#361

Reviewed-on: #366
Co-authored-by: miteruzo <miteruzo@naver.com>
Co-committed-by: miteruzo <miteruzo@naver.com>

.gitea/ISSUE_TEMPLATE.md

@@ -0,0 +1,35 @@
+## 背景
+
+なぜ必要か。
+
+## 対象範囲
+
+- backend:
+- frontend:
+- docs:
+- migration:
+
+## やること
+
+- [ ] 
+
+## 受け入れ条件
+
+- [ ] 
+
+## 実行すべき確認
+
+- [ ] `cd backend && bundle exec rspec`
+- [ ] `cd frontend && npm run build`
+- [ ] `cd frontend && npm run lint`
+
+## 禁止事項
+
+- unrelated refactor はしない
+- 既存 API response shape を壊さない
+- 認証・認可・BAN を弱めない
+
+## Codex への指示
+
+この issue を読んで実装してください。
+不明点があれば、実装前に調査結果と選択肢を提示してください。

AGENTS.md

@@ -0,0 +1,244 @@
+# AGENTS.md
+
+## Project overview
+
+BTRC Hub / タグ広場 is a split Rails API and React frontend repository.
+
+- Backend: Rails API under `backend/`.
+- Frontend: React + TypeScript + Vite under `frontend/`.
+- Docs: lightweight command notes under `docs/`.
+- There is no README or Makefile at the repository root as of this inspection.
+
+## 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`.
+- 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.
+
+## 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/config/routes.rb`: API routes.
+- `backend/db/migrate`: migrations.
+- `backend/db/schema.rb`: current schema snapshot.
+- `backend/lib/tasks`: custom Rake tasks.
+- `backend/spec`: RSpec tests.
+- `backend/test`: Rails minitest files that still exist in the tree.
+- `frontend/src/App.tsx`: frontend route definitions and initial user setup.
+- `frontend/src/pages`: page-level React components.
+- `frontend/src/components`: shared and feature components.
+- `frontend/src/lib`: API client helpers, query keys, prefetchers, and domain helpers.
+- `frontend/src/stores`: Zustand stores.
+- `docs/commands.md`: command notes.
+
+## Commands
+
+Only list commands that are backed by files inspected in this repository.
+
+### Backend
+
+The following binstubs exist under `backend/bin`:
+
+```sh
+cd backend
+bin/setup
+bin/dev
+bin/rails
+bin/rake
+bin/rubocop
+bin/brakeman
+bin/kamal
+bin/thrust
+```
+
+Common Rails/Rake usage through existing binstubs:
+
+```sh
+cd backend
+bin/rails db:prepare
+bin/rails db:migrate
+bin/rails routes
+bin/rails server
+bin/rake
+bin/rubocop
+bin/brakeman
+```
+
+RSpec is present in `Gemfile` and `.rspec` exists:
+
+```sh
+cd backend
+bundle exec rspec
+```
+
+### Frontend
+
+The following npm scripts exist in `frontend/package.json`:
+
+```sh
+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 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.
+- Ruby: never put a space before method-call parentheses.
+- Ruby: never put a line break immediately before `)`.
+- Ruby: do not use `%w` or `%i`.
+- 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.
+- 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.
+- 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` 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.
+- 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.
+- 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.
+- 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 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
+
+A task is complete only when:
+
+- implementation is complete,
+- 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.

backend/AGENTS.md

@@ -0,0 +1,219 @@
+# backend/AGENTS.md
+
+## Scope
+
+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.
+
+## Commands
+
+Use commands backed by files and dependencies in this directory:
+
+```sh
+bin/setup
+bin/dev
+bin/rails
+bin/rake
+bin/rubocop
+bin/brakeman
+bundle exec rspec
+```
+
+Common checks:
+
+```sh
+bundle exec rspec
+bin/rubocop
+bin/brakeman
+```
+
+Common Rails commands:
+
+```sh
+bin/rails db:prepare
+bin/rails db:migrate
+bin/rails routes
+bin/rails server
+```
+
+After backend behavior changes, run the relevant RSpec files. For broad backend changes, run:
+
+```sh
+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.
+- `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.
+
+## 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.
+- 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.
+- 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.
+- 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`.
+- `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.
+- 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.admin?` only for admin-only paths, such as tag child relationship changes.
+- Do not replace role checks with looser presence checks.
+
+## BAN and IP BAN
+
+- `ApplicationController` runs these before actions in order:
+  - `reject_banned_ip_address!`
+  - `authenticate_user`
+  - `reject_banned_user!`
+- 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 only when
+  the user explicitly asks for tests.
+
+## RSpec
+
+- Prefer RSpec for new backend tests.
+- Put API behavior coverage under `spec/requests`.
+- Put model behavior under `spec/models`.
+- Put service behavior under `spec/services`.
+- 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 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`.
+- 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.
+
+## 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.
+- 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:
+  - `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`.
+- 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. 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.
+
+## 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.
+- 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.

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'

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

backend/app/controllers/application_controller.rb

@@ -1,14 +1,19 @@
 class ApplicationController < ActionController::API
-  before_action :authenticate_user
+  rescue_from ActiveRecord::RecordInvalid, with: :render_record_invalid
+  rescue_from ActiveRecord::RecordNotUnique, with: :render_record_not_unique
 
-  def current_user
-    @current_user
-  end
+  before_action :reject_banned_ip_address!
+  before_action :authenticate_user
+  before_action :reject_banned_user!
+
+  def current_user = @current_user
 
   private
 
   def authenticate_user
     code = request.headers['X-Transfer-Code'] || request.headers['HTTP_X_TRANSFER_CODE']
+    return if code.blank?
+
     @current_user = User.find_by(inheritance_code: code)
   end
 
@@ -22,4 +27,62 @@ class ApplicationController < ActionController::API
       s.in?(['', '1', 'true', 'on', 'yes'])
     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?
+
+    head :forbidden
+  end
+
+  def reject_banned_user!
+    return unless current_user&.banned?
+
+    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

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!
 

backend/app/controllers/gekanator_games_controller.rb

@@ -0,0 +1,148 @@
+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.save
+      render json: { id: game.id }, status: :created
+    else
+      render json: { errors: game.errors.full_messages }, status: :unprocessable_entity
+    end
+  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 = weighted_sample_questions(
+        questions,
+        post_id: game.correct_post_id,
+        limit: 2)
+
+    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 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
+end

backend/app/controllers/gekanator_posts_controller.rb

@@ -0,0 +1,44 @@
+class GekanatorPostsController < ApplicationController
+  def index
+    posts =
+        Post
+        .preload(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'))
+
+    render json: { posts: posts.map { |post| post_json(post) } }
+  end
+
+  private
+
+  def post_json post
+    {
+      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,
+      tags: post.tags.map { |tag| tag_json(tag) }
+    }
+  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

backend/app/controllers/gekanator_question_suggestions_controller.rb

@@ -0,0 +1,56 @@
+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
+
+    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
+end

backend/app/controllers/gekanator_questions_controller.rb

@@ -0,0 +1,102 @@
+class GekanatorQuestionsController < ApplicationController
+  def index
+    questions =
+        GekanatorQuestion
+        .accepted
+        .includes(:gekanator_question_examples)
+        .order(priority_weight: :desc, id: :asc)
+
+    render json: {
+      questions: questions.map { |question| question_json(question) }
+    }
+  end
+
+  private
+
+  def question_json question
+    condition = condition_json(question.condition).deep_symbolize_keys
+    json = {
+      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'
+      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
+end

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
 

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
@@ -30,16 +73,42 @@ class NicoTagsController < ApplicationController
     id = params[:id].to_i
 
     tag = Tag.find(id)
-    return head :bad_request if tag.category != '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,
+    linked_tag_names = params[:tags].to_s.split
+    linked_tags = nil
+
+    ApplicationRecord.transaction do
+      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.category == 'nico' }
+      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
       tag.save!
 
+      NicoTagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+    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

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: [: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
@@ -95,7 +96,9 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts.preload(tags: [:materials, { tag_name: :wiki_page }])
+    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
@@ -104,12 +107,25 @@ class PostsController < ApplicationController
   end
 
   def show
-    post = Post.includes(tags: [: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.tags),
-                                related: 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.tags))
   end
 
   def create
@@ -123,26 +139,36 @@ class PostsController < ApplicationController
     tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
+    parent_post_ids = parse_parent_post_ids
 
     post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
                     original_created_from:, original_created_before:)
-    post.thumbnail.attach(thumbnail)
+    post.thumbnail.attach(thumbnail) if thumbnail.present?
 
-    ActiveRecord::Base.transaction do
+    ApplicationRecord.transaction do
       post.save!
-      tags = Tag.normalise_tags(tag_names)
+
+      tags = Tag.normalise_tags!(tag_names)
+      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
+
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      sync_parent_posts!(post, parent_post_ids)
+
       post.resized_thumbnail!
+
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
     end
 
     post.reload
     render json: PostRepr.base(post), status: :created
-  rescue ActiveRecord::RecordInvalid
-    render json: { errors: post.errors.full_messages }, status: :unprocessable_entity
   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 ArgumentError => e
+    render_validation_error fields: { parent_post_ids: [e.message] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_post_form_record_invalid e.record
   end
 
   def viewed
@@ -163,30 +189,76 @@ class PostsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    force = bool?(:force)
+    merge = bool?(: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 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
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
+    parent_post_ids = parse_parent_post_ids
 
-    post = Post.find(params[:id].to_i)
+    post = nil
+    conflict_json = nil
 
-    ActiveRecord::Base.transaction do
-      post.update!(title:, original_created_from:, original_created_before:)
-      tags = post.tags.where(category: 'nico').to_a +
-             Tag.normalise_tags(tag_names, with_tagme: false)
-      tags = Tag.expand_parent_tags(tags)
-      sync_post_tags!(post, tags)
-      PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
+    ApplicationRecord.transaction do
+      post = Post.lock.find(params[:id].to_i)
+
+      base_version = nil
+      base_snapshot = nil
+      current_snapshot = nil
+      unless force
+        base_version = post.post_versions.find_by!(version_no: base_version_no)
+
+        base_snapshot = post_snapshot_from_version(base_version)
+        current_snapshot = post_snapshot_from_record(post)
+      end
+      incoming_snapshot = post_incoming_snapshot(title:,
+                                                 original_created_from:,
+                                                 original_created_before:,
+                                                 tag_names:,
+                                                 parent_post_ids:)
+
+      snapshot_to_apply =
+          if force || post.version_no == base_version_no || current_snapshot == base_snapshot
+            incoming_snapshot
+          else
+            changes = post_snapshot_changes(base_snapshot, current_snapshot, incoming_snapshot)
+            conflicts = changes.select { |change| change[:conflict] }
+
+            if merge && conflicts.empty?
+              merge_post_snapshots(base_snapshot, current_snapshot, incoming_snapshot)
+            else
+              conflict_json = post_conflict_json(post:,
+                                                 base_version_no:,
+                                                 base_snapshot:,
+                                                 current_snapshot:,
+                                                 incoming_snapshot:,
+                                                 changes:,
+                                                 conflicts:)
+              raise ActiveRecord::Rollback
+            end
           end
 
