#399

Reviewed-on: #410
Co-authored-by: miteruzo <miteruzo@naver.com>
Co-committed-by: miteruzo <miteruzo@naver.com>

AGENTS.md

@@ -114,28 +114,142 @@ npm run preview
 - Ruby: `render` 系メソッド呼び出しでは、keyword 引数付きでも括弧を書かない。
 - Ruby: never put a line break immediately before `)`.
 - Ruby: do not use `%w` or `%i`.
+- Ruby: TypeScript / TSX の associative syntax に近い感覚で読むこと。
+  Hash の `}` は block の `}` ではない。call の `)` も function 定義の
+  parameter-list `)` ではない。delimiter の役割を見誤らないこと。
 - In Ruby, when an `if` condition is split across multiple lines and combines
   clauses with `&&` or `||`, wrap the whole condition in parentheses.
-- Ruby hashes are not blocks; keep `}` on the same line as the final pair.
-- Ruby hashes keep the first pair on the same line as `{` unless line length
-  requires a break.
-- Short Ruby hashes may stay visually compact across two lines with the first
-  pair kept on the opening line and aligned continuation pairs below it.
-- Ruby blocks use separate `{ ... }` rules from hashes, with 2-space body
-  indentation.
+- Ruby hash / block / call delimiter の詳細は、下の
+  `Ruby delimiter and wrapping rules` を正本として扱ふこと。
 - 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.
+
+### Ruby delimiter and wrapping rules
+
+- Ruby でも、closing delimiter は glyph ではなく syntax role で判定する。
+  `}` が block close なのか hash close なのか、`)` が method call なのか
+  grouping なのかを区別してから配置すること。
+- Ruby の multi-line method call では、receiver / method と opening `(` を
+  同じ行に保ち、closing `)` を単独行へ落とさない。
+- Ruby の multi-line hash literal / keyword-like argument hash では、opening
+  `{` を最初の pair と同じ行に置き、closing `}` を最後の pair と同じ行に
+  置く。Prettier 的な縦開き・縦閉じをしない。
+- Ruby の guard 条件は、1 行で収まるなら modifier 形式を優先する。
+  99 文字を超えるなら block 形式へ切り替へるか、message 定数化などで縮める。
+- Ruby の method chain や call argument を折り返す際、call-site の `)` を
+  block close のやうに独立させない。
+
+Bad:
+
+```rb
+response = Example.fetch(
+  value,
+  option: option,
+)
+```
+
+Good:
+
+```rb
+response = Example.fetch(
+    value,
+    option: option)
+```
+
+Bad:
+
+```rb
+payload = {
+  title: title,
+  url: url,
+}
+```
+
+Good:
+
+```rb
+payload = {
+    title: title,
+    url: url }
+```
+
+Bad:
+
+```rb
+raise ArgumentError, 'URL が長すぎます．' if url.bytesize > MAX_URL_BYTES && flag.present?
+```
+
+Good:
+
+```rb
+if url.bytesize > MAX_URL_BYTES && flag.present?
+  raise ArgumentError, 'URL が長すぎます．'
+end
+```
+
+Bad:
+
+```rb
+records.each {
+  do_work(_1) }
+```
+
+Good:
+
+```rb
+records.each {
+  do_work(_1)
+}
+```
 - 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.
+- In TypeScript and TSX, use 2-space block indentation.
+- In TypeScript and TSX, block bodies for components, functions, callbacks,
+  `if`, `try`, `catch`, `finally`, loops, and JSX nesting use 2 spaces per
+  level.
+- In TypeScript and TSX, put the opening brace of `try`, `catch`, and
+  `finally` blocks on the next line at the same indentation as the keyword.
+- Do not indent the opening `{` one level deeper than `try`, `catch`, or
+  `finally`.
+- Indent the block body 2 spaces deeper than the keyword and opening brace.
+- Put the closing `}` on its own line at the same indentation as the keyword.
+- Do not write `try {`, `catch {`, or `finally {`.
+- In TypeScript and TSX, use 4-space continuation indentation for wrapped
+  expressions, arguments, conditions, arrays, object literals, JSX
+  attributes, and similar continuations.
+- Treat the user's `PostImportSourcePage.tsx` and `PostImportReviewPage.tsx`
+  formatting as the local reference shape: component and callback bodies use
+  2-space block indentation, single-line bodies do not gain unnecessary
+  braces, wrapped expressions use 4-space continuation indentation, multi-
+  stage ternaries use explicit parentheses, and only complete leading runs
+  of 8 spaces are compressed to tabs.
+- In TypeScript and TSX only, tabs are for leading 8-column compression only.
+- A tab does not represent one indentation level.
+- Do not replace 2-space or 4-space indentation with tabs.
+- First determine visible indentation using 2-space block indentation and
+  4-space continuation indentation, then compress only complete leading runs
+  of 8 spaces into tabs.
+- Tabs are only for leading indentation, never for spaces after non-space
+  text.
+- Keep residual leading 2, 4, or 6 spaces after any tab compression.
+- Examples: 2 columns = 2 spaces, 4 columns = 4 spaces, 6 columns = 6
+  spaces, 8 columns = 1 tab, 10 columns = 1 tab + 2 spaces, 12 columns = 1
+  tab + 4 spaces, 16 columns = 2 tabs.
 - TypeScript and TSX imports may stay on one line if they remain within the
   line limit; do not expand short type-only imports mechanically.
+- Keep runtime value imports and type imports in separate declarations.
+- Do not write `import { value, type TypeName } from ...`.
+- Type-only declarations must use `import type`.
+- Do not merge type imports into value imports merely to save lines.
+- In TypeScript and TSX, order imports as four groups with a blank line
+  between groups: external value imports, `@/...` value imports, external
+  type imports, `@/...` type imports.
+- Do not mechanically split a short value import from one module across
+  multiple lines when it still fits within 99 characters.
 - In TypeScript and TSX, when breaking a line at an operator, break before the
   operator and put the operator at the beginning of the next line. A trailing
   operator at end of line is unacceptable. This rule does not apply to Ruby,
@@ -167,6 +281,10 @@ case 'no':
 - In TypeScript and TSX, use `value == null` and `value != null` as the
   default nullish checks. Do not use `=== null`, `=== undefined`,
   `!== null`, or `!== undefined`.
+- In JavaScript, JSX, TypeScript, and TSX, never use `_1`, `_2`, or similar
+  Ruby-style numbered parameter names. Reserve numbered parameters for Ruby.
+  Use a meaningful callback parameter name such as `row`, `item`, `value`,
+  `entry`, or `result`.
 - If code appears to need a distinction between `null` and `undefined`, treat
   that as a design smell and revise the logic to avoid the distinction.
   External library APIs that explicitly require distinguishing the two are the
@@ -190,6 +308,151 @@ const value =
   value selection. Do not replace a clear ternary with `if` statements, and do
   not introduce immediately invoked functions just to avoid or reformat a
   ternary expression.
+- In TypeScript and TSX, multi-stage ternary expressions must make branch
+  boundaries explicit. Wrap each condition group in parentheses instead of
+  relying on indentation alone to show which `?` matches which `:`.
+- In TypeScript and TSX, wrap nested ternary expressions in parentheses. Do
+  not write flat vertical chains of `?` and `:` without explicit grouping.
+- In TypeScript and TSX, when a ternary condition contains `&&` or `||`, wrap
+  the whole condition in parentheses before `?`.
+- In TypeScript and TSX, if a ternary reaches three or more stages and still
+  reads poorly after explicit grouping, extract a helper function or use `if`
+  statements instead of keeping a flat multi-stage ternary.
+
+Bad:
+
+```ts
+row.skipReason === 'existing' || row.importStatus === 'skipped'
+? 'skipped'
+: Object.keys (row.validationErrors ?? { }).length > 0
+  || row.importStatus === 'failed'
+  || row.importStatus === 'created'
+? null
+: hasWarnings (row) || row.status === 'warning'
+? 'warning'
+: 'ready'
+```
+
+Good:
+
+```ts
+(row.skipReason === 'existing' || row.importStatus === 'skipped')
+? 'skipped'
+: ((Object.keys (row.validationErrors ?? { }).length > 0
+    || row.importStatus === 'failed'
+    || row.importStatus === 'created')
+   ? null
+   : ((hasWarnings (row) || row.status === 'warning')
+      ? 'warning'
+      : 'ready'))
+```
+
+## Shared-system discovery and reuse
+
+Before creating a new component, hook, service, helper, utility, concern,
+representation, normaliser, validator, parser, fetcher, store, context, event
+bus, API client, query key, permission helper, dialogue, toast, form field, or
+version recorder, search the existing repository first.
+
+Do not search by name alone. Search by responsibility, behaviour, and usage
+intent as well. Typical search themes include:
+
+- dialogue, modal, confirm, alert, choice
+- validation error, field error, unprocessable entity
+- permission, role, member, admin, editable
+- URL normalise, sanitise, canonicalise
+- API call, query key, prefetch, cache invalidation
+- version, snapshot, history, restore
+- thumbnail, metadata, HTTP fetch, URL safety
+- form, field, input, textarea, warning, status badge
+- file storage, Active Storage, ZIP, export
+- transaction, locking, race, idempotency
+
+Before deciding that something new is needed, confirm at least:
+
+1. the existing definition
+2. its public API
+3. representative call sites
+4. other implementations with similar responsibility
+5. the nearest directory-level `AGENTS.md`
+
+Do not reject an existing implementation by name alone. Read the code and its
+usage first.
+
+When new behaviour is needed, make the decision in this order:
+
+1. use the existing common API as-is
+2. use the existing extension points of that API
+3. extend the existing common API minimally
+4. keep the implementation local when the meaning is feature-specific
+5. add a new common system only when multiple real users and a stable contract
+   are already clear
+
+Do not create a parallel foundation merely because the existing one feels
+slightly awkward, because a new one seems faster, or because the current task
+looks special.
+
+Do not create a second common platform with names such as `CommonFoo`,
+`SharedFoo`, `BaseFoo`, `FooManager`, `FooService`, `FooProvider`,
+`FooWrapper`, `FooUtils`, or `useFoo` when an existing system already owns the
+same responsibility. Judge by responsibility, not by spelling.
+
+Wrapper aliases, barrel exports, and re-export shims do not count as reuse.
+Using a different import path that merely forwards to the existing system does
+not satisfy a reuse requirement.
+
+Keep this boundary explicit:
+
+- business meaning stays in feature code
+- visual and mechanical shell stays in common code
+
+Common code may hold generic primitives, interaction shells, API transport,
+auth and permission helpers, query-key and prefetch conventions, validation
+error conversion, shared normalisation, version-recording mechanisms, storage
+helpers, HTTP safety, and other contracts that carry the same meaning across
+multiple features.
+
+Feature code should keep feature-specific states, labels, input fields,
+workflow steps, payload shapes, validation rules, and business decisions.
+
+Do not commonise business logic merely because the visuals look similar or two
+code fragments resemble each other.
+
+Create a new common system only when all of the following are true:
+
+- no existing implementation already owns the responsibility
+- there are multiple real consumers, or a clearly defined platform contract
+- the differences between consumers do not require option bloat
+- feature-specific vocabulary does not leak into common types, props, tones, or
+  state names
+- the location matches the existing directory structure
+- the new abstraction does not compete with an existing common system
+- it is not just a one-off wrapper for a single task
+
+Do not add unused tones, variants, options, callbacks, states, or abstractions
+for speculative future use.
+
+Before finishing work that touches shared systems, verify:
+
+- you searched for an existing implementation with the same responsibility
+- you are using the canonical import path or entrypoint
+- feature code is not reaching directly for a low-level primitive that already
+  has a higher-level common API
+- you did not bypass an existing common API
+- any new wrapper or shim is genuinely necessary
+- feature-specific vocabulary did not leak into common code
+- the feature did not reimplement a common shell
+- existing unrelated consumers were not changed without need
+- one task did not trigger a needless redesign of the whole foundation
+- any newly introduced common system really has multiple consumers
+
+For backend-specific discovery, Rails structure, services, representation
+selection, versioning, normalisation, and HTTP safety, follow
+`backend/AGENTS.md`.
+
+For frontend-specific component hierarchy, low-level primitive reuse, dialogue
+entrypoints, API/query helpers, validation/form infrastructure, state/storage,
+and layout reuse, follow `frontend/AGENTS.md`.
 - In TypeScript and TSX, do not write `let` followed by later `if` assignments
   when the value can be expressed as a single `const` initializer. Prefer
   `const` because it prevents accidental later reassignment.
@@ -265,6 +528,20 @@ const value =
 - For user-facing Japanese kanji spelling, do not normalize to
   《当用漢字による書きかえ》; prefer original forms such as `編輯`.
 - For user-facing Japanese ellipses, prefer `……` over ASCII `...`.
+- Frontend dialogue work must use `@/lib/dialogues/useDialogue` as the
+  feature-facing entrypoint.
+- Reuse the existing common dialogue API and common dialogue component
+  instead of building feature-local overlay, close button, header, footer,
+  focus handling, outside click handling, Escape handling, or confirmation
+  flows.
+- Do not import `@/components/ui/dialog` directly in feature code to build a
+  one-off dialogue, and do not evade this rule with aliases such as
+  `Dialog as Dialogue`.
+- Keep business-specific form content in feature code, and keep the visual
+  and behavioural dialogue shell in common code.
+- Use British spelling `Dialogue` for project-defined dialogue identifiers.
+  Keep an exact third-party API spelling only at the external boundary where
+  compatibility requires it.
 
 ### Frontend TypeScript and TSX style
 
@@ -303,14 +580,24 @@ const value =
   beginning of a line.
 - The TSX-specific self-review must confirm JSX closing markers and closing
   parentheses keep the surrounding compact style.
-- The TypeScript/TSX self-review must confirm leading indentation follows
-  4-space logical indentation with tabs only as leading 8-space compression.
+- The TypeScript/TSX self-review must confirm leading block indentation uses
+  2 spaces per level, wrapped continuations use the repository's 4-space
+  continuation alignment, and complete leading runs of 8 spaces may be
+  compressed to tabs.
 - 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.
-- In TypeScript and TSX, convert every leading run of 8 spaces to a tab
-  character.
+- In TSX, use 2-space block indentation and 4-space continuation
+  indentation.
+- In TypeScript and TSX, put the opening brace of `try`, `catch`, and
+  `finally` blocks on the next line at the same indentation as the keyword.
+- Do not indent the opening `{` one level deeper than `try`, `catch`, or
+  `finally`.
+- Indent the block body 2 spaces deeper than the keyword and opening brace.
+- Put the closing `}` on its own line at the same indentation as the keyword.
+- Do not write `try {`, `catch {`, or `finally {`.
+- In TypeScript and TSX, convert every complete leading run of 8 spaces to a
+  tab character.
 - A leading tab is exactly equivalent to 8 leading spaces.
 - In TypeScript and TSX function declarations, including `const` arrow
   function declarations, classify the parameter list before placing the closing
@@ -359,6 +646,22 @@ const value =
   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.
+- `try` / `catch` / `finally` brace placement example:
+
+```ts
+try
+{
+  doWork ()
+}
+catch
+{
+  recover ()
+}
+finally
+{
+  cleanUp ()
+}
+```
 - Do not use a leading semicolon for expression statements such as
   `;([...]).forEach(...)`; rewrite the expression to avoid ASI hazards
   explicitly, for example with `void`.
@@ -938,8 +1241,9 @@ to `.ts` and `.tsx`:
 7. JSX `>` and `/>` stay with the final prop unless nearby code proves
    otherwise.
 8. JSX closing parentheses keep the compact local style.
-9. Leading indentation is 4-space logical indentation with tabs used only as
-   leading 8-space compression.
+9. Leading block indentation uses 2 spaces per level, wrapped continuations
+   use the repository's 4-space continuation alignment, and complete leading
+   runs of 8 spaces may be compressed to tabs.
 10. No line has trailing whitespace.
 
 Preferred:

backend/AGENTS.md

@@ -67,6 +67,192 @@ pass or the remaining failure is clearly blocked.
 Before changing behavior, inspect the matching route, controller, model,
 service, representation, and spec.
 
+## Shared backend systems
+
+Before adding backend behaviour, search the existing backend first. At minimum,
+check these locations:
+
+- `app/controllers`
+- `app/controllers/concerns`
+- `app/models`
+- `app/models/concerns`
+- `app/representations`
+- `app/services`
+- `app/services/*`
+- `app/jobs`
+- `lib`
+- `lib/tasks`
+- `config/initializers`
+
+Do not infer commonality from directory names alone. Read the actual
+responsibility and representative usage sites.
+
+### Controller reuse
+
+Before adding logic to a controller, inspect:
+
+- `ApplicationController` authentication, authorization, BAN, and IP BAN
+- existing render and validation-error helpers
+- existing param parsing
+- controller concerns
+- the controller for the same resource
+- existing services
+- existing representations
+
+Keep controllers focused on:
+
+- authentication and authorization
+- parameter intake
+- service and model invocation
+- HTTP status selection
+- representation selection
+
+Do not reimplement these per controller when an existing path already owns
+them:
+
+- authentication and role checks
+- validation error JSON
+- URL normalisation
+- tag normalisation
+- thumbnail handling
+- version recording
+- complex transactions
+- external HTTP fetching
+- response representation assembly
+
+### Authentication, authorization, and BAN
+
+Treat these as the canonical backend entrypoints:
+
+- `ApplicationController#authenticate_user`
+- `current_user`
+- `X-Transfer-Code`
+- `reject_banned_ip_address!`
+- `reject_banned_user!`
+- `gte_member?`
+- `admin?`
+
+Do not create feature-local permission services, role comparisons, or header
+parsing when the existing authentication boundary already owns the behaviour.
+If the current boundary is insufficient, extend it minimally instead of adding
+another permission path.
+
+### Representations
+
+If an endpoint for the same resource already uses `app/representations`, do not
+assemble a separate JSON shape directly inside the controller without first
+checking the existing representation contract.
+
+Inspect at least:
+
+- `PostRepr`
+- `TagRepr`
+- `MaterialRepr`
+- `TheatreRepr`
+- `UserRepr`
+- `WikiPageRepr`
+- `DeerjikistRepr`
+
+When a lightweight response is genuinely different in purpose, keep it
+deliberate and compatible with the surrounding contracts. Do not force every
+identifier list into a large representation, but do not fork the same resource
+shape casually either.
+
+### Domain services
+
+When work touches multiple models, transactions, external APIs, file handling,
+history creation, or multi-step workflow, search `app/services` first.
+
+At minimum, search for existing services in these responsibility areas:
+
+- version recorder and versioning
+- wiki commit
+- YouTube or Google Drive API client
+- material sync or ZIP export
+- similarity calculation
+- theatre selection or skip finalisation
+- metadata, thumbnail, or file processing
+- URL normaliser or sanitisation
+- import or export
+- preview safety or HTTP fetch
+
+Do not create a same-responsibility service under another namespace or another
+name. If an existing service is close, extend that API minimally instead of
+wrapping it in a feature-local service.
+
+### Versioning
+
+When a feature writes history, snapshots, or restore roots, search the existing
+versioning path first. At minimum, inspect:
+
+- `VersionRecorder`
+- `PostVersionRecorder`
+- `TagVersionRecorder`
+- `TagVersioning`
+- `MaterialVersionRecorder`
+- `NicoTagVersionRecorder`
+- `WikiVersionRecorder`
+
+Do not implement history writes in controllers, callbacks, or ad hoc feature
+services when the recorder layer already owns the transaction boundary and
+meaning.
+
+### Normalisation, sanitisation, and parsing
+
+For URLs, tag names, times, video durations, identifiers, and paths, search the
+existing normaliser, sanitisation rule, parser, and model-callback path first.
+
+Do not let frontend, controller, service, and model each invent different rules
+for the same value. Use one canonical normalisation path and keep input
+validation distinct from pre-persistence normalisation.
+
+### External HTTP and URL safety
+
+When fetching external URLs, reuse the existing preview-safety stack. Search at
+least for:
+
+- URL safety
+- redirect validation
+- response size limits
+- timeouts
+- network failure mapping
+- HTML metadata extraction
+- known-site extraction
+- thumbnail fetching
+
+Do not add direct `Net::HTTP`, `Faraday`, or equivalent feature-local HTTP code
+that reimplements SSRF checks, redirect restrictions, size limits, or timeouts.
+If the current fetcher is insufficient, extend its existing safety contract.
+
+### Storage, files, and Active Storage
+
+When handling files, thumbnails, ZIP output, object storage, or Active Storage
+blobs, inspect existing storage helpers, exporters, thumbnail generators, and
+checksum helpers first. Do not reimplement the same attach, export path,
+download, resize, or checksum flow in a controller or one-off service.
+
+### Concerns
+
+Do not create controller or model concerns merely because some code is shared.
+Use a concern only when multiple classes share the same lifecycle, macro,
+callback, or tightly cohesive behaviour. Utility collections belong in explicit
+objects or services, not in `CommonConcern`, `SharedMethods`, or `Utils`.
+
+### Model boundaries
+
+Model-specific invariants, associations, validations, and normalisation may
+live in the model. Multi-model workflow, external access, complex transaction
+flow, and feature orchestration belong in services. Do not hide feature
+workflow in model callbacks.
+
+### Transactions, locking, and race handling
+
+If transactions, locking, idempotency, or race recovery already exist in a
+service or model method, do not add a second implementation in a controller or
+new service. Inspect the existing transaction boundary first, avoid wrapping
+the same operation in needless nested transactions, and handle unique-constraint
+races according to the target constraint's business meaning.
+
 ## Ruby style
 
 - Prefer precise, minimal changes.

backend/app/controllers/post_imports_controller.rb

@@ -0,0 +1,44 @@
+class PostImportsController < ApplicationController
+  before_action :require_member!
+
+  def preview
+    rows = PostImportPreviewer.new.preview_rows(
+        rows: PostImportUrlListParser.parse(params[:source]))
+    render json: { rows: }
+  rescue ArgumentError => e
+    render_bad_request e.message
+  end
+
+  def validate
+    rows = normalised_import_rows allow_warning_fields: true
+    changed_row = Integer(params[:changed_row], exception: false)
+    result =
+        PostImportPreviewer.new.preview_rows(rows:,
+                                             fetch_metadata: changed_row,
+                                             metadata_cache: { })
+    render json: { rows: result }
+  rescue ArgumentError => e
+    render_bad_request e.message
+  end
+
+  def create
+    result = PostImportRunner.new(actor: current_user,
+                                  rows: normalised_import_rows).run
+    render json: result, status: result[:created].positive? ? :created : :ok
+  rescue ArgumentError => e
+    render_bad_request e.message
+  end
+
+  private
+
+  def require_member!
+    return head :unauthorized unless current_user
+    return if current_user.gte_member?
+
+    head :forbidden
+  end
+
+  def normalised_import_rows allow_warning_fields: false
+    PostImportRowNormaliser.normalise!(params[:rows], allow_warning_fields:)
+  end
+end

backend/app/controllers/posts_controller.rb

@@ -142,37 +142,14 @@ class PostsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    # TODO: サイトに応じて thumbnail_base 設定
-    title = params[:title].presence
-    url = params[:url]
-    thumbnail = params[:thumbnail]
-    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
-    resized_thumbnail = thumbnail.present? ? Post.resized_thumbnail_attachment(thumbnail) : nil
-
-    post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
-                    original_created_from:, original_created_before:)
-    post.thumbnail.attach(resized_thumbnail) if resized_thumbnail
-
-    ApplicationRecord.transaction do
-      post.save!
-
-      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
-          { tags:, sections: }
-      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
-
-      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
-      post.video_ms = normalise_video_ms(tags)
-      validate_video_sections!(post.video_ms, sections)
-      post.save!
-      sync_post_tags!(post, tags, sections)
-
-      sync_parent_posts!(post, parent_post_ids)
-
-      PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
-    end
+    post = PostCreator.new(actor: current_user,
+                           attributes: { title: params[:title], url: params[:url],
+                                         thumbnail: params[:thumbnail], tags: params[:tags],
+                                         original_created_from: params[:original_created_from],
+                                         original_created_before: params[:original_created_before],
+                                         parent_post_ids: parse_parent_post_ids,
+                                         video_ms: params[:video_ms],
+                                         duration: params[:duration] }).create!
 
     post.reload
     render json: PostRepr.base(post), status: :created
@@ -182,7 +159,7 @@ class PostsController < ApplicationController
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue Tag::SectionLiteralParseError
     render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
-  rescue VideoMsParseError
+  rescue PostCreator::VideoMsParseError
     render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
   rescue MiniMagick::Error
     render_validation_error fields: { thumbnail: ['サムネイル画像の変換に失敗しました．'] }

backend/app/models/post.rb

@@ -1,11 +1,23 @@
 class Post < ApplicationRecord
+  require 'date'
   require 'mini_magick'
   require 'stringio'
 
+  class RemoteThumbnailFetchFailed < StandardError; end
+
+  ORIGINAL_CREATED_INVALID_MESSAGE = 'オリジナルの作成日時の形式が不正です．'.freeze
+  ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE =
+      'オリジナルの作成日時は分単位で入力してください．'.freeze
+  ORIGINAL_CREATED_ORDER_MESSAGE = 'オリジナルの作成日時の順番がをかしぃです．'.freeze
+  ORIGINAL_CREATED_MINIMUM_RANGE_MESSAGE =
+      'オリジナルの作成日時の範囲は1分以上必要です．'.freeze
+
   def self.resized_thumbnail_attachment(upload)
     upload.rewind
     image = MiniMagick::Image.read(upload.read)
-    image.resize '180x180'
+    image.resize '180x180^'
+    image.gravity 'Center'
+    image.extent '180x180'
     image.format 'jpg'
 
     { io: StringIO.new(image.to_blob),
@@ -57,9 +69,9 @@ class Post < ApplicationRecord
 
   attribute :version_no, :integer, default: 1
 
-  before_validation :normalise_url
+  before_validation :normalise_url, if: :will_save_change_to_url?
 
-  validates :url, presence: true, uniqueness: true
+  validates :url, presence: true, uniqueness: true, length: { maximum: 768 }
   validates :video_ms, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
   validate :validate_original_created_range
@@ -118,7 +130,11 @@ class Post < ApplicationRecord
           '%d:%02d' % [min, s]
         end
 
-    remainder_ms.positive? ? "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }" : base
+    if remainder_ms.positive?
+      "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }"
+    else
+      base
+    end
   end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
@@ -140,19 +156,36 @@ class Post < ApplicationRecord
     thumbnail.attach(self.class.resized_thumbnail_attachment(StringIO.new(thumbnail.download)))
   end
 
+  def attach_thumbnail_from_url! raw_url
+    response = Preview::ThumbnailFetcher.fetch_image_response(raw_url)
+    thumbnail.attach(
+        self.class.resized_thumbnail_attachment(
+            StringIO.new(response.body)))
+  rescue Preview::UrlSafety::UnsafeUrl,
+         Preview::ThumbnailFetcher::GenerationFailed,
+         Preview::HttpFetcher::FetchFailed,
+         Preview::HttpFetcher::FetchTimeout,
+         Preview::HttpFetcher::ResponseTooLarge,
+         MiniMagick::Error => e
+    raise RemoteThumbnailFetchFailed, e.message
+  end
+
   private
 
   def validate_original_created_range
-    f = original_created_from
-    b = original_created_before
-    return if f.blank? || b.blank?
+    return if skip_original_created_validation?
 
-    f = Time.zone.parse(f) if String === f
-    b = Time.zone.parse(b) if String === b
-    return if !(f) || !(b)
+    f = parse_original_created_value(:original_created_from)
+    b = parse_original_created_value(:original_created_before)
+    return if f.nil? || b.nil?
 
-    if f >= b
-      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．'
+    if b <= f
+      errors.add :original_created_at, ORIGINAL_CREATED_ORDER_MESSAGE
+      return
+    end
+
+    if b - f < 1.minute
+      errors.add :original_created_at, ORIGINAL_CREATED_MINIMUM_RANGE_MESSAGE
     end
   end
 
@@ -173,15 +206,130 @@ class Post < ApplicationRecord
   def normalise_url
     return if url.blank?
 
-    self.url = url.strip
+    self.url = PostUrlNormaliser.normalise(url) || url.strip
+  end
 
-    u = URI.parse(url)
-    return unless u in URI::HTTP
+  def parse_original_created_value field
+    raw_value = public_send("#{ field }_before_type_cast")
+    value = public_send(field)
+    return nil if raw_value.blank? && value.blank?
 
-    u.host = u.host.downcase if u.host
-    u.path = u.path.sub(/\/\Z/, '') if u.path.present?
-    self.url = u.to_s
-  rescue URI::InvalidURIError
-    ;
+    time =
+        case raw_value
+        when String
+          parse_original_created_string(raw_value)
+        when Time, ActiveSupport::TimeWithZone
+          raw_value.in_time_zone
+        else
+          value&.in_time_zone
+        end
+    if time.nil?
+      errors.add field, ORIGINAL_CREATED_INVALID_MESSAGE
+      return nil
+    end
+    unless minute_precision_time?(time)
+      errors.add field, ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE
+      return nil
+    end
+    time
+  end
+
+  def parse_original_created_string raw_value
+    value = raw_value.to_s.strip
+    return nil if value.blank?
+
+    if (match = value.match(/\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})\z/))
+      year = match[1].to_i
+      month = match[2].to_i
+      day = match[3].to_i
+      hour = match[4].to_i
+      minute = match[5].to_i
+      return nil unless valid_original_created_components?(year, month, day, hour, minute, 0)
+
+      return Time.zone.local(year, month, day, hour, minute)
+    end
+
+    match =
+        value.match(
+            /\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})/ \
+            '(?::(\d{2})(?:\.(\d+))?)?' \
+            '(Z|[+-]\d{2}:?\d{2})?\z/')
+    return nil if match.nil?
+
+    year = match[1].to_i
+    month = match[2].to_i
+    day = match[3].to_i
+    hour = match[4].to_i
+    minute = match[5].to_i
+    second = match[6]&.to_i || 0
+    fraction = match[7]
+    offset = match[8]
+    return nil unless valid_original_created_components?(year, month, day, hour, minute, second)
+    return nil if offset.present? && !(valid_original_created_offset?(offset))
+
+    if offset.present?
+      return Time.new(
+          year,
+          month,
+          day,
+          hour,
+          minute,
+          second + Rational(parse_original_created_nanoseconds(fraction), 1_000_000_000),
+          normalise_original_created_offset(offset)).in_time_zone
+    end
+
+    Time.zone.local(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second).change(nsec: parse_original_created_nanoseconds(fraction))
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def minute_precision_time? value
+    value.sec.zero? && value.nsec.zero?
+  end
+
+  def valid_original_created_components? year, month, day, hour, minute, second
+    return false unless Date.valid_date?(year, month, day)
+    return false unless hour.between?(0, 23)
+    return false unless minute.between?(0, 59)
+    return false unless second.between?(0, 59)
+
+    true
+  end
+
+  def valid_original_created_offset? value
+    match = value.match(/\A([+-])(\d{2}):?(\d{2})\z/)
+    return true if value == 'Z'
+    return false if match.nil?
+
+    hours = match[2].to_i
+    minutes = match[3].to_i
+    hours.between?(0, 23) && minutes.between?(0, 59)
+  end
+
+  def parse_original_created_nanoseconds value
+    return 0 if value.blank?
+
+    digits = value[0, 9].ljust(9, '0')
+    Integer(digits, 10)
+  end
+
+  def normalise_original_created_offset value
+    return '+00:00' if value == 'Z'
+
+    value.match?(/\A[+-]\d{2}:\d{2}\z/) ? value : "#{ value[0, 3] }:#{ value[3, 2] }"
+  end
+
+  def skip_original_created_validation?
+    return false if new_record?
+    return false if will_save_change_to_original_created_from?
+    return false if will_save_change_to_original_created_before?
+
+    true
   end
 end

backend/app/models/post_url_sanitisation_rule.rb

@@ -0,0 +1,163 @@
+class PostUrlSanitisationRule < ApplicationRecord
+  include Discard::Model
+
+  class InvalidUrlError < StandardError
+    attr_reader :invalid_rows
+
+    def initialize(invalid_rows)
+      @invalid_rows = invalid_rows
+      ids = invalid_rows.map { _1.fetch(:post_id) }.join(', ')
+      super("post URL sanitisation produced invalid URLs for posts #{ ids }")
+    end
+  end
+
+  class UrlConflictError < StandardError
+    attr_reader :conflicts
+
+    def initialize(conflicts)
+      @conflicts = conflicts
+      urls = conflicts.map { _1.fetch(:url) }.uniq.join(', ')
+      super("post URL sanitisation conflicts detected for #{ urls }")
+    end
+  end
+
+  self.primary_key = :priority
+
+  default_scope -> { kept }
+
+  validates :source_pattern, presence: true, uniqueness: true
+
+  validate :source_pattern_must_be_regexp
+
+  class << self
+    def sanitise(url) = sanitise_with_rules(url, rules)
+
+    def apply!
+      rewrites = nil
+
+      Post.transaction do
+        compiled_rules = rules
+
+        rewrites = Post.order(:id)
+                       .lock('FOR UPDATE')
+                       .pluck(:id, :url)
+                       .map do |post_id, original_url|
+          { post_id:,
+            original_url:,
+            sanitised_url: sanitise_with_rules(original_url, compiled_rules) }
+        end
+
+        invalid_rows = rewrites.filter { invalid_sanitised_url?(_1.fetch(:sanitised_url)) }
+                               .map { { post_id: _1.fetch(:post_id),
+                                        original_url: _1.fetch(:original_url),
+                                        sanitised_url: _1.fetch(:sanitised_url) } }
+        raise InvalidUrlError.new(invalid_rows) if invalid_rows.present?
+
+        conflicts = build_conflicts(rewrites)
+        raise UrlConflictError.new(conflicts) if conflicts.present?
+
+        changed = rewrites.filter { _1.fetch(:original_url) != _1.fetch(:sanitised_url) }
+        return if changed.empty?
+
+        token = SecureRandom.hex(6)
+
+        changed.each do |row|
+          Post.where(id: row.fetch(:post_id))
+              .update_all(url: temporary_url_for(row.fetch(:post_id), token))
+        end
+
+        changed.each do |row|
+          Post.where(id: row.fetch(:post_id))
+              .update_all(url: row.fetch(:sanitised_url))
+        end
+      end
+    rescue ActiveRecord::RecordNotUnique => error
+      conflicts = build_persisted_conflicts(rewrites)
+      raise error if conflicts.empty?
+
+      raise UrlConflictError.new(conflicts), cause: error
+    end
+
+    private
+
+    def rules = kept.order(:priority).map { |r| [Regexp.new(r.source_pattern), r.replacement] }
+
+    def sanitise_with_rules(url, compiled_rules)
+      compiled_rules.reduce(url.dup) do |value, (pattern, replacement)|
+        value.sub(pattern, replacement)
+      end
+    end
+
+    def temporary_url_for(post_id, token) =
+        "https://post-url-sanitising.invalid/#{ token }/#{ post_id }"
+
+    def invalid_sanitised_url?(url)
+      return true if url.blank?
+      return true if url.length > 768
+
+      parsed = URI.parse(url)
+      return true if !(parsed in URI::HTTP)
+      return true if parsed.host.blank?
+
+      false
+    rescue URI::InvalidURIError
+      true
+    end
+
+    def build_conflicts(rewrites)
+      rewrites
+          .group_by { _1.fetch(:sanitised_url).downcase }
+          .values
+          .filter { _1.size > 1 }
+          .flatten
+          .map { { url: _1.fetch(:sanitised_url),
+                   post_id: _1.fetch(:post_id),
+                   original_url: _1.fetch(:original_url) } }
+    end
+
+    def build_persisted_conflicts(rewrites)
+      return [] if rewrites.blank?
+
+      target_rows = rewrites.filter { _1.fetch(:original_url) != _1.fetch(:sanitised_url) }
+      target_keys = target_rows.map { _1.fetch(:sanitised_url).downcase }.uniq
+      return [] if target_keys.empty?
+
+      target_pairs = target_rows.to_h do |row|
+        [row.fetch(:post_id), row.fetch(:sanitised_url).downcase]
+      end
+
+      persisted_rows = Post.order(:id)
+                           .where('LOWER(url) IN (?)', target_keys)
+                           .pluck(:id, :url)
+                           .reject { |post_id, original_url| target_pairs[post_id] == original_url.downcase }
+                           .map { |post_id, original_url|
+        { url: original_url,
+          post_id:,
+          original_url:,
+          conflict_key: original_url.downcase }
+      }
+
+      target_conflicts = target_rows.map { { url: _1.fetch(:sanitised_url),
+                                             post_id: _1.fetch(:post_id),
+                                             original_url: _1.fetch(:original_url),
+                                             conflict_key: _1.fetch(:sanitised_url).downcase } }
+
+      (persisted_rows + target_conflicts)
+          .group_by { _1.fetch(:conflict_key) }
+          .values
+          .filter { _1.size > 1 }
+          .flatten
+          .map { _1.except(:conflict_key) }
+    end
+  end
+
+  private
+
+  def source_pattern_must_be_regexp
+    return if source_pattern.blank?
+
+    Regexp.new(source_pattern)
+  rescue RegexpError
+    errors.add :source_pattern, '変な正規表現だね〜（笑）'
+  end
+end

backend/app/services/post_creator.rb

@@ -0,0 +1,137 @@
+class PostCreator
+  class VideoMsParseError < ArgumentError; end
+
+  attr_reader :field_warnings
+
+  def initialize actor:, attributes:
+    @actor = actor
+    @attributes = attributes.symbolize_keys
+    @field_warnings = { }
+  end
+
+  def create!
+    post = Post.new(title: @attributes[:title].presence,
+                    url: @attributes[:url],
+                    thumbnail_base: @attributes[:thumbnail_base].presence,
+                    uploaded_user: @actor,
+                    original_created_from: @attributes[:original_created_from].presence,
+                    original_created_before: @attributes[:original_created_before].presence)
+    attach_thumbnail!(post)
+
+    ApplicationRecord.transaction do
+      post.save!
+      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
+          { tags:, sections: }
+      TagVersioning.record_tag_snapshots!(tags, created_by_user: @actor)
+      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
+      post.video_ms = normalise_video_ms(tags)
+      validate_video_sections!(post.video_ms, sections)
+      post.save!
+      sync_post_tags!(post, tags, sections)
+      sync_parent_posts!(post, parent_post_ids)
+      PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
+    end
+    post
+  end
+
+  private
+
+  def attach_thumbnail! post
+    thumbnail = @attributes[:thumbnail]
+    if thumbnail.present?
+      post.thumbnail.attach(Post.resized_thumbnail_attachment(thumbnail))
+      return
+    end
+
+    thumbnail_base = post.thumbnail_base
+    return if thumbnail_base.blank?
+
+    post.attach_thumbnail_from_url!(thumbnail_base)
+  rescue Post::RemoteThumbnailFetchFailed => e
+    @field_warnings[:thumbnail_base] = [e.message]
+  end
+
+  def tag_names = @attributes[:tags].to_s.split
+
+  def parent_post_ids
+    Array(@attributes[:parent_post_ids]).flat_map { _1.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 normalise_video_ms tags
+    return nil unless tags.any? { _1.id == Tag.video.id }
+
+    video_ms = @attributes[:video_ms]
+    if video_ms.present?
+      value = Integer(video_ms, exception: false)
+      raise VideoMsParseError unless value&.positive?
+
+      return value
+    end
+    duration = @attributes[:duration]
+    return nil if duration.blank?
+
+    value = Tag.time_to_ms!(duration.to_s, tag_name: '動画時間')
+    raise VideoMsParseError unless value.positive?
+
+    value
+  rescue Tag::SectionLiteralParseError
+    raise VideoMsParseError
+  end
+
+  def validate_video_sections! video_ms, sections
+    return unless video_ms
+
+    sections.each_value do |ranges|
+      ranges.each do |begin_ms, end_ms|
+        post = Post.new
+        if begin_ms >= video_ms
+          post.errors.add :video_ms, 'タグ区間の開始が動画時間以上です．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+        if end_ms && end_ms > video_ms
+          post.errors.add :video_ms, 'タグ区間の終端が動画時間を超えてゐます．'
+          raise ActiveRecord::RecordInvalid, post
+        end
+      end
+    end
+  end
+
+  def sync_post_tags! post, desired_tags, sections
+    desired_ids = desired_tags.map(&:id).to_set
+    current_ids = post.tags.pluck(:id).to_set
+    Tag.where(id: desired_ids - current_ids).find_each do |tag|
+      PostTag.create_or_find_by!(post:, tag:, created_user: @actor)
+    end
+    PostTagSection.where(post_id: post.id).destroy_all
+    sections.each do |tag_id, ranges|
+      ranges.each do |begin_ms, end_ms|
+        PostTagSection.create!(post_id: post.id,
+                               tag_id:,
+                               begin_ms:,
+                               end_ms:)
+      end
+    end
+    PostTag.where(post_id: post.id,
+                  tag_id: (current_ids - desired_ids).to_a).kept.find_each do |post_tag|
+      post_tag.discard_by!(@actor)
+    end
+  end
+
+  def sync_parent_posts! post, ids
+    if 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
+    missing = ids - Post.where(id: ids).pluck(:id)
+    if missing.present?
+      post.errors.add :parent_post_ids, "存在しない親投稿 Id. があります: #{ missing.join(' ') }"
+      raise ActiveRecord::RecordInvalid, post
+    end
+    ids.each { |parent_post_id| PostImplication.create_or_find_by!(post:, parent_post_id:) }
+  end
+end

