag.expand_parent_tags(tags).reject(&:deprecated?).uniq(&:id).map { |tag|
       "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
     }.sort
   end
@@ -623,14 +665,16 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false, with_sections: true) =>
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
+                                               deny_deprecated: true,
+                                               with_sections: true) =>
         { tags: editable_tags, sections: }
     TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
 
     readonly_tags = post.tags.nico.to_a
 
     tags = readonly_tags + editable_tags
-    tags = Tag.expand_parent_tags(tags)
+    tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
     sync_post_tags!(post, tags, sections)
     sync_parent_posts!(post, snapshot[:parent_post_ids])
@@ -673,4 +717,14 @@ class PostsController < ApplicationController
 
     merged.uniq.sort
   end
+
+  def render_post_form_record_invalid record
+    if record.is_a?(TagName) || record.is_a?(Tag)
+      render_validation_error fields: { tags: record.errors.full_messages.map { |message|
+        "タグ名 “#{ record.name }”: #{ message }"
+      } }
+    else
+      render_validation_error record
+    end
+  end
 end
diff --git a/backend/app/controllers/preview_controller.rb b/backend/app/controllers/preview_controller.rb
index 0590891..5486838 100644
--- a/backend/app/controllers/preview_controller.rb
+++ b/backend/app/controllers/preview_controller.rb
@@ -4,7 +4,7 @@ class PreviewController < ApplicationController
     return head :unauthorized unless current_user
 
     url = params[:url]
-    return head :bad_request unless url.present?
+    return render_bad_request('URL は必須です．') unless url.present?
 
     unless url.start_with?(/http(s)?:\/\//)
       url = 'http://' + url
@@ -16,7 +16,7 @@ class PreviewController < ApplicationController
 
     render json: { title: title }
   rescue => e
-    render json: { error: e.message }, status: :bad_request
+    render_bad_request(e.message)
   end
 
   def thumbnail
@@ -25,7 +25,7 @@ class PreviewController < ApplicationController
     return head :unauthorized unless current_user
 
     url = params[:url]
-    return head :bad_request if url.blank?
+    return render_bad_request('URL は必須です．') if url.blank?
 
     unless url.start_with?(/http(s)?:\/\//)
       url = 'http://' + url
@@ -40,7 +40,11 @@ class PreviewController < ApplicationController
       File.delete(path) rescue nil
       send_file image.path, type: 'image/png', disposition: 'inline'
     else
-      render json: { error: 'Failed to generate thumbnail' }, status: :internal_server_error
+      render json: { type: 'internal_server_error',
+                     message: 'サムネールを生成できませんでした．',
+                     errors: { },
+                     base_errors: ['サムネールを生成できませんでした．'] },
+             status: :internal_server_error
     end
   end
 end
diff --git a/backend/app/controllers/tag_children_controller.rb b/backend/app/controllers/tag_children_controller.rb
index 8eb972e..cfdde30 100644
--- a/backend/app/controllers/tag_children_controller.rb
+++ b/backend/app/controllers/tag_children_controller.rb
@@ -5,11 +5,12 @@ class TagChildrenController < ApplicationController
 
     parent_id = params[:parent_id]
     child_id = params[:child_id]
-    return head :bad_request if parent_id.blank? || child_id.blank?
+    return render_bad_request('parent_id は必須です．') if parent_id.blank?
+    return render_bad_request('child_id は必須です．') if child_id.blank?
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
-    return head :bad_request if parent.nico? || child.nico?
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
@@ -27,11 +28,12 @@ class TagChildrenController < ApplicationController
 
     parent_id = params[:parent_id]
     child_id = params[:child_id]
-    return head :bad_request if parent_id.blank? || child_id.blank?
+    return render_bad_request('parent_id は必須です．') if parent_id.blank?
+    return render_bad_request('child_id は必須です．') if child_id.blank?
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
-    return head :bad_request if parent.nico? || child.nico?
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
diff --git a/backend/app/controllers/tag_versions_controller.rb b/backend/app/controllers/tag_versions_controller.rb
index 0958c75..243a548 100644
--- a/backend/app/controllers/tag_versions_controller.rb
+++ b/backend/app/controllers/tag_versions_controller.rb
@@ -17,6 +17,7 @@ class TagVersionsController < ApplicationController
               AND prev.version_no = tag_versions.version_no - 1
         SQL
       .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
+              'prev.deprecated_at AS prev_deprecated_at',
               'prev.aliases AS prev_aliases', 'prev.parent_tag_ids AS prev_parent_tag_ids')
     q = q.where('tag_versions.tag_id = ?', tag_id) if tag_id
 
@@ -62,6 +63,8 @@ class TagVersionsController < ApplicationController
         event_type: row.event_type,
         name: { current: row.name, prev: row.attributes['prev_name'] },
         category: { current: row.category, prev: row.attributes['prev_category'] },
+        deprecated_at: { current: row.deprecated_at&.iso8601,
+                         prev: row.attributes['prev_deprecated_at']&.iso8601 },
         aliases: build_version_values(cur_aliases, prev_aliases, key: :name),
         parent_tags:,
         created_at: row.created_at.iso8601,
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index aed029f..c9e585e 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -1,5 +1,6 @@
 require 'net/http'
 require 'uri'
+require 'set'
 
 
 class TagsController < ApplicationController
@@ -14,6 +15,8 @@ class TagsController < ApplicationController
     post_count_between[1] = nil if post_count_between[1] < 0
     created_between = params[:created_from].presence, params[:created_to].presence
     updated_between = params[:updated_from].presence, params[:updated_to].presence
+    deprecated_given = params.key?(:deprecated)
+    deprecated = bool?(:deprecated)
 
     order = params[:order].to_s.split(':', 2).map(&:strip)
     unless order[0].in?(['name', 'category', 'post_count', 'created_at', 'updated_at'])
@@ -48,6 +51,9 @@ class TagsController < ApplicationController
     q = q.where('tags.created_at <= ?', created_between[1]) if created_between[1]
     q = q.where('tags.updated_at >= ?', updated_between[0]) if updated_between[0]
     q = q.where('tags.updated_at <= ?', updated_between[1]) if updated_between[1]
+    if deprecated_given
+      q = deprecated ? q.where.not(deprecated_at: nil) : q.where(deprecated_at: nil)
+    end
 
     sort_sql =
         case order[0]
@@ -77,37 +83,27 @@ class TagsController < ApplicationController
     parent_tag_id = params[:parent].to_i
     parent_tag_id = nil if parent_tag_id <= 0
 
+    graph = build_with_depth_graph
+
     tag_ids =
         if parent_tag_id
-          TagImplication.where(parent_tag_id:).select(:tag_id)
+          visible_child_tag_ids(parent_tag_id, graph)
         else
-          Tag.where.not(id: TagImplication.select(:tag_id)).select(:id)
+          visible_root_tag_ids(graph)
         end
 
     tags =
         Tag
         .joins(:tag_name)
         .includes(:tag_name, :materials, tag_name: :wiki_page)
-        .where(category: [:meme, :character, :material])
         .where(id: tag_ids)
         .order('tag_names.name')
         .distinct
         .to_a
 
-    has_children_tag_ids =
-        if tags.empty?
-          []
-        else
-          TagImplication
-              .joins(:tag)
-              .where(parent_tag_id: tags.map(&:id),
-                     tags: { category: [:meme, :character, :material] })
-              .distinct
-              .pluck(:parent_tag_id)
-        end
-
     render json: tags.map { |tag|
-      TagRepr.base(tag).merge(has_children: has_children_tag_ids.include?(tag.id), children: [])
+      TagRepr.base(tag).merge(has_children: visible_child_tag_ids(tag.id, graph).present?,
+                              children: [])
     }
   end
 
@@ -133,6 +129,7 @@ class TagsController < ApplicationController
 
     base = Tag.joins(:tag_name)
               .includes(:tag_name, :materials, tag_name: :wiki_page)
+              .where(deprecated_at: nil)
     base = base.where('tags.post_count > 0') if present_only
 
     canonical_hit =
@@ -168,7 +165,7 @@ class TagsController < ApplicationController
 
   def show_by_name
     name = params[:name].to_s.strip
-    return head :bad_request if name.blank?
+    return render_bad_request('name は必須です．') if name.blank?
 
     tag = Tag.joins(:tag_name)
              .includes(:tag_name, :materials, tag_name: :wiki_page)
@@ -192,7 +189,7 @@ class TagsController < ApplicationController
 
   def deerjikists_by_name
     name = params[:name].to_s.strip
-    return head :bad_request if name.blank?
+    return render_bad_request('name は必須です．') if name.blank?
 
     tag = Tag.joins(:tag_name)
              .includes(:tag_name, tag_name: :wiki_page)
@@ -214,21 +211,24 @@ class TagsController < ApplicationController
 
     ApplicationRecord.transaction do
       tag.deerjikists = []
-      params[:_json].each do
-        platform = _1[:platform]
-        code = normalise_deerjikist_code(platform, _1[:code])
+      params[:_json].each.with_index do |item, i|
+        platform = item[:platform]
+        code = normalise_deerjikist_code(platform, item[:code])
         deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
         deerjikist.tag = tag
-        deerjikist.save!
+        render_deerjikist_form_record_invalid(deerjikist, i) unless deerjikist.save
+        raise ActiveRecord::Rollback if performed?
       end
     end
 
+    return if performed?
+
     render json: DeerjikistRepr.many(tag.reload.deerjikists)
   end
 
   def materials_by_name
     name = params[:name].to_s.strip
-    return head :bad_request if name.blank?
+    return render_bad_request('name は必須です．') if name.blank?
 
     tag = Tag.joins(:tag_name)
              .includes(:tag_name, :materials, tag_name: :wiki_page)
@@ -247,21 +247,26 @@ class TagsController < ApplicationController
 
     name = params[:name].to_s.strip
     category = params[:category].to_s.strip
-    return head :unprocessable_entity if name.blank? || category.blank?
+    return render_unprocessable_entity('名前は必須です．', field: :name) if name.blank?
+    return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
+    return render_unprocessable_entity '廃止状態は必須です．', field: :deprecated unless params.key?(:deprecated)
 
-    if name != tag.name &&
-        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
-      return render json: { error: 'システム・タグの名称は変更できません．' },
-                    status: :unprocessable_entity
-    end
-
-    if tag.nico? || category == 'nico'
-      return render json: { error: 'ニコタグは変更できません．' },
-                    status: :unprocessable_entity
+    if (name != tag.name &&
+        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico]))
+      return render_unprocessable_entity 'システム・タグの名称は変更できません．', field: :name
     end
 
     alias_names = params[:aliases].to_s.split.uniq
     parent_names = params[:parent_tags].to_s.split.uniq
+    deprecated = bool?(:deprecated)
+
+    if tag.nico? && deprecated
+      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
+    end
+
+    if tag.nico? || category == 'nico'
+      return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
+    end
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
@@ -270,7 +275,11 @@ class TagsController < ApplicationController
       name_changed = name != old_name
       wiki_page = tag.tag_name.wiki_page if name_changed
 
-      tag.update!(category:)
+      if tag.deprecated? == deprecated
+        tag.update!(category:)
+      else
+        tag.update!(category:, deprecated_at: deprecated ? Time.current : nil)
+      end
       tag.tag_name.update!(name:)
 
       alias_names << old_name if name_changed
@@ -298,12 +307,17 @@ class TagsController < ApplicationController
 
     name = params[:name].presence
     category = params[:category].presence
+    deprecated_given = params.key?(:deprecated)
+    deprecated = bool?(:deprecated)
 
     tag = Tag.find(params[:id])
 
+    if tag.nico? && deprecated_given && deprecated
+      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
+    end
+
     if tag.nico? || (category.present? && category == 'nico')
-      return render json: { error: 'ニコタグは変更できません．' },
-                    status: :unprocessable_entity
+      return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
 
     ApplicationRecord.transaction do
@@ -315,6 +329,9 @@ class TagsController < ApplicationController
 
       tag.tag_name.update!(name:) if name.present?
       tag.update!(category:) if category.present?
+      if deprecated_given && tag.deprecated? != deprecated
+        tag.update!(deprecated_at: deprecated ? Time.current : nil)
+      end
 
       tag.reload
 
@@ -331,6 +348,93 @@ class TagsController < ApplicationController
 
   private
 
+  def build_with_depth_graph
+    children_by_parent_id = Hash.new { |h, k| h[k] = [] }
+    parent_ids_by_child_id = Hash.new { |h, k| h[k] = [] }
+
+    TagImplication.pluck(:parent_tag_id, :tag_id).each do |parent_id, child_id|
+      children_by_parent_id[parent_id] << child_id
+      parent_ids_by_child_id[child_id] << parent_id
+    end
+
+    tag_ids = (children_by_parent_id.keys +
+               parent_ids_by_child_id.keys +
+               Tag.where(category: ['meme', 'character', 'material']).pluck(:id)).uniq
+
+    tags_by_id = Tag.where(id: tag_ids)
+                    .pluck(:id, :category, :deprecated_at)
+                    .each_with_object({ }) do |(id, category, deprecated_at), h|
+      h[id] = { category:, deprecated: deprecated_at.present? }
+    end
+
+    { children_by_parent_id:, parent_ids_by_child_id:, tags_by_id:,
+      visible_child_tag_ids_by_parent_id: { } }
+  end
+
+  def visible_root_tag_ids graph
+    graph[:tags_by_id].filter_map do |tag_id, attrs|
+      next unless with_depth_visible_tag?(attrs)
+      next unless visible_root_tag?(tag_id, graph)
+
+      tag_id
+    end
+  end
+
+  def visible_root_tag? tag_id, graph
+    seen = Set.new([tag_id])
+    stack = graph[:parent_ids_by_child_id][tag_id].dup
+
+    until stack.empty?
+      parent_id = stack.pop
+      next if seen.include?(parent_id)
+
+      seen << parent_id
+
+      parent = graph[:tags_by_id][parent_id]
+      next unless parent
+
+      return false unless parent[:deprecated]
+
+      stack.concat(graph[:parent_ids_by_child_id][parent_id])
+    end
+
+    true
+  end
+
+  def visible_child_tag_ids parent_tag_id, graph
+    cache = graph[:visible_child_tag_ids_by_parent_id]
+    return cache[parent_tag_id] if cache.key?(parent_tag_id)
+
+    visible_ids = Set.new
+
+    graph[:children_by_parent_id][parent_tag_id].each do |child_tag_id|
+      collect_visible_child_tag_ids(child_tag_id, graph, visible_ids, Set.new([parent_tag_id]))
+    end
+
+    cache[parent_tag_id] = visible_ids.to_a
+  end
+
+  def collect_visible_child_tag_ids tag_id, graph, visible_ids, seen
+    return if seen.include?(tag_id)
+
+    seen = seen.dup << tag_id
+    tag = graph[:tags_by_id][tag_id]
+    return unless tag
+
+    if tag[:deprecated]
+      graph[:children_by_parent_id][tag_id].each do |child_tag_id|
+        collect_visible_child_tag_ids(child_tag_id, graph, visible_ids, seen)
+      end
+      return
+    end
+
+    visible_ids << tag_id if with_depth_visible_tag?(tag)
+  end
+
+  def with_depth_visible_tag? tag
+    tag[:category].in?(['meme', 'character', 'material']) && !tag[:deprecated]
+  end
+
   def build_tag_children tag
     material = tag.materials.first
     file = nil
@@ -437,4 +541,23 @@ class TagsController < ApplicationController
   rescue
     nil
   end
+
+  def render_deerjikist_form_record_invalid deerjikist, index
+    fields = { }
+
+    deerjikist.errors.each do |error|
+      field =
+          case error.attribute
+          when :platform, :code
+            "deerjikists.#{ index }.#{ error.attribute }"
+          else
+            :deerjikists
+          end
+
+      fields[field] ||= []
+      fields[field] << error.full_message
+    end
+
+    render_validation_error fields:
+  end
 end
diff --git a/backend/app/controllers/theatre_comments_controller.rb b/backend/app/controllers/theatre_comments_controller.rb
index 50ec9ef..599a57e 100644
--- a/backend/app/controllers/theatre_comments_controller.rb
+++ b/backend/app/controllers/theatre_comments_controller.rb
@@ -1,21 +1,28 @@
 class TheatreCommentsController < ApplicationController
   def index
+    limit = params[:limit].to_i
+    limit = 20 if limit <= 0
+
     no_gt = params[:no_gt].to_i
-    no_gt = 0 if no_gt.negative?
+    no_gt = 0 if no_gt < 0
 
     comments = TheatreComment
                .where(theatre_id: params[:theatre_id])
                .where('no > ?', no_gt)
                .order(no: :desc)
+               .limit(limit)
 
-    render json: comments.as_json(include: { user: { only: [:id, :name] } })
+    render json: comments.map {
+      _1.as_json(include: { user: { only: [:id, :name] } })
+          .merge(content: _1.discarded? ? nil : _1.content, deleted: _1.discarded?)
+    }
   end
 
   def create
     return head :unauthorized unless current_user
 
     content = params[:content]
-    return head :unprocessable_entity if content.blank?
+    return render_unprocessable_entity('本文は必須です．', field: :content) if content.blank?
 
     theatre = Theatre.find_by(id: params[:theatre_id])
     return head :not_found unless theatre
@@ -29,4 +36,19 @@ class TheatreCommentsController < ApplicationController
 
     render json: comment, status: :created
   end
+
+  def destroy
+    return head :unauthorized unless current_user
+
+    theatre_id = params[:theatre_id].to_i
+    no = params[:id].to_i
+
+    comment = TheatreComment.find_by(theatre_id:, no:)
+    return head :not_found unless comment
+    return head :forbidden unless comment.user == current_user
+
+    comment.discard!
+
+    head :no_content
+  end
 end
diff --git a/backend/app/controllers/theatre_programmes_controller.rb b/backend/app/controllers/theatre_programmes_controller.rb
new file mode 100644
index 0000000..b386f63
--- /dev/null
+++ b/backend/app/controllers/theatre_programmes_controller.rb
@@ -0,0 +1,22 @@
+class TheatreProgrammesController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 100 if limit <= 0
+
+    position_gt = params[:position_gt].to_i
+    position_gt = 0 if position_gt < 0
+
+    programmes = TheatreProgramme
+                 .where(theatre_id: params[:theatre_id])
+                 .where('position > ?', position_gt)
+                 .includes(:post)
+                 .order(position: :desc).limit(100)
+                 .limit(limit)
+
+    render json: programmes.map { |programme|
+      programme.as_json.merge(post: { id: programme.post.id,
+                                      title: programme.post.title,
+                                      url: programme.post.url })
+    }
+  end
+end
diff --git a/backend/app/controllers/theatre_skip_events_controller.rb b/backend/app/controllers/theatre_skip_events_controller.rb
new file mode 100644
index 0000000..fbbdae9
--- /dev/null
+++ b/backend/app/controllers/theatre_skip_events_controller.rb
@@ -0,0 +1,22 @@
+class TheatreSkipEventsController < ApplicationController
+  def index
+    limit = params[:limit].to_i
+    limit = 50 if limit <= 0
+
+    events =
+        TheatreSkipEvent
+        .where(theatre_id: params[:theatre_id])
+        .includes(:post, tags: :tag_name)
+        .order(created_at: :desc)
+        .limit(limit)
+
+    render json: events.map { |event|
+      { id: event.id,
+        theatre_id: event.theatre_id,
+        post: { id: event.post.id, title: event.post.title, url: event.post.url },
+        tags: event.tags.map { |tag| { id: tag.id, name: tag.name } },
+        programme_position: event.programme_position,
+        created_at: event.created_at }
+    }
+  end
+end
diff --git a/backend/app/controllers/theatres_controller.rb b/backend/app/controllers/theatres_controller.rb
index 7949045..10f4455 100644
--- a/backend/app/controllers/theatres_controller.rb
+++ b/backend/app/controllers/theatres_controller.rb
@@ -31,9 +31,7 @@ class TheatresController < ApplicationController
       post_started_at = theatre.current_post_started_at
     end
 
-    render json: {
-        host_flg:, post_id:, post_started_at:,
-        watching_users: theatre.watching_users.as_json(only: [:id, :name]) }
+    render json: theatre_info_json(theatre, host_flg:, post_id:, post_started_at:)
   end
 
   def next_post
@@ -43,12 +41,119 @@ class TheatresController < ApplicationController
     return head :not_found unless theatre
     return head :forbidden if theatre.host_user != current_user
 
-    post = Post.where("url LIKE '%nicovideo.jp%'")
-           .or(Post.where("url LIKE '%youtube.com%'"))
-           .order('RAND()')
-           .first
-    theatre.update!(current_post: post, current_post_started_at: Time.current)
+    ApplicationRecord.transaction do
+      theatre.lock!
+      TheatrePostAdvancer.call(theatre:)
+    end
 
     head :no_content
   end
+
+  def skip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+    requested_post_id = params[:post_id].to_i
+    return head :unprocessable_entity if requested_post_id <= 0
+
+    skipped = false
+    conflicted = false
+
+    ApplicationRecord.transaction do
+      theatre.lock!
+      if theatre.current_post
+        TheatreWatchingUser.find_or_initialize_by(theatre:, user: current_user).tap {
+          _1.expires_at = 30.seconds.from_now
+        }.save!
+
+        if theatre.current_post_id != requested_post_id
+          conflicted = true
+          next
+        end
+
+        TheatreSkipVote.find_or_create_by!(theatre:, post_id: requested_post_id, user: current_user)
+
+        vote_status = skip_vote_status(theatre)
+        if vote_status[:votes_count] >= vote_status[:required_count]
+          TheatreSkipFinalizer.call(theatre:, user: current_user)
+          TheatrePostAdvancer.call(theatre:)
+          skipped = true
+        end
+      end
+    end
+
+    theatre.reload
+    return render json: theatre_info_json(theatre, skipped: false), status: :conflict if conflicted
+
+    render json: theatre_info_json(theatre, skipped:)
+  end
+
+  def unskip_vote
+    return head :unauthorized unless current_user
+
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+    requested_post_id = params[:post_id].to_i
+    return head :unprocessable_entity if requested_post_id <= 0
+
+    conflicted = false
+
+    theatre.with_lock do
+      if theatre.current_post
+        if theatre.current_post_id != requested_post_id
+          conflicted = true
+        else
+          TheatreSkipVote.where(theatre:, post_id: requested_post_id, user: current_user).delete_all
+        end
+      end
+    end
+
+    theatre.reload
+    return render json: theatre_info_json(theatre, skipped: false), status: :conflict if conflicted
+
+    render json: theatre_info_json(theatre, skipped: false)
+  end
+
+  def post_selection_weights
+    theatre = Theatre.find_by(id: params[:id])
+    return head :not_found unless theatre
+
+    render json: TheatrePostSelector.new(theatre:).weight_json
+  end
+
+  private
+
+  def theatre_info_json(theatre, host_flg: nil, post_id: nil, post_started_at: nil, skipped: nil)
+    host_flg = theatre.host_user_id == current_user&.id if host_flg.nil?
+    post_id = theatre.current_post_id if post_id.nil?
+    post_started_at = theatre.current_post_started_at if post_started_at.nil?
+
+    json = { host_flg:,
+             post_id:,
+             post_started_at:,
+             post_elapsed_ms: post_started_at ? ((Time.current - post_started_at) * 1000).floor : nil,
+             watching_users: theatre.watching_users.as_json(only: [:id, :name]),
+             skip_vote: skip_vote_status(theatre) }
+    json[:skipped] = skipped unless skipped.nil?
+    json
+  end
+
+  def skip_vote_status(theatre)
+    watching_user_ids = theatre.watching_users.ids
+    watching_users_count = watching_user_ids.size
+    required_count = (watching_users_count / 2) + 1
+    post = theatre.current_post
+    votes =
+        if post
+          TheatreSkipVote.where(theatre:, post:, user_id: watching_user_ids)
+        else
+          TheatreSkipVote.none
+        end
+
+    { votes_count: post ? votes.count : 0,
+      required_count:,
+      watching_users_count:,
+      voted: post && current_user ? votes.exists?(user_id: current_user.id) : false }
+  end
 end
diff --git a/backend/app/controllers/users_controller.rb b/backend/app/controllers/users_controller.rb
index a144593..95ae677 100644
--- a/backend/app/controllers/users_controller.rb
+++ b/backend/app/controllers/users_controller.rb
@@ -42,12 +42,12 @@ class UsersController < ApplicationController
     return head :unauthorized if user&.id != params[:id].to_i
 
     name = params[:name]
-    return head :bad_request if name.blank?
+    return render_unprocessable_entity('名前は必須です．', field: :name) if name.blank?
 
     if user.update(name:)
       render json: user.slice(:id, :name, :inheritance_code, :role), status: :ok
     else
-      render json: user.errors, status: :unprocessable_entity
+      render_validation_error user
     end
   end
 
diff --git a/backend/app/controllers/wiki_pages_controller.rb b/backend/app/controllers/wiki_pages_controller.rb
index de42c52..f3ece93 100644
--- a/backend/app/controllers/wiki_pages_controller.rb
+++ b/backend/app/controllers/wiki_pages_controller.rb
@@ -4,17 +4,18 @@ class WikiPagesController < ApplicationController
   def index
     title = params[:title].to_s.strip
     if title.blank?
-      return render json: WikiPageRepr.base(WikiPage.joins(:tag_name).includes(:tag_name))
+      return render json: WikiPageRepr.base(
+          WikiPage.joins(:tag_name).includes(tag_name: :tag))
     end
 
-    q = WikiPage.joins(:tag_name).includes(:tag_name)
+    q = WikiPage.joins(:tag_name).includes(tag_name: :tag)
         .where('tag_names.name LIKE ?', "%#{ WikiPage.sanitize_sql_like(title) }%")
     render json: WikiPageRepr.base(q.limit(20))
   end
 
   def show
     page = WikiPage.joins(:tag_name)
-                   .includes(:tag_name)
+                   .includes(tag_name: :tag)
                    .find_by(id: params[:id])
     render_wiki_page_or_404 page
   end
@@ -22,7 +23,7 @@ class WikiPagesController < ApplicationController
   def show_by_title
     title = params[:title].to_s.strip
     page = WikiPage.joins(:tag_name)
-                   .includes(:tag_name)
+                   .includes(tag_name: :tag)
                    .find_by(tag_name: { name: title })
     render_wiki_page_or_404 page
   end
@@ -46,17 +47,17 @@ class WikiPagesController < ApplicationController
 
   def diff
     id = params[:id]
-    return head :bad_request if id.blank?
+    return render_bad_request('id は必須です．') if id.blank?
 
     from = params[:from].presence
     to = params[:to].presence
 
-    page = WikiPage.joins(:tag_name).includes(:tag_name).find(id)
+    page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
 
     from_rev = from && page.wiki_revisions.find(from)
     to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
     if ((from_rev && !(from_rev.content?)) || !(to_rev&.content?))
-      return head :unprocessable_entity
+      return render_unprocessable_entity('差分を表示できない版です．')
     end
 
     diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
@@ -76,6 +77,7 @@ class WikiPagesController < ApplicationController
 
     render json: { wiki_page_id:      page.id,
                    title:             page.title,
+                   deprecated_at:     page.deprecated_at,
                    older_revision_id: from_rev&.id,
                    newer_revision_id: to_rev.id,
                    diff:              diff_json }
@@ -89,7 +91,8 @@ class WikiPagesController < ApplicationController
     body = params[:body].to_s
     message = params[:message].presence
 
-    return head :unprocessable_entity if title.blank? || body.blank?
+    return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
+    return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
     tag_name = TagName.find_undiscard_or_create_by!(name: title)
 
@@ -101,8 +104,10 @@ class WikiPagesController < ApplicationController
             message:)
 
     render json: WikiPageRepr.base(page), status: :created
-  rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotUnique
-    head :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
   end
 
   def update
@@ -112,7 +117,8 @@ class WikiPagesController < ApplicationController
     title = params[:title]&.strip
     body = params[:body].to_s
 
-    return head :unprocessable_entity if title.blank? || body.blank?
+    return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
+    return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
     page = WikiPage.find(params[:id])
     base_revision_id = params[:base_revision_id].presence
@@ -153,7 +159,7 @@ class WikiPagesController < ApplicationController
   def changes
     id = params[:id].presence
     q = WikiRevision.joins(wiki_page: :tag_name)
-                    .includes(:created_user, wiki_page: :tag_name)
+                    .includes(:created_user, wiki_page: { tag_name: :tag })
                     .order(id: :desc)
     q = q.where(wiki_page_id: id) if id
 
@@ -161,7 +167,9 @@ class WikiPagesController < ApplicationController
       { revision_id:  rev.id,
         pred:         rev.base_revision_id,
         succ:         nil,
-        wiki_page:    { id: rev.wiki_page_id, title: rev.wiki_page.title },
+        wiki_page:    { id: rev.wiki_page_id,
+                        title: rev.wiki_page.title,
+                        deprecated_at: rev.wiki_page.deprecated_at },
         user:         rev.created_user && { id: rev.created_user.id, name: rev.created_user.name },
         kind:         rev.kind,
         message:      rev.message,
diff --git a/backend/app/models/gekanator_ai_run.rb b/backend/app/models/gekanator_ai_run.rb
new file mode 100644
index 0000000..3a35e29
--- /dev/null
+++ b/backend/app/models/gekanator_ai_run.rb
@@ -0,0 +1,21 @@
+class GekanatorAiRun < ApplicationRecord
+  STATUSES = ['pending', 'running', 'succeeded', 'failed', 'blocked_budget'].freeze
+
+  belongs_to :gekanator_question_suggestion
+
+  validates :model, presence: true, length: { maximum: 255 }
+  validates :status, presence: true, inclusion: { in: STATUSES }
+  validates :input_tokens,
+            presence: true,
+            numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :output_tokens,
+            presence: true,
+            numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+  validates :estimated_cost_jpy,
+            presence: true,
+            numericality: { greater_than_or_equal_to: 0 }
+
+  scope :this_month, lambda {
+    where(created_at: Time.current.beginning_of_month..Time.current.end_of_month)
+  }
+end
diff --git a/backend/app/models/gekanator_game.rb b/backend/app/models/gekanator_game.rb
new file mode 100644
index 0000000..bf223d8
--- /dev/null
+++ b/backend/app/models/gekanator_game.rb
@@ -0,0 +1,15 @@
+class GekanatorGame < ApplicationRecord
+  belongs_to :user
+  belongs_to :guessed_post, class_name: 'Post'
+  belongs_to :correct_post, class_name: 'Post'
+  has_many :question_suggestions,
+           class_name: 'GekanatorQuestionSuggestion',
+           dependent: :delete_all
+  has_many :question_examples,
+           class_name: 'GekanatorQuestionExample',
+           dependent: :delete_all
+
+  validates :answers, presence: true
+  validates :question_count, numericality: { greater_than_or_equal_to: 0 }
+  validates :won, inclusion: { in: [true, false] }
+end
diff --git a/backend/app/models/gekanator_question.rb b/backend/app/models/gekanator_question.rb
new file mode 100644
index 0000000..719da6e
--- /dev/null
+++ b/backend/app/models/gekanator_question.rb
@@ -0,0 +1,23 @@
+class GekanatorQuestion < ApplicationRecord
+  KINDS = ['tag', 'source', 'title', 'original_date', 'post_similarity'].freeze
+  SOURCES = ['user_suggested', 'ai_generated', 'admin_curated'].freeze
+  STATUSES = ['pending', 'accepted', 'rejected', 'disabled'].freeze
+
+  belongs_to :gekanator_question_suggestion, optional: true
+  belongs_to :created_by, class_name: 'User', optional: true
+  has_many :gekanator_question_examples, dependent: :delete_all
+
+  validates :kind, presence: true, inclusion: { in: KINDS }
+  validates :source, presence: true, inclusion: { in: SOURCES }
+  validates :status, presence: true, inclusion: { in: STATUSES }
+  validates :text, presence: true, length: { maximum: 1000 }
+  validates :condition, presence: true
+  validates :priority_weight,
+            presence: true,
+            numericality: {
+              greater_than: 0,
+              less_than_or_equal_to: 3
+            }
+
+  scope :accepted, -> { where(status: 'accepted') }
+end
diff --git a/backend/app/models/gekanator_question_example.rb b/backend/app/models/gekanator_question_example.rb
new file mode 100644
index 0000000..40698e9
--- /dev/null
+++ b/backend/app/models/gekanator_question_example.rb
@@ -0,0 +1,97 @@
+class GekanatorQuestionExample < ApplicationRecord
+  ANSWERS = GekanatorQuestionSuggestion::ANSWERS
+  NON_UNKNOWN_ANSWERS = ANSWERS - ['unknown']
+  SOURCES = ['initial_suggestion', 'post_game_answer', 'post_game_extra'].freeze
+
+  belongs_to :gekanator_question
+  belongs_to :post
+  belongs_to :user
+  belongs_to :gekanator_game, optional: true
+
+  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :answer_counts, presence: true
+  validates :sample_count,
+            presence: true,
+            numericality: {
+              only_integer: true,
+              greater_than: 0
+            }
+  validates :source, presence: true, inclusion: { in: SOURCES }
+  validates :weight,
+            presence: true,
+            numericality: {
+              greater_than: 0
+            }
+
+  before_validation :normalize_learning_state
+
+  def record_answer!(answer:, source:, gekanator_game: nil)
+    answer = answer.to_s
+    raise ArgumentError, 'invalid answer' unless ANSWERS.include?(answer)
+
+    counts = normalized_answer_counts
+    counts[answer] += 1
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+    self.gekanator_game = gekanator_game if gekanator_game.present?
+    self.source = source
+
+    apply_aggregated_answer!(preferred_answer: answer)
+    self
+  end
+
+  private
+
+  def normalize_learning_state
+    counts = normalized_answer_counts
+
+    if counts.values.sum.zero? && answer.present?
+      counts[answer] = 1
+    end
+
+    self.answer_counts = counts
+    self.sample_count = counts.values.sum
+
+    apply_aggregated_answer!
+  end
+
+  def apply_aggregated_answer!(preferred_answer: nil)
+    counts = normalized_answer_counts
+    known_counts = counts.slice(*NON_UNKNOWN_ANSWERS)
+    known_total = known_counts.values.sum
+
+    if known_total.zero?
+      self.answer = 'unknown'
+      self.weight = 0.1
+      return
+    else
+      max_count = known_counts.values.max
+      candidates = known_counts.select { |_answer, count| count == max_count }.keys
+      self.answer =
+          if preferred_answer.present? && candidates.include?(preferred_answer)
+            preferred_answer
+          elsif answer.present? && candidates.include?(answer)
+            answer
+          else
+            candidates.first
+          end
+    end
+
+    consensus = max_count.to_f / known_total
+    self.weight = Math.sqrt(known_total) * consensus
+  end
+
+  def normalized_answer_counts
+    base = ANSWERS.index_with(0)
+
+    answer_counts.to_h.each do |key, value|
+      answer_key = key.to_s
+      next unless ANSWERS.include?(answer_key)
+
+      base[answer_key] = value.to_i
+    end
+
+    base
+  end
+end
diff --git a/backend/app/models/gekanator_question_suggestion.rb b/backend/app/models/gekanator_question_suggestion.rb
new file mode 100644
index 0000000..4ff51a2
--- /dev/null
+++ b/backend/app/models/gekanator_question_suggestion.rb
@@ -0,0 +1,12 @@
+class GekanatorQuestionSuggestion < ApplicationRecord
+  ANSWERS = ['yes', 'no', 'partial', 'probably_no', 'unknown'].freeze
+
+  belongs_to :gekanator_game
+  belongs_to :user
+  has_many :gekanator_questions, dependent: :nullify
+  has_many :gekanator_ai_runs, dependent: :destroy
+
+  validates :question_text, presence: true, length: { maximum: 1000 }
+  validates :answer, presence: true, inclusion: { in: ANSWERS }
+  validates :processed, inclusion: { in: [true, false] }
+end
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 8970119..0342c7f 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -7,10 +7,23 @@ class Post < ApplicationRecord
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
   has_many :tags, through: :active_post_tags
+  has_many :active_tags, -> { where(tags: { deprecated_at: nil }) },
+           through: :active_post_tags, source: :tag
 
   has_many :user_post_views, dependent: :delete_all
   has_many :post_similarities, dependent: :delete_all
   has_many :post_versions
+  has_many :gekanator_guessed_games,
+           class_name: 'GekanatorGame',
+           foreign_key: :guessed_post_id,
+           dependent: :delete_all,
+           inverse_of: :guessed_post
+  has_many :gekanator_correct_games,
+           class_name: 'GekanatorGame',
+           foreign_key: :correct_post_id,
+           dependent: :delete_all,
+           inverse_of: :correct_post
+  has_many :gekanator_question_examples, dependent: :delete_all
 
   has_many :parent_post_implications,
            class_name: 'PostImplication',
@@ -125,7 +138,7 @@ class Post < ApplicationRecord
     return if !(f) || !(b)
 
     if f >= b
-      errors.add :original_created_before, 'オリジナルの作成日時の順番がをかしぃです．'
+      errors.add :original_created_at, 'オリジナルの作成日時の順番がをかしぃです．'
     end
   end
 
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 1d19df5..7cd6a48 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -8,6 +8,15 @@ class Tag < ApplicationRecord
     ;
   end
 
+  class DeprecatedTagNormalisationError < ArgumentError
+    attr_reader :tag_names
+
+    def initialize tag_names
+      @tag_names = Array(tag_names)
+      super('deprecated tags are not allowed')
+    end
+  end
+
   has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
@@ -58,6 +67,7 @@ class Tag < ApplicationRecord
   validate :nico_tag_name_must_start_with_nico
   validate :tag_name_must_be_canonical
   validate :category_must_be_deerjikist_with_deerjikists
+  validate :nico_tags_cannot_be_deprecated
 
   scope :nico_tags, -> { nico }
 
@@ -77,11 +87,13 @@ class Tag < ApplicationRecord
     (self.tag_name ||= build_tag_name).name = val
   end
 
+  def deprecated? = deprecated_at?
+
   def has_wiki = wiki_page.present?
 
   def material_id = materials.first&.id
 
-  def has_deerjikists = deerjikists.present?
+  def has_deerjikists = deerjikists.loaded? ? deerjikists.any? : deerjikists.exists?
 
   def self.tagme = find_or_create_by_tag_name!('タグ希望', category: :meta)
   def self.bot = find_or_create_by_tag_name!('bot操作', category: :meta)
@@ -93,6 +105,7 @@ class Tag < ApplicationRecord
   def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
                                       deny_nico: true,
+                                      deny_deprecated: false,
                                       with_sections: false
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
@@ -119,6 +132,10 @@ class Tag < ApplicationRecord
       name = TagName.canonicalise(name).first
 
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
+        if deny_deprecated && tag.deprecated?
+          raise DeprecatedTagNormalisationError, [tag.name]
+        end
+
         tag.update!(category: cat) if cat && tag.category != cat
         next if sections_by_tag.empty?
 
@@ -275,4 +292,10 @@ class Tag < ApplicationRecord
 
     total_s * 1_000 + ms.to_s.ljust(3, '0')[0, 3].to_i
   end
+
+  def nico_tags_cannot_be_deprecated
+    if nico? && deprecated_at.present?
+      errors.add :deprecated_at, 'ニコタグは廃止できません．'
+    end
+  end
 end
diff --git a/backend/app/models/theatre.rb b/backend/app/models/theatre.rb
index 1da8555..7912fe3 100644
--- a/backend/app/models/theatre.rb
+++ b/backend/app/models/theatre.rb
@@ -7,6 +7,10 @@ class Theatre < ApplicationRecord
            class_name: 'TheatreWatchingUser', inverse_of: :theatre
   has_many :watching_users, through: :active_theatre_watching_users, source: :user
 
+  has_many :programmes, class_name: 'TheatreProgramme'
+  has_many :skip_votes, class_name: 'TheatreSkipVote', dependent: :delete_all
+  has_many :skip_events, class_name: 'TheatreSkipEvent', dependent: :delete_all
+
   belongs_to :host_user, class_name: 'User', optional: true
   belongs_to :current_post, class_name: 'Post', optional: true
   belongs_to :created_by_user, class_name: 'User'
diff --git a/backend/app/models/theatre_programme.rb b/backend/app/models/theatre_programme.rb
new file mode 100644
index 0000000..58e2298
--- /dev/null
+++ b/backend/app/models/theatre_programme.rb
@@ -0,0 +1,6 @@
+class TheatreProgramme < ApplicationRecord
+  self.primary_key = :theatre_id, :position
+
+  belongs_to :theatre
+  belongs_to :post
+end
diff --git a/backend/app/models/theatre_skip_event.rb b/backend/app/models/theatre_skip_event.rb
new file mode 100644
index 0000000..80936ed
--- /dev/null
+++ b/backend/app/models/theatre_skip_event.rb
@@ -0,0 +1,10 @@
+class TheatreSkipEvent < ApplicationRecord
+  belongs_to :theatre
+  belongs_to :post
+  belongs_to :skipped_by_user, class_name: 'User'
+
+  has_many :voters, class_name: 'TheatreSkipEventVoter', dependent: :delete_all
+  has_many :event_tags, class_name: 'TheatreSkipEventTag', dependent: :delete_all
+  has_many :users, through: :voters
+  has_many :tags, through: :event_tags
+end
diff --git a/backend/app/models/theatre_skip_event_tag.rb b/backend/app/models/theatre_skip_event_tag.rb
new file mode 100644
index 0000000..e9ce248
--- /dev/null
+++ b/backend/app/models/theatre_skip_event_tag.rb
@@ -0,0 +1,6 @@
+class TheatreSkipEventTag < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :tag_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :tag
+end
diff --git a/backend/app/models/theatre_skip_event_voter.rb b/backend/app/models/theatre_skip_event_voter.rb
new file mode 100644
index 0000000..3db5b71
--- /dev/null
+++ b/backend/app/models/theatre_skip_event_voter.rb
@@ -0,0 +1,6 @@
+class TheatreSkipEventVoter < ApplicationRecord
+  self.primary_key = :theatre_skip_event_id, :user_id
+
+  belongs_to :theatre_skip_event
+  belongs_to :user
+end
diff --git a/backend/app/models/theatre_skip_vote.rb b/backend/app/models/theatre_skip_vote.rb
new file mode 100644
index 0000000..ecba421
--- /dev/null
+++ b/backend/app/models/theatre_skip_vote.rb
@@ -0,0 +1,7 @@
+class TheatreSkipVote < ApplicationRecord
+  self.primary_key = :theatre_id, :post_id, :user_id
+
+  belongs_to :theatre
+  belongs_to :post
+  belongs_to :user
+end
diff --git a/backend/app/models/wiki_page.rb b/backend/app/models/wiki_page.rb
index efe7868..68928f1 100644
--- a/backend/app/models/wiki_page.rb
+++ b/backend/app/models/wiki_page.rb
@@ -22,6 +22,7 @@ class WikiPage < ApplicationRecord
   validates :body, presence: true
 
   def title = tag_name.name
+  def deprecated_at = tag_name.tag&.deprecated_at
 
   def title= val
     (self.tag_name ||= build_tag_name).name = val
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index 87f59f9..1c62f1e 100644
--- a/backend/app/representations/post_repr.rb
+++ b/backend/app/representations/post_repr.rb
@@ -2,20 +2,65 @@
 
 
 module PostRepr
-  BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE },
-           methods: [:parent_posts, :child_posts, :sibling_posts] }.freeze
+  BASE_FIELDS = [
+      :id,
+      :version_no,
+      :url,
+      :title,
+      :thumbnail_base,
+      :original_created_from,
+      :original_created_before,
+      :created_at,
+      :updated_at
+  ].freeze
 
   module_function
 
   def base post, current_user = nil
-    json = post.as_json(BASE)
-    return json.merge(viewed: false) unless current_user
+    json = common(post)
+    json['tags'] = tag_json(post.tags)
+    json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
+    json['viewed'] = current_user ? current_user.viewed?(post) : false
+    json
+  end
 
-    viewed = current_user.viewed?(post)
-    json.merge(viewed:)
+  def detail post, current_user = nil, parent_posts: [], child_posts: [],
+             sibling_posts: { }, related: []
+    base(post, current_user).merge(
+        'parent_posts' => cards(parent_posts),
+        'child_posts' => cards(child_posts),
+        'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
+          cards(posts)
+        },
+        'related' => cards(related))
+  end
+
+  def card post
+    common(post).merge('parent_posts' => [], 'child_posts' => [])
+  end
+
+  def cards posts
+    posts.map { |post| card(post) }
   end
 
   def many posts, current_user = nil
     posts.map { |p| base(p, current_user) }
   end
+
+  def common post
+    BASE_FIELDS.to_h { |field| [field.to_s, post.public_send(field)] }
+               .merge('thumbnail' => thumbnail_url(post))
+  end
+
+  def tag_json tags
+    tags.reject(&:deprecated?).map { |tag| TagRepr.inline(tag) }
+  end
+
+  def thumbnail_url post
+    return nil unless post.thumbnail.attached?
+
+    Rails.application.routes.url_helpers.rails_blob_url(post.thumbnail, only_path: false)
+  rescue
+    nil
+  end
 end
diff --git a/backend/app/representations/tag_repr.rb b/backend/app/representations/tag_repr.rb
index 705c096..3958953 100644
--- a/backend/app/representations/tag_repr.rb
+++ b/backend/app/representations/tag_repr.rb
@@ -2,7 +2,7 @@
 
 
 module TagRepr
-  BASE = { only: [:id, :category, :post_count, :created_at, :updated_at],
+  BASE = { only: [:id, :category, :post_count, :created_at, :updated_at, :deprecated_at],
            methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
 
   module_function
@@ -12,5 +12,9 @@ module TagRepr
                             parents: tag.parents.map { _1.as_json(BASE) })
   end
 
+  def inline tag
+    tag.as_json(BASE).merge(aliases: [], parents: [])
+  end
+
   def many(tags) = tags.map { |t| base(t) }
 end
diff --git a/backend/app/representations/wiki_page_repr.rb b/backend/app/representations/wiki_page_repr.rb
index 3fb712c..ee09de3 100644
--- a/backend/app/representations/wiki_page_repr.rb
+++ b/backend/app/representations/wiki_page_repr.rb
@@ -2,7 +2,7 @@
 
 
 module WikiPageRepr
-  BASE = { methods: [:title] }.freeze
+  BASE = { methods: [:title, :deprecated_at] }.freeze
 
   module_function
 
diff --git a/backend/app/services/gekanator/ai_run_budget.rb b/backend/app/services/gekanator/ai_run_budget.rb
new file mode 100644
index 0000000..20115ef
--- /dev/null
+++ b/backend/app/services/gekanator/ai_run_budget.rb
@@ -0,0 +1,22 @@
+module Gekanator
+  class AiRunBudget
+    MONTHLY_LIMIT_JPY = BigDecimal('450').freeze
+    MAX_RUN_ESTIMATED_COST_JPY = BigDecimal('5').freeze
+
+    def self.remaining_monthly_budget_jpy
+      MONTHLY_LIMIT_JPY - monthly_cost_jpy
+    end
+
+    def self.monthly_cost_jpy
+      GekanatorAiRun.this_month.sum(:estimated_cost_jpy)
+    end
+
+    def self.exceeded?
+      monthly_cost_jpy >= MONTHLY_LIMIT_JPY
+    end
+
+    def self.exceeded_after_next_run?
+      monthly_cost_jpy + MAX_RUN_ESTIMATED_COST_JPY >= MONTHLY_LIMIT_JPY
+    end
+  end
+end
diff --git a/backend/app/services/gekanator/question_suggestion_ai_converter.rb b/backend/app/services/gekanator/question_suggestion_ai_converter.rb
new file mode 100644
index 0000000..5af2caf
--- /dev/null
+++ b/backend/app/services/gekanator/question_suggestion_ai_converter.rb
@@ -0,0 +1,168 @@
+module Gekanator
+  class QuestionSuggestionAiConverter
+    # Temporary heuristic converter for #361.
+    # This creates pending ai_generated questions without external LLM calls;
+    # accepted questions are still distributed only after admin approval.
+    TITLE_LENGTH_RE = /\Aタイトルは\s*(\d+)\s*文字以上[？?]\z/
+    ORIGINAL_YEAR_RE = /\Aオリジナルの投稿年は\s*(\d{4})\s*年[？?]\z/
+    ORIGINAL_MONTH_RE = /\Aオリジナルの投稿月は\s*(\d{1,2})\s*月[？?]\z/
+    ORIGINAL_MONTH_DAY_RE = /\Aオリジナルの投稿日は\s*(\d{1,2})\s*月\s*(\d{1,2})\s*日[？?]\z/
+    TITLE_CONTAINS_RE = /\A題名に「(.+?)」が含まれる[？?]\z/
+    SOURCE_RE = /\A(.+?)\s+の投稿を思[ひい]浮かべて[ゐい]る[？?]\z/
+
+    def self.call(...) = new(...).call
+
+    def initialize suggestion:, user:
+      @suggestion = suggestion
+      @user = user
+    end
+
+    def call
+      suggestion.with_lock do
+        existing = existing_generated_question
+        return existing if existing
+
+        run = suggestion.gekanator_ai_runs.create!(
+            model: 'heuristic_converter_v1',
+            status: 'running',
+            input_tokens: 0,
+            output_tokens: 0,
+            estimated_cost_jpy: 0)
+
+        question_attributes = build_question
+        question =
+            question_attributes &&
+            GekanatorQuestion.create!(
+                **question_attributes,
+                source: 'ai_generated',
+                status: 'pending',
+                gekanator_question_suggestion: suggestion,
+                created_by: user)
+
+        run.update!(status: question ? 'succeeded' : 'failed')
+        question
+      end
+    rescue => error
+      run&.update!(status: 'failed') if run&.persisted? && run.status != 'failed'
+      raise error
+    end
+
+    private
+
+    attr_reader :suggestion, :user
+
+    def existing_generated_question
+      suggestion
+          .gekanator_questions
+          .where(source: 'ai_generated')
+          .order(id: :desc)
+          .first
+    end
+
+    def build_question
+      text = normalized_text
+      return nil if text.blank?
+
+      structured_question_for(text) || post_similarity_question_for(text)
+    end
+
+    def normalized_text
+      suggestion.question_text.to_s.gsub(/[[:space:]]+/, ' ').strip
+    end
+
+    def structured_question_for text
+      case text
+      when TITLE_LENGTH_RE
+        length = Regexp.last_match(1).to_i
+        return nil if length <= 0
+
+        {
+          text:,
+          kind: 'title',
+          condition: {
+            type: 'title-length-at-least',
+            length:
+          },
+          priority_weight: 0.95
+        }
+      when /\A題名に英数字が混じって[ゐい]る[？?]\z/
+        {
+          text: '題名に英数字が混じってゐる?',
+          kind: 'title',
+          condition: { type: 'title-has-ascii' },
+          priority_weight: 0.95
+        }
+      when ORIGINAL_YEAR_RE
+        year = Regexp.last_match(1).to_i
+        {
+          text:,
+          kind: 'original_date',
+          condition: { type: 'original-year', year: },
+          priority_weight: 0.95
+        }
+      when ORIGINAL_MONTH_RE
+        month = Regexp.last_match(1).to_i
+        return nil unless month.between?(1, 12)
+
+        {
+          text:,
+          kind: 'original_date',
+          condition: { type: 'original-month', month: },
+          priority_weight: 0.95
+        }
+      when ORIGINAL_MONTH_DAY_RE
+        month = Regexp.last_match(1).to_i
+        day = Regexp.last_match(2).to_i
+        return nil unless month.between?(1, 12) && day.between?(1, 31)
+
+        {
+          text:,
+          kind: 'original_date',
+          condition: {
+            type: 'original-month-day',
+            monthDay: "#{ month }-#{ day }"
+          },
+          priority_weight: 0.95
+        }
+      when TITLE_CONTAINS_RE
+        title_text = Regexp.last_match(1).to_s.strip
+        return nil if title_text.blank?
+
+        {
+          text: "題名に「#{ title_text }」が含まれる?",
+          kind: 'title',
+          condition: { type: 'title-contains', text: title_text },
+          priority_weight: 0.95
+        }
+      when SOURCE_RE
+        host = Regexp.last_match(1).to_s.strip
+        return nil if host.blank?
+
+        {
+          text:,
+          kind: 'source',
+          condition: { type: 'source', host: },
+          priority_weight: 0.95
+        }
+      else
+        nil
+      end
+    end
+
+    def post_similarity_question_for text
+      return nil if suggestion.answer == 'unknown'
+
+      {
+        text:,
+        kind: 'post_similarity',
+        condition: {
+          type: 'post-similarity',
+          postId: suggestion.gekanator_game.correct_post_id,
+          answer: suggestion.answer,
+          threshold: 0.65
+        },
+        priority_weight: 1.0
+      }
+    end
+  end
+end
diff --git a/backend/app/services/gekanator/question_suggestion_promoter.rb b/backend/app/services/gekanator/question_suggestion_promoter.rb
new file mode 100644
index 0000000..61269bf
--- /dev/null
+++ b/backend/app/services/gekanator/question_suggestion_promoter.rb
@@ -0,0 +1,52 @@
+module Gekanator
+  class QuestionSuggestionPromoter
+    def self.call(...) = new(...).call
+
+    def initialize suggestion:, user:
+      @suggestion = suggestion
+      @user = user
+    end
+
+    def call
+      suggestion.with_lock do
+        return promoted_question if suggestion.processed?
+        return suggestion if suggestion.answer == 'unknown'
+
+        question = GekanatorQuestion.create!(
+            text: suggestion.question_text,
+            kind: 'post_similarity',
+            source: 'user_suggested',
+            status: 'accepted',
+            priority_weight: 1.2,
+            condition: {
+              type: 'post-similarity',
+              postId: suggestion.gekanator_game.correct_post_id,
+              answer: suggestion.answer,
+              threshold: 0.65
+            },
+            gekanator_question_suggestion: suggestion,
+            created_by: user)
+        example =
+            GekanatorQuestionExample.new(
+                gekanator_question: question,
+                post: suggestion.gekanator_game.correct_post,
+                user: user)
+        example.record_answer!(
+            answer: suggestion.answer,
+            source: 'initial_suggestion',
+            gekanator_game: suggestion.gekanator_game)
+        example.save!
+        suggestion.update!(processed: true)
+        question
+      end
+    end
+
+    private
+
+    attr_reader :suggestion, :user
+
+    def promoted_question
+      suggestion.gekanator_questions.order(id: :desc).first
+    end
+  end
+end
diff --git a/backend/app/services/similarity/calc.rb b/backend/app/services/similarity/calc.rb
index 40d717d..f320375 100644
--- a/backend/app/services/similarity/calc.rb
+++ b/backend/app/services/similarity/calc.rb
@@ -1,6 +1,6 @@
 module Similarity
   class Calc
-    def self.call model, tgt
+    def self.call model, tgt, scope: nil
       similarity_model = "#{ model.name }Similarity".constantize
 
       # 最大保存件数
@@ -8,7 +8,8 @@ module Similarity
 
       similarity_model.delete_all
 
-      posts = model.includes(tgt).select(:id).to_a
+      scope ||= model.all
+      posts = scope.includes(tgt).select(:id).to_a
 
       tag_ids = { }
       tag_cnts = { }
diff --git a/backend/app/services/tag_version_recorder.rb b/backend/app/services/tag_version_recorder.rb
index fe2b0c1..a786058 100644
--- a/backend/app/services/tag_version_recorder.rb
+++ b/backend/app/services/tag_version_recorder.rb
@@ -16,6 +16,7 @@ class TagVersionRecorder < VersionRecorder
   def snapshot_attributes
     { name: @record.name,
       category: @record.category,
+      deprecated_at: @record.deprecated_at,
       aliases: @record.snapshot_aliases.join(' '),
       parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
   end
diff --git a/backend/app/services/theatre_post_advancer.rb b/backend/app/services/theatre_post_advancer.rb
new file mode 100644
index 0000000..c7d9e6c
--- /dev/null
+++ b/backend/app/services/theatre_post_advancer.rb
@@ -0,0 +1,29 @@
+class TheatrePostAdvancer
+  def self.call(theatre:)
+    new(theatre:).call
+  end
+
+  def initialize(theatre:)
+    @theatre = theatre
+  end
+
+  def call
+    previous_post = theatre.current_post
+    post = TheatrePostSelector.new(theatre:).select
+
+    TheatreSkipVote.where(theatre:, post: previous_post).delete_all if previous_post
+
+    theatre.update!(current_post: post, current_post_started_at: post ? Time.current : nil)
+
+    if post
+      position = (theatre.programmes.maximum(:position) || 0) + 1
+      theatre.programmes.create!(position:, post:)
+    end
+
+    post
+  end
+
+  private
+
+  attr_reader :theatre
+end
diff --git a/backend/app/services/theatre_post_selector.rb b/backend/app/services/theatre_post_selector.rb
new file mode 100644
index 0000000..124c913
--- /dev/null
+++ b/backend/app/services/theatre_post_selector.rb
@@ -0,0 +1,119 @@
+class TheatrePostSelector
+  Candidate = Struct.new(:post, :weight, :penalty, :tags, keyword_init: true)
+  ELIGIBLE_POST_URL_CONDITION =
+      ["url LIKE '%nicovideo.jp%'",
+       "url LIKE '%youtube.com/watch%'",
+       "url LIKE '%youtu.be/%'"]
+      .join(' OR ')
+
+  def initialize theatre:
+    @theatre = theatre
+  end
+
+  def select
+    candidates = weighted_candidates
+    return nil if candidates.empty?
+
+    total = candidates.sum(&:weight)
+    target = rand * total
+
+    candidates.each do |candidate|
+      target -= candidate.weight
+      return candidate.post if target <= 0
+    end
+
+    candidates.last.post
+  end
+
+  def weight_json limit: 20
+    candidates = weighted_candidates
+    sorted = candidates.sort_by { |candidate| [candidate.weight, candidate.post.id] }
+
+    { tag_penalties: tag_penalty_json,
+      lightest_posts: post_weight_json(sorted.first(limit)),
+      heaviest_posts: post_weight_json(sorted.reverse.first(limit)) }
+  end
+
+  private
+
+  attr_reader :theatre
+
+  def weighted_candidates
+    @weighted_candidates ||= begin
+      penalties = tag_penalties
+      posts = eligible_posts.includes(tags: :tag_name).to_a
+
+      posts.map do |post|
+        post_tags = post.tags.to_a
+        penalty = post_tags.sum { |tag| penalties[tag.id].to_i }
+
+        Candidate.new(
+            post:,
+            penalty:,
+            tags: post_tags,
+            weight: 1.0 / (1.0 + penalty))
+      end
+    end
+  end
+
+  def eligible_posts
+    posts = Post.where(ELIGIBLE_POST_URL_CONDITION)
+    posts = posts.where.not(id: theatre.current_post_id) if theatre.current_post_id
+    posts
+  end
+
+  def active_user_ids
+    @active_user_ids ||= theatre.watching_users.ids
+  end
+
+  def tag_penalties
+    @tag_penalties ||=
+      if active_user_ids.empty?
+        {}
+      else
+        TheatreSkipEventVoter
+          .joins(theatre_skip_event: :event_tags)
+          .where(user_id: active_user_ids)
+          .group('theatre_skip_event_tags.tag_id')
+          .count
+      end
+  end
+
+  def tag_penalty_json
+    return [] if tag_penalties.empty?
+
+    tags = Tag.where(id: tag_penalties.keys).includes(:tag_name).index_by(&:id)
+
+    tag_penalties
+      .map { |tag_id, penalty|
+        tag = tags[tag_id]
+        next unless tag
+
+        { tag: light_tag_json(tag),
+          penalty: }
+      }
+      .compact
+      .sort_by { |row| [-row[:penalty], row[:tag][:name].to_s] }
+  end
+
+  def post_weight_json candidates
+    candidates.map { |candidate|
+      { post: light_post_json(candidate.post),
+        weight: candidate.weight,
+        penalty: candidate.penalty,
+        tags: candidate.tags.map { |tag| light_tag_json(tag) } }
+    }
+  end
+
+  def light_post_json post
+    { id: post.id,
+      title: post.title,
+      url: post.url }
+  end
+
+  def light_tag_json tag
+    { id: tag.id,
+      name: tag.name,
+      category: tag.category }
+  end
+end
diff --git a/backend/app/services/theatre_skip_finalizer.rb b/backend/app/services/theatre_skip_finalizer.rb
new file mode 100644
index 0000000..b098df1
--- /dev/null
+++ b/backend/app/services/theatre_skip_finalizer.rb
@@ -0,0 +1,40 @@
+class TheatreSkipFinalizer
+  def self.call(theatre:, user:)
+    new(theatre:, user:).call
+  end
+
+  def initialize(theatre:, user:)
+    @theatre = theatre
+    @user = user
+  end
+
+  def call
+    return unless theatre.current_post
+
+    post = theatre.current_post
+    voters = TheatreSkipVote.where(theatre:, post:).includes(:user).map(&:user)
+    return if voters.empty?
+
+    event = TheatreSkipEvent.create!(
+        theatre:,
+        post:,
+        skipped_by_user: user,
+        programme_position: theatre.programmes.maximum(:position))
+
+    voters.uniq(&:id).each do |voter|
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: voter)
+    end
+
+    post.tags.find_each do |tag|
+      TheatreSkipEventTag.create!(theatre_skip_event: event, tag:)
+    end
+
+    TheatreSkipVote.where(theatre:, post:).delete_all
+
+    event
+  end
+
+  private
+
+  attr_reader :theatre, :user
+end
diff --git a/backend/config/routes.rb b/backend/config/routes.rb
index 6e62f1e..f30959b 100644
--- a/backend/config/routes.rb
+++ b/backend/config/routes.rb
@@ -63,6 +63,24 @@ Rails.application.routes.draw do
     end
   end
 
+  namespace :gekanator do
+    resources :games, only: [:create], controller: '/gekanator_games' do
+      member do
+        get :extra_questions
+        post :extra_question_answers
+      end
+    end
+    resources :posts, only: [:index], controller: '/gekanator_posts'
+    resources :questions, only: [:index], controller: '/gekanator_questions'
+    resources :question_suggestions,
+              only: [:create],
+              controller: '/gekanator_question_suggestions' do
+      member do
+        post :ai_convert
+      end
+    end
+  end
+
   resources :users, only: [:create, :update] do
     collection do
       post :verify
@@ -85,9 +103,14 @@ Rails.application.routes.draw do
     member do
       put :watching
       patch :next_post
+      put :skip_vote
+      delete :skip_vote, action: :unskip_vote
+      get :post_selection_weights
     end
 
-    resources :comments, controller: :theatre_comments, only: [:index, :create]
+    resources :comments, controller: :theatre_comments, only: [:index, :create, :destroy]
+    resources :programmes, controller: :theatre_programmes, only: [:index]
+    resources :skip_events, controller: :theatre_skip_events, only: [:index]
   end
 
   resources :materials, only: [:index, :show, :create, :update, :destroy]
diff --git a/backend/db/migrate/20260514221900_create_theatre_programmes.rb b/backend/db/migrate/20260514221900_create_theatre_programmes.rb
new file mode 100644
index 0000000..f89f04b
--- /dev/null
+++ b/backend/db/migrate/20260514221900_create_theatre_programmes.rb
@@ -0,0 +1,10 @@
+class CreateTheatreProgrammes < ActiveRecord::Migration[8.0]
+  def change
+    create_table :theatre_programmes, primary_key: [:theatre_id, :position] do |t|
+      t.references :theatre, null: false, foreign_key: true
+      t.integer :position, null: false
+      t.references :post, null: false, foreign_key: true
+      t.datetime :created_at, null: false
+    end
+  end
+end
diff --git a/backend/db/migrate/20260606000000_create_theatre_skip_votes_and_events.rb b/backend/db/migrate/20260606000000_create_theatre_skip_votes_and_events.rb
new file mode 100644
index 0000000..8361d6a
--- /dev/null
+++ b/backend/db/migrate/20260606000000_create_theatre_skip_votes_and_events.rb
@@ -0,0 +1,36 @@
+class CreateTheatreSkipVotesAndEvents < ActiveRecord::Migration[8.0]
+  def change
+    create_table :theatre_skip_votes, primary_key: [:theatre_id, :post_id, :user_id] do |t|
+      t.references :theatre, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+      t.timestamps
+    end
+
+    create_table :theatre_skip_events do |t|
+      t.references :theatre, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :skipped_by_user, null: false, foreign_key: { to_table: :users }
+      t.integer :programme_position
+      t.datetime :created_at, null: false
+    end
+
+    create_table :theatre_skip_event_voters, primary_key: [:theatre_skip_event_id, :user_id] do |t|
+      t.references :theatre_skip_event, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+    end
+
+    create_table :theatre_skip_event_tags, primary_key: [:theatre_skip_event_id, :tag_id] do |t|
+      t.references :theatre_skip_event, null: false, foreign_key: true
+      t.references :tag, null: false, foreign_key: true
+    end
+
+    add_index :theatre_skip_events, [:theatre_id, :created_at]
+    add_index :theatre_skip_votes, [:theatre_id, :post_id, :created_at],
+              name: 'idx_theatre_skip_votes_theatre_post_created'
+    add_index :theatre_skip_event_voters, [:user_id, :theatre_skip_event_id],
+              name: 'idx_theatre_skip_event_voters_user_event'
+    add_index :theatre_skip_event_tags, [:tag_id, :theatre_skip_event_id],
+              name: 'idx_theatre_skip_event_tags_tag_event'
+  end
+end
diff --git a/backend/db/migrate/20260607000000_create_gekanator_games.rb b/backend/db/migrate/20260607000000_create_gekanator_games.rb
new file mode 100644
index 0000000..a357bf9
--- /dev/null
+++ b/backend/db/migrate/20260607000000_create_gekanator_games.rb
@@ -0,0 +1,18 @@
+class CreateGekanatorGames < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_games do |t|
+      t.references :user, null: false, foreign_key: true
+      t.references :guessed_post, null: false, foreign_key: { to_table: :posts }
+      t.references :correct_post, null: false, foreign_key: { to_table: :posts }
+      t.boolean :won, null: false
+      t.integer :question_count, null: false
+      t.json :answers, null: false
+
+      t.timestamps
+    end
+
+    add_check_constraint :gekanator_games,
+                         'question_count >= 0',
+                         name: 'chk_gekanator_games_question_count_nonnegative'
+  end
+end
diff --git a/backend/db/migrate/20260608000000_create_gekanator_question_suggestions.rb b/backend/db/migrate/20260608000000_create_gekanator_question_suggestions.rb
new file mode 100644
index 0000000..57b38bb
--- /dev/null
+++ b/backend/db/migrate/20260608000000_create_gekanator_question_suggestions.rb
@@ -0,0 +1,14 @@
+class CreateGekanatorQuestionSuggestions < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_question_suggestions do |t|
+      t.references :gekanator_game,
+                   null: false,
+                   foreign_key: { on_delete: :cascade }
+      t.references :user, null: false, foreign_key: true
+      t.text :question_text, null: false
+      t.boolean :processed, null: false, default: false
+
+      t.timestamps
+    end
+  end
+end
diff --git a/backend/db/migrate/20260608002000_add_answer_to_gekanator_question_suggestions.rb b/backend/db/migrate/20260608002000_add_answer_to_gekanator_question_suggestions.rb
new file mode 100644
index 0000000..104b156
--- /dev/null
+++ b/backend/db/migrate/20260608002000_add_answer_to_gekanator_question_suggestions.rb
@@ -0,0 +1,5 @@
+class AddAnswerToGekanatorQuestionSuggestions < ActiveRecord::Migration[8.0]
+  def change
+    add_column :gekanator_question_suggestions, :answer, :string, null: false
+  end
+end
diff --git a/backend/db/migrate/20260609000000_create_gekanator_questions.rb b/backend/db/migrate/20260609000000_create_gekanator_questions.rb
new file mode 100644
index 0000000..26d6fbd
--- /dev/null
+++ b/backend/db/migrate/20260609000000_create_gekanator_questions.rb
@@ -0,0 +1,19 @@
+class CreateGekanatorQuestions < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_questions do |t|
+      t.string :text, null: false
+      t.string :kind, null: false
+      t.json :condition, null: false
+      t.string :source, null: false, default: 'ai_generated'
+      t.string :status, null: false, default: 'pending'
+      t.float :priority_weight, null: false, default: 1.0
+      t.references :gekanator_question_suggestion,
+                   null: true,
+                   foreign_key: true
+      t.references :created_by,
+                   null: true,
+                   foreign_key: { to_table: :users }
+      t.timestamps
+    end
+  end
+end
diff --git a/backend/db/migrate/20260609001000_create_gekanator_ai_runs.rb b/backend/db/migrate/20260609001000_create_gekanator_ai_runs.rb
new file mode 100644
index 0000000..695dd03
--- /dev/null
+++ b/backend/db/migrate/20260609001000_create_gekanator_ai_runs.rb
@@ -0,0 +1,13 @@
+class CreateGekanatorAiRuns < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_ai_runs do |t|
+      t.string :model, null: false
+      t.integer :input_tokens, null: false, default: 0
+      t.integer :output_tokens, null: false, default: 0
+      t.decimal :estimated_cost_jpy, precision: 8, scale: 3, null: false, default: 0
+      t.string :status, null: false, default: 'pending'
+      t.references :gekanator_question_suggestion, null: false, foreign_key: true
+      t.timestamps
+    end
+  end
+end
diff --git a/backend/db/migrate/20260610000000_create_gekanator_question_examples.rb b/backend/db/migrate/20260610000000_create_gekanator_question_examples.rb
new file mode 100644
index 0000000..f115067
--- /dev/null
+++ b/backend/db/migrate/20260610000000_create_gekanator_question_examples.rb
@@ -0,0 +1,19 @@
+class CreateGekanatorQuestionExamples < ActiveRecord::Migration[8.0]
+  def change
+    create_table :gekanator_question_examples do |t|
+      t.references :gekanator_question, null: false, foreign_key: true
+      t.references :post, null: false, foreign_key: true
+      t.references :user, null: false, foreign_key: true
+      t.references :gekanator_game, null: true, foreign_key: true
+      t.string :answer, null: false
+      t.string :source, null: false, default: 'post_game_extra'
+      t.float :weight, null: false, default: 1.0
+      t.timestamps
+    end
+
+    add_index :gekanator_question_examples,
+              [:gekanator_question_id, :post_id, :user_id],
+              unique: true,
+              name: 'idx_gekanator_question_examples_on_question_post_user'
+  end
+end
diff --git a/backend/db/migrate/20260612000000_add_answer_statistics_to_gekanator_question_examples.rb b/backend/db/migrate/20260612000000_add_answer_statistics_to_gekanator_question_examples.rb
new file mode 100644
index 0000000..fad1e9d
--- /dev/null
+++ b/backend/db/migrate/20260612000000_add_answer_statistics_to_gekanator_question_examples.rb
@@ -0,0 +1,40 @@
+class AddAnswerStatisticsToGekanatorQuestionExamples < ActiveRecord::Migration[8.0]
+  class MigrationGekanatorQuestionExample < ApplicationRecord
+    self.table_name = 'gekanator_question_examples'
+  end
+
+  def up
+    add_column :gekanator_question_examples,
+               :answer_counts,
+               :json,
+               null: true
+    add_column :gekanator_question_examples,
+               :sample_count,
+               :integer,
+               null: false,
+               default: 1
+
+    MigrationGekanatorQuestionExample.reset_column_information
+    MigrationGekanatorQuestionExample.find_each do |example|
+      counts = {
+        'yes' => 0,
+        'no' => 0,
+        'partial' => 0,
+        'probably_no' => 0,
+        'unknown' => 0
+      }
+      counts[example.answer] = 1 if counts.key?(example.answer)
+
+      example.update_columns(
+        answer_counts: counts,
+        sample_count: 1)
+    end
+
+    change_column_null :gekanator_question_examples, :answer_counts, false
+  end
+
+  def down
+    remove_column :gekanator_question_examples, :sample_count
+    remove_column :gekanator_question_examples, :answer_counts
+  end
+end
diff --git a/backend/db/migrate/20260621000000_add_deprecated_at_to_tags.rb b/backend/db/migrate/20260621000000_add_deprecated_at_to_tags.rb
new file mode 100644
index 0000000..4456f88
--- /dev/null
+++ b/backend/db/migrate/20260621000000_add_deprecated_at_to_tags.rb
@@ -0,0 +1,20 @@
+class AddDeprecatedAtToTags < ActiveRecord::Migration[8.0]
+  def up
+    add_column :tags, :deprecated_at, :datetime, after: :category
+    add_column :tag_versions, :deprecated_at, :datetime, after: :parent_tag_ids
+
+    add_index :tags, :deprecated_at
+
+    add_check_constraint :tags, "deprecated_at IS NULL OR category <> 'nico'",
+                         name: 'chk_tags_deprecated_at_not_nico'
+  end
+
+  def down
+    remove_check_constraint :tags, name: 'chk_tags_deprecated_at_not_nico'
+
+    remove_index :tags, :deprecated_at
+
+    remove_column :tag_versions, :deprecated_at, :datetime
+    remove_column :tags, :deprecated_at
+  end
+end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 60e80eb..62f6808 100644
--- a/backend/db/schema.rb
+++ b/backend/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_21_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -48,6 +48,79 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
     t.index ["tag_id"], name: "index_deerjikists_on_tag_id"
   end
 
+  create_table "gekanator_ai_runs", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "model", null: false
+    t.integer "input_tokens", default: 0, null: false
+    t.integer "output_tokens", default: 0, null: false
+    t.decimal "estimated_cost_jpy", precision: 8, scale: 3, default: "0.0", null: false
+    t.string "status", default: "pending", null: false
+    t.bigint "gekanator_question_suggestion_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["gekanator_question_suggestion_id"], name: "index_gekanator_ai_runs_on_gekanator_question_suggestion_id"
+  end
+
+  create_table "gekanator_games", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "user_id", null: false
+    t.bigint "guessed_post_id", null: false
+    t.bigint "correct_post_id", null: false
+    t.boolean "won", null: false
+    t.integer "question_count", null: false
+    t.json "answers", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["correct_post_id"], name: "index_gekanator_games_on_correct_post_id"
+    t.index ["guessed_post_id"], name: "index_gekanator_games_on_guessed_post_id"
+    t.index ["user_id"], name: "index_gekanator_games_on_user_id"
+    t.check_constraint "`question_count` >= 0", name: "chk_gekanator_games_question_count_nonnegative"
+  end
+
+  create_table "gekanator_question_examples", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "gekanator_question_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "user_id", null: false
+    t.bigint "gekanator_game_id"
+    t.string "answer", null: false
+    t.string "source", default: "post_game_extra", null: false
+    t.float "weight", default: 1.0, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.json "answer_counts", null: false
+    t.integer "sample_count", default: 1, null: false
+    t.index ["gekanator_game_id"], name: "index_gekanator_question_examples_on_gekanator_game_id"
+    t.index ["gekanator_question_id", "post_id", "user_id"], name: "idx_gekanator_question_examples_on_question_post_user", unique: true
+    t.index ["gekanator_question_id"], name: "index_gekanator_question_examples_on_gekanator_question_id"
+    t.index ["post_id"], name: "index_gekanator_question_examples_on_post_id"
+    t.index ["user_id"], name: "index_gekanator_question_examples_on_user_id"
+  end
+
+  create_table "gekanator_question_suggestions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "gekanator_game_id", null: false
+    t.bigint "user_id", null: false
+    t.text "question_text", null: false
+    t.boolean "processed", default: false, null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.string "answer", null: false
+    t.index ["gekanator_game_id"], name: "index_gekanator_question_suggestions_on_gekanator_game_id"
+    t.index ["user_id"], name: "index_gekanator_question_suggestions_on_user_id"
+  end
+
+  create_table "gekanator_questions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "text", null: false
+    t.string "kind", null: false
+    t.json "condition", null: false
+    t.string "source", default: "ai_generated", null: false
+    t.string "status", default: "pending", null: false
+    t.float "priority_weight", default: 1.0, null: false
+    t.bigint "gekanator_question_suggestion_id"
+    t.bigint "created_by_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_id"], name: "index_gekanator_questions_on_created_by_id"
+    t.index ["gekanator_question_suggestion_id"], name: "index_gekanator_questions_on_gekanator_question_suggestion_id"
+  end
+
   create_table "ip_addresses", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.binary "ip_address", limit: 16, null: false
     t.datetime "banned_at"
@@ -262,6 +335,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
     t.string "event_type", null: false
     t.string "name", null: false
     t.string "category", null: false
+    t.datetime "deprecated_at"
     t.text "aliases", null: false
     t.text "parent_tag_ids", null: false
     t.datetime "created_at", null: false
@@ -279,10 +353,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
+    t.datetime "deprecated_at"
     t.datetime "discarded_at"
     t.integer "version_no", null: false
+    t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
     t.index ["discarded_at"], name: "index_tags_on_discarded_at"
     t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
+    t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
   end
 
@@ -299,6 +376,55 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
     t.index ["user_id"], name: "index_theatre_comments_on_user_id"
   end
 
+  create_table "theatre_programmes", primary_key: ["theatre_id", "position"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_id", null: false
+    t.integer "position", null: false
+    t.bigint "post_id", null: false
+    t.datetime "created_at", null: false
+    t.index ["post_id"], name: "index_theatre_programmes_on_post_id"
+    t.index ["theatre_id"], name: "index_theatre_programmes_on_theatre_id"
+  end
+
+  create_table "theatre_skip_event_tags", primary_key: ["theatre_skip_event_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_skip_event_id", null: false
+    t.bigint "tag_id", null: false
+    t.index ["tag_id", "theatre_skip_event_id"], name: "idx_theatre_skip_event_tags_tag_event"
+    t.index ["tag_id"], name: "index_theatre_skip_event_tags_on_tag_id"
+    t.index ["theatre_skip_event_id"], name: "index_theatre_skip_event_tags_on_theatre_skip_event_id"
+  end
+
+  create_table "theatre_skip_event_voters", primary_key: ["theatre_skip_event_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_skip_event_id", null: false
+    t.bigint "user_id", null: false
+    t.index ["theatre_skip_event_id"], name: "index_theatre_skip_event_voters_on_theatre_skip_event_id"
+    t.index ["user_id", "theatre_skip_event_id"], name: "idx_theatre_skip_event_voters_user_event"
+    t.index ["user_id"], name: "index_theatre_skip_event_voters_on_user_id"
+  end
+
+  create_table "theatre_skip_events", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "skipped_by_user_id", null: false
+    t.integer "programme_position"
+    t.datetime "created_at", null: false
+    t.index ["post_id"], name: "index_theatre_skip_events_on_post_id"
+    t.index ["skipped_by_user_id"], name: "index_theatre_skip_events_on_skipped_by_user_id"
+    t.index ["theatre_id", "created_at"], name: "index_theatre_skip_events_on_theatre_id_and_created_at"
+    t.index ["theatre_id"], name: "index_theatre_skip_events_on_theatre_id"
+  end
+
+  create_table "theatre_skip_votes", primary_key: ["theatre_id", "post_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "theatre_id", null: false
+    t.bigint "post_id", null: false
+    t.bigint "user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["post_id"], name: "index_theatre_skip_votes_on_post_id"
+    t.index ["theatre_id", "post_id", "created_at"], name: "idx_theatre_skip_votes_theatre_post_created"
+    t.index ["theatre_id"], name: "index_theatre_skip_votes_on_theatre_id"
+    t.index ["user_id"], name: "index_theatre_skip_votes_on_user_id"
+  end
+
   create_table "theatre_watching_users", primary_key: ["theatre_id", "user_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "theatre_id", null: false
     t.bigint "user_id", null: false
@@ -446,6 +572,18 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
 
   add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
   add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
+  add_foreign_key "gekanator_ai_runs", "gekanator_question_suggestions"
+  add_foreign_key "gekanator_games", "posts", column: "correct_post_id"
+  add_foreign_key "gekanator_games", "posts", column: "guessed_post_id"
+  add_foreign_key "gekanator_games", "users"
+  add_foreign_key "gekanator_question_examples", "gekanator_games"
+  add_foreign_key "gekanator_question_examples", "gekanator_questions"
+  add_foreign_key "gekanator_question_examples", "posts"
+  add_foreign_key "gekanator_question_examples", "users"
+  add_foreign_key "gekanator_question_suggestions", "gekanator_games", on_delete: :cascade
+  add_foreign_key "gekanator_question_suggestions", "users"
+  add_foreign_key "gekanator_questions", "gekanator_question_suggestions"
+  add_foreign_key "gekanator_questions", "users", column: "created_by_id"
   add_foreign_key "material_versions", "materials"
   add_foreign_key "material_versions", "materials", column: "parent_id"
   add_foreign_key "material_versions", "tags"
@@ -483,6 +621,18 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
   add_foreign_key "tags", "tag_names"
   add_foreign_key "theatre_comments", "theatres"
   add_foreign_key "theatre_comments", "users"
+  add_foreign_key "theatre_programmes", "posts"
+  add_foreign_key "theatre_programmes", "theatres"
+  add_foreign_key "theatre_skip_event_tags", "tags"
+  add_foreign_key "theatre_skip_event_tags", "theatre_skip_events"
+  add_foreign_key "theatre_skip_event_voters", "theatre_skip_events"
+  add_foreign_key "theatre_skip_event_voters", "users"
+  add_foreign_key "theatre_skip_events", "posts"
+  add_foreign_key "theatre_skip_events", "theatres"
+  add_foreign_key "theatre_skip_events", "users", column: "skipped_by_user_id"
+  add_foreign_key "theatre_skip_votes", "posts"
+  add_foreign_key "theatre_skip_votes", "theatres"
+  add_foreign_key "theatre_skip_votes", "users"
   add_foreign_key "theatre_watching_users", "theatres"
   add_foreign_key "theatre_watching_users", "users"
   add_foreign_key "theatres", "posts", column: "current_post_id"
diff --git a/backend/lib/tasks/calc_post_similarities.rake b/backend/lib/tasks/calc_post_similarities.rake
index 925770f..5f192f9 100644
--- a/backend/lib/tasks/calc_post_similarities.rake
+++ b/backend/lib/tasks/calc_post_similarities.rake
@@ -1,6 +1,6 @@
 namespace :post_similarity do
   desc '関聯投稿テーブル作成'
   task calc: :environment do
-    Similarity::Calc.call(Post, :tags)
+    Similarity::Calc.call(Post, :active_tags)
   end
 end
diff --git a/backend/lib/tasks/calc_tag_similarities.rake b/backend/lib/tasks/calc_tag_similarities.rake
index 0fc718a..e029255 100644
--- a/backend/lib/tasks/calc_tag_similarities.rake
+++ b/backend/lib/tasks/calc_tag_similarities.rake
@@ -1,6 +1,6 @@
 namespace :tag_similarity do
   desc '関聯タグ・テーブル作成'
   task calc: :environment do
-    Similarity::Calc.call(Tag, :posts)
+    Similarity::Calc.call(Tag, :posts, scope: Tag.where(deprecated_at: nil))
   end
 end
diff --git a/backend/spec/models/tag_name_sanitisation_rule_spec.rb b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
index 654f85f..ea14461 100644
--- a/backend/spec/models/tag_name_sanitisation_rule_spec.rb
+++ b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
@@ -1,6 +1,10 @@
 require 'rails_helper'
 