+      apply_post_snapshot!(post, snapshot_to_apply)
+    end
+
+    return render json: conflict_json, status: :conflict if conflict_json
+
     post.reload
-    json = post.as_json
+    json = PostRepr.base(post, current_user)
     json['tags'] = build_tag_tree_for(post.tags)
     render json:, status: :ok
-  rescue ActiveRecord::RecordInvalid
-    render json: post.errors, status: :unprocessable_entity
   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 ArgumentError => e
+    render_validation_error fields: { parent_post_ids: [e.message] }
+  rescue ActiveRecord::RecordInvalid => e
+    render_post_form_record_invalid e.record
   end
 
   def changes
@@ -204,7 +276,7 @@ class PostsController < ApplicationController
     pts = pts.where(post_id: id) if id.present?
     pts = pts.where(tag_id:) if tag_id.present?
     pts = pts.includes(:post, :created_user, :deleted_user,
-                       tag: [:materials, { tag_name: :wiki_page }])
+                       tag: [:deerjikists, :materials, { tag_name: :wiki_page }])
 
     events = []
     pts.each do |pt|
@@ -329,7 +401,7 @@ class PostsController < ApplicationController
       return nil unless tag
 
       if path.include?(tag_id)
-        return TagRepr.base(tag).merge(children: [])
+        return TagRepr.inline(tag).merge(children: [])
       end
 
       if memo.key?(tag_id)
@@ -341,9 +413,272 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.base(tag).merge(children:)
+      memo[tag_id] = TagRepr.inline(tag).merge(children:)
     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)
+
+    params[:parent_post_ids].to_s.split.map { |token|
+      id = Integer(token, exception: false)
+      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+
+      id
+    }.uniq
+  end
+
+  def sync_parent_posts! post, parent_post_ids
+    if parent_post_ids.include?(post.id)
+      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
+
+    existing_ids = Post.where(id: parent_post_ids).pluck(:id)
+    missing_ids = parent_post_ids - existing_ids
+
+    if missing_ids.present?
+      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
+
+    current_ids = post.parent_posts.pluck(:id)
+
+    ids_to_add = parent_post_ids - current_ids
+    ids_to_remove = current_ids - parent_post_ids
+
+    PostImplication.where(post_id: post.id, parent_post_id: ids_to_remove).delete_all
+
+    ids_to_add.each do |parent_post_id|
+      PostImplication.create_or_find_by!(post_id: post.id, parent_post_id:)
+    end
+  end
+
+  def parse_base_version_no
+    version_no = Integer(params[:base_version_no], exception: false)
+    if version_no&.positive?
+      version_no
+    else
+      nil
+    end
+  end
+
+  def post_snapshot_from_version version
+    { title: version.title,
+      original_created_from: snapshot_time(version.original_created_from),
+      original_created_before: snapshot_time(version.original_created_before),
+      tag_names: editable_tag_names_from_version(version),
+      parent_post_ids: snapshot_parent_post_ids_from_version(version) }
+  end
+
+  def editable_tag_names_from_version version
+    version.tags.to_s.split.reject { |name| name.downcase.start_with?('nico:') }.sort
+  end
+
+  def post_snapshot_from_record post
+    { title: post.title,
+      original_created_from: snapshot_time(post.original_created_from),
+      original_created_before: snapshot_time(post.original_created_before),
+      tag_names: editable_tag_names_from_post(post),
+      parent_post_ids: post.parent_posts.order(:id).pluck(:id) }
+  end
+
+  def editable_tag_names_from_post post
+    post.tags.not_nico.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  end
+
+  def post_incoming_snapshot title:, original_created_from:, original_created_before:,
+                             tag_names:, parent_post_ids:
+    { title:,
+      original_created_from: snapshot_time(original_created_from),
+      original_created_before: snapshot_time(original_created_before),
+      tag_names: incoming_tag_names_for_snapshot(tag_names),
+      parent_post_ids: parent_post_ids.sort }
+  end
+
+  def snapshot_parent_post_ids_from_version version
+    if version.respond_to?(:parent_post_ids)
+      version.parent_post_ids.to_s.split.map { |id| id.to_i }.sort
+    elsif version.respond_to?(:parent_id) && version.parent_id
+      [version.parent_id]
+    else
+      []
+    end
+  end
+
+  def snapshot_time value
+    return nil if value.blank?
+
+    value = Time.zone.parse(value.to_s) if value in String
+    value&.in_time_zone&.iso8601(6)
+  rescue ArgumentError, TypeError
+    value.to_s
+  end
+
+  def incoming_tag_names_for_snapshot raw_tag_names
+    tags = Tag.normalise_tags!(raw_tag_names, with_tagme: false)
+
+    Tag.expand_parent_tags(tags).map(&:name).uniq.sort
+  end
+
+  def post_conflict_json post:, base_version_no:, base_snapshot:,
+                         current_snapshot:, incoming_snapshot:, changes:, conflicts:
+    { error: 'conflict',
+      message: '競合が発生しました．',
+      post_id: post.id,
+      base_version_no:,
+      current_version_no: post.version_no,
+      base: base_snapshot,
+      current: current_snapshot,
+      mine: incoming_snapshot,
+      changes:,
+      conflicts:,
+      mergeable: conflicts.empty? }
+  end
+
+  def post_snapshot_changes base_snapshot, current_snapshot, incoming_snapshot
+    [scalar_snapshot_change(:title, 'タイトル',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     scalar_snapshot_change(:original_created_from, 'オリジナルの作成日時（以降）',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     scalar_snapshot_change(:original_created_before, 'オリジナルの作成日時（より前）',
+                            base_snapshot, current_snapshot, incoming_snapshot),
+     set_snapshot_change(:tag_names, 'タグ',
+                         base_snapshot, current_snapshot, incoming_snapshot),
+     set_snapshot_change(:parent_post_ids, '親投稿',
+                         base_snapshot, current_snapshot, incoming_snapshot)].compact
+  end
+
+  def scalar_snapshot_change field, label, base_snapshot, current_snapshot, incoming_snapshot
+    base = base_snapshot[field]
+    current = current_snapshot[field]
+    mine = incoming_snapshot[field]
+
+    return nil if current == base && mine == base
+
+    { field:, label:, base:, current:, mine:,
+      changed_by_current: current != base,
+      changed_by_me: mine != base,
+      conflict: scalar_snapshot_conflict?(base, current, mine) }
+  end
+
+  def scalar_snapshot_conflict? base, current, mine
+    current != base && mine != base && current != mine
+  end
+
+  def set_snapshot_change field, label, base_snapshot, current_snapshot, incoming_snapshot
+    base = base_snapshot[field].to_a
+    current = current_snapshot[field].to_a
+    mine = incoming_snapshot[field].to_a
+
+    added_by_current = current - base
+    removed_by_current = base - current
+    added_by_me = mine - base
+    removed_by_me = base - mine
+
+    if (added_by_current.empty? &&
+        removed_by_current.empty? &&
+        added_by_me.empty? &&
+        removed_by_me.empty?)
+      return nil
+    end
+
+    { field:, label:, base:, current:, mine:, added_by_current:, removed_by_current:,
+      added_by_me:, removed_by_me:,
+      changed_by_current: added_by_current.present? || removed_by_current.present?,
+      changed_by_me: added_by_me.present? || removed_by_me.present?,
+      conflict: set_snapshot_conflict?(added_by_current:,
+                                       removed_by_current:,
+                                       added_by_me:,
+                                       removed_by_me:) }
+  end
+
+  def set_snapshot_conflict? added_by_current:, removed_by_current:,
+                             added_by_me:, removed_by_me:
+    (added_by_current & removed_by_me).present? || (removed_by_current & added_by_me).present?
+  end
+
+  def apply_post_snapshot! post, snapshot
+    PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
+
+    post.update!(title: snapshot[:title],
+                 original_created_from: snapshot[:original_created_from],
+                 original_created_before: snapshot[:original_created_before])
+
+    editable_tags = Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false)
+    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)
+
+    sync_post_tags!(post, tags)
+    sync_parent_posts!(post, snapshot[:parent_post_ids])
+
+    PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
+  end
+
+  def merge_post_snapshots base_snapshot, current_snapshot, incoming_snapshot
+    [:title, :original_created_from, :original_created_before].map {
+      [_1, merge_scalar_snapshot_value(base_snapshot[_1],
+                                       current_snapshot[_1],
+                                       incoming_snapshot[_1])]
+    }.to_h.merge([:tag_names, :parent_post_ids].map {
+      [_1, merge_set_snapshot_value(base_snapshot[_1],
+                                    current_snapshot[_1],
+                                    incoming_snapshot[_1])]
+    }.to_h)
+  end
+
+  def merge_scalar_snapshot_value base, current, mine
+    return mine if current == base
+    return current if mine == base || current == mine
+
+    raise ArgumentError, '競合してゐる項目はマージできません．'
+  end
+
+  def merge_set_snapshot_value base, current, mine
+    base = base.to_a
+    current = current.to_a
+    mine = mine.to_a
+
+    added_by_current = current - base
+    removed_by_current = base - current
+    added_by_me = mine - base
+    removed_by_me = base - mine
+
+    merged = base + added_by_current + added_by_me
+    merged -= removed_by_current
+    merged -= removed_by_me
+
+    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

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

backend/app/controllers/tag_children_controller.rb

@@ -5,9 +5,19 @@ 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?
 
-    Tag.find(parent_id).children << Tag.find(child_id) rescue nil
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    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)
+
+      TagImplication.find_or_create_by!(parent_tag: parent, tag: child)
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
 
     head :no_content
   end
@@ -18,9 +28,19 @@ 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?
 
-    Tag.find(parent_id).children.delete(Tag.find(child_id)) rescue nil
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    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)
+
+      TagImplication.find_by(parent_tag: parent, tag: child)&.destroy!
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
 
     head :no_content
   end

backend/app/controllers/tag_versions_controller.rb

@@ -0,0 +1,92 @@
+class TagVersionsController < ApplicationController
+  def index
+    tag_id = params[:id].presence
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
+
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    offset = (page - 1) * limit
+
+    q = TagVersion.joins(<<~SQL.squish)
+          LEFT JOIN
+            tag_versions prev
+            ON
+              prev.tag_id = tag_versions.tag_id
+              AND prev.version_no = tag_versions.version_no - 1
+        SQL
+      .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
+              '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
+
+    count = q.except(:select, :order, :limit, :offset).count
+
+    versions = q.order(Arel.sql('tag_versions.created_at DESC, tag_versions.id DESC'))
+                .limit(limit)
+                .offset(offset)
+
+    render json: { versions: serialise_versions(versions), count: }
+  end
+
+  private
+
+  def serialise_versions rows
+    user_ids = rows.map(&:created_by_user_id).compact.uniq
+    users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
+
+    rows.map do |row|
+      cur_aliases = split_values(row.aliases)
+      prev_aliases = split_values(row.attributes['prev_aliases'])
+
+      cur_parent_tag_ids = split_parent_tag_ids(row.parent_tag_ids)
+      prev_parent_tag_ids = split_parent_tag_ids(row.attributes['prev_parent_tag_ids'])
+
+      all_parent_tag_ids = (cur_parent_tag_ids | prev_parent_tag_ids)
+
+      tags_by_id =
+          Tag
+          .includes(:tag_name, :materials, { tag_name: :wiki_page })
+          .where(id: all_parent_tag_ids)
+          .index_by(&:id)
+
+      parent_tags =
+          build_version_values(cur_parent_tag_ids, prev_parent_tag_ids, key: :tag_id)
+          .map do |h|
+            { tag: TagRepr.base(tags_by_id[h[:tag_id]]),
+              type: h[:type] }
+          end
+
+      { tag_id: row.tag_id,
+        version_no: row.version_no,
+        event_type: row.event_type,
+        name: { current: row.name, prev: row.attributes['prev_name'] },
+        category: { current: row.category, prev: row.attributes['prev_category'] },
+        aliases: build_version_values(cur_aliases, prev_aliases, key: :name),
+        parent_tags:,
+        created_at: row.created_at.iso8601,
+        created_by_user: row.created_by_user_id &&
+                         { id: row.created_by_user_id,
+                           name: users_by_id[row.created_by_user_id] } }
+    end
+  end
+
+  def build_version_values cur_values, prev_values, key:
+    (cur_values | prev_values).map do |value|
+      type =
+          if cur_values.include?(value) && prev_values.include?(value)
+            'context'
+          elsif cur_values.include?(value)
+            'added'
+          else
+            'removed'
+          end
+
+      { key => value, type: }
+    end
+  end
+
+  def split_values(values) = values.to_s.split(/\s+/).reject(&:blank?)
+
+  def split_parent_tag_ids(values) = split_values(values).map(&:to_i)
+end

backend/app/controllers/tags_controller.rb

@@ -1,3 +1,7 @@
+require 'net/http'
+require 'uri'
+
+
 class TagsController < ApplicationController
   def index
     post_id = params[:post]
@@ -66,7 +70,7 @@ class TagsController < ApplicationController
             .offset(offset)
             .to_a
 