backend/app/services/post_import_previewer.rb

@@ -0,0 +1,503 @@
+require 'time'
+require 'timeout'
+
+class PostImportPreviewer
+  FIELDS = [
+    'title',
+    'thumbnail_base',
+    'original_created_from',
+    'original_created_before',
+    'duration',
+    'tags',
+    'parent_post_ids'].freeze
+  FETCH_WARNING_FIELDS = ['url', 'title', 'thumbnail_base'].freeze
+  TITLE_FETCH_WARNING = 'タイトルを取得できませんでした．'.freeze
+  THUMBNAIL_FETCH_WARNING = 'サムネールを取得できませんでした．'.freeze
+  METADATA_FETCH_WARNING = 'メタデータを取得できませんでした．'.freeze
+
+  def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
+    prepared_rows = rows.map { prepare_row(_1) }
+    url_counts = prepared_rows.filter_map { _1[:normal_url] }.tally
+    existing_posts =
+        Post.where(url: prepared_rows.map { _1[:normal_url] }.compact.uniq).index_by(&:url)
+    existing_parent_ids = preload_parent_ids(prepared_rows)
+    preload_metadata!(
+        prepared_rows,
+        fetch_metadata,
+        metadata_cache,
+        existing_posts,
+        url_counts)
+    known_tags =
+        preload_known_tags(
+            prepared_rows,
+            fetch_metadata,
+            metadata_cache,
+            existing_posts,
+            url_counts)
+    prepared_rows.map { |row|
+      preview_row(row,
+                  fetch_metadata:,
+                  metadata_cache:,
+                  existing_posts:,
+                  url_counts:,
+                  known_tags:,
+                  existing_parent_ids:)
+    }
+  end
+
+  def normalised_url value
+    PostUrlNormaliser.normalise(value)
+  end
+
+  private
+
+  def prepare_row row
+    source = row.symbolize_keys
+    url = source[:url].to_s.strip
+    normal_url = normalised_url(url)
+    source.merge(url_text: url, normal_url:, url_error: validate_url_safety(normal_url))
+  end
+
+  def preview_row row,
+                  fetch_metadata:,
+                  metadata_cache:,
+                  existing_posts:,
+                  url_counts:,
+                  known_tags:,
+                  existing_parent_ids:
+    attributes = initial_attributes(row)
+    provenance = initial_provenance(row)
+    tag_sources = initial_tag_sources(row, attributes, provenance)
+    field_warnings = initial_field_warnings(row)
+    base_warnings = initial_base_warnings(row)
+    url = row[:url_text]
+    provenance['url'] = 'manual'
+    normal_url = row[:normal_url]
+    url_for_metadata = normal_url || url
+    existing_post = normal_url.present? ? existing_posts[normal_url] : nil
+
+    validation_errors = {}
+    validation_errors[:url] = ['URL が不正です．'] if normal_url.blank?
+    if row[:url_error].present?
+      validation_errors[:url] = [row[:url_error]]
+    end
+    if normal_url.present? && url_counts[normal_url].to_i > 1
+      validation_errors[:url] = ['URL が重複しています．']
+    end
+
+    if row[:metadata_url].present? && row[:metadata_url] != url_for_metadata
+      clear_automatic_values!(attributes, provenance, tag_sources)
+      field_warnings = { }
+      base_warnings = [ ]
+    end
+
+    if validation_errors.blank? && normal_url.present? && existing_post
+      attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+      warnings_present = field_warnings.values.any?(&:present?) || base_warnings.present?
+      return { source_row: row[:source_row],
+               url: normal_url,
+               attributes:,
+               provenance:,
+               tag_sources:,
+               metadata_url: url_for_metadata,
+               skip_reason: 'existing',
+               existing_post_id: existing_post.id,
+               field_warnings:,
+               base_warnings:,
+               validation_errors:,
+               status: warnings_present ? 'warning' : 'ready' }
+    end
+
+    should_fetch = validation_errors.blank?
+    should_fetch &&= should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+    if should_fetch
+      clear_fetch_warnings!(field_warnings)
+      metadata = metadata_for(url_for_metadata, metadata_cache)
+      if metadata[:validation_errors].present?
+        validation_errors.merge!(metadata[:validation_errors])
+      else
+        apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
+        apply_fetch_warnings!(field_warnings, metadata[:warnings])
+      end
+    end
+
+    attributes['url'] = url
+    validate_basic_data(attributes, validation_errors)
+    validate_preview_tags(merged_tags(tag_sources, provenance['tags']),
+                          validation_errors,
+                          field_warnings,
+                          known_tags)
+    validate_parents(attributes['parent_post_ids'], validation_errors, existing_parent_ids)
+    attributes.delete('url')
+    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+
+    warnings_present = field_warnings.values.any?(&:present?) || base_warnings.present?
+    { source_row: row[:source_row],
+      url: validation_errors[:url].present? ? url : (normal_url || url),
+      attributes:,
+      provenance:,
+      tag_sources:,
+      metadata_url: url_for_metadata,
+      skip_reason: nil,
+      existing_post_id: nil,
+      field_warnings:,
+      base_warnings:,
+      validation_errors:,
+      status: validation_errors.present? ? 'error' : (warnings_present ? 'warning' : 'ready') }
+  end
+
+  def should_fetch_metadata? fetch_metadata, source_row
+    case fetch_metadata
+    when true then true
+    when Integer then fetch_metadata == source_row
+    when false, nil then false
+    else raise ArgumentError, 'メタデータ取得対象が不正です．'
+    end
+  end
+
+  def initial_attributes row
+    attributes = row[:attributes]&.stringify_keys || { }
+    FIELDS.to_h { |field|
+      value = attributes[field]
+      normalised =
+          if field == 'duration'
+            normalise_duration_attribute(value)
+          else
+            value.to_s
+          end
+      [field, normalised] }
+  end
+
+  def initial_provenance row
+    provenance = row[:provenance]&.stringify_keys || { }
+    FIELDS.to_h { |field| [field, provenance[field].presence || 'automatic'] }
+      .merge('url' => 'manual')
+  end
+
+  def initial_tag_sources row, attributes, provenance
+    sources = row[:tag_sources]&.stringify_keys || { 'automatic' => '', 'manual' => '' }
+    sources['automatic'] = sources['automatic'].to_s
+    sources['manual'] =
+      provenance['tags'] == 'manual' ? attributes['tags'].to_s : sources['manual'].to_s
+    sources
+  end
+
+  def initial_field_warnings row
+    (row[:field_warnings] || { })
+      .stringify_keys
+      .transform_values { |value| Array(value).map(&:to_s) }
+  end
+
+  def initial_base_warnings row
+    Array(row[:base_warnings]).map(&:to_s)
+  end
+
+  def clear_automatic_values! attributes, provenance, tag_sources
+    ['title', 'thumbnail_base', 'original_created_from',
+     'original_created_before', 'duration'].each do |field|
+      attributes[field] = '' if provenance[field] == 'automatic'
+    end
+    tag_sources['automatic'] = ''
+    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+  end
+
+  def clear_fetch_warnings! field_warnings
+    FETCH_WARNING_FIELDS.each do |field|
+      field_warnings.delete(field)
+    end
+  end
+
+  def metadata_for url, cache
+    cache[url] ||= fetch_metadata(url)
+  end
+
+  def fetch_metadata url
+    return { data: { }, warnings: { 'url' => ['URL が空です．'] },
+             validation_errors: { } } if url.blank?
+
+    data = sanitise_metadata(PostMetadataFetcher.fetch(url).stringify_keys.compact)
+    warnings = { }
+    add_field_warning!(warnings, 'title', TITLE_FETCH_WARNING) if data['title'].blank?
+    if data['thumbnail_base'].blank?
+      add_field_warning!(warnings, 'thumbnail_base', THUMBNAIL_FETCH_WARNING)
+    end
+    { data:, warnings:, validation_errors: { } }
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    Rails.logger.info(
+        "post_import_metadata_fetch_unsafe_url "\
+        "#{ { error: e.class.name, message: e.message }.to_json }")
+    { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
+  rescue Preview::HttpFetcher::FetchFailed,
+         Preview::HttpFetcher::ResponseTooLarge => e
+    Rails.logger.info(
+        "post_import_metadata_fetch_failure "\
+        "#{ { error: e.class.name, message: e.message }.to_json }")
+    { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
+  end
+
+  def sanitise_metadata metadata
+    {
+        'title' => sanitise_metadata_title(metadata['title']),
+        'thumbnail_base' => sanitise_metadata_url(metadata['thumbnail_base']),
+        'original_created_from' => sanitise_metadata_time(metadata['original_created_from']),
+        'original_created_before' => sanitise_metadata_time(metadata['original_created_before']),
+        'duration' => sanitise_metadata_duration(metadata['duration']),
+        'tags' => metadata['tags'].to_s.presence }.compact
+  end
+
+  def sanitise_metadata_title value
+    value.is_a?(String) ? value.presence : nil
+  end
+
+  def sanitise_metadata_url value
+    return nil unless value.is_a?(String)
+
+    PostUrlNormaliser.normalise(value)
+  end
+
+  def sanitise_metadata_time value
+    return nil unless value.is_a?(String)
+
+    Time.iso8601(value).in_time_zone.change(sec: 0, nsec: 0).iso8601
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def sanitise_metadata_duration value
+    return nil unless value.is_a?(String)
+
+    value.presence
+  end
+
+  def normalise_duration_attribute value
+    return '' if value.nil?
+    return value if value.is_a?(String)
+
+    milliseconds = Integer(value, exception: false)
+    return value.to_s if milliseconds.nil? || milliseconds <= 0
+
+    seconds_string = (milliseconds / 1_000.0).to_s
+    seconds_string.end_with?('.0') ? seconds_string.delete_suffix('.0') : seconds_string
+  end
+
+  def preload_metadata! prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+    urls = prepared_rows.filter_map { |row|
+      next unless row[:normal_url].present?
+      next if row[:url_error].present?
+      next unless should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+      next if url_counts[row[:normal_url]].to_i > 1
+      next if existing_posts.key?(row[:normal_url])
+
+      row[:normal_url]
+    }.uniq
+    urls = urls.reject { metadata_cache.key?(_1) }
+    return if urls.empty?
+
+    url_queue = Queue.new
+    result_queue = Queue.new
+    urls.each { url_queue << _1 }
+    workers = [urls.length, 4].min.times.map {
+      Thread.new {
+        Rails.application.executor.wrap do
+          loop do
+            url = url_queue.pop(true)
+            result_queue << [url, safe_fetch_metadata(url)]
+          rescue ThreadError
+            break
+          end
+        end
+      }
+    }
+    Timeout.timeout(15) { workers.each(&:join) }
+  rescue Timeout::Error
+    workers&.each(&:kill)
+  ensure
+    workers&.each(&:join)
+    while result_queue&.size.to_i.positive?
+      url, result = result_queue.pop
+      metadata_cache[url] = result
+    end
+    urls&.each do |url|
+      metadata_cache[url] ||= { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] } }
+    end
+  end
+
+  def safe_fetch_metadata url
+    fetch_metadata(url)
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    Rails.logger.info(
+        "post_import_metadata_fetch_unsafe_url "\
+        "#{ { error: e.class.name, message: e.message }.to_json }")
+    { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
+  rescue StandardError => e
+    Rails.logger.error(
+        "post_import_metadata_fetch_unexpected_failure "\
+        "#{ { error: e.class.name, message: e.message }.to_json }")
+    { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
+  end
+
+  def preload_known_tags prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+    names = prepared_rows.flat_map { |row|
+      attributes = initial_attributes(row)
+      provenance = initial_provenance(row)
+      tag_sources = initial_tag_sources(row, attributes, provenance)
+      if metadata_url_changed?(row)
+        clear_automatic_values!(attributes, provenance, tag_sources)
+      end
+      if should_apply_metadata_to_row?(row, fetch_metadata, existing_posts, url_counts)
+        metadata = metadata_for(row[:normal_url], metadata_cache)
+        apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
+      end
+      preview_tag_names(merged_tags(tag_sources, provenance['tags']))
+    }.compact.uniq
+    return { } if names.empty?
+
+    Tag.joins(:tag_name)
+      .where(tag_names: { name: names })
+      .includes(:tag_name)
+      .to_a
+      .index_by(&:name)
+  end
+
+  def preload_parent_ids prepared_rows
+    ids = prepared_rows.flat_map { |row|
+      attributes = initial_attributes(row)
+      preview_parent_ids(attributes['parent_post_ids'])
+    }.uniq
+    return { } if ids.empty?
+
+    Post.where(id: ids).pluck(:id).to_h { [_1, true] }
+  end
+
+  def metadata_url_changed? row
+    row[:metadata_url].present? && row[:metadata_url] != (row[:normal_url] || row[:url_text])
+  end
+
+  def should_apply_metadata_to_row? row, fetch_metadata, existing_posts, url_counts
+    normal_url = row[:normal_url]
+    return false if normal_url.blank?
+    return false if row[:url_error].present?
+    return false if url_counts[normal_url].to_i > 1
+    return false if existing_posts.key?(normal_url)
+
+    should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+  end
+
+  def validate_url_safety normal_url
+    return nil if normal_url.blank?
+
+    Preview::UrlSafety.validate(normal_url)
+    nil
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    e.message
+  end
+
+  def apply_metadata! attributes, provenance, tag_sources, metadata
+    metadata.each do |field, value|
+      if field == 'tags'
+        next if provenance['tags'] == 'manual'
+
+        tag_sources['automatic'] = value.to_s
+        attributes['tags'] = merged_tags(tag_sources)
+        next
+      end
+      next unless provenance[field] == 'automatic'
+
+      attributes[field] = value
+      provenance[field] = 'automatic'
+    end
+  end
+
+  def apply_fetch_warnings! field_warnings, warnings
+    warnings.each do |field, values|
+      values.each do |value|
+        add_field_warning!(field_warnings, field, value)
+      end
+    end
+  end
+
+  def add_field_warning! field_warnings, field, message
+    field_warnings[field] ||= []
+    field_warnings[field] << message unless field_warnings[field].include?(message)
+  end
+
+  def merged_tags sources, origin = nil
+    return sources['manual'].to_s if origin == 'manual'
+
+    sources['automatic'].to_s
+  end
+
+  def preview_tag_names raw
+    names = raw.to_s.split
+    return [] if names.empty?
+    if names.any? { _1.downcase.start_with?('nico:') }
+      return []
+    end
+
+    names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+  rescue Tag::SectionLiteralParseError
+    []
+  end
+
+  def validate_preview_tags raw, errors, field_warnings, known_tags
+    names = raw.to_s.split
+    return if names.empty?
+    if names.any? { _1.downcase.start_with?('nico:') }
+      errors[:tags] = ['ニコニコ・タグは直接指定できません．']
+      return
+    end
+
+    parsed = names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+    existing = parsed.filter_map { known_tags[_1] }
+    deprecated = existing.select(&:deprecated?).map(&:name)
+    errors[:tags] = ["廃止済みタグがあります: #{ deprecated.join(' ') }"] if deprecated.present?
+    known = existing.reject(&:deprecated?).map(&:name)
+    new_tags = parsed.uniq - known
+    if new_tags.present?
+      add_field_warning!(field_warnings, 'tags', "新規タグを作成します: #{ new_tags.join(' ') }")
+    end
+  rescue Tag::SectionLiteralParseError
+    errors[:tags] = ['タグ区間の記法が不正です．']
+  end
+
+  def validate_basic_data attributes, errors
+    post = Post.new(title: attributes['title'].presence,
+                    url: attributes['url'],
+                    thumbnail_base: attributes['thumbnail_base'].presence,
+                    original_created_from: attributes['original_created_from'].presence,
+                    original_created_before: attributes['original_created_before'].presence,
+                    video_ms: parse_duration(attributes['duration'], errors))
+    post.valid?
+    post.errors.each do |error|
+      next if error.attribute == :url && error.type == :taken
+
+      (errors[error.attribute] ||= []) << error.message
+    end
+  end
+
+  def parse_duration value, errors
+    return nil if value.blank?
+
+    Tag.time_to_ms!(value.to_s, tag_name: '動画時間')
+  rescue Tag::SectionLiteralParseError
+    errors[:video_ms] = ['動画時間の記法が不正です．']
+    nil
+  end
+
+  def preview_parent_ids raw
+    raw.to_s.split.map { Integer(_1, exception: false) }.compact
+  end
+
+  def validate_parents raw, errors, existing_parent_ids
+    ids = raw.to_s.split.map { Integer(_1, exception: false) }
+    return if ids.compact.empty? && raw.to_s.blank?
+
+    if ids.any? { _1.nil? || _1 <= 0 }
+      errors[:parent_post_ids] = ['親投稿 Id. が不正です．']
+      return
+    end
+    if ids.uniq.any? { !existing_parent_ids[_1] }
+      errors[:parent_post_ids] = ['存在しない親投稿 Id. があります．']
+    end
+  end
+end

backend/app/services/post_import_row_normaliser.rb

@@ -0,0 +1,190 @@
+class PostImportRowNormaliser
+  ORIGINS = ['automatic', 'manual'].freeze
+  STRING_FIELDS = [
+    'title',
+    'thumbnail_base',
+    'original_created_from',
+    'original_created_before',
+    'duration',
+    'tags',
+    'parent_post_ids'].freeze
+  FLEXIBLE_FIELDS = ['video_ms'].freeze
+  ATTRIBUTE_FIELDS = (STRING_FIELDS + FLEXIBLE_FIELDS).freeze
+
+  def self.normalise! rows, allow_warning_fields: false
+    raise ArgumentError, '取込行の形式が不正です．' unless rows.is_a?(Array)
+    raise ArgumentError, '取込件数が多すぎます．' if rows.length > PostImportUrlListParser::MAX_ROWS
+
+    normalised_rows = rows.map { normalise_row!(_1, allow_warning_fields:) }
+    source_rows = normalised_rows.map { _1['source_row'] }
+    raise ArgumentError, '元行番号が重複しています．' if source_rows.uniq.length != source_rows.length
+    if normalised_rows.sum { row_bytesize(_1) } > PostImportUrlListParser::MAX_BYTES
+      raise ArgumentError, '取込データが大きすぎます．'
+    end
+
+    normalised_rows
+  end
+
+  def self.normalise_row! row, allow_warning_fields:
+    unless row.is_a?(Hash) || row.is_a?(ActionController::Parameters)
+      raise ArgumentError, '取込行の形式が不正です．'
+    end
+
+    parameters =
+        row.is_a?(ActionController::Parameters) ? row : ActionController::Parameters.new(row)
+    permitted = parameters.permit(*permitted_keys(allow_warning_fields))
+    normalised = permitted.to_h.deep_transform_keys { _1.to_s.underscore }
+
+    normalised['source_row'] = normalise_source_row!(normalised['source_row'])
+    normalise_url!(normalised['url'])
+    normalise_metadata_url!(normalised['metadata_url'])
+    normalise_attributes!(normalised.fetch('attributes', { }))
+    normalise_provenance!(normalised.fetch('provenance', { }))
+    normalise_tag_sources!(normalised['tag_sources'])
+    normalise_warning_values!(normalised, allow_warning_fields:)
+    if row_bytesize(normalised) > PostImportUrlListParser::MAX_BYTES
+      raise ArgumentError, '取込行が大きすぎます．'
+    end
+
+    normalised
+  end
+
+  def self.permitted_keys allow_warning_fields
+    keys = [
+      :source_row,
+      :sourceRow,
+      :url,
+      :metadata_url,
+      :metadataUrl,
+      { attributes: {} },
+      { provenance: {} },
+      { tag_sources: {} },
+      { tagSources: {} }]
+    return keys unless allow_warning_fields
+
+    keys + [
+      { field_warnings: {} },
+      { fieldWarnings: {} },
+      { base_warnings: [] },
+      { baseWarnings: [] }]
+  end
+  private_class_method :permitted_keys
+
+  def self.normalise_source_row! value
+    source_row = Integer(value, exception: false)
+    raise ArgumentError, '元行番号が不正です．' if source_row.nil? || source_row <= 0
+
+    source_row
+  end
+  private_class_method :normalise_source_row!
+
+  def self.normalise_url! value
+    unless value.is_a?(String)
+      raise ArgumentError, 'URL の形式が不正です．'
+    end
+    if value.bytesize > PostImportUrlListParser::MAX_URL_BYTES
+      raise ArgumentError, 'URL が長すぎます．'
+    end
+  end
+  private_class_method :normalise_url!
+
+  def self.normalise_metadata_url! value
+    raise ArgumentError, 'metadata_url の形式が不正です．' unless value.nil? || value.is_a?(String)
+    if value.to_s.bytesize > PostImportUrlListParser::MAX_URL_BYTES
+      raise ArgumentError, 'metadata_url が長すぎます．'
+    end
+  end
+  private_class_method :normalise_metadata_url!
+
+  def self.normalise_attributes! attributes
+    raise ArgumentError, 'attributes の形式が不正です．' unless attributes.is_a?(Hash)
+    raise ArgumentError, '取込項目が不正です．' unless (attributes.keys - ATTRIBUTE_FIELDS).empty?
+
+    attributes.each do |key, value|
+      case key
+      when *STRING_FIELDS
+        raise ArgumentError, '取込項目の型が不正です．' unless value.nil? || value.is_a?(String)
+      when *FLEXIBLE_FIELDS
+        unless value.nil? || value.is_a?(String) || value.is_a?(Numeric)
+          raise ArgumentError, '取込項目の型が不正です．'
+        end
+      end
+      if value.to_s.bytesize > PostImportUrlListParser::MAX_URL_BYTES
+        raise ArgumentError, '取込項目が大きすぎます．'
+      end
+    end
+  end
+  private_class_method :normalise_attributes!
+
+  def self.normalise_provenance! provenance
+    unless provenance.is_a?(Hash)
+      raise ArgumentError, 'provenance の形式が不正です．'
+    end
+
+    allowed = ATTRIBUTE_FIELDS + ['url']
+    unless (provenance.keys - allowed).empty?
+      raise ArgumentError, '値の由来が不正です．'
+    end
+    unless provenance.values.all? { ORIGINS.include?(_1) }
+      raise ArgumentError, '値の由来が不正です．'
+    end
+  end
+  private_class_method :normalise_provenance!
+
+  def self.normalise_tag_sources! tag_sources
+    return if tag_sources.nil?
+
+    unless tag_sources.is_a?(Hash)
+      raise ArgumentError, 'タグ由来の形式が不正です．'
+    end
+    unless (tag_sources.keys - ORIGINS).empty?
+      raise ArgumentError, 'タグ由来の形式が不正です．'
+    end
+    unless tag_sources.values.all? { _1.is_a?(String) }
+      raise ArgumentError, 'タグ由来の形式が不正です．'
+    end
+    if tag_sources.values.any? { _1.bytesize > PostImportUrlListParser::MAX_URL_BYTES }
+      raise ArgumentError, 'タグ由来が大きすぎます．'
+    end
+    if tag_sources.values.sum(&:bytesize) > PostImportUrlListParser::MAX_URL_BYTES
+      raise ArgumentError, 'タグ由来が大きすぎます．'
+    end
+  end
+  private_class_method :normalise_tag_sources!
+
+  def self.normalise_warning_values! normalised, allow_warning_fields:
+    return unless allow_warning_fields
+
+    field_warnings = normalised['field_warnings']
+    unless field_warnings.nil? || field_warnings.is_a?(Hash)
+      raise ArgumentError, '警告の形式が不正です．'
+    end
+    field_warnings&.each do |key, values|
+      unless ATTRIBUTE_FIELDS.include?(key) || key == 'url'
+        raise ArgumentError, '警告の形式が不正です．'
+      end
+      unless values.is_a?(Array) && values.all? { _1.is_a?(String) }
+        raise ArgumentError, '警告の形式が不正です．'
+      end
+      if values.any? { _1.bytesize > PostImportUrlListParser::MAX_URL_BYTES }
+        raise ArgumentError, '警告が大きすぎます．'
+      end
+    end
+
+    base_warnings = normalised['base_warnings']
+    return if base_warnings.nil?
+
+    unless base_warnings.is_a?(Array) && base_warnings.all? { _1.is_a?(String) }
+      raise ArgumentError, '警告の形式が不正です．'
+    end
+    if base_warnings.any? { _1.bytesize > PostImportUrlListParser::MAX_URL_BYTES }
+      raise ArgumentError, '警告が大きすぎます．'
+    end
+  end
+  private_class_method :normalise_warning_values!
+
+  def self.row_bytesize row
+    row.to_json.bytesize
+  end
+  private_class_method :row_bytesize
+end

backend/app/services/post_import_runner.rb

@@ -0,0 +1,109 @@
+class PostImportRunner
+  def initialize actor:, rows:
+    @actor = actor
+    @rows = rows
+  end
+
+  def run
+    normalised_rows = PostImportRowNormaliser.normalise!(@rows)
+    previews = PostImportPreviewer.new.preview_rows(rows: normalised_rows,
+                                                    fetch_metadata: false)
+    preview_map = previews.index_by { _1[:source_row] }
+
+    results = normalised_rows.map do |row|
+      run_row(row, preview_map.fetch(row['source_row']))
+    end
+
+    { created: results.count { _1[:status] == 'created' },
+      skipped: results.count { _1[:status] == 'skipped' },
+      failed: results.count { _1[:status] == 'failed' },
+      rows: results }
+  end
+
+  private
+
+  def run_row row, preview
+    attributes = row.fetch('attributes', { }).transform_keys { _1.to_s.underscore }
+    return { source_row: row['source_row'],
+             status: 'failed',
+             errors: preview[:validation_errors],
+             recoverable: true } if preview[:validation_errors].present?
+    if preview[:skip_reason] == 'existing'
+      return { source_row: row['source_row'],
+               status: 'skipped',
+               existing_post_id: preview[:existing_post_id] }
+    end
+
+    attributes['tags'] = preview[:attributes]['tags']
+    attributes['url'] = row['url']
+    creator = PostCreator.new(actor: @actor, attributes:)
+    post = creator.create!
+    result = { source_row: row['source_row'], status: 'created', post: PostRepr.base(post) }
+    if creator.field_warnings.present?
+      result[:field_warnings] = creator.field_warnings
+    end
+    result
+  rescue ActiveRecord::RecordInvalid => e
+    existing_post = existing_post_for_race(row, e.record)
+    if existing_post
+      return { source_row: row['source_row'],
+               status: 'skipped',
+               existing_post_id: existing_post.id }
+    end
+
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: e.record.errors.to_hash,
+      recoverable: true }
+  rescue ActiveRecord::RecordNotUnique => e
+    raise unless url_record_not_unique?(e)
+
+    existing_post = existing_post_for_race(row)
+    raise unless existing_post
+
+    { source_row: row['source_row'],
+      status: 'skipped',
+      existing_post_id: existing_post.id }
+  rescue Tag::NicoTagNormalisationError
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: { tags: ['ニコニコ・タグは直接指定できません．'] },
+      recoverable: true }
+  rescue Tag::DeprecatedTagNormalisationError
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: { tags: ['廃止済みタグは付与できません．'] },
+      recoverable: true }
+  rescue PostCreator::VideoMsParseError
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: { duration: ['動画時間の記法が不正です．'] },
+      recoverable: true }
+  rescue ArgumentError
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: { base: ['入力値が不正です．'] },
+      recoverable: true }
+  rescue StandardError => e
+    Rails.logger.error("post_import_runner_failure #{ { error: e.class.name,
+                                                        message: e.message }.to_json }")
+    { source_row: row['source_row'],
+      status: 'failed',
+      errors: { base: ['登録中にエラーが発生しました．'] } }
+  end
+
+  def existing_post_for_race row, record = nil
+    if record && !(record.errors.of_kind?(:url, :taken))
+      return nil
+    end
+
+    normal_url = PostUrlNormaliser.normalise(row['url'])
+    return nil if normal_url.blank?
+
+    Post.find_by(url: normal_url)
+  end
+
+  def url_record_not_unique? error
+    error.message.include?('index_posts_on_url')
+  end
+end

backend/app/services/post_import_url_list_parser.rb

@@ -0,0 +1,25 @@
+class PostImportUrlListParser
+  MAX_ROWS = 100
+  MAX_BYTES = 1.megabyte
+  MAX_URL_BYTES = 20.kilobytes
+
+  def self.parse source
+    raw = source.to_s
+    raise ArgumentError, '入力が大きすぎます．' if raw.bytesize > MAX_BYTES
+
+    rows = raw.split(/\r\n|\n|\r/).each_with_index.filter_map { |line, index|
+      url = line.strip
+      next if url.blank?
+
+      if url.bytesize > MAX_URL_BYTES
+        raise ArgumentError, "#{ index + 1 } 行目: URL が長すぎます．"
+      end
+
+      { source_row: index + 1, url: }
+    }
+    raise ArgumentError, 'URL を入力してください．' if rows.empty?
+    raise ArgumentError, "取込件数は #{ MAX_ROWS } 件までです．" if rows.length > MAX_ROWS
+
+    rows
+  end
+end

backend/app/services/post_metadata_fetcher.rb

@@ -0,0 +1,179 @@
+require 'time'
+require 'date'
+
+class PostMetadataFetcher
+  TIMESTAMP_PATTERN =
+      Regexp.new(
+          '\A(\d{4})-(\d{2})-(\d{2})T(\d{2})' \
+          '(?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?' \
+          '(Z|[+-]\d{2}:?\d{2})?\z')
+
+  def self.fetch raw_url
+    uri, = Preview::UrlSafety.validate(raw_url)
+    response = Preview::HttpFetcher.fetch(
+        uri.to_s,
+        max_bytes: Preview::ThumbnailFetcher::HTML_MAX_BYTES)
+    metadata = Preview::HtmlMetadataExtractor.extract(response)
+    document = Nokogiri::HTML.parse(response.body)
+    content = lambda { |name|
+      document
+        .at_css("meta[property='#{ name }'], meta[name='#{ name }']")
+        &.[]('content')
+        &.strip
+        &.presence
+    }
+    duration = content.call('og:video:duration') || content.call('video:duration')
+    published = content.call('article:published_time') || content.call('date')
+    created_range = original_created_range(published)
+    platform_tags = platform_tags(uri)
+    { title: metadata[:title],
+      thumbnail_base:
+          Preview::KnownSiteExtractor.thumbnail_url(uri) || metadata[:image_url],
+      original_created_from: serialise_time(created_range&.first),
+      original_created_before: serialise_time(created_range&.last),
+      duration: serialise_duration(duration),
+      tags: platform_tags.join(' ') }
+  end
+
+  def self.platform_tags uri
+    return ['動画', 'YouTube'] if Preview::KnownSiteExtractor.youtube_video_id(uri)
+    return ['動画', 'ニコニコ'] if Preview::KnownSiteExtractor.niconico_video_id(uri)
+
+    []
+  end
+
+  def self.original_created_range value
+    return nil if value.blank?
+
+    raw = value.to_s.strip
+    from, before =
+        case raw
+        when /\A(\d{4})\z/
+          year = Regexp.last_match(1).to_i
+          from = Time.zone.local(year, 1, 1)
+          [from, from + 1.year]
+        when /\A(\d{4})-(\d{2})\z/
+          year = Regexp.last_match(1).to_i
+          month = Regexp.last_match(2).to_i
+          return nil unless month.between?(1, 12)
+
+          from = Time.zone.local(year, month, 1)
+          [from, from + 1.month]
+        when /\A(\d{4})-(\d{2})-(\d{2})\z/
+          year = Regexp.last_match(1).to_i
+          month = Regexp.last_match(2).to_i
+          day = Regexp.last_match(3).to_i
+          return nil unless Date.valid_date?(year, month, day)
+
+          from = Time.zone.local(year, month, day)
+          [from, from + 1.day]
+        else
+          parse_timestamp_range(raw)
+        end
+    return nil if from.nil? || before.nil?
+
+    [from, before]
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def self.parse_timestamp_range raw
+    match = raw.match(TIMESTAMP_PATTERN)
+    return nil unless match
+
+    year = match[1].to_i
+    month = match[2].to_i
+    day = match[3].to_i
+    hour = match[4].to_i
+    minute = match[5]&.to_i || 0
+    second = match[6]&.to_i || 0
+    fraction = match[7]
+    offset = match[8]
+    return nil unless valid_timestamp_components?(year, month, day, hour, minute, second)
+    return nil unless valid_offset?(offset)
+
+    nanoseconds = parse_nanoseconds(fraction)
+    timestamp =
+        if offset.present?
+          Time.new(
+              year,
+              month,
+              day,
+              hour,
+              minute,
+              second + Rational(nanoseconds, 1_000_000_000),
+              parse_offset(offset)).in_time_zone
+        else
+          Time.zone.local(year, month, day, hour, minute, second).change(nsec: nanoseconds)
+        end
+
+    from = timestamp.change(sec: 0, nsec: 0)
+    before =
+        if match[5].nil?
+          from + 1.hour
+        else
+          from + 1.minute
+        end
+    [from, before]
+  end
+
+  def self.parse_nanoseconds value
+    return 0 if value.blank?
+
+    digits = value[0, 9].ljust(9, '0')
+    Integer(digits, 10)
+  end
+
+  def self.parse_offset value
+    return '+00:00' if value == 'Z'
+
+    value.match?(/\A[+-]\d{2}:\d{2}\z/) ? value : "#{ value[0, 3] }:#{ value[3, 2] }"
+  end
+
+  def self.serialise_duration value
+    seconds = Float(value)
+    return nil unless seconds.positive?
+
+    milliseconds = (seconds * 1_000).round
+    seconds_string = (milliseconds / 1_000.0).to_s
+    seconds_string.end_with?('.0') ? seconds_string.delete_suffix('.0') : seconds_string
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def self.valid_timestamp_components? year, month, day, hour, minute, second
+    return false unless Date.valid_date?(year, month, day)
+    return false unless hour.between?(0, 23)
+    return false unless minute.between?(0, 59)
+    return false unless second.between?(0, 59)
+
+    true
+  end
+
+  def self.valid_offset? value
+    return true if value.nil? || value == 'Z'
+
+    match = value.match(/\A([+-])(\d{2}):?(\d{2})\z/)
+    return false if match.nil?
+
+    hours = match[2].to_i
+    minutes = match[3].to_i
+    hours.between?(0, 23) && minutes.between?(0, 59)
+  end
+
+  def self.serialise_time value
+    return nil if value.nil?
+
+    value.nsec.zero? ? value.iso8601 : value.iso8601(9)
+  end
+
+  private_class_method :platform_tags,
+                       :original_created_range,
+                       :parse_timestamp_range,
+                       :parse_nanoseconds,
+                       :parse_offset,
+                       :serialise_duration,
+                       :valid_timestamp_components?,
+                       :valid_offset?,
+                       :serialise_time
+end

backend/app/services/post_url_normaliser.rb

@@ -0,0 +1,13 @@
+class PostUrlNormaliser
+  def self.normalise raw_url
+    value = raw_url.to_s.strip
+    uri = URI.parse(value)
+    return nil unless uri.is_a?(URI::HTTP) && uri.host.present?
+
+    uri.host = uri.host.downcase
+    uri.path = uri.path.sub(/\/\z/, '') if uri.path.present?
+    PostUrlSanitisationRule.sanitise(uri.to_s)
+  rescue URI::InvalidURIError
+    nil
+  end
+end

backend/app/services/preview/http_fetcher.rb

@@ -67,7 +67,8 @@ module Preview
       log_failure(:timeout, url: uri&.to_s || raw_url, error: e.class.name, message: e.message)
       raise FetchTimeout, e.message
     rescue SocketError, SystemCallError, OpenSSL::SSL::SSLError, EOFError => e
-      log_failure(:network_error, url: uri&.to_s || raw_url, error: e.class.name, message: e.message)
+      log_failure(:network_error, url: uri&.to_s || raw_url, error: e.class.name,
+                  message: e.message)
       raise FetchFailed, e.message
     end
 

backend/app/services/preview/known_site_extractor.rb

@@ -4,6 +4,15 @@ module Preview
       youtube_thumbnail(uri)
     end
 
+    def self.youtube_video_id(uri)
+      case uri.host&.downcase
+      when 'youtu.be'
+        uri.path.split('/').reject(&:blank?).first
+      when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
+        uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
+      end&.then { _1 if _1.match?(/\A[A-Za-z0-9_-]{6,20}\z/) }
+    end
+
     def self.niconico_video_id(uri)
       case uri.host&.downcase
       when 'www.nicovideo.jp', 'nicovideo.jp'
@@ -14,14 +23,8 @@ module Preview
     end
 
     def self.youtube_thumbnail(uri)
-      id =
-          case uri.host&.downcase
-          when 'youtu.be'
-            uri.path.split('/').reject(&:blank?).first
-          when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
-            uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
-          end
-      return unless id&.match?(/\A[A-Za-z0-9_-]{6,20}\z/)
+      id = youtube_video_id(uri)
+      return unless id
 
       "https://i.ytimg.com/vi/#{ id }/hqdefault.jpg"
     end

backend/app/services/preview/thumbnail_fetcher.rb

@@ -25,6 +25,22 @@ module Preview
       fetch_image!(metadata[:image_url])
     end
 
+    def self.fetch_image_response(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+      response = HttpFetcher.fetch(uri.to_s)
+      unless allowed_image_content_type?(response.content_type)
+        raise GenerationFailed, 'サムネール画像が見つかりませんでした．'
+      end
+
+      response
+    rescue HttpFetcher::FetchTimeout
+      raise
+    rescue HttpFetcher::ResponseTooLarge
+      raise
+    rescue HttpFetcher::FetchFailed
+      raise GenerationFailed, 'サムネール画像を取得できませんでした．'
+    end
+
     def self.title(raw_url)
       uri, = UrlSafety.validate(raw_url)
       HtmlMetadataExtractor.extract(
@@ -45,18 +61,7 @@ module Preview
     end
 
     def self.fetch_image!(url)
-      response = HttpFetcher.fetch(url)
-      unless allowed_image_content_type?(response.content_type)
-        raise GenerationFailed, 'サムネール画像が見つかりませんでした．'
-      end
-
-      response.body
-    rescue HttpFetcher::FetchTimeout
-      raise
-    rescue HttpFetcher::ResponseTooLarge
-      raise
-    rescue HttpFetcher::FetchFailed
-      raise GenerationFailed, 'サムネール画像を取得できませんでした．'
+      fetch_image_response(url).body
     end
 
     def self.niconico_thumbnail_url(uri)
@@ -70,16 +75,20 @@ module Preview
 
       xml.at_xpath('//thumbnail_url')&.text&.strip.presence
     rescue HttpFetcher::FetchFailed, HttpFetcher::FetchTimeout => e
-      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ { url: uri.to_s,
-                                                                     video_id:,
-                                                                     error: e.class.name,
-                                                                     message: e.message }.to_json }")
+      payload = {
+          url: uri.to_s,
+          video_id:,
+          error: e.class.name,
+          message: e.message }
+      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ payload.to_json }")
       nil
     rescue Nokogiri::XML::SyntaxError => e
-      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ { url: uri.to_s,
-                                                                     video_id:,
-                                                                     error: e.class.name,
-                                                                     message: e.message }.to_json }")
+      payload = {
+          url: uri.to_s,
+          video_id:,
+          error: e.class.name,
+          message: e.message }
+      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ payload.to_json }")
       nil
     end
 

backend/app/services/youtube/sync.rb

@@ -1,4 +1,3 @@
-require 'open-uri'
 require 'set'
 require 'time'
 
@@ -127,12 +126,12 @@ module Youtube
       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!
+      post.attach_thumbnail_from_url!(thumbnail_url)
+    rescue Post::RemoteThumbnailFetchFailed => e
+      Rails.logger.info("youtube_sync_thumbnail_fetch_failed #{ { post_id: post.id,
+                                                                  thumbnail_url:,
+                                                                  error: e.class.name,
+                                                                  message: e.message }.to_json }")
     end
 
     def youtube_url_regexp id

backend/config/routes.rb

@@ -33,6 +33,12 @@ Rails.application.routes.draw do
     get :thumbnail
   end
 
+  scope 'posts/import', controller: :post_imports do
+    post :preview
+    post :validate
+    post '', action: :create
+  end
+
   resources :wiki_pages, path: 'wiki', only: [:index, :show, :create, :update] do
     collection do
       get :search

backend/db/migrate/20260713000000_create_post_url_sanitisation_rules.rb

@@ -0,0 +1,61 @@
+class CreatePostUrlSanitisationRules < ActiveRecord::Migration[8.0]
+  class PostUrlSanitisationRule < ActiveRecord::Base
+    self.table_name = 'post_url_sanitisation_rules'
+  end
+
+  def up
+    create_table :post_url_sanitisation_rules, id: :integer, primary_key: :priority do |t|
+      t.string :source_pattern, null: false
+      t.string :replacement, null: false
+      t.timestamps
+      t.datetime :discarded_at
+
+      t.index :source_pattern, unique: true
+      t.index :discarded_at
+    end
+
+    now = Time.current
+
+    PostUrlSanitisationRule.insert_all!([
+        { priority: 10,
+          source_pattern: '\Ahttps?://youtu\.be/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 20,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/live/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 30,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/shorts/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 40,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/embed/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 50,
+          source_pattern:
+              '\Ahttps?://(?:www\.|m\.)?youtube\.com/watch\?(?:[^#&]+&)*v=([^&#]+)(?:[&#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 60,
+          source_pattern: '\Ahttps?://nico\.ms/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.nicovideo.jp/watch/\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 70,
+          source_pattern: '\Ahttps?://(?:www\.)?nicovideo\.jp/watch/([^?#/]+)(?:[?#].*)?\z',
+          replacement: 'https://www.nicovideo.jp/watch/\1',
+          created_at: now,
+          updated_at: now }])
+  end
+
+  def down
+    drop_table :post_url_sanitisation_rules
+  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_07_05_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_07_13_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
@@ -331,6 +331,16 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_05_000000) do
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
+  create_table "post_url_sanitisation_rules", primary_key: "priority", id: :integer, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "source_pattern", null: false
+    t.string "replacement", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.datetime "discarded_at"
+    t.index ["discarded_at"], name: "index_post_url_sanitisation_rules_on_discarded_at"
+    t.index ["source_pattern"], name: "index_post_url_sanitisation_rules_on_source_pattern", unique: true
+  end
+
   create_table "post_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.integer "version_no", null: false

backend/db/seeds.rb

@@ -8,6 +8,43 @@
 #     MovieGenre.find_or_create_by!(name: genre_name)
 #   end
 
+post_url_sanitisation_rules = [
+  { priority: 10,
+    source_pattern: '\Ahttps?://youtu\.be/([^/?#]+)(?:[?#].*)?\z',
+    replacement: 'https://www.youtube.com/watch?v=\1' },
+  { priority: 20,
+    source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/live/([^/?#]+)(?:[?#].*)?\z',
+    replacement: 'https://www.youtube.com/watch?v=\1' },
+  { priority: 30,
+    source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/shorts/([^/?#]+)(?:[?#].*)?\z',
+    replacement: 'https://www.youtube.com/watch?v=\1' },
+  { priority: 40,
+    source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/embed/([^/?#]+)(?:[?#].*)?\z',
+    replacement: 'https://www.youtube.com/watch?v=\1' },
+  { priority: 50,
+    source_pattern:
+        '\Ahttps?://(?:www\.|m\.)?youtube\.com/watch\?(?:[^#&]+&)*v=([^&#]+)(?:[&#].*)?\z',
+    replacement: 'https://www.youtube.com/watch?v=\1' },
+  { priority: 60,
+    source_pattern: '\Ahttps?://nico\.ms/([^/?#]+)(?:[?#].*)?\z',
+    replacement: 'https://www.nicovideo.jp/watch/\1' },
+  { priority: 70,
+    source_pattern: '\Ahttps?://(?:www\.)?nicovideo\.jp/watch/([^?#/]+)(?:[?#].*)?\z',
+    replacement: 'https://www.nicovideo.jp/watch/\1' }
+]
+
+post_url_sanitisation_rule_scope = PostUrlSanitisationRule.unscoped
+
+post_url_sanitisation_rules.each do |attributes|
+  priority = attributes.fetch(:priority)
+  source_pattern = attributes.fetch(:source_pattern)
+
+  next if post_url_sanitisation_rule_scope.exists?(priority:)
+  next if post_url_sanitisation_rule_scope.exists?(source_pattern:)
+
+  post_url_sanitisation_rule_scope.create!(attributes)
+end
+
 material_sync_source_uri = ENV['MATERIAL_SYNC_SOURCE_URI']
 material_sync_source_file_id = ENV['MATERIAL_SYNC_SOURCE_FILE_ID']
 

backend/lib/tasks/sync_nico.rake

@@ -70,11 +70,17 @@ namespace :nico do
         unless post.thumbnail.attached?
           thumbnail_base = fetch_thumbnail.(post.url) rescue nil
           if thumbnail_base.present?
-            post.thumbnail.attach(
-                io:           URI.open(thumbnail_base),
-                filename:     File.basename(URI.parse(thumbnail_base).path),
-                content_type: 'image/jpeg')
             attrs[:thumbnail_base] = thumbnail_base
+            begin
+              post.attach_thumbnail_from_url!(thumbnail_base)
+            rescue Post::RemoteThumbnailFetchFailed => e
+              payload = {
+                  post_id: post.id,
+                  thumbnail_base:,
+                  error: e.class.name,
+                  message: e.message }
+              Rails.logger.info("nico_sync_thumbnail_fetch_failed #{ payload.to_json }")
+            end
           end
         end
 