 RSpec.describe TagNameSanitisationRule, type: :model do
+  before do
+    described_class.unscoped.delete_all
+  end
+
   describe '.sanitise' do
     before do
       described_class.create!(priority: 10, source_pattern: '_', replacement: '')
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index a6d14fd..014cdde 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -1,6 +1,79 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
+  describe '.normalise_tags!' do
+    it 'rejects deprecated tags when deny_deprecated is enabled' do
+      tag_name = TagName.create!(name: 'normalise deprecated tag')
+      deprecated_tag = Tag.create!(
+        tag_name:,
+        category: :general,
+        deprecated_at: 1.day.from_now
+      )
+
+      expect {
+        described_class.normalise_tags!(
+          [deprecated_tag.name],
+          deny_deprecated: true
+        )
+      }.to raise_error(Tag::DeprecatedTagNormalisationError) { |error|
+        expect(error.tag_names).to eq([deprecated_tag.name])
+      }
+    end
+  end
+
+  describe '.expand_parent_tags' do
+    it 'expands through multiple deprecated parents to an active ancestor' do
+      child = create(:tag, name: 'expand_child')
+      deprecated_parent = create(
+        :tag,
+        name: 'expand_deprecated_parent',
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = create(
+        :tag,
+        name: 'expand_deprecated_grandparent',
+        deprecated_at: Time.current
+      )
+      active_ancestor = create(:tag, name: 'expand_active_ancestor')
+      TagImplication.create!(tag: child, parent_tag: deprecated_parent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
+
+      expanded = described_class.expand_parent_tags([child])
+
+      expect(expanded).to include(
+        child,
+        deprecated_parent,
+        deprecated_grandparent,
+        active_ancestor
+      )
+      expect(expanded.reject(&:deprecated?)).to contain_exactly(child, active_ancestor)
+    end
+
+    it 'terminates when implications contain a cycle' do
+      first = create(:tag, name: 'expand_cycle_first')
+      second = create(:tag, name: 'expand_cycle_second')
+      TagImplication.create!(tag: first, parent_tag: second)
+      TagImplication.create!(tag: second, parent_tag: first)
+
+      expect(described_class.expand_parent_tags([first])).to contain_exactly(first, second)
+    end
+  end
+
+  describe 'deprecated validation' do
+    it 'rejects deprecated nico tags' do
+      tag = build(
+        :tag,
+        name: 'nico:deprecated_validation',
+        category: :nico,
+        deprecated_at: Time.current
+      )
+
+      expect(tag).not_to be_valid
+      expect(tag.errors[:deprecated_at]).to include('ニコタグは廃止できません．')
+    end
+  end
+
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
diff --git a/backend/spec/requests/error_responses_spec.rb b/backend/spec/requests/error_responses_spec.rb
new file mode 100644
index 0000000..a7b5191
--- /dev/null
+++ b/backend/spec/requests/error_responses_spec.rb
@@ -0,0 +1,47 @@
+require 'rails_helper'
+
+RSpec.describe 'error responses', type: :request do
+  describe 'manual input errors' do
+    it 'returns a stable payload for bad requests' do
+      get '/tags/name/%20/deerjikists'
+
+      expect(response).to have_http_status(:bad_request)
+      expect(json).to include(
+          'type' => 'bad_request',
+          'message' => be_present,
+          'errors' => {},
+          'base_errors' => [be_present])
+    end
+
+    it 'returns a stable field-error payload for unprocessable requests' do
+      member = create(:user, :member)
+      tag = create(:tag, :general, name: 'error_response_tag')
+      sign_in_as(member)
+
+      patch "/tags/#{ tag.id }", params: { category: 'nico' }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include(
+          'type' => 'validation_error',
+          'message' => '入力内容を確認してください．',
+          'base_errors' => [])
+      expect(json.fetch('errors')).to include(
+          'category' => ['ニコタグは変更できません．'])
+    end
+  end
+
+  describe 'model validation errors' do
+    it 'returns field messages for model errors' do
+      user = create(:user)
+      sign_in_as(user)
+
+      put "/users/#{ user.id }", params: { name: 'a' * 256 }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include(
+          'type' => 'validation_error',
+          'message' => '入力内容を確認してください．')
+      expect(json.fetch('errors').fetch('name')).to include(be_present)
+    end
+  end
+end
diff --git a/backend/spec/requests/gekanator_games_spec.rb b/backend/spec/requests/gekanator_games_spec.rb
new file mode 100644
index 0000000..236f23e
--- /dev/null
+++ b/backend/spec/requests/gekanator_games_spec.rb
@@ -0,0 +1,76 @@
+require 'rails_helper'
+
+RSpec.describe 'Gekanator games API', type: :request do
+  let!(:admin) { create_admin_user! }
+  let!(:user) { create_member_user! }
+  let!(:guessed_post) { Post.create!(title: 'guess', url: 'https://example.com/guess') }
+  let!(:correct_post) { Post.create!(title: 'correct', url: 'https://example.com/correct') }
+
+  describe 'POST /gekanator/games' do
+    it 'stores a won game' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: guessed_post.id,
+          answers: [{ question_id: 'tag:1', answer: 'yes' }] }
+
+      expect(response).to have_http_status(:created)
+      game = GekanatorGame.find(json['id'])
+      expect(game.user).to eq(admin)
+      expect(game.guessed_post).to eq(guessed_post)
+      expect(game.correct_post).to eq(guessed_post)
+      expect(game.won).to eq(true)
+      expect(game.question_count).to eq(1)
+      expect(game.answers).to eq([{ 'question_id' => 'tag:1', 'answer' => 'yes' }])
+    end
+
+    it 'stores a lost game with the correct post' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: correct_post.id,
+          question_count: 4,
+          answers: [{ question_id: 'tag:1', answer: 'no' }] }
+
+      expect(response).to have_http_status(:created)
+      game = GekanatorGame.find(json['id'])
+      expect(game.correct_post).to eq(correct_post)
+      expect(game.won).to eq(false)
+      expect(game.question_count).to eq(1)
+    end
+
+    it 'rejects a game without the correct post' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          question_count: 4,
+          answers: [{ question_id: 'tag:1', answer: 'no' }] }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'returns unauthorized without a user' do
+      post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: guessed_post.id,
+          answers: [] }
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'stores a game for a non-admin user' do
+      sign_in_as user
+
+      post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: guessed_post.id,
+          answers: [{ question_id: 'tag:1', answer: 'yes' }] }
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorGame.find(json['id']).user).to eq(user)
+    end
+  end
+end
diff --git a/backend/spec/requests/gekanator_learning_spec.rb b/backend/spec/requests/gekanator_learning_spec.rb
new file mode 100644
index 0000000..26f271b
--- /dev/null
+++ b/backend/spec/requests/gekanator_learning_spec.rb
@@ -0,0 +1,1062 @@
+require 'rails_helper'
+
+RSpec.describe 'Gekanator learning API', type: :request do
+  let(:admin) { create(:user, :admin) }
+  let(:member) { create(:user, :member) }
+  let(:other_user) { create(:user, :member) }
+
+  let!(:guessed_post) do
+    Post.create!(
+      title: 'guessed',
+      url: 'https://example.com/guessed'
+    )
+  end
+
+  let!(:correct_post) do
+    Post.create!(
+      title: 'correct',
+      url: 'https://example.com/correct'
+    )
+  end
+
+  let!(:other_post) do
+    Post.create!(
+      title: 'other',
+      url: 'https://example.com/other'
+    )
+  end
+
+  let!(:game) do
+    GekanatorGame.create!(
+      user: admin,
+      guessed_post: guessed_post,
+      correct_post: correct_post,
+      won: false,
+      question_count: 1,
+      answers: [
+        {
+          'question_id' => 'tag:character:喜多郁代',
+          'question_text' => '喜多ちゃんが関係してる?',
+          'answer' => 'yes',
+          'original_answer' => 'yes'
+        }
+      ]
+    )
+  end
+
+  def create_post_similarity_question!(
+    text: '喜多ちゃんが泣いてる?',
+    post: correct_post,
+    answer: 'yes',
+    status: 'accepted',
+    source: 'user_suggested',
+    priority_weight: 1.2
+  )
+    GekanatorQuestion.create!(
+      text: text,
+      kind: 'post_similarity',
+      source: source,
+      status: status,
+      priority_weight: priority_weight,
+      condition: {
+        type: 'post-similarity',
+        postId: post.id,
+        answer: answer,
+        threshold: 0.65
+      },
+      created_by: admin
+    )
+  end
+
+  describe 'POST /gekanator/games' do
+    it 'stores a game result for an admin user' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+        guessed_post_id: guessed_post.id,
+        correct_post_id: correct_post.id,
+        answers: [
+          {
+            question_id: 'tag:character:喜多郁代',
+            question_text: '喜多ちゃんが関係してる?',
+            answer: 'yes',
+            original_answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:created)
+
+      created = GekanatorGame.find(json['id'])
+      expect(created.user).to eq(admin)
+      expect(created.guessed_post).to eq(guessed_post)
+      expect(created.correct_post).to eq(correct_post)
+      expect(created.won).to eq(false)
+      expect(created.question_count).to eq(1)
+      expect(created.answers).to eq([
+        {
+          'question_id' => 'tag:character:喜多郁代',
+          'question_text' => '喜多ちゃんが関係してる?',
+          'answer' => 'yes',
+          'original_answer' => 'yes'
+        }
+      ])
+    end
+
+    it 'stores a won game when guessed_post_id equals correct_post_id' do
+      sign_in_as admin
+
+      post '/gekanator/games', params: {
+        guessed_post_id: correct_post.id,
+        correct_post_id: correct_post.id,
+        answers: []
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorGame.find(json['id']).won).to eq(true)
+    end
+
+    it 'rejects a game without correct_post_id' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          answers: []
+        }
+      }.not_to change { GekanatorGame.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'stores a game result for a non-admin user' do
+      sign_in_as member
+
+      post '/gekanator/games', params: {
+        guessed_post_id: guessed_post.id,
+        correct_post_id: correct_post.id,
+        answers: []
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorGame.find(json['id']).user).to eq(member)
+    end
+
+    it 'returns unauthorized without a user' do
+      post '/gekanator/games', params: {
+        guessed_post_id: guessed_post.id,
+        correct_post_id: correct_post.id,
+        answers: []
+      }
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'learns accepted non-nico tag answers from camelCase main game logs' do
+      sign_in_as admin
+
+      tag_question = GekanatorQuestion.create!(
+        text: 'MAD 要素がある?',
+        kind: 'tag',
+        source: 'admin_curated',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'meme:MAD' },
+        created_by: admin
+      )
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: correct_post.id,
+          answers: [
+            {
+              questionId: 'tag:meme:MAD',
+              question_text: 'MAD 要素がある?',
+              answer: 'yes',
+              original_answer: 'yes'
+            },
+            {
+              questionId: 'tag:meme:missing',
+              question_text: '存在しない質問?',
+              answer: 'yes',
+              original_answer: 'yes'
+            },
+            {
+              questionId: 'tag:meme:MAD',
+              question_text: 'MAD 要素がある?',
+              answer: 'unknown',
+              original_answer: 'unknown'
+            }
+          ]
+        }
+      }.to change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json['learned_example_count']).to eq(1)
+
+      example = GekanatorQuestionExample.last
+      expect(example).to have_attributes(
+        gekanator_question_id: tag_question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        answer: 'yes',
+        source: 'post_game_answer'
+      )
+      expect(example.gekanator_game_id).to eq(json['id'])
+    end
+
+    it 'learns accepted post_similarity answers from main game logs' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: '泣いてる?')
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: correct_post.id,
+          answers: [
+            {
+              question_id: "post-similarity:#{question.id}",
+              question_text: '泣いてる?',
+              answer: 'partial',
+              original_answer: 'partial'
+            }
+          ]
+        }
+      }.to change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json['learned_example_count']).to eq(1)
+
+      example = GekanatorQuestionExample.last
+      expect(example).to have_attributes(
+        gekanator_question_id: question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        answer: 'partial',
+        source: 'post_game_answer'
+      )
+      expect(example.gekanator_game_id).to eq(json['id'])
+    end
+
+    it 'does not learn fact questions or nico tag questions from main game logs' do
+      sign_in_as admin
+
+      [
+        {
+          text: 'example.com 由来?',
+          kind: 'source',
+          condition: { type: 'source', host: 'example.com' }
+        },
+        {
+          text: '題名に結束バンドを含む?',
+          kind: 'title',
+          condition: { type: 'title-contains', text: '結束バンド' }
+        },
+        {
+          text: '2024 年投稿?',
+          kind: 'original_date',
+          condition: { type: 'original-year', year: 2024 }
+        },
+        {
+          text: 'ニコニコにぼっちタグ?',
+          kind: 'tag',
+          condition: { type: 'tag', key: 'nico:ぼっち' }
+        }
+      ].each do |attributes|
+        GekanatorQuestion.create!(
+          text: attributes[:text],
+          kind: attributes[:kind],
+          source: 'admin_curated',
+          status: 'accepted',
+          priority_weight: 1.0,
+          condition: attributes[:condition],
+          created_by: admin
+        )
+      end
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: correct_post.id,
+          answers: [
+            { question_id: 'source:example.com', answer: 'yes' },
+            { question_id: 'title:contains:結束バンド', answer: 'yes' },
+            { question_id: 'original-year:2024', answer: 'yes' },
+            { question_id: 'tag:nico:ぼっち', answer: 'yes' }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:created)
+      expect(json['learned_example_count']).to eq(0)
+    end
+
+    it 'updates an existing main game example instead of duplicating it' do
+      sign_in_as admin
+
+      tag_question = GekanatorQuestion.create!(
+        text: '喜多ちゃんが関係してる?',
+        kind: 'tag',
+        source: 'admin_curated',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'character:喜多郁代' },
+        created_by: admin
+      )
+      existing = GekanatorQuestionExample.create!(
+        gekanator_question: tag_question,
+        post: correct_post,
+        user: admin,
+        answer: 'no',
+        source: 'post_game_answer',
+        weight: 1.0
+      )
+
+      expect {
+        post '/gekanator/games', params: {
+          guessed_post_id: guessed_post.id,
+          correct_post_id: correct_post.id,
+          answers: [
+            {
+              question_id: 'tag:character:喜多郁代',
+              answer: 'yes',
+              original_answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:created)
+      expect(json['learned_example_count']).to eq(1)
+      expect(existing.reload.answer).to eq('yes')
+      expect(existing.sample_count).to eq(2)
+    end
+  end
+
+  describe 'POST /gekanator/question_suggestions' do
+    it 'creates a suggestion and promotes yes answer to an accepted post_similarity question' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: '喜多ちゃんが泣いてる?',
+          answer: 'yes'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+        .and change { GekanatorQuestion.count }.by(1)
+        .and change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+
+      suggestion = GekanatorQuestionSuggestion.last
+      question = GekanatorQuestion.last
+      example = GekanatorQuestionExample.last
+
+      expect(json).to include(
+        'id' => suggestion.id,
+        'count' => 1
+      )
+
+      expect(suggestion).to have_attributes(
+        gekanator_game_id: game.id,
+        user_id: admin.id,
+        question_text: '喜多ちゃんが泣いてる?',
+        answer: 'yes',
+        processed: true
+      )
+
+      expect(question).to have_attributes(
+        text: '喜多ちゃんが泣いてる?',
+        kind: 'post_similarity',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.2,
+        gekanator_question_suggestion_id: suggestion.id,
+        created_by_id: admin.id
+      )
+      expect(question.condition).to include(
+        'type' => 'post-similarity',
+        'postId' => correct_post.id,
+        'answer' => 'yes',
+        'threshold' => 0.65
+      )
+
+      expect(example).to have_attributes(
+        gekanator_question_id: question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        gekanator_game_id: game.id,
+        answer: 'yes',
+        source: 'initial_suggestion',
+        weight: 1.0
+      )
+    end
+
+    it 'promotes no, partial, and probably_no answers' do
+      sign_in_as admin
+
+      ['no', 'partial', 'probably_no'].each do |answer|
+        expect {
+          post '/gekanator/question_suggestions', params: {
+            gekanator_game_id: game.id,
+            question_text: "answer #{answer} question?",
+            answer: answer
+          }
+        }.to change { GekanatorQuestion.count }.by(1)
+          .and change { GekanatorQuestionExample.count }.by(1)
+
+        expect(response).to have_http_status(:created)
+        expect(GekanatorQuestion.last.condition['answer']).to eq(answer)
+        expect(GekanatorQuestionExample.last.answer).to eq(answer)
+      end
+    end
+
+    it 'does not promote unknown answers' do
+      sign_in_as admin
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'よく分からない質問?',
+          answer: 'unknown'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+        .and change { GekanatorQuestion.count }.by(0)
+        .and change { GekanatorQuestionExample.count }.by(0)
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorQuestionSuggestion.last.processed).to eq(false)
+    end
+
+    it 'allows more than three suggestions per game' do
+      sign_in_as admin
+
+      3.times do |i|
+        GekanatorQuestionSuggestion.create!(
+          gekanator_game: game,
+          user: admin,
+          question_text: "existing question #{i}",
+          answer: 'unknown'
+        )
+      end
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'fourth question?',
+          answer: 'yes'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json['count']).to eq(4)
+    end
+
+    it 'allows a non-admin user to suggest a question for their own game' do
+      member_game = GekanatorGame.create!(
+        user: member,
+        guessed_post: guessed_post,
+        correct_post: correct_post,
+        won: false,
+        question_count: 1,
+        answers: [{ 'question_id' => 'tag:1', 'answer' => 'yes' }]
+      )
+      sign_in_as member
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: member_game.id,
+          question_text: 'member question?',
+          answer: 'yes'
+        }
+      }.to change { GekanatorQuestionSuggestion.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorQuestionSuggestion.last).to have_attributes(
+        gekanator_game_id: member_game.id,
+        user_id: member.id
+      )
+    end
+
+    it 'returns not found for another user game' do
+      sign_in_as member
+
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'member question?',
+          answer: 'yes'
+        }
+      }.not_to change { GekanatorQuestionSuggestion.count }
+
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'returns unauthorized without a user' do
+      expect {
+        post '/gekanator/question_suggestions', params: {
+          gekanator_game_id: game.id,
+          question_text: 'member question?',
+          answer: 'yes'
+        }
+      }.not_to change { GekanatorQuestionSuggestion.count }
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+  end
+
+  describe 'GET /gekanator/games/:id/extra_questions' do
+    it 'returns at most six accepted user_suggested post_similarity questions without duplicates' do
+      sign_in_as admin
+
+      lowest = create_post_similarity_question!(
+        text: 'lowest?',
+        priority_weight: 0.5
+      )
+      low = create_post_similarity_question!(
+        text: 'low?',
+        priority_weight: 1.0
+      )
+      middle = create_post_similarity_question!(
+        text: 'middle?',
+        priority_weight: 1.5
+      )
+      medium_high = create_post_similarity_question!(
+        text: 'medium high?',
+        priority_weight: 2.0
+      )
+      high = create_post_similarity_question!(
+        text: 'high?',
+        priority_weight: 2.5
+      )
+      higher = create_post_similarity_question!(
+        text: 'higher?',
+        priority_weight: 2.8
+      )
+      highest = create_post_similarity_question!(
+        text: 'highest?',
+        priority_weight: 3.0
+      )
+      overflow = create_post_similarity_question!(
+        text: 'overflow?',
+        priority_weight: 2.2
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].length).to eq(6)
+      expect(json['questions'].map { _1['id'] }.uniq.length).to eq(6)
+      expect(json['questions'].map { _1['id'] }).to all(
+        be_in([
+          lowest.id,
+          low.id,
+          middle.id,
+          medium_high.id,
+          high.id,
+          higher.id,
+          highest.id,
+          overflow.id,
+        ])
+      )
+    end
+
+    it 'can return questions that already have an example for the correct post' do
+      sign_in_as admin
+
+      existing = create_post_similarity_question!(text: 'already learned?')
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: existing,
+        post: correct_post,
+        user: admin,
+        gekanator_game: game,
+        answer: 'yes',
+        source: 'post_game_extra'
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(existing.id)
+    end
+
+    it 'prioritizes questions the current user has not answered' do
+      sign_in_as admin
+
+      answered = create_post_similarity_question!(
+        text: 'already answered?',
+        priority_weight: 3.0
+      )
+      GekanatorQuestionExample.create!(
+        gekanator_question: answered,
+        post: other_post,
+        user: admin,
+        answer: 'yes',
+        source: 'post_game_extra'
+      )
+
+      unanswered =
+          6.times.map { |index|
+            create_post_similarity_question!(
+              text: "unanswered #{index}?",
+              priority_weight: 0.5
+            )
+          }
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to match_array(
+        unanswered.map(&:id)
+      )
+    end
+
+    it 'can return questions already asked in the game using snake_case question_id' do
+      sign_in_as admin
+
+      asked = create_post_similarity_question!(text: 'already asked?')
+      game.update!(
+        answers: [
+          {
+            'question_id' => "post-similarity:#{asked.id}",
+            'answer' => 'yes'
+          }
+        ]
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(asked.id)
+    end
+
+    it 'can return questions already asked in the game using camelCase questionId' do
+      sign_in_as admin
+
+      asked = create_post_similarity_question!(text: 'already asked?')
+      game.update!(
+        answers: [
+          {
+            'questionId' => "post-similarity:#{asked.id}",
+            'answer' => 'yes'
+          }
+        ]
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(asked.id)
+    end
+
+    it 'does not return non-accepted, non-user_suggested, or non-post_similarity questions' do
+      sign_in_as admin
+
+      accepted = create_post_similarity_question!(text: 'accepted?')
+      create_post_similarity_question!(text: 'disabled?', status: 'disabled')
+      create_post_similarity_question!(text: 'ai?', source: 'ai_generated')
+      GekanatorQuestion.create!(
+        text: 'tag?',
+        kind: 'tag',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'character:喜多郁代' }
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to contain_exactly(accepted.id)
+    end
+
+    it 'allows a non-admin user to fetch extra questions for their own game' do
+      member_game = GekanatorGame.create!(
+        user: member,
+        guessed_post: guessed_post,
+        correct_post: correct_post,
+        won: false,
+        question_count: 1,
+        answers: [{ 'question_id' => 'tag:1', 'answer' => 'yes' }]
+      )
+      accepted = create_post_similarity_question!(text: 'accepted?')
+      sign_in_as member
+
+      get "/gekanator/games/#{member_game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].map { _1['id'] }).to include(accepted.id)
+    end
+
+    it 'returns not found for another user game' do
+      sign_in_as member
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'returns unauthorized without a user' do
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+  end
+
+  describe 'POST /gekanator/games/:id/extra_question_answers' do
+    it 'creates examples for extra question answers' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'extra?')
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id.to_s,
+              answer: 'partial'
+            }
+          ]
+        }
+      }.to change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json).to include('count' => 1)
+
+      example = GekanatorQuestionExample.last
+      expect(example).to have_attributes(
+        gekanator_question_id: question.id,
+        post_id: correct_post.id,
+        user_id: admin.id,
+        gekanator_game_id: game.id,
+        answer: 'partial',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+    end
+
+    it 'updates an existing example for the same question, post, and user' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'extra?')
+      existing = GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: correct_post,
+        user: admin,
+        answer: 'no',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:created)
+      expect(existing.reload).to have_attributes(
+        answer: 'yes',
+        source: 'post_game_extra',
+        gekanator_game_id: game.id
+      )
+    end
+
+    it 'rejects missing questions' do
+      sign_in_as admin
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: 999_999_999,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'rejects non-accepted questions' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(
+        text: 'disabled?',
+        status: 'disabled'
+      )
+
+      post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+        answers: [
+          {
+            question_id: question.id,
+            answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'rejects non-post_similarity questions' do
+      sign_in_as admin
+
+      question = GekanatorQuestion.create!(
+        text: 'tag?',
+        kind: 'tag',
+        source: 'user_suggested',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: { type: 'tag', key: 'character:喜多郁代' }
+      )
+
+      post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+        answers: [
+          {
+            question_id: question.id,
+            answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'allows a non-admin user to answer extra questions for their own game' do
+      member_game = GekanatorGame.create!(
+        user: member,
+        guessed_post: guessed_post,
+        correct_post: correct_post,
+        won: false,
+        question_count: 1,
+        answers: [{ 'question_id' => 'tag:1', 'answer' => 'yes' }]
+      )
+      question = create_post_similarity_question!(text: 'extra?')
+      sign_in_as member
+
+      expect {
+        post "/gekanator/games/#{member_game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.to change { GekanatorQuestionExample.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(GekanatorQuestionExample.last).to have_attributes(
+        user_id: member.id,
+        gekanator_game_id: member_game.id
+      )
+    end
+
+    it 'returns not found for another user game' do
+      question = create_post_similarity_question!(text: 'extra?')
+      sign_in_as member
+
+      expect {
+        post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+          answers: [
+            {
+              question_id: question.id,
+              answer: 'yes'
+            }
+          ]
+        }
+      }.not_to change { GekanatorQuestionExample.count }
+
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'returns unauthorized without a user' do
+      question = create_post_similarity_question!(text: 'extra?')
+
+      post "/gekanator/games/#{game.id}/extra_question_answers", params: {
+        answers: [
+          {
+            question_id: question.id,
+            answer: 'yes'
+          }
+        ]
+      }
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+  end
+
+  describe 'GET /gekanator/questions' do
+    it 'omits questions for deprecated tags' do
+      active_tag = Tag.create!(name: 'active_question_tag', category: :general)
+      deprecated_tag = Tag.create!(
+        name: 'deprecated_question_tag',
+        category: :general,
+        deprecated_at: Time.current
+      )
+
+      [active_tag, deprecated_tag].each do |question_tag|
+        GekanatorQuestion.create!(
+          text: "#{ question_tag.name }?",
+          kind: 'tag',
+          source: 'admin_curated',
+          status: 'accepted',
+          priority_weight: 1.0,
+          condition: {
+            type: 'tag',
+            key: "#{ question_tag.category }:#{ question_tag.name }"
+          },
+          created_by: admin
+        )
+      end
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_ids = json.fetch('questions').map { |question| question.fetch('id') }
+      expect(question_ids).to include('tag:general:active_question_tag')
+      expect(question_ids).not_to include('tag:general:deprecated_question_tag')
+    end
+
+    it 'returns accepted questions only and includes example_answers for post_similarity questions' do
+      sign_in_as admin
+
+      accepted = create_post_similarity_question!(text: 'accepted?')
+      create_post_similarity_question!(
+        text: 'disabled?',
+        status: 'disabled'
+      )
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: accepted,
+        post: correct_post,
+        user: admin,
+        answer: 'yes',
+        source: 'initial_suggestion',
+        weight: 1.0
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].length).to eq(1)
+
+      question_json = json['questions'].first
+      expect(question_json).to include(
+        'id' => "post-similarity:#{accepted.id}",
+        'text' => 'accepted?',
+        'kind' => 'post_similarity',
+        'source' => 'user_suggested',
+        'priority_weight' => 1.2
+      )
+      expect(question_json['condition']).to include(
+        'type' => 'post-similarity',
+        'postId' => correct_post.id,
+        'answer' => 'yes',
+        'threshold' => 0.65
+      )
+      expect(question_json['example_answers']).to include(
+        correct_post.id.to_s => 'yes'
+      )
+    end
+
+    it 'aggregates example_answers by weight' do
+      sign_in_as admin
+
+      question = create_post_similarity_question!(text: 'weighted?')
+
+      GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: other_post,
+        user: admin,
+        answer: 'yes',
+        source: 'post_game_extra',
+        weight: 1.0
+      )
+      GekanatorQuestionExample.create!(
+        gekanator_question: question,
+        post: other_post,
+        user: other_user,
+        answer: 'no',
+        source: 'post_game_extra',
+        weight: 2.0
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_json = json['questions'].find { _1['id'] == "post-similarity:#{question.id}" }
+      expect(question_json['example_answers']).to include(
+        other_post.id.to_s => 'no'
+      )
+    end
+
+    it 'normalizes legacy title length questions' do
+      sign_in_as admin
+
+      GekanatorQuestion.create!(
+        text: '題名が長めの投稿?',
+        kind: 'title',
+        source: 'admin_curated',
+        status: 'accepted',
+        priority_weight: 1.0,
+        condition: {
+          type: 'title-length-greater-than',
+          length: 20
+        },
+        created_by: admin
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_json = json['questions'].find { _1['id'] == 'title:length-at-least:21' }
+      expect(question_json).to include(
+        'text' => 'タイトルは 21 文字以上?',
+        'kind' => 'title'
+      )
+      expect(question_json['condition']).to include(
+        'type' => 'title-length-at-least',
+        'length' => 21
+      )
+    end
+
+    it 'returns title-contains questions without authentication' do
+      GekanatorQuestion.create!(
+        text: '題名に「結束バンド」が含まれる?',
+        kind: 'title',
+        source: 'ai_generated',
+        status: 'accepted',
+        priority_weight: 0.95,
+        condition: {
+          type: 'title-contains',
+          text: '結束バンド'
+        },
+        created_by: admin
+      )
+
+      get '/gekanator/questions'
+
+      expect(response).to have_http_status(:ok)
+      question_json = json['questions'].find { _1['id'] == 'title:contains:結束バンド' }
+      expect(question_json).to include(
+        'text' => '題名に「結束バンド」が含まれる?',
+        'kind' => 'title'
+      )
+      expect(question_json['condition']).to include(
+        'type' => 'title-contains',
+        'text' => '結束バンド'
+      )
+    end
+  end
+end
diff --git a/backend/spec/requests/gekanator_posts_spec.rb b/backend/spec/requests/gekanator_posts_spec.rb
new file mode 100644
index 0000000..b21e414
--- /dev/null
+++ b/backend/spec/requests/gekanator_posts_spec.rb
@@ -0,0 +1,33 @@
+require 'rails_helper'
+
+
+RSpec.describe 'Gekanator posts API', type: :request do
+  describe 'GET /gekanator/posts' do
+    it 'omits deprecated tags and returns the stored similarity cosine' do
+      active_tag = Tag.create!(name: 'active tag', category: :general)
+      deprecated_tag = Tag.create!(
+        name: 'deprecated tag',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      post_record = Post.create!(title: 'source', url: 'https://example.com/source')
+      target_post = Post.create!(title: 'target', url: 'https://example.com/target')
+
+      PostTag.create!(post: post_record, tag: active_tag)
+      PostTag.create!(post: post_record, tag: deprecated_tag)
+      PostTag.create!(post: target_post, tag: deprecated_tag)
+      PostSimilarity.create!(post: post_record, target_post:, cos: 0.375)
+
+      get '/gekanator/posts'
+
+      expect(response).to have_http_status(:ok)
+
+      post_json = json.fetch('posts').find { |post| post.fetch('id') == post_record.id }
+      expect(post_json.fetch('tags').map { |tag| tag.fetch('name') }).to eq(['active tag'])
+      expect(post_json.fetch('post_similarity_edges')).to contain_exactly(
+        'target_post_id' => target_post.id,
+        'cos' => 0.375
+      )
+    end
+  end
+end
diff --git a/backend/spec/requests/materials_spec.rb b/backend/spec/requests/materials_spec.rb
index f2cc27e..d4085ec 100644
--- a/backend/spec/requests/materials_spec.rb
+++ b/backend/spec/requests/materials_spec.rb
@@ -141,16 +141,21 @@ RSpec.describe 'Materials API', type: :request do
     context 'when logged in' do
       before { sign_in_as(guest_user) }
 
-      it 'returns 400 when tag is blank' do
+      it 'returns 422 when tag is blank' do
         post '/materials', params: { tag: '   ', file: dummy_upload }
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+            'tag' => ['タグは必須です．'])
       end
 
-      it 'returns 400 when both file and url are blank' do
+      it 'returns 422 when both file and url are blank' do
         post '/materials', params: { tag: 'material_create_blank' }
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+            'file' => ['ファイルまたは URL は必須です．'],
+            'url' => ['ファイルまたは URL は必須です．'])
       end
 
       it 'creates a material with an attached file' do
@@ -261,21 +266,26 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:not_found)
       end
 
-      it 'returns 400 when tag is blank' do
+      it 'returns 422 when tag is blank' do
         put "/materials/#{ material.id }", params: {
           tag: '   ',
           file: dummy_upload
         }
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+            'tag' => ['タグは必須です．'])
       end
 
-      it 'returns 400 when both file and url are blank' do
+      it 'returns 422 when both file and url are blank' do
         put "/materials/#{ material.id }", params: {
           tag: 'material_update_no_payload'
         }
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+            'file' => ['ファイルまたは URL は必須です．'],
+            'url' => ['ファイルまたは URL は必須です．'])
       end
 
       it 'updates tag, url, file, and updated_by_user' do
diff --git a/backend/spec/requests/nico_tags_spec.rb b/backend/spec/requests/nico_tags_spec.rb
index 26d5de0..b9ac6c6 100644
--- a/backend/spec/requests/nico_tags_spec.rb
+++ b/backend/spec/requests/nico_tags_spec.rb
@@ -3,12 +3,68 @@ require 'rails_helper'
 
 RSpec.describe 'NicoTags', type: :request do
   describe 'GET /tags/nico' do
-    it 'returns tags and next_cursor when overflowing limit' do
-      create_list(:tag, 21, :nico)
-      get '/tags/nico', params: { limit: 20 }
+    it 'returns paginated tags and total count' do
+      create_list(:tag, 3, :nico)
+
+      get '/tags/nico', params: { page: 2, limit: 2 }
+
       expect(response).to have_http_status(:ok)
-      expect(json['tags'].size).to eq(20)
-      expect(json['next_cursor']).to be_present
+      expect(json['tags'].size).to eq(1)
+      expect(json['count']).to eq(3)
+    end
+
+    it 'filters by nico tag name, linked tag name, and link status' do
+      linked = create(:tag, :nico)
+      linked.tag_name.update!(name: 'nico:search_linked')
+      unlinked = create(:tag, :nico)
+      unlinked.tag_name.update!(name: 'nico:search_unlinked')
+      other = create(:tag, :nico)
+      other.tag_name.update!(name: 'nico:other')
+      destination = create(:tag, :general)
+      destination.tag_name.update!(name: 'destination_search')
+      NicoTagRelation.create!(nico_tag: linked, tag: destination)
+      NicoTagRelation.create!(nico_tag: other, tag: create(:tag, :general))
+
+      get '/tags/nico', params: {
+        name: 'search_',
+        linked_tag: 'destination_',
+        link_status: 'linked'
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(json['count']).to eq(1)
+      expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([linked.id])
+
+      get '/tags/nico', params: { name: 'search_', link_status: 'unlinked' }
+
+      expect(json['count']).to eq(1)
+      expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([unlinked.id])
+    end
+
+    it 'sorts by name and timestamps' do
+      older = create(:tag, :nico)
+      older.tag_name.update!(name: 'nico:a')
+      older.update_columns(created_at: 2.days.ago)
+      newer = create(:tag, :nico)
+      newer.tag_name.update!(name: 'nico:b')
+      newer.update_columns(created_at: 1.day.ago)
+      older_post_tag =
+        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-older'), tag: older)
+      older_post_tag.update_columns(created_at: 1.hour.ago)
+      newer_post_tag =
+        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-newer'), tag: newer)
+      newer_post_tag.update_columns(created_at: 2.hours.ago)
+
+      get '/tags/nico', params: { order: 'name:desc' }
+      expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([newer.id, older.id])
+
+      get '/tags/nico', params: { order: 'created_at:asc' }
+      expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
+
+      get '/tags/nico', params: { order: 'updated_at:desc' }
+      expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
+      expect(Time.zone.parse(json.fetch('tags').first.fetch('recent_post_tag_created_at')))
+        .to be_within(1.second).of(older_post_tag.created_at)
     end
   end
 
@@ -75,7 +131,7 @@ RSpec.describe 'NicoTags', type: :request do
       expect(versions.last.created_by_user_id).to eq(admin.id)
     end
 
-    it '400 when linked tag normalises to nico tag' do
+    it 'returns 422 when linked tag normalises to nico tag' do
       sign_in_as(member)
 
       other_nico = create(:tag, :nico, name: 'nico:linked_ng')
@@ -87,7 +143,37 @@ RSpec.describe 'NicoTags', type: :request do
         patch "/tags/nico/#{nico_tag.id}", params: { tags: 'linked_ng_alias' }
       }.not_to change(NicoTagVersion, :count)
 
-      expect(response).to have_http_status(:bad_request)
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'tags' => ['ニコニコ・タグ同士は連携できません．'])
+    end
+
+    it 'returns the tags field error when a nico tag is specified directly' do
+      sign_in_as(member)
+
+      patch "/tags/nico/#{nico_tag.id}", params: { tags: 'nico:linked_ng' }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'tags' => ['ニコニコ・タグ同士は連携できません．'])
+    end
+
+    it 'returns tag name validation errors on the tags field and rolls back created tags' do
+      sign_in_as(member)
+      TagNameSanitisationRule.create!(
+        priority: 1,
+        source_pattern: 'invalid',
+        replacement: 'valid'
+      )
+      nico_tag
+
+      expect {
+        patch "/tags/nico/#{nico_tag.id}", params: { tags: 'created_first invalid' }
+      }.not_to change(TagName, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors').fetch('tags')).to include(
+          a_string_including('タグ名 “invalid”:', '名前に使用できない文字が含まれてゐます．'))
     end
   end
 end
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 14b51e7..18d5b73 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -57,6 +57,23 @@ RSpec.describe 'Posts API', type: :request do
     post_write_params({ base_version_no: base_version.version_no }.merge(params))
   end
 
+  def count_sql_queries
+    count = 0
+
+    callback = lambda do |_name, _started, _finished, _id, payload|
+      next if payload[:cached]
+      next if ['SCHEMA', 'TRANSACTION'].include?(payload[:name])
+
+      count += 1
+    end
+
+    ActiveSupport::Notifications.subscribed(callback, 'sql.active_record') do
+      yield
+    end
+
+    count
+  end
+
   let!(:tag_name) { TagName.create!(name: 'spec_tag') }
   let!(:tag)      { Tag.create!(tag_name: tag_name, category: :general) }
 
@@ -500,6 +517,24 @@ RSpec.describe 'Posts API', type: :request do
         expect([true, false]).to include(json['viewed'])
       end
 
+      it 'omits deprecated tags' do
+        deprecated_tag = Tag.create!(
+          name: 'deprecated_post_tag',
+          category: :general,
+          deprecated_at: Time.current
+        )
+        PostTag.create!(post: post_record, tag: deprecated_tag)
+
+        request
+
+        expect(response).to have_http_status(:ok)
+        tag_names = json.fetch('tags').flat_map { |node|
+          [node.fetch('name')] + node.fetch('children').map { |child| child.fetch('name') }
+        }
+        expect(tag_names).to include('spec_tag')
+        expect(tag_names).not_to include('deprecated_post_tag')
+      end
+
       context 'when post has parent, child, and sibling posts' do
         let!(:parent_post) do
           create_parent_post!(
@@ -558,6 +593,59 @@ RSpec.describe 'Posts API', type: :request do
           expect(sibling_ids).to include(sibling_post.id)
         end
       end
+
+      it 'does not issue a query per tag or related post' do
+        user = create_member_user!
+
+        tags =
+            15.times.map do |i|
+              tag_name = TagName.create!(name: "show_query_tag_#{ i }")
+              tag = Tag.create!(tag_name:, category: :general)
+              TagName.create!(name: "show_query_alias_#{ i }", canonical: tag_name)
+              PostTag.create!(post: post_record, tag:)
+              tag
+            end
+
+        tags.each_cons(2) do |parent_tag, child_tag|
+          TagImplication.create!(parent_tag:, tag: child_tag)
+        end
+
+        parent_post = Post.create!(
+          title: 'query parent post',
+          url: 'https://example.com/query-parent-post'
+        )
+        sibling_post = Post.create!(
+          title: 'query sibling post',
+          url: 'https://example.com/query-sibling-post'
+        )
+        child_post = Post.create!(
+          title: 'query child post',
+          url: 'https://example.com/query-child-post'
+        )
+
+        PostImplication.create!(post: post_record, parent_post:)
+        PostImplication.create!(post: sibling_post, parent_post:)
+        PostImplication.create!(post: child_post, parent_post: post_record)
+
+        20.times do |i|
+          related_post = Post.create!(
+            title: "query related post #{ i }",
+            url: "https://example.com/query-related-post-#{ i }"
+          )
+          PostSimilarity.create!(post: post_record,
+                                 target_post: related_post,
+                                 cos: 1.0 - (i / 100.0))
+        end
+
+        query_count =
+            count_sql_queries do
+              get "/posts/#{ post_record.id }",
+                  headers: { 'X-Transfer-Code' => user.inheritance_code }
+            end
+
+        expect(response).to have_http_status(:ok)
+        expect(query_count).to be <= 45
+      end
     end
 
     context 'when post does not exist' do
@@ -627,6 +715,58 @@ RSpec.describe 'Posts API', type: :request do
       expect(names).not_to include('manko')
     end
 
+    it 'rejects a deprecated tag specified directly' do
+      Tag.create!(
+        name: 'deprecated_direct_tag',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'new post',
+        url: 'https://example.com/deprecated-direct-tag',
+        tags: 'deprecated_direct_tag',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'tags' => ['廃止済みタグは付与できません．']
+      )
+    end
+
+    it 'expands through multiple deprecated parent tags and saves active ancestors' do
+      child = Tag.create!(name: 'active_child', category: :general)
+      deprecated_parent = Tag.create!(
+        name: 'deprecated_parent',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = Tag.create!(
+        name: 'deprecated_grandparent',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      active_grandparent = Tag.create!(name: 'active_grandparent', category: :general)
+      TagImplication.create!(tag: child, parent_tag: deprecated_parent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_grandparent)
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+        title: 'expanded post',
+        url: 'https://example.com/expanded-deprecated-parent',
+        tags: 'active_child',
+        thumbnail: dummy_upload
+      )
+
+      expect(response).to have_http_status(:created)
+      saved_names = Post.find(json.fetch('id')).tags.map(&:name)
+      expect(saved_names).to include('active_child', 'active_grandparent')
+      expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_undiscard_or_create_by!(
@@ -634,7 +774,7 @@ RSpec.describe 'Posts API', type: :request do
             category: :nico)
       end
 
-      it 'return 400' do
+      it 'returns 422 with tag field errors' do
         sign_in_as(member)
 
         post '/posts', params: post_write_params(
@@ -644,7 +784,13 @@ RSpec.describe 'Posts API', type: :request do
           thumbnail: dummy_upload
         )
 
-        expect(response).to have_http_status(:bad_request), response.body
+        expect(response).to have_http_status(:unprocessable_entity), response.body
+        expect(json).to include(
+            'type' => 'validation_error',
+            'message' => '入力内容を確認してください．',
+            'base_errors' => [])
+        expect(json.fetch('errors')).to include(
+            'tags' => ['ニコニコ・タグは直接指定できません．'])
       end
     end
 
@@ -854,6 +1000,26 @@ RSpec.describe 'Posts API', type: :request do
       expect(names).to include('spec_tag_2')
     end
 
+    it 'rejects a deprecated tag specified directly' do
+      Tag.create!(
+        name: 'deprecated_update_tag',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      sign_in_as(member)
+
+      put "/posts/#{ post_record.id }", params: post_update_params(
+        post_record,
+        title: 'updated title',
+        tags: 'deprecated_update_tag'
+      )
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'tags' => ['廃止済みタグは付与できません．']
+      )
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_undiscard_or_create_by!(
@@ -861,7 +1027,7 @@ RSpec.describe 'Posts API', type: :request do
             category: :nico)
       end
 
-      it 'return 400' do
+      it 'returns 422 with tag field errors' do
         sign_in_as(member)
 
         put "/posts/#{post_record.id}", params: post_update_params(
@@ -869,7 +1035,13 @@ RSpec.describe 'Posts API', type: :request do
             title: 'updated title',
             tags: 'nico:nico_tag')
 
-        expect(response).to have_http_status(:bad_request), response.body
+        expect(response).to have_http_status(:unprocessable_entity), response.body
+        expect(json).to include(
+            'type' => 'validation_error',
+            'message' => '入力内容を確認してください．',
+            'base_errors' => [])
+        expect(json.fetch('errors')).to include(
+            'tags' => ['ニコニコ・タグは直接指定できません．'])
       end
     end
 
diff --git a/backend/spec/requests/tag_versions_spec.rb b/backend/spec/requests/tag_versions_spec.rb
index 8f092b3..62afeb8 100644
--- a/backend/spec/requests/tag_versions_spec.rb
+++ b/backend/spec/requests/tag_versions_spec.rb
@@ -21,6 +21,7 @@ RSpec.describe 'TagVersions API', type: :request do
     event_type:,
     name:,
     category:,
+    deprecated_at: nil,
     aliases: [],
     parent_tags: [],
     created_by_user:,
@@ -33,6 +34,7 @@ RSpec.describe 'TagVersions API', type: :request do
             event_type: event_type,
             name: name,
             category: category,
+            deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
@@ -65,6 +67,7 @@ RSpec.describe 'TagVersions API', type: :request do
       event_type: 'update',
       name: 'new_tag_name',
       category: 'meme',
+      deprecated_at: t_v2,
       aliases: ['alias_shared', 'alias_new'],
       parent_tags: [parent_shared, parent_new],
       created_by_user: member,
@@ -133,6 +136,10 @@ RSpec.describe 'TagVersions API', type: :request do
         'current' => 'meme',
         'prev' => 'general'
       )
+      expect(latest.fetch('deprecated_at')).to eq(
+        'current' => t_v2.iso8601,
+        'prev' => nil
+      )
       expect(latest.fetch('aliases')).to include(
         { 'name' => 'alias_shared', 'type' => 'context' },
         { 'name' => 'alias_new', 'type' => 'added' },
@@ -178,6 +185,10 @@ RSpec.describe 'TagVersions API', type: :request do
         'current' => 'general',
         'prev' => nil
       )
+      expect(first.fetch('deprecated_at')).to eq(
+        'current' => nil,
+        'prev' => nil
+      )
       expect(first.fetch('aliases')).to include(
         { 'name' => 'alias_shared', 'type' => 'added' },
         { 'name' => 'alias_old', 'type' => 'added' }
diff --git a/backend/spec/requests/tag_wiki_history_integrity_spec.rb b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
index 909ebe3..4914cf4 100644
--- a/backend/spec/requests/tag_wiki_history_integrity_spec.rb
+++ b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
@@ -89,6 +89,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
           category: 'general',
           aliases: '',
           parent_tags: '',
+          deprecated: '0',
         }
       }
           .to change(TagVersion, :count).by(2)
@@ -123,6 +124,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
           category: 'meme',
           aliases: '',
           parent_tags: '',
+          deprecated: '0',
         }
       }
           .to change(TagVersion, :count).by(2)
@@ -149,6 +151,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
           category: 'general',
           aliases: 'put_tag_alias_only_alias',
           parent_tags: '',
+          deprecated: '0',
         }
       }
           .to change(TagVersion, :count).by(2)
diff --git a/backend/spec/requests/tags_deerjikists_spec.rb b/backend/spec/requests/tags_deerjikists_spec.rb
index c599f17..7bbf224 100644
--- a/backend/spec/requests/tags_deerjikists_spec.rb
+++ b/backend/spec/requests/tags_deerjikists_spec.rb
@@ -275,6 +275,30 @@ RSpec.describe 'Tags deerjikists API', type: :request do
         end
       end
 
+      context 'when a row is invalid' do
+        let(:payload) do
+          [
+            { platform: '', code: code1 },
+          ]
+        end
+
+        it 'returns 422 with indexed field errors and does not replace existing deerjikists' do
+          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+
+          expect {
+            do_request
+          }.not_to change { Deerjikist.where(tag: tag).map { |d| [d.platform, d.code] } }
+
+          expect(response).to have_http_status(:unprocessable_entity)
+          expect(json).to include(
+              'type' => 'validation_error',
+              'message' => '入力内容を確認してください．',
+              'base_errors' => [])
+          expect(json.fetch('errors')).to include(
+              'deerjikists.0.platform' => [be_present])
+        end
+      end
+
       context 'when youtube code is handle' do
         let(:channel_id) { 'UCabcdefghijklmnopqrstuv' }
         let(:payload) do
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index a688598..927b4a7 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -76,6 +76,27 @@ RSpec.describe 'Tags API', type: :request do
       expect(response_tags.first['id']).to eq(meme.id)
     end
 
+    it 'filters tags by deprecated state' do
+      deprecated_tag = Tag.create!(
+        name: 'deprecated_filter',
+        category: :general,
+        deprecated_at: 1.day.from_now
+      )
+      active_tag = Tag.create!(name: 'active_filter', category: :general)
+
+      get '/tags', params: { name: '_filter', deprecated: '1' }
+
+      expect(response).to have_http_status(:ok)
+      expect(response_names).to include(deprecated_tag.name)
+      expect(response_names).not_to include(active_tag.name)
+
+      get '/tags', params: { name: '_filter', deprecated: '0' }
+
+      expect(response).to have_http_status(:ok)
+      expect(response_names).to include(active_tag.name)
+      expect(response_names).not_to include(deprecated_tag.name)
+    end
+
     it 'filters tags by post_count range' do
       low = Tag.create!(tag_name: TagName.create!(name: 'pc_low'), category: :general)
       mid = Tag.create!(tag_name: TagName.create!(name: 'pc_mid'), category: :general)
@@ -301,6 +322,21 @@ RSpec.describe 'Tags API', type: :request do
       expect(t['matched_alias']).to eq('unko')
       expect(json.map { |x| x['name'] }).not_to include('unknown')
     end
+
+    it 'omits deprecated tags' do
+      deprecated_tag = Tag.create!(
+        name: 'spec_deprecated',
+        category: :general,
+        deprecated_at: Time.current
+      )
+      deprecated_tag.update_columns(post_count: 1)
+
+      get '/tags/autocomplete', params: { q: 'spec_', present: '0' }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { |item| item.fetch('name') }).to include('spec_tag')
+      expect(json.map { |item| item.fetch('name') }).not_to include('spec_deprecated')
+    end
   end
 
   describe 'GET /tags/name/:name' do
@@ -437,6 +473,32 @@ RSpec.describe 'Tags API', type: :request do
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
 
+      it 'updates deprecated state and records it in tag versions' do
+        expect {
+          patch "/tags/#{ tag.id }", params: { deprecated: '1' }
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+        expect(tag.reload.deprecated_at).to be_present
+
+        versions = tag.tag_versions.order(:version_no)
+        expect(versions.first.deprecated_at).to be_nil
+        expect(versions.second.deprecated_at).to eq(tag.deprecated_at)
+        expect(json.fetch('deprecated_at')).to be_present
+      end
+
+      it 'rejects deprecating a nico tag' do
+        nico_tag = Tag.create!(name: 'nico:deprecated_update', category: :nico)
+
+        patch "/tags/#{ nico_tag.id }", params: { deprecated: '1' }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(nico_tag.reload.deprecated_at).to be_nil
+        expect(json.fetch('errors')).to include(
+          'deprecated' => ['ニコタグは廃止できません．']
+        )
+      end
+
       it 'returns 422 when changing normal tag category to nico' do
         expect {
           patch "/tags/#{tag.id}", params: { category: 'nico' }
@@ -585,6 +647,111 @@ RSpec.describe 'Tags API', type: :request do
       expect(row['has_children']).to eq(true)
       expect(row['children']).to eq([])
     end
+
+    it 'passes through deprecated tags when finding children' do
+      deprecated_middle = Tag.create!(
+        name: 'depth_deprecated_middle',
+        category: :character,
+        deprecated_at: Time.current
+      )
+      visible_descendant = Tag.create!(
+        name: 'depth_visible_descendant',
+        category: :material
+      )
+      TagImplication.create!(parent_tag: root_material, tag: deprecated_middle)
+      TagImplication.create!(parent_tag: deprecated_middle, tag: visible_descendant)
+
+      get '/tags/with-depth', params: { parent: root_material.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { |item| item.fetch('name') }).to eq(['depth_visible_descendant'])
+      expect(json.map { |item| item.fetch('name') }).not_to include('depth_deprecated_middle')
+    end
+
+    it 'passes through multiple deprecated tags for roots and has_children' do
+      active_child = Tag.create!(
+        name: 'depth_active_child_below_deprecated',
+        category: :character
+      )
+      deprecated_parent = Tag.create!(
+        name: 'depth_deprecated_parent',
+        category: :character,
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = Tag.create!(
+        name: 'depth_deprecated_grandparent',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      active_ancestor = Tag.create!(
+        name: 'depth_active_ancestor',
+        category: :meme
+      )
+      TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
+
+      get '/tags/with-depth'
+
+      root_names = json.map { |item| item.fetch('name') }
+      expect(root_names).to include('depth_active_ancestor')
+      expect(root_names).not_to include('depth_active_child_below_deprecated')
+      ancestor_json = json.find { |item| item.fetch('id') == active_ancestor.id }
+      expect(ancestor_json.fetch('has_children')).to eq(true)
+
+      get '/tags/with-depth', params: { parent: active_ancestor.id }
+
+      expect(json.map { |item| item.fetch('name') }).to include(
+        'depth_active_child_below_deprecated'
+      )
+      expect(json.map { |item| item.fetch('name') }).not_to include(
+        'depth_deprecated_parent',
+        'depth_deprecated_grandparent'
+      )
+    end
+
+    it 'treats an active tag with only deprecated ancestors as a root' do
+      active_child = Tag.create!(
+        name: 'depth_root_below_deprecated',
+        category: :character
+      )
+      deprecated_parent = Tag.create!(
+        name: 'depth_root_deprecated_parent',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
+
+      get '/tags/with-depth'
+
+      expect(json.map { |item| item.fetch('name') }).to include(
+        'depth_root_below_deprecated'
+      )
+      expect(json.map { |item| item.fetch('name') }).not_to include(
+        'depth_root_deprecated_parent'
+      )
+    end
+
+    it 'terminates when deprecated implications contain a cycle' do
+      first = Tag.create!(
+        name: 'depth_cycle_first',
+        category: :character,
+        deprecated_at: Time.current
+      )
+      second = Tag.create!(
+        name: 'depth_cycle_second',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      TagImplication.create!(tag: first, parent_tag: root_material)
+      TagImplication.create!(tag: second, parent_tag: first)
+      TagImplication.create!(tag: first, parent_tag: second)
+
+      get '/tags/with-depth', params: { parent: root_material.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to eq([])
+    end
   end
 
   describe 'GET /tags/name/:name/materials' do
@@ -732,6 +899,20 @@ RSpec.describe 'Tags API', type: :request do
         expect(tag.category).to eq('general')
       end
 
+      it 'deprecated がなければ 422 を返す' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'new',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to include(
+          'deprecated' => ['廃止状態は必須です．']
+        )
+      end
+
       it 'name, category, aliases, parent tags をまとめて更新できる' do
         old_parent = Tag.create!(
           tag_name: TagName.create!(name: 'put_old_parent'),
@@ -749,6 +930,7 @@ RSpec.describe 'Tags API', type: :request do
           category: 'meme',
           aliases: 'put_alias_a put_alias_b put_alias_a',
           parent_tags: 'put_kept_parent put_new_parent',
+          deprecated: '0',
         }
 
         expect(response).to have_http_status(:ok)
@@ -793,6 +975,7 @@ RSpec.describe 'Tags API', type: :request do
           category: 'general',
           aliases: 'spec_tag put_alias_self_test',
           parent_tags: '',
+          deprecated: '0',
         }
 
         expect(response).to have_http_status(:ok)
@@ -810,6 +993,7 @@ RSpec.describe 'Tags API', type: :request do
           category: 'general',
           aliases: 'unko',
           parent_tags: 'spec_tag',
+          deprecated: '0',
         }
 
         expect(response).to have_http_status(:ok)
@@ -825,6 +1009,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'meta',
             aliases: '',
             parent_tags: '',
+            deprecated: '0',
           }
         }.to change(TagVersion, :count).by(2)
 
@@ -860,6 +1045,7 @@ RSpec.describe 'Tags API', type: :request do
           category: 'general',
           aliases: 'unko',
           parent_tags: new_parent.name,
+          deprecated: '0',
         }
 
         expect(response).to have_http_status(:ok)
@@ -875,6 +1061,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'nico',
             aliases: '',
             parent_tags: '',
+            deprecated: '0',
           }
         }.not_to change(TagVersion, :count)
 
@@ -896,6 +1083,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'nico',
             aliases: '',
             parent_tags: '',
+            deprecated: '0',
           }
         }.not_to change(NicoTagVersion, :count)
 
@@ -916,6 +1104,7 @@ RSpec.describe 'Tags API', type: :request do
             category: old_category,
             aliases: '',
             parent_tags: '',
+            deprecated: '0',
           }
         }.not_to change(TagVersion, :count)
 
@@ -946,6 +1135,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'meme',
             aliases: 'unko',
             parent_tags: '',
+            deprecated: '0',
           }
         }
             .to change(TagVersion, :count).by(2)
@@ -981,6 +1171,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'general',
             aliases: 'unko put_stolen_alias',
             parent_tags: '',
+            deprecated: '0',
           }
         }
             .to change { tag.reload.tag_versions.count }.by(2)
@@ -1015,6 +1206,7 @@ RSpec.describe 'Tags API', type: :request do
           category: 'general',
           aliases: 'unko',
           parent_tags: child.name,
+          deprecated: '0',
         }
 
         expect(response).to have_http_status(:unprocessable_entity)
@@ -1036,6 +1228,7 @@ RSpec.describe 'Tags API', type: :request do
             category: 'general',
             aliases: 'unko',
             parent_tags: '',
+            deprecated: '0',
           }
         }
             .to change(TagVersion, :count).by(2)
diff --git a/backend/spec/requests/theatre_comments_spec.rb b/backend/spec/requests/theatre_comments_spec.rb
index 856b309..78295be 100644
--- a/backend/spec/requests/theatre_comments_spec.rb
+++ b/backend/spec/requests/theatre_comments_spec.rb
@@ -80,6 +80,26 @@ RSpec.describe 'TheatreComments', type: :request do
       expect(response).to have_http_status(:ok)
       expect(response.parsed_body.map { |row| row['no'] }).to eq([3, 2, 1])
     end
+
+    it '削除済みコメントは deleted として返し、本文を隠す' do
+      comment_2.discard!
+
+      get "/theatres/#{theatre.id}/comments", params: { no_gt: 1 }
+
+      expect(response).to have_http_status(:ok)
+
+      deleted_comment = response.parsed_body.find { _1['no'] == 2 }
+      expect(deleted_comment).to include(
+        'deleted' => true,
+        'content' => nil
+      )
+
+      visible_comment = response.parsed_body.find { _1['no'] == 3 }
+      expect(visible_comment).to include(
+        'deleted' => false,
+        'content' => 'third comment'
+      )
+    end
   end
 
   describe 'POST /theatres/:theatre_id/comments' do
@@ -147,4 +167,44 @@ RSpec.describe 'TheatreComments', type: :request do
       })
     end
   end
+
+  describe 'DELETE /theatres/:theatre_id/comments/:id' do
+    let(:theatre) { create(:theatre) }
+    let(:alice) { create(:user, name: 'Alice') }
+    let(:bob) { create(:user, name: 'Bob') }
+    let!(:comment) do
+      create(
+        :theatre_comment,
+        theatre: theatre,
+        no: 1,
+        user: alice,
+        content: 'delete target'
+      )
+    end
+
+    it 'returns 401 when not logged in' do
+      delete "/theatres/#{theatre.id}/comments/#{comment.no}"
+
+      expect(response).to have_http_status(:unauthorized)
+      expect(comment.reload.discarded?).to eq(false)
+    end
+
+    it 'allows the comment owner to delete it' do
+      sign_in_as(alice)
+
+      delete "/theatres/#{theatre.id}/comments/#{comment.no}"
+
+      expect(response).to have_http_status(:no_content)
+      expect(comment.reload.discarded?).to eq(true)
+    end
+
+    it 'returns 403 when another user tries to delete it' do
+      sign_in_as(bob)
+
+      delete "/theatres/#{theatre.id}/comments/#{comment.no}"
+
+      expect(response).to have_http_status(:forbidden)
+      expect(comment.reload.discarded?).to eq(false)
+    end
+  end
 end
diff --git a/backend/spec/requests/theatre_programmes_spec.rb b/backend/spec/requests/theatre_programmes_spec.rb
new file mode 100644
index 0000000..f37fa66
--- /dev/null
+++ b/backend/spec/requests/theatre_programmes_spec.rb
@@ -0,0 +1,38 @@
+require 'rails_helper'
+
+RSpec.describe 'TheatreProgrammes', type: :request do
+  describe 'GET /theatres/:theatre_id/programmes' do
+    let(:theatre) { create(:theatre) }
+    let(:other_theatre) { create(:theatre) }
+    let(:post_1) { Post.create!(title: 'first', url: 'https://www.nicovideo.jp/watch/sm1') }
+    let(:post_2) { Post.create!(title: 'second', url: 'https://www.nicovideo.jp/watch/sm2') }
+    let(:other_post) { Post.create!(title: 'other', url: 'https://www.nicovideo.jp/watch/sm3') }
+
+    before do
+      TheatreProgramme.create!(theatre:, position: 1, post: post_1, created_at: 2.minutes.ago)
+      TheatreProgramme.create!(theatre:, position: 2, post: post_2, created_at: 1.minute.ago)
+      TheatreProgramme.create!(
+        theatre: other_theatre,
+        position: 1,
+        post: other_post,
+        created_at: 1.minute.ago
+      )
+    end
+
+    it 'returns programmes for the theatre in descending position with post json' do
+      get "/theatres/#{theatre.id}/programmes"
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { _1['position'] }).to eq([2, 1])
+      expect(json.map { _1.dig('post', 'title') }).to eq(['second', 'first'])
+      expect(json.first['post']).to include('id' => post_2.id, 'url' => post_2.url)
+    end
+
+    it 'filters programmes by position_gt' do
+      get "/theatres/#{theatre.id}/programmes", params: { position_gt: 1 }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { _1['position'] }).to eq([2])
+    end
+  end
+end
diff --git a/backend/spec/requests/theatres_spec.rb b/backend/spec/requests/theatres_spec.rb
index 45a4b85..7fd3a0a 100644
--- a/backend/spec/requests/theatres_spec.rb
+++ b/backend/spec/requests/theatres_spec.rb
@@ -14,10 +14,24 @@ RSpec.describe 'Theatres API', type: :request do
   let(:member) { create(:user, :member, name: 'member user') }
   let(:other_user) { create(:user, :member, name: 'other user') }
 
+  let!(:niconico_post) do
+    Post.create!(
+      title: 'niconico post',
+      url: 'https://www.nicovideo.jp/watch/sm123'
+    )
+  end
+
+  let!(:second_niconico_post) do
+    Post.create!(
+      title: 'second niconico post',
+      url: 'https://www.nicovideo.jp/watch/sm456'
+    )
+  end
+
   let!(:youtube_post) do
     Post.create!(
       title: 'youtube post',
-      url: 'https://www.youtube.com/watch?v=spec123'
+      url: 'https://www.youtube.com/watch?v=yt123'
     )
   end
 
@@ -120,7 +134,8 @@ RSpec.describe 'Theatres API', type: :request do
         expect(json).to include(
           'host_flg' => true,
           'post_id' => nil,
-          'post_started_at' => nil
+          'post_started_at' => nil,
+          'post_elapsed_ms' => nil
         )
 
         expect(json.fetch('watching_users')).to contain_exactly(
@@ -177,7 +192,8 @@ RSpec.describe 'Theatres API', type: :request do
         expect(json).to include(
           'host_flg' => false,
           'post_id' => nil,
-          'post_started_at' => nil
+          'post_started_at' => nil,
+          'post_elapsed_ms' => nil
         )
 
         expect(json.fetch('watching_users')).to contain_exactly(
@@ -204,7 +220,7 @@ RSpec.describe 'Theatres API', type: :request do
         )
         theatre.update!(
           host_user: other_user,
-          current_post: youtube_post,
+          current_post: niconico_post,
           current_post_started_at: started_at
         )
         sign_in_as(member)
@@ -220,9 +236,11 @@ RSpec.describe 'Theatres API', type: :request do
         expect(theatre.host_user_id).to eq(member.id)
 
         expect(json['host_flg']).to eq(true)
-        expect(json['post_id']).to eq(youtube_post.id)
+        expect(json['post_id']).to eq(niconico_post.id)
         expect(Time.zone.parse(json['post_started_at']))
           .to be_within(1.second).of(started_at)
+        expect(json['post_elapsed_ms'])
+          .to be_within(1_000).of(120_000)
       end
     end
   end
@@ -273,16 +291,36 @@ RSpec.describe 'Theatres API', type: :request do
       it 'sets current_post to an eligible post and updates current_post_started_at' do
         expect { do_request }
           .to change { theatre.reload.current_post_id }
-          .from(nil).to(youtube_post.id)
 
         expect(response).to have_http_status(:no_content)
+        expect([niconico_post.id, second_niconico_post.id, youtube_post.id])
+          .to include(theatre.reload.current_post_id)
         expect(theatre.reload.current_post_started_at)
           .to be_within(1.second).of(Time.current)
+        expect(theatre.programmes.count).to eq(1)
+      end
+    end
+
+    context 'when only a YouTube post is eligible' do
+      before do
+        niconico_post.destroy!
+        second_niconico_post.destroy!
+        theatre.update!(host_user: member)
+        sign_in_as(member)
+      end
+
+      it 'sets current_post to the YouTube post' do
+        do_request
+
+        expect(response).to have_http_status(:no_content)
+        expect(theatre.reload.current_post_id).to eq(youtube_post.id)
       end
     end
 
     context 'when current user is host and no eligible post exists' do
       before do
+        niconico_post.destroy!
+        second_niconico_post.destroy!
         youtube_post.destroy!
         theatre.update!(
           host_user: member,
@@ -299,9 +337,189 @@ RSpec.describe 'Theatres API', type: :request do
 
         theatre.reload
         expect(theatre.current_post_id).to be_nil
-        expect(theatre.current_post_started_at)
-          .to be_within(1.second).of(Time.current)
+        expect(theatre.current_post_started_at).to be_nil
       end
     end
   end
+
+  describe 'PUT /theatres/:id/skip_vote' do
+    subject(:do_request) do
+      put "/theatres/#{theatre.id}/skip_vote", params: { post_id: requested_post_id }
+    end
+
+    let(:third_user) { create(:user, :member, name: 'third user') }
+    let(:requested_post_id) { niconico_post.id }
+
+    before do
+      theatre.update!(current_post: niconico_post, current_post_started_at: 10.seconds.ago)
+      [member, other_user, third_user].each do |user|
+        TheatreWatchingUser.create!(
+          theatre:,
+          user:,
+          expires_at: 10.seconds.from_now
+        )
+      end
+    end
+
+    it 'returns 401 when not logged in' do
+      sign_out
+
+      expect { do_request }.not_to change(TheatreSkipVote, :count)
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'returns 422 when post_id is invalid' do
+      sign_in_as(member)
+
+      expect {
+        put "/theatres/#{theatre.id}/skip_vote", params: { post_id: 'invalid' }
+      }.not_to change(TheatreSkipVote, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'records a vote and returns the current vote status before majority' do
+      sign_in_as(member)
+
+      expect { do_request }.to change(TheatreSkipVote, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skipped']).to eq(false)
+      expect(json['post_id']).to eq(niconico_post.id)
+      expect(json['skip_vote']).to include(
+        'votes_count' => 1,
+        'required_count' => 2,
+        'watching_users_count' => 3,
+        'voted' => true
+      )
+    end
+
+    it 'finalizes skip when votes reach majority and stores voters and tag snapshots' do
+      tag = create(:tag, name: 'skip-target')
+      PostTag.create!(post: niconico_post, tag:)
+
+      TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
+      sign_in_as(other_user)
+
+      expect { do_request }
+        .to change(TheatreSkipEvent, :count).by(1)
+        .and change(TheatreSkipEventVoter, :count).by(2)
+        .and change(TheatreSkipEventTag, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skipped']).to eq(true)
+      expect([second_niconico_post.id, youtube_post.id]).to include(json['post_id'])
+
+      event = TheatreSkipEvent.last
+      expect(event.post).to eq(niconico_post)
+      expect(event.users).to contain_exactly(member, other_user)
+      expect(event.tags).to contain_exactly(tag)
+      expect(TheatreSkipVote.where(theatre:, post: niconico_post)).to be_empty
+    end
+
+    it 'does not record a vote when requested post is no longer current' do
+      theatre.update!(current_post: second_niconico_post)
+      sign_in_as(member)
+
+      expect { do_request }.not_to change(TheatreSkipVote, :count)
+
+      expect(response).to have_http_status(:conflict)
+      expect(json['post_id']).to eq(second_niconico_post.id)
+      expect(json['skip_vote']).to include(
+        'votes_count' => 0,
+        'voted' => false
+      )
+    end
+  end
+
+  describe 'DELETE /theatres/:id/skip_vote' do
+    let(:requested_post_id) { niconico_post.id }
+
+    before do
+      theatre.update!(current_post: niconico_post, current_post_started_at: 10.seconds.ago)
+      TheatreWatchingUser.create!(theatre:, user: member, expires_at: 10.seconds.from_now)
+      TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
+      sign_in_as(member)
+    end
+
+    it 'removes the current user vote' do
+      expect {
+        delete "/theatres/#{theatre.id}/skip_vote", params: { post_id: requested_post_id }
+      }.to change(TheatreSkipVote, :count).by(-1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['skip_vote']).to include(
+        'votes_count' => 0,
+        'required_count' => 1,
+        'watching_users_count' => 1,
+        'voted' => false
+      )
+    end
+
+    it 'does not remove a vote when requested post is no longer current' do
+      theatre.update!(current_post: second_niconico_post)
+
+      expect {
+        delete "/theatres/#{theatre.id}/skip_vote", params: { post_id: requested_post_id }
+      }.not_to change(TheatreSkipVote, :count)
+
+      expect(response).to have_http_status(:conflict)
+      expect(json['post_id']).to eq(second_niconico_post.id)
+    end
+  end
+
+  describe 'GET /theatres/:id/skip_events' do
+    before do
+      sign_in_as(member)
+    end
+
+    it 'does not expose skip voters' do
+      event = TheatreSkipEvent.create!(
+        theatre:,
+        post: niconico_post,
+        skipped_by_user: member,
+        created_at: Time.current
+      )
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: member)
+
+      get "/theatres/#{theatre.id}/skip_events"
+
+      expect(response).to have_http_status(:ok)
+      expect(json.first).to include(
+        'id' => event.id,
+        'theatre_id' => theatre.id
+      )
+      expect(json.first).not_to have_key('voters')
+      expect(json.first).not_to have_key('skipped_by_user')
+    end
+  end
+
+  describe 'GET /theatres/:id/post_selection_weights' do
+    before do
+      theatre.update!(current_post: niconico_post)
+      TheatreWatchingUser.create!(theatre:, user: member, expires_at: 10.seconds.from_now)
+      sign_in_as(member)
+    end
+
+    it 'returns tag penalties and candidate weights for the current watchers' do
+      tag = create(:tag, name: 'heavy-tag')
+      PostTag.create!(post: second_niconico_post, tag:)
+      event = TheatreSkipEvent.create!(
+        theatre:,
+        post: niconico_post,
+        skipped_by_user: member,
+        created_at: Time.current
+      )
+      TheatreSkipEventVoter.create!(theatre_skip_event: event, user: member)
+      TheatreSkipEventTag.create!(theatre_skip_event: event, tag:)
+
+      get "/theatres/#{theatre.id}/post_selection_weights"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['tag_penalties'].first['penalty']).to eq(1)
+      expect(json['lightest_posts'].first['post']['id']).to eq(second_niconico_post.id)
+      expect(json['lightest_posts'].first['penalty']).to eq(1)
+    end
+  end
 end
diff --git a/backend/spec/requests/users_spec.rb b/backend/spec/requests/users_spec.rb
index 67c556f..c58f614 100644
--- a/backend/spec/requests/users_spec.rb
+++ b/backend/spec/requests/users_spec.rb
@@ -90,12 +90,14 @@ RSpec.describe 'Users', type: :request do
       expect(response).to have_http_status(:unauthorized)
     end
 
-    it 'returns 400 when name is blank' do
+    it 'returns 422 when name is blank' do
       put "/users/#{user.id}",
           params: { name: '   ' },
           headers: auth_headers(user)
 
-      expect(response).to have_http_status(:bad_request)
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'name' => ['名前は必須です．'])
     end
 
     it 'updates name and returns user slice' do
diff --git a/backend/spec/requests/wiki_spec.rb b/backend/spec/requests/wiki_spec.rb
index 9b6e8c1..614180e 100644
--- a/backend/spec/requests/wiki_spec.rb
+++ b/backend/spec/requests/wiki_spec.rb
@@ -18,6 +18,13 @@ RSpec.describe 'Wiki API', type: :request do
         created_by_user: user,
         message: 'init')
   end
+  let!(:tag) do
+    Tag.create!(
+      tag_name: tn,
+      category: :general,
+      deprecated_at: Time.zone.local(2026, 6, 1)
+    )
+  end
 
   describe 'GET /wiki' do
     it 'returns wiki pages with title' do
@@ -30,6 +37,8 @@ RSpec.describe 'Wiki API', type: :request do
 
       expect(json[0]).to have_key('title')
       expect(json.map { |p| p['title'] }).to include('spec_wiki_title')
+      wiki_json = json.find { |item| item.fetch('id') == page.id }
+      expect(wiki_json.fetch('deprecated_at')).to eq(tag.deprecated_at.iso8601(3))
     end
   end
 
@@ -48,7 +57,8 @@ RSpec.describe 'Wiki API', type: :request do
 
         expect(json).to include(
             'id' => page.id,
-            'title' => 'spec_wiki_title')
+            'title' => 'spec_wiki_title',
+            'deprecated_at' => tag.deprecated_at.iso8601(3))
       end
     end
 
@@ -409,7 +419,11 @@ RSpec.describe 'Wiki API', type: :request do
         'kind' => 'content',
         'message' => 'r2'
       )
-      expect(top['wiki_page']).to include('id' => page.id, 'title' => 'spec_wiki_title')
+      expect(top['wiki_page']).to include(
+        'id' => page.id,
+        'title' => 'spec_wiki_title',
+        'deprecated_at' => tag.deprecated_at.iso8601(3)
+      )
       expect(top['user']).to include('id' => user.id, 'name' => user.name)
       expect(top).to have_key('timestamp')
 
@@ -479,6 +493,7 @@ RSpec.describe 'Wiki API', type: :request do
       expect(json).to include(
         'wiki_page_id' => page.id,
         'title' => 'spec_wiki_title',
+        'deprecated_at' => tag.deprecated_at.iso8601(3),
         'older_revision_id' => rev_a.id,
         'newer_revision_id' => rev_b.id
       )
diff --git a/backend/spec/services/gekanator/question_suggestion_ai_converter_spec.rb b/backend/spec/services/gekanator/question_suggestion_ai_converter_spec.rb
new file mode 100644
index 0000000..5b9023a
--- /dev/null
+++ b/backend/spec/services/gekanator/question_suggestion_ai_converter_spec.rb
@@ -0,0 +1,112 @@
+require 'rails_helper'
+
+RSpec.describe Gekanator::QuestionSuggestionAiConverter do
+  let(:user) { create(:user, :member) }
+  let(:guessed_post) { Post.create!(title: 'guess', url: 'https://example.com/guess') }
+  let(:correct_post) { Post.create!(title: 'correct', url: 'https://example.com/correct') }
+  let(:game) do
+    GekanatorGame.create!(
+      user: user,
+      guessed_post: guessed_post,
+      correct_post: correct_post,
+      won: false,
+      question_count: 1,
+      answers: [{ 'question_id' => 'tag:1', 'answer' => 'yes' }]
+    )
+  end
+
+  def create_suggestion!(question_text:, answer: 'yes')
+    GekanatorQuestionSuggestion.create!(
+      gekanator_game: game,
+      user: user,
+      question_text: question_text,
+      answer: answer
+    )
+  end
+
+  it 'converts title-contains suggestions to pending ai-generated questions' do
+    suggestion = create_suggestion!(question_text: '題名に「結束バンド」が含まれる?')
+
+    expect {
+      described_class.call(suggestion: suggestion, user: user)
+    }.to change { GekanatorQuestion.count }.by(1)
+      .and change { GekanatorAiRun.count }.by(1)
+
+    question = GekanatorQuestion.last
+    expect(question).to have_attributes(
+      text: '題名に「結束バンド」が含まれる?',
+      kind: 'title',
+      source: 'ai_generated',
+      status: 'pending',
+      priority_weight: 0.95,
+      gekanator_question_suggestion_id: suggestion.id,
+      created_by_id: user.id
+    )
+    expect(question.condition).to include(
+      'type' => 'title-contains',
+      'text' => '結束バンド'
+    )
+    expect(GekanatorAiRun.last).to have_attributes(
+      gekanator_question_suggestion_id: suggestion.id,
+      model: 'heuristic_converter_v1',
+      status: 'succeeded'
+    )
+  end
+
+  it 'converts concrete non-unknown suggestions to post-similarity questions' do
+    suggestion = create_suggestion!(
+      question_text: '喜多ちゃんが泣いてる?',
+      answer: 'partial'
+    )
+
+    question = described_class.call(suggestion: suggestion, user: user)
+
+    expect(question).to have_attributes(
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'ai_generated',
+      status: 'pending',
+      priority_weight: 1.0
+    )
+    expect(question.condition).to include(
+      'type' => 'post-similarity',
+      'postId' => correct_post.id,
+      'answer' => 'partial',
+      'threshold' => 0.65
+    )
+  end
+
+  it 'records a failed run when the suggestion cannot be converted' do
+    suggestion = create_suggestion!(
+      question_text: 'よく分からない質問?',
+      answer: 'unknown'
+    )
+
+    expect {
+      expect(described_class.call(suggestion: suggestion, user: user)).to be_nil
+    }.not_to change { GekanatorQuestion.count }
+
+    expect(GekanatorAiRun.last).to have_attributes(
+      gekanator_question_suggestion_id: suggestion.id,
+      status: 'failed'
+    )
+  end
+
+  it 'returns an existing generated question without creating a duplicate run' do
+    suggestion = create_suggestion!(question_text: 'タイトルは 10 文字以上?')
+    existing = GekanatorQuestion.create!(
+      text: 'タイトルは 10 文字以上?',
+      kind: 'title',
+      source: 'ai_generated',
+      status: 'pending',
+      priority_weight: 0.95,
+      condition: { type: 'title-length-at-least', length: 10 },
+      gekanator_question_suggestion: suggestion,
+      created_by: user
+    )
+
+    expect {
+      expect(described_class.call(suggestion: suggestion, user: user)).to eq(existing)
+    }.not_to change { GekanatorAiRun.count }
+  end
+end
diff --git a/backend/spec/tasks/post_similarity_calc_spec.rb b/backend/spec/tasks/post_similarity_calc_spec.rb
index 41de663..20dd575 100644
--- a/backend/spec/tasks/post_similarity_calc_spec.rb
+++ b/backend/spec/tasks/post_similarity_calc_spec.rb
@@ -4,11 +4,12 @@ require 'rails_helper'
 RSpec.describe 'post_similarity:calc' do
   include RakeTaskHelper
 
-  it 'calls Similarity::Calc with Post and :tags' do
+  it 'calculates similarities from active tags only' do
     # 必要最低限のデータ
     t1 = Tag.create!(name: "t1")
     t2 = Tag.create!(name: "t2")
     t3 = Tag.create!(name: "t3")
+    deprecated_tag = Tag.create!(name: 'deprecated', deprecated_at: Time.current)
 
     p1 = Post.create!(url: "https://example.com/1")
     p2 = Post.create!(url: "https://example.com/2")
@@ -22,6 +23,8 @@ RSpec.describe 'post_similarity:calc' do
     PostTag.create!(post: p2, tag: t3)
 
     PostTag.create!(post: p3, tag: t3)
+    PostTag.create!(post: p1, tag: deprecated_tag)
+    PostTag.create!(post: p2, tag: deprecated_tag)
 
     expect { run_rake_task("post_similarity:calc") }
       .to change { PostSimilarity.count }.from(0)
@@ -29,6 +32,6 @@ RSpec.describe 'post_similarity:calc' do
     ps = PostSimilarity.find_by!(post_id: p1.id, target_post_id: p2.id)
     ps_rev = PostSimilarity.find_by!(post_id: p2.id, target_post_id: p1.id)
     expect(ps_rev.cos).to eq(ps.cos)
+    expect(ps.cos).to be_within(0.0001).of(0.5)
   end
 end
-
diff --git a/backend/spec/tasks/tag_similarity_calc_spec.rb b/backend/spec/tasks/tag_similarity_calc_spec.rb
index 8022231..3063010 100644
--- a/backend/spec/tasks/tag_similarity_calc_spec.rb
+++ b/backend/spec/tasks/tag_similarity_calc_spec.rb
@@ -4,11 +4,12 @@ require 'rails_helper'
 RSpec.describe 'tag_similarity:calc' do
   include RakeTaskHelper
 
-  it 'calls Similarity::Calc with Tag and :posts' do
+  it 'calculates similarities for active tags only' do
     # 必要最低限のデータ
     t1 = Tag.create!(name: "t1")
     t2 = Tag.create!(name: "t2")
     t3 = Tag.create!(name: "t3")
+    deprecated_tag = Tag.create!(name: 'deprecated', deprecated_at: Time.current)
 
     p1 = Post.create!(url: "https://example.com/1")
     p2 = Post.create!(url: "https://example.com/2")
@@ -22,6 +23,7 @@ RSpec.describe 'tag_similarity:calc' do
     PostTag.create!(post: p2, tag: t3)
 
     PostTag.create!(post: p3, tag: t3)
+    PostTag.create!(post: p1, tag: deprecated_tag)
 
     expect { run_rake_task("tag_similarity:calc") }
       .to change { TagSimilarity.count }.from(0)
@@ -29,6 +31,7 @@ RSpec.describe 'tag_similarity:calc' do
     ps = TagSimilarity.find_by!(tag_id: t1.id, target_tag_id: t2.id)
     ps_rev = TagSimilarity.find_by!(tag_id: t2.id, target_tag_id: t1.id)
     expect(ps_rev.cos).to eq(ps.cos)
+    expect(TagSimilarity.where(tag_id: deprecated_tag.id)).to be_empty
+    expect(TagSimilarity.where(target_tag_id: deprecated_tag.id)).to be_empty
   end
 end
-
diff --git a/frontend/AGENTS.md b/frontend/AGENTS.md
index d24aaa2..67f7b09 100644
--- a/frontend/AGENTS.md
+++ b/frontend/AGENTS.md
@@ -4,7 +4,8 @@
 
 These rules apply to work under `frontend/`.
 
-This is a Vite + React + TypeScript app using TanStack Query, Tailwind CSS, Framer Motion, Radix UI-style components, MDX, and Zustand.
+This is a Vite + React + TypeScript app using TanStack Query, Tailwind CSS,
+Framer Motion, Radix UI-style components, MDX, and Zustand.
 