-    render json: { tags: TagRepr.base(tags), count: q.size }
+    render json: { tags: TagRepr.many(tags), count: q.size }
   end
 
   def with_depth
@@ -164,7 +168,7 @@ 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)
@@ -182,24 +186,52 @@ class TagsController < ApplicationController
              .find_by(id: params[:id])
     return head :not_found unless tag
 
-    render json: DeerjikistRepr.many(tag.deerjikists)
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
   end
 
   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)
              .find_by(tag_names: { name: })
     return head :not_found unless tag
 
-    render json: DeerjikistRepr.many(tag.deerjikists)
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
+  end
+
+  def update_deerjikists
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    return head :not_found unless tag
+
+    ApplicationRecord.transaction do
+      tag.deerjikists = []
+      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
+        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)
@@ -209,6 +241,59 @@ class TagsController < ApplicationController
     render json: build_tag_children(tag)
   end
 
+  def update_all
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    tag = Tag.find_by(id: params[:id])
+    return head :not_found unless tag
+
+    name = params[:name].to_s.strip
+    category = params[:category].to_s.strip
+    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?
+
+    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
+
+    if tag.nico? || category == 'nico'
+      return render_unprocessable_entity('ニコタグは変更できません．', field: :category)
+    end
+
+    alias_names = params[:aliases].to_s.split.uniq
+    parent_names = params[:parent_tags].to_s.split.uniq
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.update!(category:)
+      tag.tag_name.update!(name:)
+
+      alias_names << old_name if name_changed
+      alias_names.delete(name)
+
+      update_aliases!(tag, alias_names)
+      update_parent_tags!(tag, parent_names)
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
+    end
+
+    render json: TagRepr.base(tag.reload)
+  end
+
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
@@ -218,20 +303,36 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    if name.present?
-      tag.tag_name.update!(name:)
+    if tag.nico? || (category.present? && category == 'nico')
+      return render_unprocessable_entity('ニコタグは変更できません．', field: :category)
     end
 
-    if category.present?
-      tag.update!(category:)
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name.present? && name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.tag_name.update!(name:) if name.present?
+      tag.update!(category:) if category.present?
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
     end
 
-    render json: TagRepr.base(tag)
+    render json: TagRepr.base(tag.reload)
   end
 
   private
 
-  def build_tag_children(tag)
+  def build_tag_children tag
     material = tag.materials.first
     file = nil
     content_type = nil
@@ -244,4 +345,116 @@ class TagsController < ApplicationController
         children: tag.children.sort_by { _1.name }.map { build_tag_children(_1) },
         material: material.as_json&.merge(file:, content_type:))
   end
+
+  def record_tag_version! tag, event_type:, created_by_user:, name_changed: false, wiki_page: nil
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+      return
+    end
+
+    TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+
+    return unless name_changed
+
+    wiki_page ||= tag.tag_name.wiki_page
+    return unless wiki_page&.wiki_versions&.exists?
+
+    WikiVersionRecorder.record!(
+        page: wiki_page,
+        event_type: :update,
+        created_by_user:)
+  end
+
+  def update_aliases! tag, alias_names
+    alias_names = alias_names.uniq
+
+    affected_tags = [tag]
+
+    current_aliases = tag.tag_name.aliases.to_a
+
+    current_aliases.each do |alias_tag_name|
+      next if alias_names.include?(alias_tag_name.name)
+
+      affected_tags << alias_tag_name.canonical&.tag
+    end
+
+    alias_names.each do |alias_name|
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      affected_tags << alias_tag_name.canonical&.tag
+    end
+
+    affected_tags.compact.uniq.each do |affected_tag|
+      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user)
+    end
+
+    current_aliases.each do |alias_tag_name|
+      next if alias_names.include?(alias_tag_name.name)
+
+      alias_tag_name.update!(canonical: nil)
+    end
+
+    alias_names.each do |alias_name|
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      alias_tag_name.update!(canonical: tag.tag_name)
+    end
+
+    affected_tags.compact.uniq.each do |affected_tag|
+      record_tag_version!(affected_tag, event_type: :update, created_by_user: current_user)
+    end
+  end
+
+  def update_parent_tags! tag, parent_names
+    parent_tags = Tag.normalise_tags!(parent_names, with_tagme: false,
+                                                    with_no_deerjikist: false,
+                                                    deny_nico: true)
+
+    old_parent_tags = tag.parents.to_a
+
+    TagVersioning.record_tag_snapshots!((old_parent_tags + parent_tags).uniq,
+                                        created_by_user: current_user)
+
+    tag.reversed_tag_implications.destroy_all
+
+    parent_tags.each do |parent_tag|
+      next if parent_tag == tag
+
+      TagImplication.create!(tag:, parent_tag:)
+    end
+  end
+
+  def normalise_deerjikist_code platform, code
+    return code if platform != 'youtube' || code[0] != '@'
+
+    url = "https://www.youtube.com/#{ code }"
+
+    html = Net::HTTP.get(URI(url))
+
+    canonical = html[
+        /<link rel="canonical" href="https:\/\/www\.youtube\.com\/channel\/(UC[a-zA-Z0-9_-]{22})"/,
+        1]
+    return canonical if canonical
+
+    html[/"channelId":"(UC[a-zA-Z0-9_-]{22})"/, 1] || html[/\bUC[a-zA-Z0-9_-]{22}\b/]
+  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

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

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

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

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

backend/app/controllers/users_controller.rb

@@ -1,18 +1,22 @@
 class UsersController < ApplicationController
   def create
-    user = User.create!(inheritance_code: SecureRandom.uuid, role: 'guest')
+    user = nil
+    User.transaction do
+      user = User.create!(inheritance_code: SecureRandom.uuid, role: :guest)
+      attach_ip_address!(user)
+    end
+
     render json: { code: user.inheritance_code,
-                   user: user.slice(:id, :name, :inheritance_code, :role) }
+                   user: user.slice(:id, :name, :inheritance_code, :role) },
+           status: :created
   end
 
   def verify
-    ip_bin = IPAddr.new(request.remote_ip).hton
-    ip_address = IpAddress.find_or_create_by!(ip_address: ip_bin)
-
     user = User.find_by(inheritance_code: params[:code])
     return render json: { valid: false } unless user
+    return head :forbidden if user.banned?
 
-    UserIp.find_or_create_by!(user:, ip_address:)
+    attach_ip_address!(user)
 
     render json: { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
   end
@@ -38,12 +42,21 @@ 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: :created
+      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
+
+  private
+
+  def attach_ip_address! user
+    ip_bin = IPAddr.new(request.remote_ip).hton
+    ip_address = IpAddress.create_or_find_by!(ip_address: ip_bin)
+
+    UserIp.create_or_find_by!(user:, ip_address:)
+  end
 end

backend/app/controllers/wiki_pages_controller.rb

@@ -46,7 +46,7 @@ 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
@@ -56,7 +56,7 @@ class WikiPagesController < ApplicationController
     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)
@@ -85,22 +85,27 @@ class WikiPagesController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    name = params[:title]&.strip
+    title = params[:title].to_s.strip
     body = params[:body].to_s
-
-    return head :unprocessable_entity if name.blank? || body.blank?
-
-    tag_name = TagName.find_undiscard_or_create_by!(name:)
-    page = WikiPage.new(tag_name:, created_user: current_user, updated_user: current_user)
-    if page.save
     message = params[:message].presence
-      Wiki::Commit.content!(page:, body:, created_user: current_user, message:)
+
+    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)
+
+    page =
+        Wiki::Commit.create_content!(
+            tag_name:,
+            body:,
+            created_by_user: current_user,
+            message:)
 
     render json: WikiPageRepr.base(page), status: :created
-    else
-      render json: { errors: page.errors.full_messages },
-             status: :unprocessable_entity
-    end
+  rescue ActiveRecord::RecordInvalid => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
   end
 
   def update
@@ -110,15 +115,25 @@ 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 = page.current_revision.id
+    base_revision_id = params[:base_revision_id].presence
 
-    if params[:title].present? && params[:title].strip != page.title
-      return head :unprocessable_entity
+    ApplicationRecord.transaction do
+      page.lock!
+
+      old_title = page.title
+
+      tag = Tag.find_by(tag_name_id: page.tag_name_id)
+
+      if tag && title != old_title
+        TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
       end
 
+      page.tag_name.update!(name: title) if title != old_title
+
       message = params[:message].presence
       Wiki::Commit.content!(page:,
                             body:,
@@ -126,6 +141,12 @@ class WikiPagesController < ApplicationController
                             message:,
                             base_revision_id:)
 
+      if tag && title != old_title
+        tag.reload
+        TagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+      end
+    end
+
     head :ok
   end
 

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

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

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

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_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 if new_record?
+
+    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

backend/app/models/gekanator_question_suggestion.rb

@@ -0,0 +1,25 @@
+class GekanatorQuestionSuggestion < ApplicationRecord
+  MAX_QUESTIONS_PER_GAME = 3
+  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] }
+  validate :question_suggestion_limit_per_game, on: :create
+
+  private
+
+  def question_suggestion_limit_per_game
+    return if gekanator_game_id.blank?
+
+    count = GekanatorQuestionSuggestion.where(gekanator_game_id:).count
+    if count >= MAX_QUESTIONS_PER_GAME
+      errors.add(:base, '質問追加数を超えてゐます．')
+    end
+  end
+end

backend/app/models/ip_address.rb

@@ -1,6 +1,10 @@
 class IpAddress < ApplicationRecord
   validates :ip_address, presence: true, length: { maximum: 16 }
-  validates :banned, inclusion: { in: [true, false] }
 
-  has_many :users
+  has_many :user_ips, dependent: :destroy
+  has_many :users, through: :user_ips
+
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 end

backend/app/models/my_discard.rb

@@ -1,7 +1,11 @@
 module MyDiscard
   extend ActiveSupport::Concern
 
-  included { include Discard::Model }
+  included do
+    include Discard::Model
+
+    default_scope -> { kept }
+  end
 
   class_methods do
     def find_undiscard_or_create_by! attrs, &block

backend/app/models/nico_tag_version.rb

@@ -0,0 +1,7 @@
+class NicoTagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  validates :name, presence: true
+end

backend/app/models/post.rb

@@ -1,7 +1,6 @@
 class Post < ApplicationRecord
   require 'mini_magick'
 
-  belongs_to :parent, class_name: 'Post', optional: true, foreign_key: 'parent_id'
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
@@ -12,9 +11,36 @@ class Post < ApplicationRecord
   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',
+           foreign_key: :post_id,
+           dependent: :destroy,
+           inverse_of: :post
+  has_many :parents, through: :parent_post_implications, source: :parent_post
+
+  has_many :child_post_implications,
+           class_name: 'PostImplication',
+           foreign_key: :parent_post_id,
+           dependent: :destroy,
+           inverse_of: :parent_post
+  has_many :children, through: :child_post_implications, source: :post
 
   has_one_attached :thumbnail
 
+  attribute :version_no, :integer, default: 1
+
   before_validation :normalise_url
 
   validates :url, presence: true, uniqueness: true
@@ -22,17 +48,29 @@ class Post < ApplicationRecord
   validate :validate_original_created_range
   validate :url_must_be_http_url
 