@@ -82,7 +88,6 @@ namespace :nico do
         post_changed = post.changed?
         if post_changed
           post.save!
-          post.resized_thumbnail! if post.thumbnail.attached?
         end
       else
         post_created = true
@@ -91,13 +96,18 @@ namespace :nico do
         post = Post.new(title:, url:, thumbnail_base:, uploaded_user: nil,
                         original_created_from:, original_created_before:)
         if thumbnail_base.present?
-          post.thumbnail.attach(
-              io:           URI.open(thumbnail_base),
-              filename:     File.basename(URI.parse(thumbnail_base).path),
-              content_type: 'image/jpeg')
+          begin
+            post.attach_thumbnail_from_url!(thumbnail_base)
+          rescue Post::RemoteThumbnailFetchFailed => e
+            payload = {
+                post_id: nil,
+                thumbnail_base:,
+                error: e.class.name,
+                message: e.message }
+            Rails.logger.info("nico_sync_thumbnail_fetch_failed #{ payload.to_json }")
+          end
         end
         post.save!
-        post.resized_thumbnail!
         sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.niconico.id, Tag.video.id])
       end
 

backend/spec/db/seeds_spec.rb

@@ -0,0 +1,65 @@
+require 'rails_helper'
+
+RSpec.describe 'database seeds' do
+  before do
+    PostUrlSanitisationRule.unscoped.delete_all
+  end
+
+  it 'registers the initial post URL sanitisation rules' do
+    load_seeds
+
+    urls = {
+      'https://youtu.be/abc123?si=share' => youtube_url('abc123'),
+      'https://www.youtube.com/live/abc123?t=10' => youtube_url('abc123'),
+      'https://youtube.com/shorts/abc123?feature=share' => youtube_url('abc123'),
+      'https://m.youtube.com/embed/abc123' => youtube_url('abc123'),
+      'https://youtube.com/watch?feature=share&v=abc123&t=10' => youtube_url('abc123'),
+      'https://nico.ms/sm123?from=share#fragment' => nico_url('sm123'),
+      'https://www.nicovideo.jp/watch/sm123?ref=share#fragment' => nico_url('sm123')
+    }
+
+    expect(PostUrlSanitisationRule.count).to eq(7)
+    urls.each do |url, canonical_url|
+      expect(PostUrlSanitisationRule.sanitise(url)).to eq(canonical_url)
+    end
+  end
+
+  it 'does not overwrite or restore an existing rule' do
+    rule = PostUrlSanitisationRule.create!(
+      priority: 10,
+      source_pattern: '\Ahttps://example\.com/custom\z',
+      replacement: 'https://example.com/replacement'
+    )
+    rule.discard!
+    original_attributes = rule.reload.attributes
+
+    2.times { load_seeds }
+
+    persisted_rule = PostUrlSanitisationRule.unscoped.find(10)
+    expect(persisted_rule.attributes).to eq(original_attributes)
+    expect(PostUrlSanitisationRule.unscoped.count).to eq(7)
+  end
+
+  it 'does not duplicate a rule moved to another priority' do
+    source_pattern = '\Ahttps?://youtu\.be/([^/?#]+)(?:[?#].*)?\z'
+    PostUrlSanitisationRule.create!(
+      priority: 80,
+      source_pattern:,
+      replacement: 'https://example.com/custom/\1'
+    )
+
+    load_seeds
+
+    rules = PostUrlSanitisationRule.unscoped
+    expect(rules.where(source_pattern:).count).to eq(1)
+    expect(rules.find(80).replacement).to eq('https://example.com/custom/\1')
+  end
+
+  def load_seeds
+    load Rails.root.join('db/seeds.rb')
+  end
+
+  def youtube_url(video_id) = "https://www.youtube.com/watch?v=#{ video_id }"
+
+  def nico_url(video_id) = "https://www.nicovideo.jp/watch/#{ video_id }"
+end

backend/spec/models/post_spec.rb

@@ -0,0 +1,361 @@
+require 'rails_helper'
+require 'tempfile'
+
+RSpec.describe Post, type: :model do
+  before do
+    PostUrlSanitisationRule.unscoped.delete_all
+  end
+
+  describe 'URL normalisation' do
+    it 'normalises the HTTP URL before applying sanitisation rules' do
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/videos/([^/]+)\\z',
+        replacement: 'https://example.com/watch/\\1'
+      )
+
+      post = described_class.create!(
+        title: 'normalised URL',
+        url: '  https://EXAMPLE.com/videos/123/  '
+      )
+
+      expect(post.url).to eq('https://example.com/watch/123')
+    end
+
+    it 'does not normalise an unchanged URL when another attribute changes' do
+      post = create(:post)
+      post.update_column(:url, 'https://EXAMPLE.com/unchanged/')
+
+      post.update!(title: 'updated title')
+
+      expect(post.reload.url).to eq('https://EXAMPLE.com/unchanged/')
+    end
+
+    it 'validates the sanitised URL length' do
+      path = 'a' * 375
+
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/(a+)\\z',
+        replacement: 'https://example.com/\\1\\1'
+      )
+
+      post = described_class.new(
+        title: 'long URL',
+        url: "https://example.com/#{ path }"
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors.details.fetch(:url)).to include(
+        error: :too_long,
+        count: 768
+      )
+    end
+
+    it 'validates uniqueness after sanitisation' do
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/alias\\z',
+        replacement: 'https://example.com/canonical'
+      )
+      create(:post, url: 'https://example.com/canonical')
+
+      post = described_class.new(title: 'duplicate URL', url: 'https://example.com/alias')
+
+      expect(post).to be_invalid
+      expect(post.errors.details.fetch(:url)).to include(error: :taken, value: post.url)
+    end
+  end
+
+  describe 'thumbnail processing' do
+    def image_blob(width:, height:, background:, draw: nil)
+      Tempfile.create(['post-thumbnail', '.png']) do |file|
+        MiniMagick::Tool::Convert.new do |convert|
+          convert.size "#{ width }x#{ height }"
+          convert.xc background
+          draw&.call(convert)
+          convert << file.path
+        end
+        File.binread(file.path)
+      end
+    end
+
+    def upload_for(blob)
+      StringIO.new(blob).tap(&:rewind)
+    end
+
+    def read_image(attachment)
+      blob =
+          attachment.is_a?(Hash) ? attachment.fetch(:io).read : attachment.download
+      MiniMagick::Image.read(blob)
+    end
+
+    def colour_at(image, x, y)
+      image.get_pixels.fetch(y).fetch(x)
+    end
+
+    def expect_green(pixel)
+      expect(pixel[1]).to be > pixel[0] + 40
+      expect(pixel[1]).to be > pixel[2] + 40
+    end
+
+    def expect_red(pixel)
+      expect(pixel[0]).to be > pixel[1] + 40
+      expect(pixel[0]).to be > pixel[2] + 40
+    end
+
+    def expect_blue(pixel)
+      expect(pixel[2]).to be > pixel[0] + 40
+      expect(pixel[2]).to be > pixel[1] + 40
+    end
+
+    describe '.resized_thumbnail_attachment' do
+      it 'centre-crops a wide image to 180x180 without distorting it' do
+        blob = image_blob(
+            width: 360,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 90,0 269,179'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([180, 180])
+        expect_green(colour_at(image, 0, 90))
+        expect_green(colour_at(image, 90, 90))
+        expect_green(colour_at(image, 179, 90))
+      end
+
+      it 'centre-crops a tall image to 180x180 without distorting it' do
+        blob = image_blob(
+            width: 180,
+            height: 360,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 0,90 179,269'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([180, 180])
+        expect_green(colour_at(image, 90, 0))
+        expect_green(colour_at(image, 90, 90))
+        expect_green(colour_at(image, 90, 179))
+      end
+
+      it 'keeps a square image square without distortion' do
+        blob = image_blob(
+            width: 180,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'blue'
+              convert.draw 'rectangle 90,0 179,179'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([180, 180])
+        expect_red(colour_at(image, 20, 90))
+        expect_blue(colour_at(image, 160, 90))
+      end
+    end
+
+    describe '#attach_thumbnail_from_url!' do
+      it 'attaches a fetched remote image through the common resize path' do
+        blob = image_blob(
+            width: 240,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 30,0 209,179'
+            })
+        response = Preview::HttpFetcher::Response.new(
+            blob,
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+
+        post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+        expect(post.thumbnail).to receive(:attach).once.and_call_original
+        post.attach_thumbnail_from_url!('https://example.com/thumb.png')
+
+        expect(post.thumbnail).to be_attached
+        image = read_image(post.thumbnail)
+        expect(image.dimensions).to eq([180, 180])
+      end
+
+      it 'does not attach anything when thumbnail conversion fails' do
+        response = Preview::HttpFetcher::Response.new(
+            'not-an-image',
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+        allow(described_class).to receive(:resized_thumbnail_attachment)
+            .and_raise(MiniMagick::Error, 'convert failed')
+
+        post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+        expect {
+          post.attach_thumbnail_from_url!('https://example.com/thumb.png')
+        }.to raise_error(Post::RemoteThumbnailFetchFailed, 'convert failed')
+
+        expect(post.thumbnail).not_to be_attached
+      end
+
+      it 'keeps an existing thumbnail when remote conversion fails' do
+        existing = described_class.create!(title: 'title', url: 'https://example.com/post')
+        existing.thumbnail.attach(
+            io: StringIO.new('existing'),
+            filename: 'existing.jpg',
+            content_type: 'image/jpeg')
+        blob_id = existing.thumbnail.blob.id
+        response = Preview::HttpFetcher::Response.new(
+            'not-an-image',
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+        allow(described_class).to receive(:resized_thumbnail_attachment)
+            .and_raise(MiniMagick::Error, 'convert failed')
+
+        expect {
+          existing.attach_thumbnail_from_url!('https://example.com/thumb.png')
+        }.to raise_error(Post::RemoteThumbnailFetchFailed, 'convert failed')
+
+        existing.reload
+        expect(existing.thumbnail).to be_attached
+        expect(existing.thumbnail.blob.id).to eq(blob_id)
+      end
+    end
+  end
+
+  describe 'original created datetime validation' do
+    it 'allows unrelated updates on persisted posts with second-bearing datetimes' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+      post.update_columns(
+        original_created_from: Time.zone.parse('2024-01-01T12:34:30Z'),
+        original_created_before: Time.zone.parse('2024-01-01T12:35:30Z')
+      )
+
+      post.title = 'updated title'
+
+      expect(post).to be_valid
+      expect { post.save! }.not_to raise_error
+    end
+
+    it 'rejects second-bearing updates when the datetime field changes' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+      post.original_created_from = '2024-01-01T12:34:30Z'
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+    end
+
+    it 'accepts fixing persisted datetimes to minute precision' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+      post.update_columns(
+        original_created_from: Time.zone.parse('2024-01-01T12:34:30Z'),
+        original_created_before: Time.zone.parse('2024-01-01T12:35:30Z')
+      )
+
+      post.original_created_from = '2024-01-01T12:34Z'
+      post.original_created_before = '2024-01-01T12:35Z'
+
+      expect(post).to be_valid
+      expect { post.save! }.not_to raise_error
+    end
+
+    it 'adds only the minute-precision error for second precision values' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34:30',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+      expect(post.errors[:original_created_at]).to be_empty
+    end
+
+    it 'adds only the minute-precision error for fractional-second values' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34:00.123',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+      expect(post.errors[:original_created_at]).to be_empty
+    end
+
+    it 'checks range rules only for valid minute-precision endpoints' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34',
+        original_created_before: '2024-01-01T12:34'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_at]).to eq(
+        [described_class::ORIGINAL_CREATED_ORDER_MESSAGE]
+      )
+    end
+
+    it 'accepts a one-minute range at minute precision' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_valid
+    end
+
+    it 'rejects invalid calendar dates and invalid hours' do
+      invalid_dates = [
+        '2024-02-31T12:00',
+        '2023-02-29T12:00',
+        '2024-02-29T24:00'
+      ]
+
+      invalid_dates.each do |value|
+        post = described_class.new(
+          title: 'title',
+          url: 'https://example.com/post',
+          original_created_from: value
+        )
+
+        expect(post).to be_invalid
+        expect(post.errors[:original_created_from]).to eq(
+          [described_class::ORIGINAL_CREATED_INVALID_MESSAGE]
+        )
+      end
+    end
+  end
+end

backend/spec/models/post_url_sanitisation_rule_spec.rb

@@ -0,0 +1,265 @@
+require 'rails_helper'
+
+RSpec.describe PostUrlSanitisationRule, type: :model do
+  before do
+    described_class.unscoped.delete_all
+  end
+
+  describe 'validations' do
+    it 'requires a source pattern' do
+      rule = described_class.new(priority: 10, source_pattern: nil, replacement: '')
+
+      expect(rule).to be_invalid
+      expect(rule.errors.details.fetch(:source_pattern)).to eq([{ error: :blank }])
+    end
+
+    it 'requires a unique source pattern' do
+      described_class.create!(priority: 10, source_pattern: 'source', replacement: 'first')
+      rule = described_class.new(
+        priority: 20,
+        source_pattern: 'source',
+        replacement: 'second'
+      )
+
+      expect(rule).to be_invalid
+      expect(rule.errors.details.fetch(:source_pattern)).to include(
+        error: :taken,
+        value: 'source'
+      )
+    end
+
+    it 'rejects an invalid regexp' do
+      rule = described_class.new(priority: 10, source_pattern: '[', replacement: '')
+
+      expect(rule).to be_invalid
+      expect(rule.errors[:source_pattern]).to include('変な正規表現だね〜（笑）')
+    end
+  end
+
+  describe '.sanitise' do
+    it 'applies each active rule once in priority order' do
+      described_class.create!(priority: 30, source_pattern: 'c', replacement: 'd')
+      described_class.create!(priority: 10, source_pattern: 'a', replacement: 'aa')
+      described_class.create!(priority: 20, source_pattern: 'aa', replacement: 'c')
+      discarded = described_class.create!(
+        priority: 5,
+        source_pattern: '.',
+        replacement: 'discarded'
+      )
+      discarded.discard!
+
+      expect(described_class.sanitise('a')).to eq('d')
+    end
+
+    it 'canonicalises the initial YouTube and Nico URL forms' do
+      create_initial_rules
+
+      urls = {
+        'https://youtu.be/abc123?si=share' => youtube_url('abc123'),
+        'https://www.youtube.com/live/abc123?t=10' => youtube_url('abc123'),
+        'https://youtube.com/shorts/abc123?feature=share' => youtube_url('abc123'),
+        'https://m.youtube.com/embed/abc123' => youtube_url('abc123'),
+        'https://youtube.com/watch?feature=share&v=abc123&t=10' => youtube_url('abc123'),
+        'https://nico.ms/sm123?from=share#fragment' => nico_url('sm123'),
+        'https://www.nicovideo.jp/watch/sm123?ref=share#fragment' => nico_url('sm123')
+      }
+
+      urls.each do |url, canonical_url|
+        expect(described_class.sanitise(url)).to eq(canonical_url)
+      end
+    end
+  end
+
+  describe '.apply!' do
+    it 'locks posts in ID order and updates through temporary URLs' do
+      first = create(:post, url: 'https://example.com/source/1')
+      second = create(:post, url: 'https://example.com/source/2')
+      create_source_rule
+      sql = capture_sql { described_class.apply! }
+
+      lock_sql = sql.find { _1.match?(/SELECT .*posts.*FOR UPDATE/i) }
+      expect(lock_sql).to match(/ORDER BY .*posts.*id.* ASC/i)
+      expect(sql.grep(/post-url-sanitising\.invalid/).size).to eq(2)
+      expect(first.reload.url).to eq('https://example.com/canonical/1')
+      expect(second.reload.url).to eq('https://example.com/canonical/2')
+    end
+
+    it 'loads and compiles rules only once' do
+      create(:post, url: 'https://example.com/source/1')
+      create(:post, url: 'https://example.com/source/2')
+      create_source_rule
+
+      expect(described_class).to receive(:rules).once.and_call_original
+
+      described_class.apply!
+    end
+
+    it 'does not change post versions, version_no, or updated_at' do
+      post = create(:post, url: 'https://example.com/source/1')
+      post.update_columns(version_no: 7, updated_at: 1.day.ago)
+      original_updated_at = post.reload.updated_at
+      create_source_rule
+
+      expect { described_class.apply! }.not_to change(PostVersion, :count)
+
+      post.reload
+      expect(post.url).to eq('https://example.com/canonical/1')
+      expect(post.version_no).to eq(7)
+      expect(post.updated_at).to eq(original_updated_at)
+    end
+
+    invalid_urls = {
+      'a blank URL' => '',
+      'an unparseable URL' => 'https://[',
+      'a non-HTTP URL' => 'ftp://example.com/file',
+      'an HTTP URL without a host' => 'https:/path'
+    }
+
+    invalid_urls.each do |description, sanitised_url|
+      it "rolls back every update when sanitisation produces #{ description }" do
+        valid_post = create(:post, url: 'https://example.com/source/1')
+        invalid_post = create(:post, url: 'https://example.com/invalid')
+        create_source_rule
+        described_class.create!(
+          priority: 20,
+          source_pattern: '\\Ahttps://example\\.com/invalid\\z',
+          replacement: sanitised_url
+        )
+
+        expect { described_class.apply! }
+            .to raise_error(described_class::InvalidUrlError) { |error|
+          expect(error.invalid_rows).to eq([
+            { post_id: invalid_post.id,
+              original_url: 'https://example.com/invalid',
+              sanitised_url: }
+          ])
+        }
+        expect(valid_post.reload.url).to eq('https://example.com/source/1')
+        expect(invalid_post.reload.url).to eq('https://example.com/invalid')
+      end
+    end
+
+    it 'rolls back every update when sanitisation produces a URL longer than 768 characters' do
+      path = 'a' * 375
+      original_url = "https://example.com/#{ path }"
+      sanitised_url = "https://example.com/#{ path }#{ path }"
+      valid_post = create(:post, url: 'https://example.com/source/1')
+      invalid_post = create(:post, url: original_url)
+      create_source_rule
+      described_class.create!(
+        priority: 20,
+        source_pattern: '\\Ahttps://example\\.com/(a+)\\z',
+        replacement: 'https://example.com/\\1\\1'
+      )
+
+      expect { described_class.apply! }
+          .to raise_error(described_class::InvalidUrlError) { |error|
+        expect(error.invalid_rows).to eq([
+          { post_id: invalid_post.id,
+            original_url:,
+            sanitised_url: }
+        ])
+      }
+      expect(valid_post.reload.url).to eq('https://example.com/source/1')
+      expect(invalid_post.reload.url).to eq(original_url)
+    end
+
+    it 'rejects sanitised URL collisions case-insensitively without changing posts' do
+      source = create(:post, url: 'https://example.com/source/Foo')
+      canonical = create(:post, url: 'https://example.com/canonical/foo')
+      create_source_rule
+
+      expect { described_class.apply! }
+          .to raise_error(described_class::UrlConflictError) { |error|
+        expect(error.conflicts).to contain_exactly(
+          { url: 'https://example.com/canonical/Foo',
+            post_id: source.id,
+            original_url: 'https://example.com/source/Foo' },
+          { url: 'https://example.com/canonical/foo',
+            post_id: canonical.id,
+            original_url: 'https://example.com/canonical/foo' }
+        )
+      }
+      expect(source.reload.url).to eq('https://example.com/source/Foo')
+      expect(canonical.reload.url).to eq('https://example.com/canonical/foo')
+      expect(Post.count).to eq(2)
+    end
+
+    it 'converts a persisted URL constraint race into UrlConflictError' do
+      post = create(:post, url: 'https://example.com/source/1')
+      create_source_rule
+      conflict = { url: 'https://example.com/canonical/1',
+                   post_id: post.id,
+                   original_url: post.url }
+      database_error = ActiveRecord::RecordNotUnique.new('duplicate URL')
+      allow_any_instance_of(ActiveRecord::Relation)
+          .to receive(:update_all).and_raise(database_error)
+      allow(described_class).to receive(:build_persisted_conflicts).and_return([conflict])
+
+      expect { described_class.apply! }
+          .to raise_error(described_class::UrlConflictError) { |error|
+        expect(error.conflicts).to eq([conflict])
+        expect(error.cause).to equal(database_error)
+      }
+      expect(post.reload.url).to eq('https://example.com/source/1')
+    end
+
+    it 're-raises an unidentified RecordNotUnique error' do
+      post = create(:post, url: 'https://example.com/source/1')
+      create_source_rule
+      database_error = ActiveRecord::RecordNotUnique.new('another unique constraint')
+      allow_any_instance_of(ActiveRecord::Relation)
+          .to receive(:update_all).and_raise(database_error)
+      allow(described_class).to receive(:build_persisted_conflicts).and_return([])
+
+      expect { described_class.apply! }.to raise_error(database_error)
+      expect(post.reload.url).to eq('https://example.com/source/1')
+    end
+  end
+
+  def capture_sql
+    statements = []
+    subscriber = lambda do |_name, _start, _finish, _id, payload|
+      binds = payload.fetch(:binds, []).map { _1.value_for_database.to_s }
+      statements << ([payload.fetch(:sql)] + binds).join(' ')
+    end
+    ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') { yield }
+    statements
+  end
+
+  def create_source_rule
+    described_class.create!(
+      priority: 10,
+      source_pattern: '\\Ahttps://example\\.com/source/(.+)\\z',
+      replacement: 'https://example.com/canonical/\\1'
+    )
+  end
+
+  def create_initial_rules
+    rules = [
+      ['\\Ahttps?://youtu\\.be/([^/?#]+)(?:[?#].*)?\\z', youtube_url('\\1')],
+      ['\\Ahttps?://(?:www\\.|m\\.)?youtube\\.com/live/([^/?#]+)(?:[?#].*)?\\z',
+       youtube_url('\\1')],
+      ['\\Ahttps?://(?:www\\.|m\\.)?youtube\\.com/shorts/([^/?#]+)(?:[?#].*)?\\z',
+       youtube_url('\\1')],
+      ['\\Ahttps?://(?:www\\.|m\\.)?youtube\\.com/embed/([^/?#]+)(?:[?#].*)?\\z',
+       youtube_url('\\1')],
+      ['\\Ahttps?://(?:www\\.|m\\.)?youtube\\.com/watch\\?(?:[^#&]+&)*' \
+       'v=([^&#]+)(?:[&#].*)?\\z', youtube_url('\\1')],
+      ['\\Ahttps?://nico\\.ms/([^/?#]+)(?:[?#].*)?\\z', nico_url('\\1')],
+      ['\\Ahttps?://(?:www\\.)?nicovideo\\.jp/watch/([^?#/]+)(?:[?#].*)?\\z',
+       nico_url('\\1')]
+    ]
+    rules.each_with_index do |(source_pattern, replacement), index|
+      described_class.create!(
+        priority: (index + 1) * 10,
+        source_pattern:,
+        replacement:
+      )
+    end
+  end
+
+  def youtube_url(video_id) = "https://www.youtube.com/watch?v=#{ video_id }"
+
+  def nico_url(video_id) = "https://www.nicovideo.jp/watch/#{ video_id }"
+end

backend/spec/requests/post_imports_spec.rb

@@ -0,0 +1,184 @@
+require 'rails_helper'
+
+RSpec.describe 'Post imports API', type: :request do
+  let(:member) { create(:user, :member) }
+
+  before do
+    allow(Preview::UrlSafety).to receive(:validate) do |url|
+      [URI.parse(url), ['8.8.8.8']]
+    end
+    allow(PostMetadataFetcher).to receive(:fetch).and_return(
+      title: 'fetched title',
+      thumbnail_base: nil,
+      tags: ''
+    )
+  end
+
+  describe 'POST /posts/import/preview' do
+    it 'requires a member' do
+      sign_out
+      post '/posts/import/preview', params: { source: 'https://example.com/post' }
+      expect(response).to have_http_status(:unauthorized)
+
+      sign_in_as(create(:user, :guest))
+      post '/posts/import/preview', params: { source: 'https://example.com/post' }
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it 'parses a URL list and returns preview rows' do
+      sign_in_as(member)
+
+      post '/posts/import/preview', params: {
+        source: " https://example.com/one \r\n\r\nhttps://example.com/two"
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('rows').map { _1.fetch('source_row') }).to eq([1, 3])
+      expect(json.fetch('rows').map { _1.fetch('url') }).to eq([
+        'https://example.com/one',
+        'https://example.com/two'
+      ])
+    end
+
+    it 'returns a safe 400 response for an invalid source' do
+      sign_in_as(member)
+
+      post '/posts/import/preview', params: { source: '' }
+
+      expect(response).to have_http_status(:bad_request)
+      expect(json.fetch('message')).to eq('URL を入力してください．')
+    end
+  end
+
+  describe 'POST /posts/import/validate' do
+    it 'accepts camel-case row properties and returns their warnings' do
+      sign_in_as(member)
+
+      post '/posts/import/validate', params: {
+        rows: [{
+          sourceRow: '1',
+          url: 'https://example.com/post',
+          metadataUrl: 'https://example.com/post',
+          attributes: { title: 'manual title' },
+          provenance: { url: 'manual', title: 'manual' },
+          tagSources: { automatic: '', manual: '' },
+          fieldWarnings: { title: ['old warning'] },
+          baseWarnings: ['base warning']
+        }],
+        changed_row: -1
+      }
+
+      expect(response).to have_http_status(:ok)
+      result = json.fetch('rows').first
+      expect(result.fetch('source_row')).to eq(1)
+      expect(result.fetch('tag_sources')).to eq('automatic' => '', 'manual' => '')
+      expect(result.fetch('field_warnings')).to eq('title' => ['old warning'])
+      expect(result.fetch('base_warnings')).to eq(['base warning'])
+    end
+
+    it 'rejects a non-array rows value with 400' do
+      sign_in_as(member)
+
+      post '/posts/import/validate', params: { rows: { sourceRow: 1 }, changed_row: -1 }
+
+      expect(response).to have_http_status(:bad_request)
+      expect(json.fetch('message')).to eq('取込行の形式が不正です．')
+    end
+
+    it 'returns original created datetime validation errors for minute precision' do
+      sign_in_as(member)
+
+      post '/posts/import/validate', params: {
+        rows: [{
+          sourceRow: 1,
+          url: 'https://example.com/post',
+          metadataUrl: 'https://example.com/post',
+          attributes: {
+            originalCreatedFrom: '2020-01-01T00:00:30Z',
+            originalCreatedBefore: '2020-01-01T00:01Z' },
+          provenance: {
+            url: 'manual',
+            originalCreatedFrom: 'manual',
+            originalCreatedBefore: 'manual' },
+          tagSources: { automatic: '', manual: '' }
+        }],
+        changed_row: -1
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('rows').first.fetch('validation_errors')).to include(
+        'original_created_from' => ['オリジナルの作成日時は分単位で入力してください．']
+      )
+      expect(json.fetch('rows').first.fetch('validation_errors'))
+          .not_to have_key('original_created_at')
+    end
+  end
+
+  describe 'POST /posts/import' do
+    it 'keeps the duration string contract through preview, validate, and import' do
+      sign_in_as(member)
+      allow(PostMetadataFetcher).to receive(:fetch).and_return(
+        title: 'fetched title',
+        thumbnail_base: nil,
+        duration: '2.5',
+        tags: '動画'
+      )
+
+      post '/posts/import/preview', params: {
+        source: 'https://example.com/video'
+      }
+      preview_row = json.fetch('rows').first
+      expect(preview_row.dig('attributes', 'duration')).to eq('2.5')
+
+      post '/posts/import/validate', params: {
+        rows: [{
+          sourceRow: preview_row.fetch('source_row'),
+          url: preview_row.fetch('url'),
+          attributes: preview_row.fetch('attributes'),
+          provenance: preview_row.fetch('provenance'),
+          tagSources: preview_row.fetch('tag_sources'),
+          metadataUrl: preview_row.fetch('metadata_url')
+        }],
+        changed_row: -1
+      }
+      validated_row = json.fetch('rows').first
+      expect(validated_row.dig('attributes', 'duration')).to eq('2.5')
+
+      post '/posts/import', params: {
+        rows: [{
+          sourceRow: validated_row.fetch('source_row'),
+          url: validated_row.fetch('url'),
+          attributes: validated_row.fetch('attributes'),
+          provenance: validated_row.fetch('provenance'),
+          tagSources: validated_row.fetch('tag_sources'),
+          metadataUrl: validated_row.fetch('metadata_url')
+        }]
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(Post.order(:id).last.video_ms).to eq(2_500)
+    end
+
+    it 'returns a formal skipped result for an existing post' do
+      existing = create(:post, url: 'https://example.com/existing')
+      sign_in_as(member)
+
+      post '/posts/import', params: {
+        rows: [{
+          sourceRow: 1,
+          url: existing.url,
+          attributes: { title: 'ignored' },
+          provenance: { url: 'manual', title: 'manual' },
+          tagSources: { automatic: '', manual: '' }
+        }]
+      }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('created' => 0, 'skipped' => 1, 'failed' => 0)
+      expect(json.fetch('rows').first).to include(
+        'status' => 'skipped',
+        'existing_post_id' => existing.id
+      )
+    end
+  end
+end

backend/spec/requests/posts_spec.rb

@@ -2206,6 +2206,91 @@ RSpec.describe 'Posts API', type: :request do
 
       expect(response).to have_http_status(:unprocessable_entity)
     end
+
+    it 'rejects second-bearing original created timestamps on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'invalid original created from',
+          url: 'https://example.com/invalid-original-created-from',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00:01Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_from' => ['オリジナルの作成日時は分単位で入力してください．']
+      )
+      expect(json.fetch('errors')).not_to have_key('original_created_at')
+    end
+
+    it 'rejects fractional-second original created timestamps on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'invalid original created before',
+          url: 'https://example.com/invalid-original-created-before',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_before: '2020-01-01T00:00:00.123Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_before' => ['オリジナルの作成日時は分単位で入力してください．']
+      )
+      expect(json.fetch('errors')).not_to have_key('original_created_at')
+    end
+
+    it 'rejects non-increasing original created ranges on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'non-increasing original created range',
+          url: 'https://example.com/non-increasing-original-created-range',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00Z',
+          original_created_before: '2020-01-01T00:00Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_at' => ['オリジナルの作成日時の順番がをかしぃです．']
+      )
+    end
+
+    it 'accepts original created ranges that are exactly one minute on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'valid original created range',
+          url: 'https://example.com/valid-original-created-range',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00Z',
+          original_created_before: '2020-01-01T00:01Z')
+
+      expect(response).to have_http_status(:created)
+      expect(Time.iso8601(json.fetch('original_created_from')))
+          .to eq(Time.iso8601('2020-01-01T00:00Z'))
+      expect(Time.iso8601(json.fetch('original_created_before')))
+          .to eq(Time.iso8601('2020-01-01T00:01Z'))
+    end
+
+    it 'rejects unparseable original created timestamps on PUT /posts/:id' do
+      sign_in_as(member)
+      base_version = create_post_version_for!(post_record)
+
+      put "/posts/#{post_record.id}", params: post_write_params(
+          base_version_no: base_version.version_no,
+          title: 'updated title',
+          tags: 'spec_tag',
+          original_created_from: 'not-a-time')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_from' => ['オリジナルの作成日時の形式が不正です．']
+      )
+    end
   end
 
   describe 'tag versioning from post write actions' do

backend/spec/services/post_creator_spec.rb

@@ -0,0 +1,82 @@
+require 'rails_helper'
+require 'base64'
+
+RSpec.describe PostCreator do
+  let(:actor) { create(:user, :member) }
+
+  def real_thumbnail_upload
+    gif = Base64.decode64('R0lGODdhAQABAIABAP///wAAACwAAAAAAQABAAACAkQBADs=')
+
+    Rack::Test::UploadedFile.new(
+        StringIO.new(gif),
+        'image/gif',
+        original_filename: 'thumbnail.gif')
+  end
+
+  before do
+    allow(Tag).to receive(:normalise_tags!).and_return({ tags: [], sections: {} })
+    allow(TagVersioning).to receive(:record_tag_snapshots!)
+    allow(Tag).to receive(:expand_parent_tags).and_return([])
+    allow(PostVersionRecorder).to receive(:record!)
+  end
+
+  it 'prefers an explicit upload over thumbnail_base' do
+    allow(Post).to receive(:resized_thumbnail_attachment).and_return(
+        io: StringIO.new('upload'),
+        filename: 'resized_thumbnail.jpg',
+        content_type: 'image/jpeg')
+    expect_any_instance_of(Post).not_to receive(:attach_thumbnail_from_url!)
+
+    post = described_class.new(
+        actor:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail: real_thumbnail_upload,
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' }).create!
+
+    expect(post.thumbnail).to be_attached
+    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+  end
+
+  it 'uses the common remote thumbnail attach path when thumbnail_base is given' do
+    expect_any_instance_of(Post).to receive(:attach_thumbnail_from_url!)
+        .with('https://example.com/thumb.jpg') do |post, _url|
+      post.thumbnail.attach(
+          io: StringIO.new('thumbnail'),
+          filename: 'thumbnail.jpg',
+          content_type: 'image/jpeg')
+    end
+
+    post = described_class.new(
+        actor:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' }).create!
+
+    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+    expect(post.thumbnail).to be_attached
+  end
+
+  it 'keeps creating the post and records a warning when remote thumbnail fetch fails' do
+    allow_any_instance_of(Post).to receive(:attach_thumbnail_from_url!)
+        .and_raise(Post::RemoteThumbnailFetchFailed, 'サムネール画像を取得できませんでした．')
+    creator = described_class.new(
+        actor:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' })
+
+    post = creator.create!
+
+    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+    expect(post.thumbnail).not_to be_attached
+    expect(creator.field_warnings).to eq(
+        thumbnail_base: ['サムネール画像を取得できませんでした．'])
+  end
+end

backend/spec/services/post_import_previewer_spec.rb

@@ -0,0 +1,187 @@
+require 'rails_helper'
+
+RSpec.describe PostImportPreviewer do
+  before do
+    allow(Preview::UrlSafety).to receive(:validate) do |url|
+      [URI.parse(url), ['8.8.8.8']]
+    end
+  end
+
+  def row(source_row:, url:, attributes: { }, provenance: { }, **values)
+    {
+      source_row:,
+      url:,
+      attributes:,
+      provenance:
+    }.merge(values)
+  end
+
+  describe '#preview_rows' do
+    it 'marks an existing post for skipping without fetching metadata' do
+      existing = create(:post, url: 'https://example.com/existing')
+      expect(PostMetadataFetcher).not_to receive(:fetch)
+
+      result = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://EXAMPLE.com/existing/')
+      ]).first
+
+      expect(result).to include(
+        url: 'https://example.com/existing',
+        skip_reason: 'existing',
+        existing_post_id: existing.id,
+        validation_errors: {}
+      )
+      expect(result.fetch(:field_warnings)).to eq({})
+    end
+
+    it 'reports list duplicates as URL errors instead of existing skips' do
+      create(:post, url: 'https://example.com/duplicate')
+      expect(PostMetadataFetcher).not_to receive(:fetch)
+
+      results = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://example.com/duplicate'),
+        row(source_row: 2, url: 'https://EXAMPLE.com/duplicate/')
+      ])
+
+      expect(results.map { _1[:validation_errors] }).to all(
+        include(url: ['URL が重複しています．'])
+      )
+      expect(results).to all(include(skip_reason: nil, existing_post_id: nil))
+    end
+
+    it 'does not fetch metadata for an unsafe URL' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+      expect(PostMetadataFetcher).not_to receive(:fetch)
+
+      result = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://unsafe.example/post')
+      ]).first
+
+      expect(result.fetch(:validation_errors)).to include(
+        url: ['安全でない接続先は使用できません．']
+      )
+    end
+
+    it 'applies metadata to automatic fields and recognises metadata tags' do
+      Tag.create!(name: 'known-tag', category: :general)
+      allow(PostMetadataFetcher).to receive(:fetch).and_return(
+        title: 'metadata title',
+        thumbnail_base: 'https://example.com/thumb.jpg',
+        duration: '2',
+        tags: 'known-tag'
+      )
+
+      result = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://example.com/new')
+      ]).first
+
+      expect(result.fetch(:attributes)).to include(
+        'title' => 'metadata title',
+        'thumbnail_base' => 'https://example.com/thumb.jpg',
+        'duration' => '2',
+        'tags' => 'known-tag'
+      )
+      expect(result.fetch(:field_warnings)).not_to have_key('tags')
+      expect(PostMetadataFetcher).to have_received(:fetch).once
+    end
+
+    it 'preserves manual empty values when metadata is available' do
+      allow(PostMetadataFetcher).to receive(:fetch).and_return(
+        title: 'metadata title',
+        tags: 'metadata-tag'
+      )
+
+      result = described_class.new.preview_rows(rows: [
+        row(
+          source_row: 1,
+          url: 'https://example.com/manual',
+          attributes: { title: '', tags: '' },
+          provenance: { title: 'manual', tags: 'manual' },
+          tag_sources: { automatic: 'old-tag', manual: '' }
+        )
+      ]).first
+
+      expect(result.fetch(:attributes)).to include('title' => '', 'tags' => '')
+      expect(result.fetch(:tag_sources)).to include('manual' => '')
+    end
+
+    it 'clears warnings derived from an old metadata URL' do
+      allow(PostMetadataFetcher).to receive(:fetch).and_return(
+        title: 'new title',
+        thumbnail_base: 'https://example.com/new-thumb.jpg',
+        tags: ''
+      )
+
+      result = described_class.new.preview_rows(rows: [
+        row(
+          source_row: 1,
+          url: 'https://example.com/new-url',
+          attributes: { title: 'old title', tags: 'old-tag' },
+          provenance: { title: 'automatic', tags: 'automatic' },
+          tag_sources: { automatic: 'old-tag', manual: '' },
+          metadata_url: 'https://example.com/old-url',
+          field_warnings: { tags: ['old tag warning'], url: ['old fetch warning'] },
+          base_warnings: ['old base warning']
+        )
+      ]).first
+
+      expect(result.fetch(:attributes)).to include('title' => 'new title', 'tags' => '')
+      expect(result.fetch(:base_warnings)).to eq([])
+      expect(result.fetch(:field_warnings).values.flatten)
+          .not_to include('old tag warning', 'old fetch warning')
+    end
+
+    it 'isolates an unexpected metadata failure to the affected URL' do
+      allow(PostMetadataFetcher).to receive(:fetch) do |url|
+        raise 'fetch failure' if url.include?('failure')
+
+        { title: 'successful title', tags: '' }
+      end
+      allow(Rails.logger).to receive(:error)
+
+      results = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://example.com/failure'),
+        row(source_row: 2, url: 'https://example.com/success')
+      ])
+
+      expect(results[0].fetch(:field_warnings)).to include(
+        'url' => [described_class::METADATA_FETCH_WARNING]
+      )
+      expect(results[1].fetch(:attributes)).to include('title' => 'successful title')
+    end
+
+    it 'turns an unsafe URL detected during metadata fetching into a URL error' do
+      allow(PostMetadataFetcher).to receive(:fetch)
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先です．')
+      allow(Rails.logger).to receive(:info)
+
+      result = described_class.new.preview_rows(rows: [
+        row(source_row: 1, url: 'https://example.com/redirects-to-private')
+      ]).first
+
+      expect(result.fetch(:validation_errors)).to include(
+        url: ['安全でない接続先です．']
+      )
+    end
+
+    it 'validates parent IDs from the preloaded set' do
+      parent = create(:post)
+
+      results = described_class.new.preview_rows(
+        rows: [
+          row(source_row: 1, url: 'https://example.com/valid-parent',
+              attributes: { parent_post_ids: parent.id.to_s }),
+          row(source_row: 2, url: 'https://example.com/missing-parent',
+              attributes: { parent_post_ids: '999999' })
+        ],
+        fetch_metadata: false
+      )
+
+      expect(results[0].fetch(:validation_errors)).not_to have_key(:parent_post_ids)
+      expect(results[1].fetch(:validation_errors)).to include(
+        parent_post_ids: ['存在しない親投稿 Id. があります．']
+      )
+    end
+  end
+end

backend/spec/services/post_import_row_normaliser_spec.rb

@@ -0,0 +1,77 @@
+require 'rails_helper'
+
+RSpec.describe PostImportRowNormaliser do
+  def valid_row(overrides = { })
+    {
+      sourceRow: '1',
+      url: 'https://example.com/post',
+      metadataUrl: 'https://example.com/post',
+      attributes: { title: 'title', duration: '1' },
+      provenance: { url: 'manual', title: 'automatic' },
+      tagSources: { automatic: 'tag', manual: '' }
+    }.deep_merge(overrides)
+  end
+
+  describe '.normalise!' do
+    it 'normalises aliases and source rows into a permitted plain hash' do
+      row = ActionController::Parameters.new(valid_row)
+
+      expect(described_class.normalise!([row])).to eq([
+        {
+          'source_row' => 1,
+          'url' => 'https://example.com/post',
+          'metadata_url' => 'https://example.com/post',
+          'attributes' => { 'title' => 'title', 'duration' => '1' },
+          'provenance' => { 'url' => 'manual', 'title' => 'automatic' },
+          'tag_sources' => { 'automatic' => 'tag', 'manual' => '' }
+        }
+      ])
+    end
+
+    it 'normalises source rows before checking duplicates' do
+      rows = [valid_row, valid_row(sourceRow: 1, url: 'https://example.com/other')]
+
+      expect { described_class.normalise!(rows) }
+          .to raise_error(ArgumentError, '元行番号が重複しています．')
+    end
+
+    it 'rejects non-array batches and non-hash rows' do
+      expect { described_class.normalise!({}) }
+          .to raise_error(ArgumentError, '取込行の形式が不正です．')
+      expect { described_class.normalise!(['row']) }
+          .to raise_error(ArgumentError, '取込行の形式が不正です．')
+    end
+
+    it 'rejects unknown attributes and invalid field types' do
+      expect { described_class.normalise!([valid_row(attributes: { unknown: 'x' })]) }
+          .to raise_error(ArgumentError, '取込項目が不正です．')
+      expect { described_class.normalise!([valid_row(attributes: { title: [] })]) }
+          .to raise_error(ArgumentError, '取込項目の型が不正です．')
+      expect { described_class.normalise!([valid_row(attributes: { duration: false })]) }
+          .to raise_error(ArgumentError, '取込項目の型が不正です．')
+    end
+
+    it 'rejects unknown provenance and tag-source values' do
+      expect { described_class.normalise!([valid_row(provenance: { title: 'mapped' })]) }
+          .to raise_error(ArgumentError, '値の由来が不正です．')
+      expect { described_class.normalise!([valid_row(tagSources: { mapped: 'tag' })]) }
+          .to raise_error(ArgumentError, 'タグ由来の形式が不正です．')
+    end
+
+    it 'accepts warning fields only at the validation boundary' do
+      row = valid_row.merge(
+        fieldWarnings: { title: ['取得できませんでした．'] },
+        baseWarnings: ['確認してください．']
+      )
+
+      without_warnings = described_class.normalise!([row]).first
+      with_warnings = described_class.normalise!([row], allow_warning_fields: true).first
+
+      expect(without_warnings).not_to include('field_warnings', 'base_warnings')
+      expect(with_warnings).to include(
+        'field_warnings' => { 'title' => ['取得できませんでした．'] },
+        'base_warnings' => ['確認してください．']
+      )
+    end
+  end
+end

backend/spec/services/post_import_runner_spec.rb

@@ -0,0 +1,152 @@
+require 'rails_helper'
+
+RSpec.describe PostImportRunner do
+  let(:actor) { create(:user, :member) }
+
+  def row(source_row: 1, url: 'https://example.com/post')
+    {
+      sourceRow: source_row,
+      url:,
+      attributes: { title: 'title', tags: '' },
+      provenance: { url: 'manual', title: 'manual', tags: 'manual' },
+      tagSources: { automatic: '', manual: '' }
+    }
+  end
+
+  def preview(source_row: 1, errors: { }, skip_reason: nil, existing_post_id: nil)
+    {
+      source_row:,
+      attributes: { 'title' => 'title', 'tags' => '' },
+      validation_errors: errors,
+      skip_reason:,
+      existing_post_id:
+    }
+  end
+
+  it 'previews the whole batch once before processing individual rows' do
+    rows = [row, row(source_row: 2, url: 'https://example.com/two')]
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    expect(previewer).to receive(:preview_rows)
+        .with(
+          rows: satisfy { _1.map { |row_value| row_value['source_row'] } == [1, 2] },
+          fetch_metadata: false
+        )
+        .and_return([preview, preview(source_row: 2)])
+    allow(PostCreator).to receive(:new).and_return(
+      instance_double(PostCreator, create!: create(:post))
+    )
+
+    result = described_class.new(actor:, rows:).run
+
+    expect(result).to include(created: 2, skipped: 0, failed: 0)
+  end
+
+  it 'treats validation errors as failures before an existing skip' do
+    existing = create(:post)
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([
+      preview(errors: { url: ['URL が重複しています．'] },
+              skip_reason: 'existing', existing_post_id: existing.id)
+    ])
+    expect(PostCreator).not_to receive(:new)
+
+    result = described_class.new(actor:, rows: [row]).run.fetch(:rows).first
+
+    expect(result).to include(
+      status: 'failed',
+      errors: { url: ['URL が重複しています．'] },
+      recoverable: true
+    )
+  end
+
+  it 'returns the existing post ID for skipped rows' do
+    existing = create(:post)
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([
+      preview(skip_reason: 'existing', existing_post_id: existing.id)
+    ])
+
+    result = described_class.new(actor:, rows: [row]).run.fetch(:rows).first
+
+    expect(result).to eq(
+      source_row: 1,
+      status: 'skipped',
+      existing_post_id: existing.id
+    )
+  end
+
+  it 'converts a URL uniqueness validation race into a skip' do
+    existing = create(:post, url: 'https://example.com/race')
+    invalid = Post.new(url: existing.url)
+    invalid.errors.add(:url, :taken)
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([preview])
+    creator = instance_double(PostCreator)
+    allow(PostCreator).to receive(:new).and_return(creator)
+    allow(creator).to receive(:create!).and_raise(ActiveRecord::RecordInvalid.new(invalid))
+
+    result = described_class.new(
+      actor:,
+      rows: [row(url: 'https://EXAMPLE.com/race/')]
+    ).run.fetch(:rows).first
+
+    expect(result).to include(status: 'skipped', existing_post_id: existing.id)
+  end
+
+  it 're-raises RecordNotUnique errors unrelated to the posts URL index' do
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([preview])
+    creator = instance_double(PostCreator)
+    allow(PostCreator).to receive(:new).and_return(creator)
+    allow(creator).to receive(:create!)
+        .and_raise(ActiveRecord::RecordNotUnique, 'other_unique_index')
+
+    expect {
+      described_class.new(actor:, rows: [row]).run
+    }.to raise_error(ActiveRecord::RecordNotUnique)
+  end
+
+  it 'converts a posts URL index race into a skip' do
+    existing = create(:post, url: 'https://example.com/index-race')
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([preview])
+    creator = instance_double(PostCreator)
+    allow(PostCreator).to receive(:new).and_return(creator)
+    allow(creator).to receive(:create!).and_raise(
+      ActiveRecord::RecordNotUnique,
+      'duplicate key index_posts_on_url'
+    )
+
+    result = described_class.new(
+      actor:,
+      rows: [row(url: 'https://EXAMPLE.com/index-race/')]
+    ).run.fetch(:rows).first
+
+    expect(result).to include(status: 'skipped', existing_post_id: existing.id)
+  end
+
+  it 'returns thumbnail warnings from PostCreator on a created row' do
+    previewer = instance_double(PostImportPreviewer)
+    allow(PostImportPreviewer).to receive(:new).and_return(previewer)
+    allow(previewer).to receive(:preview_rows).and_return([preview])
+    created_post = create(:post)
+    creator = instance_double(
+        PostCreator,
+        create!: created_post,
+        field_warnings: { thumbnail_base: ['サムネール画像を取得できませんでした．'] })
+    allow(PostCreator).to receive(:new).and_return(creator)
+
+    result = described_class.new(actor:, rows: [row]).run.fetch(:rows).first
+
+    expect(result).to include(
+      status: 'created',
+      field_warnings: { thumbnail_base: ['サムネール画像を取得できませんでした．'] }
+    )
+  end
+end