 ## Commands
 
@@ -17,9 +18,11 @@ npm run lint
 npm run preview
 ```
 
-`npm run build` runs `tsc -b && vite build`, and `postbuild` runs `node scripts/generate-sitemap.js`.
+`npm run build` runs `tsc -b && vite build`, and `postbuild` runs
+`node scripts/generate-sitemap.js`.
 
-There is currently no `test` script in `package.json`. Do not run or report `npm test` unless a test script is added.
+There is currently no `test` script in `package.json`. Do not run or report
+`npm test` unless a test script is added.
 
 After frontend changes, run:
 
@@ -30,20 +33,43 @@ npm run lint
 
 If either command cannot be run or fails, report the exact command and failure.
 
+Do not create, modify, or run tests unless the user explicitly asks for test
+work. When the user asks for tests, keep working and rerun them until they
+pass or the remaining failure is clearly blocked.
+
 ## TypeScript
 
-- TypeScript is strict. `tsconfig.app.json` enables `strict`, `noUnusedLocals`, `noUnusedParameters`, `erasableSyntaxOnly`, `noFallthroughCasesInSwitch`, and `noUncheckedSideEffectImports`.
+- TypeScript is strict. `tsconfig.app.json` enables `strict`,
+  `noUnusedLocals`, `noUnusedParameters`, `erasableSyntaxOnly`,
+  `noFallthroughCasesInSwitch`, and `noUncheckedSideEffectImports`.
 - Keep types explicit at module boundaries, API helpers, and exported utilities.
 - Use `import type` for type-only imports.
 - Prefer existing shared types from `src/types.ts` before adding local duplicate types.
-- Preserve the repository's existing spacing style in TypeScript, including GNU-style spacing before call parentheses where it is already used.
+- Preserve the repository's existing spacing style in TypeScript, including
+  GNU-style spacing before call parentheses where it is already used.
 - Prefer single quotes for strings unless interpolation or escaping makes double quotes better.
+- Never write a TypeScript or TSX line longer than 99 characters.
+- Aim to keep TypeScript and TSX lines within 79 characters where practical.
+- Use 4-space logical indentation in TypeScript and TSX.
+- For arrays, never put whitespace or a line break immediately before `]`.
+- Keep the first element on the same line as `[` by default.
+- If an array would exceed the line limit, break after `[` and indent
+  elements by 4 spaces.
+- In TypeScript and TSX only, replace every leading run of 8 spaces with a tab
+  to reduce bytes.
+- Treat one leading tab as exactly equivalent to 8 leading spaces.
+- Use tabs only for leading indentation. Never replace spaces that occur after
+  a non-space character on the same line.
 
 ## React
 
 - Use function components.
-- Existing page components commonly export an anonymous function satisfying `FC`; match nearby file style when editing.
+- Existing page components commonly export an anonymous function satisfying
+  `FC`; match nearby file style when editing.
 - React hooks must be called unconditionally and at the top level of components or custom hooks.
+- Gate editing and other privileged controls with shared permission helpers
+  such as `canEditContent`, instead of showing controls and relying only on a
+  later API failure.
 - Keep page-level components under `src/pages`.
 - Keep shared and feature components under `src/components`.
 - Use `react-router-dom` route params and navigation patterns already present in `src/App.tsx`.
@@ -52,17 +78,23 @@ If either command cannot be run or fails, report the exact command and failure.
 ## TanStack Query
 
 - Use `@tanstack/react-query` for server state.
-- Query keys should come from `src/lib/queryKeys.ts`; add key builders there instead of using ad hoc arrays in components.
-- Fetch functions should live in domain helpers under `src/lib`, such as `posts.ts`, `tags.ts`, or `wiki.ts`.
-- Use `useQueryClient().invalidateQueries` with the shared root keys when mutations affect cached lists or detail views.
-- The app-wide `QueryClient` is configured in `src/main.tsx`; do not create additional clients in feature code.
+- Query keys should come from `src/lib/queryKeys.ts`; add key builders there
+  instead of using ad hoc arrays in components.
+- Fetch functions should live in domain helpers under `src/lib`, such as
+  `posts.ts`, `tags.ts`, or `wiki.ts`.
+- Use `useQueryClient().invalidateQueries` with the shared root keys when
+  mutations affect cached lists or detail views.
+- The app-wide `QueryClient` is configured in `src/main.tsx`; do not create
+  additional clients in feature code.
 
 ## API calls
 
 - Use `src/lib/api.ts` for HTTP calls.
-- The API wrapper attaches `X-Transfer-Code` from `localStorage` and converts non-blob responses to camelCase.
+- The API wrapper attaches `X-Transfer-Code` from `localStorage` and converts
+  non-blob responses to camelCase.
 - Send Rails snake_case params and request body keys where the backend expects them.
-- Do not bypass the API wrapper unless there is a specific reason, such as a third-party request outside the Rails API.
+- Do not bypass the API wrapper unless there is a specific reason, such as a
+  third-party request outside the Rails API.
 - For blob responses, pass `responseType: 'blob'` so the wrapper does not camelCase the body.
 
 ## Imports and aliases
@@ -76,17 +108,41 @@ If either command cannot be run or fails, report the exact command and failure.
 
 - Tailwind scans `src/**/*.{html,js,ts,jsx,tsx,mdx}`.
 - Use `cn` from `src/lib/utils.ts` for conditional class names and class merging.
-- Reuse components from `src/components/common`, `src/components/layout`, and `src/components/ui` before adding new primitives.
+- Reuse components from `src/components/common`, `src/components/layout`, and
+  `src/components/ui` before adding new primitives.
 - Keep Tailwind classes consistent with nearby components.
-- When adding dynamic tag color classes, update `tailwind.config.js` safelist if the class cannot be statically detected.
+- Prefer restrained, content-first UI chrome: avoid adding card backgrounds,
+  heavy borders, or nested panel decoration unless the surrounding screen
+  already uses them.
+- Keep operational screens dense and direct; trim explanatory copy and use
+  short Japanese labels that fit the control.
+- Preserve existing Japanese tone and orthography in nearby UI text, including
+  old-kana wording where the file already uses it.
+- When adding dynamic tag color classes, update `tailwind.config.js` safelist
+  if the class cannot be statically detected.
 - Do not introduce new UI libraries or production dependencies without approval.
 
+## TSX formatting
+
+- Preserve compact TSX expression shapes such as inline ternary branches and
+  closing `</div>)` forms when nearby code uses them.
+- For long Tailwind `className` strings, wrap across lines only when needed.
+- Keep continuation indentation aligned with the 4-space logical indentation
+  rule, using tabs only as leading 8-space compression.
+- Do not add braces around `if`, `else`, or `for` bodies when the body is a
+  single physical line.
+- Always add braces around `if`, `else`, or `for` bodies when the body spans
+  two or more physical lines, even if it is one statement.
+- Avoid reformatting unrelated JSX.
+
 ## Lint and build constraints
 
-- ESLint uses `@eslint/js`, `typescript-eslint`, `eslint-plugin-react-hooks`, and `eslint-plugin-react-refresh`.
+- ESLint uses `@eslint/js`, `typescript-eslint`, `eslint-plugin-react-hooks`,
+  and `eslint-plugin-react-refresh`.
 - The hooks rules are enforced; fix hook ordering instead of disabling the rule.
 - `react-refresh/only-export-components` is enabled as a warning with `allowConstantExport`.
-- Build failures from unused locals or unused parameters are TypeScript errors, not lint-only issues.
+- Build failures from unused locals or unused parameters are TypeScript
+  errors, not lint-only issues.
 
 ## Files to avoid in routine work
 
diff --git a/frontend/public/assets/gekanator/mascot-celebrate.png b/frontend/public/assets/gekanator/mascot-celebrate.png
new file mode 100644
index 0000000..6af3e9f
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-celebrate.png differ
diff --git a/frontend/public/assets/gekanator/mascot-confident.png b/frontend/public/assets/gekanator/mascot-confident.png
new file mode 100644
index 0000000..cd34892
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-confident.png differ
diff --git a/frontend/public/assets/gekanator/mascot-failed.png b/frontend/public/assets/gekanator/mascot-failed.png
new file mode 100644
index 0000000..8ff846a
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-failed.png differ
diff --git a/frontend/public/assets/gekanator/mascot-idle.png b/frontend/public/assets/gekanator/mascot-idle.png
new file mode 100644
index 0000000..127028e
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-idle.png differ
diff --git a/frontend/public/assets/gekanator/mascot-thinking-far.png b/frontend/public/assets/gekanator/mascot-thinking-far.png
new file mode 100644
index 0000000..f7d38f6
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-thinking-far.png differ
diff --git a/frontend/public/assets/gekanator/mascot-thinking-mid.png b/frontend/public/assets/gekanator/mascot-thinking-mid.png
new file mode 100644
index 0000000..b71afae
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-thinking-mid.png differ
diff --git a/frontend/public/assets/gekanator/mascot-thinking-near.png b/frontend/public/assets/gekanator/mascot-thinking-near.png
new file mode 100644
index 0000000..3538a0e
Binary files /dev/null and b/frontend/public/assets/gekanator/mascot-thinking-near.png differ
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 2eeaf79..78e7676 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -18,6 +18,7 @@ import MaterialListPage from '@/pages/materials/MaterialListPage'
 import MaterialNewPage from '@/pages/materials/MaterialNewPage'
 // import MaterialSearchPage from '@/pages/materials/MaterialSearchPage'
 import MorePage from '@/pages/MorePage'
+import GekanatorPage from '@/pages/GekanatorPage'
 import NicoTagListPage from '@/pages/tags/NicoTagListPage'
 import NotFound from '@/pages/NotFound'
 import TOSPage from '@/pages/TOSPage.mdx'
@@ -62,8 +63,9 @@ const RouteTransitionWrapper = ({ user, setUser }: {
 	  <Route path="/tags/:id" element={<TagDetailPage/>}/>
 	  <Route path="/tags/:id/deerjikists" element={<DeerjikistDetailPage/>}/>
 	  <Route path="/tags/nico" element={<NicoTagListPage user={user}/>}/>
+	  <Route path="/nico/tags" element={<NicoTagListPage user={user}/>}/>
 	  <Route path="/tags/changes" element={<TagHistoryPage/>}/>
-	  <Route path="/theatres/:id" element={<TheatreDetailPage/>}/>
+	  <Route path="/theatres/:id" element={<TheatreDetailPage user={user}/>}/>
 	  <Route path="/materials" element={<MaterialBasePage/>}>
 	    <Route index element={<MaterialListPage/>}/>
 	    <Route path="new" element={<MaterialNewPage/>}/>
@@ -79,6 +81,7 @@ const RouteTransitionWrapper = ({ user, setUser }: {
 	  <Route path="/users/settings" element={<SettingPage user={user} setUser={setUser}/>}/>
 	  <Route path="/settings" element={<Navigate to="/users/settings" replace/>}/>
 	  <Route path="/tos" element={<TOSPage/>}/>
+	  <Route path="/gekanator" element={<GekanatorPage user={user}/>}/>
 	  <Route path="/more" element={<MorePage/>}/>
 	  <Route path="*" element={<NotFound/>}/>
 	</Routes>
@@ -158,4 +161,4 @@ const App: FC = () => {
       </>)
 }
 
-export default App
\ No newline at end of file
+export default App
diff --git a/frontend/src/components/NicoViewer.test.tsx b/frontend/src/components/NicoViewer.test.tsx
new file mode 100644
index 0000000..1e5789d
--- /dev/null
+++ b/frontend/src/components/NicoViewer.test.tsx
@@ -0,0 +1,83 @@
+import { act, fireEvent, render } from '@testing-library/react'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { createRef } from 'react'
+
+import NicoViewer from '@/components/NicoViewer'
+
+import type { NiconicoViewerHandle } from '@/types'
+
+
+describe ('NicoViewer', () => {
+  afterEach (() => {
+    vi.useRealTimers ()
+  })
+
+  it ('does not time out after metadata reports a playable duration', () => {
+    vi.useFakeTimers ()
+
+    const onError = vi.fn ()
+    const onMetadataChange = vi.fn ()
+    const { container } = render (
+        <NicoViewer
+            id="sm12345"
+            width={640}
+            height={360}
+            onMetadataChange={onMetadataChange}
+            onError={onError}/>,
+    )
+    const iframe = container.querySelector ('iframe')
+    expect (iframe).not.toBeNull ()
+
+    fireEvent.load (iframe!)
+    act (() => {
+      window.dispatchEvent (new MessageEvent ('message', {
+        origin: 'https://embed.nicovideo.jp',
+        source: iframe!.contentWindow,
+        data:   {
+          eventName: 'playerMetadataChange',
+          data:      {
+            currentTime:           7,
+            duration:              120,
+            isVideoMetaDataLoaded: true,
+            maximumBuffered:       30,
+            muted:                 false,
+            showComment:           true,
+            volume:                1,
+          },
+        },
+      }))
+    })
+
+    act (() => {
+      vi.advanceTimersByTime (8_000)
+    })
+
+    expect (onMetadataChange).toHaveBeenCalled ()
+    expect (onError).not.toHaveBeenCalled ()
+  })
+
+  it ('seeks with milliseconds', () => {
+    const ref = createRef<NiconicoViewerHandle> ()
+    const { container } = render (
+        <NicoViewer
+            ref={ref}
+            id="sm12345"
+            width={640}
+            height={360}/>,
+    )
+    const iframe = container.querySelector ('iframe')!
+    const postMessage = vi.spyOn (iframe.contentWindow!, 'postMessage')
+
+    act (() => {
+      ref.current!.seek (7_000)
+    })
+
+    expect (postMessage).toHaveBeenCalledWith (
+        expect.objectContaining ({
+          eventName: 'seek',
+          data:      { time: 7_000 },
+        }),
+        'https://embed.nicovideo.jp',
+    )
+  })
+})
diff --git a/frontend/src/components/NicoViewer.tsx b/frontend/src/components/NicoViewer.tsx
index a1d0390..97f1ffb 100644
--- a/frontend/src/components/NicoViewer.tsx
+++ b/frontend/src/components/NicoViewer.tsx
@@ -1,11 +1,11 @@
 import { forwardRef,
-         useCallback,
-         useEffect,
-         useImperativeHandle,
-         useLayoutEffect,
-         useMemo,
-         useRef,
-         useState } from 'react'
+	 useCallback,
+	 useEffect,
+	 useImperativeHandle,
+	 useLayoutEffect,
+	 useMemo,
+	 useRef,
+	 useState } from 'react'
 
 import type { CSSProperties, ForwardedRef } from 'react'
 
@@ -14,10 +14,20 @@ import type { NiconicoMetadata, NiconicoVideoInfo, NiconicoViewerHandle } from '
 type NiconicoPlayerMessage =
     | { eventName: 'enterProgrammaticFullScreen' }
     | { eventName: 'exitProgrammaticFullScreen' }
-    | { eventName: 'loadComplete'; playerId?: string; data: { videoInfo: NiconicoVideoInfo } }
-    | { eventName: 'playerMetadataChange'; playerId?: string; data: NiconicoMetadata }
-    | { eventName: 'playerStatusChange' | 'statusChange'; playerId?: string; data?: unknown }
-    | { eventName: 'error'; playerId?: string; data?: unknown; code?: string; message?: string }
+    | { eventName: 'loadComplete'
+	playerId?:  string
+	data:       { videoInfo: NiconicoVideoInfo } }
+    | { eventName: 'playerMetadataChange'
+	playerId?:  string
+	data:       NiconicoMetadata }
+    | { eventName: 'playerStatusChange' | 'statusChange'
+	playerId?:  string
+	data?:      unknown }
+    | { eventName: 'error'
+	playerId?:  string
+	data?:      unknown
+	code?:      string
+	message?:   string }
 
 type NiconicoCommand =
     | { eventName: 'play'; sourceConnectorType: 1; playerId: string }
@@ -30,6 +40,7 @@ type NiconicoCommand =
 	data: { commentVisibility: boolean } }
 
 const EMBED_ORIGIN = 'https://embed.nicovideo.jp'
+const LOAD_COMPLETE_TIMEOUT_MS = 8_000
 
 type Props = {
     id:                 string
@@ -37,14 +48,18 @@ type Props = {
     height:             number
     style?:             CSSProperties
     onLoadComplete?:    (info: NiconicoVideoInfo) => void
-    onMetadataChange?:  (meta: NiconicoMetadata) => void }
+    onMetadataChange?:  (meta: NiconicoMetadata) => void
+    onError?:           (data: unknown) => void }
 
 
 export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle>) => {
-  const { id, width, height, style = { }, onLoadComplete, onMetadataChange } = props
+  const { id, width, height, style = { }, onLoadComplete, onMetadataChange, onError } = props
 
   const iframeRef = useRef<HTMLIFrameElement> (null)
-  const playerId = useMemo (() => `nico-${ id }-${ Math.random ().toString (36).slice (2) }`, [id])
+  const loadCompleteTimerRef = useRef<ReturnType<typeof setTimeout> | null> (null)
+  const playerId = useMemo (
+      () => `nico-${ id }-${ Math.random ().toString (36).slice (2) }`,
+      [id])
 
   const [screenWidth, setScreenWidth] = useState<CSSProperties['width']> ()
   const [screenHeight, setScreenHeight] = useState<CSSProperties['height']> ()
@@ -64,21 +79,39 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
   const styleFullScreen: CSSProperties =
       fullScreen
       ? { top: 0,
-          left: landscape ? 0 : '100%',
-          position: 'fixed',
-          width: screenWidth,
-          height: screenHeight,
-          zIndex: 2_147_483_647,
-          maxWidth: 'none',
-          transformOrigin: '0% 0%',
-          transform: landscape ? 'none' : 'rotate(90deg)',
-          WebkitTransformOrigin: '0% 0%',
-          WebkitTransform: landscape ? 'none' : 'rotate(90deg)' }
+	  left: landscape ? 0 : '100%',
+	  position: 'fixed',
+	  width: screenWidth,
+	  height: screenHeight,
+	  zIndex: 2_147_483_647,
+	  maxWidth: 'none',
+	  transformOrigin: '0% 0%',
+	  transform: landscape ? 'none' : 'rotate(90deg)',
+	  WebkitTransformOrigin: '0% 0%',
+	  WebkitTransform: landscape ? 'none' : 'rotate(90deg)' }
       : { }
 
   const margedStyle: CSSProperties =
       { border: 'none', maxWidth: '100%', ...style, ...styleFullScreen }
 
+  const clearLoadCompleteTimer = useCallback (() => {
+    if (!(loadCompleteTimerRef.current))
+      return
+
+    clearTimeout (loadCompleteTimerRef.current)
+    loadCompleteTimerRef.current = null
+  }, [])
+
+  const startLoadCompleteTimer = useCallback (() => {
+    clearLoadCompleteTimer ()
+    loadCompleteTimerRef.current = setTimeout (() => {
+      onError?.({
+	  eventName: 'loadCompleteTimeout',
+	  reason:    'niconico video length was not reported by embed',
+      })
+    }, LOAD_COMPLETE_TIMEOUT_MS)
+  }, [clearLoadCompleteTimer, onError])
+
   const postToPlayer = useCallback ((message: NiconicoCommand) => {
     const win = iframeRef.current?.contentWindow
     if (!(win))
@@ -96,7 +129,9 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
   }, [playerId, postToPlayer])
 
   const seek = useCallback ((time: number) => {
-    postToPlayer ({ eventName: 'seek', sourceConnectorType: 1, playerId, data: { time } })
+    postToPlayer (
+	{ eventName: 'seek', sourceConnectorType: 1, playerId,
+	  data: { time } })
   }, [playerId, postToPlayer])
 
   const mute = useCallback (() => {
@@ -132,21 +167,21 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
   useEffect (() => {
     const onMessage = (event: MessageEvent<NiconicoPlayerMessage>) => {
       if (!(iframeRef.current)
-          || (event.source !== iframeRef.current.contentWindow)
-          || (event.origin !== EMBED_ORIGIN))
-        return
+	  || (event.source !== iframeRef.current.contentWindow)
+	  || (event.origin !== EMBED_ORIGIN))
+	return
 
       const data = event.data
 
       if (!(data)
 	  || typeof data !== 'object'
 	  || !('eventName' in data))
-        return
+	return
 
       if (('playerId' in data)
 	  && data.playerId
 	  && data.playerId !== playerId)
-        return
+	return
 
       if (data.eventName === 'enterProgrammaticFullScreen')
 	{
@@ -162,24 +197,34 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
 
       if (data.eventName === 'loadComplete')
 	{
+	  clearLoadCompleteTimer ()
 	  onLoadComplete?.(data.data.videoInfo)
 	  return
 	}
 
       if (data.eventName === 'playerMetadataChange')
 	{
+	  if (Number.isFinite (data.data.duration) && data.data.duration > 0)
+	    clearLoadCompleteTimer ()
+
 	  onMetadataChange?.(data.data)
 	  return
 	}
 
       if (data.eventName === 'error')
-        console.error ('niconico player error:', data)
+	{
+	  clearLoadCompleteTimer ()
+	  console.error ('niconico player error:', data)
+	  onError?.(data)
+	}
     }
 
     addEventListener ('message', onMessage)
 
     return () => removeEventListener ('message', onMessage)
-  }, [onLoadComplete, onMetadataChange, playerId])
+  }, [clearLoadCompleteTimer, onError, onLoadComplete, onMetadataChange, playerId])
+
+  useEffect (() => clearLoadCompleteTimer, [clearLoadCompleteTimer])
 
   useLayoutEffect (() => {
     if (!(fullScreen))
@@ -192,7 +237,7 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
 
     const pollingResize = () => {
       if (ended)
-        return
+	return
 
       const isLandscape = innerWidth >= innerHeight
       const windowWidth = `${ isLandscape ? innerWidth : innerHeight }px`
@@ -206,9 +251,9 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
 
     const startPollingResize = () => {
       if (requestAnimationFrame)
-        requestAnimationFrame (pollingResize)
+	requestAnimationFrame (pollingResize)
       else
-        pollingResize ()
+	pollingResize ()
     }
 
     startPollingResize ()
@@ -231,9 +276,10 @@ export default forwardRef ((props: Props, ref: ForwardedRef<NiconicoViewerHandle
       <iframe
 	  ref={iframeRef}
 	  src={src}
-	  width={width}
-	  height={height}
-	  style={margedStyle}
-	  allowFullScreen
-	  allow="autoplay"/>)
+		  width={width}
+		  height={height}
+		  style={margedStyle}
+		  onLoad={startLoadCompleteTimer}
+		  allowFullScreen
+		  allow="autoplay"/>)
 })
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 2a2083e..6e4b560 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -2,18 +2,23 @@ import { useEffect, useState } from 'react'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
-import Label from '@/components/common/Label'
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import { useDialogue } from '@/components/dialogues/DialogueProvider'
 import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { isApiError } from '@/lib/api'
 import { updatePost } from '@/lib/posts'
-import { msToTime } from '@/lib/utils'
+import { inputClass, msToTime } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC, FormEvent } from 'react'
 
 import type { Post, TagWithSections } from '@/types'
 
+type PostFormField =
+    'parentPostIds' | 'tags' | 'originalCreatedAt'
+
 
 const tagsToStr = (tags: TagWithSections[]): string => {
   const result: Omit<TagWithSections, 'children'>[] = []
@@ -39,6 +44,8 @@ type Props = { post:    Post
 
 const PostEditForm: FC<Props> = ({ post, onSave }) => {
   const [disabled, setDisabled] = useState (false)
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<PostFormField> ()
   const [originalCreatedBefore, setOriginalCreatedBefore] =
       useState<string | null> (post.originalCreatedBefore)
   const [originalCreatedFrom, setOriginalCreatedFrom] =
@@ -51,6 +58,8 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
   const dialogue = useDialogue ()
 
   const update = async (...args: Parameters<typeof updatePost>) => {
+    clearValidationErrors ()
+
     try
     {
       const data = await updatePost (...args)
@@ -71,7 +80,14 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 
       if (response?.status !== 409)
 	{
-	  toast ({ description: '更新はできなかったよ……' })
+	  if (applyValidationError (e))
+	    {
+	      toast ({ description: '更新はできなかったよ……' })
+	      return
+	    }
+
+	  toast ({ title: '失敗……', description: '入力を確認してください．' })
+
 	  return
 	}
 
@@ -126,33 +142,38 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 
   return (
       <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
+	<FieldError messages={baseErrors}/>
+
 	{/* タイトル */}
-	<div>
-	  <Label>タイトル</Label>
-	  <input
-	      type="text"
-	      disabled={disabled}
-	      className="w-full border rounded p-2"
-	      value={title ?? ''}
-	      onChange={ev => setTitle (ev.target.value)}/>
-	</div>
+	<FormField label="タイトル">
+	  {({ invalid }) => (
+	      <input
+		  type="text"
+		  disabled={disabled}
+		  className={inputClass (invalid)}
+		  value={title ?? ''}
+		  onChange={ev => setTitle (ev.target.value)}/>)}
+	</FormField>
 
 	{/* 親投稿 */}
-	<div>
-	  <Label>親投稿</Label>
-	  <input
-	      type="text"
-	      disabled={disabled}
-	      value={parentPostIds}
-	      onChange={e => setParentPostIds (e.target.value)}
-	      className="w-full border p-2 rounded"/>
-	</div>
+	<FormField label="親投稿" messages={fieldErrors.parentPostIds}>
+	  {({ describedBy, invalid }) => (
+	      <input
+		  type="text"
+		  disabled={disabled}
+		  value={parentPostIds}
+		  onChange={e => setParentPostIds (e.target.value)}
+		  aria-describedby={describedBy}
+		  aria-invalid={invalid}
+		  className={inputClass (invalid)}/>)}
+	</FormField>
 
 	{/* タグ */}
 	<PostFormTagsArea
 	    disabled={disabled}
 	    tags={tags}
-	    setTags={setTags}/>
+	    setTags={setTags}
+	    errors={fieldErrors.tags}/>
 
 	{/* オリジナルの作成日時 */}
 	<PostOriginalCreatedTimeField
@@ -160,12 +181,11 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 	    originalCreatedFrom={originalCreatedFrom}
 	    setOriginalCreatedFrom={setOriginalCreatedFrom}
 	    originalCreatedBefore={originalCreatedBefore}
-	    setOriginalCreatedBefore={setOriginalCreatedBefore}/>
+	    setOriginalCreatedBefore={setOriginalCreatedBefore}
+	    errors={fieldErrors.originalCreatedAt}/>
 
 	{/* 送信 */}
-	<Button
-	    type="submit"
-	    disabled={disabled}>
+	<Button type="submit" disabled={disabled}>
 	  更新
 	</Button>
       </form>)
diff --git a/frontend/src/components/PostEmbed.test.tsx b/frontend/src/components/PostEmbed.test.tsx
index e34713e..15cd42c 100644
--- a/frontend/src/components/PostEmbed.test.tsx
+++ b/frontend/src/components/PostEmbed.test.tsx
@@ -8,12 +8,19 @@ const dialogue = vi.hoisted (() => ({
   confirm: vi.fn (),
 }))
 
+const nicoViewer = vi.hoisted (() => ({
+  props: vi.fn (),
+}))
+
 vi.mock ('@/components/dialogues/DialogueProvider', () => ({
   useDialogue: () => dialogue,
 }))
 
 vi.mock ('@/components/NicoViewer', () => ({
-  default: ({ id }: { id: string }) => <div>Nico:{id}</div>,
+  default: (props: { id: string }) => {
+    nicoViewer.props (props)
+    return <div>Nico:{props.id}</div>
+  },
 }))
 
 vi.mock ('react-youtube', () => ({
@@ -31,6 +38,64 @@ describe ('PostEmbed', () => {
     expect (screen.getByText ('Nico:sm12345')).toBeInTheDocument ()
   })
 
+  it ('reports niconico metadata as milliseconds', () => {
+    const onVideoReady = vi.fn ()
+    const onPlaybackChange = vi.fn ()
+    render (
+        <PostEmbed
+            post={buildPost ({ url: 'https://www.nicovideo.jp/watch/sm12345' })}
+            onVideoReady={onVideoReady}
+            onPlaybackChange={onPlaybackChange}/>,
+    )
+
+    nicoViewer.props.mock.calls[0][0].onMetadataChange ({
+      currentTime:            7_000,
+      duration:               120_000,
+      isVideoMetaDataLoaded:  true,
+      maximumBuffered:        30,
+      muted:                  false,
+      showComment:            true,
+      volume:                 1,
+    })
+
+    expect (onVideoReady).toHaveBeenCalledWith (120_000)
+    expect (onPlaybackChange).toHaveBeenCalledWith (7_000)
+  })
+
+  it ('reports niconico video readiness only once', () => {
+    const onVideoReady = vi.fn ()
+    render (
+        <PostEmbed
+            post={buildPost ({ url: 'https://www.nicovideo.jp/watch/sm12345' })}
+            onVideoReady={onVideoReady}/>,
+    )
+
+    nicoViewer.props.mock.calls[0][0].onLoadComplete ({
+      title:           '動画',
+      videoId:         'sm12345',
+      lengthInSeconds: 120,
+      thumbnailUrl:    'https://example.com/thumb.jpg',
+      description:     '',
+      viewCount:       1,
+      commentCount:    2,
+      mylistCount:     3,
+      postedAt:        '2026-01-02T03:04:05.000Z',
+      watchId:         12345,
+    })
+    nicoViewer.props.mock.calls[0][0].onMetadataChange ({
+      currentTime:            7_000,
+      duration:               120_000,
+      isVideoMetaDataLoaded:  true,
+      maximumBuffered:        30,
+      muted:                  false,
+      showComment:            true,
+      volume:                 1,
+    })
+
+    expect (onVideoReady).toHaveBeenCalledTimes (1)
+    expect (onVideoReady).toHaveBeenCalledWith (120_000)
+  })
+
   it ('embeds x/twitter status URLs', () => {
     render (<PostEmbed post={buildPost ({ url: 'https://x.com/someone/status/12345' })}/>)
 
diff --git a/frontend/src/components/PostEmbed.tsx b/frontend/src/components/PostEmbed.tsx
index 8ae3220..3cbbd00 100644
--- a/frontend/src/components/PostEmbed.tsx
+++ b/frontend/src/components/PostEmbed.tsx
@@ -1,4 +1,4 @@
-import { useState } from 'react'
+import { useCallback, useEffect, useRef, useState } from 'react'
 import YoutubeEmbed from 'react-youtube'
 
 import NicoViewer from '@/components/NicoViewer'
@@ -8,17 +8,113 @@ import { useDialogue } from '@/components/dialogues/DialogueProvider'
 import type { FC, RefObject } from 'react'
 
 import type { NiconicoMetadata, NiconicoVideoInfo, NiconicoViewerHandle, Post } from '@/types'
+import type { YouTubePlayer } from 'react-youtube'
+
+type YouTubeEvent<T = unknown> = {
+    data:    T
+    target:  YouTubePlayer }
 
 type Props = {
     ref?:               RefObject<NiconicoViewerHandle | null>
     post:               Post
     onLoadComplete?:    (info: NiconicoVideoInfo) => void
-    onMetadataChange?:  (meta: NiconicoMetadata) => void }
+    onMetadataChange?:  (meta: NiconicoMetadata) => void
+    onVideoReady?:      (durationMs: number) => void
+    onPlaybackChange?:  (currentTimeMs: number) => number | void
+    onError?:           (data: unknown) => void }
 
 
-const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange }) => {
+const PostEmbed: FC<Props> = ({
+    ref,
+    post,
+    onLoadComplete,
+    onMetadataChange,
+    onVideoReady,
+    onPlaybackChange,
+    onError,
+}) => {
   const dialogue = useDialogue ()
   const [framed, setFramed] = useState (false)
+  const [youtubePlayer, setYoutubePlayer] = useState<YouTubePlayer | null> (null)
+  const niconicoVideoReadyRef = useRef (false)
+
+  const notifyNiconicoVideoReady = useCallback ((durationMs: number) => {
+    if (niconicoVideoReadyRef.current
+	|| !(Number.isFinite (durationMs))
+	|| durationMs <= 0)
+      return
+
+    niconicoVideoReadyRef.current = true
+    onVideoReady?.(durationMs)
+  }, [onVideoReady])
+
+  const reportYoutubePlayback = useCallback (async (player: YouTubePlayer) => {
+    const currentTime = await player.getCurrentTime ()
+    const currentTimeMs = currentTime * 1_000
+    const targetTimeMs = onPlaybackChange?.(currentTimeMs)
+
+    if (typeof targetTimeMs !== 'number')
+      return
+
+    if (Math.abs (currentTimeMs - targetTimeMs) > 5_000)
+      await player.seekTo (targetTimeMs / 1_000, true)
+  }, [onPlaybackChange])
+
+  const handleYoutubeReady = async (event: YouTubeEvent) => {
+    setYoutubePlayer (event.target)
+
+    try
+    {
+      await event.target.playVideo ()
+
+      const duration = await event.target.getDuration ()
+      const durationMs = duration * 1_000
+      onVideoReady?.(durationMs)
+
+      if (!(Number.isFinite (durationMs)) || durationMs <= 0)
+	return
+
+      await reportYoutubePlayback (event.target)
+    }
+    catch (error)
+    {
+      onError?.({ platform: 'youtube', error })
+    }
+  }
+
+  const handleYoutubeStateChange = (event: YouTubeEvent<number>) => {
+    void reportYoutubePlayback (event.target)
+  }
+
+  const handleYoutubeError = (event: YouTubeEvent<number>) => {
+    onError?.({ platform: 'youtube', code: event.data })
+  }
+
+  const handleNiconicoLoadComplete = (info: NiconicoVideoInfo) => {
+    notifyNiconicoVideoReady (info.lengthInSeconds * 1_000)
+    onLoadComplete?.(info)
+  }
+
+  const handleNiconicoMetadataChange = (meta: NiconicoMetadata) => {
+    notifyNiconicoVideoReady (meta.duration)
+    onPlaybackChange?.(meta.currentTime)
+    onMetadataChange?.(meta)
+  }
+
+  useEffect (() => {
+    niconicoVideoReadyRef.current = false
+  }, [post.url])
+
+  useEffect (() => {
+    if (!(youtubePlayer) || !(onPlaybackChange))
+      return
+
+    const timer = setInterval (
+	() => void reportYoutubePlayback (youtubePlayer),
+	1_000)
+
+    return () => clearInterval (timer)
+  }, [onPlaybackChange, reportYoutubePlayback, youtubePlayer])
 
   const url = new URL (post.url)
 
@@ -38,8 +134,9 @@ const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange }) =
 	      id={videoId}
 	      width={640}
 	      height={360}
-	      onLoadComplete={onLoadComplete}
-	      onMetadataChange={onMetadataChange}/>)
+	      onLoadComplete={handleNiconicoLoadComplete}
+	      onMetadataChange={handleNiconicoMetadataChange}
+	      onError={onError}/>)
     }
 
   case 'twitter.com':
@@ -69,7 +166,10 @@ const PostEmbed: FC<Props> = ({ ref, post, onLoadComplete, onMetadataChange }) =
 	      mute:         0,
 	      loop:         1,
 	      width:        '640',
-	      height:       '360' } }}/>)
+	      height:       '360' } }}
+	      onReady={handleYoutubeReady}
+	      onStateChange={handleYoutubeStateChange}
+	      onError={handleYoutubeError}/>)
     }
   }
 
diff --git a/frontend/src/components/PostFormTagsArea.tsx b/frontend/src/components/PostFormTagsArea.tsx
index 513af9d..19c1c6a 100644
--- a/frontend/src/components/PostFormTagsArea.tsx
+++ b/frontend/src/components/PostFormTagsArea.tsx
@@ -3,7 +3,7 @@
 import { useRef, useState } from 'react'
 
 import TagSearchBox from '@/components/TagSearchBox'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import TextArea from '@/components/common/TextArea'
 import { apiGet } from '@/lib/api'
 
@@ -33,10 +33,11 @@ const replaceToken = (value: string, start: number, end: number, text: string) =
 
 type Props = Omit<ComponentPropsWithoutRef<'textarea'>, 'value' | 'onChange' | 'onBlur'> & {
     tags:     string
-    setTags:  (tags: string) => void }
+    setTags:  (tags: string) => void
+    errors?:  string[] }
 
 
-const PostFormTagsArea: FC<Props> = ({ tags, setTags, ...rest }) => {
+const PostFormTagsArea: FC<Props> = ({ tags, setTags, errors, ...rest }) => {
   const ref = useRef<HTMLTextAreaElement> (null)
 
   const [bounds, setBounds] = useState<{ start: number; end: number }> ({ start: 0, end: 0 })
@@ -73,30 +74,34 @@ const PostFormTagsArea: FC<Props> = ({ tags, setTags, ...rest }) => {
   }
 
   return (
-      <div className="relative w-full">
-	<Label>タグ</Label>
-	<TextArea
-	    {...rest}
-	    ref={ref}
-	    value={tags}
-	    onChange={ev => setTags (ev.target.value)}
-	    onSelect={async (ev: SyntheticEvent<HTMLTextAreaElement>) => {
-	      const pos = (ev.target as HTMLTextAreaElement).selectionStart
-	      await recompute (pos)
-	    }}
-	    onFocus={() => setFocused (true)}
-	    onBlur={() => {
-	      setFocused (false)
-	      setSuggestionsVsbl (false)
-	    }}/>
-	{focused && (
-	    <TagSearchBox
-		suggestions={suggestionsVsbl && suggestions.length > 0
-			     ? suggestions
-			     : [] as Tag[]}
-		activeIndex={-1}
-		onSelect={handleTagSelect}/>)}
-      </div>)
+      <FormField className="relative w-full" label="タグ" messages={errors}>
+	{({ describedBy, invalid }) => (
+	    <>
+	      <TextArea
+		  {...rest}
+		  ref={ref}
+		  value={tags}
+		  aria-describedby={describedBy}
+		  invalid={invalid}
+		  onChange={ev => setTags (ev.target.value)}
+		  onSelect={async (ev: SyntheticEvent<HTMLTextAreaElement>) => {
+		    const pos = (ev.target as HTMLTextAreaElement).selectionStart
+		    await recompute (pos)
+		  }}
+		  onFocus={() => setFocused (true)}
+		  onBlur={() => {
+		    setFocused (false)
+		    setSuggestionsVsbl (false)
+		  }}/>
+	      {focused && (
+		  <TagSearchBox
+		      suggestions={suggestionsVsbl && suggestions.length > 0
+				   ? suggestions
+				   : [] as Tag[]}
+		      activeIndex={-1}
+		      onSelect={handleTagSelect}/>)}
+	    </>)}
+      </FormField>)
 }
 
-export default PostFormTagsArea
\ No newline at end of file
+export default PostFormTagsArea
diff --git a/frontend/src/components/PostOriginalCreatedTimeField.tsx b/frontend/src/components/PostOriginalCreatedTimeField.tsx
index 625b5a3..2ddbee4 100644
--- a/frontend/src/components/PostOriginalCreatedTimeField.tsx
+++ b/frontend/src/components/PostOriginalCreatedTimeField.tsx
@@ -1,5 +1,5 @@
 import DateTimeField from '@/components/common/DateTimeField'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import { Button } from '@/components/ui/button'
 
 import type { FC } from 'react'
@@ -9,68 +9,81 @@ type Props = {
     originalCreatedFrom:      string | null
     setOriginalCreatedFrom:   (x: string | null) => void
     originalCreatedBefore:    string | null
-    setOriginalCreatedBefore: (x: string | null) => void }
+    setOriginalCreatedBefore: (x: string | null) => void
+    errors?:                  string[] }
 
 
-const PostOriginalCreatedTimeField: FC<Props> = ({ disabled,
-		   originalCreatedFrom,
-		   setOriginalCreatedFrom,
-		   originalCreatedBefore,
-		   setOriginalCreatedBefore }) => (
-    <div>
-      <Label>オリジナルの作成日時</Label>
-      <div className="my-1 flex">
-	<div className="w-80">
-	  <DateTimeField
-	      className="mr-2"
-	      disabled={disabled ?? false}
-	      value={originalCreatedFrom ?? undefined}
-	      onChange={setOriginalCreatedFrom}
-	      onBlur={ev => {
-		const v = ev.target.value
-		if (!(v))
-		  return
+const PostOriginalCreatedTimeField: FC<Props> = (
+    { disabled,
+      originalCreatedFrom,
+      setOriginalCreatedFrom,
+      originalCreatedBefore,
+      setOriginalCreatedBefore,
+      errors }: Props,
+) => (
+    <FormField label="オリジナルの作成日時" messages={errors}>
+      {({ describedBy, invalid }) => (
+	  <>
+	    <div className="my-1 flex">
+	      <div className="w-80">
+		<DateTimeField
+		    className="mr-2"
+		    disabled={disabled ?? false}
+		    aria-describedby={describedBy}
+		    aria-invalid={invalid}
+		    invalid={invalid}
+		    value={originalCreatedFrom ?? undefined}
+		    onChange={setOriginalCreatedFrom}
+		    onBlur={ev => {
+		      const v = ev.target.value
+		      if (!(v))
+			return
 
-		const d = new Date (v)
-		if (d.getMinutes () === 0 && d.getHours () === 0)
-		  d.setDate (d.getDate () + 1)
-		else
-		  d.setMinutes (d.getMinutes () + 1)
-		setOriginalCreatedBefore (d.toISOString ())
-	      }}/>
-	  以降
-	</div>
-	<div>
-	  <Button
-	      className="bg-gray-600 text-white rounded"
-	      disabled={disabled}
-	      onClick={() => {
-		setOriginalCreatedFrom (null)
-	      }}>
-	    リセット
-	  </Button>
-	</div>
-      </div>
-      <div className="my-1 flex">
-	<div className="w-80">
-	  <DateTimeField
-	      className="mr-2"
-	      disabled={disabled}
-	      value={originalCreatedBefore ?? undefined}
-	      onChange={setOriginalCreatedBefore}/>
-	  より前
-	</div>
-	<div>
-	  <Button
-	      className="bg-gray-600 text-white rounded"
-	      disabled={disabled}
-	      onClick={() => {
-		setOriginalCreatedBefore (null)
-	      }}>
-	    リセット
-	  </Button>
-	</div>
-      </div>
-    </div>)
+		      const d = new Date (v)
+		      if (d.getMinutes () === 0 && d.getHours () === 0)
+			d.setDate (d.getDate () + 1)
+		      else
+			d.setMinutes (d.getMinutes () + 1)
+		      setOriginalCreatedBefore (d.toISOString ())
+		    }}/>
+		以降
+	      </div>
+	      <div>
+		<Button
+		    className="bg-gray-600 text-white rounded"
+		    disabled={disabled}
+		    onClick={() => {
+		      setOriginalCreatedFrom (null)
+		    }}>
+		  リセット
+		</Button>
+	      </div>
+	    </div>
 
-export default PostOriginalCreatedTimeField
\ No newline at end of file
+	    <div className="my-1 flex">
+	      <div className="w-80">
+		<DateTimeField
+		    className="mr-2"
+		    disabled={disabled}
+		    aria-describedby={describedBy}
+		    aria-invalid={invalid}
+		    invalid={invalid}
+		    value={originalCreatedBefore ?? undefined}
+		    onChange={setOriginalCreatedBefore}/>
+		より前
+	      </div>
+	      <div>
+		<Button
+		    className="bg-gray-600 text-white rounded"
+		    disabled={disabled}
+		    onClick={() => {
+		      setOriginalCreatedBefore (null)
+		    }}>
+		  リセット
+		</Button>
+	      </div>
+	    </div>
+	  </>)}
+    </FormField>)
+
+export default PostOriginalCreatedTimeField
diff --git a/frontend/src/components/TagLink.test.tsx b/frontend/src/components/TagLink.test.tsx
index 3c2a152..e6a073c 100644
--- a/frontend/src/components/TagLink.test.tsx
+++ b/frontend/src/components/TagLink.test.tsx
@@ -18,6 +18,21 @@ describe ('TagLink', () => {
     expect (screen.getByText ('4')).toBeInTheDocument ()
   })
 
+  it ('does not append deprecated state to the rendered tag name', () => {
+    renderWithProviders (
+        <TagLink
+            tag={buildTag ({
+                name:         '旧タグ',
+                deprecatedAt: '2026-06-01T00:00:00.000Z',
+            })}
+            withWiki={false}
+            withCount={false}/>,
+    )
+
+    expect (screen.getByRole ('link', { name: '旧タグ' })).toBeInTheDocument ()
+    expect (screen.queryByText ('（廃止）')).not.toBeInTheDocument ()
+  })
+
   it ('links wiki markers to the correct detail route', () => {
     renderWithProviders (
         <TagLink tag={buildTag ({ hasWiki: true, name: 'a/b' })}/>,
diff --git a/frontend/src/components/TagLink.tsx b/frontend/src/components/TagLink.tsx
index 33bfc40..4abdf1a 100644
--- a/frontend/src/components/TagLink.tsx
+++ b/frontend/src/components/TagLink.tsx
@@ -128,4 +128,4 @@ const TagLink: FC<Props> = ({ tag,
       </>)
 }
 
-export default TagLink
\ No newline at end of file
+export default TagLink
diff --git a/frontend/src/components/TagSearch.tsx b/frontend/src/components/TagSearch.tsx
index e9833f1..9447e1f 100644
--- a/frontend/src/components/TagSearch.tsx
+++ b/frontend/src/components/TagSearch.tsx
@@ -4,6 +4,7 @@ import { useEffect, useState } from 'react'
 import { useNavigate, useLocation } from 'react-router-dom'
 
 import { apiGet } from '@/lib/api'
+import { inputClass } from '@/lib/utils'
 
 import TagSearchBox from './TagSearchBox'
 
@@ -110,11 +111,12 @@ const TagSearch: FC = () => {
 	       onFocus={() => setSuggestionsVsbl (true)}
 	       onBlur={() => setSuggestionsVsbl (false)}
 	       onKeyDown={handleKeyDown}
-	       className="w-full px-3 py-2 border rounded dark:border-gray-600 dark:bg-gray-800 dark:text-white"/>
+	       className={inputClass (false,
+				      'px-3 py-2 dark:border-gray-600 dark:bg-gray-800 dark:text-white')}/>
 	<TagSearchBox suggestions={suggestionsVsbl && suggestions.length ? suggestions : [] as Tag[]}
 		      activeIndex={activeIndex}
 		      onSelect={handleTagSelect}/>
       </div>)
 }
 
-export default TagSearch
\ No newline at end of file
+export default TagSearch
diff --git a/frontend/src/components/TopNav.tsx b/frontend/src/components/TopNav.tsx
index c7772bb..ed2f596 100644
--- a/frontend/src/components/TopNav.tsx
+++ b/frontend/src/components/TopNav.tsx
@@ -55,12 +55,6 @@ export const menuOutline = ({ tag, wikiId, user, pathName }: {
 	  { name: '追加', to: '/materials/new' },
 	  { name: '全体履歴', to: '/materials/changes', visible: false },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:素材集' }] },
-      { name: '上映会', to: '/theatres/1', base: '/theatres', subMenu: [
-	  { name: <>第&thinsp;1&thinsp;会場</>, to: '/theatres/1' },
-	  { name: 'CyTube', to: '//cytube.mm428.net/r/deernijika' },
-	  { name: <>ニジカ放送局第&thinsp;1&thinsp;チャンネル</>,
-	    to: '//www.youtube.com/watch?v=DCU3hL4Uu6A' },
-	  { name: 'ヘルプ', to: '/wiki/ヘルプ:上映会' }] },
       { name: 'Wiki', to: '/wiki/ヘルプ:ホーム', base: '/wiki', subMenu: [
 	  { name: '検索', to: '/wiki' },
 	  { name: '新規', to: '/wiki/new' },
@@ -71,6 +65,9 @@ export const menuOutline = ({ tag, wikiId, user, pathName }: {
 	    visible: wikiPageFlg },
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
 	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`, visible: wikiPageFlg }] },
+      { name: 'おたのしみ', visible: false, subMenu: [
+	  { name: '上映会 (β)', to: '/theatres/1' },
+	  { name: 'グカネータ (β)', to: '/gekanator' }] },
       { name: 'ユーザ', to: '/users/settings', visible: false, subMenu: [
 	  { name: '一覧', to: '/users', visible: false },
 	  { name: 'お前', to: `/users/${ user?.id }`, visible: false },
@@ -132,8 +129,12 @@ const TopNav: FC<Props> = ({ user }) => {
 
   const menu = menuOutline ({ tag, wikiId, user, pathName: location.pathname })
   const visibleMenu = menu.filter ((item): item is MenuVisibleItem => item.visible ?? true)
+  const moreMenu = menu.filter (item =>
+      !(item.visible ?? true)
+      || item.subMenu.filter (subItem => subItem.visible ?? true).length > 0)
   const activeIdx =
       visibleMenu.findIndex (item => location.pathname.startsWith (item.base || item.to))
+  const submenuHeight = moreVsbl ? 40 * moreMenu.length : (activeIdx < 0 ? 0 : 40)
 
   const prevActiveIdxRef = useRef<number> (activeIdx)
 
@@ -244,9 +245,9 @@ const TopNav: FC<Props> = ({ user }) => {
 	  <motion.div
 	      key="submenu-shell"
 	      layout
-	      className="relative hidden md:block overflow-hidden
+	      className="relative z-20 hidden md:block overflow-hidden
 			 bg-yellow-200 dark:bg-red-950"
-	      style={{ height: moreVsbl ? 40 * menu.length : (activeIdx < 0 ? 0 : 40) }}
+	      animate={{ height: submenuHeight }}
 	      onMouseLeave={() => {
 		if (moreVsbl)
 		  setMoreVsbl (false)
@@ -257,7 +258,7 @@ const TopNav: FC<Props> = ({ user }) => {
 	      }}>
 	  {moreVsbl
 	   ? (
-	      menu.map ((item, i) => (
+	      moreMenu.map ((item, i) => (
 		  <div key={i} className="relative h-[40px]">
 		    <div className="absolute inset-0 flex items-center px-3">
 		      <motion.div
@@ -267,7 +268,7 @@ const TopNav: FC<Props> = ({ user }) => {
 			       : { initial: { x: 40, y: -40, opacity: 0 },
 				   animate: { x: 0, y: 0, opacity: 1 },
 				   exit: { x: 40, y: -40, opacity: 0 } })}
-			  className="z-10 h-full flex items-center px-3 font-bold w-24">
+			  className="z-10 h-full flex items-center px-3 font-bold w-28">
 			<h2>{item.name}</h2>
 		      </motion.div>
 		      {item.subMenu
diff --git a/frontend/src/components/common/DateTimeField.tsx b/frontend/src/components/common/DateTimeField.tsx
index 9e50595..0cb2210 100644
--- a/frontend/src/components/common/DateTimeField.tsx
+++ b/frontend/src/components/common/DateTimeField.tsx
@@ -22,10 +22,11 @@ type Props = Omit<ComponentPropsWithoutRef<'input'>, 'onChange'> & {
     value?:     string
     onChange?:  (isoUTC: string | null) => void
     className?: string
-    onBlur?:    (ev: FocusEvent<HTMLInputElement>) => void }
+    onBlur?:    (ev: FocusEvent<HTMLInputElement>) => void
+    invalid?:   boolean }
 
 
-const DateTimeField: FC<Props> = ({ value, onChange, className, onBlur, ...rest }) => {
+const DateTimeField: FC<Props> = ({ value, onChange, className, onBlur, invalid, ...rest }) => {
   const [local, setLocal] = useState ('')
 
   useEffect (() => {
@@ -35,9 +36,19 @@ const DateTimeField: FC<Props> = ({ value, onChange, className, onBlur, ...rest
   return (
       <input
 	  {...rest}
-	  className={cn ('border rounded p-2', className)}
+	  className={cn ('border rounded p-2',
+			 (invalid
+			  ? ['border-red-500 bg-red-50 text-red-900',
+			     'focus:border-red-500 focus:outline-none',
+			     'focus:ring-2 focus:ring-red-200',
+			     'dark:border-red-500 dark:bg-red-950/30 dark:text-red-100']
+			  : ['border-gray-300',
+			     'focus:border-blue-500 focus:outline-none',
+			     'focus:ring-2 focus:ring-blue-200']),
+			 className)}
 	  type="datetime-local"
 	  value={local}
+	  aria-invalid={invalid}
 	  onChange={ev => {
 	    const v = ev.target.value
 	    setLocal (v)
@@ -46,4 +57,4 @@ const DateTimeField: FC<Props> = ({ value, onChange, className, onBlur, ...rest
 	  onBlur={onBlur}/>)
 }
 
-export default DateTimeField
\ No newline at end of file
+export default DateTimeField
diff --git a/frontend/src/components/common/FieldError.tsx b/frontend/src/components/common/FieldError.tsx
new file mode 100644
index 0000000..01d790d
--- /dev/null
+++ b/frontend/src/components/common/FieldError.tsx
@@ -0,0 +1,18 @@
+import type { FC } from 'react'
+
+type Props = { id?:        string
+	       messages?:  string[] }
+
+
+export const FieldError: FC<Props> = ({ id, messages }: Props) => {
+  if (!(messages) || messages.length === 0)
+    return null
+
+  return (
+      <ul id={id} className="mt-1 space-y-1 text-red-700 dark:text-red-300">
+	{messages.map ((message, i) => <li key={i}>{message}</li>)}
+      </ul>)
+}
+
+
+export default FieldError
diff --git a/frontend/src/components/common/FormField.tsx b/frontend/src/components/common/FormField.tsx
new file mode 100644
index 0000000..67b1f65
--- /dev/null
+++ b/frontend/src/components/common/FormField.tsx
@@ -0,0 +1,36 @@
+import { useId } from 'react'
+
+import FieldError from '@/components/common/FieldError'
+import Label from '@/components/common/Label'
+import { cn } from '@/lib/utils'
+
+import type { FC, ReactNode } from 'react'
+
+type FieldState = { describedBy?: string
+		    invalid:      boolean }
+
+type Props = {
+    children:   (state: FieldState) => ReactNode
+    checkBox?:   { label:    string
+		   checked:  boolean
+		   onChange: (event: React.ChangeEvent<HTMLInputElement>) => void }
+    className?:  string
+    label:      ReactNode
+    messages?:  string[] }
+
+
+const FormField: FC<Props> = ({ children, checkBox, className, label, messages }: Props) => {
+  const id = useId ()
+  const invalid = messages != null && messages.length > 0
+  const errorId = invalid ? `${ id }-error` : undefined
+
+  return (
+      <div className={cn (className)}>
+	<Label checkBox={checkBox} invalid={invalid}>{label}</Label>
+	{children ({ describedBy: errorId, invalid })}
+	<FieldError id={errorId} messages={messages}/>
+      </div>)
+}
+
+
+export default FormField
diff --git a/frontend/src/components/common/Label.tsx b/frontend/src/components/common/Label.tsx
index 55a3978..d039115 100644
--- a/frontend/src/components/common/Label.tsx
+++ b/frontend/src/components/common/Label.tsx
@@ -1,32 +1,39 @@
 import React from 'react'
 
+import { cn } from '@/lib/utils'
+
 import type { FC } from 'react'
 
 type Props = { children:  React.ReactNode
-               checkBox?: { label:    string
-                            checked:  boolean
-                            onChange: (event: React.ChangeEvent<HTMLInputElement>) => void } }
+	       checkBox?: { label:    string
+			    checked:  boolean
+			    onChange: (event: React.ChangeEvent<HTMLInputElement>) => void }
+	       invalid?:  boolean }
 
 
-const Label: FC<Props> = ({ children, checkBox }) => {
+const Label: FC<Props> = ({ children, checkBox, invalid }: Props) => {
+  const labelClassName = cn ('block font-semibold mb-1',
+			     invalid && 'text-red-700 dark:text-red-300')
+
   if (!(checkBox))
     {
       return (
-          <label className="block font-semibold mb-1">
-            {children}
-          </label>)
+	  <label className={labelClassName}>
+	    {children}
+	  </label>)
     }
 
   return (
       <div className="flex gap-2 mb-1">
-        <label className="flex-1 block font-semibold">{children}</label>
-        <label className="flex items-center block gap-1">
-          <input type="checkbox"
-                 checked={checkBox.checked}
-                 onChange={checkBox.onChange}/>
-          {checkBox.label}
-        </label>
+	<label className="flex-1 block font-semibold">{children}</label>
+	<label className="flex items-center block gap-1">
+	  <input type="checkbox"
+		 checked={checkBox.checked}
+		 onChange={checkBox.onChange}/>
+	  {checkBox.label}
+	</label>
       </div>)
 }
 
+
 export default Label
diff --git a/frontend/src/components/common/TagInput.tsx b/frontend/src/components/common/TagInput.tsx
index dad1ce8..d0d6491 100644
--- a/frontend/src/components/common/TagInput.tsx
+++ b/frontend/src/components/common/TagInput.tsx
@@ -2,6 +2,7 @@ import { useState } from 'react'
 
 import TagSearchBox from '@/components/TagSearchBox'
 import { apiGet } from '@/lib/api'
+import { inputClass } from '@/lib/utils'
 
 import type { FC, ChangeEvent, KeyboardEvent } from 'react'
 
@@ -9,10 +10,13 @@ import type { Tag } from '@/types'
 
 
 type Props = {
-    value:      string
-    setValue:   (value: string) => void }
+    describedBy?:  string
+    invalid?:      boolean
+    value:         string
+    setValue:      (value: string) => void }
 
-const TagInput: FC<Props> = ({ value, setValue }) => {
+
+const TagInput: FC<Props> = ({ describedBy, invalid, value, setValue }) => {
   const [activeIndex, setActiveIndex] = useState (-1)
   const [suggestions, setSuggestions] = useState<Tag[]> ([])
   const [suggestionsVsbl, setSuggestionsVsbl] = useState (false)
@@ -85,12 +89,14 @@ const TagInput: FC<Props> = ({ value, setValue }) => {
       <div className="relative">
 	<input
 	    type="text"
+	    aria-describedby={describedBy}
+	    aria-invalid={invalid}
 	    value={value}
 	    onChange={whenChanged}
 	    onFocus={() => setSuggestionsVsbl (true)}
 	    onBlur={() => setSuggestionsVsbl (false)}
 	    onKeyDown={handleKeyDown}
-	    className="w-full border p-2 rounded"/>
+	    className={inputClass (invalid)}/>
 	<TagSearchBox
 	    suggestions={
 		suggestionsVsbl && suggestions.length > 0 ? suggestions : [] as Tag[]}
@@ -99,4 +105,4 @@ const TagInput: FC<Props> = ({ value, setValue }) => {
       </div>)
 }
 
-export default TagInput
\ No newline at end of file
+export default TagInput
diff --git a/frontend/src/components/common/TextArea.tsx b/frontend/src/components/common/TextArea.tsx
index 64178da..dbcdb18 100644
--- a/frontend/src/components/common/TextArea.tsx
+++ b/frontend/src/components/common/TextArea.tsx
@@ -1,9 +1,25 @@
 import { forwardRef } from 'react'
 
+import { cn } from '@/lib/utils'
+
 import type { TextareaHTMLAttributes } from 'react'
 
-type Props = TextareaHTMLAttributes<HTMLTextAreaElement>
+type Props = TextareaHTMLAttributes<HTMLTextAreaElement> & { invalid?: boolean }
 
 
-export default forwardRef<HTMLTextAreaElement, Props> (({ ...props }, ref) => (
-    <textarea ref={ref} className="rounded border w-full p-2 h-32" {...props}/>))
+export default forwardRef<HTMLTextAreaElement, Props> (
+    ({ className, invalid = false, ...props }, ref) => (
+	<textarea
+	    ref={ref}
+	    aria-invalid={invalid}
+	    className={cn ('rounded border w-full p-2 h-32',
+			   (invalid
+			    ? ['border-red-500 bg-red-50 text-red-900',
+			       'focus:border-red-500 focus:outline-none focus:ring-2',
+			       'focus:ring-red-200',
+			       'dark:border-red-500 dark:bg-red-950/30 dark:text-red-100']
+			    : ['border-gray-300',
+			       'focus:border-blue-500 focus:outline-none focus:ring-2',
+			       'focus:ring-blue-200']),
+			   className)}
+	    {...props}/>))
diff --git a/frontend/src/lib/api.ts b/frontend/src/lib/api.ts
index 03ba651..a93de11 100644
--- a/frontend/src/lib/api.ts
+++ b/frontend/src/lib/api.ts
@@ -64,11 +64,14 @@ export const apiPatch = async <T> (
 ): Promise<T> => apiP ('patch', path, body, opt)
 
 
-export const apiDelete = async (
+export const apiDelete = async <T = void> (
     path: string,
     opt?: Opt,
-): Promise<void> => {
-  await client.delete (path, withUserCode (opt))
+): Promise<T> => {
+  const res = await client.delete (path, withUserCode (opt))
+  if (res.data == null || res.data === '')
+    return undefined as T
+  return toCamel (res.data as Record<string, unknown>, { deep: true }) as T
 }
 
 
diff --git a/frontend/src/lib/apiErrors.test.ts b/frontend/src/lib/apiErrors.test.ts
new file mode 100644
index 0000000..fbbc67a
--- /dev/null
+++ b/frontend/src/lib/apiErrors.test.ts
@@ -0,0 +1,79 @@
+import { describe, expect, it, vi } from 'vitest'
+
+const api = vi.hoisted (() => ({
+  isApiError: vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+
+describe ('extractValidationError', () => {
+  it ('extracts field and base errors from 422 validation responses', async () => {
+    api.isApiError.mockReturnValueOnce (true)
+
+    const { extractValidationError } = await import ('@/lib/apiErrors')
+    const validationError = extractValidationError<'name'> ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      { name: ['名前は必須です．'] },
+          base_errors: ['全体エラー'],
+        },
+      },
+    })
+
+    expect (validationError).toEqual ({
+      message:     '入力内容を確認してください．',
+      fieldErrors: { name: ['名前は必須です．'] },
+      baseErrors:  ['全体エラー'],
+    })
+  })
+
+  it ('preserves dotted field keys for indexed form rows', async () => {
+    api.isApiError.mockReturnValueOnce (true)
+
+    const { extractValidationError } = await import ('@/lib/apiErrors')
+    const validationError = extractValidationError<'deerjikists.0.platform'> ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          errors:      { 'deerjikists.0.platform': ['プラットフォームを入力してください．'] },
+          base_errors: [],
+        },
+      },
+    })
+
+    expect (validationError?.fieldErrors).toEqual ({
+      'deerjikists0Platform': ['プラットフォームを入力してください．'],
+    })
+  })
+
+  it ('does not treat 400 bad requests as form validation errors', async () => {
+    api.isApiError.mockReturnValueOnce (true)
+
+    const { extractValidationError } = await import ('@/lib/apiErrors')
+    const validationError = extractValidationError ({
+      response: {
+        status: 400,
+        data:   {
+          type:        'bad_request',
+          message:     'リクエストが不正です．',
+          errors:      {},
+          base_errors: ['リクエストが不正です．'],
+        },
+      },
+    })
+
+    expect (validationError).toBeNull ()
+  })
+
+  it ('ignores non-api errors', async () => {
+    api.isApiError.mockReturnValueOnce (false)
+
+    const { extractValidationError } = await import ('@/lib/apiErrors')
+
+    expect (extractValidationError (new Error ('network'))).toBeNull ()
+  })
+})
diff --git a/frontend/src/lib/apiErrors.ts b/frontend/src/lib/apiErrors.ts
new file mode 100644
index 0000000..9a1181f
--- /dev/null
+++ b/frontend/src/lib/apiErrors.ts
@@ -0,0 +1,36 @@
+import toCamel from 'camelcase-keys'
+
+import { isApiError } from '@/lib/api'
+
+export type FieldErrors<T extends string = string> = Partial<Record<T, string[]>>
+
+export type ValidationError<T extends string = string> =
+    { message:      string
+      fieldErrors:  FieldErrors<T>
+      baseErrors:   string[] }
+
+type RawValidationError = { type?:        string
+			    message?:     string
+			    errors?:      Record<string, string[]>
+			    baseErrors?:  string[] }
+
+
+export const extractValidationError = <T extends string = string> (err: unknown) => {
+  if (!(isApiError (err)) || err.response?.status !== 422)
+    return null
+
+  const rawData = toCamel ((err.response.data ?? { }) as Record<string, unknown>,
+			   { deep: true }) as RawValidationError
+  const data: RawValidationError = {
+      type:       rawData.type as string | undefined,
+      message:    rawData.message as string | undefined,
+      errors:     rawData.errors as Record<string, string[]> | undefined,
+      baseErrors: rawData.baseErrors as string[] | undefined }
+
+  if (data.type !== 'validation_error' && !(data.errors))
+    return null
+
+  return { message: data.message ?? '入力内容を確認してください．',
+	   fieldErrors: (data.errors ?? { }) as FieldErrors<T>,
+	   baseErrors: data.baseErrors ?? [] }
+}
diff --git a/frontend/src/lib/gekanator.test.ts b/frontend/src/lib/gekanator.test.ts
new file mode 100644
index 0000000..bf8947f
--- /dev/null
+++ b/frontend/src/lib/gekanator.test.ts
@@ -0,0 +1,523 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { apiGet, apiPost } from '@/lib/api'
+import {
+  buildGekanatorQuestions,
+  expectedAnswerForQuestion,
+  fetchGekanatorPosts,
+  fetchGekanatorQuestions,
+  learnedSemanticSideForPost,
+  questionIdForCondition,
+  restoreGekanatorQuestion,
+  saveGekanatorExtraQuestionAnswers,
+  saveGekanatorGame,
+  saveGekanatorQuestionSuggestion,
+} from '@/lib/gekanator'
+
+import type {
+  GekanatorAnswerLog,
+  StoredGekanatorQuestion,
+} from '@/lib/gekanator'
+import type { Post } from '@/types'
+
+vi.mock('@/lib/api', () => ({
+  apiGet: vi.fn(),
+  apiPost: vi.fn(),
+}))
+
+const mockedApiPost = vi.mocked(apiPost)
+const mockedApiGet = vi.mocked(apiGet)
+
+const post = (overrides: Partial<Post> = {}): Post => ({
+  id: 1,
+  versionNo: 1,
+  url: 'https://example.com/posts/1',
+  title: 'post title',
+  thumbnail: null,
+  thumbnailBase: null,
+  tags: [],
+  viewed: false,
+  related: [],
+  originalCreatedFrom: null,
+  originalCreatedBefore: null,
+  createdAt: '2026-06-10T00:00:00.000Z',
+  updatedAt: '2026-06-10T00:00:00.000Z',
+  uploadedUser: null,
+  ...overrides,
+})
+
+describe('Gekanator API functions', () => {
+  it('returns posts from the Gekanator posts endpoint', async () => {
+    const posts = [post()]
+    mockedApiGet.mockResolvedValueOnce({ posts })
+
+    await expect(fetchGekanatorPosts()).resolves.toEqual(posts)
+    expect(mockedApiGet).toHaveBeenCalledWith('/gekanator/posts')
+  })
+
+  it('returns questions from the Gekanator questions endpoint', async () => {
+    const questions: StoredGekanatorQuestion[] = []
+    mockedApiGet.mockResolvedValueOnce({ questions })
+
+    await expect(fetchGekanatorQuestions()).resolves.toEqual(questions)
+    expect(mockedApiGet).toHaveBeenCalledWith('/gekanator/questions')
+  })
+})
+
+describe('expectedAnswerForQuestion', () => {
+  it('returns a direct example answer when present', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'partial',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 1 }))).toBe('partial')
+  })
+
+  it('returns the condition answer for the original post_similarity post', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 123,
+        answer: 'probably_no',
+        threshold: 0.65,
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 123 }))).toBe('probably_no')
+  })
+
+  it('returns null for an unrelated post_similarity post without examples', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 123,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 456 }))).toBeNull()
+  })
+
+  it('returns yes for a matching tag question', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    }
+
+    expect(
+      expectedAnswerForQuestion(
+        question,
+        post({
+          tags: [
+            {
+              id: 1,
+              name: '喜多郁代',
+              category: 'character',
+              aliases: [],
+              parents: [],
+              postCount: 1,
+              createdAt: '2026-06-10T00:00:00.000Z',
+              updatedAt: '2026-06-10T00:00:00.000Z',
+              deprecatedAt: null,
+              hasWiki: false,
+              hasDeerjikists: false,
+              materialId: null,
+            },
+          ],
+        }),
+      ),
+    ).toBe('yes')
+  })
+
+  it('returns no for a non-matching tag question', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ tags: [] }))).toBe('no')
+  })
+
+  it('ignores example answers for direct title facts', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'title:length-at-least:20',
+      text: 'タイトルは 20 文字以上?',
+      kind: 'title',
+      condition: {
+        type: 'title-length-at-least',
+        length: 20,
+      },
+      exampleAnswers: {
+        1: 'yes',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(question, post({ id: 1, title: 'short' }))).toBe('no')
+  })
+
+  it('returns yes for matching title-contains questions', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'title:contains:結束バンド',
+      text: '題名に「結束バンド」が含まれる?',
+      kind: 'title',
+      condition: {
+        type: 'title-contains',
+        text: '結束バンド',
+      },
+    }
+
+    expect(expectedAnswerForQuestion(
+      question,
+      post({ title: '結束バンドのライブ' }),
+    )).toBe('yes')
+    expect(expectedAnswerForQuestion(
+      question,
+      post({ title: '後藤ひとりの休日' }),
+    )).toBe('no')
+  })
+})
+
+describe('learnedSemanticSideForPost', () => {
+  it('classifies post_similarity examples as positive, negative, or unknown', () => {
+    const question: StoredGekanatorQuestion = {
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 123,
+        answer: 'partial',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'yes',
+        2: 'probably_no',
+      },
+    }
+
+    expect(learnedSemanticSideForPost(question, post({ id: 1 }))).toBe('positive')
+    expect(learnedSemanticSideForPost(question, post({ id: 2 }))).toBe('negative')
+    expect(learnedSemanticSideForPost(question, post({ id: 3 }))).toBe('unknown')
+    expect(learnedSemanticSideForPost(question, post({ id: 123 }))).toBe('positive')
+  })
+})
+
+describe('restoreGekanatorQuestion', () => {
+  it('uses default source and priority weight when omitted', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'tag:character:喜多郁代',
+      text: '喜多ちゃんが関係してる?',
+      kind: 'tag',
+      condition: {
+        type: 'tag',
+        key: 'character:喜多郁代',
+      },
+    })
+
+    expect(question.source).toBe('default')
+    expect(question.priorityWeight).toBe(1)
+  })
+
+  it('tests a post_similarity question using direct examples', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'yes',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'yes',
+        2: 'no',
+      },
+    })
+
+    expect(question.test(post({ id: 1 }))).toBe(true)
+    expect(question.test(post({ id: 2 }))).toBe(false)
+    expect(question.test(post({ id: 3 }))).toBe(false)
+  })
+
+  it('tests a post_similarity question against its configured partial answer', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'post-similarity:10',
+      text: '喜多ちゃんが泣いてる?',
+      kind: 'post_similarity',
+      source: 'user_suggested',
+      priorityWeight: 1.2,
+      condition: {
+        type: 'post-similarity',
+        postId: 999,
+        answer: 'partial',
+        threshold: 0.65,
+      },
+      exampleAnswers: {
+        1: 'partial',
+        2: 'yes',
+      },
+    })
+
+    expect(question.test(post({ id: 1 }))).toBe(true)
+    expect(question.test(post({ id: 2 }))).toBe(true)
+  })
+
+  it('normalizes legacy title-length-greater-than questions', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'title:length-greater-than:20',
+      text: '題名が長めの投稿?',
+      kind: 'title',
+      condition: {
+        type: 'title-length-greater-than',
+        length: 20,
+      },
+    })
+
+    expect(question.id).toBe('title:length-at-least:21')
+    expect(question.condition).toEqual({
+      type: 'title-length-at-least',
+      length: 21,
+    })
+    expect(question.test(post({ title: 'x'.repeat(20) }))).toBe(false)
+    expect(question.test(post({ title: 'x'.repeat(21) }))).toBe(true)
+  })
+
+  it('restores title-contains questions with a title matcher', () => {
+    const question = restoreGekanatorQuestion({
+      id: 'title:contains:結束バンド',
+      text: '題名に「結束バンド」が含まれる?',
+      kind: 'title',
+      condition: {
+        type: 'title-contains',
+        text: '結束バンド',
+      },
+    })
+
+    expect(question.test(post({ title: '結束バンドのライブ' }))).toBe(true)
+    expect(question.test(post({ title: '後藤ひとりの休日' }))).toBe(false)
+  })
+})
+
+describe('buildGekanatorQuestions', () => {
+  it('builds quantitative title length questions', () => {
+    const questions = buildGekanatorQuestions([
+      post({ id: 1, title: 'a' }),
+      post({ id: 2, title: 'bb' }),
+      post({ id: 3, title: 'ccc' }),
+      post({ id: 4, title: 'dddd' }),
+    ])
+    const titleQuestion = questions.find(question =>
+      question.condition.type === 'title-length-at-least')
+
+    expect(titleQuestion?.text).toMatch(/^タイトルは \d+ 文字以上\?$/)
+    expect(titleQuestion?.id).toMatch(/^title:length-at-least:\d+$/)
+  })
+
+  it('builds title-contains questions from repeated title words', () => {
+    const questions = buildGekanatorQuestions([
+      post({ id: 1, title: '結束バンド ライブ' }),
+      post({ id: 2, title: '結束バンド 新曲' }),
+      post({ id: 3, title: '後藤ひとり 練習' }),
+      post({ id: 4, title: '伊地知虹夏 練習' }),
+    ])
+
+    const titleContainsQuestion = questions.find(question =>
+      question.condition.type === 'title-contains'
+      && question.condition.text === '結束バンド')
+
+    expect(titleContainsQuestion).toMatchObject({
+      id: 'title:contains:結束バンド',
+      text: '題名に「結束バンド」が含まれる?',
+      kind: 'title',
+      source: 'default',
+      priorityWeight: .96,
+    })
+    expect(titleContainsQuestion?.test(post({ title: '結束バンドのライブ' }))).toBe(true)
+    expect(titleContainsQuestion?.test(post({ title: '廣井きくりのライブ' }))).toBe(false)
+  })
+
+  it('honors question caps and title-contains toggles', () => {
+    const posts = [
+      post({ id: 1, title: '結束バンド ライブ' }),
+      post({ id: 2, title: '結束バンド 新曲' }),
+      post({ id: 3, title: '後藤ひとり 練習' }),
+      post({ id: 4, title: '伊地知虹夏 練習' }),
+    ]
+
+    const capped = buildGekanatorQuestions(posts, {
+      titleContainsCap: 1,
+      totalQuestionCap: 1,
+    })
+    const withoutTitleContains = buildGekanatorQuestions(posts, {
+      includeTitleContains: false,
+    })
+
+    expect(capped).toHaveLength(1)
+    expect(withoutTitleContains.some(question =>
+      question.condition.type === 'title-contains')).toBe(false)
+  })
+})
+
+describe('questionIdForCondition', () => {
+  it('builds stable ids for title-contains questions', () => {
+    expect(questionIdForCondition({
+      type: 'title-contains',
+      text: '結束バンド',
+    })).toBe('title:contains:結束バンド')
+  })
+})
+
+describe('Gekanator API writers', () => {
+  beforeEach(() => {
+    mockedApiPost.mockReset()
+  })
+
+  it('sends game results using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({ id: 100 })
+
+    const answers: GekanatorAnswerLog[] = [
+      {
+        questionId: 'tag:character:喜多郁代',
+        questionText: '喜多ちゃんが関係してる?',
+        questionCondition: {
+          type: 'tag',
+          key: 'character:喜多郁代',
+        },
+        questionMode: 'normal',
+        questionPurpose: 'effective_user_suggested',
+        effectiveQuestion: true,
+        learningQuestion: false,
+        answer: 'yes',
+        originalAnswer: 'partial',
+      },
+    ]
+
+    await expect(
+      saveGekanatorGame({
+        guessedPostId: 1,
+        correctPostId: 2,
+        answers,
+      }),
+    ).resolves.toEqual({ id: 100 })
+
+    expect(mockedApiPost).toHaveBeenCalledWith('/gekanator/games', {
+      guessed_post_id: 1,
+      correct_post_id: 2,
+      answers: [
+        {
+          question_id: 'tag:character:喜多郁代',
+          question_text: '喜多ちゃんが関係してる?',
+          question_condition: {
+            type: 'tag',
+            key: 'character:喜多郁代',
+          },
+          question_mode: 'normal',
+          question_purpose: 'effective_user_suggested',
+          effective_question: true,
+          learning_question: false,
+          answer: 'yes',
+          original_answer: 'partial',
+        },
+      ],
+    })
+  })
+
+  it('sends question suggestions using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({
+      id: 10,
+      count: 1,
+    })
+
+    await expect(
+      saveGekanatorQuestionSuggestion({
+        gekanatorGameId: 100,
+        questionText: '喜多ちゃんが泣いてる?',
+        answer: 'yes',
+      }),
+    ).resolves.toEqual({
+      id: 10,
+      count: 1,
+    })
+
+    expect(mockedApiPost).toHaveBeenCalledWith('/gekanator/question_suggestions', {
+      gekanator_game_id: 100,
+      question_text: '喜多ちゃんが泣いてる?',
+      answer: 'yes',
+    })
+  })
+
+  it('sends extra question answers using snake_case request keys', async () => {
+    mockedApiPost.mockResolvedValue({
+      count: 2,
+    })
+
+    await saveGekanatorExtraQuestionAnswers({
+      gameId: 100,
+      answers: [
+        {
+          questionId: 10,
+          answer: 'yes',
+        },
+        {
+          questionId: 11,
+          answer: 'probably_no',
+        },
+      ],
+    })
+
+    expect(mockedApiPost).toHaveBeenCalledWith(
+      '/gekanator/games/100/extra_question_answers',
+      {
+        answers: [
+          {
+            question_id: 10,
+            answer: 'yes',
+          },
+          {
+            question_id: 11,
+            answer: 'probably_no',
+          },
+        ],
+      },
+    )
+  })
+})
diff --git a/frontend/src/lib/gekanator.ts b/frontend/src/lib/gekanator.ts
new file mode 100644
index 0000000..1299b0c
--- /dev/null
+++ b/frontend/src/lib/gekanator.ts
@@ -0,0 +1,675 @@
+import { apiGet, apiPost } from '@/lib/api'
+
+import type { Post } from '@/types'
+
+export type GekanatorAnswerValue =
+    | 'yes'
+    | 'no'
+    | 'partial'
+    | 'probably_no'
+    | 'unknown'
+
+export type LearnedSemanticSide =
+    | 'positive'
+    | 'negative'
+    | 'unknown'
+
+export type GekanatorQuestionPurpose =
+    | 'effective_user_suggested'
+    | 'learning_user_suggested'
+    | 'normal'
+
+export type GekanatorAnswerLog = {
+    questionId:       string
+    questionText:     string
+    questionCondition?:  GekanatorQuestionCondition
+    questionMode?:    'normal' | 'winning_run'
+    questionPurpose?: GekanatorQuestionPurpose
+    effectiveQuestion?: boolean
+    learningQuestion?: boolean
+    answer:           GekanatorAnswerValue
+    originalAnswer:   GekanatorAnswerValue }
+
+export type GekanatorQuestionKind =
+    | 'tag'
+    | 'source'
+    | 'title'
+    | 'original_date'
+    | 'post_similarity'
+
+export type GekanatorQuestionSource =
+    | 'default'
+    | 'user_suggested'
+    | 'ai_generated'
+    | 'admin_curated'
+
+export type GekanatorPerformanceMode = 'normal'
+
+export type GekanatorQuestionCondition =
+    | { type: 'tag'; key: string }
+    | { type: 'source'; host: string }
+    | { type: 'original-year'; year: number }
+    | { type: 'original-month'; month: number }
+    | { type: 'original-month-day'; monthDay: string }
+    | { type: 'title-length-at-least'; length: number }
+    | { type: 'title-length-greater-than'; length: number }
+    | { type: 'title-has-ascii' }
+    | { type: 'title-contains'; text: string }
+    | {
+	  type: 'post-similarity'
+	  postId: number
+	  answer: GekanatorAnswerValue
+	  threshold: number
+      }
+
+
+type NonPostSimilarityCondition = Exclude<
+    GekanatorQuestionCondition,
+    { type: 'post-similarity' }
+>
+
+export type GekanatorExtraQuestion = {
+    id:              number
+    text:            string
+    source:          GekanatorQuestionSource
+    priorityWeight:  number }
+
+export type StoredGekanatorQuestion = {
+    recordId?:       number
+    id:              string
+    text:            string
+    kind:            GekanatorQuestionKind
+    condition:       GekanatorQuestionCondition
+    source?:         GekanatorQuestionSource
+    priorityWeight?: number
+    exampleAnswers?: Record<`${ number }`, GekanatorAnswerValue> }
+
+export type GekanatorQuestion = {
+    recordId?:       number
+    id:              string
+    text:            string
+    kind:            GekanatorQuestionKind
+    condition:       GekanatorQuestionCondition
+    source:          GekanatorQuestionSource
+    priorityWeight:  number
+    exampleAnswers?: Record<`${ number }`, GekanatorAnswerValue>
+    test:            (post: Post) => boolean }
+
+export type BuildGekanatorQuestionsOptions = {
+    includeTitleContains?: boolean
+    tagQuestionCap?: number
+    titleContainsCap?: number
+    totalQuestionCap?: number
+}
+
+
+export const normalizeTitleLengthCondition = (
+    condition:  GekanatorQuestionCondition,
+): GekanatorQuestionCondition => {
+  switch (condition.type)
+  {
+  case 'title-length-greater-than':
+    return {
+	type:   'title-length-at-least',
+	length: condition.length + 1 }
+  default:
+    return condition
+  }
+}
+
+
+export const titleLengthMinimumForCondition = (
+    condition:  GekanatorQuestionCondition,
+): number | null => {
+  switch (condition.type)
+  {
+  case 'title-length-at-least':
+    return condition.length
+  case 'title-length-greater-than':
+    return condition.length + 1
+  default:
+    return null
+  }
+}
+
+
+export const questionIdForCondition = (