+  def parent_posts = parents
+
+  def child_posts = children
+
+  def sibling_posts
+    parent_post_ids = parent_posts.order(:id).pluck(:id)
+
+    parent_post_ids.to_h { [_1, PostImplication.where(parent_post: _1).map(&:post)] }
+  end
+
   def as_json options = { }
-    super(options).merge({ thumbnail: thumbnail.attached? ?
+    super(options).merge(thumbnail: thumbnail.attached? ?
                                     Rails.application.routes.url_helpers.rails_blob_url(
                                         thumbnail, only_path: false) :
-                                      nil })
+                                    nil)
   rescue
     super(options).merge(thumbnail: nil)
   end
 
   def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
 
+  def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
+
   def related limit: nil
     ids = post_similarities.order(cos: :desc)
     ids = ids.limit(limit) if limit
@@ -67,7 +105,7 @@ 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
 

backend/app/models/post_implication.rb

@@ -0,0 +1,19 @@
+class PostImplication < ApplicationRecord
+  self.primary_key = :post_id, :parent_post_id
+
+  belongs_to :post, inverse_of: :parent_post_implications
+  belongs_to :parent_post, class_name: 'Post', inverse_of: :child_post_implications
+
+  validates :post_id, presence: true, uniqueness: { scope: :parent_post_id }
+  validates :parent_post_id, presence: true
+
+  validate :parent_post_mustnt_be_itself
+
+  private
+
+  def parent_post_mustnt_be_itself
+    if parent_post_id == post_id
+      errors.add :parent_post_id, '親投稿に同じ投稿を設定することはできません．'
+    end
+  end
+end

backend/app/models/post_version.rb

@@ -1,29 +1,13 @@
 class PostVersion < ApplicationRecord
-  before_update do
-    raise ActiveRecord::ReadOnlyRecord, '版は更新できません．'
-  end
-
-  before_destroy do
-    raise ActiveRecord::ReadOnlyRecord, '版は削除できません．'
-  end
+  include VersionRecord
 
   belongs_to :post
   belongs_to :parent, class_name: 'Post', optional: true
-  belongs_to :created_by_user, class_name: 'User', optional: true
 
-  enum :event_type, { create: 'create',
-                      update: 'update',
-                      discard: 'discard',
-                      restore: 'restore' }, prefix: true, validate: true
-
-  validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
-  validates :event_type, presence: true, inclusion: { in: event_types.keys }
   validates :url, presence: true
 
   validate :validate_original_created_range
 
-  scope :chronological, -> { order(:version_no, :id) }
-
   private
 
   def validate_original_created_range

backend/app/models/tag.rb

@@ -8,8 +8,6 @@ class Tag < ApplicationRecord
     ;
   end
 
-  default_scope -> { kept }
-
   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'
@@ -36,9 +34,14 @@ class Tag < ApplicationRecord
   has_many :deerjikists, dependent: :delete_all
   has_many :materials
 
+  has_many :tag_versions
+  has_many :nico_tag_versions
+
   belongs_to :tag_name
   delegate :wiki_page, to: :tag_name
 
+  attribute :version_no, :integer, default: 1
+
   delegate :name, to: :tag_name, allow_nil: true
   validates :tag_name, presence: true
 
@@ -78,27 +81,16 @@ class Tag < ApplicationRecord
 
   def material_id = materials.first&.id
 
-  def self.tagme
-    @tagme ||= find_or_create_by_tag_name!('タグ希望', category: :meta)
-  end
+  def has_deerjikists = deerjikists.loaded? ? deerjikists.any? : deerjikists.exists?
 
-  def self.bot
-    @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
-  end
+  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)
+  def self.no_deerjikist = find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
+  def self.video = find_or_create_by_tag_name!('動画', category: :meta)
+  def self.niconico = find_or_create_by_tag_name!('ニコニコ', category: :meta)
+  def self.youtube = find_or_create_by_tag_name!('YouTube', category: :meta)
 
-  def self.no_deerjikist
-    @no_deerjikist ||= find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
-  end
-
-  def self.video
-    @video ||= find_or_create_by_tag_name!('動画', category: :meta)
-  end
-
-  def self.niconico
-    @niconico ||= find_or_create_by_tag_name!('ニコニコ', category: :meta)
-  end
-
-  def self.normalise_tags tag_names, with_tagme: true,
+  def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
                                       deny_nico: true
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
@@ -152,21 +144,25 @@ class Tag < ApplicationRecord
     retry
   end
 
-  def self.merge_tags! target_tag, source_tags
+  def self.merge_tags! target_tag, source_tags, created_by_user: nil
     target_tag => Tag
 
     affected_post_ids = Set.new
 
     Tag.transaction do
+      TagVersioning.ensure_snapshot!(target_tag, created_by_user:)
+
       Array(source_tags).compact.uniq.each do |source_tag|
         source_tag => Tag
 
         next if source_tag == target_tag
 
+        TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
+
         source_tag.post_tags.kept.find_each do |source_pt|
           post_id = source_pt.post_id
           affected_post_ids << post_id
-          source_pt.discard_by!(nil)
+          source_pt.discard_by!(created_by_user)
           unless PostTag.kept.exists?(post_id:, tag: target_tag)
             PostTag.create!(post_id:, tag: target_tag)
           end
@@ -178,6 +174,7 @@ class Tag < ApplicationRecord
           raise ActiveRecord::RecordInvalid.new(source_tag_name)
         end
 
+        TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
         source_tag.discard!
 
         if source_tag.nico?
@@ -186,10 +183,13 @@ class Tag < ApplicationRecord
           source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
                                          updated_at: Time.current)
         end
+
+        TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
       end
 
       Post.where(id: affected_post_ids.to_a).find_each do |post|
-        PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user:)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user:)
       end
 
       # 投稿件数を再集計
@@ -199,6 +199,14 @@ class Tag < ApplicationRecord
     target_tag.reload
   end
 
+  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
+
+  def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
+
+  def snapshot_linked_tag_names
+    linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  end
+
   private
 
   def nico_tag_name_must_start_with_nico

backend/app/models/tag_name.rb

@@ -1,8 +1,6 @@
 class TagName < ApplicationRecord
   include MyDiscard
 
-  default_scope -> { kept }
-
   has_one :tag
   has_one :wiki_page
 

backend/app/models/tag_version.rb

@@ -0,0 +1,15 @@
+class TagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  enum :category, { deerjikist: 'deerjikist',
+                    meme: 'meme',
+                    character: 'character',
+                    general: 'general',
+                    material: 'material',
+                    meta: 'meta' }, validate: true
+
+  validates :name, presence: true
+  validates :category, presence: true
+end

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'

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

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

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

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

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

backend/app/models/user.rb

@@ -4,7 +4,6 @@ class User < ApplicationRecord
   validates :name, length: { maximum: 255 }
   validates :inheritance_code, presence: true, length: { maximum: 64 }
   validates :role, presence: true, inclusion: { in: roles.keys }
-  validates :banned, inclusion: { in: [true, false] }
 
   has_many :created_posts,
            class_name: 'Post', foreign_key: :uploaded_user_id, dependent: :nullify
@@ -19,5 +18,10 @@ class User < ApplicationRecord
            class_name: 'WikiPage', foreign_key: :updated_user_id, dependent: :nullify
 
   def viewed?(post) = user_post_views.exists?(post_id: post.id)
+
   def gte_member? = member? || admin?
+
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 end

backend/app/models/version_record.rb

@@ -0,0 +1,19 @@
+module VersionRecord
+  extend ActiveSupport::Concern
+
+  def readonly? = persisted?
+
+  included do
+    belongs_to :created_by_user, class_name: 'User', optional: true
+
+    enum :event_type, { create: 'create',
+                        update: 'update',
+                        discard: 'discard',
+                        restore: 'restore' }, prefix: true, validate: true
+
+    validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
+    validates :event_type, presence: true
+
+    scope :chronological, -> { order(:version_no, :id) }
+  end
+end

backend/app/models/wiki_page.rb

@@ -4,8 +4,6 @@ require 'set'
 class WikiPage < ApplicationRecord
   include MyDiscard
 
-  default_scope -> { kept }
-
   has_many :wiki_revisions, dependent: :destroy
   belongs_to :created_user, class_name: 'User'
   belongs_to :updated_user, class_name: 'User'
@@ -15,8 +13,13 @@ class WikiPage < ApplicationRecord
            foreign_key: :redirect_page_id,
            dependent: :nullify
 
+  has_many :wiki_versions
+
+  attribute :version_no, :integer, default: 1
+
   belongs_to :tag_name
   validates :tag_name, presence: true
+  validates :body, presence: true
 
   def title = tag_name.name
 
@@ -26,11 +29,6 @@ class WikiPage < ApplicationRecord
 
   def current_revision = wiki_revisions.order(id: :desc).first
 
-  def body
-    rev = current_revision
-    rev.body if rev&.content?
-  end
-
   def resolve_redirect limit: 10
     page = self
     visited = Set.new

backend/app/models/wiki_version.rb

@@ -0,0 +1,8 @@
+class WikiVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :wiki_page
+
+  validates :title, presence: true
+  validates :body, presence: true
+end

backend/app/representations/post_repr.rb

@@ -2,19 +2,65 @@
 
 
 module PostRepr
-  BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE } }.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.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

backend/app/representations/tag_repr.rb

@@ -3,15 +3,18 @@
 
 module TagRepr
   BASE = { only: [:id, :category, :post_count, :created_at, :updated_at],
-           methods: [:name, :has_wiki, :material_id] }.freeze
+           methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
 
   module_function
 
   def base tag
-    tag.as_json(BASE)
+    tag.as_json(BASE).merge(aliases: tag.snapshot_aliases,
+                            parents: tag.parents.map { _1.as_json(BASE) })
   end
 
-  def many tags
-    tags.map { |t| base(t) }
+  def inline tag
+    tag.as_json(BASE).merge(aliases: [], parents: [])
   end
+
+  def many(tags) = tags.map { |t| base(t) }
 end

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

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

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

backend/app/services/nico_tag_version_recorder.rb

@@ -0,0 +1,19 @@
+class NicoTagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = NicoTagVersion
+  def version_association = :nico_tag_versions
+  def record_key = :tag
+
+  def snapshot_attributes
+    { name: @record.name, linked_tags: @record.snapshot_linked_tag_names.join(' ') }
+  end
+end

backend/app/services/post_version_recorder.rb

@@ -1,57 +1,31 @@
-class PostVersionRecorder
+class PostVersionRecorder < VersionRecorder
   def self.record! post:, event_type:, created_by_user:
     new(post:, event_type:, created_by_user:).record!
   end
 
   def initialize post:, event_type:, created_by_user:
-    @post = post
-    @event_type = event_type
-    @created_by_user = created_by_user
+    super(record: post, event_type:, created_by_user:)
   end
 
-  def record!
-    @post.with_lock do
-      latest = @post.post_versions.order(version_no: :desc).first
-      attrs = snapshot_attributes
+  def self.ensure_snapshot! post, created_by_user:
+    return if post.post_versions.exists?
 