backend/spec/services/post_import_url_list_parser_spec.rb

@@ -0,0 +1,40 @@
+require 'rails_helper'
+
+RSpec.describe PostImportUrlListParser do
+  describe '.parse' do
+    it 'trims URLs, ignores blank lines, and preserves source line numbers' do
+      source = "  https://example.com/one  \r\n\r\nhttps://example.com/two\n"
+
+      expect(described_class.parse(source)).to eq([
+        { source_row: 1, url: 'https://example.com/one' },
+        { source_row: 3, url: 'https://example.com/two' }
+      ])
+    end
+
+    it 'rejects an empty URL list' do
+      expect { described_class.parse(" \n\r\n") }
+          .to raise_error(ArgumentError, 'URL を入力してください．')
+    end
+
+    it 'rejects more than 100 non-empty rows' do
+      source = 101.times.map { |index| "https://example.com/#{ index }" }.join("\n")
+
+      expect { described_class.parse(source) }
+          .to raise_error(ArgumentError, '取込件数は 100 件までです．')
+    end
+
+    it 'includes the original line number in an oversized URL error' do
+      source = "\n#{ 'a' * (described_class::MAX_URL_BYTES + 1) }"
+
+      expect { described_class.parse(source) }
+          .to raise_error(ArgumentError, '2 行目: URL が長すぎます．')
+    end
+
+    it 'rejects an oversized request before parsing rows' do
+      source = 'a' * (described_class::MAX_BYTES + 1)
+
+      expect { described_class.parse(source) }
+          .to raise_error(ArgumentError, '入力が大きすぎます．')
+    end
+  end
+end

backend/spec/services/post_metadata_fetcher_spec.rb

@@ -0,0 +1,123 @@
+require 'rails_helper'
+
+RSpec.describe PostMetadataFetcher do
+  Response = Struct.new(:body)
+
+  def fetch_with_published_time(value, url: 'https://example.com/video')
+    html = <<~HTML
+      <html><head>
+        <meta property="article:published_time" content="#{ value }">
+      </head></html>
+    HTML
+    uri = URI.parse(url)
+    allow(Preview::UrlSafety).to receive(:validate).with(url).and_return([uri, ['8.8.8.8']])
+    allow(Preview::HttpFetcher).to receive(:fetch).and_return(Response.new(html))
+    allow(Preview::HtmlMetadataExtractor).to receive(:extract)
+        .and_return(title: 'title', image_url: nil)
+
+    described_class.fetch(url)
+  end
+
+  it 'builds ranges explicitly for year, month, and day precision' do
+    year = fetch_with_published_time('2024')
+    month = fetch_with_published_time('2024-02')
+    day = fetch_with_published_time('2024-02-03')
+
+    expect(year).to include(
+      original_created_from: Time.zone.local(2024, 1, 1).iso8601,
+      original_created_before: Time.zone.local(2025, 1, 1).iso8601
+    )
+    expect(month).to include(
+      original_created_from: Time.zone.local(2024, 2, 1).iso8601,
+      original_created_before: Time.zone.local(2024, 3, 1).iso8601
+    )
+    expect(day).to include(
+      original_created_from: Time.zone.local(2024, 2, 3).iso8601,
+      original_created_before: Time.zone.local(2024, 2, 4).iso8601
+    )
+  end
+
+  it 'rounds second and fractional-second timestamps down to one-minute ranges' do
+    result = fetch_with_published_time('2024-02-03T12:34:56.123+02:30')
+
+    expect(Time.iso8601(result.fetch(:original_created_from)))
+        .to eq(Time.iso8601('2024-02-03T12:34:00+02:30'))
+    expect(
+      Time.iso8601(result.fetch(:original_created_before)) -
+      Time.iso8601(result.fetch(:original_created_from))
+    ).to eq(60)
+    expect(result.fetch(:original_created_from)).not_to include('.')
+  end
+
+  it 'treats hour-precision timestamps as one-hour ranges with and without offsets' do
+    offset_result = fetch_with_published_time('2024-02-03T12+02:30')
+    local_result = fetch_with_published_time('2024-02-03T12')
+
+    expect(Time.iso8601(offset_result.fetch(:original_created_from)))
+        .to eq(Time.iso8601('2024-02-03T12:00:00+02:30'))
+    expect(
+      Time.iso8601(offset_result.fetch(:original_created_before)) -
+      Time.iso8601(offset_result.fetch(:original_created_from))
+    ).to eq(3600)
+    expect(local_result.fetch(:original_created_from)).to eq('2024-02-03T12:00:00Z')
+    expect(local_result.fetch(:original_created_before)).to eq('2024-02-03T13:00:00Z')
+  end
+
+  it 'adds platform tags for known video URLs' do
+    result = fetch_with_published_time('2024', url: 'https://youtu.be/abc123')
+
+    expect(result.fetch(:tags)).to eq('動画 YouTube')
+  end
+
+  it 'returns nil dates for an invalid timestamp' do
+    result = fetch_with_published_time('not-a-time')
+
+    expect(result.fetch(:original_created_from)).to be_nil
+    expect(result.fetch(:original_created_before)).to be_nil
+  end
+
+  it 'returns nil dates for an invalid timestamp second value' do
+    result = fetch_with_published_time('2024-02-03T12:34:99Z')
+
+    expect(result.fetch(:original_created_from)).to be_nil
+    expect(result.fetch(:original_created_before)).to be_nil
+  end
+
+  it 'returns nil dates for invalid calendar dates and invalid hour values' do
+    invalid_day = fetch_with_published_time('2024-02-31T12:00Z')
+    invalid_leap = fetch_with_published_time('2023-02-29T12:00Z')
+    invalid_hour = fetch_with_published_time('2024-02-29T24:00Z')
+
+    [invalid_day, invalid_leap, invalid_hour].each do |result|
+      expect(result.fetch(:original_created_from)).to be_nil
+      expect(result.fetch(:original_created_before)).to be_nil
+    end
+  end
+
+  it 'accepts a valid leap-day timestamp at minute precision' do
+    result = fetch_with_published_time('2024-02-29T12:34Z')
+
+    expect(result.fetch(:original_created_from)).to eq('2024-02-29T12:34:00Z')
+    expect(result.fetch(:original_created_before)).to eq('2024-02-29T12:35:00Z')
+  end
+
+  it 'serialises metadata duration as the same seconds string contract used by forms' do
+    html = <<~HTML
+      <html><head>
+        <meta property="article:published_time" content="2024-02-03T12:34:56.123+02:30">
+        <meta property="og:video:duration" content="2.5">
+      </head></html>
+    HTML
+    uri = URI.parse('https://example.com/video')
+    allow(Preview::UrlSafety).to receive(:validate)
+        .with('https://example.com/video')
+        .and_return([uri, ['8.8.8.8']])
+    allow(Preview::HttpFetcher).to receive(:fetch).and_return(Response.new(html))
+    allow(Preview::HtmlMetadataExtractor).to receive(:extract)
+        .and_return(title: 'title', image_url: nil)
+
+    result = described_class.fetch('https://example.com/video')
+
+    expect(result.fetch(:duration)).to eq('2.5')
+  end
+end

backend/spec/services/post_url_normaliser_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+RSpec.describe PostUrlNormaliser do
+  before do
+    PostUrlSanitisationRule.unscoped.delete_all
+  end
+
+  describe '.normalise' do
+    it 'normalises the host and trailing slash before applying sanitisation rules' do
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/source\\z',
+        replacement: 'https://example.com/canonical'
+      )
+
+      result = described_class.normalise('  https://EXAMPLE.com/source/  ')
+
+      expect(result).to eq('https://example.com/canonical')
+    end
+
+    it 'returns nil for unsupported or malformed URLs' do
+      expect(described_class.normalise('ftp://example.com/file')).to be_nil
+      expect(described_class.normalise('https://[')).to be_nil
+      expect(described_class.normalise('https:/path')).to be_nil
+    end
+  end
+end

backend/spec/services/preview/thumbnail_fetcher_spec.rb

@@ -48,4 +48,56 @@ RSpec.describe Preview::ThumbnailFetcher do
       expect(described_class.fetch('https://example.com/page')).to eq('jpeg-bytes')
     end
   end
+
+  describe '.fetch_image_response' do
+    it 'rejects an unsafe input URL before HTTP fetch' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+      expect(Preview::HttpFetcher).not_to receive(:fetch)
+
+      expect {
+        described_class.fetch_image_response('https://unsafe.example.com/thumb.jpg')
+      }.to raise_error(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+    end
+
+    it 'rejects an unsafe redirect target' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+    end
+
+    it 'rejects an oversized image response' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_raise(Preview::HttpFetcher::ResponseTooLarge, 'too large')
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::HttpFetcher::ResponseTooLarge)
+    end
+
+    it 'rejects a non-image content type' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_return(
+              Preview::HttpFetcher::Response.new(
+                  '<html></html>',
+                  'text/html',
+                  'https://example.com/thumb.jpg'))
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::ThumbnailFetcher::GenerationFailed)
+    end
+  end
 end

backend/spec/services/youtube/sync_spec.rb

@@ -10,6 +10,37 @@ RSpec.describe Youtube::Sync do
     allow(sync).to receive(:attach_thumbnail_if_needed!)
   end
 
+  describe '#attach_thumbnail_if_needed!' do
+    it 'uses the common remote thumbnail attach path' do
+      post = create(:post, thumbnail_base: nil)
+      allow(sync).to receive(:attach_thumbnail_if_needed!).and_call_original
+
+      expect(post).to receive(:attach_thumbnail_from_url!)
+          .with('https://example.com/thumb.jpg')
+
+      sync.send(
+          :attach_thumbnail_if_needed!,
+          post,
+          'https://example.com/thumb.jpg')
+    end
+
+    it 'retries on a later sync when the previous remote attach failed' do
+      post = create(:post, thumbnail_base: nil)
+      allow(sync).to receive(:attach_thumbnail_if_needed!).and_call_original
+      expect(post).to receive(:attach_thumbnail_from_url!)
+          .with('https://example.com/thumb.jpg')
+          .twice
+          .and_raise(Post::RemoteThumbnailFetchFailed, 'failed')
+
+      2.times do
+        sync.send(
+            :attach_thumbnail_if_needed!,
+            post,
+            'https://example.com/thumb.jpg')
+      end
+    end
+  end
+
   describe '#sync!' do
     it 'returns without fetching video details when no video ids are discovered' do
       allow(sync).to receive(:query_terms).and_return([])
@@ -76,7 +107,7 @@ RSpec.describe Youtube::Sync do
       sync.sync!
     end
 
-    it 'creates a YouTube post with default tags and no_deerjikist when no deerjikist mapping exists' do
+    it 'creates a YouTube post with default tags when no deerjikist mapping exists' do
       Tag.tagme
       Tag.bot
       Tag.youtube

backend/spec/tasks/nico_export_spec.rb

@@ -62,7 +62,7 @@ RSpec.describe 'nico:export' do
 
     it 'deduplicates video ids' do
       create_post('https://www.nicovideo.jp/watch/sm12345')
-      create_post('https://www.nicovideo.jp/watch/sm12345?from=1')
+      create_post('https://sp.nicovideo.jp/watch/sm12345')
 
       expect(Open3).to receive(:capture3) do |_env, *args, **_kwargs|
         expect(args.drop(3)).to eq(['sm12345'])

backend/spec/tasks/nico_sync_spec.rb

@@ -18,7 +18,11 @@ RSpec.describe "nico:sync" do
 
   it "既存 post を見つけて、nico tag と linked tag を追加し、差分が出たら bot を付ける" do
     # 既存 post（正規表現で拾われるURL）
-    post = Post.create!(title: "old", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+    post = Post.create!(
+      title: "old",
+      url: "https://www.nicovideo.jp/watch/sm9",
+      uploaded_user: nil
+    )
 
     # 既存の非nicoタグ（kept_non_nico_ids）
     kept_general = create_tag!("spec_kept", category: "general")
@@ -60,8 +64,54 @@ RSpec.describe "nico:sync" do
     expect(active_tag_names).to include("bot操作")
   end
 
+  it '既存 post のサムネール取得に共通 attach 経路を使ふ' do
+    post = Post.create!(
+        title: 'old',
+        url: 'https://www.nicovideo.jp/watch/sm9',
+        uploaded_user: nil)
+    Tag.bot
+    Tag.tagme
+
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
+    allow(URI).to receive(:open)
+        .and_return(
+            StringIO.new(
+                '<meta name="thumbnail" content="https://example.com/thumb.jpg">'))
+    expect(post).to receive(:attach_thumbnail_from_url!)
+        .with('https://example.com/thumb.jpg')
+
+    run_rake_task('nico:sync')
+  end
+
+  it 'サムネール取得失敗後も次回同期で再試行できる' do
+    post = Post.create!(
+        title: 'old',
+        url: 'https://www.nicovideo.jp/watch/sm9',
+        uploaded_user: nil)
+    Tag.bot
+    Tag.tagme
+
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
+    allow(URI).to receive(:open)
+        .and_return(
+            StringIO.new(
+                '<meta name="thumbnail" content="https://example.com/thumb.jpg">'))
+    expect(post).to receive(:attach_thumbnail_from_url!)
+        .with('https://example.com/thumb.jpg')
+        .twice
+        .and_raise(Post::RemoteThumbnailFetchFailed, 'failed')
+
+    2.times do
+      run_rake_task('nico:sync')
+    end
+  end
+
   it "既存 post にあった古い nico tag は active から外され、履歴として discard される" do
-    post = Post.create!(title: "old", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+    post = Post.create!(
+      title: "old",
+      url: "https://www.nicovideo.jp/watch/sm9",
+      uploaded_user: nil
+    )
 
     # 旧nicoタグ（今回の同期結果に含まれない）
     old_nico = create_tag!("nico:OLD", category: "nico")

frontend/AGENTS.md

@@ -50,16 +50,27 @@ pass or the remaining failure is clearly blocked.
 - Prefer single quotes for strings unless interpolation or escaping makes double quotes better.
 - Never write a TypeScript or TSX line longer than 99 characters.
 - Aim to keep TypeScript and TSX lines within 79 characters where practical.
-- Use 4-space logical indentation in TypeScript and TSX.
+- Use 2-space block indentation in TypeScript and TSX.
+- Use 4-space continuation indentation for wrapped expressions, arguments,
+  ternary branches, method chains, object pairs, arrays, and JSX attributes.
+- Treat the user's `PostImportSourcePage.tsx` and
+  `PostImportReviewPage.tsx` formatting as the local reference shape.
 - For arrays, never put whitespace or a line break immediately before `]`.
 - Keep the first element on the same line as `[` by default.
 - If an array would exceed the line limit, break after `[` and indent
   elements by 4 spaces.
-- In TypeScript and TSX only, replace every leading run of 8 spaces with a tab
-  to reduce bytes.
+- In TypeScript and TSX only, use tabs for leading 8-column compression only.
+- A tab does not represent one indentation level.
+- Determine visible indentation with 2-space block indentation and 4-space
+  continuation indentation first, then compress only complete leading runs of
+  8 spaces into tabs.
 - Treat one leading tab as exactly equivalent to 8 leading spaces.
 - Use tabs only for leading indentation. Never replace spaces that occur after
   a non-space character on the same line.
+- Keep residual leading 2, 4, or 6 spaces after any tab compression.
+- Examples: 2 columns = 2 spaces, 4 columns = 4 spaces, 6 columns = 6
+  spaces, 8 columns = 1 tab, 10 columns = 1 tab + 2 spaces, 12 columns = 1
+  tab + 4 spaces.
 
 ## React
 
@@ -97,12 +108,23 @@ pass or the remaining failure is clearly blocked.
   third-party request outside the Rails API.
 - For blob responses, pass `responseType: 'blob'` so the wrapper does not camelCase the body.
 
+## Dialogues
+
+- Dialogue work follows the shared-frontend reuse rules below.
+
 ## Imports and aliases
 
 - The `@` alias points to `frontend/src`.
 - Prefer `@/...` imports for app code instead of long relative paths.
 - Keep type imports separate with `import type`.
-- Match existing import grouping: external packages, app modules, then type imports.
+- Do not mix runtime values and `type` specifiers in one named import
+  declaration.
+- Do not write `import { value, type TypeName } from ...`.
+- Keep short value imports from one module on one line when they fit within
+  99 characters.
+- Order imports as four groups with a blank line between groups: external
+  value imports, `@/...` value imports, external type imports, `@/...`
+  type imports.
 
 ## Tailwind and UI
 
@@ -129,6 +151,41 @@ pass or the remaining failure is clearly blocked.
   it is JSX- or React-specific.
 - Preserve compact TSX expression shapes such as inline ternary branches and
   closing `</div>)` forms when nearby code uses them.
+- Block bodies for components, functions, callbacks, `if`, `try`, `catch`,
+  `finally`, loops, and JSX nesting use 2 spaces per level.
+- Put the opening brace of `try`, `catch`, and `finally` blocks on the next
+  line at the same indentation as the keyword.
+- Do not indent the opening `{` one level deeper than `try`, `catch`, or
+  `finally`.
+- Indent the block body 2 spaces deeper than the keyword and opening brace.
+- Put the closing `}` on its own line at the same indentation as the keyword.
+- Do not write `try {`, `catch {`, or `finally {`.
+- Wrapped expressions, arguments, ternary branches, method chains, and object
+  pairs use 4-space continuation indentation relative to the owning
+  expression. Do not confuse this with 2-space block indentation.
+- Tabs are leading 8-column compression only. They do not represent one
+  nesting level. Decide visible indentation first, then compress only
+  complete leading runs of 8 spaces into tabs.
+- Do not add braces around a single-line `if` body merely for formatting.
+- Use braces for multi-line `if`, `else`, and loop bodies.
+- Multi-stage ternary expressions must use explicit parentheses for each
+  condition group and nested branch. Do not rely on indentation alone to show
+  `?` / `:` pairing.
+- Keep short inline props types local when they remain readable and within the
+  line limit; do not mechanically extract a named type with no reuse benefit.
+- In JavaScript, JSX, TypeScript, and TSX, never use `_1`, `_2`, or similar
+  Ruby-style numbered parameter names. Reserve numbered parameters for Ruby.
+  Use a meaningful callback parameter name such as `row`, `item`, `value`,
+  `entry`, or `result`.
+- In multi-line object literals, keep the opening `{` with the first pair when
+  the line length allows it; do not mechanically explode short objects into
+  Prettier-style vertical blocks.
+- Method chains should align as a continuation under the receiver expression;
+  do not indent chains more deeply than the normal continuation depth.
+- `PostImportSourcePage.tsx` and `PostImportReviewPage.tsx` are the current
+  canonical examples for block indentation, continuation indentation, import
+  grouping, ternary grouping, method-chain placement, and local inline props
+  types.
 - Treat TypeScript and TSX formatting rules as hard constraints, not
   preferences. Before finishing a TypeScript or TSX edit, inspect the edited
   hunks for closing `)`, `]`, and `}` placement and fix violations instead of
@@ -158,14 +215,93 @@ pass or the remaining failure is clearly blocked.
   beginning of a line.
 - The TSX-specific self-review must confirm JSX closing markers and closing
   parentheses keep the surrounding compact style.
-- The TypeScript/TSX self-review must confirm leading indentation follows
-  4-space logical indentation with tabs only as leading 8-space compression.
+- The TypeScript/TSX self-review must confirm leading block indentation uses
+  2 spaces per level, wrapped continuations use the repository's 4-space
+  continuation alignment, and complete leading runs of 8 spaces may be
+  compressed to tabs.
 - For long Tailwind `className` strings, wrap across lines only when needed.
-- Keep continuation indentation aligned with the 4-space logical indentation
-  rule, using tabs only as leading 8-space compression.
+- Keep continuation indentation aligned with the repository's 4-space
+  continuation rule while keeping block indentation at 2 spaces.
+- Keep short value imports from one module on one line when they fit within
+  99 characters.
 - In TypeScript and TSX function declarations, including `const` arrow
   function declarations, classify the parameter list before placing the closing
   `)`.
+- Block indentation example:
+
+```ts
+const Component = () => {
+  const value = loadValue ()
+
+  useEffect (() => {
+    if (value != null)
+      useValue (value)
+  }, [value])
+}
+```
+
+- `try` / `catch` / `finally` brace placement example:
+
+```ts
+try
+{
+  doWork ()
+}
+catch
+{
+  recover ()
+}
+finally
+{
+  cleanUp ()
+}
+```
+
+- Continuation indentation example:
+
+```ts
+const editingRow =
+    Number.isFinite (editingSourceRow)
+    ? rows.find (row => row.sourceRow === editingSourceRow) ?? null
+    : null
+```
+
+- Import grouping example:
+
+```ts
+import { useNavigate, useParams, useSearchParams } from 'react-router-dom'
+
+import { loadPostImportSession } from '@/lib/postImportSession'
+
+import type { FC } from 'react'
+
+import type { PostImportRow } from '@/lib/postImportSession'
+```
+
+- Inline props type example:
+
+```ts
+const Footer = (
+    { loading,
+      onSubmit }: { loading:  boolean
+		    onSubmit: () => void },
+) => null
+```
+
+- Ternary grouping example:
+
+```ts
+const rows =
+    repairMode === 'failed'
+    ? (
+	[...source].sort ((a, b) => {
+	  const aFailed = a.failed ? 0 : 1
+	  const bFailed = b.failed ? 0 : 1
+	  return aFailed - bFailed
+	}))
+    : source
+```
+
 - If the parameter list itself is given its own multi-line block after the
   function's opening `(`, put the closing parameter `)` at the beginning of its
   own line before the return type or `=>`.
@@ -219,6 +355,237 @@ pass or the remaining failure is clearly blocked.
   `BehaviorSettingsSection.tsx`.
 - Avoid reformatting unrelated JSX.
 
+## Shared frontend systems
+
+Before creating a new component, hook, helper, store, context, or other
+frontend abstraction, search at least:
+
+- `src/components/common`
+- `src/components/layout`
+- `src/components/ui`
+- `src/components/dialogues`
+- `src/lib`
+- `src/lib/dialogues`
+- `src/stores`
+- `src/types.ts`
+
+Also inspect the existing pages and components in the same feature.
+
+Search by responsibility, not by filename alone. Check display, interaction,
+state, communication, validation, and permission behaviour before deciding that
+an existing implementation is unsuitable.
+
+### Component placement and reuse order
+
+When adding UI, use this order:
+
+1. reuse an existing feature component
+2. reuse an existing component from `components/common`
+3. reuse an existing layout component from `components/layout`
+4. use an existing primitive from `components/ui` through the established
+   common API
+5. extend an existing component minimally
+6. add a feature-local component in the feature area
+7. add a new common component only when multiple features clearly share a
+   stable visual contract
+
+Do not place a one-screen component in a common directory merely because its
+name starts with `Common`.
+
+### Low-level primitives
+
+Treat `components/ui` as low-level primitives. If a higher-level common API
+already exists for dialogues, toast, form validation, navigation, or similar
+behaviour, feature code must use that API instead of assembling primitives
+directly.
+
+Examples of existing preferred entrypoints include:
+
+- dialogue: `@/lib/dialogues/useDialogue`
+- toast: the existing toast API
+- internal navigation: `PrefetchLink`
+- form errors: `FieldError`, `FieldWarning`, `FormField`
+- buttons: `Button`
+- conditional class merge: `cn`
+
+Do not evade the rule with aliases or thin wrappers around the low-level
+primitive.
+
+### Dialogues
+
+Feature-facing dialogue work must use `@/lib/dialogues/useDialogue`.
+
+Reuse the existing common dialogue API and common dialogue component. Do not
+import `@/components/ui/dialog` directly in feature code to assemble bespoke
+dialogue shells, and do not evade this rule with aliases such as
+`Dialog as Dialogue`.
+
+Do not reimplement overlay, portal, close button, header, footer, focus
+handling, Escape handling, outside-click handling, or confirmation flow in
+feature code.
+
+Keep business-specific form content in feature code, and keep the visual and
+behavioural dialogue shell in common code.
+
+Use British spelling `Dialogue` for project-defined dialogue identifiers. Keep
+exact third-party spellings only at the external boundary where compatibility
+requires them.
+
+### API calls
+
+Rails API calls must use `src/lib/api.ts`.
+
+Do not create feature-local Axios instances, fetch wrappers, header injectors,
+camelCase converters, or generic error converters. If blob or other special
+transport behaviour is already supported by the common API, use the existing
+options instead of bypassing the wrapper.
+
+### Query keys, server state, and prefetch
+
+Before adding query state, inspect:
+
+- `src/lib/queryKeys.ts`
+- existing domain helpers
+- existing prefetchers
+- the root query-key hierarchy
+- current mutation invalidation patterns
+- the app-wide `QueryClient`
+
+Do not write ad hoc query-key arrays in feature code. Do not duplicate fetcher,
+prefetcher, or invalidation helpers for the same resource.
+
+### Domain helpers
+
+For posts, tags, wiki, materials, and other domain work, inspect the existing
+helpers in `src/lib/*.ts` before adding logic to a page component.
+
+Do not accumulate these in page components when an existing helper layer should
+own them:
+
+- API request construction
+- response-shape conversion
+- query-key construction
+- canonical URL generation
+- permission calculation
+- storage serialisation
+- domain-specific parsing
+
+Keep purely local one-screen display shaping local when that is the clearest
+place for it.
+
+### Permission helpers
+
+Use the existing permission helpers such as `src/lib/users.ts` when deciding
+editability, role checks, admin/member visibility, and similar UI behaviour.
+
+Do not scatter `user?.role`, numeric role comparisons, or string comparisons
+through components. Frontend visibility control should be consistent even though
+backend authorization remains the final gate.
+
+### Validation errors
+
+Before adding feature-local validation-error handling, inspect:
+
+- `useValidationErrors`
+- `apiErrors`
+- `FieldError`
+- `FieldWarning`
+- `FormField`
+- `inputClass`
+
+Do not create a new generic hook, field-error state shape, or error-rendering
+component for a pattern the shared error stack already covers. Keep only
+genuinely feature-specific business errors local.
+
+### Forms and fields
+
+Before creating a new input, textarea, date/time field, tag input, label, or
+error layout, inspect at least:
+
+- `Form`
+- `FormField`
+- `FieldError`
+- `FieldWarning`
+- `DateTimeField`
+- `TagInput`
+- `TextArea`
+- `Label`
+- `Button`
+
+Do not create a same-function field component merely because the spacing or
+surface styling is slightly different. Prefer feature-level composition over
+bloated common-field option lists.
+
+### Navigation and prefetch
+
+Use `PrefetchLink` and existing router helpers for internal navigation. Do not
+introduce feature-local `<a>`, `window.location`, or custom prefetch logic for
+internal routes. Keep path-segment encoding aligned with the existing rules.
+
+### State management
+
+Before adding state, decide whether the source of truth should be:
+
+- component-local state
+- URL search params
+- TanStack Query server state
+- an existing Zustand store
+- an existing event bus
+- an existing storage helper
+
+Do not create a new global store, context, or event bus for one screen when
+local state or an existing mechanism is enough. Do not create a second store
+for the same responsibility.
+
+### Storage and settings
+
+When touching localStorage, sessionStorage, or user settings, inspect existing
+settings helpers, storage helpers, expiry handling, versioning, and sanitisers.
+
+Do not reimplement per-component key naming, JSON parsing and serialisation,
+expiry, or schema checks when a shared helper already owns the pattern.
+
+### Hooks
+
+Before creating a custom hook, search existing `src/lib/use*.ts` and
+`src/lib/use*.tsx`.
+
+Hooks are for shared stateful behaviour or React lifecycle integration. Do not
+turn a pure function, one-off helper, or mere re-export shim into `useFoo`.
+
+### Stores, contexts, and event buses
+
+Add a new store, context, or event bus only when the current mechanisms cannot
+express the requirement and there are multiple genuinely separate consumers.
+
+Do not hold the same information redundantly across URL state, query cache,
+local component state, Zustand, and an event bus. Keep one source of truth.
+
+### Types
+
+If a domain type already exists in `src/types.ts` or a domain helper, reuse it
+instead of redefining the same shape in a feature file.
+
+Small local props and draft types may stay local. Do not create giant
+catch-all type files such as `CommonTypes.ts`.
+
+### Styling utilities
+
+Use existing styling utilities such as `cn` and `inputClass`.
+
+Do not add feature-local class-merge helpers, generic status-colour mappers, or
+responsive wrapper helpers when a shared utility already exists. Keep common
+tone names visual only; feature-specific state names stay in feature code.
+
+### Layout
+
+Before adding page shells, padding rules, viewport-height handling, sidebar
+offsets, or footer offsets, inspect existing layout components such as
+`MainArea`, top navigation, sidebar, page title, and section-title patterns.
+
+Do not create a second layout shell before checking whether the current layout
+can be reused or minimally extended.
+
 ### Delimiter decision table
 
 Use this table before accepting any edited TypeScript or TSX hunk. The table is
@@ -563,8 +930,9 @@ hunks line by line:
 7. JSX `>` and `/>` stay with the final prop unless nearby code proves
    otherwise.
 8. JSX closing parentheses keep the compact local style.
-9. Leading indentation is 4-space logical indentation with tabs used only as
-   leading 8-space compression.
+9. Leading block indentation uses 2 spaces per level, wrapped continuations
+   use the repository's 4-space continuation alignment, and complete leading
+   runs of 8 spaces may be compressed to tabs.
 10. No line has trailing whitespace.
 
 ## Lint and build constraints

frontend/src/App.tsx

@@ -41,6 +41,9 @@ import NotFound from '@/pages/NotFound'
 import TOSPage from '@/pages/TOSPage.mdx'
 import PostDetailPage from '@/pages/posts/PostDetailPage'
 import PostHistoryPage from '@/pages/posts/PostHistoryPage'
+import PostImportResultPage from '@/pages/posts/PostImportResultPage'
+import PostImportReviewPage from '@/pages/posts/PostImportReviewPage'
+import PostImportSourcePage from '@/pages/posts/PostImportSourcePage'
 import PostListPage from '@/pages/posts/PostListPage'
 import PostNewPage from '@/pages/posts/PostNewPage'
 import PostSearchPage from '@/pages/posts/PostSearchPage'
@@ -75,6 +78,9 @@ const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
 	    <Route path="/" element={<Navigate to="/posts" replace/>}/>
 	    <Route path="/posts" element={<PostListPage/>}/>
 	    <Route path="/posts/new" element={<PostNewPage user={user}/>}/>
+	    <Route path="/posts/import" element={<PostImportSourcePage user={user}/>}/>
+	    <Route path="/posts/import/:sessionId/review" element={<PostImportReviewPage user={user}/>}/>
+	    <Route path="/posts/import/:sessionId/result" element={<PostImportResultPage user={user}/>}/>
 	    <Route path="/posts/search" element={<PostSearchPage/>}/>
 	    <Route path="/posts/:id" element={<PostDetailRoute user={user}/>}/>
 	    <Route path="/posts/changes" element={<PostHistoryPage/>}/>
@@ -113,6 +119,9 @@ const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
 	  <Route path="/" element={<Navigate to="/posts" replace/>}/>
 	  <Route path="/posts" element={<PostListPage/>}/>
 	  <Route path="/posts/new" element={<PostNewPage user={user}/>}/>
+	  <Route path="/posts/import" element={<PostImportSourcePage user={user}/>}/>
+	  <Route path="/posts/import/:sessionId/review" element={<PostImportReviewPage user={user}/>}/>
+	  <Route path="/posts/import/:sessionId/result" element={<PostImportResultPage user={user}/>}/>
 	  <Route path="/posts/search" element={<PostSearchPage/>}/>
 	  <Route path="/posts/:id" element={<PostDetailRoute user={user}/>}/>
 	  <Route path="/posts/changes" element={<PostHistoryPage/>}/>

frontend/src/components/PostEditForm.test.tsx

@@ -19,8 +19,8 @@ const toastApi = vi.hoisted (() => ({
 vi.mock ('@/lib/posts', () => postsApi)
 vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
-vi.mock ('@/components/dialogues/DialogueProvider', () => ({
-  useDialogue: () => ({
+vi.mock ('@/lib/dialogues/useDialogue', () => ({
+  default: () => ({
     choice: vi.fn (),
   }),
 }))
@@ -78,15 +78,39 @@ describe ('PostEditForm', () => {
 
     render (<PostEditForm post={post} onSave={vi.fn ()}/>)
 
-    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('180.5')
 
     const tags = screen.getAllByRole ('textbox')[2]
     fireEvent.change (tags, { target: { value: 'general-tag' } })
-    expect (screen.queryByRole ('spinbutton')).not.toBeInTheDocument ()
+    expect (screen.queryByPlaceholderText ('例: 2 / 2.5 / 1:23')).not.toBeInTheDocument ()
 
     fireEvent.change (tags, {
       target: { value: '動画 general-tag' },
     })
-    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('180.5')
+  })
+
+  it ('shows deduplicated original-created endpoint errors on the shared datetime field', async () => {
+    const post = buildPost ()
+    api.isApiError.mockReturnValue (true)
+    postsApi.updatePost.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type: 'validation_error',
+          errors: {
+            original_created_at: ['日時を確認してください．'],
+            original_created_from: ['日時を確認してください．'],
+            original_created_before: ['終了を確認してください．'] },
+        },
+      },
+    })
+
+    render (<PostEditForm post={post} onSave={vi.fn ()}/>)
+    fireEvent.submit (screen.getByRole ('button', { name: '更新' }).closest ('form')!)
+
+    expect (await screen.findByText ('日時を確認してください．')).toBeInTheDocument ()
+    expect (screen.getByText ('終了を確認してください．')).toBeInTheDocument ()
+    expect (screen.getAllByText ('日時を確認してください．')).toHaveLength (1)
   })
 })

frontend/src/components/PostEditForm.tsx

@@ -1,15 +1,16 @@
 import { useEffect, useMemo, useState } from 'react'
 
-import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import FieldError from '@/components/common/FieldError'
-import FormField from '@/components/common/FormField'
-import { useDialogue } from '@/components/dialogues/DialogueProvider'
+import PostDurationField from '@/components/posts/PostDurationField'
+import PostTagsField from '@/components/posts/PostTagsField'
+import PostTextField from '@/components/posts/PostTextField'
 import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { isApiError } from '@/lib/api'
+import useDialogue from '@/lib/dialogues/useDialogue'
 import { updatePost } from '@/lib/posts'
-import { inputClass, msToTime } from '@/lib/utils'
+import { msToTime } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 
 import type { FC, FormEvent } from 'react'
@@ -17,7 +18,11 @@ import type { FC, FormEvent } from 'react'
 import type { Post, TagWithSections } from '@/types'
 
 type PostFormField =
-    'parentPostIds' | 'tags' | 'videoMs' | 'originalCreatedAt'
+    'parentPostIds' | 'tags' | 'videoMs'
+    | 'originalCreatedAt' | 'originalCreatedFrom' | 'originalCreatedBefore'
+
+const groupedMessages = (...values: (string[] | undefined)[]): string[] =>
+    [...new Set (values.flatMap (value => value ?? []))]
 
 const videoMsToDurationValue = (videoMs: number | null): string =>
     videoMs == null ? '' : String (videoMs / 1_000)
@@ -157,32 +162,20 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       <form onSubmit={handleSubmit} className="max-w-xl pt-2 space-y-4">
 	<FieldError messages={baseErrors}/>
 
-	{/* タイトル */}
-	<FormField label="タイトル">
-	  {({ invalid }) => (
-	      <input
-		  type="text"
-		  disabled={disabled}
-		  className={inputClass (invalid)}
-		  value={title ?? ''}
-		  onChange={e => setTitle (e.target.value)}/>)}
-	</FormField>
+	<PostTextField
+	    label="タイトル"
+	    value={title ?? ''}
+	    disabled={disabled}
+	    onChange={setTitle}/>
 
-	{/* 親投稿 */}
-	<FormField label="親投稿" messages={fieldErrors.parentPostIds}>
-	  {({ describedBy, invalid }) => (
-	      <input
-		  type="text"
-		  disabled={disabled}
-		  value={parentPostIds}
-		  onChange={e => setParentPostIds (e.target.value)}
-		  aria-describedby={describedBy}
-		  aria-invalid={invalid}
-		  className={inputClass (invalid)}/>)}
-	</FormField>
+	<PostTextField
+	    label="親投稿"
+	    value={parentPostIds}
+	    disabled={disabled}
+	    errors={fieldErrors.parentPostIds}
+	    onChange={setParentPostIds}/>
 
-	{/* タグ */}
-	<PostFormTagsArea
+	<PostTagsField
 	    disabled={disabled}
 	    tags={tags}
 	    setTags={setTags}
@@ -195,21 +188,17 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
 	    setOriginalCreatedFrom={setOriginalCreatedFrom}
 	    originalCreatedBefore={originalCreatedBefore}
 	    setOriginalCreatedBefore={setOriginalCreatedBefore}
-	    errors={fieldErrors.originalCreatedAt}/>
+	    errors={groupedMessages (
+		fieldErrors.originalCreatedAt,
+		fieldErrors.originalCreatedFrom,
+		fieldErrors.originalCreatedBefore)}/>
 
-	{/* 動画時間 */}
 	{videoFlg && (
-	    <FormField label="動画時間" messages={fieldErrors.videoMs}>
-	      {({ invalid }) => (
-		  <input
-		      type="number"
-		      min="0.001"
-		      step="0.001"
-		      disabled={disabled}
-		      className={inputClass (invalid)}
-		      value={duration}
-		      onChange={e => setDuration (e.target.value)}/>)}
-	    </FormField>)}
+	    <PostDurationField
+		value={duration}
+		disabled={disabled}
+		errors={fieldErrors.videoMs}
+		onChange={setDuration}/>)}
 
 	{/* 送信 */}
 	<Button type="submit" disabled={disabled}>

frontend/src/components/PostOriginalCreatedTimeField.test.tsx

@@ -20,8 +20,10 @@ describe ('PostOriginalCreatedTimeField', () => {
     fireEvent.change (inputs[0], { target: { value: '2026-01-02T03:04' } })
     fireEvent.change (inputs[1], { target: { value: '2026-01-03T03:04' } })
 
-    expect (setFrom).toHaveBeenCalledWith (expect.any (String))
-    expect (setBefore).toHaveBeenCalledWith (expect.any (String))
+    expect (setFrom).toHaveBeenCalledWith (expect.stringMatching (
+	/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z$/))
+    expect (setBefore).toHaveBeenCalledWith (expect.stringMatching (
+	/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z$/))
   })
 
   it ('infers an exclusive before value on blur', () => {
@@ -38,7 +40,43 @@ describe ('PostOriginalCreatedTimeField', () => {
     const input = screen.getAllByDisplayValue ('')[0]
     fireEvent.blur (input, { target: { value: '2026-01-02T03:04' } })
 
-    expect (setBefore).toHaveBeenCalledWith (expect.any (String))
+    const value = setBefore.mock.calls.at (-1)?.[0]
+    expect (value).toMatch (/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z$/)
+    expect (new Date (value).getTime () - new Date ('2026-01-02T03:04').getTime ())
+	.toBe (60_000)
+  })
+
+  it ('does not rewrite mounted values that only differ by offset notation', () => {
+    const setFrom = vi.fn ()
+    const setBefore = vi.fn ()
+
+    render (
+        <PostOriginalCreatedTimeField
+            originalCreatedFrom="2024-01-01T12:34+09:00"
+            setOriginalCreatedFrom={setFrom}
+            originalCreatedBefore="2024-01-01T12:35+09:00"
+            setOriginalCreatedBefore={setBefore}/>,
+    )
+
+    expect (setFrom).not.toHaveBeenCalled ()
+    expect (setBefore).not.toHaveBeenCalled ()
+  })
+
+  it ('emits minute-precision UTC values only when the user edits the input', () => {
+    const setFrom = vi.fn ()
+
+    render (
+        <PostOriginalCreatedTimeField
+            originalCreatedFrom="2024-01-01T12:34+09:00"
+            setOriginalCreatedFrom={setFrom}
+            originalCreatedBefore={null}
+            setOriginalCreatedBefore={vi.fn ()}/>,
+    )
+
+    const input = screen.getDisplayValue ('2024-01-01T12:34')
+    fireEvent.change (input, { target: { value: '2024-01-01T12:35' } })
+
+    expect (setFrom).toHaveBeenCalledWith ('2024-01-01T03:35Z')
   })
 
   it ('resets both values', () => {

frontend/src/components/PostOriginalCreatedTimeField.tsx

@@ -1,4 +1,4 @@
-import DateTimeField from '@/components/common/DateTimeField'
+import DateTimeField, { toMinutePrecisionIsoUtc } from '@/components/common/DateTimeField'
 import FormField from '@/components/common/FormField'
 import { Button } from '@/components/ui/button'
 
@@ -19,70 +19,74 @@ const PostOriginalCreatedTimeField: FC<Props> = (
       setOriginalCreatedFrom,
       originalCreatedBefore,
       setOriginalCreatedBefore,
-      errors }: Props) => (
-    <FormField label="オリジナルの作成日時" messages={errors}>
-      {({ describedBy, invalid }) => (
-	  <>
-	    <div className="my-1 flex">
-	      <div className="w-80">
-		<DateTimeField
-		    className="mr-2"
-		    disabled={disabled ?? false}
-		    aria-describedby={describedBy}
-		    aria-invalid={invalid}
-		    invalid={invalid}
-		    value={originalCreatedFrom ?? undefined}
-		    onChange={setOriginalCreatedFrom}
-		    onBlur={ev => {
-		      const v = ev.target.value
-		      if (!(v))
-			return
+      errors }: Props) => {
+  return (
+      <FormField label="オリジナルの作成日時" messages={errors}>
+	  {({ describedBy, invalid }) => (
+	      <>
+		<div className="my-1 flex flex-col gap-2 sm:flex-row sm:items-start">
+		  <div className="min-w-0 flex-1">
+		    <DateTimeField
+			className="w-full"
+			disabled={disabled ?? false}
+			aria-describedby={describedBy}
+			aria-invalid={invalid}
+			invalid={invalid}
+			value={originalCreatedFrom ?? undefined}
+			onChange={setOriginalCreatedFrom}
+			onBlur={ev => {
+			  const v = ev.target.value
+			  if (!(v))
+			    return
 
-		      const d = new Date (v)
-		      if (d.getMinutes () === 0 && d.getHours () === 0)
-			d.setDate (d.getDate () + 1)
-		      else
-			d.setMinutes (d.getMinutes () + 1)
-		      setOriginalCreatedBefore (d.toISOString ())
-		    }}/>
-		以降
-	      </div>
-	      <div>
-		<Button
-		    className="bg-gray-600 text-white rounded"
-		    disabled={disabled}
-		    onClick={() => {
-		      setOriginalCreatedFrom (null)
-		    }}>
-		  リセット
-		</Button>
-	      </div>
-	    </div>
+			  const d = new Date (v)
+			  if (d.getMinutes () === 0 && d.getHours () === 0)
+			    d.setDate (d.getDate () + 1)
+			  else
+			    d.setMinutes (d.getMinutes () + 1)
+			  setOriginalCreatedBefore (toMinutePrecisionIsoUtc (d.toISOString ()))
+			}}/>
+		    以降
+		  </div>
+		  <div>
+		    <Button
+			type="button"
+			className="bg-gray-600 text-white rounded"
+			disabled={disabled}
+			onClick={() => {
+			  setOriginalCreatedFrom (null)
+			}}>
+		      リセット
+		    </Button>
+		  </div>
+		</div>
 