+    condition:  NonPostSimilarityCondition,
+): string => {
+  switch (condition.type)
+  {
+  case 'tag':
+    return `tag:${ condition.key }`
+  case 'source':
+    return `source:${ condition.host }`
+  case 'original-year':
+    return `original-year:${ condition.year }`
+  case 'original-month':
+    return `original-month:${ condition.month }`
+  case 'original-month-day':
+    return `original-month-day:${ condition.monthDay }`
+  case 'title-length-at-least':
+  case 'title-length-greater-than':
+    return `title:length-at-least:${ titleLengthMinimumForCondition (condition) }`
+  case 'title-has-ascii':
+    return 'title:ascii'
+  case 'title-contains':
+    return `title:contains:${ condition.text }`
+  }
+}
+
+
+const directExampleAnswerFor = (
+    question:  StoredGekanatorQuestion,
+    post:      Post,
+): GekanatorAnswerValue | null => {
+  if (question.kind !== 'post_similarity' && question.kind !== 'tag')
+    return null
+
+  const direct = question.exampleAnswers?.[String (post.id) as `${ number }`]
+  if (direct)
+    return direct
+
+  if (question.condition.type === 'post-similarity' && question.condition.postId === post.id)
+    return question.condition.answer
+
+  return null
+}
+
+
+export const isLearnedSemanticQuestion = (
+    question:  StoredGekanatorQuestion | GekanatorQuestion,
+): boolean =>
+    question.kind === 'post_similarity'
+    && question.source === 'user_suggested'
+
+
+export const learnedSemanticSideForAnswer = (
+    answer:  GekanatorAnswerValue | null,
+): LearnedSemanticSide => {
+  if (answer === 'yes' || answer === 'partial')
+    return 'positive'
+
+  if (answer === 'no' || answer === 'probably_no')
+    return 'negative'
+
+  return 'unknown'
+}
+
+const countBy = <T extends string | number> (values: T[]): Map<T, number> => {
+  const counts = new Map<T, number> ()
+  values.forEach (value => counts.set (value, (counts.get (value) ?? 0) + 1))
+  return counts
+}
+
+
+const median = (values: number[]): number => {
+  const sorted = [...values].sort ((a, b) => a - b)
+  return sorted[Math.floor (sorted.length / 2)] ?? 0
+}
+
+
+const hostOf = (post: Post): string | null => {
+  try
+  {
+    return new URL (post.url).hostname.replace (/^www\./, '')
+  }
+  catch
+  {
+    return null
+  }
+}
+
+
+const originalYearOf = (post: Post): number | null => {
+  const value = post.originalCreatedFrom || post.originalCreatedBefore
+  if (!(value))
+    return null
+
+  const date = new Date (value)
+  if (Number.isNaN (date.getTime ()))
+    return null
+
+  return date.getFullYear ()
+}
+
+
+const originalDateOf = (post: Post): Date | null => {
+  const value = post.originalCreatedFrom || post.originalCreatedBefore
+  if (!(value))
+    return null
+
+  const date = new Date (value)
+  if (Number.isNaN (date.getTime ()))
+    return null
+
+  return date
+}
+
+
+const originalMonthOf = (post: Post): number | null => {
+  const date = originalDateOf (post)
+  if (!(date))
+    return null
+
+  return date.getMonth () + 1
+}
+
+
+const originalMonthDayOf = (post: Post): string | null => {
+  const date = originalDateOf (post)
+  if (!(date))
+    return null
+
+  return `${ date.getMonth () + 1 }-${ date.getDate () }`
+}
+
+
+const tagQuestionKey = ({ category, name }: { category: string; name: string }): string =>
+    `${ category }:${ name }`
+
+
+const tagFromQuestionKey = (key: string): { category: string; name: string } => {
+  const [category, ...rest] = key.split (':')
+  return { category: category ?? '', name: rest.join (':') }
+}
+
+
+const nicoTagLabel = (name: string): string => name.replace (/^nico:/, '')
+
+
+const tagQuestionText = (category: string, label: string): string => {
+  switch (category)
+  {
+  case 'deerjikist':
+    return `作者・ニジラーとして「${ label }」に関係してゐる?`
+  case 'meme':
+    return `元ネタ・ミームとして「${ label }」に関係しさう?`
+  case 'character':
+    return `「${ label }」といふキャラクターが関係してゐる?`
+  case 'material':
+    return `素材として「${ label }」に関係してゐる?`
+  case 'nico':
+    return `ニコニコに「${ label }」といふタグが付いてゐる?`
+  case 'general':
+  case 'meta':
+  default:
+    return `内容として「${ label }」に関係しさう?`
+  }
+}
+
+
+const questionableTag = (post: Post, key: string): boolean => {
+  const { category, name } = tagFromQuestionKey (key)
+
+  return (
+    post.tags.some (tag =>
+	tag.name === name
+	&& tag.category === category
+	&& !(tag.category === 'meta')
+	&& !(tag.name.includes ('タグ希望'))
+	&& !(tag.name.includes ('bot操作'))))
+}
+
+
+const questionMatches = (
+    post:       Post,
+    question:   StoredGekanatorQuestion,
+): boolean => {
+  const directAnswer = directExampleAnswerFor (question, post)
+  if (directAnswer)
+    return question.kind === 'post_similarity'
+	? learnedSemanticSideForAnswer (directAnswer) === 'positive'
+	: directAnswer === 'yes'
+
+  switch (question.condition.type)
+  {
+  case 'tag':
+    return questionableTag (post, question.condition.key)
+  case 'source':
+    return hostOf (post) === question.condition.host
+  case 'original-year':
+    return originalYearOf (post) === question.condition.year
+  case 'original-month':
+    return originalMonthOf (post) === question.condition.month
+  case 'original-month-day':
+    return originalMonthDayOf (post) === question.condition.monthDay
+  case 'title-length-at-least':
+    return (post.title?.length ?? 0) >= question.condition.length
+  case 'title-length-greater-than':
+    return (post.title?.length ?? 0) > question.condition.length
+  case 'title-has-ascii':
+    return /[A-Za-z0-9]/.test (post.title ?? '')
+  case 'title-contains':
+    return (post.title ?? '').includes (question.condition.text)
+  case 'post-similarity':
+    return false
+  }
+}
+
+
+export const expectedAnswerForQuestion = (
+    question:  StoredGekanatorQuestion | GekanatorQuestion | undefined,
+    post:      Post | null,
+): GekanatorAnswerValue | null => {
+  if (!(question) || !(post))
+    return null
+
+  const directAnswer = directExampleAnswerFor (question, post)
+  if (directAnswer)
+    return directAnswer
+
+  switch (question.condition.type)
+  {
+  case 'post-similarity':
+    if (question.condition.postId === post.id)
+      return question.condition.answer
+
+    return null
+  case 'tag':
+  case 'source':
+  case 'original-year':
+  case 'original-month':
+  case 'original-month-day':
+  case 'title-length-at-least':
+  case 'title-length-greater-than':
+  case 'title-has-ascii':
+  case 'title-contains':
+    return questionMatches (post, question) ? 'yes' : 'no'
+  }
+}
+
+
+export const learnedSemanticSideForPost = (
+    question:  StoredGekanatorQuestion | GekanatorQuestion | undefined,
+    post:      Post | null,
+): LearnedSemanticSide =>
+    learnedSemanticSideForAnswer (expectedAnswerForQuestion (question, post))
+
+
+export const restoreGekanatorQuestion = (
+    question:  StoredGekanatorQuestion,
+): GekanatorQuestion => {
+  const normalizedCondition = normalizeTitleLengthCondition (question.condition)
+  const normalizedQuestion = {
+      ...question,
+      recordId: question.recordId,
+      id: normalizedCondition.type === 'title-length-at-least'
+	  ? `title:length-at-least:${ normalizedCondition.length }`
+	  : question.id,
+      condition: normalizedCondition,
+      source: question.source ?? 'default',
+      priorityWeight: question.priorityWeight ?? 1 }
+
+  return {
+      ...normalizedQuestion,
+      test: (post: Post) => questionMatches (post, normalizedQuestion) }
+}
+
+
+export const storeGekanatorQuestion = (
+    question:  GekanatorQuestion,
+): StoredGekanatorQuestion => ({
+  id: question.condition.type === 'title-length-greater-than'
+      ? `title:length-at-least:${ question.condition.length + 1 }`
+      : question.id,
+  recordId: question.recordId,
+  text: question.text,
+  kind: question.kind,
+  condition: normalizeTitleLengthCondition (question.condition),
+  source: question.source,
+  priorityWeight: question.priorityWeight,
+  exampleAnswers: question.exampleAnswers })
+
+
+export const fetchGekanatorPosts = async (): Promise<Post[]> => {
+  const data = await apiGet<{ posts: Post[] }> ('/gekanator/posts')
+  return data.posts
+}
+
+
+export const fetchGekanatorQuestions = async (): Promise<StoredGekanatorQuestion[]> => {
+  const data = await apiGet<{ questions: StoredGekanatorQuestion[] }> ('/gekanator/questions')
+  return data.questions
+}
+
+
+export const fetchGekanatorExtraQuestions = async (
+    gameId:  number,
+    nonce?: string,
+): Promise<GekanatorExtraQuestion[]> => {
+  const data = await apiGet<{ questions: GekanatorExtraQuestion[] }> (
+      `/gekanator/games/${ gameId }/extra_questions`,
+      { params: nonce ? { nonce } : undefined })
+  return data.questions
+}
+
+
+export const buildGekanatorQuestions = (
+    posts:    Post[],
+    options:  BuildGekanatorQuestionsOptions = { },
+): GekanatorQuestion[] => {
+  const {
+      includeTitleContains = true,
+      tagQuestionCap = 192,
+      titleContainsCap = 24,
+      totalQuestionCap = Number.POSITIVE_INFINITY,
+  } = options
+  const tagCounts = countBy (posts.flatMap (post =>
+      post.tags
+      .filter (tag =>
+	  !(tag.category === 'meta')
+	  && !(tag.name.includes ('タグ希望'))
+	  && !(tag.name.includes ('bot操作')))
+      .map (tag => tagQuestionKey (tag))))
+  const hosts = countBy (posts.map (hostOf).filter ((host): host is string => Boolean (host)))
+  const originalYears = countBy (
+      posts
+      .map (originalYearOf)
+      .filter ((year): year is number => year != null))
+  const originalMonths = countBy (
+      posts
+      .map (originalMonthOf)
+      .filter ((month): month is number => month != null))
+  const originalMonthDays = countBy (
+      posts
+      .map (originalMonthDayOf)
+      .filter ((monthDay): monthDay is string => monthDay != null))
+  const titleLengthMedian = median (posts.map (post => post.title?.length ?? 0))
+  const titleWordCounts =
+      includeTitleContains
+	? countBy (
+	    posts.flatMap (post =>
+		Array.from (
+		    new Set (
+			(post.title ?? '')
+			.match (
+			    /[\p{Script=Han}\p{Script=Hiragana}\p{Script=Katakana}A-Za-z0-9]{2,}/gu)
+			?? []))))
+	: new Map<string, number> ()
+
+  const usefulEntries = <T extends string | number> (
+      counts:  Map<T, number>,
+      cap:     number,
+  ) =>
+      [...counts.entries ()]
+      .filter (([, count]) => count > 0 && count < posts.length)
+      .sort ((a, b) => Math.abs (posts.length / 2 - a[1])
+	       - Math.abs (posts.length / 2 - b[1]))
+      .slice (0, cap)
+
+  const tagQuestions = usefulEntries (tagCounts, Math.max (tagQuestionCap, 80))
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, tagQuestionCap)
+      .map (([key]) => {
+	const { category, name } = tagFromQuestionKey (String (key))
+	const label = category === 'nico' ? nicoTagLabel (name) : name
+
+	return {
+	    id:   `tag:${ key }`,
+	    text: tagQuestionText (category, label),
+	    kind: 'tag' as const,
+	    condition: { type: 'tag' as const, key: String (key) },
+	    source: 'default' as const,
+	    priorityWeight: 1,
+	    test: (post: Post) => questionableTag (post, String (key)) }
+      })
+
+  const sourceQuestions = usefulEntries (hosts, 20)
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, 20)
+      .map (([host]) => ({
+	  id:   `source:${ host }`,
+	  text: `${ host } の投稿を思ひ浮かべてゐる?`,
+	  kind: 'source' as const,
+	  condition: { type: 'source' as const, host },
+	  source: 'default' as const,
+	  priorityWeight: 1,
+	  test: (post: Post) => hostOf (post) === host }))
+
+  const originalYearQuestions = usefulEntries (originalYears, 20)
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, 20)
+      .map (([year]) => ({
+	  id:   `original-year:${ year }`,
+	  text: `オリジナルの投稿年は ${ year } 年?`,
+	  kind: 'original_date' as const,
+	  condition: { type: 'original-year' as const, year },
+	  source: 'default' as const,
+	  priorityWeight: 1,
+	  test: (post: Post) => originalYearOf (post) === year }))
+
+  const originalMonthQuestions = usefulEntries (originalMonths, 20)
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, 20)
+      .map (([month]) => ({
+	  id:   `original-month:${ month }`,
+	  text: `オリジナルの投稿月は ${ month } 月?`,
+	  kind: 'original_date' as const,
+	  condition: { type: 'original-month' as const, month },
+	  source: 'default' as const,
+	  priorityWeight: 1,
+	  test: (post: Post) => originalMonthOf (post) === month }))
+
+  const originalMonthDayQuestions = usefulEntries (originalMonthDays, 20)
+      .filter (([, count]) => count >= 2 && count <= Math.max (2, posts.length * .7))
+      .slice (0, 20)
+      .map (([monthDay]) => {
+	const [month, day] = String (monthDay).split ('-')
+
+	return {
+	    id:   `original-month-day:${ monthDay }`,
+	    text: `オリジナルの投稿日は ${ month } 月 ${ day } 日?`,
+	    kind: 'original_date' as const,
+	    condition: { type: 'original-month-day' as const, monthDay: String (monthDay) },
+	    source: 'default' as const,
+	    priorityWeight: 1,
+	    test: (post: Post) => originalMonthDayOf (post) === monthDay }
+      })
+
+  const titleQuestions = [
+      {
+	  id:   `title:length-at-least:${ titleLengthMedian }`,
+	  text: `タイトルは ${ titleLengthMedian } 文字以上?`,
+	  kind: 'title' as const,
+	  condition: {
+	      type: 'title-length-at-least' as const,
+	      length: titleLengthMedian },
+	  source: 'default' as const,
+	  priorityWeight: 1,
+	  test: (post: Post) => (post.title?.length ?? 0) >= titleLengthMedian },
+      {
+	  id:   'title:ascii',
+	  text: '題名に英数字が混じってゐる?',
+	  kind: 'title' as const,
+	  condition: { type: 'title-has-ascii' as const },
+	  source: 'default' as const,
+	  priorityWeight: 1,
+	  test: (post: Post) => /[A-Za-z0-9]/.test (post.title ?? '') }]
+      .filter (question => {
+	const yes = posts.filter (post => question.test (post)).length
+	const no = posts.length - yes
+	return yes >= 2 && no >= 2 && yes <= posts.length * .7 && no <= posts.length * .7
+      })
+  const titleContainsQuestions =
+      includeTitleContains
+	? usefulEntries (titleWordCounts, titleContainsCap)
+	    .filter (([word, count]) =>
+		String (word).length <= 24
+		&& count >= 2
+		&& count <= Math.max (2, posts.length * .7))
+	    .slice (0, titleContainsCap)
+	    .map (([word]) => ({
+		id:   `title:contains:${ word }`,
+		text: `題名に「${ word }」が含まれる?`,
+		kind: 'title' as const,
+		condition: { type: 'title-contains' as const, text: String (word) },
+		source: 'default' as const,
+		priorityWeight: .96,
+		test: (post: Post) => (post.title ?? '').includes (String (word)) }))
+	: []
+
+  return [
+      ...sourceQuestions,
+      ...originalYearQuestions,
+      ...originalMonthQuestions,
+      ...originalMonthDayQuestions,
+      ...titleQuestions,
+      ...titleContainsQuestions,
+      ...tagQuestions].slice (0, totalQuestionCap)
+}
+
+
+export const saveGekanatorGame = async ({
+    guessedPostId,
+    correctPostId,
+    answers,
+}: {
+    guessedPostId:  number
+    correctPostId:  number
+    answers:        GekanatorAnswerLog[]
+}): Promise<{ id: number; learnedExampleCount: number }> =>
+    await apiPost ('/gekanator/games', {
+	guessed_post_id: guessedPostId,
+	correct_post_id: correctPostId,
+	answers: answers.map (answer => ({
+	    question_id: answer.questionId,
+	    question_text: answer.questionText,
+	    question_condition: answer.questionCondition ?? null,
+	    question_mode: answer.questionMode,
+	    question_purpose: answer.questionPurpose,
+	    effective_question: answer.effectiveQuestion,
+	    learning_question: answer.learningQuestion,
+	    answer: answer.answer,
+	    original_answer: answer.originalAnswer })) })
+
+
+export const saveGekanatorQuestionSuggestion = async ({
+    gekanatorGameId,
+    existingQuestionId,
+    questionText,
+    answer,
+}: {
+    gekanatorGameId:  number
+    existingQuestionId?: number
+    questionText?:    string
+    answer:           GekanatorAnswerValue
+}): Promise<{ id: number; count: number }> =>
+    await apiPost ('/gekanator/question_suggestions', {
+	gekanator_game_id: gekanatorGameId,
+	existing_question_id: existingQuestionId,
+	question_text: questionText,
+	answer })
+
+
+export const saveGekanatorExtraQuestionAnswers = async ({
+    gameId,
+    answers,
+}: {
+    gameId:   number
+    answers:  { questionId: number; answer: GekanatorAnswerValue }[]
+}) =>
+    await apiPost (`/gekanator/games/${ gameId }/extra_question_answers`, {
+	answers: answers.map (item => ({
+	    question_id: item.questionId,
+	    answer: item.answer })) })
diff --git a/frontend/src/lib/gekanatorCandidateRecovery.test.ts b/frontend/src/lib/gekanatorCandidateRecovery.test.ts
new file mode 100644
index 0000000..ffad81a
--- /dev/null
+++ b/frontend/src/lib/gekanatorCandidateRecovery.test.ts
@@ -0,0 +1,259 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+    candidatePostsFor,
+    hardFilteredPostsForAnswer,
+    recoverCandidatePosts,
+} from '@/lib/gekanatorCandidateRecovery'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+} from '@/lib/gekanator'
+import type { RecoveredCandidateState } from '@/lib/gekanatorCandidateRecovery'
+import type { Post } from '@/types'
+
+
+const post = (id: number): Post => ({
+  id,
+  versionNo: 1,
+  url: `https://example.com/posts/${ id }`,
+  title: `post ${ id }`,
+  thumbnail: null,
+  thumbnailBase: null,
+  tags: [],
+  viewed: false,
+  related: [],
+  originalCreatedFrom: null,
+  originalCreatedBefore: null,
+  createdAt: '2026-06-10T00:00:00.000Z',
+  updatedAt: '2026-06-10T00:00:00.000Z',
+  uploadedUser: null,
+})
+
+
+const postSimilarityQuestion = (
+    id:       string,
+    answers:  Record<`${ number }`, GekanatorAnswerValue>,
+): GekanatorQuestion => ({
+  id,
+  text: `${ id }?`,
+  kind: 'post_similarity',
+  condition: {
+      type: 'post-similarity',
+      postId: 9999,
+      answer: 'yes',
+      threshold: 0.65 },
+  source: 'user_suggested',
+  priorityWeight: 1,
+  exampleAnswers: answers,
+  test: candidate => answers[String (candidate.id) as `${ number }`] === 'yes',
+})
+
+
+const sourceQuestion = (
+    host:  string,
+): GekanatorQuestion => ({
+  id: `source:${ host }`,
+  text: `${ host }?`,
+  kind: 'source',
+  condition: {
+      type: 'source',
+      host },
+  source: 'default',
+  priorityWeight: 1,
+  test: candidate => new URL (candidate.url).hostname === host,
+})
+
+
+const answer = (
+    question:  GekanatorQuestion,
+    value:     GekanatorAnswerValue,
+): GekanatorAnswerLog => ({
+  questionId: question.id,
+  questionText: question.text,
+  questionCondition: question.condition,
+  answer: value,
+  originalAnswer: value,
+})
+
+
+const recoveredState = (
+    answerCountAtRecovery:  number,
+    scoreAtRecovery = 0,
+): RecoveredCandidateState => ({
+  answerCountAtRecovery,
+  scoreAtRecovery,
+})
+
+
+describe('candidatePostsFor', () => {
+  it('does not hard-filter semantic post_similarity answers', () => {
+    const posts = [post (1), post (2), post (3)]
+    const oldQuestion = postSimilarityQuestion ('old', {
+	1: 'no',
+	2: 'yes',
+	3: 'yes',
+    })
+    const laterQuestion = postSimilarityQuestion ('later', {
+	1: 'no',
+	2: 'no',
+	3: 'yes',
+    })
+
+    const candidates = candidatePostsFor ({
+	posts,
+	questions: [oldQuestion, laterQuestion],
+	answers: [answer (oldQuestion, 'yes'), answer (laterQuestion, 'yes')],
+	softenedQuestionIds: new Set (),
+	rejectedPostIds: new Set (),
+	recoveredCandidatePosts: new Map ([
+	    [1, recoveredState (1)],
+	    [3, recoveredState (1)],
+	]) })
+
+    expect(candidates.map (candidate => candidate.id)).toEqual ([1, 2, 3])
+  })
+
+  it('lets recovered candidates ignore old fact answers but not later fact answers', () => {
+    const posts = [
+	{ ...post (1), url: 'https://other.example/posts/1' },
+	post (2),
+	{ ...post (3), url: 'https://example.com/posts/3' },
+    ]
+    const oldQuestion = sourceQuestion ('old.example.com')
+    const laterQuestion = sourceQuestion ('example.com')
+
+    const candidates = candidatePostsFor ({
+	posts,
+	questions: [oldQuestion, laterQuestion],
+	answers: [answer (oldQuestion, 'yes'), answer (laterQuestion, 'yes')],
+	softenedQuestionIds: new Set (),
+	rejectedPostIds: new Set (),
+	recoveredCandidatePosts: new Map ([
+	    [1, recoveredState (1)],
+	    [3, recoveredState (1)],
+	]) })
+
+    expect(candidates.map (candidate => candidate.id)).toEqual ([3])
+  })
+
+  it('does not let recovered candidates bypass explicit rejected posts', () => {
+    const posts = [post (1), post (2)]
+    const question = postSimilarityQuestion ('question', {
+	1: 'yes',
+	2: 'yes',
+    })
+
+    const candidates = candidatePostsFor ({
+	posts,
+	questions: [question],
+	answers: [answer (question, 'yes')],
+	softenedQuestionIds: new Set (),
+	rejectedPostIds: new Set ([1]),
+	recoveredCandidatePosts: new Map ([[1, recoveredState (1)]]) })
+
+    expect(candidates.map (candidate => candidate.id)).toEqual ([2])
+  })
+})
+
+
+describe('hardFilteredPostsForAnswer', () => {
+  it('keeps the original pool for semantic post_similarity answers', () => {
+    const posts = [post (1), post (2)]
+    const question = postSimilarityQuestion ('question', {
+	1: 'yes',
+	2: 'yes',
+    })
+
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'no',
+    })).toEqual (posts)
+  })
+
+  it('hard-filters fact answers only for yes and no', () => {
+    const posts = [
+	{ ...post (1), url: 'https://example.com/posts/1' },
+	{ ...post (2), url: 'https://other.example/posts/2' },
+    ]
+    const question = sourceQuestion ('example.com')
+
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'yes',
+    }).map (candidate => candidate.id)).toEqual ([1])
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'no',
+    }).map (candidate => candidate.id)).toEqual ([2])
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'partial',
+    })).toEqual (posts)
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'probably_no',
+    })).toEqual (posts)
+    expect(hardFilteredPostsForAnswer ({
+	posts,
+	question,
+	answer: 'unknown',
+    })).toEqual (posts)
+  })
+})
+
+
+describe('recoverCandidatePosts', () => {
+  it('recovers high-score non-rejected, non-eligible candidates in staged batches', () => {
+    const posts = Array.from ({ length: 10 }, (_value, index) => post (index + 1))
+    const scores = new Map (posts.map (candidate => [candidate.id, candidate.id]))
+
+    const recovered = recoverCandidatePosts ({
+	posts,
+	scores,
+	rejectedPostIds: new Set ([10]),
+	recoveredCandidatePosts: new Map ([[8, recoveredState (1, 8)]]),
+	eligiblePostIds: new Set ([9]),
+	answerCountAtRecovery: 2,
+	recoveryStepCount: 0,
+    })
+
+    expect(recovered?.recoveryStepCount).toBe (1)
+    expect([...(recovered?.recoveredCandidatePosts.keys () ?? [])])
+      .toEqual ([8, 7, 6, 5, 4])
+    expect(recovered?.recoveredCandidatePosts.get (7)).toEqual ({
+	answerCountAtRecovery: 2,
+	scoreAtRecovery: 7,
+    })
+  })
+
+  it('does not add posts when recovered and eligible candidates already hit the target', () => {
+    const posts = Array.from ({ length: 10 }, (_value, index) => post (index + 1))
+    const scores = new Map (posts.map (candidate => [candidate.id, candidate.id]))
+
+    const recovered = recoverCandidatePosts ({
+	posts,
+	scores,
+	rejectedPostIds: new Set (),
+	recoveredCandidatePosts: new Map ([
+	    [1, recoveredState (1, 1)],
+	    [2, recoveredState (1, 2)],
+	    [3, recoveredState (1, 3)],
+	]),
+	eligiblePostIds: new Set ([4, 5, 6]),
+	answerCountAtRecovery: 2,
+	recoveryStepCount: 0,
+    })
+
+    expect(recovered?.recoveryStepCount).toBe (1)
+    expect([...(recovered?.recoveredCandidatePosts.keys () ?? [])])
+      .toEqual ([1, 2, 3])
+  })
+})
diff --git a/frontend/src/lib/gekanatorCandidateRecovery.ts b/frontend/src/lib/gekanatorCandidateRecovery.ts
new file mode 100644
index 0000000..aec3123
--- /dev/null
+++ b/frontend/src/lib/gekanatorCandidateRecovery.ts
@@ -0,0 +1,159 @@
+import { isLearnedSemanticQuestion,
+	 learnedSemanticSideForPost } from '@/lib/gekanator'
+
+import type { GekanatorAnswerLog, GekanatorAnswerValue, GekanatorQuestion } from '@/lib/gekanator'
+import type { Post } from '@/types'
+
+export type RecoveredCandidatePost = {
+    postId:                number
+    answerCountAtRecovery: number
+    scoreAtRecovery:       number }
+
+export type RecoveredCandidateState = {
+    answerCountAtRecovery: number
+    scoreAtRecovery:       number }
+
+
+const questionSupportsAnswerBasedHardFiltering = (question:  GekanatorQuestion): boolean =>
+    !(isLearnedSemanticQuestion (question)
+      || (question.kind === 'tag'
+	  && question.condition.type === 'tag'
+	  && !(question.condition.key.startsWith ('nico:'))))
+
+
+export const candidatePostsFor = (
+    { posts,
+      questions,
+      answers,
+      softenedQuestionIds,
+      rejectedPostIds,
+      recoveredCandidatePosts }: { posts:                   Post[]
+				   questions:               GekanatorQuestion[]
+				   answers:                 GekanatorAnswerLog[]
+				   softenedQuestionIds:     Set<string>
+				   rejectedPostIds:         Set<number>
+				   recoveredCandidatePosts: Map<number, RecoveredCandidateState> },
+): Post[] => {
+  const questionById = new Map (questions.map (question => [question.id, question]))
+
+  return posts.filter (post => {
+    if (rejectedPostIds.has (post.id))
+      return false
+
+    const recoveredCandidate = recoveredCandidatePosts.get (post.id)
+
+    return answers.every ((answer, index) => {
+      if (recoveredCandidate != null && index < recoveredCandidate.answerCountAtRecovery)
+	return true
+
+      if (softenedQuestionIds.has (answer.questionId))
+	return true
+
+      const question = questionById.get (answer.questionId)
+      if (!(question))
+	return true
+      if (!(questionSupportsAnswerBasedHardFiltering (question)))
+	return true
+
+      switch (answer.answer)
+      {
+      case 'yes':
+      case 'no':
+	{
+	  const expected = learnedSemanticSideForPost (question, post)
+	  return expected === 'unknown'
+	      || (answer.answer === 'yes' && expected === 'positive')
+	      || (answer.answer === 'no' && expected === 'negative')
+	}
+      default:
+	return true
+      }
+    })
+  })
+}
+
+
+export const hardFilteredPostsForAnswer = (
+    { posts, question, answer }: { posts:     Post[]
+				   question:  GekanatorQuestion
+				   answer:    GekanatorAnswerValue },
+): Post[] => {
+  if (!(questionSupportsAnswerBasedHardFiltering (question)))
+    return posts
+
+  if (!(answer === 'yes' || answer === 'no'))
+    return posts
+
+  return posts.filter (post => {
+    const side = learnedSemanticSideForPost (question, post)
+    return side === 'unknown'
+	|| (answer === 'yes' && side === 'positive')
+	|| (answer === 'no' && side === 'negative')
+  })
+}
+
+
+const concreteAnswerOptions: GekanatorAnswerValue[] = ['yes', 'no', 'partial', 'probably_no']
+
+
+export const allConcreteAnswerOptionsExhausted = (
+    posts:      Post[],
+    question:   GekanatorQuestion | null,
+): boolean => {
+  if (!(question))
+    return false
+
+  return concreteAnswerOptions.every (answer =>
+      hardFilteredPostsForAnswer ({ posts, question, answer }).length === 0)
+}
+
+
+const nextRecoveryTargetSize = (recoveryStepCount: number): number =>
+    6 * (2 ** recoveryStepCount)
+
+
+export const recoverCandidatePosts = (
+    { posts,
+      scores,
+      rejectedPostIds,
+      recoveredCandidatePosts,
+      eligiblePostIds,
+      answerCountAtRecovery,
+      recoveryStepCount }: { posts:                   Post[]
+			     scores:                  Map<number, number>
+			     rejectedPostIds:         Set<number>
+			     recoveredCandidatePosts: Map<number, RecoveredCandidateState>
+			     eligiblePostIds:         Set<number>
+			     answerCountAtRecovery:   number
+			     recoveryStepCount:       number },
+): { recoveredCandidatePosts: Map<number, RecoveredCandidateState>
+     recoveryStepCount:       number } | null => {
+  const recovered = new Map (recoveredCandidatePosts)
+  const targetSize = nextRecoveryTargetSize (recoveryStepCount)
+  const countedPostIds = new Set ([...eligiblePostIds, ...recovered.keys ()])
+  const addCount = targetSize - countedPostIds.size
+  if (addCount <= 0)
+    {
+      return { recoveredCandidatePosts: recovered,
+	       recoveryStepCount: recoveryStepCount + 1 }
+    }
+
+  const candidates =
+      posts
+      .filter (post => (!(rejectedPostIds.has (post.id))
+			&& !(eligiblePostIds.has (post.id))
+			&& !(recovered.has (post.id))))
+      .sort ((a, b) => ((scores.get (b.id) ?? Number.NEGATIVE_INFINITY)
+			- (scores.get (a.id) ?? Number.NEGATIVE_INFINITY)))
+      .slice (0, addCount)
+
+  if (candidates.length === 0)
+    return null
+
+  candidates.forEach (post => recovered.set (post.id, {
+      answerCountAtRecovery,
+      scoreAtRecovery: scores.get (post.id) ?? 0 }))
+
+  return { recoveredCandidatePosts: recovered,
+	   recoveryStepCount: recoveryStepCount + 1 }
+}
diff --git a/frontend/src/lib/gekanatorQuestionFilters.ts b/frontend/src/lib/gekanatorQuestionFilters.ts
new file mode 100644
index 0000000..e358e38
--- /dev/null
+++ b/frontend/src/lib/gekanatorQuestionFilters.ts
@@ -0,0 +1,167 @@
+import { titleLengthMinimumForCondition } from '@/lib/gekanator'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+} from '@/lib/gekanator'
+
+
+export const monthForCondition = (
+    condition:  GekanatorQuestion['condition'],
+): number | null => {
+  if (condition.type === 'original-month')
+    return condition.month
+
+  if (condition.type !== 'original-month-day')
+    return null
+
+  const month = Number (condition.monthDay.split ('-')[0])
+  return Number.isInteger (month) ? month : null
+}
+
+
+const isTitleLengthContradiction = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  const candidateLength = titleLengthMinimumForCondition (candidate)
+  const previousLength = titleLengthMinimumForCondition (previous)
+  if (candidateLength === null || previousLength === null)
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return candidateLength <= previousLength
+  case 'no':
+    return candidateLength >= previousLength
+  default:
+    return false
+  }
+}
+
+
+const isQuestionRedundantAfterAnswers = (
+    question:  GekanatorQuestion,
+    answers:   GekanatorAnswerLog[],
+): boolean => answers.some (answer => {
+  const previous = answer.questionCondition
+  return previous !== undefined
+      && isTitleLengthContradiction (question.condition, previous, answer.answer)
+})
+
+
+const isSourceFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (candidate.type !== 'source' || previous.type !== 'source')
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return true
+  case 'no':
+    return candidate.host === previous.host
+  default:
+    return false
+  }
+}
+
+
+const isOriginalYearFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (candidate.type !== 'original-year' || previous.type !== 'original-year')
+    return false
+
+  switch (answer)
+  {
+  case 'yes':
+    return true
+  case 'no':
+    return candidate.year === previous.year
+  default:
+    return false
+  }
+}
+
+
+const isOriginalMonthFactBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  switch (answer)
+  {
+  case 'yes':
+    if (previous.type === 'original-month')
+      {
+	if (candidate.type === 'original-month')
+	  return true
+
+	if (candidate.type === 'original-month-day')
+	  return monthForCondition (candidate) !== previous.month
+
+	return false
+      }
+
+    if (previous.type === 'original-month-day')
+      return candidate.type === 'original-month'
+	  || candidate.type === 'original-month-day'
+
+    return false
+  case 'no':
+    if (previous.type === 'original-month')
+      {
+	if (candidate.type === 'original-month')
+	  return candidate.month === previous.month
+
+	if (candidate.type === 'original-month-day')
+	  return monthForCondition (candidate) === previous.month
+
+	return false
+      }
+
+    if (previous.type === 'original-month-day')
+      return candidate.type === 'original-month-day'
+	  && candidate.monthDay === previous.monthDay
+
+    return false
+  default:
+    return false
+  }
+}
+
+
+const isFactQuestionBlocked = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+    answer:     GekanatorAnswerValue,
+): boolean => {
+  if (!(answer === 'yes' || answer === 'no'))
+    return false
+
+  return isSourceFactBlocked (candidate, previous, answer)
+      || isOriginalYearFactBlocked (candidate, previous, answer)
+      || isOriginalMonthFactBlocked (candidate, previous, answer)
+}
+
+
+export const isQuestionHardFilteredAfterAnswers = (
+    question:  GekanatorQuestion,
+    answers:   GekanatorAnswerLog[],
+): boolean => answers.some (answer => {
+  const previous = answer.questionCondition
+  if (previous === undefined)
+    return false
+
+  return isQuestionRedundantAfterAnswers (question, [answer])
+      || isFactQuestionBlocked (question.condition, previous, answer.answer)
+})
diff --git a/frontend/src/lib/prefetchers.test.ts b/frontend/src/lib/prefetchers.test.ts
index b33cb65..8a341a3 100644
--- a/frontend/src/lib/prefetchers.test.ts
+++ b/frontend/src/lib/prefetchers.test.ts
@@ -10,6 +10,7 @@ const postsApi = vi.hoisted (() => ({
 }))
 
 const tagsApi = vi.hoisted (() => ({
+  fetchNicoTags:   vi.fn (),
   fetchTag:        vi.fn (),
   fetchTagByName:  vi.fn (),
   fetchTagChanges: vi.fn (),
@@ -37,6 +38,7 @@ describe ('prefetchForURL', () => {
     postsApi.fetchPost.mockResolvedValue ({ id: 1 })
     postsApi.fetchPostChanges.mockResolvedValue ({ versions: [], count: 0 })
     tagsApi.fetchTags.mockResolvedValue ({ tags: [], count: 0 })
+    tagsApi.fetchNicoTags.mockResolvedValue ({ tags: [], count: 0 })
     tagsApi.fetchTag.mockResolvedValue ({ id: 1 })
     tagsApi.fetchTagByName.mockResolvedValue (null)
     tagsApi.fetchTagChanges.mockResolvedValue ({ versions: [], count: 0 })
@@ -85,6 +87,32 @@ describe ('prefetchForURL', () => {
     )
   })
 
+  it ('prefetches nico tag indexes and their alias from query parameters', async () => {
+    await prefetchForURL (
+        qc (),
+        'http://localhost/tags/nico?name=source&linked_tag=destination'
+	    + '&link_status=linked&page=3&limit=10',
+    )
+    await prefetchForURL (qc (), 'http://localhost/nico/tags?page=2')
+
+    expect (tagsApi.fetchNicoTags).toHaveBeenNthCalledWith (1, {
+      name:       'source',
+      linkedTag:  'destination',
+      linkStatus: 'linked',
+      page:       3,
+      limit:      10,
+      order:      'updated_at:desc',
+    })
+    expect (tagsApi.fetchNicoTags).toHaveBeenNthCalledWith (2, {
+      name:       '',
+      linkedTag:  '',
+      linkStatus: 'all',
+      page:       2,
+      limit:      20,
+      order:      'updated_at:desc',
+    })
+  })
+
   it ('prefetches wiki show pages and related tag/post data', async () => {
     wikiApi.fetchWikiPageByTitle.mockResolvedValueOnce ({
       id:    3,
diff --git a/frontend/src/lib/prefetchers.ts b/frontend/src/lib/prefetchers.ts
index 5dc9d70..264a380 100644
--- a/frontend/src/lib/prefetchers.ts
+++ b/frontend/src/lib/prefetchers.ts
@@ -3,7 +3,7 @@ import { match } from 'path-to-regexp'
 
 import { fetchPost, fetchPosts, fetchPostChanges } from '@/lib/posts'
 import { postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
-import { fetchTagByName, fetchTag, fetchTagChanges, fetchTags } from '@/lib/tags'
+import { fetchNicoTags, fetchTagByName, fetchTag, fetchTagChanges, fetchTags } from '@/lib/tags'
 import { fetchWikiPage,
 	 fetchWikiPageByTitle,
 	 fetchWikiPages } from '@/lib/wiki'
@@ -17,6 +17,10 @@ const mWiki = match<{ title: string }> ('/wiki/:title')
 const mTag = match<{ id: string }> ('/tags/:id')
 
 
+const boolFromQuery = (value: string | null): boolean =>
+    ['1', 'true', 'on', 'yes', ''].includes ((value ?? '').toLowerCase ())
+
+
 const prefetchWikiPagesIndex: Prefetcher = async (qc, url) => {
   const title = url.searchParams.get ('title') ?? ''
 
@@ -156,13 +160,16 @@ const prefetchTagsIndex: Prefetcher = async (qc, url) => {
   const createdTo = url.searchParams.get ('created_to') ?? ''
   const updatedFrom = url.searchParams.get ('updated_from') ?? ''
   const updatedTo = url.searchParams.get ('updated_to') ?? ''
+  const deprecated = url.searchParams.has ('deprecated')
+      ? boolFromQuery (url.searchParams.get ('deprecated'))
+      : null
   const page = Number (url.searchParams.get ('page') || 1)
   const limit = Number (url.searchParams.get ('limit') || 20)
   const order = (url.searchParams.get ('order') ?? 'post_count:desc') as FetchTagsOrder
 
   const keys = {
       post, name, category, postCountGTE, postCountLTE, createdFrom, createdTo,
-      updatedFrom, updatedTo, page, limit, order }
+      updatedFrom, updatedTo, deprecated, page, limit, order }
 
   await qc.prefetchQuery ({
       queryKey: tagsKeys.index (keys),
@@ -170,6 +177,24 @@ const prefetchTagsIndex: Prefetcher = async (qc, url) => {
 }
 
 
+const prefetchNicoTagsIndex: Prefetcher = async (qc, url) => {
+  const keys = {
+      name:       url.searchParams.get ('name') ?? '',
+      linkedTag:  url.searchParams.get ('linked_tag') ?? '',
+      linkStatus: (url.searchParams.get ('link_status') || 'all') as
+		  'all' | 'linked' | 'unlinked',
+      page:       Number (url.searchParams.get ('page') || 1),
+      limit:      Number (url.searchParams.get ('limit') || 20),
+      order:      (url.searchParams.get ('order') || 'updated_at:desc') as
+		  'name:asc' | 'name:desc' | 'created_at:asc' | 'created_at:desc'
+		  | 'updated_at:asc' | 'updated_at:desc' }
+
+  await qc.prefetchQuery ({
+      queryKey: tagsKeys.nicoIndex (keys),
+      queryFn:  () => fetchNicoTags (keys) })
+}
+
+
 const prefetchTagShow: Prefetcher = async (qc, url) => {
   const m = mTag (url.pathname)
   if (!(m))
@@ -206,6 +231,8 @@ export const routePrefetchers: { test: (u: URL) => boolean; run: Prefetcher }[]
 		  && Boolean (mWiki (u.pathname))),
       run: prefetchWikiPageShow },
     { test: u => u.pathname === '/tags', run: prefetchTagsIndex },
+    { test: u => ['/tags/nico', '/nico/tags'].includes (u.pathname),
+      run: prefetchNicoTagsIndex },
     { test: u => (!(['/tags/nico', '/tags/changes'].includes (u.pathname))
 		  && Boolean (mTag (u.pathname))),
       run: prefetchTagShow },
diff --git a/frontend/src/lib/queryKeys.ts b/frontend/src/lib/queryKeys.ts
index 6ac3f21..7e10ab1 100644
--- a/frontend/src/lib/queryKeys.ts
+++ b/frontend/src/lib/queryKeys.ts
@@ -1,4 +1,4 @@
-import type { FetchPostsParams, FetchTagsParams } from '@/types'
+import type { FetchNicoTagsParams, FetchPostsParams, FetchTagsParams } from '@/types'
 
 export const postsKeys = {
     root:     ['posts'] as const,
@@ -8,9 +8,18 @@ export const postsKeys = {
     changes:  (p: { post?: string; tag?: string; page: number; limit: number }) =>
 		  ['posts', 'changes', p] as const }
 
+export const gekanatorKeys = {
+    root:      ['gekanator'] as const,
+    posts:     () => ['gekanator', 'posts'] as const,
+    questions: () => ['gekanator', 'questions'] as const,
+    extraQuestions: (gameId: number, nonce: string) =>
+		       ['gekanator', 'games', gameId, 'extra-questions', nonce] as const }
+
 export const tagsKeys = {
     root:         ['tags'] as const,
     index:        (p: FetchTagsParams) => ['tags', 'index', p] as const,
+    nicoRoot:     ['tags', 'nico'] as const,
+    nicoIndex:    (p: FetchNicoTagsParams) => ['tags', 'nico', 'index', p] as const,
     show:         (name: string) => ['tags', name] as const,
     changes:      (p: { id?: string; page: number; limit: number }) =>
 		      ['tags', 'changes', p] as const,
diff --git a/frontend/src/lib/tags.test.ts b/frontend/src/lib/tags.test.ts
index f51455c..7075997 100644
--- a/frontend/src/lib/tags.test.ts
+++ b/frontend/src/lib/tags.test.ts
@@ -20,6 +20,7 @@ const baseParams: FetchTagsParams = {
   createdTo:    '',
   updatedFrom:  '',
   updatedTo:    '',
+  deprecated:   null,
   page:         1,
   limit:        30,
   order:        'updated_at:desc',
@@ -57,6 +58,20 @@ describe ('tags API functions', () => {
     )
   })
 
+  it.each ([
+    [true, '1'],
+    [false, '0'],
+  ] as const) ('maps deprecated=%s to %s', async (deprecated, expected) => {
+    api.apiGet.mockResolvedValueOnce ({ tags: [], count: 0 })
+
+    await fetchTags ({ ...baseParams, deprecated })
+
+    expect (api.apiGet).toHaveBeenCalledWith (
+        '/tags',
+        { params: expect.objectContaining ({ deprecated: expected }) },
+    )
+  })
+
   it ('returns null when tag fetches fail', async () => {
     api.apiGet.mockRejectedValueOnce (new Error ('missing'))
     api.apiGet.mockRejectedValueOnce (new Error ('missing'))
diff --git a/frontend/src/lib/tags.ts b/frontend/src/lib/tags.ts
index 74eba45..31cad85 100644
--- a/frontend/src/lib/tags.ts
+++ b/frontend/src/lib/tags.ts
@@ -1,11 +1,17 @@
 import { apiGet } from '@/lib/api'
 
-import type { Deerjikist, FetchTagsParams, Tag, TagVersion } from '@/types'
+import type { Deerjikist,
+	      FetchNicoTagsParams,
+	      FetchTagsParams,
+	      NicoTag,
+	      Tag,
+	      TagVersion } from '@/types'
 
 
 export const fetchTags = async (
     { post, name, category, postCountGTE, postCountLTE, createdFrom, createdTo,
-      updatedFrom, updatedTo, page, limit, order }: FetchTagsParams,
+      updatedFrom, updatedTo, deprecated,
+      page, limit, order }: FetchTagsParams,
 ): Promise<{ tags:  Tag[]
 	     count: number }> =>
     await apiGet ('/tags', { params: {
@@ -18,11 +24,25 @@ export const fetchTags = async (
 	...(createdTo && { created_to: createdTo }),
 	...(updatedFrom && { updated_from: updatedFrom }),
 	...(updatedTo && { updated_to: updatedTo }),
+	...(deprecated != null && { deprecated: deprecated ? '1' : '0' }),
 	...(page && { page }),
 	...(limit && { limit }),
 	...(order && { order }) } })
 
 
+export const fetchNicoTags = async (
+    { name, linkedTag, linkStatus, page, limit, order }: FetchNicoTagsParams,
+): Promise<{ tags:  NicoTag[]
+	     count: number }> =>
+    await apiGet ('/tags/nico', { params: {
+	page,
+	limit,
+	name,
+	linked_tag:  linkedTag,
+	link_status: linkStatus === 'all' ? '' : linkStatus,
+	order } })
+
+
 export const fetchTag = async (id: string): Promise<Tag | null> => {
   try
   {
@@ -46,7 +66,6 @@ export const fetchTagByName = async (name: string): Promise<Tag | null> => {
   }
 }
 
-
 export const fetchTagChanges = async (
     { id, page, limit }: {
 	id?:    string
diff --git a/frontend/src/lib/useValidationErrors.ts b/frontend/src/lib/useValidationErrors.ts
new file mode 100644
index 0000000..da0ebc6
--- /dev/null
+++ b/frontend/src/lib/useValidationErrors.ts
@@ -0,0 +1,28 @@
+import { useState } from 'react'
+
+import { extractValidationError } from '@/lib/apiErrors'
+
+import type { FieldErrors } from '@/lib/apiErrors'
+
+
+export const useValidationErrors = <T extends string> () => {
+  const [baseErrors, setBaseErrors] = useState<string[]> ([])
+  const [fieldErrors, setFieldErrors] = useState<FieldErrors<T>> ({ })
+
+  const clearValidationErrors = () => {
+    setBaseErrors ([])
+    setFieldErrors ({ })
+  }
+
+  const applyValidationError = (error: unknown): boolean => {
+    const validationError = extractValidationError<T> (error)
+    if (!(validationError))
+      return false
+
+    setBaseErrors (validationError.baseErrors)
+    setFieldErrors (validationError.fieldErrors)
+    return true
+  }
+
+  return { baseErrors, fieldErrors, clearValidationErrors, applyValidationError }
+}
diff --git a/frontend/src/lib/users.test.ts b/frontend/src/lib/users.test.ts
new file mode 100644
index 0000000..aed765b
--- /dev/null
+++ b/frontend/src/lib/users.test.ts
@@ -0,0 +1,20 @@
+import { describe, expect, it } from 'vitest'
+
+import { canEditContent } from '@/lib/users'
+
+import type { UserRole } from '@/types'
+
+const userWithRole = (role: UserRole) => ({ role })
+
+describe ('user permission helpers', () => {
+  it ('allows admins and members to edit content', () => {
+    expect (canEditContent (userWithRole ('admin'))).toBe (true)
+    expect (canEditContent (userWithRole ('member'))).toBe (true)
+  })
+
+  it ('does not allow guests or missing users to edit content', () => {
+    expect (canEditContent (userWithRole ('guest'))).toBe (false)
+    expect (canEditContent (null)).toBe (false)
+    expect (canEditContent (undefined)).toBe (false)
+  })
+})
diff --git a/frontend/src/lib/users.ts b/frontend/src/lib/users.ts
new file mode 100644
index 0000000..9f31329
--- /dev/null
+++ b/frontend/src/lib/users.ts
@@ -0,0 +1,8 @@
+import type { User, UserRole } from '@/types'
+
+const CONTENT_EDITOR_ROLES: readonly UserRole[] = ['admin', 'member']
+
+
+export const canEditContent = (
+    user: Pick<User, 'role'> | null | undefined,
+): boolean => user != null && CONTENT_EDITOR_ROLES.includes (user.role)
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index 6493039..5e31026 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -83,3 +83,15 @@ export const msToTime = (ms: number): string => {
 	  ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
 	  : `${ min }:${ s.padStart (2, '0') }`)
 }
+
+
+export const inputClass = (invalid?: boolean, className?: string): string =>
+    cn ('w-full rounded border p-2',
+	(invalid
+	 ? ['border-red-500 bg-red-50 text-red-900',
+	    'placeholder:text-red-300',
+	    'focus:border-red-500 focus:outline-none focus:ring-2 focus:ring-red-200',
+	    'dark:border-red-500 dark:bg-red-950/30 dark:text-red-100']
+	 : ['border-gray-300',
+	    'focus:border-blue-500 focus:outline-none focus:ring-2 focus:ring-blue-200']),
+	className)
diff --git a/frontend/src/pages/GekanatorPage.test.tsx b/frontend/src/pages/GekanatorPage.test.tsx
new file mode 100644
index 0000000..b42617f
--- /dev/null
+++ b/frontend/src/pages/GekanatorPage.test.tsx
@@ -0,0 +1,240 @@
+import { readFileSync } from 'node:fs'
+import { resolve } from 'node:path'
+
+import { describe, expect, it } from 'vitest'
+
+import { isQuestionHardFilteredAfterAnswers } from '@/lib/gekanatorQuestionFilters'
+
+import type {
+    GekanatorAnswerLog,
+    GekanatorAnswerValue,
+    GekanatorQuestion,
+    GekanatorQuestionCondition,
+} from '@/lib/gekanator'
+
+
+const question = (
+    condition:  GekanatorQuestionCondition,
+): GekanatorQuestion => ({
+  id: `${ condition.type }:candidate`,
+  text: 'candidate?',
+  kind: condition.type === 'source'
+      ? 'source'
+      : condition.type.startsWith ('original-')
+	? 'original_date'
+	: condition.type.startsWith ('title-')
+	  ? 'title'
+	  : 'tag',
+  condition,
+  source: 'default',
+  priorityWeight: 1,
+  test: () => false,
+})
+
+
+const answer = (
+    condition:  GekanatorQuestionCondition,
+    value:      GekanatorAnswerValue,
+): GekanatorAnswerLog => ({
+  questionId: 'previous',
+  questionText: 'previous?',
+  questionCondition: condition,
+  answer: value,
+  originalAnswer: value,
+})
+
+
+const blocked = (
+    candidate:  GekanatorQuestionCondition,
+    previous:   GekanatorQuestionCondition,
+    value:      GekanatorAnswerValue,
+): boolean =>
+    isQuestionHardFilteredAfterAnswers (question (candidate), [answer (previous, value)])
+
+
+const gekanatorPageSource = readFileSync (
+    resolve (process.cwd (), 'src/pages/GekanatorPage.tsx'),
+    'utf8')
+
+const gekanatorBackdropSource = gekanatorPageSource.slice (
+    gekanatorPageSource.indexOf ('const GekanatorBackdrop'),
+    gekanatorPageSource.indexOf ('const expectedAnswerFor'))
+
+const gekanatorChooseQuestionSource = gekanatorPageSource.slice (
+    gekanatorPageSource.indexOf ('const chooseQuestion'),
+    gekanatorPageSource.indexOf ('const winningRunPriorityFor'))
+
+const gekanatorFallbackQuestionSource = gekanatorPageSource.slice (
+    gekanatorPageSource.indexOf ('const chooseFallbackQuestion'),
+    gekanatorPageSource.indexOf ('const shouldEnterGuessPhase'))
+
+
+describe('GekanatorBackdrop regression structure', () => {
+  it('keeps displayedBackdropMode as the render-time source of truth', () => {
+    expect(gekanatorBackdropSource).not.toContain ('isLeavingGuessBackdrop')
+    expect(gekanatorBackdropSource).not.toContain ('renderBackdropMode')
+    expect(gekanatorBackdropSource).not.toContain ('renderWinningRunCount')
+    expect(gekanatorBackdropSource).not.toContain ('renderThumbnails')
+    expect(gekanatorBackdropSource).not.toContain ('renderIsCrossfading')
+
+    expect(gekanatorBackdropSource).toContain (
+      "const renderedSettings = settingsForMode (displayedBackdropMode)")
+    expect(gekanatorBackdropSource).toContain (
+      'scaleForMode (displayedBackdropMode, displayedWinningRunCount)')
+    expect(gekanatorBackdropSource).toContain (
+      "backdropMode === 'guess' || displayedBackdropMode === 'guess'")
+  })
+
+  it('does not split guess into a separate renderer or force a remount', () => {
+    expect(gekanatorBackdropSource).not.toContain ('renderStaticGuessBackdrop')
+    expect(gekanatorBackdropSource).not.toContain ('guessZoomAnimationKey')
+    expect(gekanatorBackdropSource).not.toContain ('shouldAnimateGuessZoomIn')
+    expect(gekanatorBackdropSource).not.toContain ('previousBackdropModeRef')
+    expect(gekanatorBackdropSource).not.toContain (
+      'if (isGuessPresentation && guessThumbnail)')
+  })
+
+  it('keeps tile keys independent from backdrop mode', () => {
+    expect(gekanatorBackdropSource).toContain ('key={duplicate}')
+    expect(gekanatorBackdropSource).toContain ('key={`${ duplicate }:${ index }`}')
+    expect(gekanatorBackdropSource).not.toMatch (/key=\{`\$\{\s*mode/)
+    expect(gekanatorBackdropSource).not.toMatch (/key=\{`\$\{\s*displayedBackdropMode/)
+  })
+
+  it('keeps guess on the shared scale, x, and y animation path', () => {
+    expect(gekanatorBackdropSource).toContain ('animate={{ scale: renderedScale')
+    expect(gekanatorBackdropSource).toContain (
+      "x: displayedBackdropMode === 'guess' ? guessFocusOffset.x : '0%'")
+    expect(gekanatorBackdropSource).toContain (
+      "y: displayedBackdropMode === 'guess' ? guessFocusOffset.y : '0%'")
+  })
+})
+
+
+describe('Gekanator question selection regression structure', () => {
+  it('prefers normal questions after user_suggested quota has been met', () => {
+    const normalFallbackIndex = gekanatorChooseQuestionSource.indexOf (
+      'else if (normalPool.length > 0)')
+    const effectiveFallbackIndex = gekanatorChooseQuestionSource.indexOf (
+      'else if (effectiveUserSuggestedPool.length > 0)')
+
+    expect(normalFallbackIndex).toBeGreaterThan(0)
+    expect(effectiveFallbackIndex).toBeGreaterThan(0)
+    expect(normalFallbackIndex).toBeLessThan(effectiveFallbackIndex)
+  })
+
+  it('does not let fallback questions bypass user_suggested purpose tracking', () => {
+    expect(gekanatorFallbackQuestionSource).toContain (
+      "question.source !== 'user_suggested'")
+  })
+
+  it('does not show a fixed extra-question count in the extra learning UI', () => {
+    expect(gekanatorPageSource).not.toContain ('追加で 2 問まで答えてください。')
+    expect(gekanatorPageSource).toContain ('追加で質問に答えてください。')
+  })
+})
+
+
+describe('isQuestionHardFilteredAfterAnswers', () => {
+  it('blocks only contradictory or redundant month questions after a yes answer', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '2-14' }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'yes'))
+      .toBe(false)
+    expect(blocked ({ type: 'original-year', year: 2024 }, previous, 'yes')).toBe(false)
+    expect(blocked ({ type: 'source', host: 'example.com' }, previous, 'yes')).toBe(false)
+    expect(blocked ({ type: 'tag', key: 'character:喜多郁代' }, previous, 'yes')).toBe(false)
+  })
+
+  it('blocks same-month facts after a no answer', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'no')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'no')).toBe(false)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '2-14' }, previous, 'no'))
+      .toBe(false)
+  })
+
+  it('blocks all month and month-day questions after a month-day yes answer', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'original-month-day',
+      monthDay: '12-25',
+    }
+
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month', month: 2 }, previous, 'yes')).toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-26' }, previous, 'yes'))
+      .toBe(true)
+  })
+
+  it('blocks the same month-day only after a month-day no answer', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'original-month-day',
+      monthDay: '12-25',
+    }
+
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-25' }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'original-month-day', monthDay: '12-26' }, previous, 'no'))
+      .toBe(false)
+    expect(blocked ({ type: 'original-month', month: 12 }, previous, 'no')).toBe(false)
+  })
+
+  it('blocks year and source as single-value facts', () => {
+    expect(blocked (
+      { type: 'original-year', year: 2025 },
+      { type: 'original-year', year: 2024 },
+      'yes',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'original-year', year: 2024 },
+      { type: 'original-year', year: 2024 },
+      'no',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'source', host: 'b.example' },
+      { type: 'source', host: 'a.example' },
+      'yes',
+    )).toBe(true)
+    expect(blocked (
+      { type: 'source', host: 'b.example' },
+      { type: 'source', host: 'a.example' },
+      'no',
+    )).toBe(false)
+  })
+
+  it('does not hard-filter partial, probably_no, or unknown fact answers', () => {
+    const previous: GekanatorQuestionCondition = { type: 'original-month', month: 12 }
+    const candidate: GekanatorQuestionCondition = { type: 'original-month', month: 2 }
+
+    expect(blocked (candidate, previous, 'partial')).toBe(false)
+    expect(blocked (candidate, previous, 'probably_no')).toBe(false)
+    expect(blocked (candidate, previous, 'unknown')).toBe(false)
+  })
+
+  it('keeps title-length hard redundancy for yes and no only', () => {
+    const previous: GekanatorQuestionCondition = {
+      type: 'title-length-at-least',
+      length: 30,
+    }
+
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'yes'))
+      .toBe(true)
+    expect(blocked ({ type: 'title-length-at-least', length: 40 }, previous, 'yes'))
+      .toBe(false)
+    expect(blocked ({ type: 'title-length-at-least', length: 40 }, previous, 'no'))
+      .toBe(true)
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'no'))
+      .toBe(false)
+    expect(blocked ({ type: 'title-length-at-least', length: 20 }, previous, 'partial'))
+      .toBe(false)
+  })
+})
diff --git a/frontend/src/pages/GekanatorPage.tsx b/frontend/src/pages/GekanatorPage.tsx
new file mode 100644
index 0000000..1eabcd0
--- /dev/null
+++ b/frontend/src/pages/GekanatorPage.tsx
@@ -0,0 +1,5763 @@
+import { animate, motion, useMotionTemplate, useMotionValue } from 'framer-motion'
+import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import MainArea from '@/components/layout/MainArea'
+import { SITE_TITLE } from '@/config'
+import { expectedAnswerForQuestion,
+	 fetchGekanatorExtraQuestions,
+	 fetchGekanatorQuestions,
+	 fetchGekanatorPosts,
+	 isLearnedSemanticQuestion,
+	 learnedSemanticSideForPost,
+	 normalizeTitleLengthCondition,
+	 questionIdForCondition,
+	 restoreGekanatorQuestion,
+	 saveGekanatorExtraQuestionAnswers,
+	 saveGekanatorGame,
+	 saveGekanatorQuestionSuggestion,
+	 storeGekanatorQuestion,
+	 titleLengthMinimumForCondition } from '@/lib/gekanator'
+import { recoverCandidatePosts } from '@/lib/gekanatorCandidateRecovery'
+import { isQuestionHardFilteredAfterAnswers,
+	 monthForCondition } from '@/lib/gekanatorQuestionFilters'
+import { gekanatorKeys } from '@/lib/queryKeys'
+import { cn } from '@/lib/utils'
+
+import type { FC } from 'react'
+import type { Transition } from 'framer-motion'
+
+import type { GekanatorAnswerLog,
+	      GekanatorAnswerValue,
+	      GekanatorExtraQuestion,
+	      GekanatorQuestionPurpose,
+	      GekanatorQuestionCondition,
+	      GekanatorQuestionKind,
+	      GekanatorQuestion,
+	      StoredGekanatorQuestion } from '@/lib/gekanator'
+import type {
+    RecoveredCandidatePost,
+    RecoveredCandidateState,
+} from '@/lib/gekanatorCandidateRecovery'
+import type { Post, User } from '@/types'
+
+type Phase =
+    | 'intro'
+    | 'question'
+    | 'guess'
+    | 'continue'
+    | 'end'
+    | 'review'
+    | 'question_suggestion'
+    | 'extra_questions'
+    | 'learned'
+
+type AnswerOption = {
+    label:  string
+    value:  GekanatorAnswerValue }
+
+type Confidence = {
+    post:     Post
+    score:    number
+    percent:  number }
+
+type AnswerPreview = {
+    answer:              GekanatorAnswerValue
+    top:                 Confidence | null
+    candidateCount:      number
+    effectiveCandidates: number
+    entropy:             number }
+
+type GameSnapshot = {
+    phase:                   Phase
+    scores:                  Map<number, number>
+    answers:                 GekanatorAnswerLog[]
+    askedIds:                Set<string>
+    softenedQuestionIds:     Set<string>
+    recoveredCandidatePosts: Map<number, RecoveredCandidateState>
+    recoveryStepCount:       number
+    askedQuestionBank:       GekanatorQuestion[]
+    search:                  string
+    selectingCorrectPost:    boolean
+    rejectedPostIds:         Set<number>
+    lastGuessQuestionCount:  number
+    lastRejectedGuessId:     number | null
+    winningRunTargetId:      number | null
+    winningRunStartAnswerCount: number | null
+    guessReason:             GuessReason | null
+    activeGuessId:           number | null
+    reviewGuessedPostId:     number | null
+    reviewCorrectPostId:     number | null }
+
+type StoredGekanatorGame = {
+    phase:                       Phase
+    scores:                      [number, number][]
+    answers:                     GekanatorAnswerLog[]
+    askedIds:                    string[]
+    softenedQuestionIds:         string[]
+    recoveredCandidatePosts?:    RecoveredCandidatePost[]
+    recoveryStepCount?:          number
+    askedQuestionBank?:          StoredGekanatorQuestion[]
+    askedQuestionBankIds?:       string[]
+    search:                      string
+    selectingCorrectPost:        boolean
+    saved:                       boolean
+    resultWon:                   boolean | null
+    rejectedPostIds:             number[]
+    lastGuessQuestionCount:      number
+    lastRejectedGuessId:         number | null
+    winningRunTargetId?:         number | null
+    winningRunStartAnswerCount?: number | null
+    guessReason?:                GuessReason | null
+    activeGuessId:               number | null
+    reviewGuessedPostId:         number | null
+    reviewCorrectPostId:         number | null
+    savedGameId:                 number | null
+    learnedExampleCount?:        number | null
+    gameSeed?:                   string
+    questionSuggestionEntryMode?: 'search' | 'new'
+    questionSuggestionSearch?:   string
+    questionSuggestionSelectedId?: number | null
+    questionSuggestion:          string
+    questionSuggestionAnswer:    GekanatorAnswerValue
+    questionSuggestionCount?:    number
+    extraQuestions?:             GekanatorExtraQuestion[]
+    extraQuestionAnswers?:       Record<string, GekanatorAnswerValue>
+    extraQuestionState?:         'idle' | 'loading' | 'ready' | 'empty' | 'saved' }
+
+type RecentGameSummary = {
+    correctPostId:   number
+    firstQuestionId: string | null
+    savedAt:         number }
+
+type BackgroundMotionMode = 'on' | 'calm' | 'off'
+
+type GuessReason =
+    | 'hard_max_questions'
+    | 'winning_run_finished'
+    | 'question_count_checkpoint'
+    | 'question_generation_stalled'
+
+type QuestionMode =
+    | 'winning_run'
+    | 'normal'
+    | null
+
+type QuestionSelection = {
+    question:           GekanatorQuestion
+    questionPurpose:    GekanatorQuestionPurpose
+    effectiveQuestion:  boolean
+    learningQuestion:   boolean }
+
+type QuestionBuildMode =
+    | 'split'
+    | 'confirmation'
+
+type QuestionSuggestionEntryMode =
+    | 'search'
+    | 'new'
+
+type MascotState =
+    | 'idle'
+    | 'thinking_far'
+    | 'thinking_mid'
+    | 'thinking_near'
+    | 'confident'
+    | 'celebrate'
+    | 'failed'
+
+const answerOptions: AnswerOption[] = [
+    { label: 'はい', value: 'yes' },
+    { label: 'いいえ', value: 'no' },
+    { label: '部分的にそう', value: 'partial' },
+    { label: 'たぶんいいえ', value: 'probably_no' },
+    { label: 'わからない', value: 'unknown' }]
+
+const answerLabelFor = (value: GekanatorAnswerValue): string =>
+    answerOptions.find (option => option.value === value)?.label ?? value
+
+const minQuestionsBeforeCertainGuess = 25
+const hardMaxQuestions = 80
+const winningRunQuestionLimit = 3
+const softenedAnswerWeight = .35
+const confidenceTemperature = 6
+const gameStorageKey = 'gekanator:game:v1'
+const recentGamesStorageKey = 'gekanator:recent-games:v1'
+const backgroundMotionStorageKey = 'gekanator:background-motion:v1'
+const maxStoredRecentGames = 12
+const specialOriginalMonthDayLabels: Record<string, string> = {
+    '1-1': '元日',
+    '12-31': '大晦日',
+    '12-3': '12月3日',
+    '5-29': '5月29日' }
+const mascotAssetByState: Record<MascotState, string> = {
+    idle: '/assets/gekanator/mascot-idle.png',
+    thinking_far: '/assets/gekanator/mascot-thinking-far.png',
+    thinking_mid: '/assets/gekanator/mascot-thinking-mid.png',
+    thinking_near: '/assets/gekanator/mascot-thinking-near.png',
+    confident: '/assets/gekanator/mascot-confident.png',
+    celebrate: '/assets/gekanator/mascot-celebrate.png',
+    failed: '/assets/gekanator/mascot-failed.png' }
+const mascotAltByState: Record<MascotState, string> = {
+    idle: '待機する洗澡鹿',
+    thinking_far: '遠くを見つめる洗澡鹿',
+    thinking_mid: '考え込む洗澡鹿',
+    thinking_near: '見通しが立ってきた洗澡鹿',
+    confident: '見通した顔の洗澡鹿',
+    celebrate: 'ご満悦の洗澡鹿',
+    failed: 'しょんぼりした洗澡鹿' }
+
+const sourcePriorityOffset = (question: GekanatorQuestion): number => {
+  switch (question.source)
+  {
+  case 'user_suggested':
+    return -1.2
+  case 'admin_curated':
+    return -0.8
+  case 'ai_generated':
+    return -0.6
+  default:
+    return 0
+  }
+}
+
+
+const priorityWeightOffset = (question: GekanatorQuestion): number =>
+    (Math.min (3, Math.max (.2, question.priorityWeight)) - 1) * -.8
+
+
+const createGameSeed = (): string => {
+  if (typeof crypto !== 'undefined' && typeof crypto.randomUUID === 'function')
+    return crypto.randomUUID ()
+
+  return `${ Date.now () }:${ Math.random ().toString (36).slice (2) }`
+}
+
+
+const normalizeStoredQuestionId = (
+    questionId:  string,
+    condition?:  GekanatorQuestionCondition,
+): string => {
+  if (condition?.type === 'title-length-greater-than')
+    return `title:length-at-least:${ condition.length + 1 }`
+
+  if (questionId.startsWith ('title:length-greater-than:'))
+    {
+      const length = Number (questionId.split (':').pop ())
+      if (Number.isInteger (length))
+	return `title:length-at-least:${ length + 1 }`
+    }
+
+  return questionId
+}
+
+
+const normalizeStoredGame = (game: StoredGekanatorGame): StoredGekanatorGame => ({
+  ...game,
+  answers: game.answers.map (answer => {
+    const questionMode =
+	answer.questionMode === 'winning_run' || answer.questionMode === 'normal'
+	? answer.questionMode
+	: undefined
+    const questionCondition =
+	answer.questionCondition
+	? normalizeTitleLengthCondition (answer.questionCondition)
+	: undefined
+
+    return {
+	...answer,
+	questionId: normalizeStoredQuestionId (answer.questionId,
+					       answer.questionCondition),
+	questionMode,
+	questionCondition }
+  }),
+  askedIds: game.askedIds.map (questionId => normalizeStoredQuestionId (questionId)),
+  softenedQuestionIds: (game.softenedQuestionIds
+			.map (questionId => normalizeStoredQuestionId (questionId))),
+  recoveredCandidatePosts: (game.recoveredCandidatePosts ?? []).map (item => ({
+      ...item,
+      scoreAtRecovery: item.scoreAtRecovery ?? (
+	new Map (game.scores).get (item.postId) ?? 0) })),
+  recoveryStepCount: game.recoveryStepCount ?? 0,
+  winningRunTargetId: game.winningRunTargetId ?? null,
+  winningRunStartAnswerCount: game.winningRunStartAnswerCount ?? null,
+  learnedExampleCount: game.learnedExampleCount ?? null,
+  questionSuggestionEntryMode: game.questionSuggestionEntryMode ?? 'search',
+  questionSuggestionSearch: game.questionSuggestionSearch ?? '',
+  questionSuggestionSelectedId: game.questionSuggestionSelectedId ?? null,
+  askedQuestionBank: game.askedQuestionBank?.map (question => ({
+      ...question,
+      id: normalizeStoredQuestionId (question.id, question.condition),
+      condition: normalizeTitleLengthCondition (question.condition) })),
+  askedQuestionBankIds: (
+      game.askedQuestionBankIds?.map (questionId => normalizeStoredQuestionId (questionId))) })
+
+
+const sourcePriorityForMerge = (question: GekanatorQuestion): number => {
+  switch (question.source)
+  {
+  case 'user_suggested':
+    return 3
+  case 'admin_curated':
+    return 3
+  case 'ai_generated':
+    return 3
+  default:
+    return 1
+  }
+}
+
+
+const shouldReplaceMergedQuestion = (
+    current:    GekanatorQuestion | undefined,
+    candidate:  GekanatorQuestion,
+): boolean => {
+  if (!(current))
+    return true
+
+  const currentSourcePriority = sourcePriorityForMerge (current)
+  const candidateSourcePriority = sourcePriorityForMerge (candidate)
+  if (candidateSourcePriority !== currentSourcePriority)
+    return candidateSourcePriority > currentSourcePriority
+
+  if (candidate.priorityWeight !== current.priorityWeight)
+    return candidate.priorityWeight > current.priorityWeight
+
+  return true
+}
+
+
+const hashString = (value: string): number => {
+  let hash = 2_166_136_261
+
+  for (let i = 0; i < value.length; ++i)
+    {
+      hash ^= value.charCodeAt (i)
+      hash = Math.imul (hash, 16_777_619)
+    }
+
+  return hash >>> 0
+}
+
+
+const deterministicUnitFloat = (seed: string): number => hashString (seed) / 4_294_967_295
+
+
+const clearStoredGame = (): void => {
+  try
+  {
+    sessionStorage.removeItem (gameStorageKey)
+  }
+  catch
+  {
+    return
+  }
+}
+
+
+const loadStoredGame = (): StoredGekanatorGame | null => {
+  try
+  {
+    const raw = sessionStorage.getItem (gameStorageKey)
+    if (!(raw))
+      return null
+
+    return normalizeStoredGame (JSON.parse (raw) as StoredGekanatorGame)
+  }
+  catch
+  {
+    clearStoredGame ()
+    return null
+  }
+}
+
+
+const isStoredPhase = (phase: Phase): boolean => phase !== 'intro'
+
+
+const loadRecentGames = (): RecentGameSummary[] => {
+  try
+  {
+    const raw = localStorage.getItem (recentGamesStorageKey)
+    if (!(raw))
+      return []
+
+    const parsed = JSON.parse (raw)
+    if (!(Array.isArray (parsed)))
+      return []
+
+    return (
+	parsed
+	.filter ((item): item is RecentGameSummary => (
+	    typeof item === 'object'
+	    && item != null
+	    && Number.isInteger ((item as RecentGameSummary).correctPostId)
+	    && (((item as RecentGameSummary).firstQuestionId == null)
+		|| typeof (item as RecentGameSummary).firstQuestionId === 'string')
+	    && Number.isFinite ((item as RecentGameSummary).savedAt)))
+	.sort ((a, b) => b.savedAt - a.savedAt)
+	.slice (0, maxStoredRecentGames))
+  }
+  catch
+  {
+    return []
+  }
+}
+
+
+const storeRecentGameSummary = (
+    summary:  RecentGameSummary,
+): RecentGameSummary[] => {
+  const next =
+      [summary,
+       ...loadRecentGames ().filter (item => (item.savedAt !== summary.savedAt
+					      && !(item.correctPostId === summary.correctPostId
+						   && (item.firstQuestionId
+						       === summary.firstQuestionId))))]
+      .slice (0, maxStoredRecentGames)
+
+  try
+  {
+    localStorage.setItem (recentGamesStorageKey, JSON.stringify (next))
+  }
+  catch
+  {
+    return next
+  }
+
+  return next
+}
+
+
+const loadBackgroundMotionMode = (): BackgroundMotionMode => {
+  const fallbackMode = 'on'
+  try
+  {
+    const raw = localStorage.getItem (backgroundMotionStorageKey)
+    if (raw === 'off' || raw === 'calm' || raw === 'on')
+      return raw
+
+    return fallbackMode
+  }
+  catch
+  {
+    return fallbackMode
+  }
+}
+
+
+const resettableExtraQuestionState = (): {
+    extraQuestions:        GekanatorExtraQuestion[]
+    extraQuestionAnswers:  Record<string, GekanatorAnswerValue>
+    extraQuestionState:    'idle' } => (
+	{ extraQuestions: [],
+	  extraQuestionAnswers: { },
+	  extraQuestionState: 'idle' })
+
+
+const recoveredCandidateMapFromStored = (
+    items:   RecoveredCandidatePost[],
+    scores:  [number, number][],
+): Map<number, RecoveredCandidateState> => {
+  const storedScores = new Map (scores)
+
+  return new Map (items.map (item => [item.postId, {
+      answerCountAtRecovery: item.answerCountAtRecovery,
+      scoreAtRecovery: item.scoreAtRecovery ?? storedScores.get (item.postId) ?? 0 }]))
+}
+
+
+const storedRecoveredCandidatesFromMap = (
+    recoveredCandidatePosts: Map<number, RecoveredCandidateState>,
+): RecoveredCandidatePost[] =>
+    [...recoveredCandidatePosts.entries ()]
+    .map (([postId, recoveredCandidate]) => ({
+	postId,
+	answerCountAtRecovery: recoveredCandidate.answerCountAtRecovery,
+	scoreAtRecovery: recoveredCandidate.scoreAtRecovery }))
+
+
+const learnedSemanticMinKnownRatio = .08
+const learnedSemanticMinKnownCount = 4
+const learnedSemanticMinSideCount = 2
+const targetEffectiveUserSuggestedQuestionRatio = 1 / 3
+const targetLearningUserSuggestedQuestionRatio = 1 / 3
+const targetTotalUserSuggestedQuestionRatio = 2 / 3
+const scoreDropActivationThreshold = 20
+const learningUserSuggestedScoreWeight = .33
+
+
+const baseDeltaForAnswer = (answer: GekanatorAnswerValue): number => {
+  switch (answer)
+  {
+  case 'yes':
+    return 4
+  case 'no':
+    return -4
+  case 'partial':
+    return 2
+  case 'probably_no':
+    return -2
+  case 'unknown':
+    return 0
+  }
+}
+
+
+const distributionEntropy = (weights: number[]): number =>
+    weights.reduce ((sum, weight) => weight <= 0 ? sum : sum - weight * Math.log2 (weight), 0)
+
+
+const questionCategoryPenalty = (
+    question:       GekanatorQuestion,
+    answerCount:    number,
+    repeatPenalty:  number,
+): number => {
+  const earlyFactor = Math.max (0, (3 - answerCount) / 3)
+  const titleLengthPenalty = (() => {
+    if (titleLengthMinimumForCondition (question.condition) == null)
+      return 0
+
+    return (answerCount === 0 ? 8 : 3.5) * earlyFactor
+  }) ()
+
+  switch (question.kind)
+  {
+  case 'tag':
+    return -2.8 * earlyFactor + repeatPenalty
+  case 'post_similarity':
+    return -3.2 * earlyFactor + repeatPenalty
+  case 'title':
+    return 3.4 * earlyFactor + titleLengthPenalty + repeatPenalty
+  case 'source':
+  case 'original_date':
+    return 2.4 * earlyFactor + repeatPenalty
+  default:
+    return repeatPenalty
+  }
+}
+
+
+const relatedPostIdsOf = (post: Post): number[] => {
+  const siblingPosts = Object.values (post.siblingPosts ?? { }).flat ()
+
+  return [...new Set ([
+	  ...(post.related ?? []).map (related => related.id),
+	  ...(post.parentPosts ?? []).map (parent => parent.id),
+	  ...(post.childPosts ?? []).map (child => child.id),
+	  ...siblingPosts.map (sibling => sibling.id)])]
+}
+
+
+const userPriorWeightsFor = (
+    posts:        Post[],
+    recentGames:  RecentGameSummary[],
+): Map<number, number> => {
+  const postById = new Map (posts.map (post => [post.id, post]))
+  const weights = new Map<number, number> ()
+  const addWeight = (postId: number, weight: number) => {
+    if (!(postById.has (postId)) || weight <= 0)
+      return
+
+    weights.set (postId, (weights.get (postId) ?? 0) + weight)
+  }
+
+  recentGames.slice (0, 6).forEach ((game, index) => {
+    const baseWeight = Math.max (.24, 1 - index * .18)
+    addWeight (game.correctPostId, baseWeight)
+
+    const correctPost = postById.get (game.correctPostId)
+    if (!(correctPost))
+      return
+
+    relatedPostIdsOf (correctPost).forEach (postId => addWeight (postId, baseWeight * .45))
+  })
+
+  return weights
+}
+
+
+const answerWeightFor = (
+    questionId:           string,
+    softenedQuestionIds:  Set<string>,
+): number => softenedQuestionIds.has (questionId) ? softenedAnswerWeight : 1
+
+
+const scoreWeightForAnswer = (
+    answer:               GekanatorAnswerLog,
+    softenedQuestionIds:  Set<string>,
+): number =>
+    answerWeightFor (answer.questionId, softenedQuestionIds)
+    * (
+	answer.questionPurpose === 'learning_user_suggested'
+	? learningUserSuggestedScoreWeight
+	: 1)
+
+
+const questionDifficulty = (question: GekanatorQuestion): number => {
+  if (question.kind === 'source')
+    return 4
+  if (question.kind === 'original_date')
+    return 4
+  if (question.kind === 'title')
+    return 4
+  if (question.kind === 'tag')
+    return 3
+
+  return 1
+}
+
+
+type GekanatorMatchIndex = Map<string, Set<number>>
+
+type GekanatorQuestionMaterialIndex = {
+    postById:                    Map<number, Post>
+    tagKeysByPostId:             Map<number, string[]>
+    postIdsByTagKey:             Map<string, Set<number>>
+    titleTermsByPostId:          Map<number, string[]>
+    postIdsByTitleTerm:          Map<string, Set<number>>
+    hostByPostId:                Map<number, string | null>
+    postIdsByHost:               Map<string, Set<number>>
+    originalYearByPostId:        Map<number, number | null>
+    postIdsByOriginalYear:       Map<number, Set<number>>
+    originalMonthByPostId:       Map<number, number | null>
+    postIdsByOriginalMonth:      Map<number, Set<number>>
+    originalMonthDayByPostId:    Map<number, string | null>
+    postIdsByOriginalMonthDay:   Map<string, Set<number>>
+    titleLengthByPostId:         Map<number, number>
+    titleAsciiPostIds:           Set<number>
+    titleLengthThresholdCache:   Map<number, Set<number>>
+}
+
+const titleTermPattern =
+    /[\p{Script=Han}\p{Script=Hiragana}\p{Script=Katakana}A-Za-z0-9]{2,}/gu
+
+
+const addPostIdToIndex = <K extends string | number> (
+    index:   Map<K, Set<number>>,
+    key:     K,
+    postId:  number,
+) => {
+  const current = index.get (key)
+  if (current)
+    {
+      current.add (postId)
+      return
+    }
+
+  index.set (key, new Set ([postId]))
+}
+
+
+const buildMaterialIndex = (
+    posts:  Post[],
+): GekanatorQuestionMaterialIndex => {
+  const postById = new Map<number, Post> ()
+  const tagKeysByPostId = new Map<number, string[]> ()
+  const postIdsByTagKey = new Map<string, Set<number>> ()
+  const titleTermsByPostId = new Map<number, string[]> ()
+  const postIdsByTitleTerm = new Map<string, Set<number>> ()
+  const hostByPostId = new Map<number, string | null> ()
+  const postIdsByHost = new Map<string, Set<number>> ()
+  const originalYearByPostId = new Map<number, number | null> ()
+  const postIdsByOriginalYear = new Map<number, Set<number>> ()
+  const originalMonthByPostId = new Map<number, number | null> ()
+  const postIdsByOriginalMonth = new Map<number, Set<number>> ()
+  const originalMonthDayByPostId = new Map<number, string | null> ()
+  const postIdsByOriginalMonthDay = new Map<string, Set<number>> ()
+  const titleLengthByPostId = new Map<number, number> ()
+  const titleAsciiPostIds = new Set<number> ()
+
+  posts.forEach (post => {
+    postById.set (post.id, post)
+
+    const tagKeys = post.tags
+	.filter (tag =>
+	    tag.category !== 'meta'
+	    && !(tag.name.includes ('タグ希望'))
+	    && !(tag.name.includes ('bot操作')))
+	.map (tag => `${ tag.category }:${ tag.name }`)
+    tagKeysByPostId.set (post.id, tagKeys)
+    tagKeys.forEach (key => addPostIdToIndex (postIdsByTagKey, key, post.id))
+
+    const titleTerms = Array.from (
+	new Set ((post.title ?? '').match (titleTermPattern) ?? []))
+    titleTermsByPostId.set (post.id, titleTerms)
+    titleTerms.forEach (term => addPostIdToIndex (postIdsByTitleTerm, term, post.id))
+
+    const host = (() => {
+      try
+      {
+	return new URL (post.url).hostname.replace (/^www\./, '')
+      }
+      catch
+      {
+	return null
+      }
+    }) ()
+    hostByPostId.set (post.id, host)
+    if (host)
+      addPostIdToIndex (postIdsByHost, host, post.id)
+
+    const originalValue = post.originalCreatedFrom || post.originalCreatedBefore
+    const date =
+	originalValue
+	? new Date (originalValue)
+	: null
+    const validDate =
+	date && !(Number.isNaN (date.getTime ()))
+	? date
+	: null
+    const originalYear = validDate?.getFullYear () ?? null
+    const originalMonth =
+	validDate
+	? validDate.getMonth () + 1