-      return latest if @event_type == :update && latest && same_snapshot?(latest, attrs)
-
-      PostVersion.create!(
-          post: @post,
-          version_no: (latest&.version_no || 0) + 1,
-          event_type: @event_type,
-          title: attrs[:title],
-          url: attrs[:url],
-          thumbnail_base: attrs[:thumbnail_base],
-          tags: attrs[:tags],
-          parent: attrs[:parent],
-          original_created_from: attrs[:original_created_from],
-          original_created_before: attrs[:original_created_before],
-          created_at: Time.current,
-          created_by_user: @created_by_user)
-    end
+    record!(post:, event_type: :create, created_by_user:)
   end
 
   private
 
-  def snapshot_attributes
-    { title: @post.title,
-      url: @post.url,
-      thumbnail_base: @post.thumbnail_base,
-      tags: @post.snapshot_tag_names.join(' '),
-      parent: @post.parent,
-      original_created_from: @post.original_created_from,
-      original_created_before: @post.original_created_before }
-  end
+  def version_class = PostVersion
+  def version_association = :post_versions
+  def record_key = :post
 
-  def same_snapshot? version, attrs
-    true &&
-        version.title == attrs[:title] &&
-        version.url == attrs[:url] &&
-        version.thumbnail_base == attrs[:thumbnail_base] &&
-        version.tags == attrs[:tags] &&
-        version.parent_id == attrs[:parent]&.id &&
-        version.original_created_from == attrs[:original_created_from] &&
-        version.original_created_before == attrs[:original_created_before]
+  def snapshot_attributes
+    { title: @record.title,
+      url: @record.url,
+      thumbnail_base: @record.thumbnail_base,
+      tags: @record.snapshot_tag_names.join(' '),
+      parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
+      original_created_from: @record.original_created_from,
+      original_created_before: @record.original_created_before }
   end
 end

backend/app/services/tag_version_recorder.rb

@@ -0,0 +1,22 @@
+class TagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = TagVersion
+  def version_association = :tag_versions
+  def record_key = :tag
+
+  def snapshot_attributes
+    { name: @record.name,
+      category: @record.category,
+      aliases: @record.snapshot_aliases.join(' '),
+      parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
+  end
+end

backend/app/services/tag_versioning.rb

@@ -0,0 +1,38 @@
+class TagVersioning
+  def self.record! tag, event_type:, created_by_user:
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    else
+      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    end
+  end
+
+  def self.ensure_snapshot! tag, created_by_user:
+    if tag.nico?
+      return if tag.nico_tag_versions.exists?
+
+      NicoTagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    else
+      return if tag.tag_versions.exists?
+
+      TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    end
+  end
+
+  def self.record_tag_snapshot! tag, created_by_user:
+    event_type =
+        if tag.nico?
+          tag.nico_tag_versions.exists? ? :update : :create
+        else
+          tag.tag_versions.exists? ? :update : :create
+        end
+
+    record!(tag, event_type:, created_by_user:)
+  end
+
+  def self.record_tag_snapshots! tags, created_by_user:
+    tags.each do |tag|
+      record_tag_snapshot!(tag, created_by_user:)
+    end
+  end
+end

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

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

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

backend/app/services/version_recorder.rb

@@ -0,0 +1,87 @@
+class VersionRecorder
+  EVENT_TYPES = ['create', 'update', 'discard', 'restore'].freeze
+
+  def initialize record:, event_type:, created_by_user:
+    @record = record
+    @event_type = event_type.to_s
+    @created_by_user = created_by_user
+
+    validate_event_type!
+  end
+
+  def record!
+    raise "#{ record_class.name } must be persisted" unless @record.persisted?
+
+    ApplicationRecord.transaction do
+      @record = record_class.unscoped.lock.find(@record.id)
+      latest = latest_version
+
+      validate_version_sequence!(latest)
+
+      attrs = snapshot_attributes
+
+      if @event_type == 'update' && latest && same_snapshot?(latest, attrs)
+        return latest
+      end
+
+      version = version_class.create!(
+          base_attributes(latest).merge(record_key => @record).merge(attrs))
+
+      update_record_version_no!(version.version_no)
+
+      version
+    end
+  end
+
+  private
+
+  def latest_version = versions.order(version_no: :desc).first
+
+  def versions = @record.public_send(version_association)
+
+  def base_attributes latest
+    { version_no: (latest&.version_no || 0) + 1,
+      event_type: @event_type,
+      created_at: Time.current,
+      created_by_user: @created_by_user }
+  end
+
+  def update_record_version_no! version_no
+    @record.update_columns(version_no:)
+    @record.version_no = version_no
+  end
+
+  def validate_version_sequence! latest
+    if !(latest) && @event_type != 'create'
+      raise "#{ version_class.name } first event must be create"
+    end
+
+    if @event_type == 'create' && latest
+      raise "#{ version_class.name } create event already exists"
+    end
+
+    return unless latest
+
+    if @record.version_no != latest.version_no
+      raise ("#{ record_class.name }##{ @record.id } version_no is #{ @record.version_no }, " +
+             "but latest #{ version_class.name } version_no is #{ latest.version_no }")
+    end
+  end
+
+  def same_snapshot? version, attrs
+    attrs.all? { |k, v| version.public_send(k) == v }
+  end
+
+  def validate_event_type!
+    return if EVENT_TYPES.include?(@event_type)
+
+    raise ArgumentError, "Invalid event_type: #{ @event_type }"
+  end
+
+  def version_class = raise NotImplementedError
+  def version_association = raise NotImplementedError
+  def record_key = raise NotImplementedError
+  def snapshot_attributes = raise NotImplementedError
+
+  def record_class = @record.class
+end

backend/app/services/wiki/commit.rb

@@ -7,6 +7,31 @@ module Wiki
       ;
     end
 
+    def self.create_content! tag_name:, body:, created_by_user:, message: nil
+      normalised = normalise_body(body)
+
+      page = WikiPage.new(tag_name:,
+                          body: normalised,
+                          created_user: created_by_user,
+                          updated_user: created_by_user)
+
+      if normalised.blank?
+        page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, page
+      end
+
+      ActiveRecord::Base.transaction do
+        page.save!
+
+        new(page:, created_user: created_by_user).content!(
+            body: normalised,
+            message:,
+            base_revision_id: nil)
+
+        page
+      end
+    end
+
     def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
       new(page:, created_user:).content!(body:, message:, base_revision_id:)
     end
@@ -21,7 +46,12 @@ module Wiki
     end
 
     def content! body:, message:, base_revision_id:
-      normalised = normalise_body(body)
+      normalised = self.class.normalise_body(body)
+      if normalised.blank?
+        @page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, @page
+      end
+
       lines = split_lines(normalised)
 
       line_shas = lines.map { |line| Digest::SHA256.hexdigest(line) }
@@ -37,10 +67,19 @@ module Wiki
           current_id = @page.wiki_revisions.maximum(:id)
           if current_id && current_id != base_revision_id.to_i
             raise Conflict,
-                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
+                "競合が発生してゐます" +
+                "（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
           end
         end
 
+        @page.update!(body: normalised)
+
+        WikiVersionRecorder.record!(
+            page: @page,
+            event_type: @page.wiki_versions.exists? ? :update : :create,
+            reason: message,
+            created_by_user: @created_user)
+
         rev = WikiRevision.create!(
             wiki_page:        @page,
             base_revision_id:,
@@ -54,65 +93,45 @@ module Wiki
         rows = line_ids.each_with_index.map do |line_id, pos|
           { wiki_revision_id: rev.id, wiki_line_id: line_id, position: pos }
         end
-        WikiRevisionLine.insert_all!(rows)
+        WikiRevisionLine.insert_all!(rows) if rows.any?
 
         rev
       end
     end
 
-    def redirect! redirect_page:, message:, base_revision_id:
-      ActiveRecord::Base.transaction do
-        @page.lock!
+    def redirect!(redirect_page:, message:, base_revision_id:) = raise '廃止しました．'
 
-        if base_revision_id.present?
-          current_id = @page.wiki_revisions.maximum(:id)
-          if current_id && current_id != base_revision_id.to_i
-            raise Conflict,
-                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
-          end
-        end
-
-        WikiRevision.create!(
-            wiki_page:        @page,
-            base_revision_id:,
-            created_user:     @created_user,
-            kind:             :redirect,
-            redirect_page:,
-            message:,
-            lines_count:      0,
-            tree_sha256:      nil)
-      end
+    def self.normalise_body body
+      s = body.to_s
+      s.gsub!(/\r\n?/, "\n")
+      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
+      s.gsub(/\n+$/, '')
     end
 
     private
 
-    def normalise_body body
-      s = body.to_s
-      s.gsub!("\r\n", "\n")
-      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
-    end
-
-    def split_lines body
-      body.split("\n")
-    end
+    def split_lines(body) = body.split("\n")
 
     def upsert_lines! lines, line_shas
       now = Time.current
 
       id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
 
-      missing_rows = []
+      missing_by_sha = { }
+
       line_shas.each_with_index do |sha, i|
         next if id_by_sha.key?(sha)
+        next if missing_by_sha.key?(sha)
 
-        missing_rows << { sha256:     sha,
+        missing_by_sha[sha] = {
+            sha256:     sha,
             body:       lines[i],
             created_at: now,
             updated_at: now }
       end
 
-      if missing_rows.any?
-        WikiLine.upsert_all(missing_rows)
+      if missing_by_sha.any?
+        WikiLine.upsert_all(missing_by_sha.values)
         id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
       end
 

backend/app/services/wiki_version_recorder.rb

@@ -0,0 +1,21 @@
+class WikiVersionRecorder < VersionRecorder
+  def self.record! page:, event_type:, reason: nil, created_by_user:
+    new(page:, event_type:, reason:, created_by_user:).record!
+  end
+
+  def initialize page:, event_type:, reason: nil, created_by_user:
+    @reason = reason
+    super(record: page, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = WikiVersion
+  def version_association = :wiki_versions
+  def record_key = :wiki_page
+
+  def snapshot_attributes = {
+      title: @record.title,
+      body: @record.body,
+      reason: @reason }
+end

backend/app/services/youtube/api_client.rb

@@ -0,0 +1,73 @@
+require 'json'
+require 'net/http'
+require 'uri'
+
+
+module Youtube
+  class ApiClient
+    ENDPOINT = 'https://www.googleapis.com/youtube/v3'
+
+    def initialize api_key: ENV.fetch('YOUTUBE_API_KEY')
+      @api_key = api_key
+    end
+
+    def search_videos q:, published_after: nil, published_before: nil, page_token: nil
+      get_json('/search', {
+          part:           'snippet',
+          type:           'video',
+          q:,
+          order:          'date',
+          maxResults:     50,
+          regionCode:     'JP',
+          relevanceLanguage: 'ja',
+          publishedAfter: published_after&.iso8601,
+          publishedBefore: published_before&.iso8601,
+          pageToken:      page_token }.compact)
+    end
+
+    def videos ids
+      return { 'items' => [] } if ids.empty?
+
+      get_json('/videos', part: 'snippet,status,contentDetails', id: ids.join(','))
+    end
+
+    def playlist_items playlist_id:, page_token: nil
+      get_json('/playlistItems', {
+          part:       'snippet,contentDetails,status',
+          playlistId: playlist_id,
+          maxResults: 50,
+          pageToken:  page_token }.compact)
+    end
+
+    def channel id: nil, handle: nil
+      raise ArgumentError, 'id or handle is required' if id.present? == handle.present?
+
+      params = { part: 'snippet,contentDetails' }
+      params[:id] = id if id.present?
+      params[:forHandle] = handle if handle.present?
+
+      get_json('/channels', params)
+    end
+
+    private
+
+    def get_json path, params
+      uri = URI(ENDPOINT + path)
+      uri.query = URI.encode_www_form(params.merge(key: @api_key))
+
+      response = Net::HTTP.start(uri.host,
+                                 uri.port,
+                                 use_ssl: true,
+                                 open_timeout: 10,
+                                 read_timeout: 30) do |http|
+        http.get(uri)
+      end
+
+      unless response.is_a?(Net::HTTPSuccess)
+        raise "YouTube API error: #{ response.code } #{ response.body }"
+      end
+
+      JSON.parse(response.body)
+    end
+  end
+end