-	    <div className="my-1 flex">
-	      <div className="w-80">
-		<DateTimeField
-		    className="mr-2"
-		    disabled={disabled}
-		    aria-describedby={describedBy}
-		    aria-invalid={invalid}
-		    invalid={invalid}
-		    value={originalCreatedBefore ?? undefined}
-		    onChange={setOriginalCreatedBefore}/>
-		より前
-	      </div>
-	      <div>
-		<Button
-		    className="bg-gray-600 text-white rounded"
-		    disabled={disabled}
-		    onClick={() => {
-		      setOriginalCreatedBefore (null)
-		    }}>
-		  リセット
-		</Button>
-	      </div>
-	    </div>
-	  </>)}
-    </FormField>)
+		<div className="my-1 flex flex-col gap-2 sm:flex-row sm:items-start">
+		  <div className="min-w-0 flex-1">
+		    <DateTimeField
+			className="w-full"
+			disabled={disabled}
+			aria-describedby={describedBy}
+			aria-invalid={invalid}
+			invalid={invalid}
+			value={originalCreatedBefore ?? undefined}
+			onChange={setOriginalCreatedBefore}/>
+		    より前
+		  </div>
+		  <div>
+		    <Button
+			type="button"
+			className="bg-gray-600 text-white rounded"
+			disabled={disabled}
+			onClick={() => {
+			  setOriginalCreatedBefore (null)
+			}}>
+		      リセット
+		    </Button>
+		  </div>
+		</div>
+	      </>)}
+      </FormField>)
+}
 
 export default PostOriginalCreatedTimeField

frontend/src/components/TopNav.test.tsx

@@ -0,0 +1,37 @@
+import { describe, expect, it } from 'vitest'
+
+import { menuOutline } from '@/components/TopNav'
+import { buildUser } from '@/test/factories'
+
+const submenuItem = (role: 'guest' | 'member' | 'admin', section: string, item: string) => {
+  const menu = menuOutline ({
+    user: buildUser ({ role }),
+    wikiId: section === 'Wiki' ? 10 : null,
+    pathName: section === 'Wiki' ? '/wiki/page' : '/posts' })
+  return menu.find (entry => entry.name === section)?.subMenu.find (
+      subMenuItem => subMenuItem.name === item)
+}
+
+describe ('menuOutline', () => {
+  it ('uses content-edit permission for post, material, and Wiki actions', () => {
+    for (const role of ['member', 'admin'] as const)
+      {
+	expect (submenuItem (role, '広場', '追加')?.visible).toBe (true)
+	expect (submenuItem (role, '広場', '取込')?.visible).toBe (true)
+	expect (submenuItem (role, '素材', '追加')?.visible).toBe (true)
+	expect (submenuItem (role, 'Wiki', '新規')?.visible).toBe (true)
+	expect (submenuItem (role, 'Wiki', '編輯')?.visible).toBe (true)
+      }
+
+    expect (submenuItem ('guest', '広場', '追加')?.visible).toBe (false)
+    expect (submenuItem ('guest', '広場', '取込')?.visible).toBe (false)
+    expect (submenuItem ('guest', '素材', '追加')?.visible).toBe (false)
+    expect (submenuItem ('guest', 'Wiki', '新規')?.visible).toBe (false)
+    expect (submenuItem ('guest', 'Wiki', '編輯')?.visible).toBe (false)
+  })
+
+  it ('keeps material suppression admin-only', () => {
+    expect (submenuItem ('member', '素材', '抑止')?.visible).toBe (false)
+    expect (submenuItem ('admin', '素材', '抑止')?.visible).toBe (true)
+  })
+})

frontend/src/components/TopNav.tsx

@@ -9,6 +9,7 @@ import TopNavUser from '@/components/TopNavUser'
 import { WikiIdBus } from '@/lib/eventBus/WikiIdBus'
 import { materialsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
 import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { canEditContent } from '@/lib/users'
 import { fetchTag, fetchTagByName } from '@/lib/tags'
 import { fetchMaterial } from '@/lib/materials'
 import { cn } from '@/lib/utils'
@@ -26,10 +27,11 @@ export const menuOutline = (
 	tag?: Tag | null
 	material?: Material | null
 	wikiId: number | null
-	user: User | null,
+	user: User | null
 	pathName: string },
 ): Menu => {
   const postCount = tag?.postCount ?? material?.tag?.postCount ?? 0
+  const editable = canEditContent (user)
 
   const wikiPageFlg = Boolean (/^\/wiki\/(?!new|changes)[^/]+/.test (pathName) && wikiId)
   const wikiTitle = pathName.split ('/')[2] ?? ''
@@ -42,7 +44,8 @@ export const menuOutline = (
       { name: '広場', to: '/posts', subMenu: [
 	  { name: '一覧', to: '/posts' },
 	  { name: '検索', to: '/posts/search' },
-	  { name: '追加', to: '/posts/new' },
+	  { name: '追加', to: '/posts/new', visible: editable },
+	  { name: '取込', to: '/posts/import', visible: editable },
 	  { name: '全体履歴', to: '/posts/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:広場' }] },
       { name: 'タグ', to: '/tags', subMenu: [
@@ -58,8 +61,9 @@ export const menuOutline = (
 	    visible: tagFlg && tag?.category !== 'nico' }] },
       { name: '素材', to: '/materials', visible: true, subMenu: [
 	  { name: '一覧', to: '/materials' },
-	  { name: '追加', to: '/materials/new' },
-	  { name: '抑止', to: '/materials/suppressions' },
+	  { name: '追加', to: '/materials/new', visible: editable },
+	  { name: '抑止', to: '/materials/suppressions',
+	    visible: user?.role === 'admin' },
 	  { name: '全体履歴', to: '/materials/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:素材管理' },
 	  { component: <Separator/>, visible: materialFlg },
@@ -70,14 +74,15 @@ export const menuOutline = (
 	    visible: materialFlg }] },
       { name: 'Wiki', to: '/wiki/ヘルプ:ホーム', base: '/wiki', subMenu: [
 	  { name: '検索', to: '/wiki' },
-	  { name: '新規', to: '/wiki/new' },
+	  { name: '新規', to: '/wiki/new', visible: editable },
 	  { name: '全体履歴', to: '/wiki/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:Wiki' },
 	  { component: <Separator/>, visible: wikiPageFlg },
 	  { name: `広場 (${ postCount || 0 })`, to: `/posts?tags=${ wikiTitle }`,
 	    visible: wikiPageFlg },
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
-	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`, visible: wikiPageFlg }] },
+	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`,
+	    visible: wikiPageFlg && editable }] },
       { name: 'おたのしみ', visible: false, subMenu: [
 	  { name: '上映会 (β)', to: '/theatres/1' },
 	  { name: 'グカネータ (β)', to: '/gekanator' }] },

frontend/src/components/common/DateTimeField.test.tsx

@@ -21,7 +21,8 @@ describe ('DateTimeField', () => {
     fireEvent.change (input, { target: { value: '' } })
 
     const first = handleChange.mock.calls[0]?.[0]
-    expect (new Date (first).getFullYear ()).toBe (2026)
+    expect (first).toMatch (/^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}Z$/)
+    expect (new Date (first).getUTCSeconds ()).toBe (0)
     expect (handleChange).toHaveBeenLastCalledWith (null)
   })
 })

frontend/src/components/common/DateTimeField.tsx

@@ -8,13 +8,27 @@ import type { ComponentPropsWithoutRef, FC, FocusEvent } from 'react'
 const pad = (n: number): string => n.toString ().padStart (2, '0')
 
 
-const toDateTimeLocalValue = (d: Date) => {
-  const y = d.getFullYear ()
-  const m = pad (d.getMonth () + 1)
-  const day = pad (d.getDate ())
-  const h = pad (d.getHours ())
-  const min = pad (d.getMinutes ())
-  return `${ y }-${ m }-${ day }T${ h }:${ min }:00`
+const toDateTimeLocalValue = (value: Date) => {
+  const y = value.getFullYear ()
+  const m = pad (value.getMonth () + 1)
+  const day = pad (value.getDate ())
+  const h = pad (value.getHours ())
+  const min = pad (value.getMinutes ())
+  return `${ y }-${ m }-${ day }T${ h }:${ min }`
+}
+
+
+const toMinutePrecisionIsoUtc = (value: string) => {
+  const date = new Date (value)
+  if (Number.isNaN (date.getTime ()))
+    return value
+
+  const y = date.getUTCFullYear ()
+  const m = pad (date.getUTCMonth () + 1)
+  const day = pad (date.getUTCDate ())
+  const h = pad (date.getUTCHours ())
+  const min = pad (date.getUTCMinutes ())
+  return `${ y }-${ m }-${ day }T${ h }:${ min }Z`
 }
 
 
@@ -47,14 +61,16 @@ const DateTimeField: FC<Props> = ({ value, onChange, className, onBlur, invalid,
 			     'focus:ring-2 focus:ring-blue-200']),
 			 className)}
 	  type="datetime-local"
+	  step={60}
 	  value={local}
 	  aria-invalid={invalid}
 	  onChange={ev => {
 	    const v = ev.target.value
 	    setLocal (v)
-	    onChange?.(v ? (new Date (v)).toISOString () : null)
+	    onChange?.(v ? toMinutePrecisionIsoUtc (v) : null)
 	  }}
 	  onBlur={onBlur}/>)
 }
 
 export default DateTimeField
+export { toMinutePrecisionIsoUtc }

frontend/src/components/common/FieldWarning.tsx

@@ -0,0 +1,18 @@
+import type { FC } from 'react'
+
+type Props = { id?:        string
+	       messages?:  string[] }
+
+
+export const FieldWarning: FC<Props> = ({ id, messages }: Props) => {
+  if (messages == null || messages.length === 0)
+    return null
+
+  return (
+      <ul id={id} className="mt-1 space-y-1 text-amber-700 dark:text-amber-200">
+	{messages.map ((message, i) => <li key={i}>{message}</li>)}
+      </ul>)
+}
+
+
+export default FieldWarning

frontend/src/components/common/Form.tsx

@@ -1,11 +1,15 @@
+import { cn } from '@/lib/utils'
+
 import type { FC, ReactNode } from 'react'
 
-type Props = { children: ReactNode }
+type Props = {
+    children:   ReactNode
+    className?: string }
 
 
-const Form: FC<Props> = ({ children }) => (
-    <div className="max-w-xl mx-auto p-4 space-y-4">
+const Form: FC<Props> = ({ children, className }) => (
+    <div className={cn ('mx-auto max-w-xl space-y-4 p-4', className)}>
       {children}
     </div>)
 
-export default Form
+export default Form

frontend/src/components/common/StatusBadge.tsx

@@ -0,0 +1,34 @@
+import { cn } from '@/lib/utils'
+
+import type { FC, ReactNode } from 'react'
+
+export type StatusBadgeTone =
+    'success'
+    | 'neutral'
+    | 'warning'
+
+type Props = {
+    children: ReactNode
+    tone:     StatusBadgeTone }
+
+const TONES: Record<StatusBadgeTone, string[]> = {
+    success: [
+	'border-emerald-300 bg-emerald-50 text-emerald-700',
+	'dark:border-emerald-900 dark:bg-emerald-950 dark:text-emerald-200'],
+    warning: [
+	'border-amber-300 bg-amber-50 text-amber-700',
+	'dark:border-amber-900 dark:bg-amber-950 dark:text-amber-200'],
+    neutral: [
+	'border-stone-300 bg-stone-50 text-stone-700',
+	'dark:border-stone-700 dark:bg-stone-900 dark:text-stone-200'] }
+
+
+const StatusBadge: FC<Props> = ({ children, tone }) => (
+    <span
+	className={cn (
+	    'inline-flex items-center rounded-full border px-2.5 py-1 text-xs font-medium',
+	    TONES[tone])}>
+      {children}
+    </span>)
+
+export default StatusBadge

frontend/src/components/dialogues/DialogueProvider.test.tsx

@@ -0,0 +1,114 @@
+import { useCallback, useEffect } from 'react'
+import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import DialogueProvider from '@/components/dialogues/DialogueProvider'
+import useDialogue from '@/lib/dialogues/useDialogue'
+
+import type { DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+const FormBody = (
+    { controls,
+      onSelect }: { controls: DialogueFormControls
+		    onSelect: () => Promise<boolean> | boolean },
+) => {
+  useEffect (() => {
+    controls.setActions ([{
+      label: '左操作',
+      placement: 'start',
+      onSelect }, {
+      label: '保存',
+      onSelect: () => true }])
+  }, [controls, onSelect])
+
+  return <div>長いフォーム本文</div>
+}
+
+const NestedConfirmFormBody = ({ controls }: { controls: DialogueFormControls }) => {
+  const reset = useCallback (async () => {
+    await controls.confirm ({
+      title: '変更をリセットしますか?',
+      confirmText: 'リセット' })
+    return false
+  }, [controls])
+
+  return <FormBody controls={controls} onSelect={reset}/>
+}
+
+describe ('DialogueProvider', () => {
+  it ('keeps ordinary dialogues in FIFO order', async () => {
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => {
+		void dialogue.confirm ({ title: '一件目' })
+		void dialogue.confirm ({ title: '二件目' })
+	      }}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+
+    expect (screen.getByText ('一件目')).toBeInTheDocument ()
+    expect (screen.queryByText ('二件目')).not.toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: '確定' }))
+    expect (await screen.findByText ('二件目')).toBeInTheDocument ()
+  })
+
+  it ('keeps a large form open when an action returns false', async () => {
+    const action = vi.fn ().mockResolvedValue (false)
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => void dialogue.form ({
+		title: '投稿を編輯',
+		description: '説明',
+		size: 'large',
+		body: controls => <FormBody controls={controls} onSelect={action}/> })}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+
+    const dialogue = screen.getByRole ('dialog')
+    expect (dialogue).toHaveClass ('max-h-[calc(100dvh-1rem)]', 'flex-col', 'max-w-3xl')
+    await waitFor (() => expect (screen.getByRole ('button', { name: '左操作' }))
+	.toBeInTheDocument ())
+    expect (screen.getByRole ('button', { name: '左操作' })).toHaveClass ('w-full', 'sm:w-auto')
+    fireEvent.click (screen.getByRole ('button', { name: '左操作' }))
+
+    await waitFor (() => expect (action).toHaveBeenCalledTimes (1))
+    expect (screen.getByText ('投稿を編輯')).toBeInTheDocument ()
+  })
+
+  it ('opens a nested confirmation over a form and returns to the same form', async () => {
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => void dialogue.form ({
+		title: '投稿を編輯',
+		body: controls => <NestedConfirmFormBody controls={controls}/> })}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+    const action = await screen.findByRole ('button', { name: '左操作' })
+    fireEvent.click (action)
+
+    expect (await screen.findByText ('変更をリセットしますか?')).toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: 'リセット' }))
+    await waitFor (() => {
+      expect (screen.queryByText ('変更をリセットしますか?')).not.toBeInTheDocument ()
+    })
+    expect (screen.getByText ('投稿を編輯')).toBeInTheDocument ()
+  })
+})

frontend/src/components/dialogues/DialogueProvider.tsx

@@ -1,4 +1,4 @@
-import { createContext, useCallback, useContext, useMemo, useState } from 'react'
+import { useCallback, useMemo, useRef, useState } from 'react'
 
 import { Button } from '@/components/ui/button'
 import { Dialog,
@@ -7,29 +7,16 @@ import { Dialog,
 	 DialogFooter,
 	 DialogHeader,
 	 DialogTitle } from '@/components/ui/dialog'
+import { DialogueContext } from '@/lib/dialogues/useDialogue'
 
 import type { FC, ReactNode } from 'react'
-
-type DialogueVariant = 'default' | 'danger'
-
-type ConfirmOptions = { title:        string
-			description?: ReactNode
-			confirmText?: string
-			cancelText?:  string
-			variant?:     DialogueVariant }
-
-type AlertOptions = { title:        string
-		      description?: ReactNode
-		      okText?:      string }
-
-type Choice<T extends string> = { value:    T
-				  label:    string
-				  variant?: DialogueVariant }
-
-type ChoiceOptions<T extends string> = { title:         string
-					 description?:  ReactNode
-					 choices:       Choice<T>[]
-					 cancelText?:   string }
+import type { AlertOptions,
+	      ChoiceOptions,
+	      ConfirmOptions,
+	      DialogueAPI,
+	      DialogueFormAction,
+	      DialogueFormControls,
+	      DialogueFormOptions } from '@/lib/dialogues/useDialogue'
 
 type DialogueRequest =
     | { id:       number
@@ -44,13 +31,10 @@ type DialogueRequest =
 	kind:     'choice'
 	options:  ChoiceOptions<string>
 	resolve:  (value: string | null) => void }
-
-type DialogueAPI =
-    { confirm:  (options: ConfirmOptions) => Promise<boolean>
-      alert:    (options: AlertOptions) => Promise<void>
-      choice:   <T extends string> (options: ChoiceOptions<T>) => Promise<T | null> }
-
-const DialogueContext = createContext<DialogueAPI | null> (null)
+    | { id:       number
+	kind:     'form'
+	options:  DialogueFormOptions
+	resolve:  () => void }
 
 let nextDialogueId = 1
 
@@ -59,20 +43,27 @@ type Props = { children: ReactNode }
 
 const DialogueProvider: FC<Props> = ({ children }) => {
   const [queue, setQueue] = useState<DialogueRequest[]> ([])
+  const [pendingIds, setPendingIds] = useState<number[]> ([])
+  const [formActions, setFormActions] = useState<Record<number, DialogueFormAction[]>> ({ })
+  const formControls = useRef<Record<number, DialogueFormControls>> ({ })
+  const [nestedConfirm, setNestedConfirm] = useState<{
+      parentId: number
+      options:  ConfirmOptions
+      resolve:  (value: boolean) => void } | null> (null)
 
   const push = useCallback ((request: Omit<DialogueRequest, 'id'>) => {
     const id = nextDialogueId
     ++nextDialogueId
 
-    setQueue (q => [...q, { ...request, id } as DialogueRequest])
+    setQueue (current => [...current, { ...request, id } as DialogueRequest])
   }, [])
 
-  const closeActive = useCallback ((result?: unknown) => {
-    setQueue (q => {
-      const [active, ...rest] = q
+  const closeRequest = useCallback ((id: number, result?: unknown) => {
+    setQueue (current => {
+      const active = current.find (request => request.id === id)
 
-      if (!(active))
-	return rest
+      if (active == null)
+	return current
 
       switch (active.kind)
       {
@@ -87,9 +78,42 @@ const DialogueProvider: FC<Props> = ({ children }) => {
       case 'choice':
 	active.resolve ((result ?? null) as string | null)
 	break
+
+      case 'form':
+	active.resolve ()
+	break
       }
 
-      return rest
+      return current.filter (request => request.id !== id)
+    })
+    setPendingIds (current => current.filter (pendingId => pendingId !== id))
+    setFormActions (current => {
+	const { [id]: _, ...rest } = current
+	return rest
+    })
+    delete formControls.current[id]
+  }, [])
+
+  const setRequestActions = useCallback (
+      (id: number, actions: DialogueFormAction[]) => {
+	setFormActions (current => ({ ...current, [id]: actions }))
+      },
+      [])
+
+  const openNestedConfirm = useCallback (
+      (parentId: number, options: ConfirmOptions) =>
+	  new Promise<boolean> (resolve => {
+	    setNestedConfirm ({ parentId, options, resolve })
+	  }),
+      [])
+
+  const closeNestedConfirm = useCallback ((result: boolean) => {
+    setNestedConfirm (current => {
+      if (current == null)
+	return current
+
+      current.resolve (result)
+      return null
     })
   }, [])
 
@@ -103,86 +127,229 @@ const DialogueProvider: FC<Props> = ({ children }) => {
       choice: options => new Promise (resolve => {
 	push ({ kind: 'choice',
 		options: options as ChoiceOptions<string>,
-		resolve: resolve as (value: string | null) => void })}) }), [push])
+		resolve: resolve as (value: string | null) => void })
+      }),
+      form: options => new Promise<void> (resolve => {
+	push ({ kind: 'form', options, resolve })
+      }) }), [push])
+
+  const handleFormAction = useCallback (
+      async (id: number, action: DialogueFormAction) => {
+	if (pendingIds.includes (id))
+	  return
+
+	setPendingIds (current => [...current, id])
+	try
+	{
+	  const shouldClose = await action.onSelect ()
+	  if (shouldClose !== false)
+	    closeRequest (id)
+	}
+	finally
+	{
+	  setPendingIds (current => current.filter (pendingId => pendingId !== id))
+	}
+      },
+      [closeRequest, pendingIds])
 
   const active = queue[0]
+  const startActions =
+      active?.kind === 'form'
+      ? (formActions[active.id] ?? []).filter (action => action.placement === 'start')
+      : []
+  const endActions =
+      active?.kind === 'form'
+      ? (formActions[active.id] ?? []).filter (action =>
+	  action.placement == null || action.placement === 'end')
+      : []
 
   return (
       <DialogueContext.Provider value={api}>
 	{children}
 
-	<Dialog
-	    open={Boolean (active)}
-	    onOpenChange={open => {
-	      if (!(open))
-		closeActive (active?.kind !== 'confirm' && null)
-	    }}>
-	  {active && (
+	{active && (
+	    <Dialog
+		open
+		onOpenChange={open => {
+		  const blocked =
+		      nestedConfirm?.parentId === active.id
+		      || pendingIds.includes (active.id)
+		  if (!(open) && !(blocked))
+		    closeRequest (active.id, active.kind !== 'confirm' && null)
+		}}>
+	      <DialogContent
+		  className={
+		      active.kind === 'form'
+		      ? `flex max-h-[calc(100dvh-1rem)] ${ active.options.size === 'large'
+			  ? 'max-w-3xl'
+			  : 'max-w-lg' } flex-col overflow-hidden gap-0`
+		      : 'px-6 pb-6 pt-7'
+		  }
+		  onEscapeKeyDown={event => {
+		    if (nestedConfirm?.parentId === active.id || pendingIds.includes (active.id))
+		      event.preventDefault ()
+		  }}
+		  onPointerDownOutside={event => {
+		    if (nestedConfirm?.parentId === active.id || pendingIds.includes (active.id))
+		      event.preventDefault ()
+		  }}>
+		{active.kind === 'form'
+		 ? (
+		     <>
+		       <DialogHeader className="shrink-0 pb-4 pl-8 pr-0 pt-1 text-left">
+			 <DialogTitle>{active.options.title}</DialogTitle>
+
+			 {active.options.description && (
+			     <DialogDescription asChild>
+			       <div>{active.options.description}</div>
+			     </DialogDescription>)}
+		       </DialogHeader>
+
+		       <div className="min-h-0 flex-1 overflow-y-auto overscroll-contain">
+			 {active.options.body (
+			     formControls.current[active.id] ??= {
+				 close: () => closeRequest (active.id),
+				 setActions: actions => setRequestActions (active.id, actions),
+				 confirm: options => openNestedConfirm (active.id, options) })}
+		       </div>
+
+		       <DialogFooter
+			   className="shrink-0 flex-col gap-2 pt-4
+				      sm:flex-row sm:justify-between sm:gap-0 sm:space-x-0">
+			 <div className="flex w-full flex-col gap-2 sm:w-auto sm:flex-row">
+			   {startActions.map (action => (
+			       <Button
+				   key={action.label}
+				   className="w-full sm:w-auto"
+				   variant={action.variant === 'danger'
+				       ? 'destructive'
+				       : 'default'}
+				   onClick={() => void handleFormAction (active.id, action)}
+				   disabled={pendingIds.includes (active.id)
+				       || nestedConfirm?.parentId === active.id
+				       || action.disabled}>
+				 {action.label}
+			       </Button>))}
+			 </div>
+
+			 <div className="flex w-full flex-col gap-2 sm:w-auto sm:flex-row">
+			   <Button
+			       className="w-full sm:w-auto"
+			       variant="outline"
+			       onClick={() => closeRequest (active.id)}
+			       disabled={pendingIds.includes (active.id)
+				   || nestedConfirm?.parentId === active.id}>
+			     {active.options.cancelText ?? '取消'}
+			   </Button>
+
+			   {endActions.map (action => (
+			       <Button
+				   key={action.label}
+				   className="w-full sm:w-auto"
+				   variant={action.variant === 'danger'
+				       ? 'destructive'
+				       : 'default'}
+				   onClick={() => void handleFormAction (active.id, action)}
+				   disabled={pendingIds.includes (active.id)
+				       || nestedConfirm?.parentId === active.id
+				       || action.disabled}>
+				 {action.label}
+			       </Button>))}
+			 </div>
+		       </DialogFooter>
+		     </>)
+		 : (
+		     <>
+		       <DialogHeader className="pl-8">
+			 <DialogTitle>{active.options.title}</DialogTitle>
+
+			 {active.options.description && (
+			     <DialogDescription asChild>
+			       <div>{active.options.description}</div>
+			     </DialogDescription>)}
+		       </DialogHeader>
+
+		       <DialogFooter>
+			 {active.kind === 'confirm' && (
+			     <>
+			       <Button
+				   variant="outline"
+				   onClick={() => closeRequest (active.id, false)}>
+				 {active.options.cancelText ?? '取消'}
+			       </Button>
+
+			       <Button
+				   variant={(active.options.variant === 'danger')
+					    ? 'destructive'
+					    : 'default'}
+				   onClick={() => closeRequest (active.id, true)}>
+				 {active.options.confirmText ?? '確定'}
+			       </Button>
+			     </>)}
+
+			 {active.kind === 'alert' && (
+			     <Button onClick={() => closeRequest (active.id)}>
+			       {active.options.okText ?? '確定'}
+			     </Button>)}
+
+			 {active.kind === 'choice' && (
+			     <>
+			       <Button
+				   variant="outline"
+				   onClick={() => closeRequest (active.id, null)}>
+				 {active.options.cancelText ?? '取消'}
+			       </Button>
+
+			       {active.options.choices.map (choice => (
+				   <Button
+				       key={choice.value}
+				       variant={(choice.variant === 'danger')
+						? 'destructive'
+						: 'default'}
+				       onClick={() => closeRequest (active.id, choice.value)}>
+				     {choice.label}
+				   </Button>))}
+			     </>)}
+		       </DialogFooter>
+		     </>)}
+	      </DialogContent>
+	    </Dialog>)}
+
+	{nestedConfirm && (
+	    <Dialog
+		open
+		onOpenChange={open => {
+		  if (!(open))
+		    closeNestedConfirm (false)
+		}}>
 	      <DialogContent className="px-6 pb-6 pt-7">
 		<DialogHeader className="pl-8">
-		  <DialogTitle>{active.options.title}</DialogTitle>
+		  <DialogTitle>{nestedConfirm.options.title}</DialogTitle>
 
-		  {active.options.description && (
+		  {nestedConfirm.options.description && (
 		      <DialogDescription asChild>
-			<div>{active.options.description}</div>
+			<div>{nestedConfirm.options.description}</div>
 		      </DialogDescription>)}
 		</DialogHeader>
 
 		<DialogFooter>
-		  {active.kind === 'confirm' && (
-		      <>
-			<Button
-			    variant="outline"
-			    onClick={() => closeActive (false)}>
-			  {active.options.cancelText ?? '取消'}
-			</Button>
+		  <Button
+		      variant="outline"
+		      onClick={() => closeNestedConfirm (false)}>
+		    {nestedConfirm.options.cancelText ?? '取消'}
+		  </Button>
 
-			<Button
-			    variant={(active.options.variant === 'danger')
-				     ? 'destructive'
-				     : 'default'}
-			    onClick={() => closeActive (true)}>
-			  {active.options.confirmText ?? '確定'}
-			</Button>
-		      </>)}
-
-		  {active.kind === 'alert' && (
-		      <Button onClick={() => closeActive ()}>
-			{active.options.okText ?? '確定'}
-		      </Button>)}
-
-		  {active.kind === 'choice' && (
-		      <>
-			<Button
-			    variant="outline"
-			    onClick={() => closeActive (null)}>
-			  {active.options.cancelText ?? '取消'}
-			</Button>
-
-			{active.options.choices.map (choice => (
-			    <Button
-				key={choice.value}
-				variant={(choice.variant === 'danger')
-					 ? 'destructive'
-					 : 'default'}
-				onClick={() => closeActive (choice.value)}>
-			      {choice.label}
-			    </Button>))}
-		      </>)}
+		  <Button
+		      variant={nestedConfirm.options.variant === 'danger'
+			  ? 'destructive'
+			  : 'default'}
+		      onClick={() => closeNestedConfirm (true)}>
+		    {nestedConfirm.options.confirmText ?? '確定'}
+		  </Button>
 		</DialogFooter>
-	      </DialogContent>)}
-	</Dialog>
+	      </DialogContent>
+	    </Dialog>)}
       </DialogueContext.Provider>)
 }
-
-
-export const useDialogue = () => {
-  const dialogue = useContext (DialogueContext)
-
-  if (!(dialogue))
-    throw new Error ('useDialogue must be used inside DialogueProvider')
-
-  return dialogue
-}
-
+export { useDialogue } from '@/lib/dialogues/useDialogue'
 export default DialogueProvider

frontend/src/components/posts/PostDurationField.tsx

@@ -0,0 +1,28 @@
+import PostTextField from '@/components/posts/PostTextField'
+
+import type { FC } from 'react'
+
+type Props = {
+  value:     string
+  onChange:  (value: string) => void
+  errors?:   string[]
+  disabled?: boolean }
+
+
+const PostDurationField: FC<Props> = (
+    { value,
+      onChange,
+      errors,
+      disabled },
+) => (
+    <PostTextField
+        label="動画時間"
+        value={value}
+        onChange={onChange}
+        errors={errors}
+        disabled={disabled}
+        type="text"
+        placeholder="例: 2 / 2.5 / 1:23"/>
+)
+
+export default PostDurationField

frontend/src/components/posts/PostTagsField.tsx

@@ -0,0 +1,29 @@
+import PostFormTagsArea from '@/components/PostFormTagsArea'
+import FieldWarning from '@/components/common/FieldWarning'
+
+import type { ComponentPropsWithoutRef, FC } from 'react'
+
+type Props = Omit<ComponentPropsWithoutRef<'textarea'>, 'value' | 'onChange'> & {
+  tags:      string
+  setTags:   (tags: string) => void
+  warnings?: string[]
+  errors?:   string[] }
+
+
+const PostTagsField: FC<Props> = (
+    { tags,
+      setTags,
+      warnings,
+      errors,
+      ...rest },
+) => (
+    <div className="space-y-2">
+      <PostFormTagsArea
+          {...rest}
+          tags={tags}
+          setTags={setTags}
+          errors={errors}/>
+      <FieldWarning messages={warnings}/>
+    </div>)
+
+export default PostTagsField

frontend/src/components/posts/PostTextField.tsx

@@ -0,0 +1,49 @@
+import FieldWarning from '@/components/common/FieldWarning'
+import FormField from '@/components/common/FormField'
+import { inputClass } from '@/lib/utils'
+
+import type { FC, ReactNode } from 'react'
+
+type Props = {
+  label:        string
+  value:        string
+  onChange:     (value: string) => void
+  warnings?:    string[]
+  errors?:      string[]
+  disabled?:    boolean
+  type?:        string
+  placeholder?: string
+  className?:   string
+  after?:       ReactNode }
+
+
+const PostTextField: FC<Props> = (
+    { label,
+      value,
+      onChange,
+      warnings,
+      errors,
+      disabled,
+      type = 'text',
+      placeholder,
+      className,
+      after },
+) => (
+    <FormField label={label} messages={errors}>
+      {({ describedBy, invalid }) => (
+          <>
+            <input
+                type={type}
+                value={value}
+                disabled={disabled}
+                placeholder={placeholder}
+                onChange={ev => onChange (ev.target.value)}
+                aria-describedby={describedBy}
+                aria-invalid={invalid}
+                className={inputClass (invalid, className)}/>
+            <FieldWarning messages={warnings}/>
+            {after}
+          </>)}
+    </FormField>)
+
+export default PostTextField

frontend/src/components/posts/PostThumbnailPreview.test.tsx

@@ -0,0 +1,12 @@
+import { render, screen } from '@testing-library/react'
+import { describe, expect, it } from 'vitest'
+
+import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
+
+describe ('PostThumbnailPreview', () => {
+  it ('keeps an existing blob preview URL unchanged for normal post forms', () => {
+    render (<PostThumbnailPreview url="blob:preview" className="h-10 w-10"/>)
+
+    expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
+  })
+})

frontend/src/components/posts/PostThumbnailPreview.tsx

@@ -0,0 +1,50 @@
+import { useEffect, useState } from 'react'
+
+import type { FC } from 'react'
+
+type Props = {
+  url:        string
+  alt?:       string
+  className?: string }
+
+
+const PostThumbnailPreview: FC<Props> = (
+    { url, alt = 'サムネール', className = 'h-16 w-16' },
+) => {
+  const [failed, setFailed] = useState (false)
+
+  useEffect (() => {
+    setFailed (false)
+  }, [url])
+
+  if (!(url))
+    {
+      return (
+          <div
+              className={`${ className } flex items-center justify-center rounded border
+                          border-border bg-muted text-xs text-muted-foreground`}>
+            なし
+          </div>)
+    }
+
+  if (failed)
+    {
+      return (
+          <div
+              className={`${ className } flex items-center justify-center rounded border
+                          border-amber-300 bg-amber-50 p-2 text-center text-xs
+                          text-amber-700 dark:border-amber-900 dark:bg-amber-950
+                          dark:text-amber-200`}>
+            サムネールを表示できません
+          </div>)
+    }
+
+  return (
+      <img
+          src={url}
+          alt={alt}
+          className={`${ className } rounded border border-border object-cover`}
+          onError={() => setFailed (true)}/>)
+}
+
+export default PostThumbnailPreview

frontend/src/components/posts/import/PostImportRowForm.test.tsx

@@ -0,0 +1,261 @@
+import { act, render, screen, waitFor } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import PostImportRowForm from '@/components/posts/import/PostImportRowForm'
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+import type { DialogueFormAction, DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+
+describe ('PostImportRowForm', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    globalThis.URL.createObjectURL = vi.fn (() => 'blob:preview')
+    globalThis.URL.revokeObjectURL = vi.fn ()
+    api.apiGet.mockResolvedValue (new Blob (['img'], { type: 'image/png' }))
+  })
+
+  it ('resets only the draft, then saves with resetRequested', async () => {
+    const row = buildPostImportRow ()
+    row.attributes.title = 'manual title'
+    row.provenance.title = 'manual'
+    const actions: DialogueFormAction[][] = []
+    const controls: DialogueFormControls = {
+      close: vi.fn (),
+      confirm: vi.fn ().mockResolvedValue (true),
+      setActions: next => actions.push (next) }
+    const invalidRow = buildPostImportRow ({
+      validationErrors: { title: ['タイトルを確認してください．'] } })
+    const onSave = vi.fn ().mockResolvedValue ({ saved: false, row: invalidRow })
+
+    render (<PostImportRowForm row={row} controls={controls} onSave={onSave}/>)
+    const titleInput = screen.getByDisplayValue ('manual title')
+
+    await waitFor (() => expect (actions.at (-1)?.length).toBe (2))
+    const reset = actions.at (-1)?.find (action => action.label === '変更をリセット')
+    expect (reset).toMatchObject ({ placement: 'start', variant: 'danger', disabled: false })
+    await act (async () => {
+      await reset?.onSelect ()
+    })
+
+    expect (controls.confirm).toHaveBeenCalled ()
+    expect (titleInput).toHaveValue ('')
+    expect (onSave).not.toHaveBeenCalled ()
+
+    const save = actions.at (-1)?.find (action => action.label === '編輯内容を保存')
+    await act (async () => {
+      await save?.onSelect ()
+    })
+
+    expect (onSave).toHaveBeenCalledWith ({
+      draft: expect.objectContaining ({ title: '' }),
+      resetRequested: true })
+    expect (screen.getByText ('タイトルを確認してください．')).toBeInTheDocument ()
+  })
+
+  it ('does not reset the draft when confirmation is cancelled', async () => {
+    const row = buildPostImportRow ({ attributes: { title: 'manual title' } })
+    let actions: DialogueFormAction[] = []
+    const controls: DialogueFormControls = {
+      close: vi.fn (),
+      confirm: vi.fn ().mockResolvedValue (false),
+      setActions: next => {
+	actions = next
+      } }
+
+    render (
+	<PostImportRowForm
+	    row={row}
+	    controls={controls}
+	    onSave={vi.fn ()}/>)
+    await waitFor (() => expect (actions.length).toBe (2))
+
+    await act (async () => {
+      await actions.find (action => action.label === '変更をリセット')?.onSelect ()
+    })
+
+    expect (screen.getByDisplayValue ('manual title')).toBeInTheDocument ()
+  })
+
+  it ('marks edited fields and areas invalid from field errors', () => {
+    const row = buildPostImportRow ({
+      validationErrors: { url: ['URL error'], tags: ['tag error'] },
+      importErrors: { duration: ['duration error'] },
+      fieldWarnings: { title: ['title warning'] } })
+
+    render (
+	<PostImportRowForm
+	    row={row}
+	    controls={{ close: vi.fn (), confirm: vi.fn (), setActions: vi.fn () }}
+	    onSave={vi.fn ()}/>)
+
+    expect (screen.getByText ('URL error')).toBeInTheDocument ()
+    expect (screen.getByText ('tag error')).toBeInTheDocument ()
+    expect (screen.getByText ('duration error')).toBeInTheDocument ()
+    expect (screen.getByText ('title warning')).toBeInTheDocument ()
+    expect (screen.getAllByRole ('textbox').filter (
+	textbox => textbox.getAttribute ('aria-invalid') === 'true')).toHaveLength (3)
+  })
+
+  it ('keeps untouched original created values unchanged in the save payload', async () => {
+    let actions: DialogueFormAction[] = []
+    const row = buildPostImportRow ({
+      attributes: {
+        originalCreatedFrom: '2024-01-01T12:34+09:00',
+        originalCreatedBefore: '2024-01-01T12:35+09:00' } })
+    const controls: DialogueFormControls = {
+      close: vi.fn (),
+      confirm: vi.fn (),
+      setActions: next => {
+        actions = next
+      } }
+    const onSave = vi.fn ().mockResolvedValue ({ saved: true, row: null })
+
+    render (
+        <PostImportRowForm
+            row={row}
+            controls={controls}
+            onSave={onSave}/>)
+    await waitFor (() => expect (actions.length).toBe (2))
+
+    await act (async () => {
+      void actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+    })
+
+    expect (onSave).toHaveBeenCalledWith ({
+      draft: expect.objectContaining ({
+        originalCreatedFrom: '2024-01-01T12:34+09:00',
+        originalCreatedBefore: '2024-01-01T12:35+09:00' }),
+      resetRequested: false })
+  })
+
+  it ('keeps the shared duration and tags string contract without leaking file upload UI', async () => {
+    let actions: DialogueFormAction[] = []
+    const controls: DialogueFormControls = {
+      close: vi.fn (),
+      confirm: vi.fn (),
+      setActions: next => {
+        actions = next
+      } }
+    const onSave = vi.fn ().mockResolvedValue ({ saved: true, row: null })
+
+    const { container } = render (
+        <PostImportRowForm
+            row={buildPostImportRow ({
+              attributes: { duration: '2', tags: 'tag1' } })}
+            controls={controls}
+            onSave={onSave}/>)
+    await waitFor (() => expect (actions.length).toBe (2))
+
+    expect (container.querySelector ('input[type="file"]')).toBeNull ()
+    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('2')
+    expect (screen.getByDisplayValue ('tag1')).toBeInTheDocument ()
+
+    await act (async () => {
+      await actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+    })
+
+    expect (onSave).toHaveBeenCalledWith ({
+      draft: expect.objectContaining ({
+        duration: '2',
+        tags: 'tag1' }),
+      resetRequested: false })
+  })
+
+  it ('keeps reset enabled when the value matches but provenance still differs', async () => {
+    const row = buildPostImportRow ({
+      attributes: { title: 'same title' },
+      provenance: { title: 'manual' },
+      resetSnapshot: {
+        url: 'https://example.com/post',
+        attributes: {
+          title: 'same title',
+          thumbnailBase: '',
+          originalCreatedFrom: '',
+          originalCreatedBefore: '',
+          duration: '',
+          tags: '',
+          parentPostIds: '' },
+        provenance: {
+          url: 'manual',
+          title: 'automatic',
+          thumbnailBase: 'automatic',
+          originalCreatedFrom: 'automatic',
+          originalCreatedBefore: 'automatic',
+          duration: 'automatic',
+          tags: 'automatic',
+          parentPostIds: 'automatic' },
+        tagSources: { automatic: '', manual: '' },
+        fieldWarnings: { },
+        baseWarnings: [] } })
+    let actions: DialogueFormAction[] = []
+
+    render (
+        <PostImportRowForm
+            row={row}
+            controls={{
+              close: vi.fn (),
+              confirm: vi.fn (),
+              setActions: next => {
+                actions = next
+              } }}
+            onSave={vi.fn ()}/>)
+    await waitFor (() => expect (actions.length).toBe (2))
+
+    expect (actions.find (action => action.label === '変更をリセット')?.disabled).toBe (false)
+  })
+
+  it ('disables every field while save validation is pending and re-enables them afterwards', async () => {
+    let actions: DialogueFormAction[] = []
+    let resolveSave:
+        ((value: { saved: boolean
+		   row:   ReturnType<typeof buildPostImportRow> | null }) => void) | null
+        = null
+    const onSave = vi.fn (() =>
+        new Promise<{ saved: boolean
+		      row:   ReturnType<typeof buildPostImportRow> | null }> (resolve => {
+          resolveSave = resolve
+        }))
+
+    render (
+        <PostImportRowForm
+            row={buildPostImportRow ({ attributes: { title: 'draft title' } })}
+            controls={{
+              close: vi.fn (),
+              confirm: vi.fn (),
+              setActions: next => {
+                actions = next
+              } }}
+            onSave={onSave}/>)
+    await waitFor (() => expect (actions.length).toBe (2))
+
+    await act (async () => {
+      await actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+    })
+
+    await waitFor (() => {
+      screen.getAllByRole ('textbox').forEach (textbox => {
+        expect (textbox).toBeDisabled ()
+      })
+    })
+
+    resolveSave?.({
+      saved: false,
+      row: buildPostImportRow ({
+        attributes: { title: 'draft title' },
+        validationErrors: { title: ['タイトルを確認してください．'] } }) })
+
+    await waitFor (() => {
+      screen.getAllByRole ('textbox').forEach (textbox => {
+        expect (textbox).not.toBeDisabled ()
+      })
+    })
+    expect (screen.getByDisplayValue ('draft title')).toBeInTheDocument ()
+    expect (screen.getByText ('タイトルを確認してください．')).toBeInTheDocument ()
+  })
+})