+	: null
+    const originalMonthDay =
+	validDate
+	? `${ validDate.getMonth () + 1 }-${ validDate.getDate () }`
+	: null
+    originalYearByPostId.set (post.id, originalYear)
+    originalMonthByPostId.set (post.id, originalMonth)
+    originalMonthDayByPostId.set (post.id, originalMonthDay)
+    if (originalYear != null)
+      addPostIdToIndex (postIdsByOriginalYear, originalYear, post.id)
+    if (originalMonth != null)
+      addPostIdToIndex (postIdsByOriginalMonth, originalMonth, post.id)
+    if (originalMonthDay != null)
+      addPostIdToIndex (postIdsByOriginalMonthDay, originalMonthDay, post.id)
+
+    const titleLength = post.title?.length ?? 0
+    titleLengthByPostId.set (post.id, titleLength)
+    if (/[A-Za-z0-9]/.test (post.title ?? ''))
+      titleAsciiPostIds.add (post.id)
+  })
+
+  return {
+      postById,
+      tagKeysByPostId,
+      postIdsByTagKey,
+      titleTermsByPostId,
+      postIdsByTitleTerm,
+      hostByPostId,
+      postIdsByHost,
+      originalYearByPostId,
+      postIdsByOriginalYear,
+      originalMonthByPostId,
+      postIdsByOriginalMonth,
+      originalMonthDayByPostId,
+      postIdsByOriginalMonthDay,
+      titleLengthByPostId,
+      titleAsciiPostIds,
+      titleLengthThresholdCache: new Map<number, Set<number>> () }
+}
+
+const indexedQuestionTextForTag = (key: string): string => {
+  const [category, ...rest] = key.split (':')
+  const name = rest.join (':')
+  const label = category === 'nico' ? name.replace (/^nico:/, '') : name
+
+  switch (category)
+  {
+  case 'deerjikist':
+    return `${ label }（敬称略）がコンテンツ作成に関与した?`
+  case 'meme':
+    return `『${ label }』に関係しそう?`
+  case 'character':
+    return `${ label }が登場する?`
+  case 'material':
+    return `${ label }が使われている?`
+  case 'nico':
+    return `ニコニコに「${ label }」というタグがついている?`
+  default:
+    return `${ label }の要素が含まれる?`
+  }
+}
+
+const specialOriginalMonthDayLabelFor = (monthDay: string): string | null =>
+    specialOriginalMonthDayLabels[monthDay] ?? null
+
+
+const originalDateQuestionTextFor = (
+    condition:  Extract<
+	GekanatorQuestionCondition,
+	{ type: 'original-year' | 'original-month' | 'original-month-day' }
+    >,
+): string => {
+  switch (condition.type)
+  {
+  case 'original-year':
+    return `オリジナルの投稿年は ${ condition.year } 年?`
+  case 'original-month':
+    return `オリジナルの投稿月は ${ condition.month } 月?`
+  case 'original-month-day':
+    {
+      const label = specialOriginalMonthDayLabelFor (condition.monthDay)
+      if (label)
+	return `${ label }に投稿された?`
+
+      const [month, day] = condition.monthDay.split ('-')
+      return `オリジナルの投稿日は ${ month } 月 ${ day } 日?`
+    }
+  }
+}
+
+
+const humanPriorityOffsetFor = (question: GekanatorQuestion): number => {
+  switch (question.kind)
+  {
+  case 'tag':
+    return -6
+  case 'source':
+    return -2.5
+  case 'post_similarity':
+    if (question.source === 'user_suggested' || question.source === 'admin_curated')
+      return -3.5
+
+    return -1.5
+  case 'original_date':
+    switch (question.condition.type)
+    {
+    case 'original-year':
+      return -2
+    case 'original-month-day':
+      return specialOriginalMonthDayLabelFor (question.condition.monthDay) ? -1.4 : 6
+    case 'original-month':
+      return 7
+    default:
+      return 0
+    }
+  case 'title':
+    switch (question.condition.type)
+    {
+    case 'title-contains':
+      return -1.8
+    case 'title-has-ascii':
+      return 10
+    case 'title-length-at-least':
+    case 'title-length-greater-than':
+      return 9
+    default:
+      return 0
+    }
+  default:
+    return 0
+  }
+}
+
+
+const isLearnableTagKey = (key: string): boolean => !(key.startsWith ('nico:'))
+
+
+const isUserSuggestedLearnedSemanticQuestion = (
+    question:  GekanatorQuestion,
+): boolean => isLearnedSemanticQuestion (question)
+
+
+type LearnedSemanticCandidateStats = {
+    positiveIds:    Set<number>
+    negativeIds:    Set<number>
+    unknownIds:     Set<number>
+    positiveCount:  number
+    negativeCount:  number
+    unknownCount:   number
+    knownCount:     number }
+
+
+const learnedSemanticStatsForCandidateIds = (
+    { candidateIds,
+      posts,
+      question }: {
+	candidateIds:  number[]
+	posts:         Post[]
+	question:      GekanatorQuestion },
+): LearnedSemanticCandidateStats => {
+  const candidateIdSet = new Set (candidateIds)
+  const positiveIds = new Set<number> ()
+  const negativeIds = new Set<number> ()
+  const unknownIds = new Set<number> ()
+
+  posts.forEach (post => {
+    if (!(candidateIdSet.has (post.id)))
+      return
+
+    const side = learnedSemanticSideForPost (question, post)
+    if (side === 'positive')
+      {
+	positiveIds.add (post.id)
+	return
+      }
+    if (side === 'negative')
+      {
+	negativeIds.add (post.id)
+	return
+      }
+
+    unknownIds.add (post.id)
+  })
+
+  return {
+      positiveIds,
+      negativeIds,
+      unknownIds,
+      positiveCount: positiveIds.size,
+      negativeCount: negativeIds.size,
+      unknownCount: unknownIds.size,
+      knownCount: positiveIds.size + negativeIds.size }
+}
+
+
+const learnedSemanticQuestionIsEffectiveForCandidateIds = (
+    { candidateIds,
+      posts,
+      question }: {
+	candidateIds:  number[]
+	posts:         Post[]
+	question:      GekanatorQuestion },
+): boolean => {
+  if (!(isUserSuggestedLearnedSemanticQuestion (question)))
+    return false
+
+  const stats = learnedSemanticStatsForCandidateIds ({
+      candidateIds,
+      posts,
+      question })
+  const minimumKnownCount = Math.max (
+      learnedSemanticMinKnownCount,
+      Math.floor (candidateIds.length * learnedSemanticMinKnownRatio))
+
+  return stats.knownCount >= minimumKnownCount
+      && stats.positiveCount >= learnedSemanticMinSideCount
+      && stats.negativeCount >= learnedSemanticMinSideCount
+}
+
+
+const directSemanticAnswerForPost = (
+    question:  GekanatorQuestion,
+    post:      Post,
+): GekanatorAnswerValue | null => {
+  const direct = question.exampleAnswers?.[String (post.id) as `${ number }`]
+  if (direct)
+    return direct
+  if (question.condition.type === 'post-similarity' && question.condition.postId === post.id)
+    return question.condition.answer
+
+  return null
+}
+
+
+const learnedSemanticLearningValueForTopPosts = (
+    { question,
+      learningTargetPosts,
+      candidateIds,
+      posts }: {
+	question:      GekanatorQuestion
+	learningTargetPosts: Post[]
+	candidateIds:  number[]
+	posts:         Post[] },
+): { missingTopCount: number
+     knownCount:      number
+     hasLearningValue: boolean } => {
+  const missingTopCount =
+      learningTargetPosts.filter (
+	  post => directSemanticAnswerForPost (question, post) == null).length
+  const knownCount = learnedSemanticStatsForCandidateIds ({
+      candidateIds,
+      posts,
+      question }).knownCount
+
+  return {
+      missingTopCount,
+      knownCount,
+      hasLearningValue: missingTopCount > 0 }
+}
+
+
+const learningTargetPostsForCandidates = ({
+    scoredPosts,
+    gameSeed,
+}: {
+    scoredPosts:  { post: Post; score: number }[]
+    gameSeed:     string
+}): Post[] => {
+  const topPosts = scoredPosts
+      .slice (0, Math.min (6, scoredPosts.length))
+      .map (item => item.post)
+  const topPostIds = new Set (topPosts.map (post => post.id))
+  const sampledPosts = scoredPosts
+      .filter (item => !(topPostIds.has (item.post.id)))
+      .map (item => ({
+	  post: item.post,
+	  weight: deterministicUnitFloat (`${ gameSeed }:learning-sample:${ item.post.id }`) }))
+      .sort ((a, b) => a.weight - b.weight)
+      .slice (0, Math.min (4, Math.max (0, scoredPosts.length - topPosts.length)))
+      .map (item => item.post)
+
+  return [...topPosts, ...sampledPosts]
+}
+
+
+const questionPurposeCountsFor = (
+    answers:  GekanatorAnswerLog[],
+): {
+    effectiveUserSuggestedCount: number
+    learningUserSuggestedCount:  number
+    normalQuestionCount:         number
+    totalNormalPhaseQuestionCount: number
+    totalUserSuggestedCount:     number } => {
+  let effectiveUserSuggestedCount = 0
+  let learningUserSuggestedCount = 0
+  let normalQuestionCount = 0
+
+  answers.forEach (answer => {
+    if (answer.questionMode !== 'normal')
+      return
+
+    switch (answer.questionPurpose)
+    {
+    case 'effective_user_suggested':
+      ++effectiveUserSuggestedCount
+      return
+    case 'learning_user_suggested':
+      ++learningUserSuggestedCount
+      return
+    default:
+      ++normalQuestionCount
+    }
+  })
+
+  return {
+      effectiveUserSuggestedCount,
+      learningUserSuggestedCount,
+      normalQuestionCount,
+      totalNormalPhaseQuestionCount:
+	  effectiveUserSuggestedCount + learningUserSuggestedCount + normalQuestionCount,
+      totalUserSuggestedCount:
+	  effectiveUserSuggestedCount + learningUserSuggestedCount }
+}
+
+
+const learnedSemanticNarrowPenaltyForStats = (
+    candidateCount:  number,
+    stats:           LearnedSemanticCandidateStats,
+): number => {
+  const minSide = candidateCount < 10 ? 1 : Math.max (3, candidateCount * .08)
+  return stats.positiveCount < minSide || stats.negativeCount < minSide ? .15 : 0
+}
+
+
+const learnedSemanticScoreDeltaForExpectedAnswer = (
+    userAnswer:      GekanatorAnswerValue,
+    expectedAnswer:  GekanatorAnswerValue | null,
+): number => {
+  switch (userAnswer)
+  {
+  case 'yes':
+    if (expectedAnswer === 'yes' || expectedAnswer === 'partial')
+      return 4
+    if (expectedAnswer === 'no' || expectedAnswer === 'probably_no')
+      return -4
+    return 0
+  case 'no':
+    if (expectedAnswer === 'yes' || expectedAnswer === 'partial')
+      return -4
+    if (expectedAnswer === 'no' || expectedAnswer === 'probably_no')
+      return 4
+    return 0
+  case 'partial':
+    if (expectedAnswer === 'yes' || expectedAnswer === 'partial')
+      return 2
+    if (expectedAnswer === 'no')
+      return -2
+    if (expectedAnswer === 'probably_no')
+      return -1
+    return 0
+  case 'probably_no':
+    if (expectedAnswer === 'yes' || expectedAnswer === 'partial')
+      return -2
+    if (expectedAnswer === 'no' || expectedAnswer === 'probably_no')
+      return 1
+    return 0
+  case 'unknown':
+    return 0
+  }
+}
+
+
+const scoreDropDeltaForRecoveredPost = (
+    postId:                   number,
+    totalScore:               number,
+    recoveredCandidatePosts:  Map<number, RecoveredCandidateState>,
+): number => {
+  const recoveredCandidate = recoveredCandidatePosts.get (postId)
+  if (recoveredCandidate == null)
+    return totalScore
+
+  return totalScore - recoveredCandidate.scoreAtRecovery
+}
+
+
+const activeCandidateScoreDropEnabled = (scores: Map<number, number>): boolean => {
+  if (scores.size === 0)
+    return false
+
+  const maxScore = Math.max (...scores.values ())
+  return maxScore >= scoreDropActivationThreshold
+}
+
+
+const postPassesScoreDrop = (
+    { postId,
+      scores,
+      recoveredCandidatePosts }: {
+	postId:                   number
+	scores:                   Map<number, number>
+	recoveredCandidatePosts:  Map<number, RecoveredCandidateState> },
+): boolean => {
+  if (!(activeCandidateScoreDropEnabled (scores)))
+    return true
+
+  const totalScore = scores.get (postId) ?? 0
+  return scoreDropDeltaForRecoveredPost (
+      postId,
+      totalScore,
+      recoveredCandidatePosts) >= 0
+}
+
+
+// `post_similarities` is the score-propagation graph, not the question kind.
+const questionUsesPostSimilarityPropagationGraphForScoring = (
+    question:  GekanatorQuestion,
+): boolean =>
+    (question.kind === 'post_similarity'
+     && !(isUserSuggestedLearnedSemanticQuestion (question)))
+      || (question.kind === 'tag'
+	  && question.condition.type === 'tag'
+	  && !(question.condition.key.startsWith ('nico:')))
+
+
+const questionSupportsAnswerBasedHardFiltering = (
+    question:  GekanatorQuestion,
+): boolean => !(questionUsesPostSimilarityPropagationGraphForScoring (question))
+    && !(isUserSuggestedLearnedSemanticQuestion (question))
+
+
+const isLearnableQuestionForUserAnswer = (question: GekanatorQuestion): boolean =>
+    question.kind === 'post_similarity'
+      || (question.kind === 'tag'
+	  && question.condition.type === 'tag'
+	  && isLearnableTagKey (question.condition.key))
+
+
+const usesLearnedTagExamples = (question: GekanatorQuestion): boolean =>
+    question.kind === 'tag'
+      && question.condition.type === 'tag'
+      && Boolean (question.exampleAnswers)
+      && Object.keys (question.exampleAnswers ?? { }).length > 0
+
+
+const searchedQuestionsFor = (
+    questions:  GekanatorQuestion[],
+    search:     string,
+): GekanatorQuestion[] => {
+  const needle = search.trim ()
+  if (!(needle))
+    return []
+
+  const normalizedNeedle = needle.toLowerCase ()
+  const prefixMatches = questions.filter (question =>
+      isLearnableQuestionForUserAnswer (question)
+      && question.text.toLowerCase ().startsWith (normalizedNeedle))
+  const partialMatches = questions.filter (question =>
+      isLearnableQuestionForUserAnswer (question)
+      && !(question.text.toLowerCase ().startsWith (normalizedNeedle))
+      && question.text.toLowerCase ().includes (normalizedNeedle))
+
+  return [...prefixMatches, ...partialMatches].slice (0, 20)
+}
+
+const matchingPostIdsForCondition = ({
+    condition,
+    materialIndex,
+}: {
+    condition:      GekanatorQuestionCondition
+    materialIndex:  GekanatorQuestionMaterialIndex
+}): Set<number> | null => {
+  switch (condition.type)
+  {
+  case 'tag':
+    return materialIndex.postIdsByTagKey.get (condition.key) ?? new Set<number> ()
+  case 'source':
+    return materialIndex.postIdsByHost.get (condition.host) ?? new Set<number> ()
+  case 'original-year':
+    return materialIndex.postIdsByOriginalYear.get (condition.year) ?? new Set<number> ()
+  case 'original-month':
+    return materialIndex.postIdsByOriginalMonth.get (condition.month) ?? new Set<number> ()
+  case 'original-month-day':
+    return materialIndex.postIdsByOriginalMonthDay.get (condition.monthDay) ?? new Set<number> ()
+  case 'title-has-ascii':
+    return materialIndex.titleAsciiPostIds
+  case 'title-contains':
+    return materialIndex.postIdsByTitleTerm.get (condition.text) ?? new Set<number> ()
+  case 'title-length-at-least':
+  case 'title-length-greater-than': {
+    const threshold =
+	titleLengthMinimumForCondition (condition)
+    if (threshold == null)
+      return new Set<number> ()
+
+    const cached = materialIndex.titleLengthThresholdCache.get (threshold)
+    if (cached)
+      return cached
+
+    const matched = new Set<number> ()
+    materialIndex.titleLengthByPostId.forEach ((length, postId) => {
+      if (length >= threshold)
+	matched.add (postId)
+    })
+    materialIndex.titleLengthThresholdCache.set (threshold, matched)
+    return matched
+  }
+  case 'post-similarity':
+    return null
+  }
+}
+
+type QuestionMatchResolver = {
+    posts:              Post[]
+    materialIndex:      GekanatorQuestionMaterialIndex
+    matchIndex:         GekanatorMatchIndex
+    question:           GekanatorQuestion
+    dynamicMatchIndex?: GekanatorMatchIndex
+}
+
+const buildGekanatorMatchIndex = (
+    posts:      Post[],
+    questions:  GekanatorQuestion[],
+): GekanatorMatchIndex => new Map (
+    questions.map (question => [
+	question.id,
+	new Set (
+	    posts
+		.filter (post => question.test (post))
+		.map (post => post.id))]))
+
+const matchingPostIdsForQuestion = ({
+    posts,
+    materialIndex,
+    matchIndex,
+    question,
+    dynamicMatchIndex,
+}: QuestionMatchResolver): Set<number> => {
+  if (usesLearnedTagExamples (question))
+    {
+      const matched = matchIndex.get (question.id) ?? dynamicMatchIndex?.get (question.id)
+      if (matched)
+	return matched
+
+      const computed = new Set (
+	  posts
+	      .filter (post => question.test (post))
+	      .map (post => post.id))
+      dynamicMatchIndex?.set (question.id, computed)
+      return computed
+    }
+
+  const byCondition = matchingPostIdsForCondition ({
+      condition: question.condition,
+      materialIndex })
+  if (byCondition != null)
+    return byCondition
+
+  const matched = matchIndex.get (question.id) ?? dynamicMatchIndex?.get (question.id)
+  if (matched)
+    return matched
+
+  const computed = new Set (
+      posts
+	  .filter (post => question.test (post))
+	  .map (post => post.id))
+  dynamicMatchIndex?.set (question.id, computed)
+  return computed
+}
+
+
+const positiveMatchingPostIdsForQuestion = (
+    resolver:  QuestionMatchResolver,
+): Set<number> => {
+  if (isUserSuggestedLearnedSemanticQuestion (resolver.question))
+    {
+      const cached = resolver.dynamicMatchIndex?.get (resolver.question.id)
+      if (cached)
+	return cached
+
+      const computed = new Set (
+	  resolver.posts
+	      .filter (post =>
+		  learnedSemanticSideForPost (resolver.question, post) === 'positive')
+	      .map (post => post.id))
+      resolver.dynamicMatchIndex?.set (resolver.question.id, computed)
+      return computed
+    }
+
+  return matchingPostIdsForQuestion (resolver)
+}
+
+const matchingPostCountInIds = ({
+    candidateIds,
+    candidateIdSet,
+    posts,
+    materialIndex,
+    matchIndex,
+    question,
+    dynamicMatchIndex,
+}: {
+    candidateIds:       number[]
+    candidateIdSet?:    Set<number>
+    posts:              Post[]
+    materialIndex:      GekanatorQuestionMaterialIndex
+    matchIndex:         GekanatorMatchIndex
+    question:           GekanatorQuestion
+    dynamicMatchIndex?: GekanatorMatchIndex
+}): number => {
+  const matched = positiveMatchingPostIdsForQuestion ({
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex })
+  const ids = candidateIdSet ?? new Set (candidateIds)
+  let count = 0
+
+  if (matched.size < ids.size)
+    matched.forEach (postId => {
+      if (ids.has (postId))
+	++count
+    })
+  else
+    ids.forEach (postId => {
+      if (matched.has (postId))
+	++count
+    })
+
+  return count
+}
+
+const matchingWeightInCandidates = (
+    { candidates,
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex }: { candidates:          { post: Post; weight: number }[]
+			     posts:               Post[]
+			     materialIndex:       GekanatorQuestionMaterialIndex
+			     matchIndex:          GekanatorMatchIndex
+			     question:            GekanatorQuestion
+			     dynamicMatchIndex?:  GekanatorMatchIndex },
+): number => {
+  const matched = positiveMatchingPostIdsForQuestion ({
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex })
+
+  return candidates.reduce ((sum, item) =>
+      sum + (matched.has (item.post.id) ? item.weight : 0), 0)
+}
+
+const signatureForCandidateIds = (
+    { candidateIds,
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex, }: { candidateIds:       number[]
+			      posts:              Post[]
+			      materialIndex:      GekanatorQuestionMaterialIndex
+			      matchIndex:         GekanatorMatchIndex
+			      question:           GekanatorQuestion
+			      dynamicMatchIndex?: GekanatorMatchIndex },
+): string => {
+  if (isUserSuggestedLearnedSemanticQuestion (question))
+    {
+      const postById = new Map (posts.map (post => [post.id, post]))
+
+      return candidateIds.map (postId => {
+	const post = postById.get (postId) ?? null
+	const side = learnedSemanticSideForPost (question, post)
+	if (side === 'positive')
+	  return '1'
+	if (side === 'negative')
+	  return '0'
+
+	return 'u'
+      }).join ('')
+    }
+
+  const matched = positiveMatchingPostIdsForQuestion ({
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex })
+
+  return candidateIds.map (postId => matched.has (postId) ? '1' : '0').join ('')
+}
+
+const postIdsForHardAnswer = (
+    { candidateIds,
+      question,
+      answer,
+      posts,
+      materialIndex,
+      matchIndex,
+      dynamicMatchIndex }: { candidateIds:        number[]
+			     question:            GekanatorQuestion
+			     answer:              GekanatorAnswerValue
+			     posts:               Post[]
+			     materialIndex:       GekanatorQuestionMaterialIndex
+			     matchIndex:          GekanatorMatchIndex
+			     dynamicMatchIndex?:  GekanatorMatchIndex },
+): number[] => {
+  if (!(questionSupportsAnswerBasedHardFiltering (question)))
+    return candidateIds
+
+  if (answer === 'unknown'
+      || answer === 'partial'
+      || answer === 'probably_no')
+    return candidateIds
+
+  if (answer === 'yes')
+    {
+      const matched = positiveMatchingPostIdsForQuestion ({
+	  posts,
+	  materialIndex,
+	  matchIndex,
+	  question,
+	  dynamicMatchIndex })
+      return candidateIds.filter (postId => matched.has (postId))
+    }
+
+  if (answer === 'no')
+    {
+      const matched = positiveMatchingPostIdsForQuestion ({
+	  posts,
+	  materialIndex,
+	  matchIndex,
+	  question,
+	  dynamicMatchIndex })
+      return candidateIds.filter (postId => !(matched.has (postId)))
+    }
+
+  return candidateIds
+}
+
+
+const applyQuestionAnswerDeltaToScores = ({
+    posts,
+    question,
+    answer,
+    weight,
+    nextScores,
+    materialIndex,
+    matchIndex,
+    dynamicMatchIndex,
+}: {
+    posts:              Post[]
+    question:           GekanatorQuestion
+    answer:             GekanatorAnswerValue
+    weight:             number
+    nextScores:         Map<number, number>
+    materialIndex:      GekanatorQuestionMaterialIndex
+    matchIndex:         GekanatorMatchIndex
+    dynamicMatchIndex:  GekanatorMatchIndex
+}): void => {
+  if (isUserSuggestedLearnedSemanticQuestion (question))
+    {
+      posts.forEach (post => {
+	const delta = learnedSemanticScoreDeltaForExpectedAnswer (
+	    answer,
+	    expectedAnswerForQuestion (question, post))
+	if (delta === 0)
+	  return
+
+	nextScores.set (
+	    post.id,
+	    (nextScores.get (post.id) ?? 0) + delta * weight)
+      })
+      return
+    }
+
+  const baseDelta = baseDeltaForAnswer (answer) * weight
+  if (baseDelta === 0)
+    return
+
+  if (!(questionUsesPostSimilarityPropagationGraphForScoring (question)))
+    {
+      posts.forEach (post => {
+	const delta = learnedSemanticScoreDeltaForExpectedAnswer (
+	    answer,
+	    expectedAnswerForQuestion (question, post))
+	if (delta === 0)
+	  return
+
+	nextScores.set (
+	    post.id,
+	    (nextScores.get (post.id) ?? 0) + delta * weight)
+      })
+      return
+    }
+
+  const matched = positiveMatchingPostIdsForQuestion ({
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex })
+
+  matched.forEach (postId => {
+    nextScores.set (
+	postId,
+	(nextScores.get (postId) ?? 0) + baseDelta)
+  })
+
+  // `post_similarities` is the propagation graph. Directly matched posts
+  // get only the base delta; only non-direct neighbors get `base delta * cos`.
+  // When several matched posts point at the same neighbor, keep the largest
+  // absolute propagated contribution instead of summing all of them.
+  const propagatedDeltaByPostId = new Map<number, number> ()
+  matched.forEach (postId => {
+    const post = materialIndex.postById.get (postId)
+    post?.postSimilarityEdges?.forEach (edge => {
+      if (!Number.isFinite (edge.cos) || edge.cos <= 0)
+	return
+      if (matched.has (edge.targetPostId))
+	return
+
+      const propagatedDelta = baseDelta * edge.cos
+      const current = propagatedDeltaByPostId.get (edge.targetPostId)
+      if (current == null || Math.abs (propagatedDelta) > Math.abs (current))
+	propagatedDeltaByPostId.set (edge.targetPostId, propagatedDelta)
+    })
+  })
+
+  propagatedDeltaByPostId.forEach ((propagatedDelta, postId) => {
+    nextScores.set (
+	postId,
+	(nextScores.get (postId) ?? 0) + propagatedDelta)
+  })
+}
+
+const buildIndexedQuestion = (
+    { condition,
+      text,
+      kind,
+      priorityWeight,
+      materialIndex }: {
+	condition:      Exclude<GekanatorQuestionCondition, { type: 'post-similarity' }>
+	text:           string
+	kind:           GekanatorQuestionKind
+	priorityWeight: number
+	materialIndex:  GekanatorQuestionMaterialIndex },
+): GekanatorQuestion => ({
+    id: questionIdForCondition (condition),
+    text,
+    kind,
+    condition,
+    source: 'default',
+    priorityWeight,
+    test: post =>
+	(matchingPostIdsForCondition ({
+	    condition,
+	    materialIndex }) ?? new Set<number> ()).has (post.id) })
+
+const rankedEntriesForCounts = <T extends string | number> (
+    { counts, total, cap }: { counts:  Map<T, number>
+			      total:   number
+    			      cap:     number },
+): [T, number][] =>
+    ([...counts.entries ()]
+     .filter (([, count]) => count > 0 && count < total)
+     .sort ((a, b) => Math.abs (total / 2 - a[1]) - Math.abs (total / 2 - b[1]))
+     .slice (0, cap))
+
+const buildQuestionsForCandidateIds = (
+    { candidateIds,
+      materialIndex,
+      acceptedQuestions,
+      mode = 'split',
+      confirmationPostId = null }: { candidateIds:      number[]
+				     materialIndex:     GekanatorQuestionMaterialIndex
+				     acceptedQuestions: GekanatorQuestion[]
+				     mode?:            QuestionBuildMode
+				     confirmationPostId?: number | null },
+): GekanatorQuestion[] => {
+  const total = candidateIds.length
+  const confirmationPost = (() => {
+    if (confirmationPostId == null)
+      return null
+
+    return materialIndex.postById.get (confirmationPostId) ?? null
+  }) ()
+
+  if (mode === 'split' && total === 0)
+    return acceptedQuestions
+  if (mode === 'confirmation' && confirmationPost == null)
+    return acceptedQuestions
+
+  const tagCounts = new Map<string, number> ()
+  const hostCounts = new Map<string, number> ()
+  const yearCounts = new Map<number, number> ()
+  const monthDayCounts = new Map<string, number> ()
+  const titleTermCounts = new Map<string, number> ()
+  const titleLengths: number[] = []
+  let asciiCount = 0
+
+  candidateIds.forEach (postId => {
+    materialIndex.tagKeysByPostId.get (postId)?.forEach (key =>
+	tagCounts.set (key, (tagCounts.get (key) ?? 0) + 1))
+    const host = materialIndex.hostByPostId.get (postId)
+    if (host)
+      hostCounts.set (host, (hostCounts.get (host) ?? 0) + 1)
+    const year = materialIndex.originalYearByPostId.get (postId)
+    if (year != null)
+      yearCounts.set (year, (yearCounts.get (year) ?? 0) + 1)
+    const monthDay = materialIndex.originalMonthDayByPostId.get (postId)
+    if (monthDay)
+      monthDayCounts.set (monthDay, (monthDayCounts.get (monthDay) ?? 0) + 1)
+    materialIndex.titleTermsByPostId.get (postId)?.forEach (term =>
+	titleTermCounts.set (term, (titleTermCounts.get (term) ?? 0) + 1))
+    const titleLength = materialIndex.titleLengthByPostId.get (postId) ?? 0
+    titleLengths.push (titleLength)
+    if (materialIndex.titleAsciiPostIds.has (postId))
+      ++asciiCount
+  })
+
+  const tagCap = total >= 120 ? 128 : 96
+  const titleTermCap = total >= 80 ? 10 : total >= 24 ? 14 : 20
+  const factCap = total >= 80 ? 8 : 12
+  const sortedLengths = [...titleLengths].sort ((a, b) => a - b)
+  const titleLengthMedian = sortedLengths[Math.floor (sortedLengths.length / 2)] ?? 0
+
+  const questions: GekanatorQuestion[] = []
+  const addQuestion = (question: GekanatorQuestion | null) => {
+    if (question)
+      questions.push (question)
+  }
+  const buildDateQuestion = (
+      condition: Extract<
+	  GekanatorQuestionCondition,
+	  { type: 'original-year' | 'original-month' | 'original-month-day' }
+      >,
+  ): GekanatorQuestion => {
+    const priorityWeight = (() => {
+      if (condition.type === 'original-year')
+	return 1.04
+      if (condition.type === 'original-month-day')
+	return 1.01
+
+      return .92
+    }) ()
+
+    return buildIndexedQuestion ({
+      condition,
+      text: originalDateQuestionTextFor (condition),
+      kind: 'original_date',
+      priorityWeight,
+      materialIndex })
+  }
+  const specialMonthDays = rankedEntriesForCounts ({
+      counts: monthDayCounts,
+      total,
+      cap: factCap
+  }).filter (([monthDay]) => specialOriginalMonthDayLabelFor (String (monthDay)) != null)
+
+  if (mode === 'split')
+    {
+      rankedEntriesForCounts ({ counts: tagCounts, total, cap: tagCap })
+	  .forEach (([key]) => {
+	    addQuestion (buildIndexedQuestion ({
+		condition: { type: 'tag', key },
+		text: indexedQuestionTextForTag (key),
+		kind: 'tag',
+		priorityWeight: 1.08,
+		materialIndex }))
+	  })
+
+      rankedEntriesForCounts ({ counts: hostCounts, total, cap: factCap })
+	  .forEach (([host]) => {
+	    addQuestion (buildIndexedQuestion ({
+		condition: { type: 'source', host },
+		text: `${ host } の投稿を思い浮かべている?`,
+		kind: 'source',
+		priorityWeight: 1.02,
+		materialIndex }))
+	  })
+
+      rankedEntriesForCounts ({ counts: yearCounts, total, cap: factCap })
+	  .forEach (([year]) => {
+	    addQuestion (buildDateQuestion ({
+		type: 'original-year',
+		year }))
+	  })
+
+      specialMonthDays.forEach (([monthDay]) => {
+	addQuestion (buildDateQuestion ({
+	    type: 'original-month-day',
+	    monthDay: String (monthDay) }))
+      })
+
+      rankedEntriesForCounts ({ counts: titleTermCounts, total, cap: titleTermCap })
+	  .filter (([term]) => String (term).length <= 24)
+	  .forEach (([term]) => {
+	    addQuestion (buildIndexedQuestion ({
+		condition: { type: 'title-contains', text: String (term) },
+		text: `タイトルに「${ term }」が含まれる?`,
+		kind: 'title',
+		priorityWeight: .99,
+		materialIndex }))
+	  })
+
+      if (titleLengthMedian > 0)
+	addQuestion (buildIndexedQuestion ({
+	    condition: {
+		type: 'title-length-at-least',
+		length: titleLengthMedian },
+	    text: `タイトルは ${ titleLengthMedian } 文字以上?`,
+	    kind: 'title',
+	    priorityWeight: .72,
+	    materialIndex }))
+
+      if (asciiCount > 0 && asciiCount < total)
+	addQuestion (buildIndexedQuestion ({
+	    condition: { type: 'title-has-ascii' },
+	    text: 'タイトルに英数字が混じっている?',
+	    kind: 'title',
+	    priorityWeight: .68,
+	    materialIndex }))
+    }
+  else if (confirmationPost)
+    {
+      const targetPostId = confirmationPost.id
+      const host = materialIndex.hostByPostId.get (targetPostId)
+      const year = materialIndex.originalYearByPostId.get (targetPostId)
+      const monthDay = materialIndex.originalMonthDayByPostId.get (targetPostId)
+      const titleTerms = materialIndex.titleTermsByPostId.get (targetPostId) ?? []
+      const titleLength = materialIndex.titleLengthByPostId.get (targetPostId) ?? 0
+      const tagKeys = materialIndex.tagKeysByPostId.get (targetPostId) ?? []
+
+      if (host)
+	addQuestion (buildIndexedQuestion ({
+	    condition: { type: 'source', host },
+	    text: `${ host } の投稿を思い浮かべている?`,
+	    kind: 'source',
+	    priorityWeight: 1.02,
+	    materialIndex }))
+      if (year != null)
+	addQuestion (buildDateQuestion ({
+	    type: 'original-year',
+	    year }))
+      if (monthDay && specialOriginalMonthDayLabelFor (monthDay))
+	addQuestion (buildDateQuestion ({
+	    type: 'original-month-day',
+	    monthDay }))
+
+      tagKeys
+	  .slice (0, 20)
+	  .forEach (key => {
+	    addQuestion (buildIndexedQuestion ({
+		condition: { type: 'tag', key },
+		text: indexedQuestionTextForTag (key),
+		kind: 'tag',
+		priorityWeight: 1.08,
+		materialIndex }))
+	  })
+
+      titleTerms
+	  .filter (term => term.length <= 24)
+	  .slice (0, 8)
+	  .forEach (term => {
+	    addQuestion (buildIndexedQuestion ({
+		condition: { type: 'title-contains', text: term },
+		text: `タイトルに「${ term }」が含まれる?`,
+		kind: 'title',
+		priorityWeight: .99,
+		materialIndex }))
+	  })
+
+      if (titleLength > 0)
+	addQuestion (buildIndexedQuestion ({
+	    condition: {
+		type: 'title-length-at-least',
+		length: titleLength },
+	    text: `タイトルは ${ titleLength } 文字以上?`,
+	    kind: 'title',
+	    priorityWeight: .72,
+	    materialIndex }))
+
+      if (materialIndex.titleAsciiPostIds.has (targetPostId))
+	addQuestion (buildIndexedQuestion ({
+	    condition: { type: 'title-has-ascii' },
+	    text: 'タイトルに英数字が混じっている?',
+	    kind: 'title',
+	    priorityWeight: .68,
+	    materialIndex }))
+    }
+
+  return mergeQuestions ([...questions, ...acceptedQuestions])
+}
+
+const candidatePostsForState = ({
+    posts,
+    questionById,
+    materialIndex,
+    matchIndex,
+    answers,
+    softenedQuestionIds,
+    rejectedPostIds,
+    recoveredCandidatePosts,
+    scores,
+}: {
+    posts:                   Post[]
+    questionById:            Map<string, GekanatorQuestion>
+    materialIndex:           GekanatorQuestionMaterialIndex
+    matchIndex:              GekanatorMatchIndex
+    answers:                 GekanatorAnswerLog[]
+    softenedQuestionIds:     Set<string>
+    rejectedPostIds:         Set<number>
+    recoveredCandidatePosts: Map<number, RecoveredCandidateState>
+    scores:                  Map<number, number>
+}): Post[] => {
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+  const answerAllowsHardFilter = (answer: GekanatorAnswerValue): boolean =>
+      answer === 'yes' || answer === 'no'
+
+  return posts.filter (post => {
+    if (rejectedPostIds.has (post.id))
+      return false
+
+    const recoveredCandidate = recoveredCandidatePosts.get (post.id)
+
+    const survivesHardFiltering = answers.every ((answer, index) => {
+      if (recoveredCandidate != null && index < recoveredCandidate.answerCountAtRecovery)
+	return true
+      if (softenedQuestionIds.has (answer.questionId))
+	return true
+      if (!(answerAllowsHardFilter (answer.answer)))
+	return true
+
+      const question = questionById.get (answer.questionId)
+      const condition = answer.questionCondition ?? question?.condition
+      if (!(condition))
+	return true
+
+      const matched = (() => {
+	if (question)
+	  return positiveMatchingPostIdsForQuestion ({
+	      posts,
+	      materialIndex,
+	      matchIndex,
+	      question,
+	      dynamicMatchIndex })
+
+	return matchingPostIdsForCondition ({
+	    condition,
+	    materialIndex })
+      }) ()
+      const useExpectedAnswer =
+	  question != null
+	  && usesLearnedTagExamples (question)
+      if (question && !(questionSupportsAnswerBasedHardFiltering (question)))
+	return true
+
+      if (matched != null)
+	{
+	  if (useExpectedAnswer)
+	    {
+	      const expected = expectedAnswerForQuestion (question, post)
+	      return expected == null
+		  || expected === 'unknown'
+		  || expected === answer.answer
+	    }
+
+	  return answer.answer === 'yes' ? matched.has (post.id) : !(matched.has (post.id))
+	}
+
+      if (!(question))
+	return true
+
+      const expected = expectedAnswerForQuestion (question, post)
+      return expected == null || expected === 'unknown' || expected === answer.answer
+    })
+    if (!(survivesHardFiltering))
+      return false
+
+    return postPassesScoreDrop ({
+	postId: post.id,
+	scores,
+	recoveredCandidatePosts })
+  })
+}
+
+const hasDiscriminatingHardSplitForQuestion = ({
+    candidateIds,
+    question,
+    posts,
+    materialIndex,
+    matchIndex,
+}: {
+    candidateIds:   number[]
+    question:       GekanatorQuestion | null
+    posts:          Post[]
+    materialIndex:  GekanatorQuestionMaterialIndex
+    matchIndex:     GekanatorMatchIndex
+}): boolean => {
+  if (!(question))
+    return false
+
+  if (isUserSuggestedLearnedSemanticQuestion (question))
+    return learnedSemanticQuestionIsEffectiveForCandidateIds ({
+	candidateIds,
+	posts,
+	question })
+
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+  const yesCount = matchingPostCountInIds ({
+      candidateIds,
+      posts,
+      materialIndex,
+      matchIndex,
+      question,
+      dynamicMatchIndex })
+  const noCount = candidateIds.length - yesCount
+
+  return yesCount > 0 && noCount > 0
+}
+
+
+const recalculateScores = ({
+    posts,
+    questions,
+    answers,
+    softenedQuestionIds,
+    materialIndex,
+    matchIndex,
+}: {
+    posts:                Post[]
+    questions:            GekanatorQuestion[]
+    answers:              GekanatorAnswerLog[]
+    softenedQuestionIds:  Set<string>
+    materialIndex:        GekanatorQuestionMaterialIndex
+    matchIndex:           GekanatorMatchIndex
+}): Map<number, number> => {
+  const questionById = new Map (questions.map (question => [question.id, question]))
+  const nextScores = new Map<number, number> ()
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+
+  answers.forEach (answer => {
+    const question = questionById.get (answer.questionId)
+    if (!(question))
+      return
+
+    const weight = scoreWeightForAnswer (answer, softenedQuestionIds)
+    applyQuestionAnswerDeltaToScores ({
+	posts,
+	question,
+	answer: answer.answer,
+	weight,
+	nextScores,
+	materialIndex,
+	matchIndex,
+	dynamicMatchIndex })
+  })
+
+  return nextScores
+}
+
+
+const confidencesFor = (posts: Post[], scores: Map<number, number>): Confidence[] => {
+  if (posts.length === 0)
+    return []
+
+  const raw = posts.map (post => ({ post, score: scores.get (post.id) ?? 0 }))
+  const maxScore = Math.max (...raw.map (({ score }) => score))
+  const weighted = raw.map (item => ({
+      ...item,
+      weight: Math.exp ((item.score - maxScore) / confidenceTemperature) }))
+  const total = weighted.reduce ((sum, item) => sum + item.weight, 0) || 1
+
+  return weighted
+      .map (({ post, score, weight }) => ({
+	  post,
+	  score,
+	  percent: weight / total * 100 }))
+      .sort ((a, b) => b.percent - a.percent)
+}
+
+
+const entropyFor = (confidences: Confidence[]): number =>
+    confidences.reduce ((sum, item) => {
+      const p = item.percent / 100
+      return p > 0 ? sum - p * Math.log2 (p) : sum
+    }, 0)
+
+
+const effectiveCandidatesFor = (confidences: Confidence[]): number => {
+  const concentration = confidences.reduce ((sum, item) => {
+    const p = item.percent / 100
+    return sum + p * p
+  }, 0)
+
+  return concentration > 0 ? 1 / concentration : 0
+}
+
+
+const previewAnswer = ({
+    posts,
+    scores,
+    question,
+    answer,
+    materialIndex,
+    matchIndex,
+}: {
+    posts:     Post[]
+    scores:    Map<number, number>
+    question:  GekanatorQuestion
+    answer:    GekanatorAnswerValue
+    materialIndex: GekanatorQuestionMaterialIndex
+    matchIndex: GekanatorMatchIndex
+}): AnswerPreview => {
+  const postById = new Map (posts.map (post => [post.id, post]))
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+  const nextPostIds = postIdsForHardAnswer ({
+      candidateIds: posts.map (post => post.id),
+      question,
+      answer,
+      posts,
+      materialIndex,
+      matchIndex,
+      dynamicMatchIndex })
+  const nextPosts = nextPostIds
+      .map (postId => postById.get (postId))
+      .filter ((post): post is Post => post != null)
+  if (nextPosts.length === 0)
+    return {
+	answer,
+	top: null,
+	candidateCount: 0,
+	effectiveCandidates: 0,
+	entropy: 0 }
+
+  const nextScores = new Map (scores)
+  applyQuestionAnswerDeltaToScores ({
+      posts,
+      question,
+      answer,
+      weight: 1,
+      nextScores,
+      materialIndex,
+      matchIndex,
+      dynamicMatchIndex })
+
+  const confidences = confidencesFor (nextPosts, nextScores)
+
+  return {
+      answer,
+      top: confidences[0] ?? null,
+      candidateCount: nextPosts.length,
+      effectiveCandidates: effectiveCandidatesFor (confidences),
+      entropy: entropyFor (confidences) }
+}
+
+
+const mergeQuestions = (questions: GekanatorQuestion[]): GekanatorQuestion[] => {
+  const byId = new Map<string, GekanatorQuestion> ()
+  questions.forEach (question => {
+    const current = byId.get (question.id)
+    if (shouldReplaceMergedQuestion (current, question))
+      byId.set (question.id, question)
+  })
+  return [...byId.values ()]
+}
+
+
+const softenNextQuestionIds = ({
+    questions,
+    answers,
+    softenedQuestionIds,
+}: {
+    questions:            GekanatorQuestion[]
+    answers:              GekanatorAnswerLog[]
+    softenedQuestionIds:  Set<string>
+}): Set<string> | null => {
+  const questionById = new Map (questions.map (question => [question.id, question]))
+  const candidate = [...answers]
+      .reverse ()
+      .map (answer => {
+	const question = questionById.get (answer.questionId)
+	return { answer, question }
+      })
+      .filter ((item): item is {
+	  answer:    GekanatorAnswerLog
+	  question:  GekanatorQuestion } =>
+	      item.question != null
+	      && item.answer.answer !== 'unknown'
+	      && !(softenedQuestionIds.has (item.answer.questionId)))
+      .sort ((a, b) => questionDifficulty (b.question) - questionDifficulty (a.question))[0]
+
+  if (!(candidate))
+    return null
+
+  return new Set ([...softenedQuestionIds, candidate.answer.questionId])
+}
+
+
+type ExclusiveConditionGroup =
+    | 'original-month'
+    | 'original-year'
+    | 'original-month-day'
+    | 'source'
+
+
+const exclusiveConditionGroupFor = (
+    condition:  GekanatorQuestion['condition'],
+): ExclusiveConditionGroup | null => {
+  switch (condition.type)
+  {
+  case 'original-month':
+    return 'original-month'
+  case 'original-year':
+    return 'original-year'
+  case 'original-month-day':
+    return 'original-month-day'
+  case 'source':
+    return 'source'
+  default:
+    return null
+  }
+}
+
+
+const sameConditionValue = (
+    left:   GekanatorQuestion['condition'],
+    right:  GekanatorQuestion['condition'],
+): boolean => {
+  const leftTitleLength = titleLengthMinimumForCondition (left)
+  const rightTitleLength = titleLengthMinimumForCondition (right)
+  if (leftTitleLength != null || rightTitleLength != null)
+    return leftTitleLength != null
+	&& rightTitleLength != null
+	&& leftTitleLength === rightTitleLength
+
+  if (left.type !== right.type)
+    return false
+
+  const valueKeyFor = (condition: GekanatorQuestion['condition']): string => {
+    switch (condition.type)
+    {
+    case 'tag':
+      return condition.key
+    case 'source':
+      return condition.host
+    case 'original-year':
+      return String (condition.year)
+    case 'original-month':
+      return String (condition.month)
+    case 'original-month-day':
+      return condition.monthDay
+    case 'title-has-ascii':
+      return ''
+    case 'title-contains':
+      return condition.text
+    case 'post-similarity':
+      return `${ condition.postId }:${ condition.answer }:${ condition.threshold }`
+    case 'title-length-at-least':
+    case 'title-length-greater-than':
+      return String (titleLengthMinimumForCondition (condition) ?? '')
+    }
+  }
+
+  return valueKeyFor (left) === valueKeyFor (right)
+}
+
+
+const isMonthCrossMatch = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+): boolean => {
+  const candidateMonth = monthForCondition (candidate)
+  const previousMonth = monthForCondition (previous)
+  if (candidateMonth == null || previousMonth == null)
+    return false
+
+  const sameType = candidate.type === previous.type
+  if (sameType)
+    return false
+
+  return candidateMonth === previousMonth
+}
+
+
+const isExclusiveContradiction = (
+    candidate:  GekanatorQuestion['condition'],
+    previous:   GekanatorQuestion['condition'],
+): boolean => {
+  const candidateGroup = exclusiveConditionGroupFor (candidate)
+  const previousGroup = exclusiveConditionGroupFor (previous)
+
+  if (candidateGroup != null && candidateGroup === previousGroup)
+    return !(sameConditionValue (candidate, previous))
+
+  const candidateMonth = monthForCondition (candidate)
+  const previousMonth = monthForCondition (previous)
+  if (candidateMonth != null && previousMonth != null)
+    return candidateMonth !== previousMonth
+
+  return false
+}
+
+
+const contradictionPenaltyFor = ({
+    question,
+    answers,
+}: {
+    question:  GekanatorQuestion
+    answers:   GekanatorAnswerLog[]
+}): number => {
+  return answers.reduce ((sum, answer) => {
+    const previous = answer.questionCondition
+    if (!(previous))
+      return sum
+
+    switch (answer.answer)
+    {
+    case 'yes':
+      return sum + (isExclusiveContradiction (question.condition, previous) ? 100 : 0)
+    case 'partial':
+      return sum + (isExclusiveContradiction (question.condition, previous) ? 25 : 0)
+    case 'no':
+      if (
+	  sameConditionValue (question.condition, previous)
+	  || isMonthCrossMatch (question.condition, previous)
+      )
+	return sum + 40
+
+      return sum
+    case 'probably_no':
+      if (
+	  sameConditionValue (question.condition, previous)
+	  || isMonthCrossMatch (question.condition, previous)
+      )
+	return sum + 20
+
+      return sum
+    default:
+      return sum
+    }
+  }, 0)
+}
+
+
+const chooseQuestion = (
+    { posts,
+      questions,
+      scores,
+      answers,
+      askedIds,
+      gameSeed,
+      recentFirstQuestionPenaltyById,
+      userPriorWeights,
+      materialIndex,
+      matchIndex }: { posts:      Post[]
+		      questions:  GekanatorQuestion[]
+		      scores:     Map<number, number>
+		      answers:    GekanatorAnswerLog[]
+		      askedIds:   Set<string>
+		      gameSeed:   string
+		      recentFirstQuestionPenaltyById: Map<string, number>
+		      userPriorWeights: Map<number, number>
+		      materialIndex: GekanatorQuestionMaterialIndex
+		      matchIndex: GekanatorMatchIndex },
+): QuestionSelection | null => {
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+
+  const invertedSignature = (signature: string): string =>
+      signature.replace (/[01]/g, value => value === '1' ? '0' : '1')
+
+  const redundantSignatures = (candidates:  Post[]): Set<string> => {
+    const signatures = new Set<string> ()
+    questions
+	.filter (question => askedIds.has (question.id))
+	.forEach (question => {
+	  const signature = signatureForCandidateIds ({
+	      candidateIds: candidates.map (post => post.id),
+	      posts,
+	      materialIndex,
+	      matchIndex,
+	      question,
+	      dynamicMatchIndex })
+	  signatures.add (signature)
+	  signatures.add (invertedSignature (signature))
+	})
+
+    return signatures
+  }
+
+  const scoredPosts = posts
+      .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
+      .sort ((a, b) => b.score - a.score)
+  const maxScore = scoredPosts[0]?.score ?? 0
+  const weightedPosts = scoredPosts.map (item => ({
+      ...item,
+      weight: Math.exp ((item.score - maxScore) / confidenceTemperature) }))
+  const totalWeight =
+      weightedPosts.reduce ((sum, item) => sum + item.weight, 0) || 1
+  const normalisedWeightedPosts =
+      weightedPosts.map (item => ({ ...item, weight: item.weight / totalWeight }))
+  const weightedEntropy = distributionEntropy (
+      normalisedWeightedPosts.map (item => item.weight))
+  const learningTargetPosts = learningTargetPostsForCandidates ({
+      scoredPosts,
+      gameSeed })
+
+  const rank = (
+      questionsToRank:    GekanatorQuestion[],
+      candidates:         { post: Post; score: number }[],
+      weightedCandidates: { post: Post; score: number; weight: number }[],
+  ) => {
+    const redundant = redundantSignatures (candidates.map (item => item.post))
+    const candidateById = new Map (candidates.map (item => [item.post.id, item.post]))
+    const candidateIds = candidates.map (item => item.post.id)
+    const candidateIdSet = new Set (candidateIds)
+    const priorEntries = [...userPriorWeights.entries ()]
+	.filter (([postId]) => candidateById.has (postId))
+    const priorWeightTotal =
+	priorEntries.reduce ((sum, [, weight]) => sum + weight, 0)
+    const nonTagCount =
+	questions.filter (question => askedIds.has (question.id) && question.kind !== 'tag').length
+
+    return questionsToRank
+      .map (question => {
+	if (isQuestionHardFilteredAfterAnswers (question, answers))
+	  return null
+
+	const signature = signatureForCandidateIds ({
+	    candidateIds,
+	    posts,
+	    materialIndex,
+	    matchIndex,
+	    question,
+	    dynamicMatchIndex })
+	if (redundant.has (signature))
+	  return null
+
+	if (isUserSuggestedLearnedSemanticQuestion (question))
+	  {
+	    const stats = learnedSemanticStatsForCandidateIds ({
+		candidateIds,
+		posts,
+		question })
+	    const effective =
+		learnedSemanticQuestionIsEffectiveForCandidateIds ({
+		    candidateIds,
+		    posts,
+		    question })
+	    const learningValue = learnedSemanticLearningValueForTopPosts ({
+		question,
+		learningTargetPosts,
+		candidateIds,
+		posts })
+	    if (!(effective) && !(learningValue.hasLearningValue))
+	      return null
+
+	    const contradictionPenalty = contradictionPenaltyFor ({ question, answers })
+	    const humanOffset = humanPriorityOffsetFor (question)
+	    const sourceBonus = sourcePriorityOffset (question)
+	    const priorityBonus = priorityWeightOffset (question)
+	    const repeatPenalty = (() => {
+	      if (answers.length === 0)
+		return (recentFirstQuestionPenaltyById.get (question.id) ?? 0) * 4.5
+
+	      return 0
+	    }) ()
+	    const categoryPenalty = questionCategoryPenalty (
+		question,
+		answers.length,
+		repeatPenalty)
+	    if (!(effective))
+	      {
+		return {
+		    question,
+		    score: (
+			-(learningValue.missingTopCount * 20)
+			+ learningValue.knownCount * .5
+			+ contradictionPenalty
+			+ humanOffset
+			+ sourceBonus
+			+ priorityBonus
+			+ categoryPenalty),
+		    narrow: false,
+		    effectiveUserSuggested: false,
+		    learningUserSuggested: true }
+	      }
+
+	    const positiveWeight = weightedCandidates.reduce ((sum, item) =>
+		sum + (
+		  stats.positiveIds.has (item.post.id)
+		  ? item.weight
+		  : 0),
+	    0)
+	    const negativeWeight = weightedCandidates.reduce ((sum, item) =>
+		sum + (
+		  stats.negativeIds.has (item.post.id)
+		  ? item.weight
+		  : 0),
+	    0)
+	    const unknownWeight = Math.max (0, 1 - positiveWeight - negativeWeight)
+	    if (positiveWeight <= 0 || negativeWeight <= 0)
+	      return null
+
+	    const positivePosteriorWeights = weightedCandidates
+		.filter (item => stats.positiveIds.has (item.post.id))
+		.map (item => item.weight / positiveWeight)
+	    const negativePosteriorWeights = weightedCandidates
+		.filter (item => stats.negativeIds.has (item.post.id))
+		.map (item => item.weight / negativeWeight)
+	    const unknownPosteriorWeights =
+		unknownWeight > 0
+		? weightedCandidates
+		      .filter (item => stats.unknownIds.has (item.post.id))
+		      .map (item => item.weight / unknownWeight)
+		: []
+	    const infoGain =
+		weightedEntropy
+		- (
+		    positiveWeight * distributionEntropy (positivePosteriorWeights)
+		    + negativeWeight * distributionEntropy (negativePosteriorWeights)
+		    + unknownWeight * distributionEntropy (unknownPosteriorWeights))
+	    if (infoGain < (candidates.length >= 10 ? .02 : .008))
+	      return null
+
+	    const weightedSplitScore = Math.abs (.5 - positiveWeight)
+	    const unweightedSplitScore =
+		Math.abs (candidates.length / 2 - stats.positiveCount) / candidates.length
+	    const narrowPenalty =
+		learnedSemanticNarrowPenaltyForStats (candidates.length, stats)
+	    const infoGainBonus = -Math.min (1.2, infoGain) * 4
+
+	    return {
+		question,
+		score: weightedSplitScore * 100
+		    + unweightedSplitScore * 8
+		    + narrowPenalty
+		    + contradictionPenalty
+		    + humanOffset
+		    + sourceBonus
+		    + priorityBonus
+		    + categoryPenalty
+		    + infoGainBonus,
+		narrow: narrowPenalty > 0,
+		effectiveUserSuggested: true,
+		learningUserSuggested: false }
+	  }
+
+	const yes = matchingPostCountInIds ({
+	    candidateIds,
+	    candidateIdSet,
+	    posts,
+	    materialIndex,
+	    matchIndex,
+	    question,
+	    dynamicMatchIndex })
+	const no = candidates.length - yes
+	if (yes === 0 || no === 0)
+	  return null
+
+	const yesWeight = matchingWeightInCandidates ({
+	    candidates: weightedCandidates.map (item => ({
+		post: item.post,
+		weight: item.weight })),
+	    posts,
+	    materialIndex,
+	    matchIndex,
+	    question,
+	    dynamicMatchIndex })
+	const noWeight = 1 - yesWeight
+	if (yesWeight <= 0 || noWeight <= 0)
+	  return null
+	if (Math.min (yesWeight, noWeight) < .08)
+	  return null
+
+	const matched = positiveMatchingPostIdsForQuestion ({
+	    posts,
+	    materialIndex,
+	    matchIndex,
+	    question,
+	    dynamicMatchIndex })
+	const yesPosteriorWeights = weightedCandidates
+	    .filter (item => matched.has (item.post.id))
+	    .map (item => item.weight / yesWeight)
+	const noPosteriorWeights = weightedCandidates
+	    .filter (item => !(matched.has (item.post.id)))
+	    .map (item => item.weight / noWeight)
+	const infoGain =
+	    weightedEntropy
+	    - (
+		yesWeight * distributionEntropy (yesPosteriorWeights)
+		+ noWeight * distributionEntropy (noPosteriorWeights))
+	if (infoGain < (candidates.length >= 10 ? .02 : .008))
+	  return null
+
+	const weightedSplitScore = Math.abs (.5 - yesWeight)
+	const unweightedSplitScore = Math.abs (candidates.length / 2 - yes) / candidates.length
+	const tagPenalty = question.kind === 'tag' && nonTagCount < 4 ? .12 : 0
+	const minSide = candidates.length < 10 ? 1 : Math.max (3, candidates.length * .08)
+	const narrowPenalty = yes < minSide || no < minSide ? .15 : 0
+	const contradictionPenalty = contradictionPenaltyFor ({ question, answers })
+	const humanOffset = humanPriorityOffsetFor (question)
+	const sourceBonus = sourcePriorityOffset (question)
+	const priorityBonus = priorityWeightOffset (question)
+	const repeatPenalty = (() => {
+	  if (answers.length === 0)
+	    return (recentFirstQuestionPenaltyById.get (question.id) ?? 0) * 4.5
+
+	  return 0
+	}) ()
+	const categoryPenalty = questionCategoryPenalty (
+	    question,
+	    answers.length,
+	    repeatPenalty)
+	const priorSplitScore = (() => {
+	  if (priorWeightTotal <= 0)
+	    return null
+
+	  return Math.abs (
+	      .5 - (
+		priorEntries.reduce (
+		    (sum, [postId, weight]) => {
+		      return sum + (matched.has (postId) ? weight : 0)
+		    },
+		    0) / priorWeightTotal))
+	}) ()
+	const priorBonus = (() => {
+	  if (priorSplitScore == null)
+	    return 0
+
+	  return Math.max (0, .22 - priorSplitScore) * -18
+	}) ()
+	const infoGainBonus = -Math.min (1.2, infoGain) * 4
+
+	return { question,
+		 score: weightedSplitScore * 100
+		     + unweightedSplitScore * 8
+		     + tagPenalty
+		     + narrowPenalty
+		     + contradictionPenalty
+		     + humanOffset
+		     + sourceBonus
+		     + priorityBonus
+		     + categoryPenalty
+		     + priorBonus
+		     + infoGainBonus,
+		 narrow: narrowPenalty > 0,
+		 effectiveUserSuggested: false,
+		 learningUserSuggested: false }
+      })
+      .filter ((item): item is {
+	  question:  GekanatorQuestion
+	  score:     number
+	  narrow:    boolean
+	  effectiveUserSuggested: boolean
+	  learningUserSuggested: boolean } => item != null && Number.isFinite (item.score))
+      .sort ((a, b) => a.score - b.score)
+  }
+
+  const unansweredQuestions =
+      questions.filter (question => !(askedIds.has (question.id)))
+  const ranked = rank (unansweredQuestions, scoredPosts, normalisedWeightedPosts)
+  const generalRankedPool =
+      ranked.some (item => !(item.narrow)) ? ranked.filter (item => !(item.narrow)) : ranked
+  const effectiveUserSuggestedPool =
+      ranked
+      .filter (item => item.effectiveUserSuggested)
+      .slice (0, 16)
+  const learningUserSuggestedPool =
+      ranked
+      .filter (item => item.learningUserSuggested)
+      .slice (0, 16)
+  const normalPool =
+      generalRankedPool
+      .filter (item => !(item.effectiveUserSuggested) && !(item.learningUserSuggested))
+      .slice (0, 16)
+  const purposeCounts = questionPurposeCountsFor (answers)
+  const totalNormalPhaseQuestionCount = purposeCounts.totalNormalPhaseQuestionCount
+  const effectiveRatio =
+      totalNormalPhaseQuestionCount > 0
+      ? purposeCounts.effectiveUserSuggestedCount / totalNormalPhaseQuestionCount
+      : 0
+  const learningRatio =
+      totalNormalPhaseQuestionCount > 0
+      ? purposeCounts.learningUserSuggestedCount / totalNormalPhaseQuestionCount
+      : 0
+  const totalUserSuggestedRatio =
+      totalNormalPhaseQuestionCount > 0
+      ? purposeCounts.totalUserSuggestedCount / totalNormalPhaseQuestionCount
+      : 0
+  let selectedPool = normalPool
+  let selectedPurpose: GekanatorQuestionPurpose = 'normal'
+
+  if (
+	effectiveRatio < targetEffectiveUserSuggestedQuestionRatio
+	&& totalUserSuggestedRatio < targetTotalUserSuggestedQuestionRatio
+	&& effectiveUserSuggestedPool.length > 0
+  )
+    {
+      selectedPool = effectiveUserSuggestedPool
+      selectedPurpose = 'effective_user_suggested'
+    }
+  else if (
+	learningRatio < targetLearningUserSuggestedQuestionRatio
+	&& totalUserSuggestedRatio < targetTotalUserSuggestedQuestionRatio
+	&& learningUserSuggestedPool.length > 0
+  )
+    {
+      selectedPool = learningUserSuggestedPool
+      selectedPurpose = 'learning_user_suggested'
+    }
+  else if (normalPool.length > 0)
+    {
+      selectedPool = normalPool
+      selectedPurpose = 'normal'
+    }
+  else if (effectiveUserSuggestedPool.length > 0)
+    {
+      selectedPool = effectiveUserSuggestedPool
+      selectedPurpose = 'effective_user_suggested'
+    }
+  else if (learningUserSuggestedPool.length > 0)
+    {
+      selectedPool = learningUserSuggestedPool
+      selectedPurpose = 'learning_user_suggested'
+    }
+
+  if (selectedPool.length === 0)
+    return null
+
+  const bestScore = selectedPool[0]?.score ?? 0
+  const weightedPool = selectedPool.map (item => ({
+      ...item,
+      weight: Math.exp ((bestScore - item.score) / (answers.length === 0 ? 2.8 : 2.1)) }))
+  const totalPoolWeight =
+      weightedPool.reduce ((sum, item) => sum + item.weight, 0) || 1
+  const seed = `${ gameSeed }:${ [...askedIds].sort ().join ('|') }:${
+      weightedPool.map (item => `${ item.question.id }:${ item.score.toFixed (4) }`).join ('|')
+  }`
+  const target = deterministicUnitFloat (seed) * totalPoolWeight
+  let cumulative = 0
+
+  for (const item of weightedPool)
+    {
+	cumulative += item.weight
+	if (target <= cumulative)
+	  return {
+	      question: item.question,
+	      questionPurpose: selectedPurpose,
+	      effectiveQuestion: selectedPurpose === 'effective_user_suggested',
+	      learningQuestion: selectedPurpose === 'learning_user_suggested' }
+    }
+
+  const selectedQuestion = weightedPool[weightedPool.length - 1]?.question
+  if (selectedQuestion == null)
+    return null
+
+  return {
+      question: selectedQuestion,
+      questionPurpose: selectedPurpose,
+      effectiveQuestion: selectedPurpose === 'effective_user_suggested',
+      learningQuestion: selectedPurpose === 'learning_user_suggested' }
+}
+
+
+const winningRunPriorityFor = (
+    expected:    GekanatorAnswerValue,
+): number | null => {
+  if (expected === 'yes')
+    return 0
+  if (expected === 'partial')
+    return 1
+  if (expected === 'no' || expected === 'probably_no')
+    return 2
+
+  return null
+}
+
+
+const chooseWinningRunQuestion = ({
+    posts,
+    targetPost,
+    answers,
+    askedIds,
+    acceptedQuestions,
+    materialIndex,
+    matchIndex,
+}: {
+    posts:      Post[]
+    targetPost: Post
+    answers:    GekanatorAnswerLog[]
+    askedIds:   Set<string>
+    acceptedQuestions: GekanatorQuestion[]
+    materialIndex: GekanatorQuestionMaterialIndex
+    matchIndex: GekanatorMatchIndex
+}): GekanatorQuestion | null => {
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+  const ranked = buildQuestionsForCandidateIds ({
+      candidateIds: posts.map (post => post.id),
+      materialIndex,
+      acceptedQuestions,
+      mode: 'confirmation',
+      confirmationPostId: targetPost.id
+  })
+      .filter (question => {
+	if (askedIds.has (question.id))
+	  return false
+	if (isQuestionHardFilteredAfterAnswers (question, answers))
+	  return false
+
+	const expected = expectedAnswerForQuestion (question, targetPost)
+	return expected != null && expected !== 'unknown'
+      })
+      .map (question => {
+	const expected = expectedAnswerForQuestion (question, targetPost)
+	const priority = expected == null ? null : winningRunPriorityFor (expected)
+	if (priority == null)
+	  return null
+
+	let matchingCount = 0
+	if (isUserSuggestedLearnedSemanticQuestion (question))
+	  {
+	    const stats = learnedSemanticStatsForCandidateIds ({
+		candidateIds: posts.map (post => post.id),
+		posts,
+		question })
+	    matchingCount =
+		expected === 'yes' || expected === 'partial'
+		? stats.positiveCount
+		: stats.negativeCount
+	  }
+	else
+	  {
+	    const yesCount = matchingPostCountInIds ({
+		candidateIds: posts.map (post => post.id),
+		posts,
+		materialIndex,
+		matchIndex,
+		question,
+		dynamicMatchIndex })
+	    matchingCount =
+		expected === 'yes' || expected === 'partial' ? yesCount : posts.length - yesCount
+	  }
+
+	return {
+	    question,
+	    priority,
+	    humanOffset: humanPriorityOffsetFor (question),
+	    matchingCount }
+      })
+      .filter ((item): item is {
+	  question:      GekanatorQuestion
+	  priority:      number
+	  humanOffset:   number
+	  matchingCount: number } => item != null)
+      .sort ((a, b) => {
+	if (a.priority !== b.priority)
+	  return a.priority - b.priority
+
+	if (a.humanOffset !== b.humanOffset)
+	  return a.humanOffset - b.humanOffset
+
+	if (a.question.priorityWeight !== b.question.priorityWeight)
+	  return b.question.priorityWeight - a.question.priorityWeight
+
+	if (a.matchingCount !== b.matchingCount)
+	  return a.matchingCount - b.matchingCount
+
+	return a.question.id.localeCompare (b.question.id)
+      })
+
+  if (ranked.length > 0)
+    return ranked[0]?.question ?? null
+
+  return null
+}
+
+
+const chooseFallbackQuestion = ({
+    posts,
+    allPosts,
+    questions,
+    answers,
+    askedIds,
+    scores,
+    materialIndex,
+    matchIndex,
+}: {
+    posts:      Post[]
+    allPosts:   Post[]
+    questions:  GekanatorQuestion[]
+    answers:    GekanatorAnswerLog[]
+    askedIds:   Set<string>
+    scores:     Map<number, number>
+    materialIndex: GekanatorQuestionMaterialIndex
+    matchIndex: GekanatorMatchIndex
+}): GekanatorQuestion | null => {
+  if (posts.length === 0)
+    return null
+
+  const candidateIds = posts.map (post => post.id)
+  const fallbackPosts = posts
+      .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
+      .sort ((a, b) => b.score - a.score)
+      .slice (0, Math.min (6, posts.length))
+      .map (item => item.post)
+  const fallbackQuestions = mergeQuestions (
+      fallbackPosts.flatMap (post => buildQuestionsForCandidateIds ({
+	  candidateIds,
+	  materialIndex,
+	  acceptedQuestions: [],
+	  mode: 'confirmation',
+	  confirmationPostId: post.id
+      })))
+      .slice (0, 32)
+  const dynamicMatchIndex = new Map<string, Set<number>> ()
+  const ranked = mergeQuestions ([
+      ...questions,
+      ...fallbackQuestions])
+      .filter (question =>
+	  question.source !== 'user_suggested'
+	  &&
+	  !(askedIds.has (question.id))
+	  && !(isQuestionHardFilteredAfterAnswers (question, answers)))
+      .map (question => {
+	if (isUserSuggestedLearnedSemanticQuestion (question))
+	  {
+	    if (!(learnedSemanticQuestionIsEffectiveForCandidateIds ({
+		candidateIds,
+		posts: allPosts,
+		question })))
+	      return null
+
+	    const stats = learnedSemanticStatsForCandidateIds ({
+		candidateIds,
+		posts: allPosts,
+		question })
+
+	    return {
+		question,
+		knownCount: stats.knownCount,
+		balance: Math.abs (stats.positiveCount - stats.negativeCount),
+		humanOffset: humanPriorityOffsetFor (question) }
+	  }
+
+	const yesCount = matchingPostCountInIds ({
+	    candidateIds,
+	    posts: allPosts,
+	    materialIndex,
+	    matchIndex,
+	    question,
+	    dynamicMatchIndex })
+	const noCount = candidateIds.length - yesCount
+	if (yesCount === 0 || noCount === 0)
+	  return null
+
+	return {
+	    question,
+	    knownCount: candidateIds.length,
+	    balance: Math.abs (yesCount - noCount),
+	    humanOffset: humanPriorityOffsetFor (question) }
+      })
+      .filter ((item): item is {
+	  question:   GekanatorQuestion
+	  knownCount: number
+	  balance:    number
+	  humanOffset: number } => item != null)
+      .sort ((a, b) => {
+	if (a.humanOffset !== b.humanOffset)
+	  return a.humanOffset - b.humanOffset
+
+	if (a.balance !== b.balance)
+	  return a.balance - b.balance
+
+	if (a.knownCount !== b.knownCount)
+	  return b.knownCount - a.knownCount
+
+	if (a.question.priorityWeight !== b.question.priorityWeight)
+	  return b.question.priorityWeight - a.question.priorityWeight
+
+	return a.question.id.localeCompare (b.question.id)
+      })
+
+  return ranked[0]?.question ?? null
+}
+
+
+const shouldEnterGuessPhase = (
+    reason: GuessReason | null,
+): reason is 'hard_max_questions' | 'winning_run_finished' | 'question_count_checkpoint' =>
+    (reason === 'hard_max_questions'
+     || reason === 'winning_run_finished'
+     || reason === 'question_count_checkpoint')
+
+
+const isWinningRunActive = (
+    winningRunTargetId:         number | null,
+    winningRunStartAnswerCount: number | null,
+): boolean =>
+    winningRunTargetId != null && winningRunStartAnswerCount != null
+
+
+const winningRunQuestionCount = (
+    answers:                    GekanatorAnswerLog[],
+    winningRunStartAnswerCount: number | null,
+): number => {
+  if (winningRunStartAnswerCount == null)
+    return 0
+
+  return answers
+      .slice (winningRunStartAnswerCount)
+      .filter (answer => answer.questionMode === 'winning_run')
+      .length
+}
+
+
+const nextQuestionPlanFor = (
+    { posts,
+      eligiblePosts,
+      availablePosts,
+      acceptedQuestions,
+      scores,
+      answers,
+      askedIds,
+      gameSeed,
+      recentFirstQuestionPenaltyById,
+      userPriorWeights,
+      materialIndex,
+      matchIndex,
+      lastGuessQuestionCount,
+      winningRunTargetId,
+      winningRunStartAnswerCount }: { posts:      Post[]
+				      eligiblePosts: Post[]
+    				      availablePosts: Post[]
+    				      acceptedQuestions: GekanatorQuestion[]
+    				      scores:     Map<number, number>
+    				      answers:    GekanatorAnswerLog[]
+    				      askedIds:   Set<string>
+    				      gameSeed:   string
+    				      recentFirstQuestionPenaltyById: Map<string, number>
+    				      userPriorWeights: Map<number, number>
+    				      materialIndex: GekanatorQuestionMaterialIndex
+    				      matchIndex: GekanatorMatchIndex
+    				      lastGuessQuestionCount: number
+    				      winningRunTargetId: number | null
+    				      winningRunStartAnswerCount: number | null },
+): { question: GekanatorQuestion | null
+     guess: Post | null
+     guessReason: GuessReason | null
+     questionMode: QuestionMode
+     questionPurpose?: GekanatorQuestionPurpose
+     effectiveQuestion?: boolean
+     learningQuestion?: boolean
+     winningRunTargetId: number | null
+     winningRunStartAnswerCount: number | null } => {
+  const guessablePosts = eligiblePosts.length > 0 ? eligiblePosts : availablePosts
+
+  const checkpointGuess =
+      answers.length > 0
+      && answers.length - lastGuessQuestionCount >= minQuestionsBeforeCertainGuess
+
+  if (answers.length >= hardMaxQuestions)
+    {
+      return {
+	  question: null,
+	  guess: bestPost (guessablePosts, scores),
+	  guessReason: 'hard_max_questions',
+	  questionMode: null,
+	  questionPurpose: undefined,
+	  effectiveQuestion: false,
+	  learningQuestion: false,
+	  winningRunTargetId,
+	  winningRunStartAnswerCount }
+    }
+
+  if (checkpointGuess)
+    {
+      return {
+	  question: null,
+	  guess: bestPost (guessablePosts, scores),
+	  guessReason: 'question_count_checkpoint',
+	  questionMode: null,
+	  questionPurpose: undefined,
+	  effectiveQuestion: false,
+	  learningQuestion: false,
+	  winningRunTargetId,
+	  winningRunStartAnswerCount }
+    }
+
+  const nextWinningRunTargetId = eligiblePosts.length === 1 ? eligiblePosts[0]?.id ?? null : null
+  const nextWinningRunStartAnswerCount = (() => {
+    if (nextWinningRunTargetId == null)
+      return null
+    if (
+	isWinningRunActive (winningRunTargetId, winningRunStartAnswerCount)
+	&& winningRunTargetId === nextWinningRunTargetId
+	&& winningRunStartAnswerCount != null
+    )
+      return winningRunStartAnswerCount
+
+    return answers.length
+  }) ()
+  const nextWinningRunTargetPost = (() => {
+    if (nextWinningRunTargetId == null)
+      return null
+
+    return posts.find (post => post.id === nextWinningRunTargetId) ?? null
+  }) ()
+  const buildQuestionsForPosts = (scopePosts: Post[]): GekanatorQuestion[] =>
+      buildQuestionsForCandidateIds ({
+	  candidateIds: scopePosts.map (post => post.id),
+	  materialIndex,
+	  acceptedQuestions,
+	  mode: 'split' })
+
+  if (eligiblePosts.length === 1)
+    {
+      const winningRunFinished =
+	  nextWinningRunTargetId != null
+	  && nextWinningRunStartAnswerCount != null
+	  && eligiblePosts[0]?.id === nextWinningRunTargetId
+	  && winningRunQuestionCount (
+	      answers,
+	      nextWinningRunStartAnswerCount) >= winningRunQuestionLimit
+      if (winningRunFinished)
+	return {
+	    question: null,
+	    guess: bestPost (eligiblePosts, scores),
+	    guessReason: 'winning_run_finished',
+	    questionMode: null,
+	    questionPurpose: undefined,
+	    effectiveQuestion: false,
+	    learningQuestion: false,
+	    winningRunTargetId: nextWinningRunTargetId,
+	    winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+      if (!(nextWinningRunTargetPost) || nextWinningRunStartAnswerCount == null)
+	return {
+	    question: null,
+	    guess: null,
+	    guessReason: null,
+	    questionMode: null,
+	    questionPurpose: undefined,
+	    effectiveQuestion: false,
+	    learningQuestion: false,
+	    winningRunTargetId: nextWinningRunTargetId,
+	    winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+
+      const winningRunQuestion = chooseWinningRunQuestion ({
+	  posts,
+	  targetPost: nextWinningRunTargetPost,
+	  answers,
+	  askedIds,
+	  acceptedQuestions,
+	  materialIndex,
+	  matchIndex })
+      if (winningRunQuestion)
+	return {
+	    question: winningRunQuestion,
+	    guess: null,
+	    guessReason: null,
+	    questionMode: 'winning_run',
+	    questionPurpose: undefined,
+	    effectiveQuestion: false,
+	    learningQuestion: false,
+	    winningRunTargetId: nextWinningRunTargetId,
+	    winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+      return {
+	  question: null,
+	  guess: null,
+	  guessReason: null,
+	  questionMode: null,
+	  questionPurpose: undefined,
+	  effectiveQuestion: false,
+	  learningQuestion: false,
+	  winningRunTargetId: nextWinningRunTargetId,
+	  winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+    }
+
+  const evaluationPosts =
+      eligiblePosts
+
+  const evaluationQuestions = buildQuestionsForPosts (evaluationPosts)
+  const normalQuestionSelection = chooseQuestion ({
+      posts: evaluationPosts,
+      questions: evaluationQuestions,
+      scores,
+      answers,
+      askedIds,
+      gameSeed,
+      recentFirstQuestionPenaltyById,
+      userPriorWeights,
+      materialIndex,
+      matchIndex })
+
+  const fallbackQuestion = normalQuestionSelection?.question ?? chooseFallbackQuestion ({
+      posts: evaluationPosts,
+      allPosts: posts,
+      questions: evaluationQuestions,
+      answers,
+      askedIds,
+      scores,
+      materialIndex,
+      matchIndex })
+
+  if (fallbackQuestion)
+    {
+      return {
+	  question: fallbackQuestion,
+	  guess: null,
+	  guessReason: null,
+	  questionMode: 'normal',
+	  questionPurpose: normalQuestionSelection?.question?.id === fallbackQuestion.id
+	      ? normalQuestionSelection.questionPurpose
+	      : 'normal',
+	  effectiveQuestion: normalQuestionSelection?.question?.id === fallbackQuestion.id
+	      ? normalQuestionSelection.effectiveQuestion
+	      : false,
+	  learningQuestion: normalQuestionSelection?.question?.id === fallbackQuestion.id
+	      ? normalQuestionSelection.learningQuestion
+	      : false,
+	  winningRunTargetId: nextWinningRunTargetId,
+	  winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+    }
+
+  return {
+      question: null,
+      guess: null,
+      guessReason: null,
+      questionMode: null,
+      questionPurpose: undefined,
+      effectiveQuestion: false,
+      learningQuestion: false,
+      winningRunTargetId: nextWinningRunTargetId,
+      winningRunStartAnswerCount: nextWinningRunStartAnswerCount }
+}
+
+
+const bestPost = (posts: Post[], scores: Map<number, number>): Post | null =>
+    posts
+    .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
+    .sort ((a, b) => b.score - a.score)[0]?.post ?? null
+
+
+const PostMiniCard: FC<{ post: Post }> = ({ post }) => (
+    <div className="flex gap-3 items-center min-w-0">
+      <img
+	  src={post.thumbnail || post.thumbnailBase || undefined}
+	  alt={post.title || post.url}
+	  className="w-16 h-16 rounded object-cover bg-yellow-100"/>
+      <div className="min-w-0">
+	<PrefetchLink
+	    to={`/posts/${ post.id }`}
+	    className="font-bold text-pink-700 dark:text-pink-200 break-words">
+	  #{post.id} {post.title || post.url}
+	</PrefetchLink>
+	<div className="text-sm text-neutral-600 dark:text-neutral-300 line-clamp-1">
+	  {post.tags.slice (0, 6).map (tag => tag.name).join (' / ')}
+	</div>
+      </div>
+    </div>)
+
+
+const backgroundThumbnailUrl = (post: Post): string | undefined =>
+    post.thumbnail || post.thumbnailBase || undefined
+
+
+const mascotStateFor = (
+    phase:                 Phase,
+    resultWon:             boolean | null,
+    eligiblePostCount:     number,
+    bestConfidencePercent: number,
+    winningRunActive:      boolean,
+): MascotState => {
+  const resultPhase =
+      phase === 'end'
+      || phase === 'review'
+      || phase === 'learned'
+
+  if (resultPhase && !(resultWon))
+    return 'failed'
+
+  if (resultPhase && resultWon)
+    return 'celebrate'
+
+  switch (phase)
+  {
+  case 'question':
+  case 'continue':
+  case 'extra_questions':
+  case 'question_suggestion':
+    if (
+	winningRunActive
+	|| eligiblePostCount <= 2
+	|| bestConfidencePercent >= 70
+    )
+      return 'thinking_near'
+    if (
+	eligiblePostCount >= 15
+	&& bestConfidencePercent < 45
+    )
+      return 'thinking_far'
+    return 'thinking_mid'
+  case 'guess':
+  case 'end':
+  case 'review':
+  case 'learned':
+    return 'confident'
+  default:
+    return 'idle'
+  }
+}
+
+
+const backgroundPostsFor = ({
+    phase,
+    eligiblePosts,
+    availablePosts,
+    displayedGuess,
+    reviewCorrectPost,
+    reviewGuessedPost,
+}: {
+    phase:              Phase
+    eligiblePosts:      Post[]
+    availablePosts:     Post[]
+    displayedGuess:     Post | null
+    reviewCorrectPost:  Post | null
+    reviewGuessedPost:  Post | null
+}): Post[] => {
+  const focusPosts =
+      phase === 'end' || phase === 'review' || phase === 'learned'
+      ? [reviewCorrectPost, reviewGuessedPost].filter ((post): post is Post => post != null)
+      : phase === 'guess'
+      ? [displayedGuess, ...eligiblePosts].filter ((post): post is Post => post != null)
+      : eligiblePosts.length > 0
+      ? eligiblePosts
+      : availablePosts
+
+  return [...new Map (focusPosts.map (post => [post.id, post])).values ()]
+}
+
+
+const GekanatorBackdrop: FC<{
+    posts:                    Post[]
+    mascotAsset:              string
+    phase:                    Phase
+    displayedGuess?:          Post | null
+    visualSeed:               string
+    motionMode:               BackgroundMotionMode
+    winningRunTargetPost?:    Post | null
+    winningRunQuestionCount?: number }> = ({ posts,
+					     mascotAsset,
+					     phase,
+  					     displayedGuess = null,
+  					     visualSeed,
+  					     motionMode,
+  					     winningRunTargetPost = null,
+  					     winningRunQuestionCount = 0 }) => {
+  const guessFocusOffset = useMemo (() => {
+    const focusTiles = [
+	{ x: 'calc(max(100vw, 100vh) * 0.5)',
+	  y: 'calc(max(100vw, 100vh) * 0.5)' },
+	{ x: 'calc(max(100vw, 100vh) * -0.5)',
+	  y: 'calc(max(100vw, 100vh) * 0.5)' },
+	{ x: 'calc(max(100vw, 100vh) * 0.5)',
+	  y: 'calc(max(100vw, 100vh) * -0.5)' },
+	{ x: 'calc(max(100vw, 100vh) * -0.5)',
+	  y: 'calc(max(100vw, 100vh) * -0.5)' }]
+
+    return (focusTiles[Math.abs (hashString (`${ visualSeed }:guess-focus`)) % focusTiles.length]
+	    ?? focusTiles[0])
+  }, [visualSeed])
+
+  const directions = useMemo (
+      () => [
+	  { x: 0, y: -33.333333 },
+	  { x: 33.333333, y: -33.333333 },
+	  { x: 33.333333, y: 0 },
+	  { x: 33.333333, y: 33.333333 },
+	  { x: 0, y: 33.333333 },
+	  { x: -33.333333, y: 33.333333 },