backend/app/services/youtube/sync.rb

@@ -0,0 +1,168 @@
+require 'open-uri'
+require 'set'
+require 'time'
+
+
+module Youtube
+  class Sync
+    def initialize client: ApiClient.new
+      @client = client
+    end
+
+    def sync!
+      video_ids = discover_video_ids
+      return if video_ids.empty?
+
+      video_ids.each_slice(50) do |ids|
+        @client.videos(ids).fetch('items', []).each do |item|
+          sync_video!(VideoItem.new(item))
+        end
+      end
+    end
+
+    private
+
+    def discover_video_ids
+      ids = Set.new
+
+      query_terms.each do |q|
+        response = @client.search_videos(q:, published_after: sync_since)
+
+        response.fetch('items', []).each do |item|
+          video_id = item.dig('id', 'videoId')
+          ids << video_id if video_id.present?
+        end
+      end
+
+      playlist_ids.each do |playlist_id|
+        each_playlist_item(playlist_id) do |item|
+          video_id = item.dig('contentDetails', 'videoId')
+          video_id ||= item.dig('snippet', 'resourceId', 'videoId')
+
+          ids << video_id if video_id.present?
+        end
+      end
+
+      ids.to_a
+    end
+
+    def sync_video! video
+      post = Post.where('url REGEXP ?', youtube_url_regexp(video.id)).first
+
+      original_created_from = video.published_at.change(sec: 0)
+      original_created_before = original_created_from + 1.minute
+
+      post_created = false
+      post_changed = false
+
+      if post
+        post.assign_attributes(title: video.title,
+                               original_created_from:,
+                               original_created_before:,
+                               thumbnail_base: video.thumbnail_url)
+
+        post_changed = post.changed?
+        post.save! if post_changed
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+      else
+        post_created = true
+        post = Post.create!(
+            title: video.title,
+            url: video.url,
+            thumbnail_base: video.thumbnail_url,
+            uploaded_user_id: nil,
+            original_created_from:,
+            original_created_before:)
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+
+        sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.youtube.id, Tag.video.id])
+      end
+
+      kept_tag_ids = post.tags.pluck(:id).to_set
+      desired_tag_ids = kept_tag_ids.to_a
+
+      deerjikist = Deerjikist.find_by(platform: :youtube, code: video.channel_id)
+      if deerjikist
+        desired_tag_ids.delete(Tag.no_deerjikist.id)
+        desired_tag_ids << deerjikist.tag_id
+      elsif post.tags.where(category: :deerjikist).none?
+        desired_tag_ids << Tag.no_deerjikist.id
+      end
+
+      desired_tag_ids.uniq!
+
+      sync_post_tags!(post, desired_tag_ids, current_tag_ids: kept_tag_ids)
+
+      if post_created
+        PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
+      elsif post_changed || kept_tag_ids != desired_tag_ids.to_set
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
+      end
+    end
+
+    def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
+      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      desired_tag_ids = desired_tag_ids.compact.to_set
+
+      to_add = desired_tag_ids - current_tag_ids
+      to_remove = current_tag_ids - desired_tag_ids
+
+      Tag.where(id: to_add.to_a).find_each do |tag|
+        begin
+          PostTag.create!(post:, tag:)
+        rescue ActiveRecord::RecordNotUnique
+          ;
+        end
+      end
+
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+        pt.discard_by!(nil)
+      end
+    end
+
+    def attach_thumbnail_if_needed! post, thumbnail_url
+      return if post.thumbnail.attached?
+      return if thumbnail_url.blank?
+
+      post.thumbnail.attach(
+          io:           URI.open(thumbnail_url),
+          filename:     File.basename(URI.parse(thumbnail_url).path),
+          content_type: 'image/jpeg')
+
+      post.resized_thumbnail!
+    end
+
+    def youtube_url_regexp id
+      escaped = Regexp.escape(id)
+      "(youtube\\.com/watch\\?v=#{ escaped }|youtu\\.be/#{ escaped })([^A-Za-z0-9_-]|$)"
+    end
+
+    def query_terms = ['ぼざろクリーチャーシリーズ', '伊地知ニジカ', '伊地知虹鹿']
+
+    def playlist_ids
+      ['PLrOch4zHkI5vu29b-f9umUQQ4tQkuWLPX',
+       'PLrOch4zHkI5vOK0RaytQq6PbucxQkkL0K',
+       'PLrOch4zHkI5tdwm9vSegiDQJOM-hgpcOC']
+    end
+
+    def sync_since = 14.days.ago
+
+    def each_playlist_item playlist_id
+      page_token = nil
+
+      loop do
+        response = @client.playlist_items(playlist_id:, page_token:)
+
+        response.fetch('items', []).each do |item|
+          yield item
+        end
+
+        page_token = response['nextPageToken']
+        break if page_token.blank?
+      end
+    end
+  end
+end

backend/app/services/youtube/video_item.rb

@@ -0,0 +1,32 @@
+require 'time'
+
+
+module Youtube
+  class VideoItem
+    attr_reader :id, :title, :channel_id, :published_at, :thumbnail_url, :raw_tags
+
+    def initialize item
+      snippet = item.fetch('snippet')
+
+      @id = item.fetch('id')
+      @title = snippet['title']
+      @channel_id = snippet['channelId']
+      @published_at = Time.iso8601(snippet['publishedAt'])
+      @thumbnail_url = pick_thumbnail(snippet['thumbnails'] || { })
+      @raw_tags = snippet['tags'] || []
+    end
+
+    def url = "https://www.youtube.com/watch?v=#{ @id }"
+
+    private
+
+    def pick_thumbnail thumbnails
+      ['maxres', 'standard', 'high', 'medium', 'default'].each do |key|
+        url = thumbnails.dig(key, 'url')
+        return url if url.present?
+      end
+
+      nil
+    end
+  end
+end

backend/config/routes.rb

@@ -6,10 +6,11 @@ Rails.application.routes.draw do
     delete ':child_id', action: :destroy
   end
 
-  resources :tags, only: [:index, :show, :update] do
+  resources :tags, only: [:index, :show] do
     collection do
       get :autocomplete
       get :'with-depth', action: :with_depth
+      get :versions, to: 'tag_versions#index'
 
       scope :name do
         get ':name/deerjikists', action: :deerjikists_by_name
@@ -19,7 +20,11 @@ Rails.application.routes.draw do
     end
 
     member do
+      put '', action: :update_all
+      patch '', action: :update
+
       get :deerjikists
+      put :deerjikists, action: :update_deerjikists
     end
   end
 
@@ -58,6 +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
@@ -80,9 +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]

backend/config/schedule.rb

@@ -1,12 +1,27 @@
 env :PATH, '/root/.rbenv/shims:/root/.rbenv/bin:/usr/local/bin:/usr/bin:/bin'
 
+set :path, '/var/www/btrc-hub/backend'
+set :environment, 'production'
 set :output, standard: '/var/log/btrc_hub_nico_sync.log',
              error:    '/var/log/btrc_hub_nico_sync_err.log'
 
-every 1.day, at: '3:00 pm' do
+job_type :rake,
+         'cd :path && set -a && . /etc/btrc-hub/backend.env && set +a && ' \
+         ':environment_variable=:environment bundle exec rake :task --silent :output'
+
+every 1.day, at: '11:00 am' do
   rake 'nico:sync', environment: 'production'
 end
 
 every 1.day, at: '0:00 am' do
   rake 'post_similarity:calc', environment: 'production'
+  rake 'tag_similarity:calc', environment: 'production'
+end
+
+every 1.day, at: '7:50 am' do
+  rake 'nico:export', environment: 'production'
+end
+
+every :hour do
+  rake 'post:sync', environment: 'production'
 end

backend/db/migrate/20260409123700_create_post_versions.rb

@@ -2,15 +2,15 @@ require 'set'
 
 
 class CreatePostVersions < ActiveRecord::Migration[8.0]
-  class Post < ApplicationRecord
+  class Post < ActiveRecord::Base
     self.table_name = 'posts'
   end
 
-  class PostTag < ApplicationRecord
+  class PostTag < ActiveRecord::Base
     self.table_name = 'post_tags'
   end
 
-  class PostVersion < ApplicationRecord
+  class PostVersion < ActiveRecord::Base
     self.table_name = 'post_versions'
   end
 

backend/db/migrate/20260419035400_create_tag_versions.rb

@@ -0,0 +1,156 @@
+class CreateTagVersions < ActiveRecord::Migration[8.0]
+  class Tag < ActiveRecord::Base
+    self.table_name = 'tags'
+  end
+
+  class TagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  class TagImplication < ActiveRecord::Base
+    self.table_name = 'tag_implications'
+  end
+
+  class TagVersion < ActiveRecord::Base
+    self.table_name = 'tag_versions'
+  end
+
+  class NicoTagVersion < ActiveRecord::Base
+    self.table_name = 'nico_tag_versions'
+  end
+
+  class NicoTagRelation < ActiveRecord::Base
+    self.table_name = 'nico_tag_relations'
+  end
+
+  def up
+    create_table :tag_versions do |t|
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :name, null: false
+      t.string :category, null: false
+      t.text :aliases, null: false
+      t.text :parent_tag_ids, null: false
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }, index: false
+
+      t.index [:tag_id, :version_no], unique: true
+      t.index :created_at
+      t.index [:tag_id, :created_at], order: { created_at: :desc }
+      t.index [:created_by_user_id, :created_at], order: { created_at: :desc }
+      t.check_constraint 'version_no > 0',
+                         name: 'tag_versions_version_no_positive'
+    end
+
+    create_table :nico_tag_versions do |t|
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :name, null: false
+      t.text :linked_tags, null: false
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }, index: false
+
+      t.index [:tag_id, :version_no], unique: true
+      t.index :created_at
+      t.index [:tag_id, :created_at], order: { created_at: :desc }
+      t.index [:created_by_user_id, :created_at], order: { created_at: :desc }
+      t.check_constraint 'version_no > 0',
+                         name: 'nico_tag_versions_version_no_positive'
+    end
+
+    TagVersion.reset_column_information
+    say_with_time 'Backfilling tag_versions' do
+      Tag.where(discarded_at: nil)
+         .where.not(category: 'nico')
+         .find_in_batches(batch_size: 500) do |tags|
+        tag_ids = tags.map(&:id)
+
+        tag_implication_rows_by_tag_id =
+            TagImplication
+            .where(tag_id: tag_ids)
+            .pluck(:tag_id, :parent_tag_id)
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        tag_name_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+            .where(tags: { id: tag_ids })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object({ }) do |row, h|
+              h[row[0]] = row[1]
+            end
+
+        tag_alias_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.canonical_id')
+            .where(tags: { id: tag_ids })
+            .where(tag_names: { discarded_at: nil })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        TagVersion.insert_all(tags.map { |tag|
+          { tag_id: tag.id,
+            version_no: 1,
+            event_type: 'create',
+            name: tag_name_rows_by_tag_id[tag.id],
+            category: tag.category,
+            aliases: tag_alias_rows_by_tag_id[tag.id].sort.join(' '),
+            parent_tag_ids: tag_implication_rows_by_tag_id[tag.id].sort.join(' '),
+            created_at: tag.created_at,
+            created_by_user_id: nil }
+        })
+      end
+    end
+
+    NicoTagVersion.reset_column_information
+    say_with_time 'Backfilling nico_tag_versions' do
+      Tag.where(discarded_at: nil, category: 'nico')
+         .find_in_batches(batch_size: 500) do |tags|
+        tag_ids = tags.map(&:id)
+
+        tag_name_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+            .where(tags: { id: tag_ids })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object({ }) do |row, h|
+              h[row[0]] = row[1]
+            end
+
+        nico_tag_relation_rows_by_tag_id =
+            NicoTagRelation
+            .joins('INNER JOIN tags nico_tags ON nico_tags.id = nico_tag_relations.nico_tag_id')
+            .joins('INNER JOIN tags linked_tags ON linked_tags.id = nico_tag_relations.tag_id')
+            .joins('INNER JOIN tag_names ON tag_names.id = linked_tags.tag_name_id')
+            .where(nico_tags: { id: tag_ids })
+            .where(linked_tags: { discarded_at: nil })
+            .where(tag_names: { discarded_at: nil })
+            .pluck('nico_tags.id', 'tag_names.name')
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        NicoTagVersion.insert_all(tags.map { |tag|
+          { tag_id: tag.id,
+            version_no: 1,
+            event_type: 'create',
+            name: tag_name_rows_by_tag_id[tag.id],
+            linked_tags: nico_tag_relation_rows_by_tag_id[tag.id].sort.join(' '),
+            created_at: tag.created_at,
+            created_by_user_id: nil }
+        })
+      end
+    end
+  end
+
+  def down
+    drop_table :nico_tag_versions
+    drop_table :tag_versions
+  end
+end