frontend/src/components/posts/import/PostImportRowForm.tsx

@@ -0,0 +1,250 @@
+import { useCallback, useEffect, useMemo, useState } from 'react'
+
+import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
+import FieldError from '@/components/common/FieldError'
+import FieldWarning from '@/components/common/FieldWarning'
+import PostDurationField from '@/components/posts/PostDurationField'
+import PostTagsField from '@/components/posts/PostTagsField'
+import PostTextField from '@/components/posts/PostTextField'
+import PostImportThumbnailPreview from '@/components/posts/import/PostImportThumbnailPreview'
+
+import type { FC } from 'react'
+
+import type { PostImportEditableDraft, PostImportRow } from '@/lib/postImportSession'
+import type { DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+type Draft = PostImportEditableDraft
+
+type Props = {
+  row:          PostImportRow
+  controls:     DialogueFormControls
+  onSave:       (args: { draft:          Draft
+			 resetRequested: boolean }) => Promise<{
+			     saved: boolean
+			     row:   PostImportRow | null }> }
+
+const buildDraft = (row: PostImportRow): Draft => ({
+    url: row.url,
+    title: String (row.attributes.title ?? ''),
+    thumbnailBase: String (row.attributes.thumbnailBase ?? ''),
+    originalCreatedFrom: String (row.attributes.originalCreatedFrom ?? ''),
+    originalCreatedBefore: String (row.attributes.originalCreatedBefore ?? ''),
+    duration: String (row.attributes.duration ?? ''),
+    tags: String (row.attributes.tags ?? ''),
+    parentPostIds: String (row.attributes.parentPostIds ?? '') })
+
+const buildResetDraft = (row: PostImportRow): Draft => ({
+    url: row.resetSnapshot.url,
+    title: String (row.resetSnapshot.attributes.title ?? ''),
+    thumbnailBase: String (row.resetSnapshot.attributes.thumbnailBase ?? ''),
+    originalCreatedFrom: String (row.resetSnapshot.attributes.originalCreatedFrom ?? ''),
+    originalCreatedBefore: String (row.resetSnapshot.attributes.originalCreatedBefore ?? ''),
+    duration: String (row.resetSnapshot.attributes.duration ?? ''),
+    tags: String (row.resetSnapshot.attributes.tags ?? ''),
+    parentPostIds: String (row.resetSnapshot.attributes.parentPostIds ?? '') })
+
+const groupedMessages = (...values: (string[] | undefined)[]): string[] =>
+    [...new Set (values.flatMap (value => value ?? []))]
+
+const sameDraft = (left:  Draft, right: Draft): boolean =>
+    left.url === right.url
+    && left.title === right.title
+    && left.thumbnailBase === right.thumbnailBase
+    && left.originalCreatedFrom === right.originalCreatedFrom
+    && left.originalCreatedBefore === right.originalCreatedBefore
+    && left.duration === right.duration
+    && left.tags === right.tags
+    && left.parentPostIds === right.parentPostIds
+
+const sameProvenance = (
+    current: PostImportRow['provenance'],
+    reset:   PostImportRow['resetSnapshot']['provenance'],
+): boolean =>
+    Object.keys (reset).every (field => current[field] === reset[field])
+
+const sameTagSources = (
+    current: PostImportRow['tagSources'],
+    reset:   PostImportRow['resetSnapshot']['tagSources'],
+): boolean =>
+    (current?.automatic ?? '') === reset.automatic
+    && (current?.manual ?? '') === reset.manual
+
+
+const PostImportRowForm: FC<Props> = (
+    { row,
+      controls,
+      onSave },
+) => {
+  const [draft, setDraft] = useState<Draft> (() => buildDraft (row))
+  const [messageRow, setMessageRow] = useState<PostImportRow | null> (null)
+  const [saving, setSaving] = useState (false)
+  const [resetRequested, setResetRequested] = useState (false)
+
+  useEffect (() => {
+    const nextDraft = buildDraft (row)
+    setDraft (nextDraft)
+    setMessageRow (null)
+    setResetRequested (false)
+  }, [row])
+
+  const displayRow = messageRow ?? row
+  const resetDraft = useMemo (
+      () => buildResetDraft (row),
+      [row])
+  const resetDisabled =
+      saving
+      || (sameDraft (draft, resetDraft)
+          && sameProvenance (row.provenance, row.resetSnapshot.provenance)
+          && sameTagSources (row.tagSources, row.resetSnapshot.tagSources)
+          && row.metadataUrl === row.resetSnapshot.metadataUrl)
+
+  const update = <Key extends keyof Draft,> (
+      key:   Key,
+      value: Draft[Key],
+  ) => {
+    if (messageRow != null)
+      setMessageRow (null)
+    setDraft (current => ({ ...current, [key]: value }))
+  }
+
+  const reset = useCallback (async (): Promise<boolean> => {
+    if (resetDisabled)
+      return false
+
+    const confirmed = await controls.confirm ({
+	title: '変更をリセットしますか?',
+	description: '現在の URL に対する自動取得直後の内容へ戻します．',
+	confirmText: 'リセット',
+	cancelText: '取消',
+	variant: 'danger' })
+    if (!(confirmed))
+      return false
+
+    setDraft (resetDraft)
+    setResetRequested (true)
+    setMessageRow (null)
+    return false
+  }, [controls, resetDisabled, resetDraft])
+
+  const save = useCallback (async (): Promise<boolean> => {
+    setSaving (true)
+    try
+    {
+      const result = await onSave ({ draft, resetRequested })
+      if (result.saved)
+        return true
+
+      if (result.row != null)
+        setMessageRow (result.row)
+      return false
+    }
+    finally
+    {
+      setSaving (false)
+    }
+  }, [draft, onSave, resetRequested])
+
+  useEffect (() => {
+    controls.setActions ([{
+	label: '変更をリセット',
+	placement: 'start',
+	variant: 'danger',
+	disabled: resetDisabled,
+	onSelect: reset },
+	{
+	  label: '編輯内容を保存',
+	  disabled: saving,
+	  onSelect: save }])
+  }, [controls, resetDisabled, reset, save, saving])
+
+  return (
+      <>
+	<div className="px-6 pb-6">
+	  <div className="space-y-4">
+	    <div className="grid gap-6 md:grid-cols-[7rem_minmax(0,1fr)]">
+	      <div className="space-y-3 md:sticky md:top-0 md:self-start">
+		<PostImportThumbnailPreview
+		    url={draft.thumbnailBase}
+		    className="h-28 w-28"/>
+	      </div>
+
+	      <div className="space-y-4">
+		<PostTextField
+		    label="URL"
+		    value={draft.url}
+		    disabled={saving}
+		    warnings={displayRow.fieldWarnings.url}
+		    errors={groupedMessages (
+			displayRow.validationErrors.url,
+			displayRow.importErrors?.url)}
+		    onChange={value => update ('url', value)}/>
+		<PostTextField
+		    label="タイトル"
+		    value={draft.title}
+		    disabled={saving}
+		    warnings={displayRow.fieldWarnings.title}
+		    errors={groupedMessages (
+			displayRow.validationErrors.title,
+			displayRow.importErrors?.title)}
+		    onChange={value => update ('title', value)}/>
+		<PostTextField
+		    label="サムネール基底 URL"
+		    value={draft.thumbnailBase}
+		    disabled={saving}
+		    warnings={displayRow.fieldWarnings.thumbnailBase}
+		    errors={groupedMessages (
+			displayRow.validationErrors.thumbnailBase,
+			displayRow.importErrors?.thumbnailBase)}
+		    onChange={value => update ('thumbnailBase', value)}/>
+		<PostOriginalCreatedTimeField
+		    disabled={saving}
+		    originalCreatedFrom={draft.originalCreatedFrom || null}
+		    setOriginalCreatedFrom={value => update ('originalCreatedFrom', value ?? '')}
+		    originalCreatedBefore={draft.originalCreatedBefore || null}
+		    setOriginalCreatedBefore={value => update ('originalCreatedBefore', value ?? '')}
+		    errors={groupedMessages (
+			displayRow.validationErrors.originalCreatedAt,
+			displayRow.validationErrors.originalCreatedFrom,
+			displayRow.validationErrors.originalCreatedBefore,
+			displayRow.importErrors?.originalCreatedAt,
+			displayRow.importErrors?.originalCreatedFrom,
+			displayRow.importErrors?.originalCreatedBefore)}/>
+		<PostDurationField
+		    value={draft.duration}
+		    disabled={saving}
+		    errors={groupedMessages (
+			displayRow.validationErrors.duration,
+			displayRow.validationErrors.videoMs,
+			displayRow.importErrors?.duration,
+			displayRow.importErrors?.videoMs)}
+		    onChange={value => update ('duration', value)}/>
+		<PostTagsField
+		    tags={draft.tags}
+		    disabled={saving}
+		    setTags={value => update ('tags', value)}
+		    warnings={displayRow.fieldWarnings.tags}
+		    errors={groupedMessages (
+			displayRow.validationErrors.tags,
+			displayRow.importErrors?.tags)}
+		    rows={4}/>
+		<PostTextField
+		    label="親投稿"
+		    value={draft.parentPostIds}
+		    disabled={saving}
+		    errors={groupedMessages (
+			displayRow.validationErrors.parentPostIds,
+			displayRow.importErrors?.parentPostIds)}
+		    onChange={value => update ('parentPostIds', value)}/>
+		<FieldWarning messages={displayRow.baseWarnings}/>
+		<FieldError messages={displayRow.validationErrors.base}/>
+		<FieldError messages={displayRow.importErrors?.base}/>
+	      </div>
+	    </div>
+	  </div>
+	</div>
+      </>)
+}
+
+export default PostImportRowForm
+export { buildDraft }
+export type { Draft as PostImportRowDraft }

frontend/src/components/posts/import/PostImportRowSummary.tsx

@@ -0,0 +1,120 @@
+import { Button } from '@/components/ui/button'
+import PostImportThumbnailPreview from '@/components/posts/import/PostImportThumbnailPreview'
+import PostImportStatusBadge from '@/components/posts/import/PostImportStatusBadge'
+import { displayPostImportStatus } from '@/components/posts/import/postImportRowStatus'
+import { canEditReviewRow } from '@/lib/postImportSession'
+import { cn, originalCreatedAtString } from '@/lib/utils'
+
+import type { FC } from 'react'
+
+import type { PostImportRow } from '@/lib/postImportSession'
+
+type Props = {
+    row:           PostImportRow
+    onEdit:        () => void
+    editDisabled?: boolean }
+
+const summaryWarning = (row: PostImportRow): string | null =>
+    Object.values (row.fieldWarnings ?? { }).flat ()[0]
+    ?? row.baseWarnings?.[0]
+    ?? null
+
+const summaryDate = (row: PostImportRow): string =>
+    originalCreatedAtString (
+	row.attributes.originalCreatedFrom?.toString () ?? null,
+	row.attributes.originalCreatedBefore?.toString () ?? null)
+
+
+const PostImportRowSummary: FC<Props> = ({ row, onEdit, editDisabled }) => {
+  const warning = summaryWarning (row)
+  const displayStatus = displayPostImportStatus (row)
+
+  return (
+      <>
+        <div
+            className={cn (
+                'hidden items-center gap-4 rounded-lg border p-4 md:grid',
+                'md:grid-cols-[4rem_5rem_minmax(0,1fr)_auto_auto]',
+                'transition-shadow hover:shadow-sm')}>
+          <div className="space-y-1">
+            <div className="text-sm font-medium">#{row.sourceRow}</div>
+          </div>
+          <PostImportThumbnailPreview
+              url={String (row.attributes.thumbnailBase ?? '')}
+              className="h-16 w-16"/>
+          <div className="min-w-0 space-y-1">
+            <div className="line-clamp-2 text-sm font-medium">
+              {String (row.attributes.title ?? '') || '（タイトル未取得）'}
+            </div>
+            <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
+              {row.url}
+            </div>
+            <div className="truncate text-xs text-neutral-500 dark:text-neutral-400">
+              {String (row.attributes.tags ?? '') || 'タグなし'}
+            </div>
+            <div className="text-xs text-neutral-500 dark:text-neutral-400">
+              {summaryDate (row)}
+              {row.attributes.duration ? ` / ${ row.attributes.duration }` : ''}
+            </div>
+            {warning && (
+                <div className="text-xs text-amber-700 dark:text-amber-200">
+                  {warning}
+                </div>)}
+          </div>
+          <div className="space-y-1">
+            {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
+          </div>
+          <div className="flex justify-end">
+            <Button
+                type="button"
+                variant="outline"
+                onClick={onEdit}
+                disabled={!(canEditReviewRow (row)) || editDisabled === true}>
+              編輯
+            </Button>
+          </div>
+        </div>
+
+        <div
+            className={cn (
+                'space-y-3 rounded-lg border p-4 md:hidden',
+                'transition-shadow hover:shadow-sm')}>
+          <div className="flex items-start gap-3">
+            <PostImportThumbnailPreview
+                url={String (row.attributes.thumbnailBase ?? '')}
+                className="h-20 w-20 shrink-0"/>
+            <div className="min-w-0 flex-1 space-y-2">
+              <div className="line-clamp-2 text-sm font-medium">
+                {String (row.attributes.title ?? '') || '（タイトル未取得）'}
+              </div>
+              <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
+                {row.url}
+              </div>
+              <div className="flex flex-wrap gap-2">
+                {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
+              </div>
+              <div className="text-xs text-neutral-500 dark:text-neutral-400">
+                {String (row.attributes.tags ?? '') || 'タグなし'}
+              </div>
+              <div className="text-xs text-neutral-500 dark:text-neutral-400">
+                {summaryDate (row)}
+                {row.attributes.duration ? ` / ${ row.attributes.duration }` : ''}
+              </div>
+              {warning && (
+                  <div className="text-xs text-amber-700 dark:text-amber-200">
+                    {warning}
+                  </div>)}
+            </div>
+          </div>
+          <Button
+              type="button"
+              variant="outline"
+              onClick={onEdit}
+              disabled={!(canEditReviewRow (row)) || editDisabled === true}>
+            編輯
+          </Button>
+        </div>
+      </>)
+}
+
+export default PostImportRowSummary

frontend/src/components/posts/import/PostImportStatusBadge.tsx

@@ -0,0 +1,27 @@
+import StatusBadge from '@/components/common/StatusBadge'
+
+import type { FC } from 'react'
+
+import type { StatusBadgeTone } from '@/components/common/StatusBadge'
+import type { PostImportBadgeValue } from '@/components/posts/import/postImportRowStatus'
+
+type Props = {
+    value: PostImportBadgeValue }
+
+const LABELS: Record<PostImportBadgeValue, string> = {
+    ready: '登録可能',
+    warning: '警告',
+    skipped: 'スキップ' }
+
+const TONES: Record<PostImportBadgeValue, StatusBadgeTone> = {
+    ready: 'success',
+    warning: 'warning',
+    skipped: 'neutral' }
+
+
+const PostImportStatusBadge: FC<Props> = ({ value }) => (
+    <StatusBadge tone={TONES[value]}>
+      {LABELS[value]}
+    </StatusBadge>)
+
+export default PostImportStatusBadge

frontend/src/components/posts/import/PostImportThumbnailPreview.test.tsx

@@ -0,0 +1,78 @@
+import { render, screen, waitFor } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import PostImportThumbnailPreview from '@/components/posts/import/PostImportThumbnailPreview'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+
+describe ('PostImportThumbnailPreview', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    globalThis.URL.createObjectURL = vi.fn (() => 'blob:preview')
+    globalThis.URL.revokeObjectURL = vi.fn ()
+  })
+
+  it ('uses a backend-fetched blob URL instead of the external thumbnail URL directly', async () => {
+    api.apiGet.mockResolvedValueOnce (new Blob (['img'], { type: 'image/png' }))
+
+    render (
+        <PostImportThumbnailPreview
+            url="https://example.com/thumbnail.jpg"
+            className="h-10 w-10"/>)
+
+    await waitFor (() => {
+      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
+    })
+    expect (screen.getByRole ('img')).not.toHaveAttribute (
+        'src',
+        'https://example.com/thumbnail.jpg')
+    expect (api.apiGet).toHaveBeenCalledWith ('/preview/thumbnail', {
+      params: { url: 'https://example.com/thumbnail.jpg' },
+      responseType: 'blob' })
+  })
+
+  it ('does not render the unsafe URL directly when preview fetching fails', async () => {
+    api.apiGet.mockRejectedValueOnce (new Error ('unsafe'))
+
+    render (
+        <PostImportThumbnailPreview
+            url="http://127.0.0.1/private.png"
+            className="h-10 w-10"/>)
+
+    expect (await screen.findByText ('サムネールを表示できません')).toBeInTheDocument ()
+    expect (screen.queryByRole ('img')).toBeNull ()
+  })
+
+  it ('revokes the old object URL when the source URL changes', async () => {
+    const createObjectUrlMock =
+        globalThis.URL.createObjectURL as unknown as ReturnType<typeof vi.fn>
+    createObjectUrlMock
+        .mockReturnValueOnce ('blob:first')
+        .mockReturnValueOnce ('blob:second')
+    api.apiGet
+        .mockResolvedValueOnce (new Blob (['first'], { type: 'image/png' }))
+        .mockResolvedValueOnce (new Blob (['second'], { type: 'image/png' }))
+
+    const { rerender } = render (
+        <PostImportThumbnailPreview
+            url="https://example.com/first.jpg"
+            className="h-10 w-10"/>)
+    await waitFor (() => {
+      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:first')
+    })
+
+    rerender (
+        <PostImportThumbnailPreview
+            url="https://example.com/second.jpg"
+            className="h-10 w-10"/>)
+
+    await waitFor (() => {
+      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:second')
+    })
+    expect (globalThis.URL.revokeObjectURL).toHaveBeenCalledWith ('blob:first')
+  })
+})

frontend/src/components/posts/import/PostImportThumbnailPreview.tsx

@@ -0,0 +1,89 @@
+import { useEffect, useRef, useState } from 'react'
+
+import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
+import { apiGet } from '@/lib/api'
+import { cn } from '@/lib/utils'
+
+import type { FC } from 'react'
+
+type Props = {
+  url:        string
+  alt?:       string
+  className?: string }
+
+
+const PostImportThumbnailPreview: FC<Props> = (
+    { url,
+      alt = 'サムネール',
+      className = 'h-16 w-16' },
+) => {
+  const [previewUrl, setPreviewUrl] = useState ('')
+  const [unavailable, setUnavailable] = useState (false)
+  const previewUrlRef = useRef ('')
+
+  useEffect (() => {
+    if (previewUrlRef.current)
+      {
+        URL.revokeObjectURL (previewUrlRef.current)
+        previewUrlRef.current = ''
+      }
+    setPreviewUrl ('')
+    setUnavailable (false)
+
+    if (!(url))
+      return
+
+    let active = true
+
+    const loadPreview = async () => {
+      try
+      {
+        const blob = await apiGet<Blob> ('/preview/thumbnail', {
+            params: { url },
+            responseType: 'blob' })
+        if (!(active))
+          return
+
+        const nextPreviewUrl = URL.createObjectURL (blob)
+        previewUrlRef.current = nextPreviewUrl
+        setPreviewUrl (nextPreviewUrl)
+      }
+      catch
+      {
+        if (active)
+          setUnavailable (true)
+      }
+    }
+
+    void loadPreview ()
+
+    return () => {
+      active = false
+      if (previewUrlRef.current)
+        {
+          URL.revokeObjectURL (previewUrlRef.current)
+          previewUrlRef.current = ''
+        }
+    }
+  }, [url])
+
+  if (unavailable)
+    {
+      return (
+          <div
+              className={`${ className } flex items-center justify-center rounded border
+                          border-amber-300 bg-amber-50 p-2 text-center text-xs
+                          text-amber-700 dark:border-amber-900 dark:bg-amber-950
+                          dark:text-amber-200`}>
+            サムネールを表示できません
+          </div>)
+    }
+
+  return (
+      <PostThumbnailPreview
+          url={previewUrl}
+          alt={alt}
+          className={className}/>)
+}
+
+export default PostImportThumbnailPreview

frontend/src/components/posts/import/postImportRowStatus.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest'
+
+import { displayPostImportStatus } from '@/components/posts/import/postImportRowStatus'
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+describe ('displayPostImportStatus', () => {
+  it ('shows only ready, warning, and skipped states', () => {
+    expect (displayPostImportStatus (buildPostImportRow ())).toBe ('ready')
+    expect (displayPostImportStatus (buildPostImportRow ({
+      status: 'warning',
+      fieldWarnings: { title: ['warning'] } }))).toBe ('warning')
+    expect (displayPostImportStatus (buildPostImportRow ({
+      skipReason: 'existing',
+      existingPostId: 2 }))).toBe ('skipped')
+  })
+
+  it ('does not expose validation, failure, or created states as badges', () => {
+    expect (displayPostImportStatus (buildPostImportRow ({
+      status: 'error',
+      validationErrors: { title: ['invalid'] } }))).toBeNull ()
+    expect (displayPostImportStatus (buildPostImportRow ({
+      importStatus: 'failed' }))).toBeNull ()
+    expect (displayPostImportStatus (buildPostImportRow ({
+      importStatus: 'created',
+      createdPostId: 3 }))).toBeNull ()
+  })
+})

frontend/src/components/posts/import/postImportRowStatus.ts

@@ -0,0 +1,22 @@
+import type { PostImportRow } from '@/lib/postImportSession'
+
+export type PostImportDisplayStatus = 'ready' | 'skipped' | 'warning'
+
+export type PostImportBadgeValue = PostImportDisplayStatus
+
+const hasWarnings = (row: PostImportRow): boolean =>
+    Object.values (row.fieldWarnings ?? { }).some (messages => messages.length > 0)
+    || row.baseWarnings.length > 0
+
+export const displayPostImportStatus = (
+    row: PostImportRow,
+): PostImportDisplayStatus | null =>
+    (row.skipReason === 'existing' || row.importStatus === 'skipped')
+    ? 'skipped'
+    : ((Object.keys (row.validationErrors ?? { }).length > 0
+	|| row.importStatus === 'failed'
+	|| row.importStatus === 'created')
+       ? null
+       : ((hasWarnings (row) || row.status === 'warning')
+	  ? 'warning'
+	  : 'ready'))

frontend/src/lib/dialogues/useDialogue.ts

@@ -0,0 +1,72 @@
+import { createContext, useContext } from 'react'
+
+import type { ReactNode } from 'react'
+
+type DialogueVariant = 'default' | 'danger'
+
+type ConfirmOptions = { title:        string
+			description?: ReactNode
+			confirmText?: string
+			cancelText?:  string
+			variant?:     DialogueVariant }
+
+type AlertOptions = { title:        string
+		      description?: ReactNode
+		      okText?:      string }
+
+type Choice<T extends string> = { value:    T
+				  label:    string
+				  variant?: DialogueVariant }
+
+type ChoiceOptions<T extends string> = { title:         string
+					 description?:  ReactNode
+					 choices:       Choice<T>[]
+					 cancelText?:   string }
+
+type DialogueFormAction = {
+  label:      string
+  placement?: 'start' | 'end'
+  variant?:   DialogueVariant
+  disabled?:  boolean
+  onSelect:   () => Promise<boolean | void> | boolean | void }
+
+type DialogueFormControls = {
+  close:      () => void
+  setActions: (actions: DialogueFormAction[]) => void
+  confirm:    (options: ConfirmOptions) => Promise<boolean> }
+
+type DialogueFormOptions = { title:         string
+			     description?:  ReactNode
+			     body:          (controls: DialogueFormControls) => ReactNode
+			     cancelText?:   string
+			     size?:         'default' | 'large' }
+
+type DialogueAPI =
+    { confirm:  (options: ConfirmOptions) => Promise<boolean>
+      alert:    (options: AlertOptions) => Promise<void>
+      choice:   <T extends string> (options: ChoiceOptions<T>) => Promise<T | null>
+      form:     (options: DialogueFormOptions) => Promise<void> }
+
+const DialogueContext = createContext<DialogueAPI | null> (null)
+
+const useDialogue = () => {
+  const dialogue = useContext (DialogueContext)
+
+  if (dialogue == null)
+    throw new Error ('useDialogue must be used inside DialogueProvider')
+
+  return dialogue
+}
+
+export { DialogueContext, useDialogue }
+export default useDialogue
+export type {
+    AlertOptions,
+    Choice,
+    ChoiceOptions,
+    ConfirmOptions,
+    DialogueAPI,
+    DialogueFormAction,
+    DialogueFormControls,
+    DialogueFormOptions,
+    DialogueVariant }

frontend/src/lib/postImportRows.test.ts

@@ -0,0 +1,288 @@
+import { describe, expect, it } from 'vitest'
+
+import { creatableImportRows,
+	 buildNextEditedRow,
+	 canEditResultRow,
+	 canEditReviewRow,
+	 canRetryResultRow,
+	 hasExactSourceRows,
+	 initialisePreviewRows,
+	 mergeImportResults,
+	 mergeValidatedImportRow,
+	 mergeValidatedImportRows,
+	 processableImportRows,
+	 replaceImportRow,
+	 resultRepairMode,
+	 resultRowMessages,
+	 resultSummaryCounts,
+	 retryImportRow,
+	 reviewSummaryCounts } from '@/lib/postImportSession'
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+describe ('post import row state', () => {
+  it ('separates processable existing rows from creatable rows', () => {
+    const ready = buildPostImportRow ({ sourceRow: 1 })
+    const existing = buildPostImportRow ({
+      sourceRow: 2,
+      skipReason: 'existing',
+      existingPostId: 20 })
+    const invalid = buildPostImportRow ({
+      sourceRow: 3,
+      status: 'error',
+      validationErrors: { url: ['invalid'] } })
+    const created = buildPostImportRow ({
+      sourceRow: 4,
+      importStatus: 'created',
+      createdPostId: 40 })
+    const rows = [ready, existing, invalid, created]
+
+    expect (processableImportRows (rows)).toEqual ([ready, existing])
+    expect (creatableImportRows (rows)).toEqual ([ready])
+    expect (reviewSummaryCounts (rows)).toEqual ({
+      total: 4,
+      submittable: 1,
+      skipPlanned: 1 })
+  })
+
+  it ('preserves terminal rows while merging validation results', () => {
+    const created = buildPostImportRow ({
+      sourceRow: 1,
+      importStatus: 'created',
+      createdPostId: 10,
+      attributes: { title: 'created title' } })
+    const pending = buildPostImportRow ({
+      sourceRow: 2,
+      fieldWarnings: { title: ['old warning'] },
+      provenance: { title: 'manual' },
+      attributes: { title: 'manual title' } })
+    const validated = [
+      buildPostImportRow ({ sourceRow: 1, attributes: { title: 'changed' } }),
+      buildPostImportRow ({
+	sourceRow: 2,
+	fieldWarnings: { title: ['fetch warning'], tags: ['tag warning'] },
+	provenance: { title: 'manual' },
+	attributes: { title: 'manual title' } })]
+
+    const result = mergeValidatedImportRows ([created, pending], validated)
+
+    expect (result[0]).toBe (created)
+    expect (result[1]?.fieldWarnings).toEqual ({ tags: ['tag warning'] })
+  })
+
+  it ('updates the reset snapshot only after metadata URL changes', () => {
+    const current = buildPostImportRow ({
+      attributes: { title: 'manual title' },
+      metadataUrl: 'https://example.com/old' })
+    const validated = buildPostImportRow ({
+      attributes: { title: 'new metadata title' },
+      metadataUrl: 'https://example.com/new',
+      fieldWarnings: { title: ['warning'] },
+      baseWarnings: ['base warning'] })
+
+    const result = mergeValidatedImportRows ([current], [validated])[0]
+
+    expect (result?.resetSnapshot).toMatchObject ({
+      attributes: { title: 'new metadata title' },
+      fieldWarnings: { title: ['warning'] },
+      baseWarnings: ['base warning'],
+      metadataUrl: 'https://example.com/new' })
+  })
+
+  it ('merges result states and clears incompatible post identifiers', () => {
+    const created = mergeImportResults ([buildPostImportRow ({
+      skipReason: 'existing',
+      existingPostId: 2,
+      recoverable: true,
+      importStatus: 'pending' })], [{
+      sourceRow: 1,
+      status: 'created',
+      post: { id: 3 } }])[0]
+    const skipped = mergeImportResults ([buildPostImportRow ({
+      createdPostId: 3,
+      importStatus: 'created',
+      recoverable: true })], [{
+      sourceRow: 1,
+      status: 'skipped',
+      existingPostId: 4 }])[0]
+    const failed = mergeImportResults ([buildPostImportRow ({
+      skipReason: 'existing',
+      existingPostId: 4 })], [{
+      sourceRow: 1,
+      status: 'failed',
+      recoverable: true,
+      errors: { base: ['failure'] } }])[0]
+
+    expect (created).toMatchObject ({
+      importStatus: 'created',
+      createdPostId: 3,
+      existingPostId: undefined,
+      recoverable: undefined,
+      skipReason: undefined })
+    expect (skipped).toMatchObject ({
+      importStatus: 'skipped',
+      existingPostId: 4,
+      createdPostId: undefined,
+      recoverable: undefined,
+      skipReason: 'existing' })
+    expect (failed).toMatchObject ({
+      importStatus: 'failed',
+      recoverable: true,
+      createdPostId: undefined,
+      existingPostId: undefined,
+      skipReason: undefined,
+      importErrors: { base: ['failure'] } })
+  })
+
+  it ('retries only the selected failed row and counts results exclusively', () => {
+    const rows = [
+      buildPostImportRow ({ sourceRow: 1, importStatus: 'created', createdPostId: 1 }),
+      buildPostImportRow ({ sourceRow: 2, importStatus: 'skipped',
+	existingPostId: 2, skipReason: 'existing' }),
+      buildPostImportRow ({ sourceRow: 3, importStatus: 'failed',
+	recoverable: true, importErrors: { base: ['failed'] } }),
+      buildPostImportRow ({ sourceRow: 4, importStatus: 'pending',
+	recoverable: true, validationErrors: { base: ['failed'] } })]
+
+    expect (resultSummaryCounts (rows)).toEqual ({ created: 1, skipped: 1, failed: 2 })
+    expect (retryImportRow (rows, 3)[2]).toMatchObject ({
+      importStatus: 'pending',
+      importErrors: undefined })
+    expect (retryImportRow (rows, 4)[3]).toBe (rows[3])
+  })
+
+  it ('deduplicates messages and keeps repair mode only for repairable rows', () => {
+    const repairable = buildPostImportRow ({
+      sourceRow: 1,
+      importStatus: 'pending',
+      validationErrors: { title: ['invalid'], base: ['duplicate'] },
+      importErrors: { base: ['duplicate'], url: ['network'] } })
+    const complete = buildPostImportRow ({
+      sourceRow: 2,
+      importStatus: 'created',
+      createdPostId: 2 })
+
+    expect (resultRowMessages (repairable)).toEqual (['invalid', 'duplicate', 'network'])
+    expect (resultRepairMode ([repairable, complete])).toBe ('failed')
+    expect (resultRepairMode ([complete])).toBe ('all')
+  })
+
+  it ('classifies editable and retryable rows by terminal and recoverable state', () => {
+    const ready = buildPostImportRow ()
+    const skipped = buildPostImportRow ({
+      importStatus: 'skipped',
+      skipReason: 'existing',
+      existingPostId: 2 })
+    const hardFailed = buildPostImportRow ({
+      importStatus: 'failed',
+      importErrors: { base: ['failed'] } })
+    const pendingInvalid = buildPostImportRow ({
+      importStatus: 'pending',
+      recoverable: true,
+      validationErrors: { title: ['invalid'] } })
+    const pendingValid = buildPostImportRow ({
+      importStatus: 'pending',
+      recoverable: true })
+
+    expect (canEditReviewRow (ready)).toBe (true)
+    expect (canEditReviewRow (skipped)).toBe (false)
+    expect (canEditReviewRow (hardFailed)).toBe (false)
+    expect (canEditResultRow (pendingInvalid)).toBe (true)
+    expect (canRetryResultRow (pendingInvalid)).toBe (false)
+    expect (canRetryResultRow (pendingValid)).toBe (true)
+  })
+
+  it ('detects missing, duplicate, and extra source rows exactly', () => {
+    expect (hasExactSourceRows ([1, 2], [{ sourceRow: 1 }, { sourceRow: 2 }])).toBe (true)
+    expect (hasExactSourceRows ([1, 2], [{ sourceRow: 1 }])).toBe (false)
+    expect (hasExactSourceRows ([1, 2], [{ sourceRow: 1 }, { sourceRow: 1 }])).toBe (false)
+    expect (hasExactSourceRows ([1, 2], [{ sourceRow: 1 }, { sourceRow: 3 }])).toBe (false)
+  })
+
+  it ('merges only the validated source row and preserves other row edits', () => {
+    const edited = buildPostImportRow ({
+      sourceRow: 1,
+      attributes: { title: 'edited row' },
+      provenance: { title: 'manual' } })
+    const other = buildPostImportRow ({
+      sourceRow: 2,
+      attributes: { title: 'keep me' },
+      provenance: { title: 'manual' } })
+    const validated = buildPostImportRow ({
+      sourceRow: 1,
+      attributes: { title: 'validated row' } })
+
+    const result = mergeValidatedImportRow ([edited, other], validated)
+
+    expect (result[0]?.attributes.title).toBe ('validated row')
+    expect (result[1]?.attributes.title).toBe ('keep me')
+  })
+
+  it ('replaces only the targeted source row and preserves the others', () => {
+    const original = buildPostImportRow ({
+      sourceRow: 1,
+      importStatus: 'failed',
+      recoverable: true,
+      importErrors: { base: ['failed'] } })
+    const other = buildPostImportRow ({
+      sourceRow: 2,
+      attributes: { title: 'keep edited row' } })
+    const restored = buildPostImportRow ({
+      sourceRow: 1,
+      importStatus: 'failed',
+      recoverable: true,
+      importErrors: { base: ['failed'] } })
+
+    const result = replaceImportRow ([original, other], restored)
+
+    expect (result[0]).toEqual (restored)
+    expect (result[1]?.attributes.title).toBe ('keep edited row')
+  })
+
+  it ('copies reset snapshot values instead of sharing mutable records', () => {
+    const row = buildPostImportRow ({ fieldWarnings: { title: ['warning'] } })
+    const initialised = initialisePreviewRows ([row])[0]
+    expect (initialised).toBeDefined ()
+    if (initialised == null)
+      return
+
+    initialised.attributes.title = 'changed'
+    initialised.fieldWarnings.title?.push ('another')
+
+    expect (initialised.resetSnapshot.attributes.title).toBe ('')
+    expect (initialised.resetSnapshot.fieldWarnings.title).toEqual (['warning'])
+  })
+
+  it ('builds the next edited row with shared repair semantics', () => {
+    const row = buildPostImportRow ({
+      url: 'https://example.com/original',
+      importStatus: 'failed',
+      recoverable: true,
+      importErrors: { base: ['failed'] },
+      attributes: { title: 'old title', tags: 'old-tag', duration: '2' },
+      provenance: { title: 'automatic', tags: 'automatic', url: 'manual' },
+      tagSources: { automatic: 'old-tag', manual: '' } })
+
+    const nextRow = buildNextEditedRow (
+        row,
+        {
+          url: 'https://example.com/edited',
+          title: 'edited title',
+          thumbnailBase: '',
+          originalCreatedFrom: '',
+          originalCreatedBefore: '',
+          duration: '2.5',
+          tags: 'edited-tag',
+          parentPostIds: '' },
+        true)
+
+    expect (nextRow.importStatus).toBe ('pending')
+    expect (nextRow.importErrors).toBeUndefined ()
+    expect (nextRow.url).toBe ('https://example.com/edited')
+    expect (nextRow.attributes.title).toBe ('edited title')
+    expect (nextRow.attributes.duration).toBe ('2.5')
+    expect (nextRow.attributes.tags).toBe ('edited-tag')
+    expect (nextRow.provenance.title).toBe ('manual')
+    expect (nextRow.provenance.url).toBe ('manual')
+    expect (nextRow.tagSources?.manual).toBe ('edited-tag')
+  })
+})

frontend/src/lib/postImportRows.ts

@@ -0,0 +1,312 @@
+import type { PostImportEditableDraft,
+	      PostImportResultRow,
+	      PostImportRow } from '@/lib/postImportTypes'
+
+const hasSkipReason = (row: PostImportRow): boolean =>
+    row.skipReason === 'existing'
+
+const hasValidationErrors = (row: PostImportRow): boolean =>
+    Object.keys (row.validationErrors ?? { }).length > 0
+
+const isRecoverableRow = (row: PostImportRow): boolean =>
+    row.recoverable === true
+
+const isRepairableImportStatus = (row: PostImportRow): boolean =>
+    isRecoverableRow (row)
+    && (row.importStatus === 'failed' || row.importStatus === 'pending')
+
+const buildResetSnapshot = (row: PostImportRow) => ({
+    url: row.url,
+    attributes: { ...row.attributes },
+    provenance: { ...row.provenance },
+    tagSources: {
+	automatic: row.tagSources?.automatic ?? '',
+	manual: row.tagSources?.manual ?? '' },
+    fieldWarnings: Object.fromEntries (
+	Object.entries (row.fieldWarnings).map (([key, values]) => [key, [...values]])),
+    baseWarnings: [...row.baseWarnings],
+    metadataUrl: row.metadataUrl })
+
+
+export const processableImportRows = (rows: PostImportRow[]): PostImportRow[] =>
+    rows.filter (row => {
+      if (row.importStatus === 'created')
+        return false
+      if (row.importStatus === 'skipped')
+        return false
+      if (row.importStatus === 'failed')
+        return false
+      if (hasValidationErrors (row))
+        return false
+      return row.importStatus == null || row.importStatus === 'pending'
+    })
+
+export const creatableImportRows = (rows: PostImportRow[]): PostImportRow[] =>
+    processableImportRows (rows).filter (row => !(hasSkipReason (row)))
+
+
+export const reviewSummaryCounts = (rows: PostImportRow[]) => ({
+    total: rows.length,
+    submittable: rows.filter (row =>
+        creatableImportRows ([row]).length > 0
+        && !(hasValidationErrors (row))).length,
+    skipPlanned: rows.filter (row =>
+        processableImportRows ([row]).length > 0
+        && hasSkipReason (row)).length })
+
+
+export const resultSummaryCounts = (rows: PostImportRow[]) =>
+    rows.reduce (
+        (counts, row) => {
+          if (row.importStatus === 'created')
+            {
+              ++counts.created
+              return counts
+            }
+          if (row.importStatus === 'skipped')
+            {
+              ++counts.skipped
+              return counts
+            }
+          if (row.importStatus === 'failed'
+              || (row.recoverable === true && row.importStatus === 'pending'))
+            ++counts.failed
+          return counts
+        },
+        { created: 0, skipped: 0, failed: 0 })
+
+
+export const resultRepairMode = (
+    rows: PostImportRow[],
+): 'all' | 'failed' =>
+    rows.some (row => hasValidationErrors (row) || isRepairableImportStatus (row))
+    ? 'failed'
+    : 'all'
+
+
+export const canEditReviewRow = (row: PostImportRow): boolean =>
+    !(row.importStatus === 'created'
+      || row.importStatus === 'skipped'
+      || (row.importStatus === 'failed' && row.recoverable !== true))
+
+
+export const canEditResultRow = (row: PostImportRow): boolean =>
+    row.recoverable === true
+    && (row.importStatus === 'failed'
+        || (row.importStatus === 'pending' && hasValidationErrors (row)))
+
+
+export const canRetryResultRow = (row: PostImportRow): boolean =>
+    row.recoverable === true
+    && (row.importStatus === 'failed'
+        || (row.importStatus === 'pending' && !(hasValidationErrors (row))))
+
+
+export const resultRowMessages = (row: PostImportRow): string[] =>
+    [...new Set ([
+        ...Object.values (row.validationErrors ?? { }).flat (),
+        ...Object.values (row.importErrors ?? { }).flat ()])]
+
+
+export const resultRowWarnings = (row: PostImportRow): string[] =>
+    [...new Set ([
+        ...Object.values (row.fieldWarnings ?? { }).flat (),
+        ...row.baseWarnings])]
+
+export const buildNextEditedRow = (
+    editingRow:  PostImportRow,
+    draft:       PostImportEditableDraft,
+    urlChanged:  boolean,
+): PostImportRow => {
+    const nextProvenance = { ...editingRow.provenance }
+    const nextAttributes = { ...editingRow.attributes }
+    const nextTagSources = {
+	automatic: editingRow.tagSources?.automatic ?? '',
+	manual: editingRow.tagSources?.manual ?? '' }
+    const draftFields = [
+	['title', draft.title],
+	['thumbnailBase', draft.thumbnailBase],
+	['originalCreatedFrom', draft.originalCreatedFrom],
+	['originalCreatedBefore', draft.originalCreatedBefore],
+	['duration', draft.duration],
+	['parentPostIds', draft.parentPostIds]] as const
+    draftFields.forEach (([field, value]) => {
+	nextAttributes[field] = value
+	nextProvenance[field] =
+	    value !== String (editingRow.attributes[field] ?? '')
+	    ? 'manual'
+	    : (editingRow.provenance[field] ?? 'automatic')
+    })
+    nextAttributes.tags = draft.tags
+    if (draft.tags !== String (editingRow.attributes.tags ?? ''))
+      {
+	nextProvenance.tags = 'manual'
+	nextTagSources.manual = draft.tags
+      }
+    else
+      {
+	nextProvenance.tags = editingRow.provenance.tags ?? 'automatic'
+	nextTagSources.manual = editingRow.tagSources?.manual ?? ''
+      }
+
+    return {
+	...editingRow,
+	url: draft.url,
+	attributes: nextAttributes,
+	provenance: {
+	    ...nextProvenance,
+	    url: urlChanged ? 'manual' : (editingRow.provenance.url ?? 'manual') },
+	tagSources: nextTagSources,
+	importStatus: editingRow.importStatus === 'created' ? 'created' : 'pending',
+	importErrors: undefined }
+}
+
+
+export const hasExactSourceRows = (
+    expected: number[],
+    actual:   Array<{ sourceRow: number }>,
+): boolean => {
+    if (expected.length !== actual.length)
+      return false
+
+    const expectedSorted = [...expected].sort ((a, b) => a - b)
+    const actualSorted = actual.map (row => row.sourceRow).sort ((a, b) => a - b)
+    return expectedSorted.every ((value, index) => value === actualSorted[index])
+}
+
+
+export const replaceImportRow = (
+    rows:      PostImportRow[],
+    nextRow:   PostImportRow,
+): PostImportRow[] =>
+    rows.map (row => row.sourceRow === nextRow.sourceRow ? nextRow : row)
+
+
+export const mergeValidatedImportRow = (
+    rows:      PostImportRow[],
+    validated: PostImportRow,
+): PostImportRow[] => {
+    const current = rows.find (row => row.sourceRow === validated.sourceRow)
+    if (current == null)
+      return rows
+
+    const [merged] = mergeValidatedImportRows ([current], [validated])
+    return merged == null ? rows : replaceImportRow (rows, merged)
+}
+
+
+export const mergeValidatedImportRows = (
+    current:   PostImportRow[],
+    validated: PostImportRow[],
+): PostImportRow[] => {
+    const validatedMap = new Map (validated.map (row => [row.sourceRow, row]))
+    return current.map (previous => {
+      if (
+          previous.importStatus === 'created'
+          || previous.importStatus === 'skipped'
+          || previous.importStatus === 'failed')
+        return previous
+
+      const row = validatedMap.get (previous.sourceRow)
+      if (row == null)
+        return previous
+
+      const fieldWarnings =
+          Object.keys (row.fieldWarnings).length > 0 || row.metadataUrl !== previous.metadataUrl
+          ? { ...row.fieldWarnings }
+          : { ...previous.fieldWarnings }
+      for (const [field, origin] of Object.entries (row.provenance))
+        {
+          if (origin === 'manual')
+            delete fieldWarnings[field]
+        }
+
+      return {
+          ...previous,
+          url: row.url,
+          attributes: row.attributes,
+          provenance: row.provenance,
+          tagSources: row.tagSources,
+          skipReason: row.skipReason,
+          existingPostId: row.existingPostId,
+          fieldWarnings,
+          baseWarnings:
+              row.baseWarnings.length > 0 || row.metadataUrl !== previous.metadataUrl
+              ? row.baseWarnings
+              : previous.baseWarnings,
+          validationErrors: row.validationErrors,
+          status: row.status,
+          metadataUrl: row.metadataUrl,
+          resetSnapshot:
+              row.metadataUrl !== previous.metadataUrl
+              ? buildResetSnapshot (row)
+              : previous.resetSnapshot }
+    })
+}
+
+
+export const mergeImportResults = (
+    rows:    PostImportRow[],
+    results: PostImportResultRow[],
+): PostImportRow[] => {
+    const resultMap = new Map (results.map (row => [row.sourceRow, row]))
+    return rows.map (row => {
+      const result = resultMap.get (row.sourceRow)
+      if (result == null)
+        return row
+
+      switch (result.status)
+        {
+        case 'created':
+          return {
+              ...row,
+              importStatus: 'created',
+              recoverable: undefined,
+              skipReason: undefined,
+              createdPostId: result.post.id,
+              existingPostId: undefined,
+              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              baseWarnings: result.baseWarnings ?? row.baseWarnings,
+              importErrors: result.errors }
+        case 'skipped':
+          return {
+              ...row,
+              importStatus: 'skipped',
+              recoverable: undefined,
+              skipReason: 'existing',
+              createdPostId: undefined,
+              existingPostId: result.existingPostId,
+              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              baseWarnings: result.baseWarnings ?? row.baseWarnings,
+              importErrors: result.errors }
+        case 'failed':
+          return {
+              ...row,
+              importStatus: 'failed',
+              recoverable: result.recoverable === true ? true : undefined,
+              skipReason: undefined,
+              createdPostId: undefined,
+              existingPostId: undefined,
+              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              baseWarnings: result.baseWarnings ?? row.baseWarnings,
+              importErrors: result.errors }
+        }
+    })
+}
+
+
+export const retryImportRow = (
+    rows:      PostImportRow[],
+    sourceRow: number,
+): PostImportRow[] =>
+    rows.map (row =>
+        row.sourceRow === sourceRow
+        && row.importStatus === 'failed'
+        && row.recoverable === true
+        ? { ...row, importStatus: 'pending', importErrors: undefined }
+        : row)
+
+export const initialisePreviewRows = (rows: PostImportRow[]): PostImportRow[] =>
+    rows.map (row => ({
+        ...row,
+        resetSnapshot: buildResetSnapshot (row) }))

frontend/src/lib/postImportSession.ts

@@ -0,0 +1,4 @@
+export * from '@/lib/postImportTypes'
+export * from '@/lib/postImportStorage'
+export * from '@/lib/postImportSourceValidation'
+export * from '@/lib/postImportRows'

frontend/src/lib/postImportSourceValidation.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from 'vitest'
+
+import { countImportSourceLines, validateImportSource } from '@/lib/postImportSession'
+
+describe ('post import source validation', () => {
+  it ('counts trimmed non-empty CRLF and LF rows', () => {
+    expect (countImportSourceLines (' one \r\n\r\n two\n')).toBe (2)
+  })
+
+  it ('reports invalid protocols and malformed URLs with original line numbers', () => {
+    const issues = validateImportSource (
+        '\nftp://example.com/file\nhttps://exa mple.com/path')
+
+    expect (issues).toEqual ([
+      {
+	sourceRow: 2,
+	message: 'HTTP または HTTPS の URL ではありません．',
+	url: 'ftp://example.com/file' },
+      {
+	sourceRow: 3,
+	message: 'URL の形式が不正です．',
+	url: 'https://exa mple.com/path' }])
+  })
+
+  it ('detects duplicates after frontend URL normalisation', () => {
+    const issues = validateImportSource (
+        'https://EXAMPLE.com/path/\nhttps://example.com/path')
+
+    expect (issues).toEqual ([{
+      sourceRow: 2,
+      message: '1 行目と同じ URL です．',
+      url: 'https://example.com/path' }])
+  })
+
+  it ('rejects oversized URLs and rows beyond the maximum count', () => {
+    const oversized = `https://example.com/${ 'a'.repeat (20 * 1024) }`
+    const tooMany = Array.from (
+        { length: 101 },
+        (_, index) => `https://example.com/${ index }`).join ('\n')
+
+    expect (validateImportSource (oversized)[0]).toMatchObject ({
+      sourceRow: 1,
+      message: 'URL が長すぎます．' })
+    expect (validateImportSource (tooMany).at (-1)).toEqual ({
+      sourceRow: 101,
+      message: '取込件数は 100 件までです．',
+      url: 'https://example.com/100' })
+  })
+})