+	  { x: -33.333333, y: 0 },
+	  { x: -33.333333, y: -33.333333 }],
+      [])
+  const guessThumbnail =
+      phase === 'guess' && displayedGuess ? backgroundThumbnailUrl (displayedGuess) : null
+  const isWinningRunBackdrop =
+      !(guessThumbnail)
+      && phase === 'question'
+      && winningRunTargetPost != null
+      && Boolean (backgroundThumbnailUrl (winningRunTargetPost))
+  const backdropMode = (() => {
+    if (guessThumbnail)
+      return 'guess'
+    if (isWinningRunBackdrop)
+      return 'winning_run'
+
+    return 'normal'
+  }) ()
+
+  const normalVisiblePosts = useMemo (
+      () => posts
+	.filter (post => Boolean (backgroundThumbnailUrl (post)))
+	.sort ((left, right) =>
+	    hashString (`${ visualSeed }:${ left.id }`)
+		- hashString (`${ visualSeed }:${ right.id }`))
+	.slice (0, motionMode === 'calm' ? 24 : 36),
+      [posts, visualSeed, motionMode])
+
+  const settingsForMode = useCallback (
+      (
+	  mode: 'normal' | 'winning_run' | 'guess',
+      ): { columns: number; rows: number; opacity: number } => {
+	if (mode === 'winning_run' || mode === 'guess')
+	  return { columns: 8, rows: 8, opacity: motionMode === 'calm' ? .18 : .24 }
+
+	if (motionMode === 'calm')
+	  return { columns: 7, rows: 7, opacity: .14 }
+
+	return { columns: 10, rows: 10, opacity: .2 }
+      },
+      [motionMode])
+
+  const scaleForMode = useCallback (
+      (
+	  mode:                    'normal' | 'winning_run' | 'guess',
+	  displayedWinningCount:   number,
+      ): number => {
+	if (mode === 'guess')
+	  return 8
+
+	if (mode === 'winning_run')
+	  return [1, 8 / 6, 8 / 4, 8 / 2][Math.max (0, Math.min (3, displayedWinningCount))] ?? 1
+
+	return 1
+      },
+      [])
+
+  const postsForMode = useCallback ((
+      mode: 'normal' | 'winning_run' | 'guess',
+  ): Post[] => {
+    if (mode === 'guess' && displayedGuess)
+      return [displayedGuess]
+    if (mode === 'winning_run' && winningRunTargetPost)
+      return [winningRunTargetPost]
+    return normalVisiblePosts
+  }, [displayedGuess, winningRunTargetPost, normalVisiblePosts])
+
+  const thumbnailsForMode = useCallback ((
+      mode:      'normal' | 'winning_run' | 'guess',
+      count:     number,
+  ): string[] => {
+    const modePosts = postsForMode (mode)
+    if (modePosts.length === 0)
+      return []
+
+    return Array.from ({ length: count }, (_, index) => {
+      const post = modePosts[index % modePosts.length]
+      return backgroundThumbnailUrl (post) ?? null
+    }).filter ((thumbnail): thumbnail is string => Boolean (thumbnail))
+  }, [postsForMode])
+
+  const targetSettings = settingsForMode (backdropMode)
+  const targetTileCount = targetSettings.columns * targetSettings.rows
+
+  const nextThumbnails = useMemo (
+      () => thumbnailsForMode (backdropMode, targetTileCount),
+      [backdropMode, targetTileCount, thumbnailsForMode])
+
+  const nextDirection = useMemo (
+      () => directions[
+	  Math.abs (hashString (`${ visualSeed }:direction`)) % directions.length]
+	      ?? directions[0],
+      [visualSeed, directions])
+
+  const marqueeDuration = (() => {
+    if (backdropMode === 'winning_run')
+      return motionMode === 'calm' ? 28 : 20
+
+    return motionMode === 'calm' ? 34 : 24
+  }) ()
+  const tileFlipDuration = motionMode === 'calm' ? .6 : .45
+  const x = useMotionValue (0)
+  const y = useMotionValue (0)
+  const marqueeTransform = useMotionTemplate`translate(${ x }%, ${ y }%)`
+  const [activeDirection, setActiveDirection] = useState (nextDirection)
+  const activeDirectionRef = useRef (activeDirection)
+  const guessAnimationControlsRef = useRef<ReturnType<typeof animate>[]> ([])
+  const flipTimerRef = useRef<number | null> (null)
+  const [displayedBackdropMode, setDisplayedBackdropMode] =
+      useState<'normal' | 'winning_run' | 'guess'> (backdropMode)
+  const [displayedWinningRunCount, setDisplayedWinningRunCount] =
+      useState (winningRunQuestionCount)
+  const [displayedThumbnails, setDisplayedThumbnails] = useState<string[]> (
+      nextThumbnails)
+  const [fromThumbnails, setFromThumbnails] = useState<string[]> (
+      nextThumbnails)
+  const [toThumbnails, setToThumbnails] = useState<string[]> (
+      nextThumbnails)
+  const [flipVisualSeed, setFlipVisualSeed] = useState (visualSeed)
+  const [isFlippingTiles, setIsFlippingTiles] = useState (false)
+
+  const renderedSettings = settingsForMode (displayedBackdropMode)
+  const renderedTileCount = renderedSettings.columns * renderedSettings.rows
+  const renderedScale = scaleForMode (displayedBackdropMode, displayedWinningRunCount)
+
+  const isGuessPresentation =
+      backdropMode === 'guess' || displayedBackdropMode === 'guess'
+
+  useEffect (() => {
+    guessAnimationControlsRef.current.forEach (control => control.stop ())
+    guessAnimationControlsRef.current = []
+
+    if (motionMode === 'off')
+      return
+
+    if (!(isGuessPresentation))
+      return
+
+    const duration = motionMode === 'calm' ? .95 : .75
+    const ease = [0.16, 1, 0.3, 1] as const
+
+    const controls = [
+	animate (x, 0, { duration, ease }),
+	animate (y, 0, { duration, ease })]
+    guessAnimationControlsRef.current = controls
+
+    return () => {
+      controls.forEach (control => control.stop ())
+      guessAnimationControlsRef.current = []
+    }
+  }, [isGuessPresentation, motionMode, visualSeed, x, y])
+
+  useEffect (() => {
+    activeDirectionRef.current = activeDirection
+  }, [activeDirection])
+
+  useEffect (() => {
+    const wrap = (value: number): number => {
+      const cell = 33.333333
+      const wrapped = ((value % cell) + cell) % cell
+      return wrapped > cell / 2 ? wrapped - cell : wrapped
+    }
+
+    if (motionMode === 'off' || nextThumbnails.length === 0)
+      {
+	guessAnimationControlsRef.current.forEach (control => control.stop ())
+	guessAnimationControlsRef.current = []
+	x.set (0)
+	y.set (0)
+	return
+      }
+
+    if (isGuessPresentation)
+      {
+	guessAnimationControlsRef.current.forEach (control => control.stop ())
+	guessAnimationControlsRef.current = []
+	x.set (0)
+	y.set (0)
+	return
+      }
+
+    const speed = 33.333333 / marqueeDuration
+    let animationFrame: number
+    let previousTime = performance.now ()
+
+    const tick = (time: number) => {
+      const elapsedSeconds = (time - previousTime) / 1000
+      previousTime = time
+      const direction = activeDirectionRef.current
+      x.set (wrap (x.get () + Math.sign (direction.x) * speed * elapsedSeconds))
+      y.set (wrap (y.get () + Math.sign (direction.y) * speed * elapsedSeconds))
+      animationFrame = window.requestAnimationFrame (tick)
+    }
+
+    animationFrame = window.requestAnimationFrame (tick)
+
+    return () => window.cancelAnimationFrame (animationFrame)
+  }, [x,
+      y,
+      marqueeDuration,
+      motionMode,
+      isGuessPresentation,
+      nextThumbnails.length])
+
+  useEffect (() => {
+    const applyDirection = () => {
+      activeDirectionRef.current = nextDirection
+      setActiveDirection (nextDirection)
+    }
+
+    if (flipTimerRef.current != null)
+      {
+	window.clearTimeout (flipTimerRef.current)
+	flipTimerRef.current = null
+      }
+
+    if (motionMode === 'off')
+      {
+	applyDirection ()
+	setIsFlippingTiles (false)
+	setFlipVisualSeed (visualSeed)
+	return
+      }
+
+    if (backdropMode === 'guess' && guessThumbnail)
+      {
+	setIsFlippingTiles (false)
+	setDisplayedBackdropMode ('guess')
+	setDisplayedWinningRunCount (winningRunQuestionCount)
+	setDisplayedThumbnails (nextThumbnails)
+	setFromThumbnails (nextThumbnails)
+	setToThumbnails (nextThumbnails)
+	setFlipVisualSeed (visualSeed)
+	return
+      }
+
+    if (displayedBackdropMode === 'winning_run'
+	&& backdropMode === 'winning_run')
+      {
+	applyDirection ()
+	setDisplayedBackdropMode ('winning_run')
+	setDisplayedWinningRunCount (winningRunQuestionCount)
+	setDisplayedThumbnails (nextThumbnails)
+	setFromThumbnails (nextThumbnails)
+	setToThumbnails (nextThumbnails)
+	setIsFlippingTiles (false)
+	setFlipVisualSeed (visualSeed)
+	return
+      }
+
+    if (nextThumbnails.length === 0)
+      {
+	applyDirection ()
+	setIsFlippingTiles (false)
+	setFlipVisualSeed (visualSeed)
+	return
+      }
+
+    const sameTiles =
+	displayedThumbnails.length === nextThumbnails.length
+	&& displayedThumbnails.every ((thumbnail, index) => thumbnail === nextThumbnails[index])
+
+    if (sameTiles && flipVisualSeed === visualSeed)
+      {
+	if (activeDirection.x !== nextDirection.x
+	    || activeDirection.y !== nextDirection.y)
+	  applyDirection ()
+
+	return
+      }
+
+    const currentThumbnails =
+	displayedThumbnails.length > 0 ? displayedThumbnails : nextThumbnails
+
+    setFromThumbnails (currentThumbnails)
+    setToThumbnails (nextThumbnails)
+    setIsFlippingTiles (true)
+
+    flipTimerRef.current = window.setTimeout (() => {
+      setDisplayedBackdropMode (backdropMode)
+      setDisplayedWinningRunCount (winningRunQuestionCount)
+      setDisplayedThumbnails (nextThumbnails)
+      setFromThumbnails (nextThumbnails)
+      setToThumbnails (nextThumbnails)
+      setIsFlippingTiles (false)
+      applyDirection ()
+      setFlipVisualSeed (visualSeed)
+      flipTimerRef.current = null
+    }, tileFlipDuration * 1000)
+
+    return () => {
+      if (flipTimerRef.current != null)
+	{
+	  window.clearTimeout (flipTimerRef.current)
+	  flipTimerRef.current = null
+	}
+    }
+  }, [motionMode,
+      backdropMode,
+      displayedBackdropMode,
+      guessThumbnail,
+      nextThumbnails,
+      nextDirection,
+      displayedThumbnails,
+      flipVisualSeed,
+      visualSeed,
+      activeDirection,
+      winningRunQuestionCount,
+      tileFlipDuration,
+      x,
+      y])
+
+  if (motionMode === 'off' || nextThumbnails.length === 0)
+    return (
+	<div className="absolute inset-0 bg-gradient-to-br from-yellow-50 via-white
+			to-pink-50 dark:from-red-950 dark:via-red-975 dark:to-red-900"/>)
+
+  const backdropTransition: Transition = (() => {
+    if (displayedBackdropMode === 'winning_run' || displayedBackdropMode === 'guess')
+      return { duration: motionMode === 'calm' ? .95 : .75, ease: [.16, 1, .3, 1] }
+
+    return { duration: .2 }
+  }) ()
+
+  return (
+      <div className="fixed [inset:48px_0_0_0] z-0 overflow-hidden pointer-events-none">
+	<div className="absolute inset-0 flex items-center justify-center">
+	  <motion.div
+	      className="relative shrink-0"
+	      style={{
+		  transform: marqueeTransform,
+		  width: 'calc(max(100vw, 100vh) * 3)',
+		  height: 'calc(max(100vw, 100vh) * 3)' }}>
+	    <motion.div
+		className="relative h-full w-full"
+		animate={{ scale: renderedScale,
+			   x: displayedBackdropMode === 'guess' ? guessFocusOffset.x : '0%',
+			   y: displayedBackdropMode === 'guess' ? guessFocusOffset.y : '0%' }}
+		transition={backdropTransition}>
+	      {Array.from ({ length: 9 }, (_, duplicate) => {
+		const column = duplicate % 3
+		const row = Math.floor (duplicate / 3)
+
+		return (
+		    <motion.div
+			key={duplicate}
+			className="absolute grid overflow-hidden"
+			layout={displayedBackdropMode !== 'normal'}
+			style={{
+			    left: `${ column * 33.333333 }%`,
+			    top: `${ row * 33.333333 }%`,
+			    width: '33.333333%',
+			    height: '33.333333%',
+			    gridTemplateColumns:
+				`repeat(${ renderedSettings.columns }, minmax(0, 1fr))`,
+			    gridTemplateRows:
+				`repeat(${ renderedSettings.rows }, minmax(0, 1fr))` }}
+			transition={{ duration: tileFlipDuration, ease: 'easeInOut' }}>
+		      {Array.from ({ length: renderedTileCount }, (_, index) => {
+			const currentThumbnail =
+			    displayedThumbnails[
+				index % Math.max (displayedThumbnails.length, 1)]
+			const frontThumbnail =
+			    isFlippingTiles
+			    ? fromThumbnails[index % Math.max (fromThumbnails.length, 1)]
+			    : currentThumbnail
+			const backThumbnail =
+			    isFlippingTiles
+			    ? toThumbnails[index % Math.max (toThumbnails.length, 1)]
+			    : currentThumbnail
+			const thumbnail =
+			    displayedBackdropMode === 'winning_run'
+			    || displayedBackdropMode === 'guess'
+			    ? nextThumbnails[index % Math.max (nextThumbnails.length, 1)]
+			    : currentThumbnail
+			if (!(thumbnail) || !(frontThumbnail) || !(backThumbnail))
+			  return null
+
+			const imageSource = ['intro', 'end'].includes (phase) ? mascotAsset : thumbnail
+			const showStaticTile =
+			    displayedBackdropMode !== 'normal' || !(isFlippingTiles)
+
+			return (
+			    <motion.div
+				key={`${ duplicate }:${ index }`}
+				className="relative overflow-hidden"
+				layout={displayedBackdropMode !== 'normal'}
+				transition={{ duration: tileFlipDuration, ease: 'easeInOut' }}
+				style={{ perspective: 1600 }}>
+			      {showStaticTile && (
+				  <img
+				      src={imageSource}
+				      alt=""
+				      className="absolute inset-0 h-full w-full object-cover"
+				      style={{ opacity: renderedSettings.opacity }}/>)
+			      }
+			      {!(showStaticTile) && (
+				  <motion.div
+				      className="absolute inset-0"
+				      initial={{ rotateY: 0 }}
+				      animate={{ rotateY: 180 }}
+				      transition={{
+					  duration: tileFlipDuration,
+					  ease: 'easeInOut' }}
+				      style={{ transformStyle: 'preserve-3d' }}>
+				    <img
+					src={backThumbnail}
+					alt=""
+					className="absolute inset-0 h-full w-full object-cover"
+					style={{
+					    backfaceVisibility: 'hidden',
+					    opacity: renderedSettings.opacity,
+					    transform: 'rotateY(180deg)' }}/>
+				    <img
+					src={frontThumbnail}
+					alt=""
+					className="absolute inset-0 h-full w-full object-cover"
+					style={{
+					    backfaceVisibility: 'hidden',
+					    opacity: renderedSettings.opacity }}/>
+				  </motion.div>)}
+			    </motion.div>)
+		      })}
+		    </motion.div>)
+	      })}
+	    </motion.div>
+	  </motion.div>
+	</div>
+	<div className="fixed inset-0 z-0 bg-gradient-to-br from-yellow-50/76 via-white/58
+			to-pink-100/62 dark:from-red-950/78 dark:via-red-975/60
+			dark:to-red-900/66"/>
+      </div>)
+}
+
+
+const expectedAnswerFor = (
+    question:     GekanatorQuestion | undefined,
+    correctPost:  Post | null,
+): GekanatorAnswerValue | null =>
+    expectedAnswerForQuestion (question, correctPost)
+
+
+const GekanatorPage: FC<{ user: User | null }> = ({ user }) => {
+  const storedGame = useMemo (loadStoredGame, [])
+  const hasStoredRestore = storedGame != null && isStoredPhase (storedGame.phase)
+  const queryClient = useQueryClient ()
+  const isAdmin = user?.role === 'admin'
+  const canPersistGame = user != null
+  const [recentGames, setRecentGames] = useState<RecentGameSummary[]> (
+      () => loadRecentGames ())
+  const [backgroundMotionMode, setBackgroundMotionMode] = useState<BackgroundMotionMode> (
+      () => loadBackgroundMotionMode ())
+  const [prefersReducedMotion, setPrefersReducedMotion] = useState (false)
+  const [gameSeed, setGameSeed] = useState (
+      storedGame?.gameSeed ?? createGameSeed ())
+  const [restorePromptVisible, setRestorePromptVisible] = useState (hasStoredRestore)
+  const [phase, setPhase] = useState<Phase> (
+      hasStoredRestore ? 'intro' : storedGame?.phase ?? 'intro')
+  const [scores, setScores] = useState<Map<number, number>> (
+      () => new Map (storedGame?.scores ?? []))
+  const [answers, setAnswers] = useState<GekanatorAnswerLog[]> (
+      storedGame?.answers ?? [])
+  const [askedIds, setAskedIds] = useState<Set<string>> (
+      () => new Set (storedGame?.askedIds ?? []))
+  const [softenedQuestionIds, setSoftenedQuestionIds] = useState<Set<string>> (
+      () => new Set (storedGame?.softenedQuestionIds ?? []))
+  const [recoveredCandidatePosts, setRecoveredCandidatePosts] = useState<
+      Map<number, RecoveredCandidateState>
+  > (() => recoveredCandidateMapFromStored (
+      storedGame?.recoveredCandidatePosts ?? [],
+      storedGame?.scores ?? []))
+  const [recoveryStepCount, setRecoveryStepCount] = useState (
+      storedGame?.recoveryStepCount ?? 0)
+  const [askedQuestionBank, setAskedQuestionBank] = useState<GekanatorQuestion[]> (
+      () => (storedGame?.askedQuestionBank ?? []).map (restoreGekanatorQuestion))
+  const [storedAskedQuestionBankIds, setStoredAskedQuestionBankIds] = useState<string[]> (
+      () => {
+	if ((storedGame?.askedQuestionBank?.length ?? 0) > 0)
+	  return []
+
+	return storedGame?.askedQuestionBankIds ?? []
+      })
+  const [search, setSearch] = useState (storedGame?.search ?? '')
+  const [selectingCorrectPost, setSelectingCorrectPost] = useState (
+      storedGame?.selectingCorrectPost ?? false)
+  const [saved, setSaved] = useState (storedGame?.saved ?? false)
+  const [resultWon, setResultWon] = useState<boolean | null> (
+      storedGame?.resultWon ?? null)
+  const [rejectedPostIds, setRejectedPostIds] = useState<Set<number>> (
+      () => new Set (storedGame?.rejectedPostIds ?? []))
+  const [lastGuessQuestionCount, setLastGuessQuestionCount] = useState (
+      storedGame?.lastGuessQuestionCount ?? 0)
+  const [lastRejectedGuessId, setLastRejectedGuessId] = useState<number | null> (
+      storedGame?.lastRejectedGuessId ?? null)
+  const [winningRunTargetId, setWinningRunTargetId] = useState<number | null> (
+      storedGame?.winningRunTargetId ?? null)
+  const [winningRunStartAnswerCount, setWinningRunStartAnswerCount] =
+      useState<number | null> (storedGame?.winningRunStartAnswerCount ?? null)
+  const [guessReason, setGuessReason] = useState<GuessReason | null> (
+      storedGame?.guessReason ?? null)
+  const [activeGuessId, setActiveGuessId] = useState<number | null> (
+      storedGame?.activeGuessId ?? null)
+  const [reviewGuessedPostId, setReviewGuessedPostId] = useState<number | null> (
+      storedGame?.reviewGuessedPostId ?? null)
+  const [reviewCorrectPostId, setReviewCorrectPostId] = useState<number | null> (
+      storedGame?.reviewCorrectPostId ?? null)
+  const [savedGameId, setSavedGameId] = useState<number | null> (
+      storedGame?.savedGameId ?? null)
+  const [learnedExampleCount, setLearnedExampleCount] = useState<number | null> (
+      storedGame?.learnedExampleCount ?? null)
+  const [questionSuggestionEntryMode, setQuestionSuggestionEntryMode] =
+      useState<QuestionSuggestionEntryMode> (
+	  storedGame?.questionSuggestionEntryMode ?? 'search')
+  const [questionSuggestionSearch, setQuestionSuggestionSearch] = useState (
+      storedGame?.questionSuggestionSearch ?? '')
+  const [questionSuggestionSelectedId, setQuestionSuggestionSelectedId] =
+      useState<number | null> (storedGame?.questionSuggestionSelectedId ?? null)
+  const [questionSuggestion, setQuestionSuggestion] = useState (
+      storedGame?.questionSuggestion ?? '')
+  const [questionSuggestionAnswer, setQuestionSuggestionAnswer] =
+      useState<GekanatorAnswerValue> (storedGame?.questionSuggestionAnswer ?? 'yes')
+  const [questionSuggestionCount, setQuestionSuggestionCount] = useState (
+      storedGame?.questionSuggestionCount ?? 0)
+  const [extraQuestions, setExtraQuestions] = useState<GekanatorExtraQuestion[]> (
+      storedGame?.extraQuestions ?? [])
+  const [extraQuestionAnswers, setExtraQuestionAnswers] =
+      useState<Record<string, GekanatorAnswerValue>> (
+	  storedGame?.extraQuestionAnswers ?? { })
+  const [extraQuestionState, setExtraQuestionState] = useState<
+      'idle' | 'loading' | 'ready' | 'empty' | 'saved'
+  > (storedGame?.extraQuestionState ?? 'idle')
+  const [history, setHistory] = useState<GameSnapshot[]> ([])
+
+  const { data: posts = [], isLoading, error } = useQuery ({
+      queryKey: gekanatorKeys.posts (),
+      queryFn: fetchGekanatorPosts,
+      refetchOnWindowFocus: false })
+  const {
+      data: acceptedQuestions = [],
+      isFetched: acceptedQuestionsFetched,
+      isLoading: acceptedQuestionsLoading,
+      error: acceptedQuestionsError
+  } = useQuery ({
+      queryKey: gekanatorKeys.questions (),
+      queryFn: fetchGekanatorQuestions,
+      select: questions => questions.map (restoreGekanatorQuestion),
+      refetchOnWindowFocus: false })
+  const materialIndex = useMemo (() => buildMaterialIndex (posts), [posts])
+  const acceptedQuestionMatchIndex = useMemo (
+      () => buildGekanatorMatchIndex (posts, acceptedQuestions),
+      [posts, acceptedQuestions])
+
+  useEffect (() => {
+    if (posts.length === 0
+	|| storedAskedQuestionBankIds.length === 0
+	|| !(acceptedQuestionsFetched))
+      return
+
+    const questionById = new Map (
+	mergeQuestions ([
+	    ...acceptedQuestions,
+	    ...askedQuestionBank])
+	    .map (question => [question.id, question]))
+    setAskedQuestionBank (
+	storedAskedQuestionBankIds
+	    .map (questionId => questionById.get (questionId))
+	    .filter ((question): question is GekanatorQuestion => question != null))
+    setStoredAskedQuestionBankIds ([])
+  }, [posts,
+      storedAskedQuestionBankIds,
+      acceptedQuestionsFetched,
+      askedQuestionBank,
+      acceptedQuestions])
+
+  useEffect (() => {
+    if (restorePromptVisible)
+      return
+
+    if (!(isStoredPhase (phase)) && answers.length === 0)
+      {
+	clearStoredGame ()
+	return
+      }
+
+    const stored: StoredGekanatorGame = {
+	phase,
+	scores: [...scores.entries ()],
+	answers,
+	askedIds: [...askedIds],
+	softenedQuestionIds: [...softenedQuestionIds],
+	recoveredCandidatePosts: storedRecoveredCandidatesFromMap (recoveredCandidatePosts),
+	recoveryStepCount,
+	askedQuestionBank: askedQuestionBank.map (storeGekanatorQuestion),
+	askedQuestionBankIds: storedAskedQuestionBankIds,
+	search,
+	selectingCorrectPost,
+	saved,
+	resultWon,
+	rejectedPostIds: [...rejectedPostIds],
+	lastGuessQuestionCount,
+	lastRejectedGuessId,
+	winningRunTargetId,
+	winningRunStartAnswerCount,
+	guessReason,
+	activeGuessId,
+	reviewGuessedPostId,
+	reviewCorrectPostId,
+	savedGameId,
+	learnedExampleCount,
+	gameSeed,
+	questionSuggestionEntryMode,
+	questionSuggestionSearch,
+	questionSuggestionSelectedId,
+	questionSuggestion,
+	questionSuggestionAnswer,
+	questionSuggestionCount,
+	extraQuestions,
+	extraQuestionAnswers,
+	extraQuestionState }
+
+    try
+    {
+      sessionStorage.setItem (gameStorageKey, JSON.stringify (stored))
+    }
+    catch
+    {
+      return
+    }
+  }, [
+      phase,
+      scores,
+      answers,
+      askedIds,
+      softenedQuestionIds,
+      recoveredCandidatePosts,
+      recoveryStepCount,
+      askedQuestionBank,
+      storedAskedQuestionBankIds,
+      search,
+      selectingCorrectPost,
+      saved,
+      resultWon,
+      rejectedPostIds,
+      lastGuessQuestionCount,
+      lastRejectedGuessId,
+      winningRunTargetId,
+      winningRunStartAnswerCount,
+      guessReason,
+      activeGuessId,
+      reviewGuessedPostId,
+      reviewCorrectPostId,
+      savedGameId,
+      learnedExampleCount,
+      gameSeed,
+      questionSuggestionEntryMode,
+      questionSuggestionSearch,
+      questionSuggestionSelectedId,
+      questionSuggestion,
+      questionSuggestionAnswer,
+      questionSuggestionCount,
+      extraQuestions,
+      extraQuestionAnswers,
+      extraQuestionState,
+      restorePromptVisible])
+
+  useEffect (() => {
+    if (typeof window === 'undefined' || typeof window.matchMedia !== 'function')
+      return
+
+    const media = window.matchMedia ('(prefers-reduced-motion: reduce)')
+    const sync = () => setPrefersReducedMotion (media.matches)
+
+    sync ()
+    media.addEventListener ('change', sync)
+    return () => media.removeEventListener ('change', sync)
+  }, [])
+
+  useEffect (() => {
+    try
+    {
+      localStorage.setItem (backgroundMotionStorageKey, backgroundMotionMode)
+    }
+    catch
+    {
+      return
+    }
+  }, [backgroundMotionMode])
+
+  const askedQuestionById = useMemo (
+      () => new Map (askedQuestionBank.map (question => [question.id, question])),
+      [askedQuestionBank])
+  const eligiblePosts = useMemo (
+      () => candidatePostsForState ({
+	  posts,
+	  questionById: askedQuestionById,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex,
+	  answers,
+	  softenedQuestionIds,
+	  rejectedPostIds,
+	  recoveredCandidatePosts,
+	  scores }),
+      [posts, askedQuestionById, materialIndex, acceptedQuestionMatchIndex,
+	  answers, softenedQuestionIds, rejectedPostIds, recoveredCandidatePosts, scores])
+  const scoringQuestions = useMemo (() => {
+    return mergeQuestions ([...acceptedQuestions, ...askedQuestionBank])
+  }, [acceptedQuestions, askedQuestionBank])
+  const scoringQuestionById = useMemo (
+      () => new Map (scoringQuestions.map (question => [question.id, question])),
+      [scoringQuestions])
+  const searchableSuggestedQuestions = useMemo (
+      () => searchedQuestionsFor (acceptedQuestions, questionSuggestionSearch),
+      [acceptedQuestions, questionSuggestionSearch])
+  const selectedSuggestedQuestion = useMemo (
+      () => acceptedQuestions.find (
+	  question => question.recordId === questionSuggestionSelectedId)
+	  ?? null,
+      [acceptedQuestions, questionSuggestionSelectedId])
+  const canSubmitQuestionSuggestion = useMemo (() => {
+    if (!(canPersistGame) || reviewCorrectPostId == null)
+      return false
+
+    if (questionSuggestionEntryMode === 'search')
+      return selectedSuggestedQuestion != null
+
+    return questionSuggestion.trim () !== ''
+  }, [
+      canPersistGame,
+      reviewCorrectPostId,
+      questionSuggestionEntryMode,
+      selectedSuggestedQuestion,
+      questionSuggestion])
+  const recentFirstQuestionPenaltyById = useMemo (() => {
+    const penalties = new Map<string, number> ()
+
+    recentGames.forEach ((game, index) => {
+      if (!(game.firstQuestionId))
+	return
+
+      penalties.set (
+	  game.firstQuestionId,
+	  (penalties.get (game.firstQuestionId) ?? 0) + Math.max (.2, 1 - index * .22))
+    })
+
+    return penalties
+  }, [recentGames])
+  const userPriorWeights = useMemo (
+      () => userPriorWeightsFor (posts, recentGames),
+      [posts, recentGames])
+  const availablePosts = useMemo (
+      () => posts.filter (post => !(rejectedPostIds.has (post.id))),
+      [posts, rejectedPostIds])
+  const questionPlan = useMemo (
+      () => nextQuestionPlanFor ({
+	  posts,
+	  eligiblePosts,
+	  availablePosts,
+	  acceptedQuestions,
+	  scores,
+	  answers,
+	  askedIds,
+	  gameSeed,
+	  recentFirstQuestionPenaltyById,
+	  userPriorWeights,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex,
+	  lastGuessQuestionCount,
+	  winningRunTargetId,
+	  winningRunStartAnswerCount }),
+      [posts, eligiblePosts, availablePosts, acceptedQuestions, scores,
+	  answers, askedIds, gameSeed, recentFirstQuestionPenaltyById,
+	  userPriorWeights, materialIndex, acceptedQuestionMatchIndex,
+	  lastGuessQuestionCount, winningRunTargetId, winningRunStartAnswerCount])
+  const winningRunTargetPost = useMemo (
+      () => {
+	if (questionPlan.winningRunTargetId == null)
+	  return null
+
+	return posts.find (post => post.id === questionPlan.winningRunTargetId) ?? null
+      },
+      [posts, questionPlan.winningRunTargetId])
+  const winningRunQuestionsAsked = winningRunQuestionCount (
+      answers,
+      questionPlan.winningRunStartAnswerCount)
+  const winningRunActive =
+      isWinningRunActive (
+	  questionPlan.winningRunTargetId,
+	  questionPlan.winningRunStartAnswerCount)
+      && winningRunQuestionsAsked < winningRunQuestionLimit
+      && eligiblePosts.length === 1
+      && eligiblePosts[0]?.id === questionPlan.winningRunTargetId
+      && winningRunTargetPost != null
+  const topScoredPosts = useMemo (
+      () => eligiblePosts
+      .map (post => ({ post, score: scores.get (post.id) ?? 0 }))
+      .sort ((a, b) => b.score - a.score)
+      .slice (0, 3),
+      [eligiblePosts, scores])
+  const currentQuestion = questionPlan.question
+  const answerPreviews = useMemo (
+      () => {
+	if (!(isAdmin) || !(currentQuestion))
+	  return []
+
+	return answerOptions.map (option => previewAnswer ({
+	    posts: eligiblePosts,
+	    scores,
+	    question: currentQuestion,
+	    answer: option.value,
+	    materialIndex,
+	    matchIndex: acceptedQuestionMatchIndex }))
+      },
+      [isAdmin, currentQuestion, eligiblePosts, materialIndex,
+	  acceptedQuestionMatchIndex, scores])
+  const guessablePosts = eligiblePosts.length > 0 ? eligiblePosts : availablePosts
+  const guessConfidences = useMemo (
+      () => confidencesFor (guessablePosts, scores),
+      [guessablePosts, scores])
+  const bestConfidencePercent = guessConfidences[0]?.percent ?? 0
+  const guess = bestPost (guessablePosts, scores)
+  const displayedGuess =
+      posts.find (post => post.id === activeGuessId) ?? guess
+  const reviewGuessedPost =
+      posts.find (post => post.id === reviewGuessedPostId) ?? null
+  const reviewCorrectPost =
+      posts.find (post => post.id === reviewCorrectPostId) ?? null
+  const effectiveResultWon = (() => {
+    if (resultWon != null)
+      return resultWon
+    if (reviewGuessedPostId == null || reviewCorrectPostId == null)
+      return null
+
+    return reviewGuessedPostId === reviewCorrectPostId
+  }) ()
+  const effectiveBackgroundMotionMode = (() => {
+    if (backgroundMotionMode === 'off')
+      return 'off'
+    if (prefersReducedMotion)
+      return 'calm'
+
+    return backgroundMotionMode
+  }) ()
+  const backgroundPosts = useMemo (
+      () => backgroundPostsFor ({
+	      phase,
+	      eligiblePosts,
+	      availablePosts,
+	      displayedGuess,
+	      reviewCorrectPost,
+	      reviewGuessedPost }),
+      [phase, eligiblePosts, availablePosts, displayedGuess, reviewCorrectPost,
+	  reviewGuessedPost])
+  const backgroundVisualSeed =
+	`${ gameSeed }:${ phase }:${ answers.length }:${ activeGuessId ?? '' }:${
+	    questionPlan.question?.id ?? ''
+	}:${ questionPlan.questionMode ?? '' }:${ winningRunQuestionsAsked }:${
+	    rejectedPostIds.size
+	}:${ backgroundPosts.slice (0, 8).map (post => post.id).join ('|') }`
+  const mascot = mascotStateFor (phase, effectiveResultWon, eligiblePosts.length,
+				 bestConfidencePercent, winningRunActive)
+  const mascotAsset = mascotAssetByState[mascot]
+  const mascotAlt = mascotAltByState[mascot]
+  const saveMutation = useMutation ({
+      mutationFn: saveGekanatorGame,
+      onSuccess: (data, variables) => {
+	setRecentGames (storeRecentGameSummary ({
+	    correctPostId: variables.correctPostId,
+	    firstQuestionId: variables.answers[0]?.questionId ?? null,
+	    savedAt: Date.now () }))
+	setSaved (true)
+	setSavedGameId (data.id)
+	setLearnedExampleCount (data.learnedExampleCount)
+	setResultWon (variables.guessedPostId === variables.correctPostId)
+      }})
+  const questionSuggestionMutation = useMutation ({
+      mutationFn: saveGekanatorQuestionSuggestion,
+      onSuccess: async data => {
+	await queryClient.refetchQueries ({ queryKey: gekanatorKeys.questions () })
+	setQuestionSuggestionCount (data.count)
+	setQuestionSuggestionEntryMode ('search')
+	setQuestionSuggestionSearch ('')
+	setQuestionSuggestionSelectedId (null)
+	setQuestionSuggestion ('')
+	setQuestionSuggestionAnswer ('yes')
+      }})
+  const extraQuestionAnswersMutation = useMutation ({
+      mutationFn: saveGekanatorExtraQuestionAnswers,
+      onSuccess: async () => {
+	await queryClient.refetchQueries ({ queryKey: gekanatorKeys.questions () })
+	setExtraQuestionState ('saved')
+	setPhase ('end')
+      }})
+
+  const resetExtraQuestionState = () => {
+    const next = resettableExtraQuestionState ()
+    setExtraQuestions (next.extraQuestions.slice (0, 2))
+    setExtraQuestionAnswers (next.extraQuestionAnswers)
+    setExtraQuestionState (next.extraQuestionState)
+    extraQuestionAnswersMutation.reset ()
+  }
+
+  const reset = () => {
+    clearStoredGame ()
+    saveMutation.reset ()
+    questionSuggestionMutation.reset ()
+    setRestorePromptVisible (false)
+    setPhase ('intro')
+    setScores (new Map ())
+    setAnswers ([])
+    setAskedIds (new Set ())
+    setSoftenedQuestionIds (new Set ())
+    setRecoveredCandidatePosts (new Map ())
+    setRecoveryStepCount (0)
+    setAskedQuestionBank ([])
+    setSearch ('')
+    setSelectingCorrectPost (false)
+    setSaved (false)
+    setResultWon (null)
+    setRejectedPostIds (new Set ())
+    setLastGuessQuestionCount (0)
+    setLastRejectedGuessId (null)
+    setWinningRunTargetId (null)
+    setWinningRunStartAnswerCount (null)
+    setGuessReason (null)
+    setActiveGuessId (null)
+    setReviewGuessedPostId (null)
+    setReviewCorrectPostId (null)
+    setSavedGameId (null)
+    setLearnedExampleCount (null)
+    setGameSeed (createGameSeed ())
+    setQuestionSuggestionEntryMode ('search')
+    setQuestionSuggestionSearch ('')
+    setQuestionSuggestionSelectedId (null)
+    setQuestionSuggestion ('')
+    setQuestionSuggestionAnswer ('yes')
+    setQuestionSuggestionCount (0)
+    resetExtraQuestionState ()
+    setHistory ([])
+  }
+
+  const continueStoredGame = () => {
+    setRestorePromptVisible (false)
+    setPhase (storedGame?.phase ?? 'question')
+  }
+
+  const recoverQuestionState = useCallback (({
+      nextAnswers,
+      nextAskedIds,
+      nextAskedQuestionBank,
+      nextSoftenedQuestionIds,
+      nextRejectedPostIds,
+      nextRecoveredCandidatePosts,
+      nextRecoveryStepCount,
+      allowPreQuestionRecovery,
+  }: {
+      nextAnswers:              GekanatorAnswerLog[]
+      nextAskedIds:             Set<string>
+      nextAskedQuestionBank:    GekanatorQuestion[]
+      nextSoftenedQuestionIds:  Set<string>
+      nextRejectedPostIds:      Set<number>
+      nextRecoveredCandidatePosts: Map<number, RecoveredCandidateState>
+      nextRecoveryStepCount:    number
+      allowPreQuestionRecovery?: boolean
+  }) => {
+    let recoveredSoftenedQuestionIds = new Set (nextSoftenedQuestionIds)
+    let recoveredCandidatePosts = new Map (nextRecoveredCandidatePosts)
+    let recoveredStepCount = nextRecoveryStepCount
+    const nextAskedQuestionById =
+	new Map (nextAskedQuestionBank.map (question => [question.id, question]))
+    const answerCountAtRecovery = (() => {
+      if (allowPreQuestionRecovery)
+	return nextAnswers.length
+
+      return Math.max (nextAnswers.length - 1, 0)
+    }) ()
+    let recoveredScores = recalculateScores ({
+	posts,
+	questions: nextAskedQuestionBank,
+	answers: nextAnswers,
+	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	materialIndex,
+	matchIndex: acceptedQuestionMatchIndex })
+    let recoveredEligiblePosts = candidatePostsForState ({
+	posts,
+	questionById: nextAskedQuestionById,
+	materialIndex,
+	matchIndex: acceptedQuestionMatchIndex,
+	answers: nextAnswers,
+	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	rejectedPostIds: nextRejectedPostIds,
+	recoveredCandidatePosts,
+	scores: recoveredScores })
+    let recoveredQuestions = buildQuestionsForCandidateIds ({
+	candidateIds: recoveredEligiblePosts.map (post => post.id),
+	materialIndex,
+	acceptedQuestions,
+	mode: 'split' })
+    let recoveredScoringQuestions = mergeQuestions ([
+	...recoveredQuestions,
+	...nextAskedQuestionBank])
+
+    const refreshRecoveredState = () => {
+      recoveredScores = recalculateScores ({
+	  posts,
+	  questions: nextAskedQuestionBank,
+	  answers: nextAnswers,
+	  softenedQuestionIds: recoveredSoftenedQuestionIds,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex })
+      recoveredEligiblePosts = candidatePostsForState ({
+	  posts,
+	  questionById: nextAskedQuestionById,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex,
+	  answers: nextAnswers,
+	  softenedQuestionIds: recoveredSoftenedQuestionIds,
+	  rejectedPostIds: nextRejectedPostIds,
+	  recoveredCandidatePosts,
+	  scores: recoveredScores })
+      recoveredQuestions = buildQuestionsForCandidateIds ({
+	  candidateIds: recoveredEligiblePosts.map (post => post.id),
+	  materialIndex,
+	  acceptedQuestions,
+	  mode: 'split' })
+      recoveredScoringQuestions = mergeQuestions ([
+	  ...recoveredQuestions,
+	  ...nextAskedQuestionBank])
+    }
+
+    const needsPreQuestionRecovery = () => {
+      if (
+	  !(allowPreQuestionRecovery)
+	  || recoveredEligiblePosts.length === 0
+	  || recoveredEligiblePosts.length === 1
+      )
+	return false
+
+      const nextQuestion = chooseQuestion ({
+	  posts: recoveredEligiblePosts,
+	  questions: recoveredScoringQuestions,
+	  scores: recoveredScores,
+	  answers: nextAnswers,
+	  askedIds: nextAskedIds,
+	  gameSeed,
+	  recentFirstQuestionPenaltyById,
+	  userPriorWeights,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex })
+      const fallbackQuestion = nextQuestion?.question ?? chooseFallbackQuestion ({
+	  posts: recoveredEligiblePosts,
+	  allPosts: posts,
+	  questions: recoveredScoringQuestions,
+	  answers: nextAnswers,
+	  askedIds: nextAskedIds,
+	  scores: recoveredScores,
+	  materialIndex,
+	  matchIndex: acceptedQuestionMatchIndex })
+
+      return !(fallbackQuestion)
+	  || !(hasDiscriminatingHardSplitForQuestion ({
+	      candidateIds: recoveredEligiblePosts.map (post => post.id),
+	      question: fallbackQuestion,
+	      posts,
+	      materialIndex,
+	      matchIndex: acceptedQuestionMatchIndex }))
+    }
+
+    while (recoveredEligiblePosts.length === 0 || needsPreQuestionRecovery ())
+      {
+	const recoveredPosts = recoverCandidatePosts ({
+	    posts,
+	    scores: recoveredScores,
+	    rejectedPostIds: nextRejectedPostIds,
+	    recoveredCandidatePosts,
+	    eligiblePostIds: new Set (recoveredEligiblePosts.map (post => post.id)),
+	    answerCountAtRecovery,
+	    recoveryStepCount: recoveredStepCount })
+	if (recoveredPosts)
+	  {
+	    recoveredCandidatePosts = recoveredPosts.recoveredCandidatePosts
+	    recoveredStepCount = recoveredPosts.recoveryStepCount
+	    refreshRecoveredState ()
+	    if (recoveredEligiblePosts.length > 0 && !(needsPreQuestionRecovery ()))
+	      break
+	  }
+
+	if (nextAnswers.length >= hardMaxQuestions)
+	  break
+
+	if (recoveredEligiblePosts.length > 0 && !(needsPreQuestionRecovery ()))
+	  break
+
+	const softened = softenNextQuestionIds ({
+	    questions: nextAskedQuestionBank,
+	    answers: nextAnswers,
+	    softenedQuestionIds: recoveredSoftenedQuestionIds })
+	if (!(softened))
+	  break
+
+	recoveredSoftenedQuestionIds = softened
+	refreshRecoveredState ()
+      }
+
+    return {
+	softenedQuestionIds: recoveredSoftenedQuestionIds,
+	recoveredCandidatePosts,
+	recoveryStepCount: recoveredStepCount,
+	scores: recoveredScores,
+	eligiblePosts: recoveredEligiblePosts,
+	scoringQuestions: recoveredScoringQuestions }
+  }, [
+      posts,
+      gameSeed,
+      materialIndex,
+      acceptedQuestions,
+      acceptedQuestionMatchIndex,
+      recentFirstQuestionPenaltyById,
+      userPriorWeights])
+
+  const answer = (value: GekanatorAnswerValue) => {
+    if (!(currentQuestion))
+      {
+	if (questionPlan.guess && shouldEnterGuessPhase (questionPlan.guessReason))
+	  {
+	    setActiveGuessId (questionPlan.guess.id)
+	    setLastGuessQuestionCount (answers.length)
+	    setGuessReason (questionPlan.guessReason)
+	    setPhase ('guess')
+	  }
+	return
+      }
+
+    setHistory ([...history, {
+	phase,
+	scores: new Map (scores),
+	answers: [...answers],
+	askedIds: new Set (askedIds),
+	softenedQuestionIds: new Set (softenedQuestionIds),
+	recoveredCandidatePosts: new Map (recoveredCandidatePosts),
+	recoveryStepCount,
+	askedQuestionBank: [...askedQuestionBank],
+	search,
+	selectingCorrectPost,
+	rejectedPostIds: new Set (rejectedPostIds),
+	lastGuessQuestionCount,
+	lastRejectedGuessId,
+	winningRunTargetId,
+	winningRunStartAnswerCount,
+	guessReason,
+	activeGuessId,
+	reviewGuessedPostId,
+	reviewCorrectPostId }])
+    const nextAnswers = [...answers, {
+	questionId:      currentQuestion.id,
+	questionText:    currentQuestion.text,
+	questionCondition: currentQuestion.condition,
+	questionMode:    questionPlan.questionMode ?? undefined,
+	questionPurpose: questionPlan.questionPurpose,
+	effectiveQuestion: questionPlan.effectiveQuestion,
+	learningQuestion: questionPlan.learningQuestion,
+	answer:          value,
+	originalAnswer:  value }]
+    const nextAskedIds = new Set ([...askedIds, currentQuestion.id])
+    const nextAskedQuestionBank = [
+	...askedQuestionBank.filter (question => question.id !== currentQuestion.id),
+	currentQuestion]
+    const recovered = recoverQuestionState ({
+	nextAnswers,
+	nextAskedIds,
+	nextAskedQuestionBank,
+	nextSoftenedQuestionIds: softenedQuestionIds,
+	nextRejectedPostIds: rejectedPostIds,
+	nextRecoveredCandidatePosts: recoveredCandidatePosts,
+	nextRecoveryStepCount: recoveryStepCount })
+    const nextEligiblePosts = recovered.eligiblePosts
+    let nextPlan = nextQuestionPlanFor ({
+	posts,
+	eligiblePosts: nextEligiblePosts,
+	availablePosts,
+	acceptedQuestions,
+	scores: recovered.scores,
+	answers: nextAnswers,
+	askedIds: nextAskedIds,
+	gameSeed,
+	recentFirstQuestionPenaltyById,
+	userPriorWeights,
+	materialIndex,
+	matchIndex: acceptedQuestionMatchIndex,
+	lastGuessQuestionCount,
+	winningRunTargetId,
+	winningRunStartAnswerCount })
+    let finalRecovered = recovered
+
+    if (
+	!(nextPlan.question)
+	&& !(shouldEnterGuessPhase (nextPlan.guessReason))
+	&& recovered.eligiblePosts.length !== 1
+    )
+      {
+	const recoveredForQuestion = recoverQuestionState ({
+	    nextAnswers,
+	    nextAskedIds,
+	    nextAskedQuestionBank,
+	    nextSoftenedQuestionIds: recovered.softenedQuestionIds,
+	    nextRejectedPostIds: rejectedPostIds,
+	    nextRecoveredCandidatePosts: recovered.recoveredCandidatePosts,
+	    nextRecoveryStepCount: recovered.recoveryStepCount,
+	    allowPreQuestionRecovery: true })
+	nextPlan = nextQuestionPlanFor ({
+	    posts,
+	    eligiblePosts: recoveredForQuestion.eligiblePosts,
+	    availablePosts,
+	    acceptedQuestions,
+	    scores: recoveredForQuestion.scores,
+	    answers: nextAnswers,
+	    askedIds: nextAskedIds,
+	    gameSeed,
+	    recentFirstQuestionPenaltyById,
+	    userPriorWeights,
+	    materialIndex,
+	    matchIndex: acceptedQuestionMatchIndex,
+	    lastGuessQuestionCount,
+	    winningRunTargetId,
+	    winningRunStartAnswerCount })
+	finalRecovered = recoveredForQuestion
+      }
+
+    setScores (finalRecovered.scores)
+    setAskedIds (nextAskedIds)
+    setSoftenedQuestionIds (finalRecovered.softenedQuestionIds)
+    setRecoveredCandidatePosts (finalRecovered.recoveredCandidatePosts)
+    setRecoveryStepCount (finalRecovered.recoveryStepCount)
+    setAskedQuestionBank (nextAskedQuestionBank)
+    setAnswers (nextAnswers)
+    setWinningRunTargetId (nextPlan.winningRunTargetId)
+    setWinningRunStartAnswerCount (nextPlan.winningRunStartAnswerCount)
+
+    if (nextPlan.question)
+      {
+	setGuessReason (null)
+	setActiveGuessId (null)
+	setPhase ('question')
+	return
+      }
+
+    setGuessReason (nextPlan.guessReason)
+    if (nextPlan.guess && shouldEnterGuessPhase (nextPlan.guessReason))
+      {
+	setActiveGuessId (nextPlan.guess.id)
+	setLastGuessQuestionCount (nextAnswers.length)
+	setPhase ('guess')
+      }
+  }
+
+  const finishGame = (correctPostId: number) => {
+    const guessedPostId = (() => {
+      if (phase === 'end' || phase === 'review')
+	return reviewGuessedPostId
+      if (phase === 'continue')
+	return lastRejectedGuessId ?? displayedGuess?.id
+
+      return displayedGuess?.id ?? lastRejectedGuessId
+    }) ()
+    if (!(guessedPostId))
+      return
+
+    saveMutation.reset ()
+    questionSuggestionMutation.reset ()
+    resetExtraQuestionState ()
+    setSaved (false)
+    setSavedGameId (null)
+    setLearnedExampleCount (null)
+    setQuestionSuggestionEntryMode ('search')
+    setQuestionSuggestionSearch ('')
+    setQuestionSuggestionSelectedId (null)
+    setReviewGuessedPostId (guessedPostId)
+    setReviewCorrectPostId (correctPostId)
+    setSearch ('')
+    setSelectingCorrectPost (false)
+    setPhase ('end')
+  }
+
+  const startReview = () => {
+    if (reviewGuessedPostId == null || reviewCorrectPostId == null)
+      return
+
+    saveMutation.reset ()
+    questionSuggestionMutation.reset ()
+    resetExtraQuestionState ()
+    setSaved (false)
+    setSavedGameId (null)
+    setLearnedExampleCount (null)
+    setQuestionSuggestionEntryMode ('search')
+    setQuestionSuggestionSearch ('')
+    setQuestionSuggestionSelectedId (null)
+    setSelectingCorrectPost (false)
+    setSearch ('')
+    setPhase ('review')
+  }
+
+  const saveReviewedResult = (onSuccess: (gameId: number) => void) => {
+    if (
+	!(canPersistGame)
+	|| reviewGuessedPostId == null
+	|| reviewCorrectPostId == null
+	|| saveMutation.isPending
+    )
+      return
+
+    if (savedGameId != null)
+      {
+	onSuccess (savedGameId)
+	return
+      }
+
+    saveMutation.mutate ({
+	guessedPostId: reviewGuessedPostId,
+	correctPostId: reviewCorrectPostId,
+	answers },
+	{ onSuccess: data => onSuccess (data.id) })
+  }
+
+  const saveAndReset = () => {
+    if (saveMutation.isError)
+      {
+	reset ()
+	return
+      }
+
+    if (!(canPersistGame))
+      {
+	reset ()
+	return
+      }
+
+    saveReviewedResult (reset)
+  }
+
+  const saveAndLearn = () => {
+    if (!(canPersistGame))
+      {
+	setPhase ('end')
+	return
+      }
+
+    resetExtraQuestionState ()
+    saveReviewedResult (() => setPhase ('end'))
+  }
+
+  const submitQuestionSuggestion = () => {
+    const questionText = questionSuggestion.trim ()
+    const selectedQuestion = selectedSuggestedQuestion
+    if (!(canSubmitQuestionSuggestion) || questionSuggestionMutation.isPending)
+      return
+
+    saveReviewedResult (gekanatorGameId => {
+      questionSuggestionMutation.mutate ({
+	  gekanatorGameId,
+	  existingQuestionId: selectedQuestion?.recordId,
+	  questionText: selectedQuestion ? undefined : questionText,
+	  answer: questionSuggestionAnswer })
+    })
+  }
+
+  const saveExtraQuestions = () => {
+    if (
+	!(canPersistGame)
+	|| savedGameId == null
+	|| extraQuestionAnswersMutation.isPending
+	|| extraQuestions.some (question => !(extraQuestionAnswers[String (question.id)]))
+    )
+      return
+
+    extraQuestionAnswersMutation.mutate ({
+	gameId: savedGameId,
+	answers: extraQuestions.map (question => ({
+	    questionId: question.id,
+	    answer: extraQuestionAnswers[String (question.id)] })) })
+  }
+
+  const rejectGuess = () => {
+    if (!(displayedGuess))
+      return
+
+    setLastRejectedGuessId (displayedGuess.id)
+    if (answers.length >= hardMaxQuestions)
+      {
+	setSelectingCorrectPost (true)
+	return
+      }
+
+    setRejectedPostIds (new Set ([...rejectedPostIds, displayedGuess.id]))
+    setRecoveredCandidatePosts (
+	new Map (
+	    [...recoveredCandidatePosts.entries ()].filter (
+		([postId]) => postId !== displayedGuess.id)))
+    setWinningRunTargetId (null)
+    setWinningRunStartAnswerCount (null)
+    setGuessReason (null)
+    setActiveGuessId (null)
+    setSearch ('')
+    setSelectingCorrectPost (false)
+    setLastGuessQuestionCount (answers.length)
+    setPhase ('continue')
+  }
+
+  const undoAnswer = () => {
+    const snapshot = history[history.length - 1]
+    if (!(snapshot) || saved)
+      return
+
+    setPhase (snapshot.phase)
+    setScores (snapshot.scores)
+    setAnswers (snapshot.answers)
+    setAskedIds (snapshot.askedIds)
+    setSoftenedQuestionIds (snapshot.softenedQuestionIds)
+    setRecoveredCandidatePosts (snapshot.recoveredCandidatePosts)
+    setRecoveryStepCount (snapshot.recoveryStepCount)
+    setAskedQuestionBank (snapshot.askedQuestionBank)
+    setSearch (snapshot.search)
+    setSelectingCorrectPost (snapshot.selectingCorrectPost)
+    setRejectedPostIds (snapshot.rejectedPostIds)
+    setLastGuessQuestionCount (snapshot.lastGuessQuestionCount)
+    setLastRejectedGuessId (snapshot.lastRejectedGuessId)
+    setWinningRunTargetId (snapshot.winningRunTargetId)
+    setWinningRunStartAnswerCount (snapshot.winningRunStartAnswerCount)
+    setGuessReason (snapshot.guessReason)
+    setActiveGuessId (snapshot.activeGuessId)
+    setReviewGuessedPostId (snapshot.reviewGuessedPostId)
+    setReviewCorrectPostId (snapshot.reviewCorrectPostId)
+    setHistory (history.slice (0, -1))
+  }
+
+  const continueGame = () => {
+    setSearch ('')
+    setSelectingCorrectPost (false)
+
+    const recovered = recoverQuestionState ({
+	nextAnswers: answers,
+	nextAskedIds: askedIds,
+	nextAskedQuestionBank: askedQuestionBank,
+	nextSoftenedQuestionIds: softenedQuestionIds,
+	nextRejectedPostIds: rejectedPostIds,
+	nextRecoveredCandidatePosts: recoveredCandidatePosts,
+	nextRecoveryStepCount: recoveryStepCount,
+	allowPreQuestionRecovery: true })
+
+    setSoftenedQuestionIds (recovered.softenedQuestionIds)
+    setRecoveredCandidatePosts (recovered.recoveredCandidatePosts)
+    setRecoveryStepCount (recovered.recoveryStepCount)
+    setScores (recovered.scores)
+    const nextPlan = nextQuestionPlanFor ({
+	posts,
+	eligiblePosts: recovered.eligiblePosts,
+	availablePosts,
+	acceptedQuestions,
+	scores: recovered.scores,
+	answers,
+	askedIds,
+	gameSeed,
+	recentFirstQuestionPenaltyById,
+	userPriorWeights,
+	materialIndex,
+	matchIndex: acceptedQuestionMatchIndex,
+	lastGuessQuestionCount,
+	winningRunTargetId,
+	winningRunStartAnswerCount })
+
+    setWinningRunTargetId (nextPlan.winningRunTargetId)
+    setWinningRunStartAnswerCount (nextPlan.winningRunStartAnswerCount)
+
+    if (nextPlan.question)
+      {
+	setGuessReason (null)
+	setActiveGuessId (null)
+	setPhase ('question')
+	return
+      }
+
+    setGuessReason (nextPlan.guessReason)
+    if (nextPlan.guess && shouldEnterGuessPhase (nextPlan.guessReason))
+      {
+	setActiveGuessId (nextPlan.guess.id)
+	setLastGuessQuestionCount (answers.length)
+	setPhase ('guess')
+      }
+  }
+
+  const correctAnswerAt = (index: number, value: GekanatorAnswerValue) => {
+    setSaved (false)
+    setSavedGameId (null)
+    setLearnedExampleCount (null)
+    setQuestionSuggestionEntryMode ('search')
+    setQuestionSuggestionSearch ('')
+    setQuestionSuggestionSelectedId (null)
+    resetExtraQuestionState ()
+    setAnswers (answers.map ((answer, i) =>
+	i === index ? { ...answer, answer: value } : answer))
+  }
+
+  const selectCorrectPost = (post: Post) => {
+    if (phase === 'review')
+      {
+	setSaved (false)
+	setSavedGameId (null)
+	setLearnedExampleCount (null)
+	setQuestionSuggestionEntryMode ('search')
+	setQuestionSuggestionSearch ('')
+	setQuestionSuggestionSelectedId (null)
+	resetExtraQuestionState ()
+	setReviewCorrectPostId (post.id)
+	setSelectingCorrectPost (false)
+	setSearch ('')
+	return
+      }
+
+    finishGame (post.id)
+  }
+
+  const filteredPosts = posts
+      .filter (post => {
+	const needle = search.trim ().toLowerCase ()
+	if (!(needle))
+	  return false
+	if (/^\d+$/.test (needle) && post.id === Number (needle))
+	  return true
+
+	return [post.title, post.url, ...post.tags.map (tag => tag.name)]
+	    .filter ((value): value is string => Boolean (value))
+	    .some (value => value.toLowerCase ().includes (needle))
+      })
+      .sort ((a, b) => {
+	const id = Number (search.trim ())
+	if (Number.isFinite (id))
+	  return Number (b.id === id) - Number (a.id === id)
+
+	return 0
+      })
+      .slice (0, 20)
+
+  const loadExtraQuestions = async (gameId: number) => {
+    extraQuestionAnswersMutation.reset ()
+    setExtraQuestionState ('loading')
+    setExtraQuestions ([])
+    setExtraQuestionAnswers ({ })
+    setPhase ('extra_questions')
+    const nonce = createGameSeed ()
+
+    try
+    {
+      const questions = await queryClient.fetchQuery ({
+	  queryKey: gekanatorKeys.extraQuestions (gameId, nonce),
+	  queryFn: () => fetchGekanatorExtraQuestions (gameId, nonce) })
+      setExtraQuestions (questions.slice (0, 2))
+      setExtraQuestionState (questions.length > 0 ? 'ready' : 'empty')
+    }
+    catch
+    {
+      setExtraQuestionState ('empty')
+    }
+  }
+
+  const startExtraQuestions = () => {
+    if (reviewCorrectPostId == null || saveMutation.isPending)
+      return
+
+    saveReviewedResult (gameId => {
+      void loadExtraQuestions (gameId)
+    })
+  }
+
+  const answerExtraQuestion = (
+      questionId:  number,
+      value:       GekanatorAnswerValue,
+  ) => {
+    setExtraQuestionAnswers ({
+	...extraQuestionAnswers,
+	[String (questionId)]: value })
+  }
+
+  const introDialogue =
+      <>私は<ruby>洗澡鹿<rt>シーザオグカ</rt></ruby>。質問から投稿を何でも当ててみせるよ。</>
+
+  const winDialogue =
+      <>グカカカカwwwww&emsp;<ruby>洗澡鹿<rt>シーザオグカ</rt></ruby>は何でもお見通し!</>
+
+  const loseDialogue =
+      <>ぬわーん!&emsp;<ruby>洗澡鹿<rt>シーザオグカ</rt></ruby>外しちゃったグカー!!!!!</>
+
+  const resultDialogue = effectiveResultWon ? winDialogue : loseDialogue
+
+  const dialogue = phase === 'learned' ? resultDialogue : introDialogue
+  const introLoadingMessage =
+      phase === 'intro' ? '投稿を読み込んでいます……' : '前回のグカネータ状態を復元しています……'
+  const questionSuggestionTitle =
+      questionSuggestionEntryMode === 'search' ? 'まず既存質問を探してください。' : '新しい質問を追加します。'
+
+  const introLoading = isLoading || acceptedQuestionsLoading
+  const readyToStart =
+      !(introLoading)
+      && acceptedQuestionsFetched
+      && posts.length > 0
+      && !(error)
+      && !(acceptedQuestionsError)
+
+  useEffect (() => {
+    if (
+	phase !== 'question'
+	|| currentQuestion
+	|| isLoading
+	|| acceptedQuestionsLoading
+	|| shouldEnterGuessPhase (questionPlan.guessReason)
+	|| eligiblePosts.length === 1
+    )
+      return
+
+    const recovered = recoverQuestionState ({
+	nextAnswers: answers,
+	nextAskedIds: askedIds,
+	nextAskedQuestionBank: askedQuestionBank,
+	nextSoftenedQuestionIds: softenedQuestionIds,
+	nextRejectedPostIds: rejectedPostIds,
+	nextRecoveredCandidatePosts: recoveredCandidatePosts,
+	nextRecoveryStepCount: recoveryStepCount,
+	allowPreQuestionRecovery: true })
+
+    if (
+	recovered.recoveryStepCount === recoveryStepCount
+	&& recovered.recoveredCandidatePosts.size === recoveredCandidatePosts.size
+	&& recovered.softenedQuestionIds.size === softenedQuestionIds.size
+    )
+      return
+
+    setSoftenedQuestionIds (recovered.softenedQuestionIds)
+    setRecoveredCandidatePosts (recovered.recoveredCandidatePosts)
+    setRecoveryStepCount (recovered.recoveryStepCount)
+    setScores (recovered.scores)
+  }, [
+      phase,
+      currentQuestion,
+      questionPlan,
+      answers,
+      askedIds,
+      askedQuestionBank,
+      softenedQuestionIds,
+      rejectedPostIds,
+      recoveredCandidatePosts,
+      recoveryStepCount,
+      eligiblePosts,
+      recoverQuestionState,
+      isLoading,
+      acceptedQuestionsLoading])
+
+  useEffect (() => {
+    if (
+	phase !== 'question'
+	|| isLoading
+	|| acceptedQuestionsLoading
+    )
+      return
+
+    if (
+	currentQuestion
+	|| !(questionPlan.guess)
+	|| !(shouldEnterGuessPhase (questionPlan.guessReason))
+    )
+      return
+
+    setWinningRunTargetId (questionPlan.winningRunTargetId)
+    setWinningRunStartAnswerCount (questionPlan.winningRunStartAnswerCount)
+    setActiveGuessId (questionPlan.guess.id)
+    setLastGuessQuestionCount (answers.length)
+    setGuessReason (questionPlan.guessReason)
+    setPhase ('guess')
+  }, [
+      phase,
+      currentQuestion,
+      questionPlan,
+      answers,
+      isLoading,
+      acceptedQuestionsLoading])
+
+  return (
+      <MainArea className="relative isolate overflow-x-hidden bg-yellow-50 dark:bg-red-975">
+	<Helmet>
+	  <title>{`グカネータ | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<GekanatorBackdrop
+	    posts={backgroundPosts}
+	    mascotAsset={mascotAsset}
+	    phase={phase}
+	    displayedGuess={displayedGuess}
+	    visualSeed={backgroundVisualSeed}
+	    motionMode={effectiveBackgroundMotionMode}
+	    winningRunTargetPost={winningRunActive ? winningRunTargetPost : null}
+	    winningRunQuestionCount={winningRunQuestionsAsked}/>
+
+	<div className="relative z-10 mx-auto max-w-4xl space-y-6">
+	  <header className="flex flex-wrap items-end justify-between gap-3">
+	    <div className="space-y-2">
+	      <h1 className="text-3xl font-bold text-pink-700 dark:text-pink-200">
+		グカネータ
+	      </h1>
+	    </div>
+	    <div className="flex flex-wrap justify-end gap-2">
+	      <div className="rounded-full border border-yellow-300 bg-white/80 px-2 py-1
+			      text-xs shadow-sm backdrop-blur dark:border-red-800
+			      dark:bg-red-950/75">
+		<span className="mr-2 font-bold text-neutral-600 dark:text-neutral-300">
+		  背景
+		</span>
+		{[{ mode: 'off' as const, label: 'オフ' },
+		  { mode: 'on' as const, label: 'オン' }]
+		 .map (({ mode, label }) => {
+		   const modeClass =
+		       backgroundMotionMode === mode
+		       ? 'bg-pink-600 text-white'
+		       : 'text-neutral-600 hover:bg-yellow-100 dark:text-neutral-300 dark:hover:bg-red-900'
+
+		   return (
+		       <button
+			   key={mode}
+			   type="button"
+			   className={cn (
+			       'rounded-full px-2.5 py-1 transition-colors',
+			       modeClass)}
+			   onClick={() => setBackgroundMotionMode (mode)}>
+			 {label}
+		       </button>)
+		 })}
+		{prefersReducedMotion && effectiveBackgroundMotionMode !== 'off' && (
+		    <span className="ml-2 text-[11px] text-neutral-500 dark:text-neutral-400">
+		      端末設定により控えめ表示
+		    </span>)}
+	      </div>
+	    </div>
+	  </header>
+
+	  <section className="relative z-10 rounded-lg border border-yellow-300
+			      bg-white/90 p-4 shadow-sm backdrop-blur-sm
+			      dark:border-red-800 dark:bg-red-950/90">
+	    <div className="relative z-10 flex gap-4">
+	      <div className="shrink-0 space-y-2">
+		<div className="overflow-hidden rounded-[1.4rem] border border-white/70
+				bg-white/75 shadow-lg backdrop-blur dark:border-red-900/80
+				dark:bg-red-950/70">
+		  <img
+		      src={mascotAsset}
+		      alt={mascotAlt}
+		      className="h-28 w-28 object-cover md:h-32 md:w-32"/>
+		</div>
+	      </div>
+	      <div className="min-w-0 flex-1 space-y-3">
+		{phase === 'intro' && (
+		    <p className="text-lg font-bold">
+		      {dialogue}
+		    </p>)}
+
+		{introLoading && (
+		    <p>
+		      {introLoadingMessage}
+		    </p>)}
+		{(Boolean (error) || Boolean (acceptedQuestionsError))
+		    && <p>グカネータの質問データを読み込めませんでした．</p>}
+
+		{phase === 'intro' && readyToStart && restorePromptVisible && (
+		    <div className="flex flex-wrap gap-2">
+		      <button
+			  type="button"
+			  className="rounded border border-yellow-300 px-4 py-2
+				     hover:bg-yellow-100 dark:border-red-700
+				     dark:hover:bg-red-900"
+			  onClick={() => {
+			    reset ()
+			    setRestorePromptVisible (false)
+			    setPhase ('question')
+			  }}>
+			最初からやり直す
+		      </button>
+		      <button
+			  type="button"
+			  className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				     hover:bg-pink-500"
+			  onClick={continueStoredGame}>
+			続きから
+		      </button>
+		    </div>)}
+
+		{phase === 'intro' && readyToStart && !(restorePromptVisible) && (
+		    <button
+			type="button"
+			className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				   hover:bg-pink-500"
+			onClick={() => {
+			  setRestorePromptVisible (false)
+			  setPhase ('question')
+			}}>
+		      始める
+		    </button>)}
+
+		{phase === 'question' && currentQuestion && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-sm text-neutral-500">
+			  質問 {answers.length + 1}
+			</p>
+			<p className="text-xl font-bold">{currentQuestion.text}</p>
+		      </div>
+		      {isAdmin && (
+			  <div className="rounded border border-yellow-100 px-3 py-2
+					  text-sm dark:border-red-900">
+			    <div className="font-bold">現在候補: {eligiblePosts.length} 件</div>
+			    <div className="mt-1 text-xs text-neutral-600 dark:text-neutral-300">
+			      winningRunTargetId: {String (questionPlan.winningRunTargetId)}
+			      {' / '}
+			      winningRunQuestionCount: {winningRunQuestionsAsked}
+			      {' / '}
+			      guessReason: {guessReason ?? '-'}
+			      {' / '}
+			      questionMode: {questionPlan.questionMode ?? '-'}
+			      {' / '}
+			      recoveryStepCount: {recoveryStepCount}
+			      {' / '}
+			      currentQuestion===null: {String (currentQuestion == null)}
+			    </div>
+			    {topScoredPosts.length > 0 && (
+				<div className="mt-1 flex flex-wrap gap-x-4 gap-y-1">
+				  {topScoredPosts.map (item => (
+				      <span key={item.post.id}>
+					#{item.post.id}: score {item.score.toFixed (1)}
+				      </span>))}
+				</div>)}
+			  </div>)}
+		      {isAdmin && answerPreviews.length > 0 && (
+			  <div className="grid gap-2 text-sm md:grid-cols-2">
+			    {answerOptions.map (option => {
+			      const preview =
+				  answerPreviews.find (item => item.answer === option.value)
+			      return (
+				  <div
+				      key={option.value}
+				      className="rounded border border-yellow-100 px-3 py-2
+						 dark:border-red-900">
+				    <span className="font-bold">{option.label}</span>
+				    {' '}
+				    <span className="text-neutral-600 dark:text-neutral-300">
+				      候補 {preview ? preview.candidateCount : 0} 件
+				    </span>
+				    <div className="mt-1 text-xs text-neutral-500 dark:text-neutral-400">
+				      effective {preview?.effectiveCandidates.toFixed (2) ?? '0.00'}
+				      {' / '}
+				      entropy {preview?.entropy.toFixed (2) ?? '0.00'}
+				    </div>
+				  </div>)
+			    })}
+			  </div>)}
+		      <div className="flex flex-wrap gap-2">
+			{answerOptions.map (option => (
+			    <button
+				key={option.value}
+				type="button"
+				className="rounded border border-yellow-300 px-3 py-2
+					   hover:bg-yellow-100 dark:border-red-700
+					   dark:hover:bg-red-900"
+				onClick={() => answer (option.value)}>
+			      {option.label}
+			    </button>))}
+			{history.length > 0 && (
+			    <button
+				type="button"
+				className="rounded border border-neutral-300 px-3 py-2
+					   hover:bg-neutral-100 dark:border-neutral-700
+					   dark:hover:bg-red-900"
+				onClick={undoAnswer}>
+			      戻る
+			    </button>)}
+		      </div>
+		    </div>)}
+		{phase === 'question' && !(currentQuestion) && isAdmin && (
+		    <div className="rounded border border-yellow-100 px-3 py-2 text-sm
+				    dark:border-red-900">
+		      <div className="font-bold">question stalled</div>
+		      <div className="mt-1 text-xs text-neutral-600 dark:text-neutral-300">
+			winningRunTargetId: {String (questionPlan.winningRunTargetId)}
+			{' / '}
+			winningRunQuestionCount: {winningRunQuestionsAsked}
+			{' / '}
+			guessReason: {questionPlan.guessReason ?? '-'}
+			{' / '}
+			questionMode: {questionPlan.questionMode ?? '-'}
+			{' / '}
+			recoveryStepCount: {recoveryStepCount}
+			{' / '}
+			candidateCount: {eligiblePosts.length}
+		      </div>
+		    </div>)}
+		{phase === 'guess' && displayedGuess && (
+		    <div className="space-y-4">
+		      <p className="text-xl font-bold">思い浮かべているのは、これだね?</p>
+		      {isAdmin && (
+			  <div className="rounded border border-yellow-100 px-3 py-2
+					  text-sm dark:border-red-900">
+			    winningRunTargetId: {String (questionPlan.winningRunTargetId)}
+			    {' / '}
+			    winningRunQuestionCount: {winningRunQuestionsAsked}
+			    {' / '}
+			    guessReason: {guessReason ?? '-'}
+			    {' / '}
+			    questionMode: {questionPlan.questionMode ?? '-'}
+			    {' / '}
+			    recoveryStepCount: {recoveryStepCount}
+			    {' / '}
+			    currentQuestion===null: {String (currentQuestion == null)}
+			  </div>)}
+		      <PostMiniCard post={displayedGuess}/>
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500"
+			    onClick={() => {
+			      if (displayedGuess)
+				finishGame (displayedGuess.id)
+			    }}>
+			  当たり
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900"
+			    onClick={rejectGuess}>
+			  違う
+			</button>
+			{history.length > 0 && (
+			    <button
+				type="button"
+				className="rounded border border-neutral-300 px-4 py-2
+					   hover:bg-neutral-100 dark:border-neutral-700
+					   dark:hover:bg-red-900"
+				onClick={undoAnswer}>
+			      戻る
+			    </button>)}
+		      </div>
+		      {saveMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    記録できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+		    </div>)}
+
+		{phase === 'continue' && (
+		    <div className="space-y-4">
+		      <p className="text-xl font-bold">続けますか?</p>
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500"
+			    onClick={continueGame}>
+			  はい
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setSelectingCorrectPost (true)}>
+			  いいえ
+			</button>
+			{history.length > 0 && (
+			    <button
+				type="button"
+				className="rounded border border-neutral-300 px-4 py-2
+					   hover:bg-neutral-100 dark:border-neutral-700
+					   dark:hover:bg-red-900"
+				onClick={undoAnswer}>
+			      戻る
+			    </button>)}
+		      </div>
+		    </div>)}
+
+		{phase === 'end' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-xl font-bold">{resultDialogue}</p>
+		      </div>
+
+		      {reviewGuessedPost && (
+			  <div className="space-y-2">
+			    <div className="font-bold">推測した投稿</div>
+			    <PostMiniCard post={reviewGuessedPost}/>
+			  </div>)}
+
+		      <div className="space-y-2">
+			<div className="font-bold">正解の投稿</div>
+			{reviewCorrectPost && <PostMiniCard post={reviewCorrectPost}/>}
+			{!(reviewCorrectPost) && (
+			    <p className="text-sm text-red-600">正解投稿を選んでください。</p>)}
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-3 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setSelectingCorrectPost (true)}>
+			  正解投稿を変更
+			</button>
+		      </div>
+
+		      {reviewGuessedPostId != null && reviewCorrectPostId != null && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    判定: {reviewGuessedPostId === reviewCorrectPostId ? '当たり' : 'はずれ'}
+			  </p>)}
+
+		      {saveMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    記録できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+		      {!(canPersistGame) && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    未ログインのため今回の結果は保存されません。
+			    <PrefetchLink to="/users/settings" className="ml-1 underline">
+			      設定
+			    </PrefetchLink>
+			    から引継ぎコードを復元すると、質問追加や追加学習も使へます。
+			  </p>)}
+
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500 disabled:opacity-50"
+			    disabled={reviewCorrectPostId == null || saveMutation.isPending}
+			    onClick={saveAndReset}>
+			  もう一度
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={
+			      !(canPersistGame)
+			      || reviewCorrectPostId == null
+			      || saveMutation.isPending
+			    }
+			    onClick={startReview}>
+			  修正
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={!(canPersistGame)
+				      || saveMutation.isPending
+				      || questionSuggestionMutation.isPending}
+			    onClick={() => setPhase ('question_suggestion')}>
+			  質問を追加
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={!(canPersistGame)
+				      || reviewCorrectPostId == null
+				      || saveMutation.isPending
+				      || extraQuestionState === 'loading'
+				      || extraQuestionAnswersMutation.isPending}
+			    onClick={startExtraQuestions}>
+			  追加で質問に答える
+			</button>
+		      </div>
+		    </div>)}
+
+		{phase === 'review' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-xl font-bold">結果修正</p>
+		      </div>
+
+		      {reviewGuessedPost && (
+			  <div className="space-y-2">
+			    <div className="font-bold">推測した投稿</div>
+			    <PostMiniCard post={reviewGuessedPost}/>
+			  </div>)}
+
+		      <div className="space-y-2">
+			<div className="font-bold">正解の投稿</div>
+			{reviewCorrectPost && <PostMiniCard post={reviewCorrectPost}/>}
+			{!(reviewCorrectPost) && (
+			    <p className="text-sm text-red-600">正解投稿を選んでください。</p>)}
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-3 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setSelectingCorrectPost (true)}>
+			  正解投稿を変更
+			</button>
+		      </div>
+
+		      <div className="space-y-2">
+			<div className="font-bold">質問と回答</div>
+			<div className="space-y-2">
+			  {answers.map ((answer, index) => {
+			    const expectedAnswer = expectedAnswerFor (
+				scoringQuestionById.get (answer.questionId),
+				reviewCorrectPost)
+
+			    return (
+				<div
+				    key={`${ answer.questionId }:${ index }`}
+				    className="rounded border border-yellow-100 p-3
+					       dark:border-red-900">
+				  <div className="text-sm text-neutral-600 dark:text-neutral-300">
+				    質問 {index + 1}
+				  </div>
+				  <div className="font-bold">{answer.questionText}</div>
+				  <div className="mt-2 grid gap-1 text-sm md:grid-cols-3">
+				    <div>
+				      <span className="text-neutral-500">グカネータ判定: </span>
+				      {expectedAnswer ? answerLabelFor (expectedAnswer) : '不明'}
+				    </div>
+				    <div>
+				      <span className="text-neutral-500">実際の回答: </span>
+				      {answerLabelFor (answer.originalAnswer)}
+				    </div>
+				    <label className="block">
+				      <span className="text-neutral-500">修正後: </span>
+				      <select
+					  value={answer.answer}
+					  className="rounded border border-yellow-300 bg-white px-2
+						     py-1
+						     dark:border-red-700 dark:bg-red-950"
+					  onChange={ev =>
+					    correctAnswerAt (
+						index,
+						ev.target.value as GekanatorAnswerValue)}>
+					{answerOptions.map (option => (
+					    <option key={option.value} value={option.value}>
+					      {option.label}
+					    </option>))}
+				      </select>
+				    </label>
+				  </div>
+				</div>)
+			  })}
+			</div>
+		      </div>
+
+		      {reviewGuessedPostId != null && reviewCorrectPostId != null && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    判定:
+			    {reviewGuessedPostId === reviewCorrectPostId ? '当たり' : 'はずれ'}
+			  </p>)}
+
+		      {saveMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    記録できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded border border-neutral-300 px-4 py-2
+				       hover:bg-neutral-100 dark:border-neutral-700
+				       dark:hover:bg-red-900"
+			    onClick={() => setPhase ('end')}>
+			  戻る
+			</button>
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500 disabled:opacity-50"
+			    disabled={
+			      !(canPersistGame)
+			      || reviewCorrectPostId == null
+			      || saveMutation.isPending
+			      || questionSuggestionMutation.isPending
+			    }
+			    onClick={saveAndLearn}>
+			  完了
+			</button>
+		      </div>
+		    </div>)}
+
+		{phase === 'question_suggestion' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-sm text-neutral-500">質問追加</p>
+			<p className="text-xl font-bold">{questionSuggestionTitle}</p>
+		      </div>
+		      {questionSuggestionEntryMode === 'search' && (
+			  <>
+			    <label className="block space-y-2">
+			      <span className="font-bold">既存質問を検索</span>
+			      <input
+				  value={questionSuggestionSearch}
+				  onChange={ev => {
+				    setQuestionSuggestionSearch (ev.target.value)
+				    setQuestionSuggestionSelectedId (null)
+				  }}
+				  className="w-full rounded border border-yellow-300 bg-white px-3 py-2
+					     dark:border-red-700 dark:bg-red-950"
+				  placeholder="バーカ?wwwwwwwwwwwww"/>
+			    </label>
+			    {searchableSuggestedQuestions.length > 0 && (
+				<>
+				  <div className="space-y-2">
+				    <div className="font-bold">既存質問候補</div>
+				    <div className="max-h-64 space-y-2 overflow-y-auto">
+				      {searchableSuggestedQuestions.map (question => {
+					const questionClass =
+					    questionSuggestionSelectedId === (question.recordId ?? null)
+					    ? 'border-pink-600 bg-pink-50 dark:bg-red-900/50'
+					    : 'border-yellow-200 hover:bg-yellow-100 dark:border-red-800 dark:hover:bg-red-900'
+
+					return (
+					    <button
+						key={question.id}
+						type="button"
+						className={cn (
+						    'block w-full rounded border px-3 py-2 text-left',
+						    questionClass)}
+						onClick={() => {
+						  setQuestionSuggestionSelectedId (question.recordId ?? null)
+						  setQuestionSuggestion ('')
+						}}>
+					      <div className="font-bold">{question.text}</div>
+					    </button>)
+				      })}
+				    </div>
+				  </div>
+				  {selectedSuggestedQuestion && (
+				      <p className="text-sm text-neutral-600 dark:text-neutral-300">
+					既存質問を選択中: {selectedSuggestedQuestion.text}
+				      </p>)}
+				</>)}
+			  </>)}
+		      {questionSuggestionEntryMode === 'new' && (
+			  <div className="space-y-2">
+			    <div className="font-bold">新規質問</div>
+			    <textarea
+				value={questionSuggestion}
+				onChange={ev => {
+				  setQuestionSuggestion (ev.target.value)
+				  if (ev.target.value.trim () !== '')
+				    setQuestionSuggestionSelectedId (null)
+				}}
+				className="min-h-24 w-full rounded border border-yellow-300
+					   bg-white px-3 py-2 dark:border-red-700
+					   dark:bg-red-950"
+				placeholder="おっと、彼は逃げている?"/>
+			  </div>)}
+		      {(canSubmitQuestionSuggestion
+			&& !(saveMutation.isPending)
+			&& !(questionSuggestionMutation.isPending))
+		       && (
+			  <label className="block space-y-2">
+			    <span className="font-bold">この正解投稿に対する答え</span>
+			    <select
+				value={questionSuggestionAnswer}
+				className="rounded border border-yellow-300 bg-white px-2 py-1
+					   dark:border-red-700 dark:bg-red-950"
+				onChange={ev =>
+				  setQuestionSuggestionAnswer (
+				      ev.target.value as GekanatorAnswerValue)}>
+			      {answerOptions.map (option => (
+				  <option key={option.value} value={option.value}>
+				    {option.label}
+				  </option>))}
+			    </select>
+			  </label>)}
+		      {questionSuggestionEntryMode !== 'new' && (
+			  <div className="space-y-2">
+			    <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			      適切な質問がない場合は新規追加してください。
+			    </p>
+			    <div className="flex flex-wrap gap-2">
+			      <button
+				  type="button"
+				  className="rounded border border-yellow-300 px-4 py-2
+					     hover:bg-yellow-100 dark:border-red-700
+					     dark:hover:bg-red-900"
+				  onClick={() => {
+				    setQuestionSuggestionEntryMode ('new')
+				    setQuestionSuggestionSelectedId (null)
+				    setQuestionSuggestionSearch ('')
+				  }}>
+				新規追加
+			      </button>
+			    </div>
+			  </div>)}
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded border border-neutral-300 px-4 py-2
+				       hover:bg-neutral-100 dark:border-neutral-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={!(canPersistGame)
+				      || saveMutation.isPending
+				      || questionSuggestionMutation.isPending}
+			    onClick={() => {
+			      if (questionSuggestionEntryMode === 'new')
+				{
+				  setQuestionSuggestionEntryMode ('search')
+				  setQuestionSuggestion ('')
+				}
+			      else
+				setPhase ('end')
+			    }}>
+			  戻る
+			</button>
+			<button
+			    type="button"
+			    className="rounded border border-yellow-300 px-4 py-2
+				       hover:bg-yellow-100 dark:border-red-700
+				       dark:hover:bg-red-900 disabled:opacity-50"
+			    disabled={!(canSubmitQuestionSuggestion)
+				      || saveMutation.isPending
+				      || questionSuggestionMutation.isPending}
+			    onClick={() => {
+			      submitQuestionSuggestion ()
+			      setPhase ('end')
+			    }}>
+			  保存
+			</button>
+		      </div>
+		      {!(canPersistGame) && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    未ログインのため質問追加は送信できません。
+			  </p>)}
+		      {(saveMutation.isError || questionSuggestionMutation.isError) && (
+			  <p className="text-sm text-red-600">
+			    記録できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+		    </div>)}
+
+		{phase === 'extra_questions' && (
+		    <div className="space-y-4">
+		      <div>
+			<p className="text-sm text-neutral-500">追加学習</p>
+			<p className="text-xl font-bold">追加で質問に答えてください。</p>
+		      </div>
+
+		      {extraQuestionState === 'loading' && (
+			  <p>追加質問を読み込んでいます……</p>)}
+
+		      {extraQuestionState === 'empty' && (
+			  <p>追加で学習できる質問はありませんでした。</p>)}
+
+		      {extraQuestionState === 'ready' && (
+			  <div className="space-y-3">
+			    {extraQuestions.map ((question, index) => (
+				<div
+				    key={question.id}
+				    className="rounded border border-yellow-100 p-3
+					       dark:border-red-900">
+				  <div className="text-sm text-neutral-600 dark:text-neutral-300">
+				    追加質問 {index + 1}
+				  </div>
+				  <div className="font-bold">{question.text}</div>
+				  <div className="mt-3 flex flex-wrap gap-2">
+				    {answerOptions.map (option => {
+				      const optionClass =
+					  extraQuestionAnswers[String (question.id)] === option.value
+					  ? 'border-pink-600 bg-pink-600 text-white'