backend/db/migrate/20260426120600_create_wiki_versions.rb

@@ -0,0 +1,91 @@
+class CreateWikiVersions < ActiveRecord::Migration[8.0]
+  class WikiPage < ActiveRecord::Base
+    self.table_name = 'wiki_pages'
+  end
+
+  class WikiRevision < ActiveRecord::Base
+    self.table_name = 'wiki_revisions'
+  end
+
+  class WikiRevisionLine < ActiveRecord::Base
+    self.table_name = 'wiki_revision_lines'
+  end
+
+  class WikiLine < ActiveRecord::Base
+    self.table_name = 'wiki_lines'
+  end
+
+  class WikiVersion < ActiveRecord::Base
+    self.table_name = 'wiki_versions'
+  end
+
+  class TagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  def up
+    add_column :wiki_pages, :body, :text, after: :tag_name_id
+
+    create_table :wiki_versions do |t|
+      t.references :wiki_page, null: false, foreign_key: true
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :title, null: false
+      t.text :body, null: false
+      t.text :reason
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }
+
+      t.index [:wiki_page_id, :version_no], unique: true
+      t.check_constraint 'version_no > 0',
+                         name: 'wiki_versions_version_no_positive'
+      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')",
+                         name: 'wiki_versions_event_type_valid'
+    end
+
+    WikiPage.reset_column_information
+    WikiVersion.reset_column_information
+
+    say_with_time 'Backfilling wiki_versions' do
+      WikiPage.find_each do |page|
+        base_revision_id = nil
+        version_no = 1
+        title = TagName.find(page.tag_name_id).name
+        body = nil
+        loop do
+          rev = WikiRevision.where(wiki_page_id: page.id).find_by(base_revision_id:)
+          break unless rev
+
+          body = WikiRevisionLine.where(wiki_revision_id: rev.id).order(:position).map { |wrl|
+            WikiLine.find(wrl.wiki_line_id).body
+          }.join("\n")
+
+          WikiVersion.create!(
+              wiki_page_id: page.id,
+              version_no:,
+              event_type: version_no == 1 ? 'create' : 'update',
+              title:,
+              body:,
+              reason: rev.message,
+              created_at: rev.created_at,
+              created_by_user_id: rev.created_user_id)
+
+          version_no += 1
+          base_revision_id = rev.id
+        end
+        if body
+          page.update!(body:)
+        else
+          page.destroy!
+        end
+      end
+    end
+
+    change_column_null :wiki_pages, :body, false
+  end
+
+  def down
+    drop_table :wiki_versions
+    remove_column :wiki_pages, :body
+  end
+end

backend/db/migrate/20260427214800_create_post_implications.rb

@@ -0,0 +1,24 @@
+class CreatePostImplications < ActiveRecord::Migration[8.0]
+  def up
+    create_table :post_implications, primary_key: [:post_id, :parent_post_id] do |t|
+      t.references :post, null: false, foreign_key: true, index: false
+      t.references :parent_post, null: false, foreign_key: { to_table: :posts }
+      t.timestamps
+
+      t.check_constraint 'post_id <> parent_post_id',
+                         name: 'chk_post_implications_no_self'
+    end
+
+    add_column :post_versions, :parent_post_ids, :text, null: false, after: :parent_id
+    remove_column :post_versions, :parent_id, :bigint
+    remove_reference :posts, :parent, foreign_key: { to_table: :posts }
+  end
+
+  def down
+    add_reference :posts, :parent, foreign_key: { to_table: :posts }, after: :thumbnail_base
+    add_column :post_versions, :parent_id, :bigint, after: :post_id
+    remove_column :post_versions, :parent_post_ids, :text
+
+    drop_table :post_implications
+  end
+end

backend/db/migrate/20260501153900_rename_banned_to_banned_at_in_users_and_ip_addresses.rb

@@ -0,0 +1,16 @@
+class RenameBannedToBannedAtInUsersAndIpAddresses < ActiveRecord::Migration[8.0]
+  def up
+    [:users, :ip_addresses].each do
+      add_column _1, :banned_at, :datetime, after: :banned
+      add_index _1, :banned_at
+      remove_column _1, :banned
+    end
+  end
+
+  def down
+    [:ip_addresses, :users].each do
+      add_column _1, :banned, :boolean, null: false, default: false, after: :banned_at
+      remove_column _1, :banned_at
+    end
+  end
+end

backend/db/migrate/20260507124000_add_version_no_to_posts.rb

@@ -0,0 +1,27 @@
+class AddVersionNoToPosts < ActiveRecord::Migration[8.0]
+  def up
+    add_column :posts, :version_no, :integer
+
+    execute <<~SQL
+      UPDATE
+        posts
+      SET
+        version_no = (
+          SELECT
+            MAX(version_no)
+          FROM
+            post_versions
+          WHERE
+            post_id = posts.id)
+    SQL
+
+    change_column_null :posts, :version_no, false
+
+    add_check_constraint :posts, 'version_no > 0', name: 'chk_posts_version_no_positive'
+  end
+
+  def down
+    remove_check_constraint :posts, name: 'chk_posts_version_no_positive'
+    remove_column :posts, :version_no
+  end
+end

backend/db/migrate/20260507211600_add_version_no_to_tags.rb

@@ -0,0 +1,37 @@
+class AddVersionNoToTags < ActiveRecord::Migration[8.0]
+  def up
+    add_column :tags, :version_no, :integer
+
+    execute <<~SQL
+      UPDATE
+        tags
+      SET
+        version_no = (
+          CASE category
+          WHEN 'nico' THEN
+            (SELECT
+               MAX(version_no)
+             FROM
+               nico_tag_versions
+             WHERE
+               tag_id = tags.id)
+          ELSE
+            (SELECT
+               MAX(version_no)
+             FROM
+               tag_versions
+             WHERE
+               tag_id = tags.id)
+          END)
+    SQL
+
+    change_column_null :tags, :version_no, false
+
+    add_check_constraint :tags, 'version_no > 0', name: 'chk_tags_version_no_positive'
+  end
+
+  def down
+    remove_check_constraint :tags, name: 'chk_tags_version_no_positive'
+    remove_column :tags, :version_no
+  end
+end

backend/db/migrate/20260507213300_add_version_no_to_wiki_pages.rb

@@ -0,0 +1,27 @@
+class AddVersionNoToWikiPages < ActiveRecord::Migration[8.0]
+  def up
+    add_column :wiki_pages, :version_no, :integer
+
+    execute <<~SQL
+      UPDATE
+        wiki_pages
+      SET
+        version_no = (
+          SELECT
+            MAX(version_no)
+          FROM
+            wiki_versions
+          WHERE
+            wiki_page_id = wiki_pages.id)
+    SQL
+
+    change_column_null :wiki_pages, :version_no, false
+
+    add_check_constraint :wiki_pages, 'version_no > 0', name: 'chk_wiki_pages_version_no_positive'
+  end
+
+  def down
+    remove_check_constraint :wiki_pages, name: 'chk_wiki_pages_version_no_positive'
+    remove_column :wiki_pages, :version_no
+  end
+end

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

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

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

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

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

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

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

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

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

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_04_09_123700) do
+ActiveRecord::Schema[8.0].define(version: 2026_06_12_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
@@ -48,11 +48,85 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["tag_id"], name: "index_deerjikists_on_tag_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.boolean "banned", default: false, null: false
+  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"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["banned_at"], name: "index_ip_addresses_on_banned_at"
     t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
@@ -104,6 +178,30 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["tag_id"], name: "index_nico_tag_relations_on_tag_id"
   end
 
+  create_table "nico_tag_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.text "linked_tags", null: false
+    t.datetime "created_at", null: false
+    t.bigint "created_by_user_id"
+    t.index ["created_at"], name: "index_nico_tag_versions_on_created_at"
+    t.index ["created_by_user_id", "created_at"], name: "index_nico_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
+    t.index ["tag_id", "created_at"], name: "index_nico_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
+    t.index ["tag_id", "version_no"], name: "index_nico_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "nico_tag_versions_version_no_positive"
+  end
+
+  create_table "post_implications", primary_key: ["post_id", "parent_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "parent_post_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["parent_post_id"], name: "index_post_implications_on_parent_post_id"
+    t.check_constraint "`post_id` <> `parent_post_id`", name: "chk_post_implications_no_self"
+  end
+
   create_table "post_similarities", primary_key: ["post_id", "target_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "target_post_id", null: false
@@ -140,13 +238,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
     t.text "tags", null: false
-    t.bigint "parent_id"
+    t.text "parent_post_ids", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_by_user_id"], name: "index_post_versions_on_created_by_user_id"
-    t.index ["parent_id"], name: "index_post_versions_on_parent_id"
     t.index ["post_id", "version_no"], name: "index_post_versions_on_post_id_and_version_no", unique: true
     t.index ["post_id"], name: "index_post_versions_on_post_id"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
@@ -157,15 +254,15 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "title"
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
-    t.bigint "parent_id"
     t.bigint "uploaded_user_id"
     t.datetime "created_at", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
     t.datetime "updated_at", null: false
-    t.index ["parent_id"], name: "index_posts_on_parent_id"
+    t.integer "version_no", null: false
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
+    t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -216,6 +313,23 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
   end
 
+  create_table "tag_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.string "category", null: false
+    t.text "aliases", null: false
+    t.text "parent_tag_ids", null: false
+    t.datetime "created_at", null: false
+    t.bigint "created_by_user_id"
+    t.index ["created_at"], name: "index_tag_versions_on_created_at"
+    t.index ["created_by_user_id", "created_at"], name: "index_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
+    t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
+    t.index ["tag_id", "version_no"], name: "index_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "tag_versions_version_no_positive"
+  end
+
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_name_id", null: false
     t.string "category", default: "general", null: false
@@ -223,8 +337,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
     t.datetime "discarded_at"
+    t.integer "version_no", null: false
     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 "`version_no` > 0", name: "chk_tags_version_no_positive"
   end
 
   create_table "theatre_comments", primary_key: ["theatre_id", "no"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -240,6 +356,55 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) 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
@@ -294,9 +459,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "name"
     t.string "inheritance_code", limit: 64, null: false
     t.string "role", null: false
-    t.boolean "banned", default: false, null: false
+    t.datetime "banned_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
   create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -322,16 +488,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
 
   create_table "wiki_pages", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_name_id", null: false
+    t.text "body", null: false
     t.bigint "created_user_id", null: false
     t.bigint "updated_user_id", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "discarded_at"
     t.integer "next_asset_no", default: 1, null: false
+    t.integer "version_no", null: false
     t.index ["created_user_id"], name: "index_wiki_pages_on_created_user_id"
     t.index ["discarded_at"], name: "index_wiki_pages_on_discarded_at"
     t.index ["tag_name_id"], name: "index_wiki_pages_on_tag_name_id", unique: true
     t.index ["updated_user_id"], name: "index_wiki_pages_on_updated_user_id"
+    t.check_constraint "`version_no` > 0", name: "chk_wiki_pages_version_no_positive"
   end
 
   create_table "wiki_revision_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -364,8 +533,36 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["wiki_page_id"], name: "index_wiki_revisions_on_wiki_page_id"
   end
 