frontend/src/lib/postImportSourceValidation.ts

@@ -0,0 +1,110 @@
+import type { PostImportSourceIssue } from '@/lib/postImportTypes'
+
+const MAX_ROWS = 100
+const MAX_URL_BYTES = 20 * 1024
+
+
+const truncateUrl = (value: string): string =>
+    value.length > 120 ? `${ value.slice (0, 117) }…` : value
+
+
+const bytesize = (value: string): number =>
+    new TextEncoder ().encode (value).length
+
+
+const normaliseImportUrl = (value: string): string | null => {
+    const trimmed = value.trim ()
+    if (!(trimmed))
+      return null
+
+    try
+    {
+      const url = new URL (trimmed)
+      if (!(url.protocol === 'http:' || url.protocol === 'https:'))
+        return null
+      if (!(url.host))
+        return null
+
+      url.hostname = url.hostname.toLowerCase ()
+      if (url.pathname.endsWith ('/'))
+        url.pathname = url.pathname.replace (/\/+$/, '')
+      return url.toString ()
+    }
+    catch
+    {
+      return null
+    }
+}
+
+
+export const countImportSourceLines = (source: string): number =>
+    source
+        .split (/\r\n|\n|\r/)
+        .map (line => line.trim ())
+        .filter (line => line !== '')
+        .length
+
+
+export const validateImportSource = (
+    source: string,
+): PostImportSourceIssue[] => {
+    const lines = source.split (/\r\n|\n|\r/)
+    const issues: PostImportSourceIssue[] = []
+    const seen = new Map<string, number> ()
+    let count = 0
+
+    lines.forEach ((rawLine, index) => {
+      const value = rawLine.trim ()
+      if (!(value))
+        return
+
+      ++count
+      const sourceRow = index + 1
+      const displayUrl = truncateUrl (value)
+      const normalised = normaliseImportUrl (value)
+      if (count > MAX_ROWS)
+        {
+          issues.push ({
+              sourceRow,
+              message: `取込件数は ${ MAX_ROWS } 件までです．`,
+              url: displayUrl })
+          return
+        }
+      if (!(value.startsWith ('http://') || value.startsWith ('https://')))
+        {
+          issues.push ({
+              sourceRow,
+              message: 'HTTP または HTTPS の URL ではありません．',
+              url: displayUrl })
+          return
+        }
+      if (bytesize (value) > MAX_URL_BYTES)
+        {
+          issues.push ({
+              sourceRow,
+              message: 'URL が長すぎます．',
+              url: displayUrl })
+          return
+        }
+      if (normalised == null)
+        {
+          issues.push ({
+              sourceRow,
+              message: 'URL の形式が不正です．',
+              url: displayUrl })
+          return
+        }
+      const duplicateRow = seen.get (normalised)
+      if (duplicateRow != null)
+        {
+          issues.push ({
+              sourceRow,
+              message: `${ duplicateRow } 行目と同じ URL です．`,
+              url: displayUrl })
+          return
+        }
+      seen.set (normalised, sourceRow)
+    })
+
+    return issues
+}

frontend/src/lib/postImportStorage.test.ts

@@ -0,0 +1,126 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { cleanupExpiredPostImportSessions,
+	 clearPostImportSourceDraft,
+	 loadPostImportSession,
+	 loadPostImportSourceDraft,
+	 savePostImportSession,
+	 savePostImportSourceDraft } from '@/lib/postImportSession'
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+describe ('post import storage', () => {
+  beforeEach (() => {
+    sessionStorage.clear ()
+    vi.useRealTimers ()
+  })
+
+  it ('round-trips a valid session and source draft', () => {
+    const row = buildPostImportRow ({
+      attributes: { duration: '2.5' },
+      recoverable: true,
+      importStatus: 'pending',
+      validationErrors: { title: ['invalid'] } })
+    const skipped = buildPostImportRow ({
+      importStatus: 'skipped',
+      skipReason: 'existing',
+      existingPostId: 10 })
+
+    expect (savePostImportSession ('session', {
+      source: skipped.url,
+      rows: [row, skipped],
+      repairMode: 'all' })).toBe (true)
+    expect (loadPostImportSession ('session')).toMatchObject ({
+      version: 2,
+      source: skipped.url,
+      rows: [{
+	attributes: { duration: '2.5' },
+	recoverable: true,
+	importStatus: 'pending' },
+	      {
+	importStatus: 'skipped',
+	skipReason: 'existing',
+	existingPostId: 10 }] })
+
+    expect (savePostImportSourceDraft ('https://example.com')).toBe (true)
+    expect (loadPostImportSourceDraft ()).toEqual ({ source: 'https://example.com' })
+    clearPostImportSourceDraft ()
+    expect (loadPostImportSourceDraft ()).toEqual ({ source: '' })
+  })
+
+  it ('rejects inconsistent post IDs and terminal statuses', () => {
+    const session = {
+      version: 2,
+      savedAt: new Date ().toISOString (),
+      source: '',
+      repairMode: 'all',
+      rows: [buildPostImportRow ()] }
+    const invalidRows = [
+      { ...session.rows[0], skipReason: 'existing', existingPostId: undefined },
+      { ...session.rows[0], existingPostId: 2, skipReason: undefined },
+      { ...session.rows[0], importStatus: 'created', createdPostId: undefined },
+      { ...session.rows[0], importStatus: 'failed', createdPostId: 3 },
+      { ...session.rows[0], importStatus: 'created', recoverable: true },
+      { ...session.rows[0], importStatus: 'skipped', recoverable: true },
+      { ...session.rows[0], recoverable: true }]
+
+    for (const [index, row] of invalidRows.entries ())
+      {
+	sessionStorage.setItem (`post-import-session:invalid-${ index }`, JSON.stringify ({
+	  ...session,
+	  rows: [row] }))
+	expect (loadPostImportSession (`invalid-${ index }`)).toBeNull ()
+      }
+  })
+
+  it ('rejects invalid attribute, provenance, tag-source, and snapshot data', () => {
+    const row = buildPostImportRow ()
+    const invalidRows = [
+      { ...row, attributes: { title: [] } },
+      { ...row, attributes: { unknown: 'value' } },
+      { ...row, provenance: { title: 'mapped' } },
+      { ...row, tagSources: { mapped: 'tag' } },
+      { ...row, resetSnapshot: { ...row.resetSnapshot,
+	fieldWarnings: { title: 'warning' } } }]
+
+    invalidRows.forEach ((invalidRow, index) => {
+      sessionStorage.setItem (`post-import-session:shape-${ index }`, JSON.stringify ({
+	version: 2,
+	savedAt: new Date ().toISOString (),
+	source: '',
+	rows: [invalidRow],
+	repairMode: 'all' }))
+      expect (loadPostImportSession (`shape-${ index }`)).toBeNull ()
+    })
+  })
+
+  it ('removes expired and malformed sessions without touching current sessions', () => {
+    const current = {
+      version: 2,
+      savedAt: new Date ().toISOString (),
+      source: '',
+      rows: [buildPostImportRow ()],
+      repairMode: 'all' }
+    const expired = {
+      ...current,
+      savedAt: new Date (Date.now () - 25 * 60 * 60 * 1000).toISOString () }
+    sessionStorage.setItem ('post-import-session:current', JSON.stringify (current))
+    sessionStorage.setItem ('post-import-session:expired', JSON.stringify (expired))
+    sessionStorage.setItem ('post-import-session:malformed', '{')
+
+    cleanupExpiredPostImportSessions ()
+
+    expect (sessionStorage.getItem ('post-import-session:current')).not.toBeNull ()
+    expect (sessionStorage.getItem ('post-import-session:expired')).toBeNull ()
+    expect (sessionStorage.getItem ('post-import-session:malformed')).toBeNull ()
+  })
+
+  it ('reports storage access failures without throwing', () => {
+    const onError = vi.fn ()
+    vi.spyOn (Storage.prototype, 'setItem').mockImplementation (() => {
+      throw new DOMException ('quota')
+    })
+
+    expect (savePostImportSourceDraft ('source', onError)).toBe (false)
+    expect (onError).toHaveBeenCalledWith ('ブラウザへ保存できませんでした．')
+  })
+})

frontend/src/lib/postImportStorage.ts

@@ -0,0 +1,418 @@
+import type { PostImportOrigin,
+	      PostImportResetSnapshot,
+	      PostImportRow,
+	      PostImportSession,
+	      PostImportStatus,
+	      PostImportSkipReason,
+	      StorageErrorHandler } from '@/lib/postImportTypes'
+
+const SESSION_VERSION = 2
+const SESSION_PREFIX = 'post-import-session:'
+const SOURCE_DRAFT_KEY = 'post-import-source-draft'
+const SESSION_MAX_AGE_MS = 24 * 60 * 60 * 1000
+const ATTRIBUTE_KEYS = [
+    'title',
+    'thumbnailBase',
+    'originalCreatedFrom',
+    'originalCreatedBefore',
+    'duration',
+    'videoMs',
+    'tags',
+    'parentPostIds'] as const
+const PROVENANCE_KEYS = [...ATTRIBUTE_KEYS, 'url'] as const
+const TAG_SOURCE_KEYS = ['automatic', 'manual'] as const
+const WARNING_KEYS = [...ATTRIBUTE_KEYS, 'url'] as const
+
+
+const isPlainObject = (value: unknown): value is Record<string, unknown> =>
+    typeof value === 'object' && value != null && !(Array.isArray (value))
+
+
+const sessionKey = (sessionId: string): string => `${ SESSION_PREFIX }${ sessionId }`
+
+
+const readStorage = (
+    key:       string,
+    onError?:  StorageErrorHandler,
+): string | null => {
+    if (typeof window === 'undefined')
+      return null
+
+    try
+    {
+      return sessionStorage.getItem (key)
+    }
+    catch
+    {
+      onError?.('保存済みデータを読み込めませんでした．')
+      return null
+    }
+}
+
+
+const writeStorage = (
+    key:       string,
+    value:     string,
+    onError?:  StorageErrorHandler,
+): boolean => {
+    if (typeof window === 'undefined')
+      return false
+
+    try
+    {
+      sessionStorage.setItem (key, value)
+      return true
+    }
+    catch
+    {
+      onError?.('ブラウザへ保存できませんでした．')
+      return false
+    }
+}
+
+
+const removeStorage = (
+    key:       string,
+    onError?:  StorageErrorHandler,
+) => {
+    if (typeof window === 'undefined')
+      return
+
+    try
+    {
+      sessionStorage.removeItem (key)
+    }
+    catch
+    {
+      onError?.('保存済みデータを削除できませんでした．')
+    }
+}
+
+
+const ensureStringListRecord = (value: unknown): Record<string, string[]> | null => {
+    if (!(isPlainObject (value)))
+      return null
+
+    const result: Record<string, string[]> = { }
+    for (const [key, entry] of Object.entries (value))
+      {
+        if (!(Array.isArray (entry)) || !(entry.every (item => typeof item === 'string')))
+          return null
+        result[key] = entry
+      }
+    return result
+}
+
+
+const isValidStatus = (
+    value: unknown,
+): value is PostImportRow['status'] =>
+    value === 'ready' || value === 'warning' || value === 'error'
+
+
+const isValidImportStatus = (
+    value: unknown,
+): value is PostImportStatus =>
+    value === 'pending'
+    || value === 'created'
+    || value === 'skipped'
+    || value === 'failed'
+
+
+const isValidOrigin = (
+    value: unknown,
+): value is PostImportOrigin =>
+    value === 'automatic' || value === 'manual'
+
+
+const isValidSkipReason = (
+    value: unknown,
+): value is PostImportSkipReason =>
+    value === 'existing'
+
+const isPositiveInteger = (value: unknown): value is number =>
+    Number.isInteger (value) && Number (value) > 0
+
+const hasOnlyKeys = (
+    value:        Record<string, unknown>,
+    allowedKeys:  readonly string[],
+): boolean =>
+    Object.keys (value).every (key => allowedKeys.includes (key))
+
+const sanitiseResetSnapshot = (value: unknown): PostImportResetSnapshot | null => {
+    if (!(isPlainObject (value)))
+      return null
+    if (typeof value.url !== 'string')
+      return null
+    if (!(isPlainObject (value.attributes)))
+      return null
+    if (!(hasOnlyKeys (value.attributes, ATTRIBUTE_KEYS)))
+      return null
+    if (!(Object.values (value.attributes).every (entry =>
+        typeof entry === 'string' || typeof entry === 'number')))
+      return null
+    if (!(isPlainObject (value.provenance)))
+      return null
+    if (!(hasOnlyKeys (value.provenance, PROVENANCE_KEYS)))
+      return null
+    if (!(Object.values (value.provenance).every (origin => isValidOrigin (origin))))
+      return null
+    if (!(isPlainObject (value.tagSources)))
+      return null
+    if (!(hasOnlyKeys (value.tagSources, TAG_SOURCE_KEYS)))
+      return null
+    if (!(Object.values (value.tagSources).every (entry => typeof entry === 'string')))
+      return null
+    const fieldWarnings = ensureStringListRecord (value.fieldWarnings)
+    if (fieldWarnings == null)
+      return null
+    if (!(hasOnlyKeys (fieldWarnings, WARNING_KEYS)))
+      return null
+    if (!(Array.isArray (value.baseWarnings))
+        || !(value.baseWarnings.every (warning => typeof warning === 'string')))
+      return null
+    if (value.metadataUrl != null && typeof value.metadataUrl !== 'string')
+      return null
+
+    return {
+        url: value.url,
+        attributes: value.attributes as Record<string, string | number>,
+        provenance: value.provenance as Record<string, PostImportOrigin>,
+        tagSources: value.tagSources as Record<PostImportOrigin, string>,
+        fieldWarnings,
+        baseWarnings: value.baseWarnings,
+        metadataUrl: value.metadataUrl as string | undefined }
+}
+
+
+const sanitiseRow = (value: unknown): PostImportRow | null => {
+    if (!(isPlainObject (value)))
+      return null
+    if (!(Number.isInteger (value.sourceRow)) || Number (value.sourceRow) <= 0)
+      return null
+    if (typeof value.url !== 'string')
+      return null
+    if (!(isPlainObject (value.attributes)))
+      return null
+    if (!(isPlainObject (value.provenance)))
+      return null
+    if (!(isValidStatus (value.status)))
+      return null
+    if (value.importStatus != null && !(isValidImportStatus (value.importStatus)))
+      return null
+    if (value.skipReason != null && !(isValidSkipReason (value.skipReason)))
+      return null
+    if (value.recoverable != null && value.recoverable !== true)
+      return null
+    if (value.skipReason === 'existing' && !(isPositiveInteger (value.existingPostId)))
+      return null
+    if (value.skipReason !== 'existing' && value.existingPostId != null)
+      return null
+    if (value.importStatus === 'created' && !(isPositiveInteger (value.createdPostId)))
+      return null
+    if (value.importStatus !== 'created' && value.createdPostId != null)
+      return null
+    if (value.recoverable === true
+        && value.importStatus !== 'failed'
+        && value.importStatus !== 'pending')
+      return null
+    if ((value.importStatus === 'created' || value.importStatus === 'skipped')
+        && value.recoverable != null)
+      return null
+
+    const validationErrors = ensureStringListRecord (value.validationErrors)
+    const fieldWarnings = ensureStringListRecord (value.fieldWarnings)
+    const resetSnapshot = sanitiseResetSnapshot (value.resetSnapshot)
+    if (validationErrors == null || fieldWarnings == null)
+      return null
+    if (resetSnapshot == null)
+      return null
+
+    const importErrors =
+        value.importErrors == null
+        ? undefined
+        : ensureStringListRecord (value.importErrors)
+    if (importErrors === null)
+      return null
+    if (!(Array.isArray (value.baseWarnings))
+        || !(value.baseWarnings.every (warning => typeof warning === 'string')))
+      return null
+
+    const provenanceEntries = Object.entries (value.provenance)
+    if (!(hasOnlyKeys (value.attributes, ATTRIBUTE_KEYS)))
+      return null
+    if (!(Object.values (value.attributes).every (entry =>
+        typeof entry === 'string' || typeof entry === 'number')))
+      return null
+    if (!(hasOnlyKeys (value.provenance, PROVENANCE_KEYS)))
+      return null
+    if (!(provenanceEntries.every (([, origin]) => isValidOrigin (origin))))
+      return null
+
+    if (value.tagSources != null)
+      {
+        if (!(isPlainObject (value.tagSources)))
+          return null
+        if (!(hasOnlyKeys (value.tagSources, TAG_SOURCE_KEYS)))
+          return null
+        if (!(Object.values (value.tagSources).every (entry => typeof entry === 'string')))
+          return null
+      }
+
+    return {
+        sourceRow: Number (value.sourceRow),
+        url: value.url,
+        attributes: value.attributes as Record<string, string | number>,
+        fieldWarnings,
+        baseWarnings: value.baseWarnings,
+        validationErrors,
+        importErrors,
+        provenance: value.provenance as Record<string, PostImportOrigin>,
+        tagSources: value.tagSources as Record<PostImportOrigin, string> | undefined,
+        status: value.status,
+        skipReason: value.skipReason ?? undefined,
+        existingPostId:
+            isPositiveInteger (value.existingPostId) ? Number (value.existingPostId) : undefined,
+        metadataUrl: typeof value.metadataUrl === 'string' ? value.metadataUrl : undefined,
+        resetSnapshot,
+        createdPostId:
+            isPositiveInteger (value.createdPostId) ? Number (value.createdPostId) : undefined,
+        importStatus: value.importStatus ?? undefined,
+        recoverable: value.recoverable === true ? true : undefined }
+}
+
+
+const isExpiredSession = (savedAt: string): boolean => {
+    const value = Date.parse (savedAt)
+    return Number.isNaN (value) || Date.now () - value > SESSION_MAX_AGE_MS
+}
+
+
+export const createPostImportSessionId = (): string =>
+    typeof crypto !== 'undefined' && 'randomUUID' in crypto
+    ? crypto.randomUUID ()
+    : `${ Date.now () }-${ Math.random ().toString (36).slice (2) }`
+
+
+export const cleanupExpiredPostImportSessions = (
+    onError?: StorageErrorHandler,
+) => {
+    if (typeof window === 'undefined')
+      return
+
+    try
+    {
+      for (let i = 0; i < sessionStorage.length; ++i)
+        {
+          const key = sessionStorage.key (i)
+          if (key == null || !(key.startsWith (SESSION_PREFIX)))
+            continue
+
+          const raw = sessionStorage.getItem (key)
+          if (raw == null)
+            continue
+          try
+          {
+            const value = JSON.parse (raw) as { savedAt?: string }
+            if (typeof value.savedAt !== 'string' || isExpiredSession (value.savedAt))
+              {
+                sessionStorage.removeItem (key)
+                --i
+              }
+          }
+          catch
+          {
+            sessionStorage.removeItem (key)
+            --i
+          }
+        }
+    }
+    catch
+    {
+      onError?.('保存済みデータを整理できませんでした．')
+    }
+}
+
+
+export const loadPostImportSourceDraft = (
+    onError?: StorageErrorHandler,
+): { source: string } => {
+    const raw = readStorage (SOURCE_DRAFT_KEY, onError)
+    if (raw == null)
+      return { source: '' }
+
+    try
+    {
+      const value = JSON.parse (raw) as { source?: string }
+      return { source: typeof value.source === 'string' ? value.source : '' }
+    }
+    catch
+    {
+      return { source: '' }
+    }
+}
+
+
+export const savePostImportSourceDraft = (
+    source:    string,
+    onError?:  StorageErrorHandler,
+): boolean =>
+    writeStorage (SOURCE_DRAFT_KEY, JSON.stringify ({ source }), onError)
+
+
+export const clearPostImportSourceDraft = (
+    onError?: StorageErrorHandler,
+) => {
+    removeStorage (SOURCE_DRAFT_KEY, onError)
+}
+
+
+export const savePostImportSession = (
+    sessionId: string,
+    session:   Omit<PostImportSession, 'version' | 'savedAt'>,
+    onError?:  StorageErrorHandler,
+): boolean =>
+    writeStorage (
+        sessionKey (sessionId),
+        JSON.stringify ({
+            ...session,
+            version: SESSION_VERSION,
+            savedAt: new Date ().toISOString () }),
+        onError)
+
+
+export const loadPostImportSession = (
+    sessionId: string,
+    onError?: StorageErrorHandler,
+): PostImportSession | null => {
+    const raw = readStorage (sessionKey (sessionId), onError)
+    if (raw == null)
+      return null
+
+    try
+    {
+      const value = JSON.parse (raw) as Partial<PostImportSession>
+      if (value.version !== SESSION_VERSION || !(Array.isArray (value.rows)))
+        return null
+      if (typeof value.savedAt !== 'string' || isExpiredSession (value.savedAt))
+        {
+          removeStorage (sessionKey (sessionId), onError)
+          return null
+        }
+
+      const rows = value.rows.map (sanitiseRow)
+      if (rows.some (row => row == null))
+        return null
+
+      return {
+          version: SESSION_VERSION,
+          savedAt: value.savedAt,
+          source: typeof value.source === 'string' ? value.source : '',
+          rows: rows as PostImportRow[],
+          repairMode: value.repairMode === 'failed' ? 'failed' : 'all' }
+    }
+    catch
+    {
+      return null
+    }
+}

frontend/src/lib/postImportTypes.ts

@@ -0,0 +1,85 @@
+export type PostImportOrigin = 'automatic' | 'manual'
+export type PostImportRepairMode = 'all' | 'failed'
+export type PostImportStatus =
+    'pending'
+    | 'created'
+    | 'skipped'
+    | 'failed'
+export type PostImportSkipReason = 'existing'
+export type PostImportResultStatus = 'created' | 'skipped' | 'failed'
+export type PostImportAttributeValue = string | number
+
+export type PostImportResetSnapshot = {
+    url:         string
+    attributes:  Record<string, PostImportAttributeValue>
+    provenance:  Record<string, PostImportOrigin>
+    tagSources:  Record<PostImportOrigin, string>
+    fieldWarnings: Record<string, string[]>
+    baseWarnings: string[]
+    metadataUrl?: string }
+
+export type PostImportRow = {
+    sourceRow:         number
+    url:               string
+    attributes:        Record<string, PostImportAttributeValue>
+    fieldWarnings:     Record<string, string[]>
+    baseWarnings:      string[]
+    validationErrors:  Record<string, string[]>
+    importErrors?:     Record<string, string[]>
+    provenance:        Record<string, PostImportOrigin>
+    tagSources?:       Record<PostImportOrigin, string>
+    status:            'ready' | 'warning' | 'error'
+    skipReason?:       PostImportSkipReason
+    existingPostId?:   number
+    metadataUrl?:      string
+    resetSnapshot:     PostImportResetSnapshot
+    createdPostId?:    number
+    importStatus?:     PostImportStatus
+    recoverable?:      boolean }
+
+export type PostImportResultRow =
+    | {
+	sourceRow: number
+	status:    'created'
+	post:      { id: number }
+	fieldWarnings?: Record<string, string[]>
+	baseWarnings?:  string[]
+	errors?:   Record<string, string[]> }
+    | {
+	sourceRow:      number
+	status:         'skipped'
+	existingPostId: number
+	fieldWarnings?: Record<string, string[]>
+	baseWarnings?:  string[]
+	errors?:        Record<string, string[]> }
+    | {
+	sourceRow: number
+	status:    'failed'
+	fieldWarnings?: Record<string, string[]>
+	baseWarnings?:  string[]
+	errors?:   Record<string, string[]>
+	recoverable?: boolean }
+
+export type PostImportSession = {
+    version:    number
+    savedAt:    string
+    source:     string
+    rows:       PostImportRow[]
+    repairMode: PostImportRepairMode }
+
+export type PostImportSourceIssue = {
+    sourceRow: number
+    message:   string
+    url:       string }
+
+export type PostImportEditableDraft = {
+    url:                   string
+    title:                 string
+    thumbnailBase:         string
+    originalCreatedFrom:   string
+    originalCreatedBefore: string
+    duration:              string
+    tags:                  string
+    parentPostIds:         string }
+
+export type StorageErrorHandler = (message: string) => void

frontend/src/pages/posts/PostImportResultPage.test.tsx

@@ -0,0 +1,402 @@
+import { act, fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { HelmetProvider } from 'react-helmet-async'
+import { MemoryRouter, Route, Routes } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import {
+  loadPostImportSession,
+  savePostImportSession,
+} from '@/lib/postImportSession'
+import PostImportResultPage from '@/pages/posts/PostImportResultPage'
+import { buildUser } from '@/test/factories'
+import { buildPostImportRow } from '@/test/postImportFactories'
+import { originalCreatedAtString } from '@/lib/utils'
+
+import type { PostImportRow } from '@/lib/postImportSession'
+import type { DialogueFormAction, DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+  apiPost: vi.fn (),
+}))
+
+const toastApi = vi.hoisted (() => ({
+  toast: vi.fn (),
+}))
+
+const dialogue = vi.hoisted (() => ({
+  form: vi.fn (() => Promise.resolve ()),
+}))
+
+vi.mock ('@/components/ui/use-toast', () => toastApi)
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/lib/dialogues/useDialogue', () => ({
+  default: () => dialogue,
+}))
+
+describe ('PostImportResultPage', () => {
+  beforeEach (() => {
+    sessionStorage.clear ()
+    vi.clearAllMocks ()
+    globalThis.URL.createObjectURL = vi.fn (() => 'blob:preview')
+    globalThis.URL.revokeObjectURL = vi.fn ()
+    api.apiGet.mockResolvedValue (new Blob (['img'], { type: 'image/png' }))
+  })
+
+  it ('shows edit and retry only for recoverable failures and shows warnings', () => {
+    savePostImportSession ('result-session', {
+      source: '',
+      repairMode: 'failed',
+      rows: [
+        buildPostImportRow ({
+          sourceRow: 1,
+          attributes: { title: 'recoverable row' },
+          importStatus: 'failed',
+          recoverable: true,
+          importErrors: { base: ['recoverable failed'] } }),
+        buildPostImportRow ({
+          sourceRow: 2,
+          attributes: { title: 'hard failed row' },
+          importStatus: 'failed',
+          importErrors: { base: ['hard failed'] } }),
+        buildPostImportRow ({
+          sourceRow: 3,
+          attributes: {
+            title: 'created row',
+            originalCreatedFrom: '2024-01-01T00:00:00Z',
+            originalCreatedBefore: '2024-01-02T00:00:00Z' },
+          importStatus: 'created',
+          createdPostId: 3,
+          fieldWarnings: {
+            thumbnailBase: ['サムネール画像を取得できませんでした．'] } })] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-session/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    expect (screen.getAllByRole ('button', { name: '編輯' })).toHaveLength (1)
+    expect (screen.getAllByRole ('button', { name: '再試行' })).toHaveLength (1)
+    expect (screen.getByText ('サムネール画像を取得できませんでした．'))
+        .toBeInTheDocument ()
+    expect (screen.getByText (
+        originalCreatedAtString ('2024-01-01T00:00:00Z', '2024-01-02T00:00:00Z'),
+    )).toBeInTheDocument ()
+  })
+
+  it ('shows hour-precision original-created ranges with the shared utility output', () => {
+    const from = '2024-01-01T12:00:00Z'
+    const before = '2024-01-01T13:00:00Z'
+    savePostImportSession ('result-hour-range', {
+      source: '',
+      repairMode: 'all',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        importStatus: 'created',
+        createdPostId: 1,
+        attributes: {
+          title: 'created row',
+          originalCreatedFrom: from,
+          originalCreatedBefore: before } })] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-hour-range/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    expect (screen.getByText (originalCreatedAtString (from, before))).toBeInTheDocument ()
+  })
+
+  it ('keeps recoverable pending rows actionable and hides actions for hard failures', () => {
+    savePostImportSession ('result-pending', {
+      source: '',
+      repairMode: 'failed',
+      rows: [
+        buildPostImportRow ({
+          sourceRow: 1,
+          importStatus: 'pending',
+          recoverable: true,
+          validationErrors: { title: ['invalid'] } }),
+        buildPostImportRow ({
+          sourceRow: 2,
+          importStatus: 'pending',
+          recoverable: true }),
+        buildPostImportRow ({
+          sourceRow: 3,
+          importStatus: 'failed',
+          importErrors: { base: ['hard failed'] } })] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-pending/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    expect (screen.getAllByRole ('button', { name: '編輯' })).toHaveLength (1)
+    expect (screen.getAllByRole ('button', { name: '再試行' })).toHaveLength (1)
+    expect (screen.getByText ('invalid')).toBeInTheDocument ()
+    expect (screen.getByText ('hard failed')).toBeInTheDocument ()
+  })
+
+  it ('disables editing, retry, and navigation while retry is running', async () => {
+    let resolveValidation: ((value: { rows: PostImportRow[] }) => void) | null = null
+    savePostImportSession ('result-retry-busy', {
+      source: '',
+      repairMode: 'failed',
+      rows: [
+        buildPostImportRow ({
+          sourceRow: 1,
+          importStatus: 'failed',
+          recoverable: true,
+          importErrors: { base: ['failed'] } }),
+        buildPostImportRow ({
+          sourceRow: 2,
+          importStatus: 'failed',
+          recoverable: true,
+          importErrors: { base: ['failed'] } })] })
+    api.apiPost.mockImplementationOnce (() =>
+        new Promise<{ rows: PostImportRow[] }> (resolve => {
+          resolveValidation = resolve
+        }))
+    api.apiPost.mockResolvedValueOnce ({
+      created: 0,
+      skipped: 0,
+      failed: 0,
+      rows: [] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-retry-busy/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getAllByRole ('button', { name: '再試行' })[0])
+
+    await waitFor (() => {
+      screen.getAllByRole ('button', { name: '編輯' }).forEach (button => {
+        expect (button).toBeDisabled ()
+      })
+      screen.getAllByRole ('button', { name: '再試行' }).forEach (button => {
+        expect (button).toBeDisabled ()
+      })
+      expect (screen.getByRole ('button', { name: '確認画面へ戻る' })).toBeDisabled ()
+      expect (screen.getByRole ('button', { name: '新しい URL リストを入力' })).toBeDisabled ()
+    })
+
+    resolveValidation?.({ rows: [buildPostImportRow ({ sourceRow: 1 })] })
+  })
+
+  it ('persists retry success to sessionStorage', async () => {
+    savePostImportSession ('result-retry-success', {
+      source: '',
+      repairMode: 'failed',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        importStatus: 'failed',
+        recoverable: true,
+        importErrors: { base: ['failed'] } })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          created: 1,
+          skipped: 0,
+          failed: 0,
+          rows: [{
+            sourceRow: 1,
+            status: 'created',
+            post: { id: 10 } }] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-retry-success/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '再試行' }))
+
+    await waitFor (() => {
+      expect (loadPostImportSession ('result-retry-success')?.rows[0]?.importStatus)
+          .toBe ('created')
+    })
+  })
+
+  it ('keeps edited recoverable rows in session and retries with the edited values', async () => {
+    savePostImportSession ('result-edit-retry', {
+      source: '',
+      repairMode: 'failed',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        attributes: { title: 'old title' },
+        importStatus: 'failed',
+        recoverable: true,
+        importErrors: { base: ['failed'] } })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            attributes: { title: 'edited title' },
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            attributes: { title: 'edited title' },
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          created: 1,
+          skipped: 0,
+          failed: 0,
+          rows: [{
+            sourceRow: 1,
+            status: 'created',
+            post: { id: 11 } }] })
+    dialogue.form.mockImplementationOnce (async options => {
+      let actions: DialogueFormAction[] = []
+      const controls: DialogueFormControls = {
+        close: vi.fn (),
+        confirm: vi.fn (),
+        setActions: next => {
+          actions = next
+        } }
+
+      render (options.body (controls))
+      await waitFor (() => expect (actions.length).toBe (2))
+      fireEvent.change (screen.getByDisplayValue ('old title'), {
+        target: { value: 'edited title' } })
+      await act (async () => {
+        await actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+      })
+    })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-edit-retry/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '編輯' }))
+
+    await waitFor (() => {
+      const saved = loadPostImportSession ('result-edit-retry')
+      expect (saved?.rows[0]?.attributes.title).toBe ('edited title')
+      expect (saved?.rows[0]?.importStatus).toBe ('pending')
+    })
+
+    fireEvent.click (screen.getByRole ('button', { name: '再試行' }))
+
+    await waitFor (() => {
+      expect (api.apiPost.mock.calls[2]?.[1]?.rows?.[0]?.attributes?.title)
+          .toBe ('edited title')
+    })
+  })
+
+  it ('persists restored failed state when retry fails', async () => {
+    savePostImportSession ('result-retry-failure', {
+      source: '',
+      repairMode: 'failed',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        importStatus: 'failed',
+        recoverable: true,
+        importErrors: { base: ['failed'] } })] })
+    api.apiPost.mockRejectedValueOnce (new Error ('network error'))
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-retry-failure/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '再試行' }))
+
+    await waitFor (() => {
+      const saved = loadPostImportSession ('result-retry-failure')
+      expect (saved?.rows[0]?.importStatus).toBe ('failed')
+      expect (saved?.rows[0]?.recoverable).toBe (true)
+    })
+  })
+
+  it ('restores the failed row when the retry import response is incomplete', async () => {
+    savePostImportSession ('result-retry-missing-row', {
+      source: '',
+      repairMode: 'failed',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        importStatus: 'failed',
+        recoverable: true,
+        importErrors: { base: ['failed'] } })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          created: 1,
+          skipped: 0,
+          failed: 0,
+          rows: [] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/result-retry-missing-row/result']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<PostImportResultPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '再試行' }))
+
+    await waitFor (() => {
+      const saved = loadPostImportSession ('result-retry-missing-row')
+      expect (saved?.rows[0]?.importStatus).toBe ('failed')
+      expect (toastApi.toast).toHaveBeenCalledWith (
+          expect.objectContaining ({ title: '登録結果が不完全でした' }))
+    })
+  })
+})

frontend/src/pages/posts/PostImportResultPage.tsx

@@ -0,0 +1,544 @@
+import { useEffect, useMemo, useRef, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useNavigate, useParams } from 'react-router-dom'
+
+import FieldError from '@/components/common/FieldError'
+import FieldWarning from '@/components/common/FieldWarning'
+import PageTitle from '@/components/common/PageTitle'
+import PrefetchLink from '@/components/PrefetchLink'
+import MainArea from '@/components/layout/MainArea'
+import PostImportRowForm from '@/components/posts/import/PostImportRowForm'
+import PostImportStatusBadge from '@/components/posts/import/PostImportStatusBadge'
+import { displayPostImportStatus } from '@/components/posts/import/postImportRowStatus'
+import { Button } from '@/components/ui/button'
+import { toast } from '@/components/ui/use-toast'
+import { SITE_TITLE } from '@/config'
+import { apiPost } from '@/lib/api'
+import useDialogue from '@/lib/dialogues/useDialogue'
+import { canEditContent } from '@/lib/users'
+import { clearPostImportSourceDraft,
+	 buildNextEditedRow,
+	 canEditResultRow,
+	 canRetryResultRow,
+	 hasExactSourceRows,
+	 initialisePreviewRows,
+	 loadPostImportSession,
+	 mergeImportResults,
+	 mergeValidatedImportRow,
+	 replaceImportRow,
+	 resultRepairMode,
+	 resultRowMessages,
+	 resultRowWarnings,
+	 resultSummaryCounts,
+	 retryImportRow,
+	 savePostImportSession } from '@/lib/postImportSession'
+import { originalCreatedAtString } from '@/lib/utils'
+import Forbidden from '@/pages/Forbidden'
+
+import type { FC } from 'react'
+
+import type { PostImportRowDraft } from '@/components/posts/import/PostImportRowForm'
+import type { PostImportResultRow, PostImportRow } from '@/lib/postImportSession'
+import type { PostImportSession } from '@/lib/postImportSession'
+import type { User } from '@/types'
+
+type Props = { user: User | null }
+
+
+const PostImportResultPage: FC<Props> = ({ user }) => {
+  const editable = canEditContent (user)
+  const dialogue = useDialogue ()
+  const navigate = useNavigate ()
+  const { sessionId } = useParams ()
+
+  const [session, setSession] = useState<PostImportSession | null> (null)
+  const [missing, setMissing] = useState (false)
+  const [loadingRow, setLoadingRow] = useState<number | null> (null)
+  const [, setEditingRow] = useState<PostImportRow | null> (null)
+  const sessionRef = useRef<PostImportSession | null> (null)
+
+  useEffect (() => {
+    if (sessionId == null)
+      return
+
+    const loaded = loadPostImportSession (sessionId, message =>
+	toast ({ title: '取込状態を復元できませんでした', description: message }))
+    setSession (loaded)
+    setMissing (loaded == null)
+  }, [sessionId])
+
+  useEffect (() => {
+    if (sessionId == null || session == null)
+      return
+
+    savePostImportSession (sessionId, session, message =>
+	toast ({ title: '取込状態を保存できませんでした', description: message }))
+  }, [session, sessionId])
+
+  useEffect (() => {
+    sessionRef.current = session
+  }, [session])
+
+  const counts = useMemo (
+      () => resultSummaryCounts (session?.rows ?? []),
+      [session])
+  const busy = loadingRow != null
+
+  const persistSession = (nextSession: PostImportSession) => {
+    if (sessionId == null)
+      return
+
+    savePostImportSession (sessionId, nextSession, message =>
+        toast ({ title: '取込状態を保存できませんでした', description: message }))
+  }
+
+  const saveDraft = async (
+      row: PostImportRow,
+      { draft, resetRequested }: {
+	  draft:            PostImportRowDraft
+	  resetRequested:   boolean },
+  ): Promise<{ saved: boolean
+	       row:   PostImportRow | null }> => {
+    const currentSession = sessionRef.current
+    if (currentSession == null)
+      return { saved: false, row: null }
+    if (!(canEditResultRow (row)))
+      return { saved: false, row: null }
+
+    const baseRow =
+	resetRequested
+	? { ...row,
+	    url: row.resetSnapshot.url,
+	    attributes: { ...row.resetSnapshot.attributes },
+	    provenance: { ...row.resetSnapshot.provenance },
+	    tagSources: { ...row.resetSnapshot.tagSources },
+	    fieldWarnings: Object.fromEntries (
+		Object.entries (row.resetSnapshot.fieldWarnings)
+		    .map (([key, values]) => [key, [...values]])),
+	    baseWarnings: [...row.resetSnapshot.baseWarnings],
+	    metadataUrl: row.resetSnapshot.metadataUrl }
+	: row
+    const urlChanged = draft.url !== baseRow.url
+    const nextRow = buildNextEditedRow (baseRow, draft, urlChanged)
+
+    const nextRows = currentSession.rows.map (row =>
+		row.sourceRow === baseRow.sourceRow
+		? nextRow
+		: row)
+    try
+    {
+      const validated = await apiPost<{ rows: PostImportRow[] }> ('/posts/import/validate', {
+	  rows:
+	      nextRows
+	      .filter (row => row.importStatus !== 'created')
+	      .map (row => ({ sourceRow: row.sourceRow,
+			      url: row.url,
+			      attributes: row.attributes,
+			      provenance: row.provenance,
+			      tagSources: row.tagSources,
+			      metadataUrl: row.metadataUrl })),
+	  changed_row: urlChanged ? baseRow.sourceRow : -1 })
+      const validatedRows = initialisePreviewRows (validated.rows)
+      const target = validatedRows.find (
+          validatedRow => validatedRow.sourceRow === baseRow.sourceRow)
+      const latestSession = sessionRef.current
+      if (latestSession == null)
+        return { saved: false, row: null }
+      if (target == null)
+        {
+          const restoredRows = replaceImportRow (latestSession.rows, row)
+          const restoredSession = {
+              ...latestSession,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          toast ({ title: '行の再検証結果が不完全でした' })
+          return { saved: false, row: null }
+        }
+      const editedRows = replaceImportRow (latestSession.rows, nextRow)
+      const rows = mergeValidatedImportRow (editedRows, target)
+      const nextSession = {
+          ...latestSession,
+          rows,
+          repairMode: resultRepairMode (rows) }
+      sessionRef.current = nextSession
+      setSession (nextSession)
+      persistSession (nextSession)
+      const mergedTarget =
+          rows.find (mergedRow => mergedRow.sourceRow === baseRow.sourceRow)
+          ?? target
+      if (Object.keys (mergedTarget.validationErrors).length > 0)
+        return { saved: false, row: mergedTarget }
+      return { saved: true, row: null }
+    }
+    catch
+    {
+      toast ({ title: '行の再検証に失敗しました' })
+      return { saved: false, row: null }
+    }
+  }
+
+  const openEditingDialogue = async (row: PostImportRow) => {
+    const saveRowDraft = (
+	{ draft, resetRequested }: {
+	    draft:          PostImportRowDraft
+	    resetRequested: boolean },
+    ) =>
+	saveDraft (row, { draft, resetRequested })
+
+    await dialogue.form ({
+	title: '投稿を編輯',
+	description: `投稿 ${ row.sourceRow } の内容を確認し、必要な項目を編輯してください．`,
+	cancelText: '取消',
+	size: 'large',
+	body: controls => (
+	    <PostImportRowForm
+		row={row}
+		controls={controls}
+		onSave={saveRowDraft}/>) })
+  }
+
+  const editRow = async (row: PostImportRow) => {
+    setEditingRow (row)
+    try
+    {
+      await openEditingDialogue (row)
+    }
+    finally
+    {
+      setEditingRow (current =>
+          current?.sourceRow === row.sourceRow
+          ? null
+          : current)
+    }
+  }
+
+  const retry = async (sourceRow: number) => {
+    if (session == null || sessionId == null || loadingRow != null)
+      return
+
+    const initialSession = sessionRef.current
+    if (initialSession == null)
+      return
+
+    setLoadingRow (sourceRow)
+    const originalRow = initialSession.rows.find (row => row.sourceRow === sourceRow)
+    if (originalRow == null)
+      {
+        setLoadingRow (null)
+        return
+      }
+    try
+    {
+      const pendingRows = retryImportRow (initialSession.rows, sourceRow)
+      const pendingSession = { ...initialSession, rows: pendingRows }
+      sessionRef.current = pendingSession
+      setSession (pendingSession)
+      persistSession (pendingSession)
+      const requestedRows = pendingRows.filter (row => row.importStatus !== 'created')
+      const validated = await apiPost<{ rows: PostImportRow[] }> ('/posts/import/validate', {
+          rows: requestedRows.map (row => ({
+                  sourceRow: row.sourceRow,
+                  url: row.url,
+                  attributes: row.attributes,
+                  provenance: row.provenance,
+                  tagSources: row.tagSources,
+                  metadataUrl: row.metadataUrl })),
+          changed_row: -1 })
+      const validatedRows = initialisePreviewRows (validated.rows)
+      if (!(hasExactSourceRows (requestedRows.map (row => row.sourceRow), validatedRows)))
+        {
+          const latest = sessionRef.current ?? pendingSession
+          const restoredRows = replaceImportRow (latest.rows, originalRow)
+          const restoredSession = {
+              ...latest,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          persistSession (restoredSession)
+          toast ({ title: '再検証結果が不完全でした' })
+          return
+        }
+      const validatedTarget = validatedRows.find (
+          row => row.sourceRow === sourceRow)
+      if (validatedTarget == null)
+        {
+          const latest = sessionRef.current ?? pendingSession
+          const restoredRows = replaceImportRow (latest.rows, originalRow)
+          const restoredSession = {
+              ...latest,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          persistSession (restoredSession)
+          toast ({ title: '再検証結果が不完全でした' })
+          return
+        }
+      const latestAfterValidate = sessionRef.current ?? pendingSession
+      const mergedValidatedRows = mergeValidatedImportRow (
+          latestAfterValidate.rows,
+          validatedTarget)
+      const nextSession = {
+          ...latestAfterValidate,
+          rows: mergedValidatedRows,
+          repairMode: resultRepairMode (mergedValidatedRows) }
+      sessionRef.current = nextSession
+      setSession (nextSession)
+      persistSession (nextSession)
+      const target = mergedValidatedRows.find (row => row.sourceRow === sourceRow)
+      if (target == null)
+        {
+          const restoredRows = replaceImportRow (latestAfterValidate.rows, originalRow)
+          const restoredSession = {
+              ...latestAfterValidate,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          persistSession (restoredSession)
+          toast ({ title: '再検証結果が不完全でした' })
+          return
+        }
+      if (Object.keys (target.validationErrors ?? { }).length > 0)
+        {
+          const saved = savePostImportSession (sessionId, nextSession, message =>
+              toast ({ title: '取込状態を保存できませんでした', description: message }))
+          if (saved)
+            void editRow (target)
+          return
+        }
+
+      const result = await apiPost<{
+          created: number
+          skipped: number
+          failed:  number
+          rows:    PostImportResultRow[] }> ('/posts/import', {
+              rows: [{
+                  sourceRow: target.sourceRow,
+                  url: target.url,
+                  attributes: target.attributes,
+                  provenance: target.provenance,
+                  tagSources: target.tagSources,
+                  metadataUrl: target.metadataUrl }] })
+      if (!(hasExactSourceRows ([sourceRow], result.rows)))
+        {
+          const latest = sessionRef.current ?? nextSession
+          const restoredRows = replaceImportRow (latest.rows, originalRow)
+          const restoredSession = {
+              ...latest,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          persistSession (restoredSession)
+          toast ({ title: '登録結果が不完全でした' })
+          return
+        }
+      const latestAfterImport = sessionRef.current ?? nextSession
+      const mergedRows = mergeImportResults (latestAfterImport.rows, result.rows)
+      const recoverableRows = result.rows.filter (row =>
+          row.status === 'failed'
+          && row.recoverable
+          && Object.keys (row.errors ?? { }).length > 0)
+      const nextRows = mergedRows.map ((row): PostImportRow => {
+        const recoverable = recoverableRows.find (
+            recoverableRow => recoverableRow.sourceRow === row.sourceRow)
+        if (recoverable == null)
+          return row
+        return {
+            ...row,
+            importStatus: 'pending',
+            recoverable: true,
+            validationErrors: recoverable.errors ?? { },
+            importErrors: undefined }
+      })
+      const recoverableTarget = nextRows.find (row => row.sourceRow === sourceRow)
+      const resultSession = {
+          ...nextSession,
+          rows: nextRows,
+          repairMode: resultRepairMode (nextRows) }
+      sessionRef.current = resultSession
+      setSession (resultSession)
+      persistSession (resultSession)
+      if (recoverableTarget != null
+          && Object.keys (recoverableTarget.validationErrors).length > 0)
+        {
+          const saved = savePostImportSession (sessionId, resultSession, message =>
+              toast ({ title: '取込状態を保存できませんでした', description: message }))
+          if (saved)
+            void editRow (recoverableTarget)
+          return
+        }
+    }
+    catch
+    {
+      const latest = sessionRef.current
+      if (latest != null)
+        {
+          const restoredRows = replaceImportRow (latest.rows, originalRow)
+          const restoredSession = {
+              ...latest,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          persistSession (restoredSession)
+        }
+      toast ({ title: '再試行に失敗しました' })
+    }
+    finally
+    {
+      setLoadingRow (null)
+    }
+  }
+
+  const openRepair = (sourceRow: number) => {
+    const currentSession = sessionRef.current
+    if (currentSession == null || sessionId == null || loadingRow != null)
+      return
+
+    const nextSession = { ...currentSession, repairMode: 'failed' as const }
+    sessionRef.current = nextSession
+    setSession (nextSession)
+    const saved = savePostImportSession (sessionId, nextSession, message =>
+	toast ({ title: '取込状態を保存できませんでした', description: message }))
+    if (!(saved))
+      return
+    const row = nextSession.rows.find (rowValue => rowValue.sourceRow === sourceRow)
+    if (row != null)
+      void editRow (row)
+  }
+
+  if (!(editable))
+    return <Forbidden/>
+
+  if (missing || sessionId == null || session == null)
+    {
+      return (
+	  <MainArea>
+	    <div className="mx-auto max-w-4xl space-y-4 p-4">
+	      <PageTitle>投稿インポート結果</PageTitle>
+	      <FieldError messages={['取込状態が見つかりません．']}/>
+	      <Button type="button" onClick={() => navigate ('/posts/import')}>
+		URL リスト入力へ戻る
+	      </Button>
+	    </div>
+	  </MainArea>)
+    }
+
+  return (
+      <MainArea>
+	<Helmet>
+	  <title>{`投稿インポート結果 | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<div className="mx-auto max-w-5xl space-y-4 p-4">
+	  <PageTitle>登録結果</PageTitle>
+
+	  <div className="text-sm text-neutral-700 dark:text-neutral-200">
+	    登録成功 {counts.created}件　スキップ {counts.skipped}件　失敗 {counts.failed}件
+	  </div>
+
+	  <div className="space-y-3">
+	    {session.rows.map (row => {
+	      const displayStatus = displayPostImportStatus (row)
+	      const canEdit = canEditResultRow (row)
+	      const canRetry = canRetryResultRow (row)
+	      return (
+		  <div
+		      key={row.sourceRow}
+		      className="rounded-lg border p-4 transition-shadow hover:shadow-sm">
+		    <div className="flex flex-col gap-3 md:flex-row md:items-start
+				    md:justify-between">
+		      <div className="space-y-2">
+			<div className="flex flex-wrap items-center gap-2">
+			  <span className="text-sm font-medium">行 {row.sourceRow}</span>
+			  {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
+			</div>
+			<div className="text-sm text-neutral-700 dark:text-neutral-200">
+			  {String (row.attributes.title ?? '') || row.url}
+			</div>
+			<div className="text-xs text-neutral-500 dark:text-neutral-400">
+			  {row.url}
+			</div>
+			<div className="text-xs text-neutral-500 dark:text-neutral-400">
+			  {String (row.attributes.tags ?? '') || 'タグなし'}
+			</div>
+			<div className="text-xs text-neutral-500 dark:text-neutral-400">
+			  {originalCreatedAtString (
+			      row.attributes.originalCreatedFrom?.toString () ?? null,
+			      row.attributes.originalCreatedBefore?.toString () ?? null)}
+			  {row.attributes.duration ? ` / ${ row.attributes.duration }` : ''}
+			</div>
+			<FieldWarning messages={resultRowWarnings (row)}/>
+			<FieldError messages={resultRowMessages (row)}/>
+		      </div>
+
+		      <div className="flex flex-col gap-2 sm:flex-row">
+			{(row.createdPostId != null || row.existingPostId != null) && (
+			    <Button type="button" variant="outline" asChild>
+			      <PrefetchLink
+				  to={`/posts/${ row.createdPostId ?? row.existingPostId }`}>
+				投稿を開く
+			      </PrefetchLink>
+			    </Button>)}
+			{canEdit && (
+			    <Button
+				type="button"
+				variant="outline"
+				onClick={() => openRepair (row.sourceRow)}
+				disabled={busy}>
+			      編輯
+			    </Button>)}
+			{canRetry && (
+			    <Button
+				type="button"
+				onClick={() => retry (row.sourceRow)}
+				disabled={busy}>
+			      再試行
+			    </Button>)}
+		      </div>
+		    </div>
+		  </div>)})}
+	    </div>
+
+	    <div className="flex flex-col gap-2 sm:flex-row">
+	      <Button
+		  type="button"
+		  variant="outline"
+		  disabled={busy}
+		  onClick={() => {
+		      const currentSession = sessionRef.current
+		      if (currentSession == null)
+			return
+		      const nextSession = { ...currentSession, repairMode: 'all' as const }
+		      sessionRef.current = nextSession
+		      setSession (nextSession)
+		      const saved = savePostImportSession (sessionId, nextSession, message =>
+			  toast ({ title: '取込状態を保存できませんでした', description: message }))
+		      if (!(saved))
+			return
+		      navigate (`/posts/import/${ sessionId }/review`)
+		  }}>
+		確認画面へ戻る
+	      </Button>
+	      <Button
+		  type="button"
+		  variant="outline"
+		  disabled={busy}
+		  onClick={() => {
+		      clearPostImportSourceDraft (message =>
+			  toast ({ title: '入力内容を削除できませんでした', description: message }))
+		      navigate ('/posts/import')
+		  }}>
+		新しい URL リストを入力
+	      </Button>
+	    </div>
+	  </div>
+	</MainArea>)
+}
+
+export default PostImportResultPage