+					  : 'border-yellow-300 hover:bg-yellow-100 dark:border-red-700 dark:hover:bg-red-900'
+
+				      return (
+					  <button
+					      key={option.value}
+					      type="button"
+					      className={cn (
+						  'rounded border px-3 py-2',
+						  optionClass)}
+					      onClick={() =>
+						answerExtraQuestion (question.id, option.value)}>
+					    {option.label}
+					  </button>)
+				    })}
+				  </div>
+				</div>))}
+			  </div>)}
+
+		      {extraQuestionAnswersMutation.isError && (
+			  <p className="text-sm text-red-600">
+			    学習内容を保存できませんでした。通信状態を確認してもう一度試して。
+			  </p>)}
+
+		      <div className="flex flex-wrap gap-2">
+			<button
+			    type="button"
+			    className="rounded border border-neutral-300 px-4 py-2
+				       hover:bg-neutral-100 dark:border-neutral-700
+				       dark:hover:bg-red-900"
+			    disabled={extraQuestionAnswersMutation.isPending}
+			    onClick={() => setPhase ('end')}>
+			  戻る
+			</button>
+			<button
+			    type="button"
+			    className="rounded bg-pink-600 px-4 py-2 font-bold text-white
+				       hover:bg-pink-500 disabled:opacity-50"
+			    disabled={
+			      !(canPersistGame)
+			      ||
+			      extraQuestionState !== 'ready'
+			      || extraQuestionAnswersMutation.isPending
+			      || extraQuestions.some (
+				  question => !(extraQuestionAnswers[String (question.id)]))
+			    }
+			    onClick={saveExtraQuestions}>
+			  送信
+			</button>
+		      </div>
+		      {!(canPersistGame) && (
+			  <p className="text-sm text-neutral-600 dark:text-neutral-300">
+			    未ログインのため追加学習は保存されません。
+			  </p>)}
+		    </div>)}
+	      </div>
+	    </div>
+	  </section>
+
+	  {['guess', 'continue', 'question', 'end', 'review'].includes (phase)
+	   && selectingCorrectPost && (
+	      <section className="rounded-lg border border-yellow-300 bg-white p-4
+				  dark:border-red-800 dark:bg-red-950">
+		<label className="block space-y-2">
+		  <span className="font-bold">正解の投稿</span>
+		  <input
+		      value={search}
+		      onChange={ev => setSearch (ev.target.value)}
+		      className="w-full rounded border border-yellow-300 bg-white px-3 py-2
+				 dark:border-red-700 dark:bg-red-950"
+		      placeholder="投稿 Id.・タイトル・URL・タグで検索"/>
+		</label>
+		<div className="mt-4 space-y-3">
+		  {filteredPosts.map (post => (
+		      <button
+			  key={post.id}
+			  type="button"
+			  className={cn ('block w-full rounded border border-yellow-200 p-3',
+					 'text-left hover:bg-yellow-100',
+					 'dark:border-red-800 dark:hover:bg-red-900')}
+			  onClick={() => selectCorrectPost (post)}>
+			<PostMiniCard post={post}/>
+		      </button>))}
+		  {search.trim () && filteredPosts.length === 0 && '見つかりません．'}
+		  {saveMutation.isError && (
+		      <p className="text-sm text-red-600">
+			記録できませんでした。通信状態を確認してもう一度試して。
+		      </p>)}
+		</div>
+	      </section>)}
+	</div>
+      </MainArea>)
+}
+
+
+export default GekanatorPage
diff --git a/frontend/src/pages/deerjikists/DeerjikistDetailPage.test.tsx b/frontend/src/pages/deerjikists/DeerjikistDetailPage.test.tsx
new file mode 100644
index 0000000..ae60500
--- /dev/null
+++ b/frontend/src/pages/deerjikists/DeerjikistDetailPage.test.tsx
@@ -0,0 +1,72 @@
+import { fireEvent, screen, waitFor } from '@testing-library/react'
+import { Route, Routes } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import DeerjikistDetailPage from '@/pages/deerjikists/DeerjikistDetailPage'
+import { buildTag } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+const tagsApi = vi.hoisted (() => ({
+  fetchDeerjikistsByTag: vi.fn (),
+}))
+
+const api = vi.hoisted (() => ({
+  apiPut:     vi.fn (),
+  isApiError: vi.fn (),
+}))
+
+const toastApi = vi.hoisted (() => ({
+  toast: vi.fn (),
+}))
+
+vi.mock ('@/lib/tags', () => tagsApi)
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/components/ui/use-toast', () => toastApi)
+
+const renderPage = () =>
+  renderWithProviders (
+      <Routes>
+        <Route path="/tags/:id/deerjikists" element={<DeerjikistDetailPage/>}/>
+      </Routes>,
+      { route: '/tags/7/deerjikists' },
+  )
+
+describe ('DeerjikistDetailPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+  })
+
+  it ('shows indexed validation errors returned for deerjikist rows', async () => {
+    tagsApi.fetchDeerjikistsByTag.mockResolvedValueOnce ({
+      tag:         buildTag ({ id: 7, name: 'deerjika', category: 'deerjikist' }),
+      deerjikists: [{ platform: null, code: 'abc' }],
+    })
+    api.isApiError.mockReturnValue (true)
+    api.apiPut.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      { 'deerjikists.0.platform': ['プラットフォームを入力してください．'] },
+          base_errors: [],
+        },
+      },
+    })
+
+    renderPage ()
+
+    await screen.findByDisplayValue ('abc')
+    fireEvent.submit (screen.getByRole ('button', { name: '更新' }).closest ('form')!)
+
+    await waitFor (() => {
+      expect (api.apiPut).toHaveBeenCalledWith (
+          '/tags/7/deerjikists',
+          [{ platform: null, code: 'abc' }],
+      )
+    })
+    expect (await screen.findByText ('プラットフォームを入力してください．')).toBeInTheDocument ()
+    expect (screen.getByRole ('combobox')).toHaveAttribute ('aria-invalid', 'true')
+  })
+})
diff --git a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
index 4901116..2db0f58 100644
--- a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
+++ b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
@@ -4,7 +4,8 @@ import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
-import Label from '@/components/common/Label'
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
@@ -12,12 +13,16 @@ import { PLATFORM_NAMES, PLATFORMS } from '@/consts'
 import { apiPut } from '@/lib/api'
 import { tagsKeys } from '@/lib/queryKeys'
 import { fetchDeerjikistsByTag } from '@/lib/tags'
-import { cn } from '@/lib/utils'
+import { cn, inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC, FormEvent } from 'react'
 
 import type { Deerjikist, Platform } from '@/types'
 
+type DeerjikistFormField =
+    'deerjikists' | `deerjikists${ number }Platform` | `deerjikists${ number }Code`
+
 
 const DeerjikistDetailPage: FC = () => {
   const { id } = useParams ()
@@ -32,11 +37,14 @@ const DeerjikistDetailPage: FC = () => {
   const [data, setData] =
       useState<(Omit<Deerjikist, 'platform'> & { platform: Platform | null })[]> ([])
   const [disabled, setDisabled] = useState (true)
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<DeerjikistFormField> ()
 
   const qc = useQueryClient ()
 
   const handleSubmit = async (e: FormEvent) => {
     e.preventDefault ()
+    clearValidationErrors ()
 
     try
     {
@@ -47,8 +55,9 @@ const DeerjikistDetailPage: FC = () => {
 
       toast ({ description: '更新しました．' })
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '更新失敗', description: '入力内容を確認してください．' })
     }
     finally
@@ -82,6 +91,9 @@ const DeerjikistDetailPage: FC = () => {
 	      </PageTitle>
 
 	      <form onSubmit={handleSubmit} className="my-4 space-y-2">
+		<FieldError messages={baseErrors}/>
+		<FieldError messages={fieldErrors.deerjikists}/>
+
 		{data.map ((datum, i) => (
 		    <fieldset key={i} className="min-w-0 rounded-lg border border-gray-300
 						 dark:border-gray-700 p-4">
@@ -97,40 +109,48 @@ const DeerjikistDetailPage: FC = () => {
 		      </legend>
 
 		      {/* プラットフォーム */}
-		      <div>
-			<Label>プラットフォーム</Label>
-			<select
-			    className="w-full border p-2 rounded"
-			    disabled={disabled}
-			    value={datum.platform ?? ''}
-			    onChange={e => setData (prev => {
-			      const rtn = [...prev]
-			      rtn[i] = { ...rtn[i],
-					 platform: (e.target.value || null) as Platform | null }
-			      return rtn
-			    })}>
-			  <option value="">&nbsp;</option>
-			  {PLATFORMS.map (p => (
-			      <option key={p} value={p}>
-				{PLATFORM_NAMES[p]}
-			      </option>))}
-			</select>
-		      </div>
+		      <FormField
+			  label="プラットフォーム"
+			  messages={fieldErrors[`deerjikists${ i }Platform`]}>
+			{({ describedBy, invalid }) => (
+			    <select
+				disabled={disabled}
+				value={datum.platform ?? ''}
+				aria-describedby={describedBy}
+				aria-invalid={invalid}
+				className={inputClass (invalid)}
+				onChange={e => setData (prev => {
+				  const rtn = [...prev]
+				  rtn[i] = { ...rtn[i],
+					     platform: (e.target.value || null) as Platform | null }
+				  return rtn
+				})}>
+			      <option value="">&nbsp;</option>
+			      {PLATFORMS.map (p => (
+				  <option key={p} value={p}>
+				    {PLATFORM_NAMES[p]}
+				  </option>))}
+			    </select>)}
+		      </FormField>
 
 		      {/* コード */}
-		      <div>
-			<Label>コード</Label>
-			<input
-			    type="text"
-			    disabled={disabled}
-			    className="w-full border p-2 rounded"
-			    value={datum.code}
-			    onChange={e => setData (prev => {
-			      const rtn = [...prev]
-			      rtn[i] = { ...rtn[i], code: e.target.value }
-			      return rtn
-			    })}/>
-		      </div>
+		      <FormField
+			  label="コード"
+			  messages={fieldErrors[`deerjikists${ i }Code`]}>
+			{({ describedBy, invalid }) => (
+			    <input
+				type="text"
+				disabled={disabled}
+				value={datum.code}
+				aria-describedby={describedBy}
+				aria-invalid={invalid}
+				className={inputClass (invalid)}
+				onChange={e => setData (prev => {
+				  const rtn = [...prev]
+				  rtn[i] = { ...rtn[i], code: e.target.value }
+				  return rtn
+				})}/>)}
+		      </FormField>
 		    </fieldset>
 		))}
 
diff --git a/frontend/src/pages/materials/MaterialDetailPage.tsx b/frontend/src/pages/materials/MaterialDetailPage.tsx
index 55e242b..09f537e 100644
--- a/frontend/src/pages/materials/MaterialDetailPage.tsx
+++ b/frontend/src/pages/materials/MaterialDetailPage.tsx
@@ -4,7 +4,8 @@ import { useParams } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
 import WikiBody from '@/components/WikiBody'
-import Label from '@/components/common/Label'
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import TabGroup, { Tab } from '@/components/common/TabGroup'
 import TagInput from '@/components/common/TagInput'
@@ -13,6 +14,8 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiGet, apiPut } from '@/lib/api'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC } from 'react'
 
@@ -20,6 +23,8 @@ import type { Material, Tag } from '@/types'
 
 type MaterialWithTag = Material & { tag: Tag }
 
+type MaterialFormField = 'tag' | 'file' | 'url'
+
 
 const MaterialDetailPage: FC = () => {
   const { id } = useParams ()
@@ -31,8 +36,12 @@ const MaterialDetailPage: FC = () => {
   const [sending, setSending] = useState (false)
   const [tag, setTag] = useState ('')
   const [url, setURL] = useState ('')
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<MaterialFormField> ()
 
   const handleSubmit = async () => {
+    clearValidationErrors ()
+
     const formData = new FormData
     if (tag.trim ())
       formData.append ('tag', tag)
@@ -48,8 +57,9 @@ const MaterialDetailPage: FC = () => {
       setMaterial (data)
       toast ({ title: '更新成功!' })
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '更新失敗……', description: '入力を見直してください．' })
     }
     finally
@@ -118,54 +128,66 @@ const MaterialDetailPage: FC = () => {
 
 		<Tab name="編輯">
 		  <div className="max-w-wl pt-2 space-y-4">
+		    <FieldError messages={baseErrors}/>
+
 		    {/* タグ */}
-		    <div>
-		      <Label>タグ</Label>
-		      <TagInput value={tag} setValue={setTag}/>
-		    </div>
+		    <FormField label="タグ" messages={fieldErrors.tag}>
+		      {({ describedBy, invalid }) => (
+			  <TagInput
+			      describedBy={describedBy}
+			      invalid={invalid}
+			      value={tag}
+			      setValue={setTag}/>)}
+		    </FormField>
 
 		    {/* ファイル */}
-		    <div>
-		      <Label>ファイル</Label>
-		      <input
-			  type="file"
-			  accept="image/*,video/*,audio/*"
-			  onChange={e => {
-			    const f = e.target.files?.[0]
-			    setFile (f ?? null)
-			    setFilePreview (f ? URL.createObjectURL (f) : '')
-			  }}/>
-		      {(file && filePreview) && (
-			  (/image\/.*/.test (file.type) && (
-			      <img
-				  src={filePreview}
-				  alt="preview"
-				  className="mt-2 max-h-48 rounded border"/>))
-			  || (/video\/.*/.test (file.type) && (
-			      <video
-				  src={filePreview}
-				  controls
-				  className="mt-2 max-h-48 rounded border"/>))
-			  || (/audio\/.*/.test (file.type) && (
-			      <audio
-				  src={filePreview}
-				  controls
-				  className="mt-2 max-h-48"/>))
-			  || (
-			      <p className="text-red-600 dark:text-red-400">
-				その形式のファイルには対応していません．
-			      </p>))}
-		    </div>
+		    <FormField label="ファイル" messages={fieldErrors.file}>
+		      {({ describedBy, invalid }) => (
+			  <>
+			    <input
+				type="file"
+				accept="image/*,video/*,audio/*"
+				aria-describedby={describedBy}
+				aria-invalid={invalid}
+				onChange={e => {
+				  const f = e.target.files?.[0]
+				  setFile (f ?? null)
+				  setFilePreview (f ? URL.createObjectURL (f) : '')
+				}}/>
+			    {(file && filePreview) && (
+				(/image\/.*/.test (file.type) && (
+				    <img
+					src={filePreview}
+					alt="preview"
+					className="mt-2 max-h-48 rounded border"/>))
+				|| (/video\/.*/.test (file.type) && (
+				    <video
+					src={filePreview}
+					controls
+					className="mt-2 max-h-48 rounded border"/>))
+				|| (/audio\/.*/.test (file.type) && (
+				    <audio
+					src={filePreview}
+					controls
+					className="mt-2 max-h-48"/>))
+				|| (
+				    <p className="text-red-600 dark:text-red-400">
+				      その形式のファイルには対応していません．
+				    </p>))}
+			  </>)}
+		    </FormField>
 
 		    {/* 参考 URL */}
-		    <div>
-		      <Label>参考 URL</Label>
-		      <input
-			  type="url"
-			  value={url}
-			  onChange={e => setURL (e.target.value)}
-			  className="w-full border p-2 rounded"/>
-		    </div>
+		    <FormField label="参考 URL" messages={fieldErrors.url}>
+		      {({ describedBy, invalid }) => (
+			  <input
+			      type="url"
+			      value={url}
+			      onChange={e => setURL (e.target.value)}
+			      aria-describedby={describedBy}
+			      aria-invalid={invalid}
+			      className={inputClass (invalid)}/>)}
+		    </FormField>
 
 		    {/* 送信 */}
 		    <Button
@@ -181,4 +203,4 @@ const MaterialDetailPage: FC = () => {
       </MainArea>)
 }
 
-export default MaterialDetailPage
\ No newline at end of file
+export default MaterialDetailPage
diff --git a/frontend/src/pages/materials/MaterialNewPage.test.tsx b/frontend/src/pages/materials/MaterialNewPage.test.tsx
index c33a5dc..c67e55b 100644
--- a/frontend/src/pages/materials/MaterialNewPage.test.tsx
+++ b/frontend/src/pages/materials/MaterialNewPage.test.tsx
@@ -1,11 +1,13 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import MaterialNewPage from '@/pages/materials/MaterialNewPage'
 import { renderWithProviders } from '@/test/render'
 
 const api = vi.hoisted (() => ({
-  apiPost: vi.fn (),
+  apiGet:     vi.fn (),
+  apiPost:    vi.fn (),
+  isApiError: vi.fn (),
 }))
 
 const toastApi = vi.hoisted (() => ({
@@ -16,6 +18,12 @@ vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
 
 describe ('MaterialNewPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.apiGet.mockResolvedValue ([])
+    api.isApiError.mockReturnValue (false)
+  })
+
   it ('initializes tag from query and submits form data', async () => {
     api.apiPost.mockResolvedValueOnce ({})
 
@@ -35,4 +43,30 @@ describe ('MaterialNewPage', () => {
     expect (formData.get ('url')).toBe ('https://example.com/ref')
     expect (toastApi.toast).toHaveBeenCalledWith ({ title: '送信成功!' })
   })
+
+  it ('shows validation errors for file and url fields', async () => {
+    api.isApiError.mockReturnValue (true)
+    api.apiPost.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      {
+            file: ['ファイルまたは URL は必須です．'],
+            url:  ['ファイルまたは URL は必須です．'],
+          },
+          base_errors: [],
+        },
+      },
+    })
+
+    renderWithProviders (<MaterialNewPage/>)
+
+    fireEvent.change (screen.getAllByRole ('textbox')[0], { target: { value: '虹夏' } })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    expect (await screen.findAllByText ('ファイルまたは URL は必須です．')).toHaveLength (2)
+    expect (screen.getAllByRole ('textbox')[1]).toHaveAttribute ('aria-invalid', 'true')
+  })
 })
diff --git a/frontend/src/pages/materials/MaterialNewPage.tsx b/frontend/src/pages/materials/MaterialNewPage.tsx
index f2a1832..bfbb357 100644
--- a/frontend/src/pages/materials/MaterialNewPage.tsx
+++ b/frontend/src/pages/materials/MaterialNewPage.tsx
@@ -2,8 +2,9 @@ import { useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useLocation, useNavigate } from 'react-router-dom'
 
+import FieldError from '@/components/common/FieldError'
 import Form from '@/components/common/Form'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import TagInput from '@/components/common/TagInput'
 import MainArea from '@/components/layout/MainArea'
@@ -11,9 +12,13 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiPost } from '@/lib/api'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC } from 'react'
 
+type MaterialFormField = 'tag' | 'file' | 'url'
+
 
 const MaterialNewPage: FC = () => {
   const location = useLocation ()
@@ -27,8 +32,12 @@ const MaterialNewPage: FC = () => {
   const [sending, setSending] = useState (false)
   const [tag, setTag] = useState (tagQuery)
   const [url, setURL] = useState ('')
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<MaterialFormField> ()
 
   const handleSubmit = async () => {
+    clearValidationErrors ()
+
     const formData = new FormData
     if (tag)
       formData.append ('tag', tag)
@@ -44,8 +53,9 @@ const MaterialNewPage: FC = () => {
       toast ({ title: '送信成功!' })
       navigate (`/materials?tag=${ encodeURIComponent (tag) }`)
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '送信失敗……', description: '入力を見直してください．' })
     }
     finally
@@ -62,55 +72,66 @@ const MaterialNewPage: FC = () => {
 
 	<Form>
 	  <PageTitle>素材追加</PageTitle>
+	  <FieldError messages={baseErrors}/>
 
 	  {/* タグ */}
-	  <div>
-	    <Label>タグ</Label>
-	    <TagInput value={tag} setValue={setTag}/>
-	  </div>
+	  <FormField label="タグ" messages={fieldErrors.tag}>
+	    {({ describedBy, invalid }) => (
+		<TagInput
+		    describedBy={describedBy}
+		    invalid={invalid}
+		    value={tag}
+		    setValue={setTag}/>)}
+	  </FormField>
 
 	  {/* ファイル */}
-	  <div>
-	    <Label>ファイル</Label>
-	    <input
-		type="file"
-		accept="image/*,video/*,audio/*"
-		onChange={e => {
-		  const f = e.target.files?.[0]
-		  setFile (f ?? null)
-		  setFilePreview (f ? URL.createObjectURL (f) : '')
-		}}/>
-	    {(file && filePreview) && (
-		(/image\/.*/.test (file.type) && (
-		    <img
-			src={filePreview}
-			alt="preview"
-			className="mt-2 max-h-48 rounded border"/>))
-		|| (/video\/.*/.test (file.type) && (
-		    <video
-			src={filePreview}
-			controls
-			className="mt-2 max-h-48 rounded border"/>))
-		|| (/audio\/.*/.test (file.type) && (
-		    <audio
-			src={filePreview}
-			controls
-			className="mt-2 max-h-48"/>))
-		|| (
-		    <p className="text-red-600 dark:text-red-400">
-		      その形式のファイルには対応していません．
-		    </p>))}
-	  </div>
+	  <FormField label="ファイル" messages={fieldErrors.file}>
+	    {({ describedBy, invalid }) => (
+		<>
+		  <input
+		      type="file"
+		      accept="image/*,video/*,audio/*"
+		      aria-describedby={describedBy}
+		      aria-invalid={invalid}
+		      onChange={e => {
+			const f = e.target.files?.[0]
+			setFile (f ?? null)
+			setFilePreview (f ? URL.createObjectURL (f) : '')
+		      }}/>
+		  {(file && filePreview) && (
+		      (/image\/.*/.test (file.type) && (
+			  <img
+			      src={filePreview}
+			      alt="preview"
+			      className="mt-2 max-h-48 rounded border"/>))
+		      || (/video\/.*/.test (file.type) && (
+			  <video
+			      src={filePreview}
+			      controls
+			      className="mt-2 max-h-48 rounded border"/>))
+		      || (/audio\/.*/.test (file.type) && (
+			  <audio
+			      src={filePreview}
+			      controls
+			      className="mt-2 max-h-48"/>))
+		      || (
+			  <p className="text-red-600 dark:text-red-400">
+			    その形式のファイルには対応していません．
+			  </p>))}
+		</>)}
+	  </FormField>
 
 	  {/* 参考 URL */}
-	  <div>
-	    <Label>参考 URL</Label>
-	    <input
-		type="url"
-		value={url}
-		onChange={e => setURL (e.target.value)}
-		className="w-full border p-2 rounded"/>
-	  </div>
+	  <FormField label="参考 URL" messages={fieldErrors.url}>
+	    {({ describedBy, invalid }) => (
+		<input
+		    type="url"
+		    value={url}
+		    onChange={e => setURL (e.target.value)}
+		    aria-describedby={describedBy}
+		    aria-invalid={invalid}
+		    className={inputClass (invalid)}/>)}
+	  </FormField>
 
 	  {/* 送信 */}
 	  <Button
@@ -123,4 +144,4 @@ const MaterialNewPage: FC = () => {
       </MainArea>)
 }
 
-export default MaterialNewPage
\ No newline at end of file
+export default MaterialNewPage
diff --git a/frontend/src/pages/materials/MaterialSearchPage.tsx b/frontend/src/pages/materials/MaterialSearchPage.tsx
index f8f3634..ca5888a 100644
--- a/frontend/src/pages/materials/MaterialSearchPage.tsx
+++ b/frontend/src/pages/materials/MaterialSearchPage.tsx
@@ -1,7 +1,7 @@
 import { useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import TagInput from '@/components/common/TagInput'
 import MainArea from '@/components/layout/MainArea'
@@ -29,23 +29,23 @@ const MaterialSearchPage: FC = () => {
 
 	  <form onSubmit={handleSearch} className="space-y-2">
 	    {/* タグ */}
-	    <div>
-	      <Label>タグ</Label>
-	      <TagInput
-		  value={tagName}
-		  setValue={setTagName}/>
-	    </div>
+	    <FormField label="タグ">
+	      {() => (
+		  <TagInput
+		      value={tagName}
+		      setValue={setTagName}/>)}
+	    </FormField>
 
 	    {/* 親タグ */}
-	    <div>
-	      <Label>親タグ</Label>
-	      <TagInput
-		  value={parentTagName}
-		  setValue={setParentTagName}/>
-	    </div>
+	    <FormField label="親タグ">
+	      {() => (
+		  <TagInput
+		      value={parentTagName}
+		      setValue={setParentTagName}/>)}
+	    </FormField>
 	  </form>
 	</div>
       </MainArea>)
 }
 
-export default MaterialSearchPage
\ No newline at end of file
+export default MaterialSearchPage
diff --git a/frontend/src/pages/posts/PostDetailPage.tsx b/frontend/src/pages/posts/PostDetailPage.tsx
index 906c5cb..7c7f958 100644
--- a/frontend/src/pages/posts/PostDetailPage.tsx
+++ b/frontend/src/pages/posts/PostDetailPage.tsx
@@ -3,7 +3,6 @@ import { motion } from 'framer-motion'
 import { useEffect, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
-
 import PostEditForm from '@/components/PostEditForm'
 import PostEmbed from '@/components/PostEmbed'
 import PostList from '@/components/PostList'
@@ -16,6 +15,7 @@ import { SITE_TITLE } from '@/config'
 import { isApiError } from '@/lib/api'
 import { fetchPost, toggleViewedFlg } from '@/lib/posts'
 import { postsKeys, tagsKeys } from '@/lib/queryKeys'
+import { canEditContent } from '@/lib/users'
 import { cn } from '@/lib/utils'
 import NotFound from '@/pages/NotFound'
 import ServiceUnavailable from '@/pages/ServiceUnavailable'
@@ -28,6 +28,7 @@ type Props = { user: User | null }
 
 
 const PostDetailPage: FC<Props> = ({ user }) => {
+  const editable = canEditContent (user)
   const { id } = useParams ()
   const postId = String (id ?? '')
   const postKey = postsKeys.show (postId)
@@ -164,7 +165,7 @@ const PostDetailPage: FC<Props> = ({ user }) => {
 		     ? <PostList posts={post.related}/>
 		     : 'まだないよ（笑）'}
 		  </Tab>
-		  {['admin', 'member'].some (r => user?.role === r) && (
+		  {editable && (
 		      <Tab name="編輯">
 			<PostEditForm
 			    post={post}
diff --git a/frontend/src/pages/posts/PostNewPage.test.tsx b/frontend/src/pages/posts/PostNewPage.test.tsx
index f14b318..b8c909e 100644
--- a/frontend/src/pages/posts/PostNewPage.test.tsx
+++ b/frontend/src/pages/posts/PostNewPage.test.tsx
@@ -1,13 +1,14 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import PostNewPage from '@/pages/posts/PostNewPage'
 import { buildUser } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
 const api = vi.hoisted (() => ({
-  apiGet:  vi.fn (),
-  apiPost: vi.fn (),
+  apiGet:     vi.fn (),
+  apiPost:    vi.fn (),
+  isApiError: vi.fn (),
 }))
 
 const toastApi = vi.hoisted (() => ({
@@ -18,6 +19,11 @@ vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
 
 describe ('PostNewPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+  })
+
   it ('blocks guests', () => {
     renderWithProviders (<PostNewPage user={buildUser ({ role: 'guest' })}/>)
 
@@ -55,4 +61,36 @@ describe ('PostNewPage', () => {
     expect (formData.get ('tags')).toBe ('tag1 tag2')
     expect (toastApi.toast).toHaveBeenCalledWith ({ title: '投稿成功!' })
   })
+
+  it ('shows 422 validation errors for post fields', async () => {
+    api.apiGet.mockResolvedValue ([])
+    api.isApiError.mockReturnValue (true)
+    api.apiPost.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      { tags: ['ニコニコ・タグは直接指定できません．'] },
+          base_errors: ['投稿内容を確認してください．'],
+        },
+      },
+    })
+
+    renderWithProviders (<PostNewPage user={buildUser ({ role: 'member' })}/>)
+
+    const checkboxes = screen.getAllByRole ('checkbox', { name: '自動' })
+    fireEvent.click (checkboxes[0])
+    fireEvent.click (checkboxes[1])
+
+    const textboxes = screen.getAllByRole ('textbox')
+    fireEvent.change (textboxes[0], { target: { value: 'https://example.com/post' } })
+    fireEvent.change (textboxes[1], { target: { value: '投稿タイトル' } })
+    fireEvent.change (textboxes[3], { target: { value: 'nico:nico_tag' } })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    expect (await screen.findByText ('投稿内容を確認してください．')).toBeInTheDocument ()
+    expect (screen.getByText ('ニコニコ・タグは直接指定できません．')).toBeInTheDocument ()
+    expect (screen.getAllByRole ('textbox')[3]).toHaveAttribute ('aria-invalid', 'true')
+  })
 })
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index d8588d9..f5915db 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -4,14 +4,18 @@ import { useNavigate } from 'react-router-dom'
 
 import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
+import FieldError from '@/components/common/FieldError'
 import Form from '@/components/common/Form'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
 import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiGet, apiPost } from '@/lib/api'
+import { canEditContent } from '@/lib/users'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 import Forbidden from '@/pages/Forbidden'
 
 import type { FC } from 'react'
@@ -20,12 +24,18 @@ import type { User } from '@/types'
 
 type Props = { user: User | null }
 
+type PostFormField =
+    'url' | 'title' | 'tags' | 'parentPostIds' | 'originalCreatedAt' | 'thumbnail'
+
 
 const PostNewPage: FC<Props> = ({ user }) => {
-  const editable = ['admin', 'member'].some (r => user?.role === r)
+  const editable = canEditContent (user)
 
   const navigate = useNavigate ()
 
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<PostFormField> ()
+
   const [originalCreatedBefore, setOriginalCreatedBefore] = useState<string | null> (null)
   const [originalCreatedFrom, setOriginalCreatedFrom] = useState<string | null> (null)
   const [parentPostIds, setParentPostIds] = useState ('')
@@ -43,6 +53,8 @@ const PostNewPage: FC<Props> = ({ user }) => {
   const thumbnailPreviewRef = useRef ('')
 
   const handleSubmit = async () => {
+    clearValidationErrors ()
+
     const formData = new FormData
     formData.append ('title', title)
     formData.append ('url', url)
@@ -61,8 +73,9 @@ const PostNewPage: FC<Props> = ({ user }) => {
       toast ({ title: '投稿成功!' })
       navigate ('/posts')
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '投稿失敗', description: '入力を確認してください。' })
     }
   }
@@ -126,85 +139,99 @@ const PostNewPage: FC<Props> = ({ user }) => {
 	</Helmet>
 	<Form>
 	  <PageTitle>広場に投稿を追加する</PageTitle>
+	  <FieldError messages={baseErrors}/>
 
 	  {/* URL */}
-	  <div>
-	    <Label>URL</Label>
-	    <input type="url"
-		   placeholder="例：https://www.nicovideo.jp/watch/..."
-		   value={url}
-		   onChange={e => setURL (e.target.value)}
-		   className="w-full border p-2 rounded"
-		   onBlur={handleURLBlur}/>
-	  </div>
+	  <FormField label="URL" messages={fieldErrors.url}>
+	    {({ describedBy, invalid }) => (
+		<input type="url"
+		       placeholder="例：https://www.nicovideo.jp/watch/..."
+		       value={url}
+		       onChange={e => setURL (e.target.value)}
+		       aria-describedby={describedBy}
+		       aria-invalid={invalid}
+		       className={inputClass (invalid)}
+		       onBlur={handleURLBlur}/>)}
+	  </FormField>
 
 	  {/* タイトル */}
-	  <div>
-	    <Label checkBox={{
-		label:    '自動',
-		checked:  titleAutoFlg,
-		onChange: ev => setTitleAutoFlg (ev.target.checked)}}>
-	      タイトル
-	    </Label>
-	    <input type="text"
-		   className="w-full border rounded p-2"
-		   value={title}
-		   placeholder={titleLoading ? 'Loading...' : ''}
-		   onChange={ev => setTitle (ev.target.value)}
-		   disabled={titleAutoFlg}/>
-	  </div>
+	  <FormField
+	      checkBox={{
+		  label:    '自動',
+		  checked:  titleAutoFlg,
+		  onChange: ev => setTitleAutoFlg (ev.target.checked)}}
+	      label="タイトル"
+	      messages={fieldErrors.title}>
+	    {({ describedBy, invalid }) => (
+		<input type="text"
+		       aria-describedby={describedBy}
+		       aria-invalid={invalid}
+		       className={inputClass (invalid)}
+		       value={title}
+		       placeholder={titleLoading ? 'Loading...' : ''}
+		       onChange={ev => setTitle (ev.target.value)}
+		       disabled={titleAutoFlg}/>)}
+	  </FormField>
 
 	  {/* サムネール */}
-	  <div>
-	    <Label checkBox={{
-		label:    '自動',
-		checked:  thumbnailAutoFlg,
-		onChange: ev => setThumbnailAutoFlg (ev.target.checked)}}>
-	      サムネール
-	    </Label>
-	    {thumbnailAutoFlg
-	     ? (thumbnailLoading
-		? <p className="text-gray-500 text-sm">Loading...</p>
-		: !(thumbnailPreview) && (
-		    <p className="text-gray-500 text-sm">
-		      URL から自動取得されます。
-		    </p>))
-	     : (
-		<input type="file"
-		       accept="image/*"
-		       onChange={e => {
-			 const file = e.target.files?.[0]
-			 if (file)
-			   {
-			     setThumbnailFile (file)
-			     setThumbnailPreview (URL.createObjectURL (file))
-			   }
-		       }}/>)}
-	    {thumbnailPreview && (
-		<img src={thumbnailPreview}
-		     alt="preview"
-		     className="mt-2 max-h-48 rounded border"/>)}
-	  </div>
+	  <FormField
+	      checkBox={{
+		  label:    '自動',
+		  checked:  thumbnailAutoFlg,
+		  onChange: ev => setThumbnailAutoFlg (ev.target.checked)}}
+	      label="サムネール"
+	      messages={fieldErrors.thumbnail}>
+	    {({ describedBy, invalid }) => (
+		<>
+		  {thumbnailAutoFlg
+		   ? (thumbnailLoading
+		      ? <p className="text-gray-500 text-sm">Loading...</p>
+		      : !(thumbnailPreview) && (
+			  <p className="text-gray-500 text-sm">
+			    URL から自動取得されます。
+			  </p>))
+		   : (
+		      <input type="file"
+			     accept="image/*"
+			     aria-describedby={describedBy}
+			     aria-invalid={invalid}
+			     onChange={e => {
+			       const file = e.target.files?.[0]
+			       if (file)
+				 {
+				   setThumbnailFile (file)
+				   setThumbnailPreview (URL.createObjectURL (file))
+				 }
+			     }}/>)}
+		  {thumbnailPreview && (
+		      <img src={thumbnailPreview}
+			   alt="preview"
+			   className="mt-2 max-h-48 rounded border"/>)}
+		</>)}
+	  </FormField>
 
 	  {/* 親投稿 */}
-	  <div>
-	    <Label>親投稿</Label>
-	    <input
-		type="text"
-		value={parentPostIds}
-		onChange={e => setParentPostIds (e.target.value)}
-		className="w-full border p-2 rounded"/>
-	  </div>
+	  <FormField label="親投稿" messages={fieldErrors.parentPostIds}>
+	    {({ describedBy, invalid }) => (
+		<input
+		    type="text"
+		    value={parentPostIds}
+		    onChange={e => setParentPostIds (e.target.value)}
+		    aria-describedby={describedBy}
+		    aria-invalid={invalid}
+		    className={inputClass (invalid)}/>)}
+	  </FormField>
 
 	  {/* タグ */}
-	  <PostFormTagsArea tags={tags} setTags={setTags}/>
+	  <PostFormTagsArea tags={tags} setTags={setTags} errors={fieldErrors.tags}/>
 
 	  {/* オリジナルの作成日時 */}
 	  <PostOriginalCreatedTimeField
 	      originalCreatedFrom={originalCreatedFrom}
 	      setOriginalCreatedFrom={setOriginalCreatedFrom}
 	      originalCreatedBefore={originalCreatedBefore}
-	      setOriginalCreatedBefore={setOriginalCreatedBefore}/>
+	      setOriginalCreatedBefore={setOriginalCreatedBefore}
+	      errors={fieldErrors.originalCreatedAt}/>
 
 	  {/* 送信 */}
 	  <Button onClick={handleSubmit}
diff --git a/frontend/src/pages/posts/PostSearchPage.tsx b/frontend/src/pages/posts/PostSearchPage.tsx
index d68909d..7237c9a 100644
--- a/frontend/src/pages/posts/PostSearchPage.tsx
+++ b/frontend/src/pages/posts/PostSearchPage.tsx
@@ -8,7 +8,7 @@ import PrefetchLink from '@/components/PrefetchLink'
 import SortHeader from '@/components/SortHeader'
 import TagLink from '@/components/TagLink'
 import DateTimeField from '@/components/common/DateTimeField'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
 import TagInput from '@/components/common/TagInput'
@@ -16,7 +16,7 @@ import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
 import { fetchPosts } from '@/lib/posts'
 import { postsKeys } from '@/lib/queryKeys'
-import { dateString, originalCreatedAtString } from '@/lib/utils'
+import { dateString, inputClass, originalCreatedAtString } from '@/lib/utils'
 
 import type { FC, FormEvent } from 'react'
 
@@ -138,31 +138,33 @@ const PostSearchPage: FC = () => {
 
 	  <form onSubmit={handleSearch} className="space-y-2">
 	    {/* タイトル */}
-	    <div>
-	      <Label>タイトル</Label>
-	      <input
-		  type="text"
-		  value={title}
-		  onChange={e => setTitle (e.target.value)}
-		  className="w-full border p-2 rounded"/>
-	    </div>
+	    <FormField label="タイトル">
+	      {({ invalid }) => (
+		  <input
+		      type="text"
+		      value={title}
+		      onChange={e => setTitle (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
 
 	    {/* URL */}
-	    <div>
-	      <Label>URL</Label>
-	      <input
-		  type="text"
-		  value={url}
-		  onChange={e => setURL (e.target.value)}
-		  className="w-full border p-2 rounded"/>
-	    </div>
+	    <FormField label="URL">
+	      {({ invalid }) => (
+		  <input
+		      type="text"
+		      value={url}
+		      onChange={e => setURL (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
 
 	    {/* タグ */}
+	    <FormField label="タグ">
+	      {() => (
+		  <TagInput
+		      value={tagsStr}
+		      setValue={setTagsStr}/>)}
+	    </FormField>
 	    <div>
-	      <Label>タグ</Label>
-	      <TagInput
-		  value={tagsStr}
-		  setValue={setTagsStr}/>
 	      <fieldset className="w-full my-2">
 		<label>検索区分：</label>
 		<label className="mx-2">
@@ -185,40 +187,46 @@ const PostSearchPage: FC = () => {
 	    </div>
 
 	    {/* オリジナルの投稿日時 */}
-	    <div>
-	      <Label>オリジナルの投稿日時</Label>
-	      <DateTimeField
-		  value={originalCreatedFrom ?? undefined}
-		  onChange={setOriginalCreatedFrom}/>
-	      <span className="mx-1">〜</span>
-	      <DateTimeField
-		  value={originalCreatedTo ?? undefined}
-		  onChange={setOriginalCreatedTo}/>
-	    </div>
+	    <FormField label="オリジナルの投稿日時">
+	      {() => (
+		  <>
+		    <DateTimeField
+			value={originalCreatedFrom ?? undefined}
+			onChange={setOriginalCreatedFrom}/>
+		    <span className="mx-1">〜</span>
+		    <DateTimeField
+			value={originalCreatedTo ?? undefined}
+			onChange={setOriginalCreatedTo}/>
+		  </>)}
+	    </FormField>
 
 	    {/* 投稿日時 */}
-	    <div>
-	      <Label>投稿日時</Label>
-	      <DateTimeField
-		  value={createdFrom ?? undefined}
-		  onChange={setCreatedFrom}/>
-	      <span className="mx-1">〜</span>
-	      <DateTimeField
-		  value={createdTo ?? undefined}
-		  onChange={setCreatedTo}/>
-	    </div>
+	    <FormField label="投稿日時">
+	      {() => (
+		  <>
+		    <DateTimeField
+			value={createdFrom ?? undefined}
+			onChange={setCreatedFrom}/>
+		    <span className="mx-1">〜</span>
+		    <DateTimeField
+			value={createdTo ?? undefined}
+			onChange={setCreatedTo}/>
+		  </>)}
+	    </FormField>
 
 	    {/* 更新日時 */}
-	    <div>
-	      <Label>更新日時</Label>
-	      <DateTimeField
-		  value={updatedFrom ?? undefined}
-		  onChange={setUpdatedFrom}/>
-	      <span className="mx-1">〜</span>
-	      <DateTimeField
-		  value={updatedTo ?? undefined}
-		  onChange={setUpdatedTo}/>
-	    </div>
+	    <FormField label="更新日時">
+	      {() => (
+		  <>
+		    <DateTimeField
+			value={updatedFrom ?? undefined}
+			onChange={setUpdatedFrom}/>
+		    <span className="mx-1">〜</span>
+		    <DateTimeField
+			value={updatedTo ?? undefined}
+			onChange={setUpdatedTo}/>
+		  </>)}
+	    </FormField>
 
 	    {/* 検索 */}
 	    <div className="py-3">
diff --git a/frontend/src/pages/tags/NicoTagListPage.test.tsx b/frontend/src/pages/tags/NicoTagListPage.test.tsx
new file mode 100644
index 0000000..c5efcd3
--- /dev/null
+++ b/frontend/src/pages/tags/NicoTagListPage.test.tsx
@@ -0,0 +1,273 @@
+import { fireEvent, screen, waitFor } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import NicoTagListPage from '@/pages/tags/NicoTagListPage'
+import { dateString } from '@/lib/utils'
+import { buildTag, buildUser } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+import type { NicoTag } from '@/types'
+
+const api = vi.hoisted (() => ({
+  apiGet:     vi.fn (),
+  apiPut:     vi.fn (),
+  isApiError: vi.fn (),
+}))
+
+const toastApi = vi.hoisted (() => ({
+  toast: vi.fn (),
+}))
+
+const dialogue = vi.hoisted (() => ({
+  confirm: vi.fn (),
+}))
+
+const scrollIntoView = vi.fn ()
+
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/components/ui/use-toast', () => toastApi)
+vi.mock ('@/components/dialogues/DialogueProvider', () => ({
+  useDialogue: () => dialogue,
+}))
+
+const buildNicoTag = (values: Partial<NicoTag> = {}): NicoTag => ({
+    ...buildTag (),
+    ...values,
+    category:               'nico',
+    linkedTags:             values.linkedTags ?? [],
+    recentPostTagCreatedAt: values.recentPostTagCreatedAt ?? null,
+})
+
+const renderPage = (route = '/tags/nico') =>
+  renderWithProviders (
+      <NicoTagListPage user={buildUser ({ role: 'member' })}/>,
+      { route },
+  )
+
+describe ('NicoTagListPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+    dialogue.confirm.mockResolvedValue (true)
+    Element.prototype.scrollIntoView = scrollIntoView
+    scrollIntoView.mockClear ()
+  })
+
+  it ('loads a filtered page from URL search parameters', async () => {
+    api.apiGet.mockResolvedValue ({
+      tags:  [buildNicoTag ({
+        id:                     1,
+        name:                   'nico:linked',
+        createdAt:              '2024-01-02T03:04:05Z',
+        recentPostTagCreatedAt: '2025-01-02T03:04:05Z',
+        updatedAt:              '2026-01-02T03:04:05Z',
+      })],
+      count: 21,
+    })
+
+    renderPage (
+        '/tags/nico?name=linked&linked_tag=destination&link_status=linked'
+	+ '&page=2&order=name:asc',
+    )
+
+    await waitFor (() => {
+      expect (api.apiGet).toHaveBeenCalledWith (
+          '/tags/nico',
+          { params: {
+            page:        2,
+            limit:       20,
+            name:        'linked',
+            linked_tag:  'destination',
+            link_status: 'linked',
+            order:       'name:asc',
+          } },
+      )
+    })
+    expect (await screen.findByText ('21 件')).toBeInTheDocument ()
+    expect (screen.getByLabelText ('前のページ')).toBeInTheDocument ()
+    expect (screen.queryByText ('なし')).not.toBeInTheDocument ()
+    expect (screen.getByText (dateString ('2025-01-02T03:04:05Z'))).toBeInTheDocument ()
+    expect (screen.queryByText (dateString ('2026-01-02T03:04:05Z'))).not.toBeInTheDocument ()
+    expect (screen.getByRole ('link', { name: 'ニコニコタグ ▲' })).toHaveAttribute (
+        'href',
+        expect.stringContaining ('order=name%3Adesc'),
+    )
+    expect (screen.getByRole ('link', { name: '最初に記載された日時' })).toHaveAttribute (
+        'href',
+        expect.stringContaining ('order=created_at%3Adesc'),
+    )
+    expect (screen.getByRole ('link', { name: '最近記載された日時' })).toHaveAttribute (
+        'href',
+        expect.stringContaining ('order=updated_at%3Adesc'),
+    )
+
+    fireEvent.mouseEnter (screen.getByLabelText ('前のページ'))
+    await waitFor (() => {
+      expect (api.apiGet).toHaveBeenLastCalledWith (
+          '/tags/nico',
+          { params: {
+            page:        1,
+            limit:       20,
+            name:        'linked',
+            linked_tag:  'destination',
+            link_status: 'linked',
+            order:       'name:asc',
+          } },
+      )
+    })
+  })
+
+  it ('scrolls to the table when moving between pages', async () => {
+    api.apiGet.mockResolvedValue ({
+      tags:  [buildNicoTag ({ id: 1, name: 'nico:linked' })],
+      count: 21,
+    })
+
+    renderPage ()
+
+    fireEvent.click (await screen.findByLabelText ('次のページ'))
+
+    await waitFor (() => {
+      expect (scrollIntoView).toHaveBeenCalledWith ({ behavior: 'smooth' })
+    })
+  })
+
+  it ('navigates with submitted search conditions', async () => {
+    api.apiGet.mockResolvedValue ({ tags: [], count: 0 })
+    renderPage ()
+
+    fireEvent.change (screen.getByLabelText ('ニコニコタグ'), {
+      target: { value: 'source' },
+    })
+    fireEvent.change (screen.getByLabelText ('連携タグ'), {
+      target: { value: 'destination' },
+    })
+    fireEvent.change (screen.getByLabelText ('連携状態'), {
+      target: { value: 'unlinked' },
+    })
+    fireEvent.submit (screen.getByRole ('button', { name: '検索' }).closest ('form')!)
+
+    await waitFor (() => {
+      expect (api.apiGet).toHaveBeenLastCalledWith (
+          '/tags/nico',
+          { params: expect.objectContaining ({
+            page:        1,
+            name:        'source',
+            linked_tag:  'destination',
+            link_status: 'unlinked',
+          }) },
+      )
+    })
+  })
+
+  it ('updates links from a tag card', async () => {
+    api.apiGet
+      .mockResolvedValueOnce ({
+        tags:  [buildNicoTag ({ id: 7, name: 'nico:source' })],
+        count: 1,
+      })
+      .mockResolvedValueOnce ({
+        tags: [
+          buildNicoTag ({
+            id:         7,
+            name:       'nico:source',
+            linkedTags: [buildTag ({ id: 8, name: '連携先' })],
+          }),
+        ],
+        count: 1,
+      })
+    api.apiPut.mockResolvedValueOnce ([buildTag ({ id: 8, name: '連携先' })])
+
+    renderPage ()
+
+    fireEvent.click (await screen.findByRole ('button', { name: '編集' }))
+    fireEvent.change (screen.getByLabelText ('連携する広場タグ'), {
+      target: { value: '連携先' },
+    })
+    fireEvent.click (screen.getByRole ('button', { name: '保存' }))
+
+    await waitFor (() => {
+      expect (api.apiPut).toHaveBeenCalledWith (
+          '/tags/nico/7',
+          expect.any (FormData),
+          { headers: { 'Content-Type': 'multipart/form-data' } },
+      )
+    })
+    expect (await screen.findByText ('1 件')).toBeInTheDocument ()
+  })
+
+  it ('asks before discarding changes when editing another tag', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      tags: [
+        buildNicoTag ({ id: 1, name: 'nico:first' }),
+        buildNicoTag ({ id: 2, name: 'nico:second' }),
+      ],
+      count: 2,
+    })
+
+    renderPage ()
+    dialogue.confirm.mockResolvedValueOnce (false)
+
+    const editButtons = await screen.findAllByRole ('button', { name: '編集' })
+    fireEvent.click (editButtons[0])
+    fireEvent.change (screen.getByLabelText ('連携する広場タグ'), {
+      target: { value: '入力中' },
+    })
+    fireEvent.click (screen.getAllByRole ('button', { name: '編集' })[0])
+
+    await waitFor (() => {
+      expect (dialogue.confirm).toHaveBeenCalledWith ({
+        title:       '編集中の内容を破棄しますか?',
+        confirmText: '破棄',
+        variant:     'danger',
+      })
+    })
+    expect (screen.getAllByLabelText ('連携する広場タグ')).toHaveLength (1)
+    expect (screen.getByLabelText ('連携する広場タグ')).toHaveValue ('入力中')
+  })
+
+  it ('switches editing rows without confirmation when unchanged', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      tags: [
+        buildNicoTag ({ id: 1, name: 'nico:first' }),
+        buildNicoTag ({ id: 2, name: 'nico:second' }),
+      ],
+      count: 2,
+    })
+
+    renderPage ()
+
+    const editButtons = await screen.findAllByRole ('button', { name: '編集' })
+    fireEvent.click (editButtons[0])
+    fireEvent.click (screen.getAllByRole ('button', { name: '編集' })[0])
+
+    expect (dialogue.confirm).not.toHaveBeenCalled ()
+    expect (screen.getAllByLabelText ('連携する広場タグ')).toHaveLength (1)
+  })
+
+  it ('shows tags field validation errors inside the edited card', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      tags:  [buildNicoTag ({ id: 7, name: 'nico:source' })],
+      count: 1,
+    })
+    api.isApiError.mockReturnValue (true)
+    api.apiPut.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          errors:      { tags: ['タグ名を確認してください．'] },
+          base_errors: [],
+        },
+      },
+    })
+
+    renderPage ()
+
+    fireEvent.click (await screen.findByRole ('button', { name: '編集' }))
+    fireEvent.click (screen.getByRole ('button', { name: '保存' }))
+
+    expect (await screen.findByText ('タグ名を確認してください．')).toBeInTheDocument ()
+    expect (screen.getByLabelText ('連携する広場タグ')).toHaveAttribute ('aria-invalid', 'true')
+  })
+})
diff --git a/frontend/src/pages/tags/NicoTagListPage.tsx b/frontend/src/pages/tags/NicoTagListPage.tsx
index e3c45bc..39ebd93 100644
--- a/frontend/src/pages/tags/NicoTagListPage.tsx
+++ b/frontend/src/pages/tags/NicoTagListPage.tsx
@@ -1,104 +1,179 @@
-import type { FC } from 'react'
-
-import { useCallback, useEffect, useRef, useState } from 'react'
+import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { Check, LoaderCircle, Pencil, X } from 'lucide-react'
+import { useEffect, useMemo, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
+import { useLocation, useNavigate } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
+import SortHeader from '@/components/SortHeader'
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
+import Pagination from '@/components/common/Pagination'
 import TextArea from '@/components/common/TextArea'
+import { useDialogue } from '@/components/dialogues/DialogueProvider'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
-import { apiGet, apiPut } from '@/lib/api'
+import { apiPut } from '@/lib/api'
+import { extractValidationError } from '@/lib/apiErrors'
+import { tagsKeys } from '@/lib/queryKeys'
+import { fetchNicoTags } from '@/lib/tags'
+import { cn, dateString, inputClass } from '@/lib/utils'
+import { canEditContent } from '@/lib/users'
 
-import type { NicoTag, Tag, User } from '@/types'
+import type { FC, FormEvent } from 'react'
 
+import type { FetchNicoTagsOrder, FetchNicoTagsOrderField, NicoTag, Tag, User } from '@/types'
+
+type LinkStatus = 'all' | 'linked' | 'unlinked'
 type Props = { user: User | null }
 
 
+const setIf = (qs: URLSearchParams, key: string, value: string) => {
+  const trimmed = value.trim ()
+  if (trimmed)
+    qs.set (key, trimmed)
+}
+
+
 const NicoTagListPage: FC<Props> = ({ user }) => {
-  const [cursor, setCursor] = useState ('')
-  const [editing, setEditing] = useState<{ [key: number]: boolean }> ({ })
-  const [loading, setLoading] = useState (false)
-  const [nicoTags, setNicoTags] = useState<NicoTag[]> ([])
-  const [rawTags, setRawTags] = useState<{ [key: number]: string }> ({ })
+  const dialogue = useDialogue ()
+  const location = useLocation ()
+  const navigate = useNavigate ()
+  const queryClient = useQueryClient ()
+  const query = useMemo (() => new URLSearchParams (location.search), [location.search])
 
-  const loaderRef = useRef<HTMLDivElement | null> (null)
+  const page = Number (query.get ('page') ?? 1)
+  const limit = Number (query.get ('limit') ?? 20)
+  const qName = query.get ('name') ?? ''
+  const qLinkedTag = query.get ('linked_tag') ?? ''
+  const qLinkStatus = (query.get ('link_status') || 'all') as LinkStatus
+  const order = (query.get ('order') || 'updated_at:desc') as FetchNicoTagsOrder
 
-  const memberFlg = ['admin', 'member'].some (r => user?.role === r)
+  const [editingId, setEditingId] = useState<number | null> (null)
+  const [errorsByTagId, setErrorsByTagId] = useState<Record<number, string[]>> ({ })
+  const [linkStatus, setLinkStatus] = useState<LinkStatus> ('all')
+  const [linkedTag, setLinkedTag] = useState ('')
+  const [name, setName] = useState ('')
+  const [rawTags, setRawTags] = useState<Record<number, string>> ({ })
+  const [savingId, setSavingId] = useState<number | null> (null)
 
-  const applyLoadedTags = useCallback ((data: { tags: NicoTag[]; nextCursor: string },
-					withCursor: boolean) => {
-    setNicoTags (tags => [...(withCursor ? tags : []), ...data.tags])
-    setCursor (data.nextCursor)
+  const keys = {
+      name: qName, linkedTag: qLinkedTag, linkStatus: qLinkStatus, page, limit, order }
+  const { data, isError, isLoading: loading } = useQuery ({
+      queryKey: tagsKeys.nicoIndex (keys),
+      queryFn:  () => fetchNicoTags (keys) })
+  const nicoTags = data?.tags ?? []
+  const count = data?.count ?? 0
 
-    const newEditing = Object.fromEntries (data.tags.map (t => [t.id, false]))
-    setEditing (editing => ({ ...editing, ...newEditing }))
+  const editable = canEditContent (user)
+  const totalPages = Math.ceil (count / limit)
 
-    const newRawTags = Object.fromEntries (
-	data.tags.map (t => [t.id, t.linkedTags.map (lt => lt.name).join (' ')]))
-    setRawTags (rawTags => ({ ...rawTags, ...newRawTags }))
-  }, [])
+  const handleSearch = (e: FormEvent) => {
+    e.preventDefault ()
 
-  const loadInitial = useCallback (async () => {
-    setLoading (true)
-
-    const data = await apiGet<{ tags: NicoTag[]; nextCursor: string }> ('/tags/nico')
-    applyLoadedTags (data, false)
-
-    setLoading (false)
-  }, [applyLoadedTags])
-
-  const loadMore = useCallback (async () => {
-    setLoading (true)
-
-    const data = await apiGet<{ tags: NicoTag[]; nextCursor: string }> (
-	'/tags/nico', { params: { cursor } })
-    applyLoadedTags (data, true)
-
-    setLoading (false)
-  }, [applyLoadedTags, cursor])
-
-  const handleEdit = async (id: number) => {
-    if (editing[id])
-      {
-	const formData = new FormData
-	formData.append ('tags', rawTags[id])
-
-	const data = await apiPut<Tag[]> (`/tags/nico/${ id }`, formData,
-				    { headers: { 'Content-Type': 'multipart/form-data' } })
-	setNicoTags (nicoTags => {
-	  nicoTags.find (t => t.id === id)!.linkedTags = data
-	  return [...nicoTags]
-	})
-	setRawTags (rawTags => ({ ...rawTags, [id]: data.map (t => t.name).join (' ') }))
-
-	toast ({ title: '更新しました．' })
-      }
-
-    setEditing (editing => ({ ...editing, [id]: !(editing[id]) }))
+    const qs = new URLSearchParams ()
+    setIf (qs, 'name', name)
+    setIf (qs, 'linked_tag', linkedTag)
+    if (linkStatus !== 'all')
+      qs.set ('link_status', linkStatus)
+    qs.set ('page', '1')
+    qs.set ('limit', String (limit))
+    qs.set ('order', order)
+    navigate (`${ location.pathname }?${ qs.toString () }`)
   }
 
-  useEffect(() => {
-    const observer = new IntersectionObserver (entries => {
-      if (entries[0].isIntersecting && !(loading) && cursor)
-	loadMore ()
-    }, { threshold: 1 })
+  const defaultDirection = {
+      name:       'asc',
+      created_at: 'desc',
+      updated_at: 'desc',
+  } as const
 
-    const target = loaderRef.current
-    if (target)
-      observer.observe (target)
+  const beginEdit = async (tag: NicoTag) => {
+    const editingTag = nicoTags.find (tag => tag.id === editingId)
+    const editingValue = editingTag?.linkedTags.map (tag => tag.name).join (' ') ?? ''
+    const editingChanged = editingId != null && rawTags[editingId] !== editingValue
 
-    return () => {
-      if (target)
-	observer.unobserve (target)
+    if (editingId != null && editingId !== tag.id && editingChanged
+	&& !(await dialogue.confirm ({
+	  title:       '編集中の内容を破棄しますか?',
+	  confirmText: '破棄',
+	  variant:     'danger',
+	})))
+      return
+
+    setEditingId (tag.id)
+    setRawTags (rawTags => ({
+	...rawTags,
+	[tag.id]: tag.linkedTags.map (linkedTag => linkedTag.name).join (' '),
+    }))
+    setErrorsByTagId (errors => ({ ...errors, [tag.id]: [] }))
+  }
+
+  const cancelEdit = (tag: NicoTag) => {
+    setEditingId (null)
+    setRawTags (rawTags => ({
+	...rawTags,
+	[tag.id]: tag.linkedTags.map (linkedTag => linkedTag.name).join (' '),
+    }))
+    setErrorsByTagId (errors => ({ ...errors, [tag.id]: [] }))
+  }
+
+  const saveLinks = async (id: number) => {
+    const formData = new FormData
+    formData.append ('tags', rawTags[id] ?? '')
+    setSavingId (id)
+
+    try
+    {
+      await apiPut<Tag[]> (`/tags/nico/${ id }`, formData,
+			   { headers: { 'Content-Type': 'multipart/form-data' } })
+      setErrorsByTagId (errors => ({ ...errors, [id]: [] }))
+      setEditingId (null)
+      await queryClient.invalidateQueries ({ queryKey: tagsKeys.nicoRoot })
+      toast ({ description: '連携を更新しました．' })
     }
-  }, [cursor, loadMore, loading])
+    catch (e)
+    {
+      const validationError = extractValidationError<'tags'> (e)
+      setErrorsByTagId (errors => ({
+	  ...errors,
+	  [id]: validationError?.fieldErrors.tags
+	      ?? validationError?.baseErrors
+	      ?? ['更新できませんでした．'],
+      }))
+      toast ({ title: '更新失敗', description: '入力内容を確認してください．' })
+    }
+    finally
+    {
+      setSavingId (null)
+    }
+  }
 
   useEffect (() => {
-    setNicoTags ([])
-    loadInitial ()
-  }, [loadInitial])
+    setName (qName)
+    setLinkedTag (qLinkedTag)
+    setLinkStatus (qLinkStatus)
+    setEditingId (null)
+
+    document.querySelector ('table')?.scrollIntoView ({ behavior: 'smooth' })
+  }, [location.search, qLinkedTag, qLinkStatus, qName])
+
+  useEffect (() => {
+    if (!(data))
+      return
+
+    setRawTags (Object.fromEntries (data.tags.map (tag => [
+      tag.id,
+      tag.linkedTags.map (linkedTag => linkedTag.name).join (' '),
+    ])))
+  }, [data])
+
+  useEffect (() => {
+    if (isError)
+      toast ({ title: '読込失敗', description: 'ニコニコ連携を読み込めませんでした．' })
+  }, [isError])
 
   return (
       <MainArea>
@@ -108,58 +183,201 @@ const NicoTagListPage: FC<Props> = ({ user }) => {
 
 	<div className="max-w-xl">
 	  <PageTitle>ニコニコ連携</PageTitle>
+	  <p className="mb-4 text-sm text-gray-600 dark:text-gray-300">
+	    ニコニコタグを広場のタグへ結び付けます．
+	  </p>
+
+	  <form onSubmit={handleSearch} className="space-y-2">
+	    <FormField label="ニコニコタグ">
+	      {({ invalid }) => (
+		  <input
+		      type="text"
+		      aria-label="ニコニコタグ"
+		      value={name}
+		      onChange={e => setName (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
+
+	    <FormField label="連携タグ">
+	      {({ invalid }) => (
+		  <input
+		      type="text"
+		      aria-label="連携タグ"
+		      value={linkedTag}
+		      onChange={e => setLinkedTag (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
+
+	    <FormField label="連携状態">
+	      {({ invalid }) => (
+		  <select
+		      aria-label="連携状態"
+		      value={linkStatus}
+		      onChange={e => setLinkStatus (e.target.value as LinkStatus)}
+		      className={inputClass (invalid)}>
+		    <option value="all">すべて</option>
+		    <option value="linked">連携済み</option>
+		    <option value="unlinked">未連携</option>
+		  </select>)}
+	    </FormField>
+
+	    <div className="py-3">
+	      <button
+		  type="submit"
+		  className="rounded bg-blue-500 px-4 py-2 text-white">
+		検索
+	      </button>
+	    </div>
+	  </form>
 	</div>
 
-	<div className="mt-4">
-	  {nicoTags.length > 0 && (
-	      <table className="table-auto w-full border-collapse mb-4">
-		<thead className="border-b-2 border-black dark:border-white">
-		  <tr>
-		    <th className="p-2 text-left">ニコニコタグ</th>
-		    <th className="p-2 text-left">連携タグ</th>
-		    {memberFlg && <th></th>}
-		  </tr>
-		</thead>
-		<tbody>
-		  {nicoTags.map ((tag, i) => (
-		      <tr key={i} className="even:bg-gray-100 dark:even:bg-gray-700">
-			<td className="p-2">
-			  <TagLink tag={tag} withWiki={false} withCount={false}/>
-			</td>
-			<td className="p-2">
-			  {editing[tag.id]
-			   ? (
-			      <TextArea value={rawTags[tag.id]} onChange={ev => {
-				setRawTags (rawTags => ({ ...rawTags, [tag.id]: ev.target.value }))
-			      }}/>)
-			   : tag.linkedTags.map((lt, j) => (
-			      <span key={j} className="mr-2">
-				<TagLink tag={lt}
-					 linkFlg={false}
-					 withCount={false}/>
-			      </span>))}
-			</td>
-			{memberFlg && (
-			    <td className="p-2">
-			      <a href="#" onClick={ev => {
-				ev.preventDefault ()
-				handleEdit (tag.id)
-			      }}>
-			        {editing[tag.id]
-				 ? (
-				    <span className="text-red-600 hover:text-red-400
-						     dark:text-red-300 dark:hover:text-red-100">
-				      更新
-				    </span>)
-				 : <span>編輯</span>}
-			      </a>
-			    </td>)}
-		      </tr>))}
-		</tbody>
-	      </table>)}
-	  {loading && 'Loading...'}
-	  <div ref={loaderRef} className="h-12"></div>
-	</div>
+	{loading
+	 ? 'Loading...'
+	 : (
+	    <div className="mt-6">
+	      <div className="mb-3 flex items-baseline justify-between gap-4">
+		<h2 className="text-lg font-bold">検索結果</h2>
+		<span className="text-sm text-gray-500 dark:text-gray-400">{count} 件</span>
+	      </div>
+
+	      {nicoTags.length > 0
+	       ? (
+		  <div className="overflow-x-auto">
+		    <table className="w-full min-w-[800px] table-fixed border-collapse">
+		      <colgroup>
+			<col className="w-64"/>
+			<col className="w-[48rem]"/>
+			<col className="w-56"/>
+			<col className="w-56"/>
+			{editable && <col className="w-24"/>}
+		      </colgroup>
+		      <thead className="border-b-2 border-black dark:border-white">
+			<tr>
+			  <th className="p-2 text-left whitespace-nowrap">
+			    <SortHeader<FetchNicoTagsOrderField>
+				by="name"
+				label="ニコニコタグ"
+				currentOrder={order}
+				defaultDirection={defaultDirection}/>
+			  </th>
+			  <th className="p-2 text-left">連携タグ</th>
+			  <th className="p-2 text-left whitespace-nowrap">
+			    <SortHeader<FetchNicoTagsOrderField>
+				by="created_at"
+				label="最初に記載された日時"
+				currentOrder={order}
+				defaultDirection={defaultDirection}/>
+			  </th>
+			  <th className="p-2 text-left whitespace-nowrap">
+			    <SortHeader<FetchNicoTagsOrderField>
+				by="updated_at"
+				label="最近記載された日時"
+				currentOrder={order}
+				defaultDirection={defaultDirection}/>
+			  </th>
+			  {editable && <th className="p-2"></th>}
+			</tr>
+		      </thead>
+		      <tbody>
+			{nicoTags.map (tag => {
+			  const isEditing = editingId === tag.id
+
+			  return [
+			    <tr
+				key={tag.id}
+				className={cn (
+				    'border-b border-gray-200 dark:border-gray-700',
+				    isEditing
+				    ? 'bg-rose-50 dark:bg-rose-950/30'
+				    : 'even:bg-gray-100 dark:even:bg-gray-800')}>
+			      <td className="p-2 align-top font-semibold">
+				<TagLink tag={tag} withWiki={false} withCount={false}/>
+			      </td>
+			      <td className="p-2 align-top">
+				{tag.linkedTags.map ((linkedTag, i) => (
+				    <span key={linkedTag.id}>
+				      {i > 0 && ' '}
+				      <TagLink
+					  tag={linkedTag}
+					  linkFlg={false}
+					  withCount={false}/>
+				    </span>))}
+			      </td>
+			      <td className="p-2 align-top whitespace-nowrap">
+				{dateString (tag.createdAt)}
+			      </td>
+			      <td className="p-2 align-top whitespace-nowrap">
+				{tag.recentPostTagCreatedAt && dateString (tag.recentPostTagCreatedAt)}
+			      </td>
+			      {editable && (
+				  <td className="p-2 text-right align-top">
+				    {!(isEditing) && (
+					<button
+					    type="button"
+					    onClick={() => beginEdit (tag)}
+					    className="inline-flex items-center gap-1 text-sm text-blue-700
+						       hover:underline dark:text-blue-300">
+					  <Pencil className="size-3.5"/>
+					  編集
+					</button>)}
+				  </td>)}
+			    </tr>,
+			    isEditing && (
+				<tr key={`${ tag.id }-edit`}
+				    className="border-b border-rose-200 bg-rose-50 dark:border-rose-900
+					       dark:bg-rose-950/30">
+				  <td colSpan={editable ? 5 : 4} className="p-3">
+				    <div className="space-y-2">
+				      <label htmlFor={`nico-links-${ tag.id }`}
+					     className="block text-sm font-semibold">
+					連携する広場タグ
+				      </label>
+				      <TextArea
+					  id={`nico-links-${ tag.id }`}
+					  value={rawTags[tag.id] ?? ''}
+					  invalid={(errorsByTagId[tag.id] ?? []).length > 0}
+					  className="min-h-24 resize-y"
+					  placeholder="タグ名を空白または改行で区切って入力"
+					  onChange={e => setRawTags (rawTags => ({
+					      ...rawTags,
+					      [tag.id]: e.target.value,
+					  }))}/>
+				      <FieldError messages={errorsByTagId[tag.id]}/>
+				      <div className="flex justify-end gap-2">
+					<button
+					    type="button"
+					    disabled={savingId === tag.id}
+					    onClick={() => cancelEdit (tag)}
+					    className="inline-flex items-center gap-1 rounded border
+						       border-gray-300 px-3 py-1.5 text-sm
+						       disabled:opacity-50 dark:border-gray-700">
+					  <X className="size-3.5"/>
+					  取消
+					</button>
+					<button
+					    type="button"
+					    disabled={savingId === tag.id}
+					    onClick={() => saveLinks (tag.id)}
+					    className="inline-flex items-center gap-1 rounded bg-rose-700
+						       px-3 py-1.5 text-sm text-white disabled:opacity-50">
+					  {savingId === tag.id
+					   ? <LoaderCircle className="size-3.5 animate-spin"/>
+					   : <Check className="size-3.5"/>}
+					  保存
+					</button>
+				      </div>
+				    </div>
+				  </td>
+				</tr>),
+			  ]
+			})}
+		      </tbody>
+		    </table>
+		  </div>)
+	       : <p>結果ないよ（笑）</p>}
+
+	      <Pagination page={page} totalPages={totalPages}/>
+	    </div>)}
       </MainArea>)
 }
 
diff --git a/frontend/src/pages/tags/TagDetailPage.test.tsx b/frontend/src/pages/tags/TagDetailPage.test.tsx
index e5380cc..9b9ca2c 100644
--- a/frontend/src/pages/tags/TagDetailPage.test.tsx
+++ b/frontend/src/pages/tags/TagDetailPage.test.tsx
@@ -1,6 +1,6 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
 import { Route, Routes } from 'react-router-dom'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import TagDetailPage from '@/pages/tags/TagDetailPage'
 import { buildTag } from '@/test/factories'
@@ -11,7 +11,8 @@ const tagsApi = vi.hoisted (() => ({
 }))
 
 const api = vi.hoisted (() => ({
-  apiPut: vi.fn (),
+  apiPut:     vi.fn (),
+  isApiError: vi.fn (),
 }))
 
 const toastApi = vi.hoisted (() => ({
@@ -28,9 +29,14 @@ const renderPage = () =>
         <Route path="/tags/:id" element={<TagDetailPage/>}/>
       </Routes>,
       { route: '/tags/7' },
-  )
+)
 
 describe ('TagDetailPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+  })
+
   it ('loads and displays an editable tag', async () => {
     tagsApi.fetchTag.mockResolvedValueOnce (
         buildTag ({ id: 7, name: '虹夏', category: 'character', aliases: ['drums'] }),
@@ -68,4 +74,28 @@ describe ('TagDetailPage', () => {
 
     expect (await screen.findByRole ('button', { name: '更新' })).toBeDisabled ()
   })
+
+  it ('shows validation errors returned for tag fields', async () => {
+    tagsApi.fetchTag.mockResolvedValueOnce (buildTag ({ id: 7, name: 'old' }))
+    api.isApiError.mockReturnValue (true)
+    api.apiPut.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      { category: ['ニコタグは変更できません．'] },
+          base_errors: [],
+        },
+      },
+    })
+
+    renderPage ()
+
+    await screen.findByDisplayValue ('old')
+    fireEvent.submit (screen.getByRole ('button', { name: '更新' }).closest ('form')!)
+
+    expect (await screen.findByText ('ニコタグは変更できません．')).toBeInTheDocument ()
+    expect (screen.getByRole ('combobox')).toHaveAttribute ('aria-invalid', 'true')
+  })
 })
diff --git a/frontend/src/pages/tags/TagDetailPage.tsx b/frontend/src/pages/tags/TagDetailPage.tsx
index 7d6eb57..d1e3e76 100644
--- a/frontend/src/pages/tags/TagDetailPage.tsx
+++ b/frontend/src/pages/tags/TagDetailPage.tsx
@@ -3,7 +3,8 @@ import { useEffect, useState } from 'react'
 import { useParams } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
-import Label from '@/components/common/Label'
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
@@ -11,12 +12,20 @@ import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
 import { apiPut } from '@/lib/api'
 import { postsKeys, tagsKeys } from '@/lib/queryKeys'
 import { fetchTag } from '@/lib/tags'
-import { cn } from '@/lib/utils'
+import { cn, inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC, FormEvent } from 'react'
 
 import type { Category, Tag } from '@/types'
 
+type TagFormField =
+    | 'name'
+    | 'category'
+    | 'aliases'
+    | 'parentTags'
+    | 'deprecated'
+
 
 const TagDetailPage: FC = () => {
   const { id } = useParams ()
@@ -31,18 +40,23 @@ const TagDetailPage: FC = () => {
   const [category, setCategory] = useState<Category> ('general')
   const [aliases, setAliases] = useState ('')
   const [parentTags, setParentTags] = useState ('')
+  const [deprecated, setDeprecated] = useState (false)
   const [disabled, setDisabled] = useState (true)
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<TagFormField> ()
 
   const qc = useQueryClient ()
 
   const handleSubmit = async (e: FormEvent) => {
     e.preventDefault ()
+    clearValidationErrors ()
 
     const formData = new FormData
     formData.append ('name', name)
     formData.append ('category', category)
     formData.append ('aliases', aliases)
     formData.append ('parent_tags', parentTags)
+    formData.append ('deprecated', deprecated ? '1' : '0')
 
     try
     {
@@ -52,13 +66,15 @@ const TagDetailPage: FC = () => {
       setCategory (data.category as Category)
       setAliases (data.aliases.join (' '))
       setParentTags (data.parents.map (t => t.name).join (' '))
+      setDeprecated (Boolean (data.deprecatedAt))
 
       qc.invalidateQueries ({ queryKey: postsKeys.root })
       qc.invalidateQueries ({ queryKey: tagsKeys.root })
       toast ({ description: '更新しました．' })
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ description: '更新に失敗しました．' })
     }
   }
@@ -74,6 +90,7 @@ const TagDetailPage: FC = () => {
     setCategory (tag.category as Category)
     setAliases (tag.aliases.join (' '))
     setParentTags (tag.parents.map (t => t.name).join (' '))
+    setDeprecated (Boolean (tag.deprecatedAt))
     setDisabled (tag.category === 'nico')
   }, [tag])
 
@@ -89,57 +106,84 @@ const TagDetailPage: FC = () => {
 	      </PageTitle>
 
 	      <form onSubmit={handleSubmit} className="my-4 space-y-2">
+		<FieldError messages={baseErrors}/>
+
 		{/* 名称 */}
-		<div>
-		  <Label>名称</Label>
-		  {/* TODO: 補完に対応させる */}
-		  <input
-		      type="text"
-		      disabled={disabled}
-		      value={name}
-		      onChange={e => setName (e.target.value)}
-		      className="w-full border p-2 rounded"/>
-		</div>
+		<FormField label="名称" messages={fieldErrors.name}>
+		  {({ describedBy, invalid }) => (
+		      <>
+			{/* TODO: 補完に対応させる */}
+			<input
+			    type="text"
+			    disabled={disabled}
+			    value={name}
+			    onChange={e => setName (e.target.value)}
+			    aria-describedby={describedBy}
+			    aria-invalid={invalid}
+			    className={inputClass (invalid)}/>
+		      </>)}
+		</FormField>
 
 		{/* カテゴリ */}
-		<div>
-		  <Label>カテゴリ</Label>
+		<FormField label="カテゴリ" messages={fieldErrors.category}>
+		  {({ describedBy, invalid }) => (
 		  <select
 		      disabled={disabled}
 		      value={category ?? ''}
 		      onChange={e => setCategory(e.target.value as Category)}
-		      className="w-full border p-2 rounded">
+		      aria-describedby={describedBy}
+		      aria-invalid={invalid}
+		      className={inputClass (invalid)}>
 		    {CATEGORIES.filter (cat => tag.category === 'nico' || cat !== 'nico')
 			       .map (cat => (
 			<option key={cat} value={cat}>
 			  {CATEGORY_NAMES[cat]}
 			</option>))}
-		  </select>
-		</div>
+		  </select>)}
+		</FormField>
 
 		{/* 別名 */}
-		<div>
-		  <Label>別名</Label>
-		  {/* TODO: 補完に対応させる */}
-		  <input
-		      type="text"
-		      disabled={disabled}
-		      value={aliases}
-		      onChange={e => setAliases (e.target.value)}
-		      className="w-full border p-2 rounded"/>
-		</div>
+		<FormField label="別名" messages={fieldErrors.aliases}>
+		  {({ describedBy, invalid }) => (
+		      <>
+			{/* TODO: 補完に対応させる */}
+			<input
+			    type="text"
+			    disabled={disabled}
+			    value={aliases}
+			    onChange={e => setAliases (e.target.value)}
+			    aria-describedby={describedBy}
+			    aria-invalid={invalid}
+			    className={inputClass (invalid)}/>
+		      </>)}
+		</FormField>
 
 		{/* 上位タグ */}
-		<div>
-		  <Label>上位タグ</Label>
-		  {/* TODO: 補完に対応させる */}
-		  <input
-		      type="text"
-		      disabled={disabled}
-		      value={parentTags}
-		      onChange={e => setParentTags (e.target.value)}
-		      className="w-full border p-2 rounded"/>
-		</div>
+		<FormField label="上位タグ" messages={fieldErrors.parentTags}>
+		  {({ describedBy, invalid }) => (
+		      <>
+			{/* TODO: 補完に対応させる */}
+			<input
+			    type="text"
+			    disabled={disabled}
+			    value={parentTags}
+			    onChange={e => setParentTags (e.target.value)}
+			    aria-describedby={describedBy}
+			    aria-invalid={invalid}
+			    className={inputClass (invalid)}/>
+		      </>)}
+		</FormField>
+
+		<FormField label="廃止済" messages={fieldErrors.deprecated}>
+		  {({ describedBy, invalid }) => (
+		      <input
+			  type="checkbox"
+			  disabled={disabled}
+			  checked={deprecated}
+			  onChange={e => setDeprecated (e.target.checked)}
+			  aria-describedby={describedBy}
+			  aria-invalid={invalid}/>)}
+		</FormField>
 
 		<div className="py-3">
 		  <button
diff --git a/frontend/src/pages/tags/TagHistoryPage.tsx b/frontend/src/pages/tags/TagHistoryPage.tsx
index 8f672dd..8ce1d1c 100644
--- a/frontend/src/pages/tags/TagHistoryPage.tsx
+++ b/frontend/src/pages/tags/TagHistoryPage.tsx
@@ -20,17 +20,28 @@ import type { FC } from 'react'
 
 const renderDiff = (diff: { current: string | null; prev: string | null }) => (
     <>
-      {(diff.prev && diff.prev !== diff.current) && (
+      {diff.prev !== diff.current
+       ? (
 	  <>
 	    <del className="text-red-600 dark:text-red-400">
-	      {diff.prev}
+	      {diff.prev && <>{diff.prev}<br/></>}
 	    </del>
-	    {diff.current && <br/>}
-	  </>)}
-      {diff.current}
+	    <ins className="text-green-600 dark:text-green-400">
+	      {diff.current}
+	    </ins>
+	  </>)
+       : diff.current}
     </>)
 
 
+const tagStateLabel = (deprecatedAt: string | null) => deprecatedAt ? '廃止' : ''
+
+
+const renderStateDiff = (diff: { current: string | null; prev: string | null }) =>
+    renderDiff ({ current: tagStateLabel (diff.current),
+		  prev: tagStateLabel (diff.prev) })
+
+
 const TagHistoryPage: FC = () => {
   const location = useLocation ()
   const query = new URLSearchParams (location.search)
@@ -72,6 +83,8 @@ const TagHistoryPage: FC = () => {
 		    <col className="w-96"/>
 		    {/* カテゴリ */}
 		    <col className="w-96"/>
+		    {/* 状態 */}
+		    <col className="w-32"/>
 		    {/* 別名 */}
 		    <col className="w-[48rem]"/>
 		    {/* 上位タグ */}
@@ -87,6 +100,7 @@ const TagHistoryPage: FC = () => {
 		      <th className="p-2 text-left">版</th>
 		      <th className="p-2 text-left">名称</th>
 		      <th className="p-2 text-left">カテゴリ</th>
+		      <th className="p-2 text-left">状態</th>
 		      <th className="p-2 text-left">別名</th>
 		      <th className="p-2 text-left">上位タグ</th>
 		      <th className="p-2 text-left">更新日時</th>
@@ -106,6 +120,9 @@ const TagHistoryPage: FC = () => {
 				prev: (change.category.prev
 				       && CATEGORY_NAMES[change.category.prev]) })}
 			  </td>
+			  <td className="p-2 break-all">
+			    {renderStateDiff (change.deprecatedAt)}
+			  </td>
 			  <td className="p-2">
 			    {change.aliases.map ((tag, i) => (
 				tag.type === 'added'
@@ -178,6 +195,7 @@ const TagHistoryPage: FC = () => {
 					`/tags/${ change.tagId }`,
 					{ name: change.name.current,
 					  category: change.category.current,
+					  deprecated: change.deprecatedAt.current ? '1' : '0',
 					  aliases:
 					      change.aliases
 					      .filter (t => t.type !== 'removed')
@@ -211,4 +229,5 @@ const TagHistoryPage: FC = () => {
       </MainArea>)
 }
 
-export default TagHistoryPage
\ No newline at end of file
+
+export default TagHistoryPage
diff --git a/frontend/src/pages/tags/TagListPage.test.tsx b/frontend/src/pages/tags/TagListPage.test.tsx
index e4eb159..f13f3eb 100644
--- a/frontend/src/pages/tags/TagListPage.test.tsx
+++ b/frontend/src/pages/tags/TagListPage.test.tsx
@@ -14,13 +14,22 @@ vi.mock ('@/lib/tags', () => tagsApi)
 describe ('TagListPage', () => {
   it ('loads tags from URL filters and renders the results table', async () => {
     tagsApi.fetchTags.mockResolvedValueOnce ({
-      tags: [buildTag ({ id: 7, name: '虹夏', category: 'character', postCount: 99 })],
+      tags: [buildTag ({
+        id: 7,
+        name: '虹夏',
+        category: 'character',
+        postCount: 99,
+        deprecatedAt: '2026-06-01T00:00:00.000Z',
+      })],
       count: 1,
     })
 
     renderWithProviders (
         <TagListPage/>,
-        { route: '/tags?name=%E8%99%B9&category=character&page=3&post_count_gte=5' },
+        {
+          route:
+              '/tags?name=%E8%99%B9&category=character&page=3&post_count_gte=5&deprecated=1',
+        },
     )
 
     await waitFor (() => {
@@ -30,6 +39,7 @@ describe ('TagListPage', () => {
             category:     'character',
             page:         3,
             postCountGTE: 5,
+            deprecated:   true,
           }),
       )
     })
@@ -38,6 +48,8 @@ describe ('TagListPage', () => {
         '/tags/7',
     )
     expect (screen.getAllByText ('キャラクター').length).toBeGreaterThan (0)
+    expect (screen.getAllByRole ('combobox')[1]).toHaveValue ('1')
+    expect (screen.getAllByText ('廃止')).toHaveLength (2)
   })
 
   it ('navigates to a normalized search URL on submit', async () => {
@@ -46,7 +58,9 @@ describe ('TagListPage', () => {
     renderWithProviders (<TagListPage/>, { route: '/tags' })
 
     fireEvent.change (screen.getByRole ('textbox'), { target: { value: '虹夏' } })
-    fireEvent.change (screen.getByRole ('combobox'), { target: { value: 'character' } })
+    fireEvent.change (screen.getAllByRole ('combobox')[0], {
+      target: { value: 'character' },
+    })
     fireEvent.submit (screen.getByRole ('button', { name: '検索' }).closest ('form')!)
 
     await waitFor (() => {
diff --git a/frontend/src/pages/tags/TagListPage.tsx b/frontend/src/pages/tags/TagListPage.tsx
index 7e2b039..f39c58a 100644
--- a/frontend/src/pages/tags/TagListPage.tsx
+++ b/frontend/src/pages/tags/TagListPage.tsx
@@ -7,7 +7,7 @@ import PrefetchLink from '@/components/PrefetchLink'
 import SortHeader from '@/components/SortHeader'
 import TagLink from '@/components/TagLink'
 import DateTimeField from '@/components/common/DateTimeField'
-import Label from '@/components/common/Label'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
 import MainArea from '@/components/layout/MainArea'
@@ -15,7 +15,7 @@ import { SITE_TITLE } from '@/config'
 import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
 import { tagsKeys } from '@/lib/queryKeys'
 import { fetchTags } from '@/lib/tags'
-import { dateString } from '@/lib/utils'
+import { dateString, inputClass } from '@/lib/utils'
 
 import type { FC, FormEvent } from 'react'
 
@@ -29,6 +29,13 @@ const setIf = (qs: URLSearchParams, k: string, v: string | null) => {
 }
 
 
+const boolFromQuery = (value: string | null): boolean =>
+    ['1', 'true', 'on', 'yes', ''].includes ((value ?? '').toLowerCase ())
+
+
+const tagStateLabel = (deprecatedAt: string | null) => deprecatedAt ? '廃止' : ''
+
+
 const TagListPage: FC = () => {
   const location = useLocation ()
 
@@ -48,6 +55,9 @@ const TagListPage: FC = () => {
   const qCreatedTo = query.get ('created_to') ?? ''
   const qUpdatedFrom = query.get ('updated_from') ?? ''
   const qUpdatedTo = query.get ('updated_to') ?? ''
+  const qDeprecated = query.has ('deprecated')
+      ? boolFromQuery (query.get ('deprecated'))
+      : null