+  create_table "wiki_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "title", null: false
+    t.text "body", null: false
+    t.text "reason"
+    t.datetime "created_at", null: false
+    t.bigint "created_by_user_id"
+    t.index ["created_by_user_id"], name: "index_wiki_versions_on_created_by_user_id"
+    t.index ["wiki_page_id", "version_no"], name: "index_wiki_versions_on_wiki_page_id_and_version_no", unique: true
+    t.index ["wiki_page_id"], name: "index_wiki_versions_on_wiki_page_id"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "wiki_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "wiki_versions_version_no_positive"
+  end
+
   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"
@@ -377,6 +574,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   add_foreign_key "materials", "users", column: "updated_by_user_id"
   add_foreign_key "nico_tag_relations", "tags"
   add_foreign_key "nico_tag_relations", "tags", column: "nico_tag_id"
+  add_foreign_key "nico_tag_versions", "tags"
+  add_foreign_key "nico_tag_versions", "users", column: "created_by_user_id"
+  add_foreign_key "post_implications", "posts"
+  add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
   add_foreign_key "post_tags", "posts"
@@ -384,9 +585,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   add_foreign_key "post_tags", "users", column: "created_user_id"
   add_foreign_key "post_tags", "users", column: "deleted_user_id"
   add_foreign_key "post_versions", "posts"
-  add_foreign_key "post_versions", "posts", column: "parent_id"
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
-  add_foreign_key "posts", "posts", column: "parent_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
   add_foreign_key "tag_implications", "tags"
@@ -394,9 +593,23 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   add_foreign_key "tag_names", "tag_names", column: "canonical_id"
   add_foreign_key "tag_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
+  add_foreign_key "tag_versions", "tags"
+  add_foreign_key "tag_versions", "users", column: "created_by_user_id"
   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"
@@ -417,4 +630,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   add_foreign_key "wiki_revisions", "wiki_pages"
   add_foreign_key "wiki_revisions", "wiki_pages", column: "redirect_page_id"
   add_foreign_key "wiki_revisions", "wiki_revisions", column: "base_revision_id"
+  add_foreign_key "wiki_versions", "users", column: "created_by_user_id"
+  add_foreign_key "wiki_versions", "wiki_pages"
 end

backend/lib/tasks/export_nico.rake

@@ -0,0 +1,23 @@
+namespace :nico do
+  desc 'ニコニコ DB 逆連携'
+  task export: :environment do
+    require 'open3'
+
+    mysql_user = ENV.fetch('MYSQL_USER')
+    mysql_pass = ENV.fetch('MYSQL_PASS')
+    nizika_nico_path = ENV.fetch('NIZIKA_NICO_PATH')
+
+    videos = Post.where('url LIKE ?', '%nicovideo.jp/watch/%').pluck(:url).filter_map {
+      _1[%r{nicovideo\.jp/watch/([^/?#]+)}, 1]
+    }.uniq
+
+    next if videos.empty?
+
+    _, stderr, status = Open3.capture3(
+        { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
+        'python3', '-m', 'tracked_videos.put_bulk_upsert', *videos,
+        chdir: nizika_nico_path)
+
+    raise stderr unless status.success?
+  end
+end

backend/lib/tasks/sync_nico.rake

@@ -115,6 +115,10 @@ namespace :nico do
       datum['tags'].each do |raw|
         name = TagNameSanitisationRule.sanitise("nico:#{ raw }")
         tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
+
+        event_type = tag.nico_tag_versions.exists? ? :update : :create
+        NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user: nil)
+
         desired_nico_tag_based_ids << tag.id
 
         # 新たに記載される外部タグと連携される内部タグを記載
@@ -149,6 +153,7 @@ namespace :nico do
       if post_created
         PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
       elsif post_changed || kept_tag_ids != desired_all_tag_ids.to_set
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
         PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
       end
     end

backend/lib/tasks/sync_posts.rake

@@ -0,0 +1,6 @@
+namespace :post do
+  desc '投稿同期（ニコニコ以外）'
+  task sync: :environment do
+    Youtube::Sync.new.sync!
+  end
+end

backend/spec/factories/ip_addresses.rb

@@ -0,0 +1,10 @@
+FactoryBot.define do
+  factory :ip_address do
+    ip_address { IPAddr.new('203.0.113.10').hton }
+    banned_at { nil }
+
+    trait :banned do
+      banned_at { Time.current }
+    end
+  end
+end

backend/spec/factories/users.rb

@@ -1,15 +1,24 @@
 FactoryBot.define do
   factory :user do
-    name { "test-user" }
+    name { nil }
     inheritance_code { SecureRandom.uuid }
-    role { "guest" }
+    role { 'guest' }
+    banned_at { nil }
+
+    trait :guest do
+      role { 'guest' }
+    end
 
     trait :member do
-      role { "member" }
+      role { 'member' }
     end
 
     trait :admin do
       role { 'admin' }
     end
+
+    trait :banned do
+      banned_at { Time.current }
+    end
   end
 end

backend/spec/factories/wiki_pages.rb

@@ -3,5 +3,7 @@ FactoryBot.define do
     title { "TestPage" }
     association :created_user, factory: :user
     association :updated_user, factory: :user
+
+    body { ' ' }
   end
 end

backend/spec/models/post_implication_spec.rb

@@ -0,0 +1,51 @@
+require 'rails_helper'
+
+RSpec.describe PostImplication, type: :model do
+  let!(:post_record) do
+    Post.create!(
+      title: 'post',
+      url: 'https://example.com/post-implication-post'
+    )
+  end
+
+  let!(:parent_post) do
+    Post.create!(
+      title: 'parent post',
+      url: 'https://example.com/post-implication-parent'
+    )
+  end
+
+  it 'is valid with post and parent_post' do
+    implication = described_class.new(
+      post: post_record,
+      parent_post:
+    )
+
+    expect(implication).to be_valid
+  end
+
+  it 'does not allow same post as parent_post' do
+    implication = described_class.new(
+      post: post_record,
+      parent_post: post_record
+    )
+
+    expect(implication).not_to be_valid
+    expect(implication.errors[:parent_post_id]).to be_present
+  end
+
+  it 'does not allow duplicate pair' do
+    described_class.create!(
+      post: post_record,
+      parent_post:
+    )
+
+    duplicate = described_class.new(
+      post: post_record,
+      parent_post:
+    )
+
+    expect(duplicate).not_to be_valid
+    expect(duplicate.errors[:post_id]).to be_present
+  end
+end

backend/spec/models/post_version_spec.rb

@@ -19,7 +19,7 @@ RSpec.describe PostVersion, type: :model do
       url: post_record.url,
       thumbnail_base: post_record.thumbnail_base,
       tags: post_record.snapshot_tag_names.join(' '),
-      parent: post_record.parent,
+      parent_post_ids: post_record.snapshot_parent_post_ids.join(' '),
       original_created_from: post_record.original_created_from,
       original_created_before: post_record.original_created_before,
       created_at: Time.current,

backend/spec/models/tag_spec.rb

@@ -107,11 +107,13 @@ RSpec.describe Tag, type: :model do
     context 'when the source tag_name has a wiki_page' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
       let!(:wiki_page) do
-        WikiPage.create!(
+        admin = create_admin_user!
+
+        Wiki::Commit.create_content!(
             tag_name: source_tag_name,
-          created_user: create_admin_user!,
-          updated_user: create_admin_user!
-        )
+            body: 'source wiki body',
+            created_by_user: admin,
+            message: 'init')
       end
 
       it 'rolls back the transaction' do
@@ -159,7 +161,7 @@ RSpec.describe Tag, type: :model do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
-        parent: post.parent,
+        parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
         created_at: Time.current,

backend/spec/models/version_record_spec.rb

@@ -0,0 +1,74 @@
+require 'rails_helper'
+
+RSpec.describe VersionRecord, type: :model do
+  let!(:tag) { create(:tag, name: 'version_record_tag') }
+  let!(:nico_tag) { create(:tag, :nico, name: 'nico:version_record_tag') }
+
+  it 'makes TagVersion read only after create' do
+    version = TagVersion.create!(
+      tag: tag,
+      version_no: 1,
+      event_type: 'create',
+      name: tag.name,
+      category: tag.category,
+      aliases: '',
+      parent_tag_ids: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.update!(name: 'changed')
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'prevents TagVersion destroy' do
+    version = TagVersion.create!(
+      tag: tag,
+      version_no: 1,
+      event_type: 'create',
+      name: tag.name,
+      category: tag.category,
+      aliases: '',
+      parent_tag_ids: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.destroy!
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'makes NicoTagVersion read only after create' do
+    version = NicoTagVersion.create!(
+      tag: nico_tag,
+      version_no: 1,
+      event_type: 'create',
+      name: nico_tag.name,
+      linked_tags: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.update!(name: 'nico:changed')
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'prevents NicoTagVersion destroy' do
+    version = NicoTagVersion.create!(
+      tag: nico_tag,
+      version_no: 1,
+      event_type: 'create',
+      name: nico_tag.name,
+      linked_tags: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.destroy!
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+end

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

backend/spec/requests/gekanator_games_spec.rb

@@ -0,0 +1,75 @@
+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 not found without an admin 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(:not_found)
+    end
+
+    it 'returns not found 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(:not_found)
+    end
+  end
+end

backend/spec/requests/gekanator_learning_spec.rb

@@ -0,0 +1,612 @@
+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 'returns not found 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(:not_found)
+    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 'limits suggestions to three 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'
+        }
+      }.not_to change { GekanatorQuestionSuggestion.count }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+    end
+
+    it 'returns not found for a non-admin user' do
+      sign_in_as member
+
+      post '/gekanator/question_suggestions', params: {
+        gekanator_game_id: game.id,
+        question_text: 'member question?',
+        answer: 'yes'
+      }
+
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'GET /gekanator/games/:id/extra_questions' do
+    it 'returns at most two accepted user_suggested post_similarity questions without duplicates' do
+      sign_in_as admin
+
+      low = create_post_similarity_question!(
+        text: 'low?',
+        priority_weight: 1.0
+      )
+      high = create_post_similarity_question!(
+        text: 'high?',
+        priority_weight: 3.0
+      )
+      middle = create_post_similarity_question!(
+        text: 'middle?',
+        priority_weight: 2.0
+      )
+
+      get "/gekanator/games/#{game.id}/extra_questions"
+
+      expect(response).to have_http_status(:ok)
+      expect(json['questions'].length).to eq(2)
+      expect(json['questions'].map { _1['id'] }.uniq.length).to eq(2)
+      expect(json['questions'].map { _1['id'] }).to all(be_in([low.id, high.id, middle.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 '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
+  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
+  end
+
+  describe 'GET /gekanator/questions' do
+    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
+  end
+end

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