   const order = (query.get ('order') || 'post_count:desc') as FetchTagsOrder
 
   const [name, setName] = useState ('')
@@ -58,6 +68,7 @@ const TagListPage: FC = () => {
   const [createdTo, setCreatedTo] = useState<string | null> (null)
   const [updatedFrom, setUpdatedFrom] = useState<string | null> (null)
   const [updatedTo, setUpdatedTo] = useState<string | null> (null)
+  const [deprecated, setDeprecated] = useState<boolean | null> (null)
 
   const keys = {
       page, limit, order,
@@ -69,7 +80,8 @@ const TagListPage: FC = () => {
       createdFrom: qCreatedFrom,
       createdTo: qCreatedTo,
       updatedFrom: qUpdatedFrom,
-      updatedTo: qUpdatedTo }
+      updatedTo: qUpdatedTo,
+      deprecated: qDeprecated }
   const { data, isLoading: loading } = useQuery ({
       queryKey: tagsKeys.index (keys),
       queryFn: () => fetchTags (keys) })
@@ -85,10 +97,11 @@ const TagListPage: FC = () => {
     setCreatedTo (qCreatedTo)
     setUpdatedFrom (qUpdatedFrom)
     setUpdatedTo (qUpdatedTo)
+    setDeprecated (qDeprecated)
 
     document.querySelector ('table')?.scrollIntoView ({ behavior: 'smooth' })
   }, [location.search, qCategory, qCreatedFrom, qCreatedTo, qName, qPostCountGTE,
-      qPostCountLTE, qUpdatedFrom, qUpdatedTo])
+      qPostCountLTE, qUpdatedFrom, qUpdatedTo, qDeprecated])
 
   const handleSearch = (e: FormEvent) => {
     e.preventDefault ()
@@ -104,6 +117,8 @@ const TagListPage: FC = () => {
     setIf (qs, 'created_to', createdTo)
     setIf (qs, 'updated_from', updatedFrom)
     setIf (qs, 'updated_to', updatedTo)
+    if (deprecated != null)
+      qs.set ('deprecated', deprecated ? '1' : '0')
     qs.set ('page', '1')
     qs.set ('order', order)
 
@@ -127,71 +142,94 @@ const TagListPage: FC = () => {
 
 	  <form onSubmit={handleSearch} className="space-y-2">
 	    {/* 名前 */}
-	    <div>
-	      <Label>名前</Label>
-	      <input
-		  type="text"
-		  value={name}
-		  onChange={e => setName (e.target.value)}
-		  className="w-full border p-2 rounded"/>
-	    </div>
+	    <FormField label="名前">
+	      {({ invalid }) => (
+		  <input
+		      type="text"
+		      value={name}
+		      onChange={e => setName (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
 
 	    {/* カテゴリ */}
-	    <div>
-	      <Label>カテゴリ</Label>
-	      <select
-		  value={category ?? ''}
-		  onChange={e => setCategory((e.target.value || null) as Category | null)}
-		  className="w-full border p-2 rounded">
-		<option value="">&nbsp;</option>
-		{CATEGORIES.map (cat => (
-		    <option key={cat} value={cat}>
-		      {CATEGORY_NAMES[cat]}
-		    </option>))}
-	      </select>
-	    </div>
+	    <FormField label="カテゴリ">
+	      {({ invalid }) => (
+		  <select
+		      value={category ?? ''}
+		      onChange={e => setCategory((e.target.value || null) as Category | null)}
+		      className={inputClass (invalid)}>
+		    <option value="">&nbsp;</option>
+		    {CATEGORIES.map (cat => (
+			<option key={cat} value={cat}>
+			  {CATEGORY_NAMES[cat]}
+			</option>))}
+		  </select>)}
+	    </FormField>
 
 	    {/* 広場の投稿数 */}
-	    <div>
-	      <Label>広場の投稿数</Label>
-	      <input
-		  type="number"
-		  min="0"
-		  value={postCountGTE < 0 ? 0 : String (postCountGTE)}
-		  onChange={e => setPostCountGTE (Number (e.target.value || 0))}
-		  className="border rounded p-2"/>
-	      <span className="mx-1">〜</span>
-	      <input
-		  type="number"
-		  min="0"
-		  value={postCountLTE == null ? '' : String (postCountLTE)}
-		  onChange={e => setPostCountLTE (e.target.value ? Number (e.target.value) : null)}
-		  className="border rounded p-2"/>
-	    </div>
+	    <FormField label="広場の投稿数">
+	      {({ invalid }) => (
+		  <>
+		    <input
+			type="number"
+			min="0"
+			value={postCountGTE < 0 ? 0 : String (postCountGTE)}
+			onChange={e => setPostCountGTE (Number (e.target.value || 0))}
+			className={inputClass (invalid, 'w-auto')}/>
+		    <span className="mx-1">〜</span>
+		    <input
+			type="number"
+			min="0"
+			value={postCountLTE == null ? '' : String (postCountLTE)}
+			onChange={e => setPostCountLTE (e.target.value
+							? Number (e.target.value)
+							: null)}
+			className={inputClass (invalid, 'w-auto')}/>
+		  </>)}
+	    </FormField>
 
 	    {/* はじめて記載された日時 */}
-	    <div>
-	      <Label>はじめて記載された日時</Label>
-	      <DateTimeField
-		  value={createdFrom ?? undefined}
-		  onChange={setCreatedFrom}/>
-	      <span className="mx-1">〜</span>
-	      <DateTimeField
-		  value={createdTo ?? undefined}
-		  onChange={setCreatedTo}/>
-	    </div>
+	    <FormField label="はじめて記載された日時">
+	      {() => (
+		  <>
+		    <DateTimeField
+			value={createdFrom ?? undefined}
+			onChange={setCreatedFrom}/>
+		    <span className="mx-1">〜</span>
+		    <DateTimeField
+			value={createdTo ?? undefined}
+			onChange={setCreatedTo}/>
+		  </>)}
+	    </FormField>
 
 	    {/* 定義の更新日時 */}
-	    <div>
-	      <Label>定義の更新日時</Label>
-	      <DateTimeField
-		  value={updatedFrom ?? undefined}
-		  onChange={setUpdatedFrom}/>
-	      <span className="mx-1">〜</span>
-	      <DateTimeField
-		  value={updatedTo ?? undefined}
-		  onChange={setUpdatedTo}/>
-	    </div>
+	    <FormField label="定義の更新日時">
+	      {() => (
+		  <>
+		    <DateTimeField
+			value={updatedFrom ?? undefined}
+			onChange={setUpdatedFrom}/>
+		    <span className="mx-1">〜</span>
+		    <DateTimeField
+			value={updatedTo ?? undefined}
+			onChange={setUpdatedTo}/>
+		  </>)}
+	    </FormField>
+
+	    <FormField label="状態">
+	      {({ invalid }) => (
+		  <select
+		      value={deprecated == null ? '' : (deprecated ? '1' : '0')}
+		      onChange={e => setDeprecated (
+			  e.target.value === ''
+			  ? null
+			  : e.target.value === '1')}
+		      className={inputClass (invalid)}>
+		    <option value="">&nbsp;</option>
+		    <option value="0">有効</option>
+		    <option value="1">廃止</option>
+		  </select>)}
+	    </FormField>
 
 	    <div className="py-3">
 	      <button
@@ -211,6 +249,7 @@ const TagListPage: FC = () => {
 		    <col className="w-72"/>
 		    <col className="w-16"/>
 		    <col className="w-48"/>
+		    <col className="w-32"/>
 		    <col className="w-72"/>
 		    <col className="w-48"/>
 		    <col className="w-56"/>
@@ -241,6 +280,7 @@ const TagListPage: FC = () => {
 			    currentOrder={order}
 			    defaultDirection={defaultDirection}/>
 		      </th>
+		      <th className="p-2 text-left whitespace-nowrap">状態</th>
 		      <th className="p-2 text-left whitespace-nowrap">別名</th>
 		      <th className="p-2 text-left whitespace-nowrap">上位タグ</th>
 		      <th className="p-2 text-left whitespace-nowrap">
@@ -272,6 +312,7 @@ const TagListPage: FC = () => {
 			  </td>
 			  <td className="p-2 text-right">{row.postCount}</td>
 			  <td className="p-2">{CATEGORY_NAMES[row.category]}</td>
+			  <td className="p-2">{tagStateLabel (row.deprecatedAt)}</td>
 			  <td className="p-2">{row.aliases.join (' ')}</td>
 			  <td className="p-2">
 			    {row.parents.map (t => (
diff --git a/frontend/src/pages/theatres/TheatreDetailPage.test.tsx b/frontend/src/pages/theatres/TheatreDetailPage.test.tsx
new file mode 100644
index 0000000..7adab24
--- /dev/null
+++ b/frontend/src/pages/theatres/TheatreDetailPage.test.tsx
@@ -0,0 +1,298 @@
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
+import { Route, Routes } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import TheatreDetailPage from '@/pages/theatres/TheatreDetailPage'
+import { buildPost,
+	 buildTheatre,
+	 buildTheatreComment,
+	 buildTheatreInfo,
+	 buildTheatrePostSelectionWeights,
+	 buildTheatreProgramme,
+	 buildUser } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+import type { ReactNode } from 'react'
+
+const api = vi.hoisted (() => ({
+  apiDelete:  vi.fn (),
+  apiGet:     vi.fn (),
+  apiPatch:   vi.fn (),
+  apiPost:    vi.fn (),
+  apiPut:     vi.fn (),
+  isApiError: vi.fn (() => false),
+}))
+
+const postsApi = vi.hoisted (() => ({
+  fetchPost: vi.fn (),
+}))
+
+const dialogue = vi.hoisted (() => ({
+  confirm: vi.fn (),
+}))
+
+const postEmbed = vi.hoisted (() => ({
+  props: vi.fn (),
+  play:  vi.fn (),
+  seek:  vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/lib/posts', () => postsApi)
+vi.mock ('@/components/dialogues/DialogueProvider', () => ({
+  useDialogue: () => dialogue,
+}))
+vi.mock ('@/components/PostEmbed', () => ({
+  default: (props: {
+    ref?: { current: unknown }
+    post: { title: string | null; url: string }
+  }) => {
+    postEmbed.props (props)
+    if (props.ref)
+      props.ref.current = {
+        play: postEmbed.play,
+        seek: postEmbed.seek,
+      }
+
+    return <div>Embed:{props.post.title || props.post.url}</div>
+  },
+}))
+vi.mock ('@/components/PostEditForm', () => ({
+  default: () => <div>Post edit form</div>,
+}))
+vi.mock ('framer-motion', () => ({
+  motion: {
+    aside: ({ children }: { children?: ReactNode }) => <aside>{children}</aside>,
+    div:   ({ children }: { children?: ReactNode }) => <div>{children}</div>,
+    main:  ({ children }: { children?: ReactNode }) => <main>{children}</main>,
+  },
+}))
+
+const currentPost = buildPost ({
+  id:    10,
+  title: '上映中の投稿',
+  url:   'https://www.nicovideo.jp/watch/sm10',
+})
+const theatre = buildTheatre ({ id: 7, name: '上映室' })
+const programme = buildTheatreProgramme ({
+  theatreId: 7,
+  position:  3,
+  post:      currentPost,
+})
+const weights = buildTheatrePostSelectionWeights ({
+  lightestPosts: [{
+    post:    currentPost,
+    penalty: 2,
+    weight:  0.5,
+    tags:    [],
+  }],
+})
+
+const renderPage = (user = buildUser ({ id: 1, role: 'member' })) =>
+  renderWithProviders (
+      <Routes>
+        <Route path="/theatres/:id" element={<TheatreDetailPage user={user}/>}/>
+      </Routes>,
+      { route: '/theatres/7' },
+  )
+
+const mockDefaultApi = () => {
+  api.apiGet.mockImplementation ((path: string) => {
+    switch (path)
+    {
+    case '/theatres/7':
+      return Promise.resolve (theatre)
+
+    case '/theatres/7/comments':
+      return Promise.resolve ([
+        buildTheatreComment ({
+          theatreId: 7,
+          no:        2,
+          user:      { id: 1, name: 'tester' },
+          content:   '視聴コメント',
+        }),
+      ])
+
+    case '/theatres/7/programmes':
+      return Promise.resolve ([programme])
+
+    case '/theatres/7/post_selection_weights':
+      return Promise.resolve (weights)
+
+    default:
+      return Promise.reject (new Error (`Unexpected GET ${ path }`))
+    }
+  })
+
+  api.apiPut.mockImplementation ((path: string) => {
+    switch (path)
+    {
+    case '/theatres/7/watching':
+      return Promise.resolve (buildTheatreInfo ({
+        postId:        currentPost.id,
+        postStartedAt: '2026-01-02T03:04:05.000Z',
+        postElapsedMs: 1_000,
+        watchingUsers: [{ id: 1, name: 'tester' }],
+        skipVote:      {
+          votesCount:         0,
+          requiredCount:      2,
+          watchingUsersCount: 1,
+          voted:              false,
+        },
+      }))
+
+    case '/theatres/7/skip_vote':
+      return Promise.resolve (buildTheatreInfo ({
+        postId:        currentPost.id,
+        postStartedAt: '2026-01-02T03:04:05.000Z',
+        postElapsedMs: 2_000,
+        watchingUsers: [{ id: 1, name: 'tester' }],
+        skipVote:      {
+          votesCount:         1,
+          requiredCount:      2,
+          watchingUsersCount: 1,
+          voted:              true,
+        },
+      }))
+
+    default:
+      return Promise.reject (new Error (`Unexpected PUT ${ path }`))
+    }
+  })
+
+  api.apiDelete.mockResolvedValue (undefined)
+  api.apiPatch.mockResolvedValue (undefined)
+  api.apiPost.mockResolvedValue (undefined)
+  postsApi.fetchPost.mockResolvedValue (currentPost)
+  dialogue.confirm.mockResolvedValue (true)
+}
+
+describe ('TheatreDetailPage', () => {
+  beforeEach (() => {
+    vi.useRealTimers ()
+    vi.clearAllMocks ()
+    mockDefaultApi ()
+  })
+
+  it ('loads theatre state, comments, current post, programme history, and weights', async () => {
+    renderPage ()
+
+    expect (await screen.findByText ('上映会場『上映室』')).toBeInTheDocument ()
+    expect (await screen.findByText ('Embed:上映中の投稿')).toBeInTheDocument ()
+    expect (screen.getAllByText ('視聴コメント')[0]).toBeInTheDocument ()
+    expect (screen.getAllByText ('上映中の投稿')[0]).toBeInTheDocument ()
+    expect (screen.getByText ('penalty 2')).toBeInTheDocument ()
+
+    await waitFor (() => {
+      expect (postsApi.fetchPost).toHaveBeenCalledWith ('10')
+    })
+  })
+
+  it ('votes to skip the current post', async () => {
+    renderPage ()
+
+    await screen.findByText ('Embed:上映中の投稿')
+
+    fireEvent.click (screen.getByRole ('button', { name: 'スキップ 0 / 2' }))
+
+    await waitFor (() => {
+      expect (api.apiPut).toHaveBeenCalledWith (
+          '/theatres/7/skip_vote',
+          { post_id: 10 },
+      )
+    })
+    expect (await screen.findByRole ('button', { name: 'スキップ取消 1 / 2' }))
+      .toBeInTheDocument ()
+  })
+
+  it ('does not seek to zero while applying video length from the player', async () => {
+    api.apiPut.mockImplementation ((path: string) => {
+      switch (path)
+      {
+      case '/theatres/7/watching':
+        return Promise.resolve (buildTheatreInfo ({
+          hostFlg:       true,
+          postId:        currentPost.id,
+          postStartedAt: '2026-01-02T03:04:05.000Z',
+          postElapsedMs: 7_000,
+          watchingUsers: [{ id: 1, name: 'tester' }],
+          skipVote:      {
+            votesCount:         0,
+            requiredCount:      2,
+            watchingUsersCount: 1,
+            voted:              false,
+          },
+        }))
+
+      default:
+        return Promise.reject (new Error (`Unexpected PUT ${ path }`))
+      }
+    })
+
+    renderPage ()
+    await screen.findByText ('Embed:上映中の投稿')
+
+    const props = postEmbed.props.mock.calls.at (-1)![0]
+
+    act (() => {
+      props.onVideoReady (120_000)
+      props.onPlaybackChange (0)
+    })
+
+    const seekMs = postEmbed.seek.mock.calls[0][0]
+    expect (seekMs).toBeGreaterThanOrEqual (7_000)
+    expect (seekMs).toBeLessThan (10_000)
+    expect (postEmbed.seek).not.toHaveBeenCalledWith (0)
+  })
+
+  it ('does not advance host post while video length is unknown', async () => {
+    api.apiPut.mockImplementation ((path: string) => {
+      switch (path)
+      {
+      case '/theatres/7/watching':
+        return Promise.resolve (buildTheatreInfo ({
+          hostFlg:       true,
+          postId:        currentPost.id,
+          postStartedAt: '2026-01-02T03:04:05.000Z',
+          postElapsedMs: 4_000,
+          watchingUsers: [{ id: 1, name: 'tester' }],
+          skipVote:      {
+            votesCount:         0,
+            requiredCount:      2,
+            watchingUsersCount: 1,
+            voted:              false,
+          },
+        }))
+
+      default:
+        return Promise.reject (new Error (`Unexpected PUT ${ path }`))
+      }
+    })
+
+    renderPage ()
+
+    await screen.findByText ('Embed:上映中の投稿')
+    await waitFor (() => {
+      expect (api.apiPut).toHaveBeenCalledWith ('/theatres/7/watching')
+    })
+
+    await waitFor (() => {
+      expect (api.apiPut).toHaveBeenCalledTimes (2)
+    }, { timeout: 2_500 })
+    expect (api.apiPatch).not.toHaveBeenCalledWith ('/theatres/7/next_post')
+  })
+
+  it ('deletes an owned comment after confirmation', async () => {
+    renderPage ()
+
+    fireEvent.click ((await screen.findAllByLabelText ('コメントを削除'))[0])
+
+    await waitFor (() => {
+      expect (dialogue.confirm).toHaveBeenCalled ()
+    })
+    await waitFor (() => {
+      expect (api.apiDelete).toHaveBeenCalledWith ('/theatres/7/comments/2')
+    })
+    expect (await screen.findAllByText ('削除されました．')).toHaveLength (2)
+  })
+})
diff --git a/frontend/src/pages/theatres/TheatreDetailPage.tsx b/frontend/src/pages/theatres/TheatreDetailPage.tsx
index 0b626bd..2a206b6 100644
--- a/frontend/src/pages/theatres/TheatreDetailPage.tsx
+++ b/frontend/src/pages/theatres/TheatreDetailPage.tsx
@@ -1,58 +1,270 @@
-import { useEffect, useRef, useState } from 'react'
+import { motion } from 'framer-motion'
+import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
 import ErrorScreen from '@/components/ErrorScreen'
+import PostEditForm from '@/components/PostEditForm'
 import PostEmbed from '@/components/PostEmbed'
 import PrefetchLink from '@/components/PrefetchLink'
-import TagDetailSidebar from '@/components/TagDetailSidebar'
-import MainArea from '@/components/layout/MainArea'
-import SidebarComponent from '@/components/layout/SidebarComponent'
+import TagLink from '@/components/TagLink'
+import FieldError from '@/components/common/FieldError'
+import { useDialogue } from '@/components/dialogues/DialogueProvider'
+import { Button } from '@/components/ui/button'
 import { SITE_TITLE } from '@/config'
-import { apiGet, apiPatch, apiPost, apiPut, isApiError } from '@/lib/api'
+import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
+import { apiDelete, apiGet, apiPatch, apiPost, apiPut, isApiError } from '@/lib/api'
 import { fetchPost } from '@/lib/posts'
-import { dateString } from '@/lib/utils'
+import { canEditContent } from '@/lib/users'
+import { cn, dateString, inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
-import type { FC } from 'react'
+import type { FC, FormEvent, ReactNode } from 'react'
 
-import type { NiconicoMetadata,
-	      NiconicoViewerHandle,
+import type { NiconicoViewerHandle,
 	      Post,
+	      Category,
+	      Tag,
 	      Theatre,
-	      TheatreComment } from '@/types'
+	      TheatreComment,
+	      TheatreInfo,
+	      TheatrePostSelectionWeights,
+	      TheatreProgramme,
+	      User } from '@/types'
 
-type TheatreInfo = {
-    hostFlg:        boolean
-    postId:         number | null
-    postStartedAt:  string | null
-    watchingUsers:  { id: number; name: string }[] }
+type TheatreCommentField = 'content'
+type TheatreLayoutMode = 'threeColumns' | 'tagsBottom' | 'commentsBottom'
+type TagFlow = 'vertical' | 'horizontal'
 
-const INITIAL_THEATRE_INFO =
+const INITIAL_THEATRE_INFO: TheatreInfo =
     { hostFlg: false,
       postId: null,
       postStartedAt: null,
-      watchingUsers: [] as { id: number; name: string }[] } as const
+      postElapsedMs: null,
+      watchingUsers: [],
+      skipVote: { votesCount: 0,
+		  requiredCount: 1,
+		  watchingUsersCount: 0,
+		  voted: false } }
+
+const INITIAL_WEIGHTS: TheatrePostSelectionWeights =
+    { tagPenalties: [], lightestPosts: [], heaviestPosts: [] }
+
+const LAYOUT_STORAGE_KEY = 'theatre-layout-mode'
+const TAG_FLOW_STORAGE_KEY = 'theatre-tag-flow'
+
+const LAYOUT_LABELS: Record<TheatreLayoutMode, string> = {
+    threeColumns:   '3 列',
+    tagsBottom:     '2 列 A 型',
+    commentsBottom: '2 列 B 型' }
+
+const TAG_FLOW_LABELS: Record<TagFlow, string> = {
+    vertical:   '縦並び',
+    horizontal: '横並び' }
 
 
-const TheatreDetailPage: FC = () => {
+const userName = (user: Pick<User, 'id' | 'name'> | null | undefined): string =>
+    user ? (user.name || `名もなきニジラー（#${ user.id }）`) : '運営'
+
+
+const commentBox = (
+    comment: TheatreComment,
+    programme: TheatreProgramme | null = null,
+): ReactNode[] =>
+    [(
+	<div key={`${ comment.no }-content`} className="w-full">
+	  {comment.deleted
+	   ? <span className="text-sm font-bold">削除されました．</span>
+	   : comment.content}
+	</div>),
+     (
+	<div key={`${ comment.no }-user`} className="w-full text-sm text-right">
+	  by {userName (comment.user)}
+	</div>),
+     (
+	<div key={`${ comment.no }-createdAt`} className="w-full text-sm text-right">
+	  {dateString (comment.createdAt)}
+	</div>),
+     (
+	<div
+	    key={`${ comment.no }-post`}
+	    className="mt-1 w-full text-xs text-zinc-500 dark:text-zinc-400">
+	  {programme && (
+	      <>
+		<PrefetchLink to={`/posts/${ programme.post.id }`} className="font-bold hover:underline">
+		  {programme.post.title || programme.post.url}
+		</PrefetchLink>
+		&thinsp;へのコメント
+	      </>)}
+	</div>)]
+
+
+const compareTagName = (a: Tag, b: Tag): number =>
+    a.name === b.name ? 0 : (a.name < b.name ? -1 : 1)
+
+
+const tagsByCategory = (tags: Tag[]): Partial<Record<Category, Tag[]>> => {
+  const grouped: Partial<Record<Category, Tag[]>> = { }
+
+  for (const tag of tags)
+    {
+      grouped[tag.category] ??= []
+      grouped[tag.category]!.push (tag)
+    }
+
+  for (const cat of CATEGORIES)
+    grouped[cat]?.sort (compareTagName)
+
+  return grouped
+}
+
+
+const TagList: FC<{ tags: Tag[]; compact?: boolean; flow?: TagFlow }> = (
+    { tags, compact, flow = 'vertical' },
+) => {
+  const grouped = tagsByCategory (tags)
+
+  if (flow === 'horizontal')
+    {
+      return (
+	  <ul className={cn ('flex flex-wrap gap-x-3 gap-y-1', compact && 'text-sm')}>
+	    {CATEGORIES.flatMap (cat => grouped[cat] ?? []).map (tag => (
+		<li key={tag.id} className="text-left leading-tight">
+		  <TagLink tag={tag} withCount={false}/>
+		</li>))}
+	  </ul>)
+    }
+
+  return (
+      <div className="space-y-3">
+	{CATEGORIES.map (cat => {
+	  const rows = grouped[cat] ?? []
+	  if (rows.length === 0)
+	    return null
+
+	  return (
+	      <div key={cat}>
+		<div className="mb-1 shrink-0 text-xs font-bold text-zinc-500 dark:text-zinc-400">
+		  {CATEGORY_NAMES[cat]}
+		</div>
+		<ul className={cn ('space-y-1', compact && 'text-sm')}>
+		  {rows.map (tag => (
+		      <li key={tag.id} className="text-left leading-tight">
+			<TagLink tag={tag} withCount={false}/>
+		      </li>))}
+		</ul>
+	      </div>)
+	})}
+      </div>)
+}
+
+
+type Props = { user: User | null }
+
+
+const TheatreDetailPage: FC<Props> = ({ user }: Props) => {
   const { id } = useParams ()
+  const dialogue = useDialogue ()
 
   const commentsRef = useRef<HTMLDivElement> (null)
   const embedRef = useRef<NiconicoViewerHandle> (null)
   const loadingRef = useRef (false)
   const theatreInfoRef = useRef<TheatreInfo> (INITIAL_THEATRE_INFO)
+  const theatreInfoReceivedAtRef = useRef (performance.now ())
   const videoLengthRef = useRef (0)
   const lastCommentNoRef = useRef (0)
 
   const [comments, setComments] = useState<TheatreComment[]> ([])
   const [content, setContent] = useState ('')
+  const [editingPost, setEditingPost] = useState<Post | null> (null)
   const [loading, setLoading] = useState (false)
+  const [programmes, setProgrammes] = useState<TheatreProgramme[]> ([])
   const [sending, setSending] = useState (false)
   const [status, setStatus] = useState (200)
   const [theatre, setTheatre] = useState<Theatre | null> (null)
   const [theatreInfo, setTheatreInfo] = useState<TheatreInfo> (INITIAL_THEATRE_INFO)
   const [post, setPost] = useState<Post | null> (null)
   const [videoLength, setVideoLength] = useState (0)
+  const [weights, setWeights] = useState<TheatrePostSelectionWeights> (INITIAL_WEIGHTS)
+  const [layoutMode, setLayoutMode] = useState<TheatreLayoutMode> (() => {
+    const stored = localStorage.getItem (LAYOUT_STORAGE_KEY)
+    return (
+	((['threeColumns', 'tagsBottom', 'commentsBottom'] as TheatreLayoutMode[])
+	 .includes (stored as TheatreLayoutMode))
+	? (stored as TheatreLayoutMode)
+	: 'threeColumns')
+  })
+  const [tagFlow, setTagFlow] = useState<TagFlow> (() => {
+    const stored = localStorage.getItem (TAG_FLOW_STORAGE_KEY)
+    return (
+	(['vertical', 'horizontal'] as TagFlow[]).includes (stored as TagFlow)
+	? (stored as TagFlow)
+	: 'vertical')
+  })
+  const { fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<TheatreCommentField> ()
+
+  const changeLayoutMode = (mode: TheatreLayoutMode) => {
+    setLayoutMode (mode)
+    localStorage.setItem (LAYOUT_STORAGE_KEY, mode)
+  }
+
+  const changeTagFlow = (flow: TagFlow) => {
+    setTagFlow (flow)
+    localStorage.setItem (TAG_FLOW_STORAGE_KEY, flow)
+  }
+
+  const applyTheatreInfo = useCallback ((nextInfo: TheatreInfo) => {
+    theatreInfoReceivedAtRef.current = performance.now ()
+    setTheatreInfo (nextInfo)
+  }, [])
+
+  const currentPostElapsedMs = useCallback (
+      (info: TheatreInfo = theatreInfoRef.current): number => {
+	if (info.postElapsedMs == null)
+	  return 0
+
+	return Math.max (
+	    info.postElapsedMs + performance.now () - theatreInfoReceivedAtRef.current,
+	    0)
+      }, [])
+
+  const refreshProgrammes = useCallback (async () => {
+    if (!(id))
+      return
+
+    setProgrammes (await apiGet<TheatreProgramme[]> (
+	`/theatres/${ id }/programmes`, { params: { limit: '100' } }))
+  }, [id])
+
+  const refreshWeights = useCallback (async () => {
+    if (!(id))
+      return
+
+    setWeights (await apiGet<TheatrePostSelectionWeights> (
+	`/theatres/${ id }/post_selection_weights`))
+  }, [id])
+
+  const advancePost = useCallback (async () => {
+    if (!(id))
+      return
+
+    setLoading (true)
+    try
+    {
+      await apiPatch<void> (`/theatres/${ id }/next_post`)
+      await refreshProgrammes ()
+      await refreshWeights ()
+    }
+    catch (error)
+    {
+      console.error (error)
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }, [id, refreshProgrammes, refreshWeights])
 
   useEffect (() => {
     loadingRef.current = loading
@@ -77,10 +289,14 @@ const TheatreDetailPage: FC = () => {
     let cancelled = false
 
     setComments ([])
-    setTheatre (null)
+    setEditingPost (null)
     setPost (null)
+    setProgrammes ([])
+    setTheatre (null)
+    theatreInfoReceivedAtRef.current = performance.now ()
     setTheatreInfo (INITIAL_THEATRE_INFO)
     setVideoLength (0)
+    setWeights (INITIAL_WEIGHTS)
     lastCommentNoRef.current = 0
 
     void (async () => {
@@ -96,10 +312,13 @@ const TheatreDetailPage: FC = () => {
       }
     }) ()
 
+    void refreshProgrammes ()
+    void refreshWeights ()
+
     return () => {
       cancelled = true
     }
-  }, [id])
+  }, [id, refreshProgrammes, refreshWeights])
 
   useEffect (() => {
     if (!(id))
@@ -118,11 +337,11 @@ const TheatreDetailPage: FC = () => {
       {
 	const newComments = await apiGet<TheatreComment[]> (
 	    `/theatres/${ id }/comments`,
-	    { params: { no_gt: lastCommentNoRef.current } })
+	    { params: { no_gt: lastCommentNoRef.current, limit: '20' } })
 
 	if (!(cancelled) && newComments.length > 0)
 	  {
-	    lastCommentNoRef.current = newComments[newComments.length - 1].no
+	    lastCommentNoRef.current = newComments[0].no
 	    setComments (prev => [...newComments, ...prev])
 	  }
 
@@ -130,20 +349,26 @@ const TheatreDetailPage: FC = () => {
 	const ended =
 	    currentInfo.hostFlg
 	    && currentInfo.postStartedAt
-	    && ((Date.now () - (new Date (currentInfo.postStartedAt)).getTime ())
-	        > videoLengthRef.current + 3_000)
+	    && videoLengthRef.current > 0
+	    && currentPostElapsedMs (currentInfo) > videoLengthRef.current + 3_000
 
 	if (ended)
 	  {
 	    if (!(cancelled))
-	      setTheatreInfo (prev => ({ ...prev, postId: null, postStartedAt: null }))
+	      {
+		setTheatreInfo (prev => ({
+		    ...prev,
+		    postId: null,
+		    postStartedAt: null,
+		    postElapsedMs: null }))
+	      }
 
 	    return
 	  }
 
 	const nextInfo = await apiPut<TheatreInfo> (`/theatres/${ id }/watching`)
 	if (!(cancelled))
-	  setTheatreInfo (nextInfo)
+	  applyTheatreInfo (nextInfo)
       }
       catch (error)
       {
@@ -162,7 +387,7 @@ const TheatreDetailPage: FC = () => {
       cancelled = true
       clearInterval (interval)
     }
-  }, [id])
+  }, [applyTheatreInfo, currentPostElapsedMs, id])
 
   useEffect (() => {
     if (!(id) || !(theatreInfo.hostFlg) || loadingRef.current || theatreInfo.postId != null)
@@ -171,33 +396,24 @@ const TheatreDetailPage: FC = () => {
     let cancelled = false
 
     void (async () => {
-      setLoading (true)
-
-      try
-      {
-	await apiPatch<void> (`/theatres/${ id }/next_post`)
-      }
-      catch (error)
-      {
-	console.error (error)
-      }
-      finally
-      {
-	if (!(cancelled))
-	  setLoading (false)
-      }
+      await advancePost ()
+      if (cancelled)
+	setLoading (false)
     }) ()
 
     return () => {
       cancelled = true
     }
-  }, [id, theatreInfo.hostFlg, theatreInfo.postId])
+  }, [advancePost, id, theatreInfo.hostFlg, theatreInfo.postId])
 
   useEffect (() => {
     setVideoLength (0)
 
     if (theatreInfo.postId == null)
-      return
+      {
+	setPost (null)
+	return
+      }
 
     let cancelled = false
 
@@ -219,130 +435,526 @@ const TheatreDetailPage: FC = () => {
     }
   }, [theatreInfo.postId])
 
-  const syncPlayback = (meta: NiconicoMetadata) => {
+  useEffect (() => {
+    void refreshProgrammes ()
+  }, [refreshProgrammes, theatreInfo.postId])
+
+  const syncPlaybackTime = (currentTimeMs: number): number | void => {
     if (!(theatreInfo.postStartedAt))
       return
 
-    const targetTime = Math.min (
-	Math.max (0, Date.now () - (new Date (theatreInfo.postStartedAt)).getTime ()),
-	videoLength)
+    const currentVideoLength = videoLengthRef.current
+    if (currentVideoLength <= 0)
+      return
 
-    const drift = Math.abs (meta.currentTime - targetTime)
+    const targetTime = Math.min (
+	currentPostElapsedMs (theatreInfo),
+	currentVideoLength)
+
+    const drift = Math.abs (currentTimeMs - targetTime)
 
     if (drift > 5_000)
       embedRef.current?.seek (targetTime)
+
+    return targetTime
   }
 
+  const handlePlaybackError = async () => {
+    if (!(theatreInfoRef.current.hostFlg) || loadingRef.current)
+      return
+
+    loadingRef.current = true
+    try
+    {
+      await advancePost ()
+    }
+    finally
+    {
+      loadingRef.current = false
+    }
+  }
+
+  const handleVideoReady = (durationMs: number) => {
+    const playableDurationMs =
+	Number.isFinite (durationMs)
+	? durationMs
+	: 0
+
+    setVideoLength (playableDurationMs)
+    videoLengthRef.current = playableDurationMs
+
+    if (playableDurationMs <= 0)
+      {
+	void handlePlaybackError ()
+	return
+      }
+
+    embedRef.current?.play ()
+  }
+
+  const handleSkipVote = async () => {
+    if (!(id) || !(post))
+      return
+
+    setLoading (true)
+    try
+    {
+      const nextInfo =
+	  theatreInfo.skipVote.voted
+	  ? await apiDelete<TheatreInfo> (
+	      `/theatres/${ id }/skip_vote`, { params: { post_id: post.id } })
+	  : await apiPut<TheatreInfo> (
+	      `/theatres/${ id }/skip_vote`, { post_id: post.id })
+
+      applyTheatreInfo (nextInfo)
+
+      if (nextInfo.skipped)
+	{
+	  setPost (null)
+	  await refreshProgrammes ()
+	  await refreshWeights ()
+	}
+    }
+    catch (error)
+    {
+      if (isApiError (error) && error.response?.status === 409)
+	applyTheatreInfo (await apiPut<TheatreInfo> (`/theatres/${ id }/watching`))
+
+      console.error (error)
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }
+
+  const handleDelete = async (commentNo: number) => {
+    try
+    {
+      await apiDelete (`/theatres/${ id }/comments/${ commentNo }`)
+      setComments (prev => {
+	const rtn = [...prev]
+	const idx = rtn.findIndex (x => x.no === commentNo)
+	if (idx >= 0)
+	  rtn[idx] = { ...rtn[idx], deleted: true, content: null }
+	return rtn
+      })
+    }
+    catch
+    {
+      ;
+    }
+  }
+
+  const handleCommentSubmit = async (e: FormEvent) => {
+    e.preventDefault ()
+
+    if (!(content))
+      return
+
+    try
+    {
+      setSending (true)
+      clearValidationErrors ()
+      await apiPost (`/theatres/${ id }/comments`, { content })
+      setContent ('')
+      commentsRef.current?.scrollTo ({ top: 0, behavior: 'smooth' })
+    }
+    catch (error)
+    {
+      applyValidationError (error)
+    }
+    finally
+    {
+      setSending (false)
+    }
+  }
+
+  const skipVote = theatreInfo.skipVote
+  const theatreTitle = theatre?.name ? `上映会場『${ theatre.name }』` : '上映会場'
+  const postTags = post?.tags ?? []
+  const programmesAsc = useMemo (
+      () => [...programmes].sort (
+	  (a, b) => Date.parse (a.createdAt) - Date.parse (b.createdAt)),
+      [programmes])
+
+  const programmeForComment = useCallback ((comment: TheatreComment): TheatreProgramme | null => {
+    const commentedAt = Date.parse (comment.createdAt)
+    let found: TheatreProgramme | null = null
+
+    for (const programme of programmesAsc)
+      {
+	const startedAt = Date.parse (programme.createdAt)
+	if (startedAt > commentedAt)
+	  break
+
+	found = programme
+      }
+
+    return found
+  }, [programmesAsc])
+
   if (status >= 400)
     return <ErrorScreen status={status}/>
 
-  return (
-      <div className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
-	<Helmet>
-	  {theatre && (
-	      <title>
-		{'上映会場'
-		 + (theatre.name ? `『${ theatre.name }』` : ` #${ theatre.id }`)
-		 + ` | ${ SITE_TITLE }`}
-	      </title>)}
-	</Helmet>
+  const tagPanel = (
+      <section className="rounded border-zinc-300 p-4 dark:border-zinc-800">
+	<div className="mb-3 flex items-center justify-between gap-3">
+	  <h2 className="font-bold">タグ</h2>
+	  {layoutMode === 'tagsBottom' && (
+	      <div className="hidden gap-2 md:flex">
+		{(Object.keys (TAG_FLOW_LABELS) as TagFlow[]).map (flow => (
+		    <Button
+			key={flow}
+			type="button"
+			size="sm"
+			variant={tagFlow === flow ? 'default' : 'outline'}
+			onClick={() => changeTagFlow (flow)}>
+		      {TAG_FLOW_LABELS[flow]}
+		    </Button>))}
+	      </div>)}
+	</div>
+	{postTags.length === 0
+	 ? <div className="text-sm text-zinc-500">タグはありません。</div>
+	 : <TagList tags={postTags} flow={layoutMode === 'tagsBottom' ? tagFlow : 'vertical'}/>}
+      </section>)
 
-	<div className="hidden md:block">
-	  {post && <TagDetailSidebar post={post}/>}
+  const commentsPanel = (
+      <section className="rounded border-zinc-300 p-4 dark:border-zinc-800">
+	<h2 className="mb-3 font-bold">コメント</h2>
+	<form onSubmit={handleCommentSubmit}>
+	  <input
+	      className={inputClass ((fieldErrors.content ?? []).length > 0)}
+	      type="text"
+	      placeholder="ここにコメントを入力"
+	      value={content}
+	      onChange={e => setContent (e.target.value)}
+	      disabled={sending}/>
+	  <FieldError messages={fieldErrors.content}/>
+	</form>
+
+	<div
+	    ref={commentsRef}
+	    className="mt-3 max-h-[48vh] overflow-y-auto rounded border border-zinc-200
+		       dark:border-zinc-800">
+	  {comments.map (comment => {
+	    const commentProgramme = programmeForComment (comment)
+	    return (
+		<div
+		    key={comment.no}
+		    className="group relative border-t border-zinc-100 p-2 first:border-t-0
+			       hover:bg-zinc-50 dark:border-zinc-800 dark:hover:bg-zinc-800">
+		  {(user && comment.user?.id === user.id && !(comment.deleted)) && (
+		      <button
+			  type="button"
+			  className="absolute left-1 top-1 hidden rounded px-1 text-red-600
+				     hover:bg-red-100 group-hover:inline-block dark:text-red-300
+				     dark:hover:bg-red-950"
+			  aria-label="コメントを削除"
+			  onClick={async e => {
+			    e.stopPropagation ()
+
+			    if (!(await dialogue.confirm ({
+				title: 'このコメントを削除しますか?',
+				description: (
+				    <div className="my-3 w-120 rounded border border-black p-2
+						    dark:border-white">
+				      {commentBox (comment, commentProgramme)}
+				    </div>),
+				confirmText: '削除',
+				variant: 'danger' })))
+			      return
+
+			    await handleDelete (comment.no)
+			  }}>
+			&times;
+		      </button>)}
+		  {commentBox (comment, commentProgramme)}
+		</div>)
+	  })}
+	</div>
+      </section>)
+
+  const participantsPanel = (
+      <section className="rounded border-zinc-300 p-4 dark:border-zinc-800">
+	<h2 className="mb-3 font-bold">参加者</h2>
+	<div className="space-y-1">
+	  {theatreInfo.watchingUsers.map (watchingUser => (
+	      <div key={watchingUser.id} className="flex justify-between gap-2 text-sm">
+		<span>{userName (watchingUser)}</span>
+		{watchingUser.id === user?.id && <span className="text-zinc-500">お前</span>}
+	      </div>))}
+	</div>
+      </section>)
+
+  const historyPanel = (
+      <section className="rounded border-zinc-300 p-4 dark:border-zinc-800">
+	<h2 className="mb-3 font-bold">再生履歴</h2>
+	<div className="rounded border border-zinc-300 dark:border-zinc-800 max-h-72
+			overflow-y-auto">
+	  {programmes.length === 0
+	   ? <div className="text-sm text-zinc-500">まだ履歴はありません。</div>
+	   : (
+	      programmes.map (programme => (
+		  <div
+		      key={`${ programme.theatreId }-${ programme.position }`}
+		      className="border-zinc-100 p-2 text-sm first:border-t-0
+				 dark:border-zinc-800">
+		    <PrefetchLink
+			to={`/posts/${ programme.post.id }`}
+			className="font-bold hover:underline">
+		      {programme.post.title || programme.post.url}
+		    </PrefetchLink>
+		    <div className="text-xs text-zinc-500">
+		      {dateString (programme.createdAt)}
+		    </div>
+		  </div>)))}
+	</div>
+      </section>)
+
+  const weightsPanel = (
+      <section className="rounded border-zinc-300 p-4 dark:border-zinc-800">
+	<div className="mb-3 flex items-center justify-between gap-3">
+	  <h2 className="font-bold">抽選重み</h2>
+	  <Button type="button" variant="outline" size="sm" onClick={() => void refreshWeights ()}>
+	    更新
+	  </Button>
 	</div>
 
-	<MainArea>
-	  {post ? (
-	      <>
-		<PostEmbed
-		    key={post.id}
-		    ref={embedRef}
-		    post={post}
-		    onLoadComplete={info => {
-		      embedRef.current?.play ()
-		      setVideoLength (info.lengthInSeconds * 1_000)
-		    }}
-		    onMetadataChange={syncPlayback}/>
-		<div className="m-2">
-		  <>再生中：</>
-		  <PrefetchLink to={`/posts/${ post.id }`} className="font-bold">
-		    {post.title || post.url}
-		  </PrefetchLink>
-		</div>
-	      </>) : 'Loading...'}
-	</MainArea>
-
-	<SidebarComponent>
-	  <form
-	      className="w-auto h-auto border border-black dark:border-white rounded mx-2"
-	      onSubmit={async e => {
-		e.preventDefault ()
-
-		if (!(content))
-		  return
-
-		try
-		{
-		  setSending (true)
-		  await apiPost (`/theatres/${ id }/comments`, { content })
-		  setContent ('')
-		  commentsRef.current?.scrollTo ({ top: 0, behavior: 'smooth' })
-		}
-		finally
-		{
-		  setSending (false)
-		}
-	      }}>
-	    <input
-		className="w-full p-2 border rounded"
-		type="text"
-		placeholder="ここにコメントを入力"
-		value={content}
-		onChange={e => setContent (e.target.value)}
-		disabled={sending}/>
-
-	    <div
-		ref={commentsRef}
-		className="overflow-x-hidden overflow-y-scroll text-wrap w-full
-			   h-[32vh] md:h-[64vh] border rounded">
-	      {comments.map (comment => (
-		  <div key={comment.no} className="p-2">
-		    <div className="w-full">
-		      {comment.content}
-		    </div>
-		    <div className="w-full text-sm text-right">
-		      by {comment.user
-			  ? (comment.user.name || `名もなきニジラー（#${ comment.user.id }）`)
-			  : '運営'}
-		    </div>
-		    <div className="w-full text-sm text-right">
-		      {dateString (comment.createdAt)}
-		    </div>
-		  </div>))}
-	    </div>
-	  </form>
-
-	  <div className="w-auto h-auto border border-black dark:border-white rounded mx-2 mt-4">
-	    <div className="p-2">
-		現在の同接数：{theatreInfo.watchingUsers.length}
-	    </div>
-
-	    <div className="overflow-x-hidden overflow-y-scroll text-wrap w-full h-32
-			    border rounded">
-	      <ul className="list-inside list-disc">
-		{theatreInfo.watchingUsers.map (user => (
-		    <li key={user.id} className="px-4 py-1 text-sm">
-		      {user.name || `名もなきニジラー（#${ user.id }）`}
-		    </li>))}
-	      </ul>
+	<div className="mx-4 grid gap-16 xl:grid-cols-3">
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">出にくいタグ</h3>
+	    <div className="space-y-1 text-sm">
+	      {weights.tagPenalties.length === 0
+	       ? <div className="text-zinc-500">まだ減点はありません。</div>
+	       : (
+		  weights.tagPenalties.slice (0, 12).map (row => (
+		      <div
+			  key={row.tag.id}
+			  className="grid grid-cols-[minmax(0,1fr)_auto] items-baseline gap-2
+				     text-left">
+			<div className="min-w-0 text-left">
+			  <TagLink tag={row.tag} withCount={false}/>
+			</div>
+			<span className="font-mono">{row.penalty}</span>
+		      </div>)))}
 	    </div>
 	  </div>
-	</SidebarComponent>
 
-	<div className="md:hidden">
-	  {post && <TagDetailSidebar post={post} sp/>}
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">出にくい候補</h3>
+	    <WeightRows rows={weights.lightestPosts}/>
+	  </div>
+
+	  <div>
+	    <h3 className="mb-2 text-sm font-bold">出やすい候補</h3>
+	    <WeightRows rows={weights.heaviestPosts}/>
+	  </div>
 	</div>
-      </div>)
+      </section>)
+
+  return (
+      <motion.div
+	  layout="position"
+	  transition={{ layout: { duration: .2, ease: 'easeOut' } }}
+	  className="min-h-0 flex-1 overflow-y-auto bg-zinc-50 text-zinc-950
+		     md:overflow-hidden dark:bg-zinc-950 dark:text-zinc-50">
+	<Helmet>
+	  <meta name="robots" content="noindex"/>
+	  {theatre && <title>{`${ theatreTitle } | ${ SITE_TITLE }`}</title>}
+	</Helmet>
+
+	<div className={cn (
+	    'grid min-h-full gap-4 overflow-visible md:h-full md:overflow-hidden',
+	    (layoutMode === 'threeColumns'
+	     && ['md:grid-cols-[16rem_minmax(0,1fr)_22rem]',
+		 'xl:grid-cols-[18rem_minmax(0,1fr)_24rem]']),
+	    (layoutMode === 'tagsBottom'
+	     && 'md:grid-cols-[minmax(0,1fr)_22rem] xl:grid-cols-[minmax(0,1fr)_24rem]'),
+	    (layoutMode === 'commentsBottom'
+	     && 'md:grid-cols-[16rem_minmax(0,1fr)] xl:grid-cols-[18rem_minmax(0,1fr)]'))}>
+	  {layoutMode !== 'tagsBottom' && (
+	      <motion.aside
+		  layout="position"
+		  className="hidden min-w-0 space-y-4 md:order-none md:block md:overflow-y-auto
+			     md:[direction:rtl]">
+		<div className="md:[direction:ltr]">
+		  {tagPanel}
+		</div>
+	      </motion.aside>)}
+
+	  <motion.main
+	      layout="position"
+	      className={cn ('order-1 min-w-0 space-y-4 md:order-none md:overflow-y-auto',
+			     layoutMode === 'tagsBottom' && 'md:[direction:rtl]')}>
+	    <div className={cn ('space-y-4', layoutMode === 'tagsBottom' && 'md:[direction:ltr]')}>
+	      <section className="overflow-hidden rounded border-zinc-300
+				  dark:border-zinc-800">
+		<div className="flex flex-wrap items-center justify-between gap-3
+				border-zinc-200 px-4 py-3 dark:border-zinc-800">
+		  <div>
+		    <h1 className="text-lg font-bold">{theatreTitle}</h1>
+		    <p className="text-sm text-zinc-500 dark:text-zinc-400">
+		      同接 {theatreInfo.watchingUsers.length} 人
+		    </p>
+		  </div>
+
+		  <div className="flex flex-wrap gap-2">
+		    <div className="hidden flex-wrap gap-2 md:flex">
+		      {(Object.keys (LAYOUT_LABELS) as TheatreLayoutMode[]).map (mode => (
+			  <Button
+			      key={mode}
+			      type="button"
+			      size="sm"
+			      variant={layoutMode === mode ? 'default' : 'outline'}
+			      onClick={() => changeLayoutMode (mode)}>
+			    {LAYOUT_LABELS[mode]}
+			  </Button>))}
+		    </div>
+
+		    <Button
+			type="button"
+			size="sm"
+			variant={skipVote.voted ? 'secondary' : 'destructive'}
+			disabled={loading || !(post)}
+			onClick={handleSkipVote}>
+		      {skipVote.voted ? 'スキップ取消' : 'スキップ'}
+		      {` ${ skipVote.votesCount } / ${ skipVote.requiredCount }`}
+		    </Button>
+
+		  </div>
+		</div>
+
+		<div className="flex justify-center bg-black mx-4">
+		  {post ? (
+		      <PostEmbed
+			  key={post.id}
+			  ref={embedRef}
+			  post={post}
+			  onVideoReady={handleVideoReady}
+			  onPlaybackChange={syncPlaybackTime}
+			  onError={handlePlaybackError}/>) : (
+		      <div className="grid min-h-72 place-items-center text-zinc-400">
+			{loading ? '次の投稿を選んでゐます……' : '上映待機中'}
+		      </div>)}
+		</div>
+
+		<div className="flex flex-wrap items-center justify-between gap-3 px-4 py-3">
+		  <div className="min-w-0">
+		    <div className="text-xs font-bold text-zinc-500 dark:text-zinc-400">
+		      再生中
+		    </div>
+		    {post ? (
+			<PrefetchLink
+			    to={`/posts/${ post.id }`}
+			    className="font-bold hover:underline">
+			  {post.title || post.url}
+			</PrefetchLink>) : (
+			<span className="text-zinc-500">未選択</span>)}
+		  </div>
+
+		  {(post && canEditContent (user)) && (
+		      <Button
+			  type="button"
+			  size="sm"
+			  variant="outline"
+			  disabled={!(post)}
+			  onClick={() => post && setEditingPost (ep => ep ? null : post)}>
+			{editingPost ? '閉じる' : '編輯'}
+		      </Button>)}
+		</div>
+	      </section>
+
+	      {editingPost && (
+		  <section className="rounded border border-amber-300 bg-amber-50 mx-4 p-4
+				      dark:border-amber-800 dark:bg-amber-950/30">
+		    <div className="mb-3">
+		      <h2 className="font-bold">編輯中の投稿</h2>
+		      <p className="text-sm text-amber-900 dark:text-amber-100">
+			<PrefetchLink
+			    to={`/posts/${ editingPost.id }`}
+			    className="mx-1 font-bold underline">
+			  {editingPost.title || editingPost.url}
+			</PrefetchLink>
+			を編輯中……
+		      </p>
+		    </div>
+
+		    <PostEditForm
+			post={editingPost}
+			onSave={newPost => {
+			  setEditingPost (newPost)
+			  if (post?.id === newPost.id)
+			    setPost (newPost)
+			  void refreshWeights ()
+			}}/>
+		  </section>)}
+
+	      <div className="md:hidden">
+		{commentsPanel}
+	      </div>
+
+	      {layoutMode === 'commentsBottom' && (
+		  <div className="hidden md:block">
+		    {commentsPanel}
+		  </div>)}
+
+	      <div className="md:hidden">
+		{tagPanel}
+	      </div>
+
+	      {layoutMode === 'tagsBottom' && (
+		  <div className="hidden md:block">
+		    {tagPanel}
+		  </div>)}
+
+	      {historyPanel}
+	      {weightsPanel}
+
+	      <div className="md:hidden">
+		{participantsPanel}
+	      </div>
+
+	      {layoutMode === 'commentsBottom' && (
+		  <div className="hidden md:block">
+		    {participantsPanel}
+		  </div>)}
+	    </div>
+	  </motion.main>
+
+	  {layoutMode !== 'commentsBottom' && (
+	      <motion.aside
+		  layout="position"
+		  className="hidden min-w-0 space-y-4 md:order-none md:block md:overflow-y-auto">
+		{commentsPanel}
+		{participantsPanel}
+	      </motion.aside>)}
+	</div>
+      </motion.div>)
 }
 
+
+const WeightRows: FC<{ rows: TheatrePostSelectionWeights['lightestPosts'] }> = ({ rows }) => (
+    <div className="space-y-2 text-sm">
+      {rows.length === 0
+       ? <div className="text-zinc-500">候補はありません。</div>
+       : (
+	  rows.slice (0, 8).map (row => (
+	      <div
+		  key={row.post.id}
+		  className="border-zinc-100 pt-2 first:border-t-0 first:pt-0
+			     dark:border-zinc-800">
+		<PrefetchLink
+		    to={`/posts/${ row.post.id }`}
+		    className="line-clamp-1 font-bold hover:underline">
+		  {row.post.title || row.post.url}
+		</PrefetchLink>
+		<div className="flex justify-between gap-2 text-xs text-zinc-500">
+		  <span>penalty {row.penalty}</span>
+		  <span>weight {row.weight.toFixed (3)}</span>
+		</div>
+	      </div>)))}
+    </div>)
+
+
 export default TheatreDetailPage
diff --git a/frontend/src/pages/users/SettingPage.test.tsx b/frontend/src/pages/users/SettingPage.test.tsx
index 3e1a232..0595642 100644
--- a/frontend/src/pages/users/SettingPage.test.tsx
+++ b/frontend/src/pages/users/SettingPage.test.tsx
@@ -1,12 +1,13 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import SettingPage from '@/pages/users/SettingPage'
 import { buildUser } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
 const api = vi.hoisted (() => ({
-  apiPut: vi.fn (),
+  apiPut:     vi.fn (),
+  isApiError: vi.fn (),
 }))
 
 const toastApi = vi.hoisted (() => ({
@@ -23,6 +24,11 @@ vi.mock ('@/components/users/InheritDialogue', () => ({
 }))
 
 describe ('SettingPage', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+  })
+
   it ('shows loading when user is absent', () => {
     renderWithProviders (<SettingPage user={null} setUser={vi.fn ()}/>)
 
@@ -51,4 +57,28 @@ describe ('SettingPage', () => {
     expect (setUser).toHaveBeenCalled ()
     expect (toastApi.toast).toHaveBeenCalledWith ({ title: '設定を更新しました．' })
   })
+
+  it ('shows validation errors returned for the name field', async () => {
+    const user = buildUser ({ id: 11, name: 'old' })
+    api.isApiError.mockReturnValue (true)
+    api.apiPut.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type:        'validation_error',
+          message:     '入力内容を確認してください．',
+          errors:      { name: ['名前は必須です．'] },
+          base_errors: [],
+        },
+      },
+    })
+
+    renderWithProviders (<SettingPage user={user} setUser={vi.fn ()}/>)
+
+    fireEvent.change (screen.getByRole ('textbox'), { target: { value: '' } })
+    fireEvent.click (screen.getByRole ('button', { name: '更新' }))
+
+    expect (await screen.findByText ('名前は必須です．')).toBeInTheDocument ()
+    expect (screen.getByRole ('textbox')).toHaveAttribute ('aria-invalid', 'true')
+  })
 })
diff --git a/frontend/src/pages/users/SettingPage.tsx b/frontend/src/pages/users/SettingPage.tsx
index 6632e5f..a271da9 100644
--- a/frontend/src/pages/users/SettingPage.tsx
+++ b/frontend/src/pages/users/SettingPage.tsx
@@ -3,7 +3,9 @@ import type { FC } from 'react'
 import { useEffect, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 
+import FieldError from '@/components/common/FieldError'
 import Form from '@/components/common/Form'
+import FormField from '@/components/common/FormField'
 import Label from '@/components/common/Label'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
@@ -13,22 +15,30 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiPut } from '@/lib/api'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { User } from '@/types'
 
 type Props = { user:    User | null
 	       setUser: React.Dispatch<React.SetStateAction<User | null>> }
 
+type UserFormField = 'name'
+
 
 const SettingPage: FC<Props> = ({ user, setUser }) => {
   const [name, setName] = useState ('')
   const [userCodeVsbl, setUserCodeVsbl] = useState (false)
   const [inheritVsbl, setInheritVsbl] = useState (false)
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<UserFormField> ()
 
   const handleSubmit = async () => {
     if (!(user))
       return
 
+    clearValidationErrors ()
+
     const formData = new FormData
     formData.append ('name', name)
 
@@ -40,8 +50,9 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
       setUser (user => ({ ...user, ...data }))
       toast ({ title: '設定を更新しました．' })
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: 'しっぱい……' })
     }
   }
@@ -65,11 +76,16 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 
 	  {user ? (
 	      <>
+		<FieldError messages={baseErrors}/>
+
 		{/* 名前 */}
-		<div>
-		  <Label>表示名</Label>
+		<FormField label="表示名" messages={fieldErrors.name}>
+		  {({ describedBy, invalid }) => (
+		      <>
 		  <input type="text"
-			 className="w-full border rounded p-2"
+			 aria-describedby={describedBy}
+			 aria-invalid={invalid}
+			 className={inputClass (invalid)}
 			 value={name}
 			 placeholder="名もなきニジラー"
 			 onChange={ev => setName (ev.target.value)}/>
@@ -77,7 +93,8 @@ const SettingPage: FC<Props> = ({ user, setUser }) => {
 		      <p className="mt-1 text-sm text-red-500">
 			名前が未設定のアカウントは 30 日間アクセスしないと削除されます!!!!
 		      </p>)}
-		</div>
+		      </>)}
+		</FormField>
 
 		{/* 送信 */}
 		<Button onClick={handleSubmit}
diff --git a/frontend/src/pages/wiki/WikiDetailPage.test.tsx b/frontend/src/pages/wiki/WikiDetailPage.test.tsx
new file mode 100644
index 0000000..4b7b8c7
--- /dev/null
+++ b/frontend/src/pages/wiki/WikiDetailPage.test.tsx
@@ -0,0 +1,54 @@
+import { screen } from '@testing-library/react'
+import { Route, Routes } from 'react-router-dom'
+import { describe, expect, it, vi } from 'vitest'
+
+import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
+import { buildTag, buildWikiPage } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+const wikiApi = vi.hoisted (() => ({
+  fetchWikiPage:        vi.fn (),
+  fetchWikiPageByTitle: vi.fn (),
+}))
+
+const tagsApi = vi.hoisted (() => ({
+  fetchTagByName: vi.fn (),
+}))
+
+const postsApi = vi.hoisted (() => ({
+  fetchPosts: vi.fn (),
+}))
+
+vi.mock ('@/lib/wiki', () => wikiApi)
+vi.mock ('@/lib/tags', () => tagsApi)
+vi.mock ('@/lib/posts', () => postsApi)
+
+describe ('WikiDetailPage', () => {
+  it ('renders deprecated state outside the wiki title link', async () => {
+    wikiApi.fetchWikiPageByTitle.mockResolvedValueOnce (buildWikiPage ({
+      title:        '旧タグ',
+      deprecatedAt: '2026-06-01T00:00:00.000Z',
+    }))
+    tagsApi.fetchTagByName.mockResolvedValueOnce (buildTag ({
+      name:         '旧タグ',
+      deprecatedAt: '2026-06-01T00:00:00.000Z',
+    }))
+    postsApi.fetchPosts.mockResolvedValueOnce ({ posts: [], count: 0 })
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+        </Routes>,
+        { route: '/wiki/%E6%97%A7%E3%82%BF%E3%82%B0' },
+    )
+
+    const marker = await screen.findByText ('（廃止）')
+    const heading = marker.closest ('h1')
+    const link = screen.getByRole ('link', { name: '旧タグ' })
+
+    expect (heading).not.toBeNull ()
+    expect (heading!).toHaveTextContent ('旧タグ（廃止）')
+    expect (link).toBeInTheDocument ()
+    expect (marker.closest ('a')).toBeNull ()
+  })
+})
diff --git a/frontend/src/pages/wiki/WikiDetailPage.tsx b/frontend/src/pages/wiki/WikiDetailPage.tsx
index 249bf84..15b7f93 100644
--- a/frontend/src/pages/wiki/WikiDetailPage.tsx
+++ b/frontend/src/pages/wiki/WikiDetailPage.tsx
@@ -39,6 +39,7 @@ const WikiDetailPage: FC = () => {
       queryFn:  () => fetchWikiPageByTitle (title, { version }) })
 
   const effectiveTitle = wikiPage?.title ?? title
+  const deprecated = wikiPage?.deprecatedAt != null
 
   const { data: tag } = useQuery ({
       enabled:  Boolean (effectiveTitle),
@@ -88,7 +89,7 @@ const WikiDetailPage: FC = () => {
   return (
       <MainArea>
 	<Helmet>
-	  <title>{`${ title } Wiki | ${ SITE_TITLE }`}</title>
+	  <title>{`${ effectiveTitle }${ deprecated ? '（廃止）' : '' } Wiki | ${ SITE_TITLE }`}</title>
 	  {!(wikiPage?.body) && <meta name="robots" content="noindex"/>}
 	</Helmet>
 
@@ -110,10 +111,13 @@ const WikiDetailPage: FC = () => {
 
 	<article className="prose dark:prose-invert mx-auto p-4">
 	  <h1 className="prose-a:no-underline">
-	    <TagLink tag={tag ?? defaultTag}
+	    <TagLink tag={tag ?? { ...defaultTag,
+				   name: effectiveTitle,
+				   deprecatedAt: wikiPage?.deprecatedAt ?? null }}
 		     withWiki={false}
 		     withCount={false}
 		     {...(version && { to: `/wiki/${ encodeURIComponent (title) }` })}/>
+	    {deprecated && <span>（廃止）</span>}
 	  </h1>
 	  {loading ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
 
diff --git a/frontend/src/pages/wiki/WikiDiffPage.test.tsx b/frontend/src/pages/wiki/WikiDiffPage.test.tsx
index 24d71eb..185b904 100644
--- a/frontend/src/pages/wiki/WikiDiffPage.test.tsx
+++ b/frontend/src/pages/wiki/WikiDiffPage.test.tsx
@@ -16,6 +16,7 @@ describe ('WikiDiffPage', () => {
     api.apiGet.mockResolvedValueOnce ({
       wikiPageId:      3,
       title:           '差分対象',
+      deprecatedAt:    null,
       olderRevisionId: 1,
       newerRevisionId: 2,
       diff: [
@@ -43,4 +44,26 @@ describe ('WikiDiffPage', () => {
     expect (screen.getByText ('added line')).toBeInTheDocument ()
     expect (screen.getByText ('removed line')).toBeInTheDocument ()
   })
+
+  it ('appends deprecated state to the wiki title', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      wikiPageId:      3,
+      title:           '廃止 Wiki',
+      deprecatedAt:    '2026-06-01T00:00:00.000Z',
+      olderRevisionId: 1,
+      newerRevisionId: 2,
+      diff:            [],
+    })
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/wiki/:id/diff" element={<WikiDiffPage/>}/>
+        </Routes>,
+        { route: '/wiki/3/diff?from=1&to=2' },
+    )
+
+    expect (await screen.findByRole ('heading', {
+      name: '廃止 Wiki（廃止）',
+    })).toBeInTheDocument ()
+  })
 })
diff --git a/frontend/src/pages/wiki/WikiDiffPage.tsx b/frontend/src/pages/wiki/WikiDiffPage.tsx
index 3a1d0dd..5206f2e 100644
--- a/frontend/src/pages/wiki/WikiDiffPage.tsx
+++ b/frontend/src/pages/wiki/WikiDiffPage.tsx
@@ -23,6 +23,9 @@ const WikiDiffPage: FC = () => {
   const query = new URLSearchParams (location.search)
   const from = query.get ('from')
   const to = query.get ('to')
+  const displayTitle = diff
+      ? `${ diff.title }${ diff.deprecatedAt != null ? '（廃止）' : '' }`
+      : ''
 
   useEffect (() => {
     void (async () => {
@@ -33,9 +36,9 @@ const WikiDiffPage: FC = () => {
   return (
       <MainArea>
 	<Helmet>
-	  <title>{`Wiki 差分: ${ diff?.title } | ${ SITE_TITLE }`}</title>
+	  <title>{`Wiki 差分: ${ displayTitle } | ${ SITE_TITLE }`}</title>
 	</Helmet>
-	<PageTitle>{diff?.title}</PageTitle>
+	<PageTitle>{displayTitle}</PageTitle>
 	<div className="prose mx-auto p-4">
 	  {diff
 	   ? (
diff --git a/frontend/src/pages/wiki/WikiEditPage.tsx b/frontend/src/pages/wiki/WikiEditPage.tsx
index c524b39..dcbe12c 100644
--- a/frontend/src/pages/wiki/WikiEditPage.tsx
+++ b/frontend/src/pages/wiki/WikiEditPage.tsx
@@ -5,11 +5,16 @@ import { Helmet } from 'react-helmet-async'
 import MdEditor from 'react-markdown-editor-lite'
 import { useParams, useNavigate } from 'react-router-dom'
 
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiGet, apiPut } from '@/lib/api'
 import { wikiKeys } from '@/lib/queryKeys'
+import { canEditContent } from '@/lib/users'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 import Forbidden from '@/pages/Forbidden'
 
 import 'react-markdown-editor-lite/lib/index.css'
@@ -22,9 +27,11 @@ const mdParser = new MarkdownIt
 
 type Props = { user: User | null }
 
+type WikiFormField = 'title' | 'body'
+
 
 const WikiEditPage: FC<Props> = ({ user }) => {
-  const editable = ['admin', 'member'].some (r => user?.role === r)
+  const editable = canEditContent (user)
 
   const { id } = useParams ()
 
@@ -35,8 +42,12 @@ const WikiEditPage: FC<Props> = ({ user }) => {
   const [body, setBody] = useState ('')
   const [loading, setLoading] = useState (true)
   const [title, setTitle] = useState ('')
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<WikiFormField> ()
 
   const handleSubmit = async () => {
+    clearValidationErrors ()
+
     const formData = new FormData ()
     formData.append ('title', title)
     formData.append ('body', body)
@@ -51,8 +62,9 @@ const WikiEditPage: FC<Props> = ({ user }) => {
       toast ({ title: '投稿成功!' })
       navigate (`/wiki/${ title }`)
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '投稿失敗', description: '入力を確認してください。' })
     }
   }
@@ -83,24 +95,28 @@ const WikiEditPage: FC<Props> = ({ user }) => {
 
 	  {loading ? 'Loading...' : (
 	      <>
+		<FieldError messages={baseErrors}/>
+
 		{/* タイトル */}
 		{/* TODO: タグ補完 */}
-		<div>
-		  <label className="block font-semibold mb-1">タイトル</label>
-		  <input type="text"
-			 value={title}
-			 onChange={e => setTitle (e.target.value)}
-			 className="w-full border p-2 rounded"/>
-		</div>
+		<FormField label="タイトル" messages={fieldErrors.title}>
+		  {({ describedBy, invalid }) => (
+		      <input type="text"
+			     value={title}
+			     onChange={e => setTitle (e.target.value)}
+			     aria-describedby={describedBy}
+			     aria-invalid={invalid}
+			     className={inputClass (invalid)}/>)}
+		</FormField>
 
 		{/* 本文 */}
-		<div>
-		  <label className="block font-semibold mb-1">本文</label>
-		  <MdEditor value={body}
-			    style={{ height: '500px' }}
-			    renderHTML={text => mdParser.render (text)}
-			    onChange={({ text }) => setBody (text)}/>
-		</div>
+		<FormField label="本文" messages={fieldErrors.body}>
+		  {() => (
+		      <MdEditor value={body}
+				style={{ height: '500px' }}
+				renderHTML={text => mdParser.render (text)}
+				onChange={({ text }) => setBody (text)}/>)}
+		</FormField>
 
 		{/* 送信 */}
 		<button onClick={handleSubmit}
diff --git a/frontend/src/pages/wiki/WikiHistoryPage.test.tsx b/frontend/src/pages/wiki/WikiHistoryPage.test.tsx
new file mode 100644
index 0000000..35aa8f5
--- /dev/null
+++ b/frontend/src/pages/wiki/WikiHistoryPage.test.tsx
@@ -0,0 +1,38 @@
+import { screen } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import WikiHistoryPage from '@/pages/wiki/WikiHistoryPage'
+import { renderWithProviders } from '@/test/render'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+
+describe ('WikiHistoryPage', () => {
+  it ('renders deprecated state outside the wiki title link', async () => {
+    api.apiGet.mockResolvedValueOnce ([{
+      revisionId:  2,
+      pred:        1,
+      succ:        null,
+      wikiPage:    {
+	id:           3,
+	title:        '旧タグ',
+	deprecatedAt: '2026-06-01T00:00:00.000Z',
+      },
+      user:        { id: 4, name: 'tester' },
+      kind:        'content',
+      message:     'updated',
+      timestamp:   '2026-06-02T00:00:00.000Z',
+    }])
+
+    renderWithProviders (<WikiHistoryPage/>)
+
+    const link = await screen.findByRole ('link', { name: '旧タグ' })
+    const marker = screen.getByText ('（廃止）')
+
+    expect (link).toHaveAttribute ('href', '/wiki/%E6%97%A7%E3%82%BF%E3%82%B0?version=2')
+    expect (marker.closest ('a')).toBeNull ()
+  })
+})
diff --git a/frontend/src/pages/wiki/WikiHistoryPage.tsx b/frontend/src/pages/wiki/WikiHistoryPage.tsx
index 973a812..0affe21 100644
--- a/frontend/src/pages/wiki/WikiHistoryPage.tsx
+++ b/frontend/src/pages/wiki/WikiHistoryPage.tsx
@@ -59,6 +59,7 @@ const WikiHistoryPage: FC = () => {
 			to={`/wiki/${ encodeURIComponent (change.wikiPage.title) }?version=${ change.revisionId }`}>
 		      {change.wikiPage.title}
 		    </PrefetchLink>
+		    {change.wikiPage.deprecatedAt != null && <span>（廃止）</span>}
 		  </td>
 		  <td className="p-2">
 		    {change.pred == null ? '新規' : '更新'}
diff --git a/frontend/src/pages/wiki/WikiNewPage.tsx b/frontend/src/pages/wiki/WikiNewPage.tsx
index 4dfd960..fffb690 100644
--- a/frontend/src/pages/wiki/WikiNewPage.tsx
+++ b/frontend/src/pages/wiki/WikiNewPage.tsx
@@ -6,10 +6,15 @@ import { Helmet } from 'react-helmet-async'
 import MdEditor from 'react-markdown-editor-lite'
 import { useLocation, useNavigate } from 'react-router-dom'
 
+import FieldError from '@/components/common/FieldError'
+import FormField from '@/components/common/FormField'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiPost } from '@/lib/api'
+import { canEditContent } from '@/lib/users'
+import { inputClass } from '@/lib/utils'
+import { useValidationErrors } from '@/lib/useValidationErrors'
 import Forbidden from '@/pages/Forbidden'
 
 import 'react-markdown-editor-lite/lib/index.css'
@@ -20,9 +25,11 @@ const mdParser = new MarkdownIt
 
 type Props = { user: User | null }
 
+type WikiFormField = 'title' | 'body'
+
 
 const WikiNewPage: FC<Props> = ({ user }) => {
-  const editable = ['admin', 'member'].some (r => user?.role === r)
+  const editable = canEditContent (user)
 
   const location = useLocation ()
   const navigate = useNavigate ()
@@ -32,8 +39,12 @@ const WikiNewPage: FC<Props> = ({ user }) => {
 
   const [title, setTitle] = useState (titleQuery)
   const [body, setBody] = useState ('')
+  const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
+      useValidationErrors<WikiFormField> ()
 
   const handleSubmit = async () => {
+    clearValidationErrors ()
+
     const formData = new FormData
     formData.append ('title', title)
     formData.append ('body', body)
@@ -45,8 +56,9 @@ const WikiNewPage: FC<Props> = ({ user }) => {
       toast ({ title: '投稿成功!' })
       navigate (`/wiki/${ data.title }`)
     }
-    catch
+    catch (e)
     {
+      applyValidationError (e)
       toast ({ title: '投稿失敗', description: '入力を確認してください。' })
     }
   }
@@ -61,25 +73,28 @@ const WikiNewPage: FC<Props> = ({ user }) => {
 	</Helmet>
 	<div className="max-w-xl mx-auto p-4 space-y-4">
 	  <h1 className="text-2xl font-bold mb-2">新規 Wiki ページ</h1>
+	  <FieldError messages={baseErrors}/>
 
 	  {/* タイトル */}
 	  {/* TODO: タグ補完 */}
-	  <div>
-	    <label className="block font-semibold mb-1">タイトル</label>
-	    <input type="text"
-		   value={title}
-		   onChange={e => setTitle (e.target.value)}
-		   className="w-full border p-2 rounded"/>
-	  </div>
+	  <FormField label="タイトル" messages={fieldErrors.title}>
+	    {({ describedBy, invalid }) => (
+		<input type="text"
+		       value={title}
+		       onChange={e => setTitle (e.target.value)}
+		       aria-describedby={describedBy}
+		       aria-invalid={invalid}
+		       className={inputClass (invalid)}/>)}
+	  </FormField>
 
 	  {/* 本文 */}
-	  <div>
-	    <label className="block font-semibold mb-1">本文</label>
-	    <MdEditor value={body}
-		      style={{ height: '500px' }}
-		      renderHTML={text => mdParser.render (text)}
-		      onChange={({ text }) => setBody (text)}/>
-	  </div>
+	  <FormField label="本文" messages={fieldErrors.body}>
+	    {() => (
+		<MdEditor value={body}
+			  style={{ height: '500px' }}
+			  renderHTML={text => mdParser.render (text)}
+			  onChange={({ text }) => setBody (text)}/>)}
+	  </FormField>
 
 	  {/* 送信 */}
 	  <button onClick={handleSubmit}
diff --git a/frontend/src/pages/wiki/WikiSearchPage.test.tsx b/frontend/src/pages/wiki/WikiSearchPage.test.tsx
index 82213ca..e831035 100644
--- a/frontend/src/pages/wiki/WikiSearchPage.test.tsx
+++ b/frontend/src/pages/wiki/WikiSearchPage.test.tsx
@@ -42,4 +42,21 @@ describe ('WikiSearchPage', () => {
     })
     expect (await screen.findByRole ('link', { name: '検索結果' })).toBeInTheDocument ()
   })
+
+  it ('marks deprecated wiki tags in the result title', async () => {
+    api.apiGet.mockResolvedValueOnce ([
+        buildWikiPage ({
+            title:        '旧タグ',
+            deprecatedAt: '2026-06-01T00:00:00.000Z',
+        }),
+    ])
+
+    renderWithProviders (<WikiSearchPage/>)
+
+    const link = await screen.findByRole ('link', { name: '旧タグ' })
+    const marker = screen.getByText ('（廃止）')
+
+    expect (link).toBeInTheDocument ()
+    expect (marker.closest ('a')).toBeNull ()
+  })
 })
diff --git a/frontend/src/pages/wiki/WikiSearchPage.tsx b/frontend/src/pages/wiki/WikiSearchPage.tsx
index 6eb190e..b7b671d 100644
--- a/frontend/src/pages/wiki/WikiSearchPage.tsx
+++ b/frontend/src/pages/wiki/WikiSearchPage.tsx
@@ -2,11 +2,12 @@ import { useEffect, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 
 import PrefetchLink from '@/components/PrefetchLink'
+import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
 import { apiGet } from '@/lib/api'
-import { dateString } from '@/lib/utils'
+import { dateString, inputClass } from '@/lib/utils'
 
 import type { FormEvent , FC } from 'react'
 
@@ -43,22 +44,22 @@ const WikiSearchPage: FC = () => {
 	  <PageTitle>Wiki</PageTitle>
 	  <form onSubmit={handleSearch} className="space-y-2">
 	    {/* タイトル */}
-	    <div>
-	      <label>タイトル：</label><br />
-	      <input type="text"
-		     value={title}
-		     onChange={e => setTitle (e.target.value)}
-		     className="border p-1 w-full" />
-	    </div>
+	    <FormField label="タイトル">
+	      {({ invalid }) => (
+		  <input type="text"
+			 value={title}
+			 onChange={e => setTitle (e.target.value)}
+			 className={inputClass (invalid)}/>)}
+	    </FormField>
 
 	    {/* 内容 */}
-	    <div>
-	      <label>内容：</label><br />
-	      <input type="text"
-		     value={text}
-		     onChange={e => setText (e.target.value)}
-		     className="border p-1 w-full" />
-	    </div>
+	    <FormField label="内容">
+	      {({ invalid }) => (
+		  <input type="text"
+			 value={text}
+			 onChange={e => setText (e.target.value)}
+			 className={inputClass (invalid)}/>)}
+	    </FormField>
 
 	    {/* 検索 */}
 	    <div className="py-3">
@@ -85,6 +86,7 @@ const WikiSearchPage: FC = () => {
 		      <PrefetchLink to={`/wiki/${ encodeURIComponent (page.title) }`}>
 			{page.title}
 		      </PrefetchLink>
+		      {page.deprecatedAt != null && <span>（廃止）</span>}
 		    </td>
 		    <td className="p-2">
 		      {dateString (page.updatedAt)}
diff --git a/frontend/src/test/factories.ts b/frontend/src/test/factories.ts
index 929f4f1..0222e48 100644
--- a/frontend/src/test/factories.ts
+++ b/frontend/src/test/factories.ts
@@ -1,9 +1,19 @@
-import type { Material, Post, TagWithSections, User, WikiPage } from '@/types'
+import type { Material,
+	      Post,
+	      TagWithSections,
+	      Theatre,
+	      TheatreComment,
+	      TheatreInfo,
+	      TheatrePostSelectionWeights,
+	      TheatreProgramme,
+	      User,
+	      WikiPage } from '@/types'
 
 export const buildTag = (overrides: Partial<TagWithSections> = {}): TagWithSections => ({
   id:             1,
   name:           'テストタグ',
   category:       'general',
+  deprecatedAt:   null,
   aliases:        [],
   parents:        [],
   postCount:      12,
@@ -50,6 +60,7 @@ export const buildUser = (overrides: Partial<User> = {}): User => ({
 export const buildWikiPage = (overrides: Partial<WikiPage> = {}): WikiPage => ({
   id:            1,
   title:         'テストWiki',
+  deprecatedAt:  null,
   createdUserId: 1,
   updatedUserId: 1,
   createdAt:     '2026-01-02T03:04:05.000Z',
@@ -74,3 +85,62 @@ export const buildMaterial = (overrides: Partial<Material> = {}): Material => ({
   updatedByUser: { id: 2, name: 'updater' },
   ...overrides,
 })
+
+export const buildTheatre = (overrides: Partial<Theatre> = {}): Theatre => ({
+  id:            1,
+  name:          'テスト劇場',
+  opensAt:       '2026-01-02T03:04:05.000Z',
+  closesAt:      null,
+  createdByUser: { id: 1, name: 'creator' },
+  createdAt:     '2026-01-02T03:04:05.000Z',
+  updatedAt:     '2026-01-03T03:04:05.000Z',
+  ...overrides,
+})
+
+export const buildTheatreInfo = (
+    overrides: Partial<TheatreInfo> = {},
+): TheatreInfo => ({
+  hostFlg:       false,
+  postId:        null,
+  postStartedAt: null,
+  postElapsedMs: null,
+  watchingUsers: [],
+  skipVote:      {
+    votesCount:         0,
+    requiredCount:      1,
+    watchingUsersCount: 0,
+    voted:              false,
+  },
+  ...overrides,
+})
+
+export const buildTheatreComment = (
+    overrides: Partial<TheatreComment> = {},
+): TheatreComment => ({
+  theatreId: 1,
+  no:        1,
+  deleted:   false,
+  user:      { id: 1, name: 'tester' },
+  content:   'テストコメント',
+  createdAt: '2026-01-02T03:04:05.000Z',
+  ...overrides,
+} as TheatreComment)
+
+export const buildTheatreProgramme = (
+    overrides: Partial<TheatreProgramme> = {},
+): TheatreProgramme => ({
+  theatreId: 1,
+  position:  1,
+  post:      buildPost (),
+  createdAt: '2026-01-02T03:04:05.000Z',
+  ...overrides,
+})
+
+export const buildTheatrePostSelectionWeights = (
+    overrides: Partial<TheatrePostSelectionWeights> = {},
+): TheatrePostSelectionWeights => ({
+  tagPenalties:  [],
+  lightestPosts: [],
+  heaviestPosts: [],
+  ...overrides,
+})
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index a4a7950..641af6c 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -39,18 +39,31 @@ export type FetchTagsOrderField =
     | 'updated_at'
 
 export type FetchTagsParams = {
-    post:         number | null
-    name:         string
-    category:     Category | null
-    postCountGTE: number
-    postCountLTE: number | null
-    createdFrom:  string
-    createdTo:    string
-    updatedFrom:  string
-    updatedTo:    string
-    page:         number
-    limit:        number
-    order:        FetchTagsOrder }
+    post:           number | null
+    name:           string
+    category:       Category | null
+    postCountGTE:   number
+    postCountLTE:   number | null
+    createdFrom:    string
+    createdTo:      string
+    updatedFrom:    string
+    updatedTo:      string
+    deprecated:     boolean | null
+    page:           number
+    limit:          number
+    order:          FetchTagsOrder }
+
+export type FetchNicoTagsParams = {
+    name:       string
+    linkedTag:  string
+    linkStatus: 'all' | 'linked' | 'unlinked'
+    page:       number
+    limit:      number
+    order:      FetchNicoTagsOrder }
+
+export type FetchNicoTagsOrder = `${ FetchNicoTagsOrderField }:${ 'asc' | 'desc' }`
+
+export type FetchNicoTagsOrderField = 'name' | 'created_at' | 'updated_at'
 
 export type Material = {
     id:             number
@@ -83,8 +96,9 @@ export type MenuVisibleItem = {
     subMenu:  SubMenuItem[] }
 
 export type NicoTag = Tag & {
-    category:   'nico'
-    linkedTags: Tag[] }
+    category:               'nico'
+    linkedTags:             Tag[]
+    recentPostTagCreatedAt: string | null }
 
 export type NiconicoMetadata = {
     currentTime:            number
@@ -126,6 +140,10 @@ export type Post = {
     title:                  string | null
     thumbnail:              string | null
     thumbnailBase:          string | null
+    postSimilarityEdges?:   {
+			      targetPostId: number
+			      cos:          number
+			  }[]
     tags:                   TagWithSections[]
     parentPosts?:           Post[]
     childPosts?:            Post[]
@@ -179,6 +197,7 @@ export type Tag = {
     id:             number
     name:           string
     category:       Category
+    deprecatedAt:   string | null
     aliases:        string[]
     parents:        Tag[]
     postCount:      number
@@ -195,6 +214,7 @@ export type TagVersion = {
     eventType:              'create' | 'update' | 'discard' | 'restore'
     name:                   { current: string; prev: string | null }
     category:               { current: Category; prev: Category | null }
+    deprecatedAt:           { current: string | null; prev: string | null }
     aliases:                { name: string; type: 'context' | 'added' | 'removed' }[]
     parentTags:             { tag: Tag; type: 'context' | 'added' | 'removed' }[]
     createdAt:              string
@@ -213,13 +233,64 @@ export type Theatre = {
     createdAt:      string
     updatedAt:      string }
 
-export type TheatreComment = {
-    theatreId:  number,
-    no:         number,
-    user:       { id: number, name: string } | null
-    content:    string
+export type TheatreComment =
+    | { theatreId:  number
+	no:         number
+	deleted:    false
+	user:       { id: number, name: string } | null
+	content:    string
+	createdAt:  string }
+    | { theatreId:  number
+	no:         number
+	deleted:    true
+	user:       { id: number, name: string } | null
+	content:    null,
+	createdAt:  string }
+
+export type TheatreProgramme = {
+    theatreId:  number
+    position:   number
+    post:       Post
     createdAt:  string }
 
+export type TheatreSkipVoteStatus = {
+    votesCount:          number
+    requiredCount:       number
+    watchingUsersCount:  number
+    voted:               boolean }
+
+export type TheatreInfo = {
+    hostFlg:        boolean
+    postId:         number | null
+    postStartedAt:  string | null
+    postElapsedMs:  number | null
+    watchingUsers:  Pick<User, 'id' | 'name'>[]
+    skipVote:       TheatreSkipVoteStatus
+    skipped?:       boolean }
+
+export type TheatreSkipEvent = {
+    id:                 number
+    theatreId:          number
+    post:               Post
+    tags:               Tag[]
+    programmePosition:  number | null
+    createdAt:          string }
+
+export type TheatrePostWeight = {
+    post:     Post
+    weight:   number
+    penalty:  number
+    tags:     Tag[] }
+
+export type TheatreTagPenalty = {
+    tag:      Tag
+    penalty:  number }
+
+export type TheatrePostSelectionWeights = {
+    tagPenalties:  TheatreTagPenalty[]
+    lightestPosts: TheatrePostWeight[]
+    heaviestPosts: TheatrePostWeight[] }
+
 export type User = {
     id:               number
     name:             string | null
@@ -231,6 +302,7 @@ export type ViewFlagBehavior = typeof ViewFlagBehavior[keyof typeof ViewFlagBeha
 export type WikiPage = {
     id:             number
     title:          string
+    deprecatedAt:   string | null
     createdUserId:  number
     updatedUserId:  number
     createdAt:      string
@@ -244,7 +316,7 @@ export type WikiPageChange = {
     revisionId: number
     pred:       number | null
     succ:       null
-    wikiPage:   Pick<WikiPage, 'id' | 'title'>
+    wikiPage:   Pick<WikiPage, 'id' | 'title' | 'deprecatedAt'>
     user:       Pick<User, 'id' | 'name'>
     kind:       'content' | 'redirect'
     message:    string | null
@@ -253,6 +325,7 @@ export type WikiPageChange = {
 export type WikiPageDiff = {
     wikiPageId:       number
     title:            string
+    deprecatedAt:     string | null
     olderRevisionId:  number | null
     newerRevisionId:  number
     diff:             WikiPageDiffDiff[] }
diff --git a/frontend/tsconfig.app.json b/frontend/tsconfig.app.json
index 17e49c8..0cb3927 100644
--- a/frontend/tsconfig.app.json
+++ b/frontend/tsconfig.app.json
@@ -27,5 +27,6 @@
       "@/*": ["*"]
     }
   },
-  "include": ["src"]
+  "include": ["src"],
+  "exclude": ["src/**/*.test.ts", "src/**/*.test.tsx", "src/test"]
 }