frontend/src/pages/posts/PostImportReviewPage.test.tsx

@@ -0,0 +1,295 @@
+import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { HelmetProvider } from 'react-helmet-async'
+import { MemoryRouter, Route, Routes } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { loadPostImportSession, savePostImportSession } from '@/lib/postImportSession'
+import PostImportReviewPage from '@/pages/posts/PostImportReviewPage'
+import { buildUser } from '@/test/factories'
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+import type { DialogueFormAction, DialogueFormControls } from '@/lib/dialogues/useDialogue'
+import type { PostImportRow } from '@/lib/postImportSession'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+  apiPost: vi.fn (),
+}))
+
+const toastApi = vi.hoisted (() => ({
+  toast: vi.fn (),
+}))
+
+const dialogue = vi.hoisted (() => ({
+  form: vi.fn (() => Promise.resolve ()),
+}))
+
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/components/ui/use-toast', () => toastApi)
+vi.mock ('@/lib/dialogues/useDialogue', () => ({
+  default: () => dialogue,
+}))
+
+describe ('PostImportReviewPage', () => {
+  beforeEach (() => {
+    sessionStorage.clear ()
+    vi.clearAllMocks ()
+    globalThis.URL.createObjectURL = vi.fn (() => 'blob:preview')
+    globalThis.URL.revokeObjectURL = vi.fn ()
+    api.apiGet.mockResolvedValue (new Blob (['img'], { type: 'image/png' }))
+  })
+
+  it ('navigates to the result route after an initial recoverable failure', async () => {
+    savePostImportSession ('review-session', {
+      source: 'https://example.com/post',
+      repairMode: 'all',
+      rows: [buildPostImportRow ({ sourceRow: 1 })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({ sourceRow: 1 })] })
+        .mockResolvedValueOnce ({
+          created: 0,
+          skipped: 0,
+          failed: 1,
+          rows: [{
+            sourceRow: 1,
+            status: 'failed',
+            recoverable: true,
+            errors: { title: ['invalid'] } }] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-session/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<div>RESULT ROUTE</div>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '取込実行' }))
+
+    await waitFor (() => {
+      expect (screen.getByText ('RESULT ROUTE')).toBeInTheDocument ()
+    })
+    expect (dialogue.form).not.toHaveBeenCalled ()
+  })
+
+  it ('disables row editing and navigation while batch import is running', async () => {
+    let resolveValidation: ((value: { rows: PostImportRow[] }) => void) | null = null
+    savePostImportSession ('review-loading', {
+      source: 'https://example.com/post',
+      repairMode: 'all',
+      rows: [buildPostImportRow ({ sourceRow: 1 })] })
+    api.apiPost.mockImplementationOnce (() =>
+        new Promise<{ rows: PostImportRow[] }> (resolve => {
+          resolveValidation = resolve
+        }))
+    api.apiPost.mockResolvedValueOnce ({
+      created: 0,
+      skipped: 0,
+      failed: 0,
+      rows: [] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-loading/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '取込実行' }))
+
+    await waitFor (() => {
+      expect (screen.getByRole ('button', { name: '編輯' })).toBeDisabled ()
+      expect (screen.getByRole ('button', { name: 'URL リスト入力へ戻る' })).toBeDisabled ()
+      expect (screen.getByRole ('button', { name: '取込実行' })).toBeDisabled ()
+    })
+
+    resolveValidation?.({ rows: [buildPostImportRow ({ sourceRow: 1 })] })
+  })
+
+  it ('does not call import when validation omits a requested source row', async () => {
+    savePostImportSession ('review-missing-row', {
+      source: 'https://example.com/post-1\nhttps://example.com/post-2',
+      repairMode: 'all',
+      rows: [
+        buildPostImportRow ({ sourceRow: 1 }),
+        buildPostImportRow ({ sourceRow: 2 })] })
+    api.apiPost.mockResolvedValueOnce ({
+      rows: [buildPostImportRow ({ sourceRow: 1 })] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-missing-row/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '取込実行' }))
+
+    await waitFor (() => {
+      expect (toastApi.toast).toHaveBeenCalledWith (
+          expect.objectContaining ({ title: '再検証結果が不完全でした' }))
+    })
+    expect (api.apiPost).toHaveBeenCalledTimes (1)
+  })
+
+  it ('does not navigate to result when import omits a requested source row', async () => {
+    savePostImportSession ('review-missing-import-row', {
+      source: 'https://example.com/post',
+      repairMode: 'all',
+      rows: [buildPostImportRow ({ sourceRow: 1 })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({ sourceRow: 1 })] })
+        .mockResolvedValueOnce ({
+          created: 1,
+          skipped: 0,
+          failed: 0,
+          rows: [] })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-missing-import-row/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<div>RESULT ROUTE</div>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '取込実行' }))
+
+    await waitFor (() => {
+      expect (toastApi.toast).toHaveBeenCalledWith (
+          expect.objectContaining ({ title: '登録結果が不完全でした' }))
+    })
+    expect (screen.queryByText ('RESULT ROUTE')).not.toBeInTheDocument ()
+  })
+
+  it ('keeps edited recoverable rows in session before the next batch submit', async () => {
+    savePostImportSession ('review-edit-retry', {
+      source: 'https://example.com/post',
+      repairMode: 'failed',
+      rows: [buildPostImportRow ({
+        sourceRow: 1,
+        attributes: { title: 'old title' },
+        importStatus: 'failed',
+        recoverable: true,
+        importErrors: { base: ['failed'] } })] })
+    api.apiPost
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            attributes: { title: 'edited title' },
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          rows: [buildPostImportRow ({
+            sourceRow: 1,
+            attributes: { title: 'edited title' },
+            importStatus: 'pending',
+            recoverable: true })] })
+        .mockResolvedValueOnce ({
+          created: 0,
+          skipped: 0,
+          failed: 1,
+          rows: [{
+            sourceRow: 1,
+            status: 'failed',
+            recoverable: true,
+            errors: { title: ['invalid'] } }] })
+    dialogue.form.mockImplementationOnce (async options => {
+      let actions: DialogueFormAction[] = []
+      const controls: DialogueFormControls = {
+        close: vi.fn (),
+        confirm: vi.fn (),
+        setActions: next => {
+          actions = next
+        } }
+
+      render (options.body (controls))
+      await waitFor (() => expect (actions.length).toBe (2))
+      fireEvent.change (screen.getByDisplayValue ('old title'), {
+        target: { value: 'edited title' } })
+      await actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+    })
+
+    render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-edit-retry/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+              <Route
+                  path="/posts/import/:sessionId/result"
+                  element={<div>RESULT ROUTE</div>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '編輯' }))
+
+    await waitFor (() => {
+      const saved = loadPostImportSession ('review-edit-retry')
+      expect (saved?.rows[0]?.attributes.title).toBe ('edited title')
+      expect (saved?.rows[0]?.importStatus).toBe ('pending')
+    })
+
+    fireEvent.click (screen.getByRole ('button', { name: '取込実行' }))
+
+    await waitFor (() => {
+      expect (api.apiPost.mock.calls[1]?.[1]?.rows?.[0]?.attributes?.title)
+          .toBe ('edited title')
+    })
+  })
+
+  it ('sorts recoverable pending validation rows to the top in repair mode', () => {
+    savePostImportSession ('review-repair-sort', {
+      source: '',
+      repairMode: 'failed',
+      rows: [
+        buildPostImportRow ({
+          sourceRow: 2,
+          attributes: { title: 'normal row' } }),
+        buildPostImportRow ({
+          sourceRow: 1,
+          attributes: { title: 'repair row' },
+          importStatus: 'pending',
+          recoverable: true,
+          validationErrors: { title: ['invalid'] } })] })
+
+    const { container } = render (
+        <HelmetProvider>
+          <MemoryRouter initialEntries={['/posts/import/review-repair-sort/review']}>
+            <Routes>
+              <Route
+                  path="/posts/import/:sessionId/review"
+                  element={<PostImportReviewPage user={buildUser ()}/>}/>
+            </Routes>
+          </MemoryRouter>
+        </HelmetProvider>)
+
+    const titles = Array.from (container.querySelectorAll ('.line-clamp-2')).map (
+        node => node.textContent)
+    expect (titles[0]).toBe ('repair row')
+  })
+})

frontend/src/pages/posts/PostImportReviewPage.tsx

@@ -0,0 +1,423 @@
+import { useEffect, useMemo, useRef, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useNavigate, useParams } from 'react-router-dom'
+
+import PageTitle from '@/components/common/PageTitle'
+import MainArea from '@/components/layout/MainArea'
+import PostImportRowForm from '@/components/posts/import/PostImportRowForm'
+import PostImportRowSummary from '@/components/posts/import/PostImportRowSummary'
+import { Button } from '@/components/ui/button'
+import { toast } from '@/components/ui/use-toast'
+import { SITE_TITLE } from '@/config'
+import { apiPost } from '@/lib/api'
+import useDialogue from '@/lib/dialogues/useDialogue'
+import { canEditContent } from '@/lib/users'
+import { loadPostImportSession,
+	 buildNextEditedRow,
+	 canEditReviewRow,
+	 creatableImportRows,
+	 hasExactSourceRows,
+	 initialisePreviewRows,
+	 mergeImportResults,
+	 mergeValidatedImportRow,
+	 mergeValidatedImportRows,
+	 processableImportRows,
+	 replaceImportRow,
+	 resultRepairMode,
+	 reviewSummaryCounts,
+	 savePostImportSession } from '@/lib/postImportSession'
+import Forbidden from '@/pages/Forbidden'
+
+import type { FC } from 'react'
+
+import type { PostImportRowDraft } from '@/components/posts/import/PostImportRowForm'
+import type { PostImportResultRow,
+	      PostImportRow,
+	      PostImportSession } from '@/lib/postImportSession'
+import type { User } from '@/types'
+
+type Props = { user: User | null }
+
+const isRepairRow = (row: PostImportRow): boolean =>
+    row.recoverable === true
+    && (row.importStatus === 'failed'
+        || (row.importStatus === 'pending'
+            && Object.keys (row.validationErrors).length > 0))
+
+
+const PostImportReviewPage: FC<Props> = ({ user }) => {
+  const editable = canEditContent (user)
+  const dialogue = useDialogue ()
+  const navigate = useNavigate ()
+  const { sessionId } = useParams ()
+
+  const [session, setSession] = useState<PostImportSession | null> (null)
+  const [loading, setLoading] = useState (false)
+  const [missing, setMissing] = useState (false)
+  const [editingRow, setEditingRow] = useState<PostImportRow | null> (null)
+  const sessionRef = useRef<PostImportSession | null> (null)
+
+  useEffect (() => {
+    if (sessionId == null)
+      return
+
+    const loaded = loadPostImportSession (sessionId, message =>
+	toast ({ title: '取込状態を復元できませんでした', description: message }))
+    setSession (loaded)
+    setMissing (loaded == null)
+  }, [sessionId])
+
+  useEffect (() => {
+    if (sessionId == null || session == null)
+      return
+
+    savePostImportSession (sessionId, session, message =>
+	toast ({ title: '取込状態を保存できませんでした', description: message }))
+  }, [session, sessionId])
+
+  useEffect (() => {
+    sessionRef.current = session
+  }, [session])
+
+  const rows = session?.rows ?? []
+  const counts = useMemo (() => reviewSummaryCounts (rows), [rows])
+  const processable = useMemo (
+      () => processableImportRows (rows),
+      [rows])
+  const creatable = useMemo (
+      () => creatableImportRows (rows),
+      [rows])
+  const reviewRows =
+      session?.repairMode === 'failed'
+      ? (
+	  [...rows].sort ((a, b) => {
+	    const aRepair = isRepairRow (a) ? 0 : 1
+	    const bRepair = isRepairRow (b) ? 0 : 1
+	    return aRepair - bRepair || a.sourceRow - b.sourceRow
+	  }))
+      : rows
+
+  useEffect (() => {
+    if (editingRow == null || session?.repairMode !== 'failed')
+      return
+
+    const element = document.getElementById (`post-import-row-${ editingRow.sourceRow }`)
+    element?.scrollIntoView ({ block: 'center', behavior: 'smooth' })
+  }, [editingRow, session?.repairMode])
+
+  const saveDraft = async (
+      row: PostImportRow,
+      { draft, resetRequested }: {
+	  draft:            PostImportRowDraft
+	  resetRequested:   boolean },
+  ): Promise<{ saved: boolean
+	       row:   PostImportRow | null }> => {
+    const currentSession = sessionRef.current
+    if (currentSession == null)
+      return { saved: false, row: null }
+    if (!(canEditReviewRow (row)))
+      return { saved: false, row: null }
+
+    const baseRow =
+	resetRequested
+	? { ...row,
+	    url: row.resetSnapshot.url,
+	    attributes: { ...row.resetSnapshot.attributes },
+	    provenance: { ...row.resetSnapshot.provenance },
+	    tagSources: { ...row.resetSnapshot.tagSources },
+	    fieldWarnings: Object.fromEntries (
+		Object.entries (row.resetSnapshot.fieldWarnings)
+		    .map (([key, values]) => [key, [...values]])),
+	    baseWarnings: [...row.resetSnapshot.baseWarnings],
+	    metadataUrl: row.resetSnapshot.metadataUrl }
+	: row
+    const urlChanged = draft.url !== baseRow.url
+    const nextRow = buildNextEditedRow (baseRow, draft, urlChanged)
+
+    const nextRows = currentSession.rows.map (row =>
+		row.sourceRow === baseRow.sourceRow
+		? nextRow
+		: row)
+    try
+    {
+      const validated = await apiPost<{ rows: PostImportRow[] }> ('/posts/import/validate', {
+	  rows:
+	      nextRows
+	      .filter (row => row.importStatus !== 'created')
+	      .map (row => ({ sourceRow: row.sourceRow,
+			      url: row.url,
+			      attributes: row.attributes,
+			      provenance: row.provenance,
+			      tagSources: row.tagSources,
+			      metadataUrl: row.metadataUrl })),
+	  changed_row: urlChanged ? baseRow.sourceRow : -1 })
+      const validatedRows = initialisePreviewRows (validated.rows)
+      const target = validatedRows.find (
+          validatedRow => validatedRow.sourceRow === baseRow.sourceRow)
+      const latestSession = sessionRef.current
+      if (latestSession == null)
+        return { saved: false, row: null }
+      if (target == null)
+        {
+          const restoredRows = replaceImportRow (latestSession.rows, row)
+          const restoredSession = {
+              ...latestSession,
+              rows: restoredRows,
+              repairMode: resultRepairMode (restoredRows) }
+          sessionRef.current = restoredSession
+          setSession (restoredSession)
+          toast ({ title: '行の再検証結果が不完全でした' })
+          return { saved: false, row: null }
+        }
+      const editedRows = replaceImportRow (latestSession.rows, nextRow)
+      const rows = mergeValidatedImportRow (editedRows, target)
+      const nextSession = {
+          ...latestSession,
+          rows,
+          repairMode: resultRepairMode (rows) }
+      sessionRef.current = nextSession
+      setSession (nextSession)
+      const mergedTarget =
+          rows.find (mergedRow => mergedRow.sourceRow === baseRow.sourceRow)
+          ?? target
+      if (Object.keys (mergedTarget.validationErrors).length > 0)
+        return { saved: false, row: mergedTarget }
+      return { saved: true, row: null }
+    }
+    catch
+    {
+      toast ({ title: '行の再検証に失敗しました' })
+      return { saved: false, row: null }
+    }
+  }
+
+  const openEditingDialogue = async (row: PostImportRow) => {
+    const saveRowDraft = (
+	{ draft, resetRequested }: {
+	    draft:          PostImportRowDraft
+	    resetRequested: boolean },
+    ) =>
+	saveDraft (row, { draft, resetRequested })
+
+    await dialogue.form ({
+	title: '投稿を編輯',
+	description: `投稿 ${ row.sourceRow } の内容を確認し、必要な項目を編輯してください．`,
+	cancelText: '取消',
+	size: 'large',
+	body: controls => (
+	    <PostImportRowForm
+		row={row}
+		controls={controls}
+		onSave={saveRowDraft}/>) })
+  }
+
+  const editRow = async (row: PostImportRow) => {
+    setEditingRow (row)
+    try
+    {
+      await openEditingDialogue (row)
+    }
+    finally
+    {
+      setEditingRow (current =>
+          current?.sourceRow === row.sourceRow
+          ? null
+          : current)
+    }
+  }
+
+  const submit = async () => {
+    const currentSession = sessionRef.current
+    if (sessionId == null || currentSession == null || processable.length === 0)
+      return
+
+    setLoading (true)
+    try
+    {
+      const validatableRows =
+          currentSession.rows.filter (row => row.importStatus !== 'created')
+      const validated = await apiPost<{ rows: PostImportRow[] }> ('/posts/import/validate', {
+	  rows:
+	      validatableRows.map (row => ({ sourceRow: row.sourceRow,
+					     url: row.url,
+					     attributes: row.attributes,
+					     provenance: row.provenance,
+					     tagSources: row.tagSources,
+					     metadataUrl: row.metadataUrl })),
+	  changed_row: -1 })
+      const validatedRows = initialisePreviewRows (validated.rows)
+      const expectedSourceRows = validatableRows.map (row => row.sourceRow)
+      if (!(hasExactSourceRows (expectedSourceRows, validatedRows)))
+        {
+          toast ({ title: '再検証結果が不完全でした' })
+          return
+        }
+      const latestAfterValidate = sessionRef.current ?? currentSession
+      const mergedRows = mergeValidatedImportRows (latestAfterValidate.rows, validatedRows)
+      const firstInvalid = mergedRows.find (row => Object.keys (row.validationErrors).length > 0)
+      if (firstInvalid != null)
+	{
+	  const nextSession = {
+              ...latestAfterValidate,
+              rows: mergedRows,
+              repairMode: resultRepairMode (mergedRows) }
+	  sessionRef.current = nextSession
+	  setSession (nextSession)
+	  void editRow (firstInvalid)
+	  return
+	}
+      const validatedSession = {
+          ...latestAfterValidate,
+          rows: mergedRows,
+          repairMode: resultRepairMode (mergedRows) }
+      sessionRef.current = validatedSession
+      setSession (validatedSession)
+      const savedValidated = savePostImportSession (sessionId, validatedSession, message =>
+	  toast ({ title: '取込状態を保存できませんでした', description: message }))
+      if (!(savedValidated))
+	return
+
+      const result = await apiPost<{
+	  created: number
+	  skipped: number
+	  failed:  number
+	  rows:    PostImportResultRow[] }> ('/posts/import', {
+	      rows: processableImportRows (mergedRows).map (row => ({
+		  sourceRow: row.sourceRow,
+		  url: row.url,
+		  attributes: row.attributes,
+		  provenance: row.provenance,
+		  tagSources: row.tagSources,
+		  metadataUrl: row.metadataUrl })) })
+      const expectedImportRows = processableImportRows (mergedRows).map (row => row.sourceRow)
+      if (!(hasExactSourceRows (expectedImportRows, result.rows)))
+	{
+	  toast ({ title: '登録結果が不完全でした' })
+	  return
+	}
+      const latestAfterImport = sessionRef.current ?? validatedSession
+      const mergedResults = mergeImportResults (latestAfterImport.rows, result.rows)
+      const recoverableRows = result.rows.filter (row =>
+	  row.status === 'failed'
+	  && row.recoverable
+	  && Object.keys (row.errors ?? { }).length > 0)
+      const nextRows = mergedResults.map ((row): PostImportRow => {
+	const recoverable = recoverableRows.find (rr => rr.sourceRow === row.sourceRow)
+	if (recoverable == null)
+	  return row
+	return {
+	    ...row,
+	    importStatus: 'pending',
+	    recoverable: true,
+	    validationErrors: recoverable.errors ?? { },
+	    importErrors: undefined }
+      })
+      const nextSession = {
+          ...latestAfterImport,
+          rows: nextRows,
+          repairMode: resultRepairMode (nextRows) }
+      sessionRef.current = nextSession
+      setSession (nextSession)
+      const saved = savePostImportSession (sessionId, nextSession, message =>
+	  toast ({ title: '取込状態を保存できませんでした', description: message }))
+      if (!(saved))
+	return
+      navigate (`/posts/import/${ sessionId }/result`)
+    }
+    catch
+    {
+      toast ({ title: '登録に失敗しました' })
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }
+
+  if (!(editable))
+    return <Forbidden/>
+
+  if (missing || sessionId == null || session == null)
+    {
+      return (
+	  <MainArea>
+	    <div className="mx-auto max-w-4xl space-y-4 p-4">
+	      <PageTitle>投稿インポート</PageTitle>
+	      <div className="text-red-700 dark:text-red-300">取込状態が見つかりません．</div>
+	      <Button type="button" onClick={() => navigate ('/posts/import')}>
+		URL リスト入力へ戻る
+	      </Button>
+	    </div>
+	  </MainArea>)
+    }
+
+  return (
+      <>
+	<Helmet>
+	  <title>{`投稿インポート確認 | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<MainArea className="min-h-0">
+	  <div className="mx-auto max-w-6xl space-y-4 p-4">
+	    <PageTitle>投稿情報の確認</PageTitle>
+
+	    <div className="space-y-3">
+	      {reviewRows.map (row => (
+		  <div key={row.sourceRow} id={`post-import-row-${ row.sourceRow }`}>
+		    <PostImportRowSummary
+			row={row}
+			editDisabled={loading}
+			onEdit={() => void editRow (row)}/>
+		  </div>))}
+	    </div>
+	  </div>
+	</MainArea>
+
+	<PostImportFooter
+	    loading={loading}
+	    processableCount={processable.length}
+	    creatableCount={creatable.length}
+	    skipPlannedCount={counts.skipPlanned}
+	    onBack={() => navigate ('/posts/import')}
+	    onSubmit={submit}/>
+      </>)
+}
+
+const PostImportFooter = (
+    { loading,
+      processableCount,
+      creatableCount,
+      skipPlannedCount,
+      onBack,
+      onSubmit }: { loading:            boolean
+		    processableCount:   number
+		    creatableCount:     number
+		    skipPlannedCount:   number
+		    onBack:             () => void
+		    onSubmit:           () => void },
+) => (
+    <div
+	className="shrink-0 border-t bg-white/95 p-4 backdrop-blur
+		   dark:border-neutral-700 dark:bg-neutral-950/95">
+      <div className="mx-auto flex max-w-6xl flex-col gap-3 md:flex-row
+		      md:items-center md:justify-between">
+	<div className="flex flex-wrap items-center gap-2 text-sm">
+	  <span>処理対象 {processableCount}件</span>
+	  <span>登録対象 {creatableCount}件</span>
+	  <span>スキップ予定 {skipPlannedCount}件</span>
+	</div>
+	<div className="flex flex-col gap-2 sm:flex-row">
+	  <Button type="button" variant="outline" onClick={onBack} disabled={loading}>
+	    URL リスト入力へ戻る
+	  </Button>
+	  <Button
+	      type="button"
+	      onClick={onSubmit}
+	      disabled={loading || processableCount === 0}>
+	    取込実行
+	  </Button>
+	</div>
+      </div>
+    </div>)
+
+export default PostImportReviewPage

frontend/src/pages/posts/PostImportSourcePage.test.tsx

@@ -0,0 +1,93 @@
+import { fireEvent, screen, waitFor } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import PostImportSourcePage from '@/pages/posts/PostImportSourcePage'
+import { buildUser } from '@/test/factories'
+import { buildPostImportRow } from '@/test/postImportFactories'
+import { renderWithProviders } from '@/test/render'
+
+const api = vi.hoisted (() => ({
+  apiPost: vi.fn (),
+  isApiError: vi.fn () }))
+
+const router = vi.hoisted (() => ({ navigate: vi.fn () }))
+
+const toastApi = vi.hoisted (() => ({ toast: vi.fn () }))
+
+vi.mock ('@/lib/api', () => api)
+vi.mock ('@/components/ui/use-toast', () => toastApi)
+vi.mock ('react-router-dom', async importOriginal => ({
+  ...await importOriginal<typeof import('react-router-dom')> (),
+  useNavigate: () => router.navigate }))
+
+describe ('PostImportSourcePage', () => {
+  beforeEach (() => {
+    sessionStorage.clear ()
+    vi.clearAllMocks ()
+    api.isApiError.mockReturnValue (false)
+  })
+
+  it ('shows no empty error initially and validates only after Next is pressed', () => {
+    renderWithProviders (<PostImportSourcePage user={buildUser ()}/>)
+
+    expect (screen.queryByText ('URL を入力してください．')).not.toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: '次へ' }))
+    expect (screen.getByText ('URL を入力してください．')).toBeInTheDocument ()
+    expect (api.apiPost).not.toHaveBeenCalled ()
+  })
+
+  it ('shows frontend URL issues with line numbers without requesting preview', () => {
+    renderWithProviders (<PostImportSourcePage user={buildUser ()}/>)
+    const input = screen.getByRole ('textbox', { name: '' })
+
+    fireEvent.change (input, {
+      target: { value: '\nftp://example.com/file\nhttps://example.com/valid' } })
+    expect (screen.queryByText (/2 行目/)).not.toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: '次へ' }))
+
+    expect (screen.getByText (/2 行目: HTTP または HTTPS/)).toBeInTheDocument ()
+    expect (screen.getByText ('ftp://example.com/file')).toBeInTheDocument ()
+    expect (input).toHaveAttribute ('aria-invalid', 'true')
+    expect (input.getAttribute ('aria-describedby')).toContain ('post-import-source-issues')
+    expect (api.apiPost).not.toHaveBeenCalled ()
+  })
+
+  it ('shows backend URL errors against original input without a session', async () => {
+    api.apiPost.mockResolvedValue ({
+      rows: [buildPostImportRow ({
+	sourceRow: 2,
+	url: 'https://example.com/canonical',
+	status: 'error',
+	validationErrors: { url: ['URL が重複しています．'] } })] })
+    renderWithProviders (<PostImportSourcePage user={buildUser ()}/>)
+
+    fireEvent.change (screen.getByRole ('textbox', { name: '' }), {
+      target: { value: '\nhttps://example.com/original' } })
+    fireEvent.click (screen.getByRole ('button', { name: '次へ' }))
+
+    expect (await screen.findByText ('2 行目: URL が重複しています．')).toBeInTheDocument ()
+    expect (screen.getAllByText ('https://example.com/original')).toHaveLength (2)
+    expect (router.navigate).not.toHaveBeenCalled ()
+    expect (Array.from ({ length: sessionStorage.length }, (_, index) =>
+	sessionStorage.key (index))).not.toContainEqual(
+	    expect.stringMatching (/^post-import-session:/))
+  })
+
+  it ('stores a successful preview before navigating to the review route', async () => {
+    api.apiPost.mockResolvedValue ({ rows: [buildPostImportRow ()] })
+    renderWithProviders (<PostImportSourcePage user={buildUser ()}/>)
+
+    fireEvent.change (screen.getByRole ('textbox', { name: '' }), {
+      target: { value: 'https://example.com/post' } })
+    fireEvent.click (screen.getByRole ('button', { name: '次へ' }))
+
+    await waitFor (() => {
+      expect (router.navigate).toHaveBeenCalledWith (
+	  expect.stringMatching (/^\/posts\/import\/[^/]+\/review$/))
+    })
+    const sessionKeys = Array.from ({ length: sessionStorage.length }, (_, index) =>
+	sessionStorage.key (index)).filter (
+	    key => key?.startsWith ('post-import-session:'))
+    expect (sessionKeys).toHaveLength (1)
+  })
+})

frontend/src/pages/posts/PostImportSourcePage.tsx

@@ -0,0 +1,208 @@
+import { useEffect, useRef, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useNavigate } from 'react-router-dom'
+
+import FieldError from '@/components/common/FieldError'
+import Form from '@/components/common/Form'
+import FormField from '@/components/common/FormField'
+import PageTitle from '@/components/common/PageTitle'
+import TextArea from '@/components/common/TextArea'
+import MainArea from '@/components/layout/MainArea'
+import { Button } from '@/components/ui/button'
+import { toast } from '@/components/ui/use-toast'
+import { SITE_TITLE } from '@/config'
+import { apiPost, isApiError } from '@/lib/api'
+import { canEditContent } from '@/lib/users'
+import { countImportSourceLines,
+	 cleanupExpiredPostImportSessions,
+	 createPostImportSessionId,
+	 initialisePreviewRows,
+	 loadPostImportSourceDraft,
+	 savePostImportSession,
+	 savePostImportSourceDraft,
+	 validateImportSource } from '@/lib/postImportSession'
+import Forbidden from '@/pages/Forbidden'
+
+import type { FC } from 'react'
+
+import type { PostImportRow } from '@/lib/postImportSession'
+import type { User } from '@/types'
+
+type Props = { user: User | null }
+
+const MAX_ROWS = 100
+const SOURCE_ERROR_ID = 'post-import-source-error'
+const SOURCE_ISSUES_ID = 'post-import-source-issues'
+
+const urlIssuesFromRows = (rows: PostImportRow[], source: string) => {
+  const sourceLines = source.split (/\r\n|\n|\r/)
+
+  return rows.flatMap (row =>
+      (row.validationErrors.url ?? []).map (message => ({
+	  sourceRow: row.sourceRow,
+	  message,
+	  url: sourceLines[row.sourceRow - 1]?.trim () ?? row.url })))
+}
+
+
+const PostImportSourcePage: FC<Props> = ({ user }) => {
+  const editable = canEditContent (user)
+  const navigate = useNavigate ()
+  const [source, setSource] = useState ('')
+  const [loading, setLoading] = useState (false)
+  const [sourceIssues, setSourceIssues] = useState<ReturnType<typeof validateImportSource>> ([])
+  const [sourceError, setSourceError] = useState<string | null> (null)
+  const saveTimer = useRef<number | null> (null)
+  const editedRef = useRef (false)
+
+  const lineCount = countImportSourceLines (source)
+  const messages = sourceError != null ? [sourceError] : []
+  const sourceDescribedBy =
+      [sourceError != null ? SOURCE_ERROR_ID : null,
+       sourceIssues.length > 0 ? SOURCE_ISSUES_ID : null]
+      .filter (value => value != null)
+      .join (' ')
+
+  useEffect (() => {
+    cleanupExpiredPostImportSessions (message =>
+	toast ({ title: '保存済みデータを整理できませんでした', description: message }))
+
+    const draft = loadPostImportSourceDraft (message =>
+	toast ({ title: '保存済み入力を復元できませんでした', description: message }))
+
+    if (!(editedRef.current))
+      setSource (current => current === '' ? draft.source : current)
+  }, [])
+
+  useEffect (() => {
+    if (saveTimer.current != null)
+      window.clearTimeout (saveTimer.current)
+
+    saveTimer.current = window.setTimeout (() => {
+      savePostImportSourceDraft (source, message =>
+	  toast ({ title: '入力内容を保存できませんでした', description: message }))
+    }, 300)
+
+    return () => {
+      if (saveTimer.current != null)
+	window.clearTimeout (saveTimer.current)
+    }
+  }, [source])
+
+  const preview = async () => {
+    if (lineCount === 0)
+      {
+	setSourceIssues ([])
+	setSourceError ('URL を入力してください．')
+	return
+      }
+
+    const issues = validateImportSource (source)
+    if (issues.length > 0)
+      {
+	setSourceIssues (issues)
+	setSourceError (null)
+	return
+      }
+
+    setLoading (true)
+    setSourceIssues ([])
+    setSourceError (null)
+    try
+    {
+      const data = await apiPost<{ rows: PostImportRow[] }> ('/posts/import/preview', { source })
+      const urlIssues = urlIssuesFromRows (data.rows, source)
+      if (urlIssues.length > 0)
+	{
+	  setSourceIssues (urlIssues)
+	  return
+	}
+      const sessionId = createPostImportSessionId ()
+      const saved = savePostImportSession (
+	  sessionId,
+	  { source,
+	    rows: initialisePreviewRows (data.rows),
+	    repairMode: 'all' },
+	  message => toast ({ title: '取込状態を保存できませんでした', description: message }))
+      if (!(saved))
+	return
+      navigate (`/posts/import/${ sessionId }/review`)
+    }
+    catch (requestError)
+    {
+      const message =
+	  isApiError<{ message?: string, baseErrors?: string[] }> (requestError)
+	  ? (requestError.response?.data?.message
+	     ?? requestError.response?.data?.baseErrors?.[0])
+	  : undefined
+      setSourceError (message ?? '入力を確認してください．')
+      toast ({ title: '投稿情報の取得に失敗しました',
+	       description: message ?? '入力を確認してください．' })
+    }
+    finally
+    {
+      setLoading (false)
+    }
+  }
+
+  if (!(editable))
+    return <Forbidden/>
+
+  return (
+      <MainArea>
+	<Helmet>
+	  <title>{`投稿インポート | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<Form className="max-w-4xl">
+	  <PageTitle>投稿インポート</PageTitle>
+	  <FormField label="URL リスト">
+	    {() => (
+		<TextArea
+		    value={source}
+		    rows={14}
+		    invalid={messages.length > 0 || sourceIssues.length > 0}
+		    aria-describedby={sourceDescribedBy || undefined}
+		    className="h-80 font-mono text-sm"
+		    onBlur={() => {
+		      savePostImportSourceDraft (source, message =>
+			  toast ({ title: '入力内容を保存できませんでした',
+				   description: message }))
+		    }}
+		    onChange={ev => {
+		      editedRef.current = true
+		      setSource (ev.target.value)
+		      setSourceError (null)
+		      setSourceIssues ([])
+		    }}/>)}
+	  </FormField>
+	  <div id={messages.length > 0 ? SOURCE_ERROR_ID : undefined}>
+	    <FieldError messages={messages}/>
+	  </div>
+	  <ul
+	      id={SOURCE_ISSUES_ID}
+	      className="space-y-2 text-sm text-red-700 dark:text-red-300">
+	    {sourceIssues.map (issue => (
+		<li key={`${ issue.sourceRow }-${ issue.message }-${ issue.url }`}>
+		  <div>{issue.sourceRow} 行目: {issue.message}</div>
+		  <div className="break-all font-mono text-xs">{issue.url}</div>
+		</li>))}
+	  </ul>
+
+	  <div className="flex items-center justify-between gap-3">
+	    <div className="text-sm text-neutral-600 dark:text-neutral-300">
+	      入力行数 {lineCount} / {MAX_ROWS}
+	    </div>
+	    <Button
+		type="button"
+		className="shrink-0"
+		onClick={preview}
+		disabled={loading}>
+	      次へ
+	    </Button>
+	  </div>
+	</Form>
+      </MainArea>)
+}
+
+export default PostImportSourcePage

frontend/src/pages/posts/PostNewPage.test.tsx

@@ -1,6 +1,7 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
+import { toMinutePrecisionIsoUtc } from '@/components/common/DateTimeField'
 import PostNewPage from '@/pages/posts/PostNewPage'
 import { buildUser } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
@@ -39,8 +40,8 @@ describe ('PostNewPage', () => {
     const textboxes = screen.getAllByRole ('textbox')
     fireEvent.change (textboxes[0], { target: { value: 'https://example.com/post' } })
     fireEvent.change (textboxes[1], { target: { value: '投稿タイトル' } })
-    fireEvent.change (textboxes[2], { target: { value: '1 2' } })
-    fireEvent.change (textboxes[3], { target: { value: 'tag1 tag2' } })
+    fireEvent.change (textboxes[3], { target: { value: '1 2' } })
+    fireEvent.change (textboxes[4], { target: { value: 'tag1 tag2' } })
     fireEvent.click (screen.getByRole ('button', { name: '追加' }))
 
     await waitFor (() => {
@@ -63,17 +64,19 @@ describe ('PostNewPage', () => {
 
     renderWithProviders (<PostNewPage user={buildUser ({ role: 'member' })}/>)
 
-    const tags = screen.getAllByRole ('textbox')[3]
+    const tags = screen.getAllByRole ('textbox')[4]
     fireEvent.change (tags, { target: { value: '動画' } })
-    fireEvent.change (screen.getByRole ('spinbutton'), { target: { value: '180.5' } })
+    fireEvent.change (
+        screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23'),
+        { target: { value: '180.5' } })
 
     fireEvent.change (tags, { target: { value: 'general-tag' } })
-    expect (screen.queryByRole ('spinbutton')).not.toBeInTheDocument ()
+    expect (screen.queryByPlaceholderText ('例: 2 / 2.5 / 1:23')).not.toBeInTheDocument ()
 
     fireEvent.change (tags, {
       target: { value: '動画 general-tag' },
     })
-    expect (screen.getByRole ('spinbutton')).toHaveValue (180.5)
+    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('180.5')
   })
 
   it ('shows 422 validation errors for post fields', async () => {
@@ -96,11 +99,64 @@ describe ('PostNewPage', () => {
     const textboxes = screen.getAllByRole ('textbox')
     fireEvent.change (textboxes[0], { target: { value: 'https://example.com/post' } })
     fireEvent.change (textboxes[1], { target: { value: '投稿タイトル' } })
-    fireEvent.change (textboxes[3], { target: { value: 'nico:nico_tag' } })
+    fireEvent.change (textboxes[4], { target: { value: 'nico:nico_tag' } })
     fireEvent.click (screen.getByRole ('button', { name: '追加' }))
 
     expect (await screen.findByText ('投稿内容を確認してください．')).toBeInTheDocument ()
     expect (screen.getByText ('ニコニコ・タグは直接指定できません．')).toBeInTheDocument ()
-    expect (screen.getAllByRole ('textbox')[3]).toHaveAttribute ('aria-invalid', 'true')
+    expect (screen.getAllByRole ('textbox')[4]).toHaveAttribute ('aria-invalid', 'true')
+  })
+
+  it ('uses the shared duration, tags, and datetime value contract for post submission', async () => {
+    api.apiPost.mockResolvedValueOnce ({})
+    api.apiGet.mockResolvedValue ([])
+
+    const { container } = renderWithProviders (<PostNewPage user={buildUser ({ role: 'member' })}/>)
+
+    const textboxes = screen.getAllByRole ('textbox')
+    fireEvent.change (textboxes[0], { target: { value: 'https://example.com/post' } })
+    fireEvent.change (textboxes[1], { target: { value: '投稿タイトル' } })
+    fireEvent.change (textboxes[4], { target: { value: '動画 tag1 tag2' } })
+    fireEvent.change (
+        screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23'),
+        { target: { value: '2.5' } })
+    const datetimeInputs = container.querySelectorAll ('input[type="datetime-local"]')
+    fireEvent.change (datetimeInputs[0] as HTMLInputElement, {
+      target: { value: '2024-01-01T12:34' } })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    await waitFor (() => expect (api.apiPost).toHaveBeenCalled ())
+
+    const formData = api.apiPost.mock.calls[0]?.[1] as FormData
+    expect (container.querySelector ('input[type="file"]')).not.toBeNull ()
+    expect (formData.get ('duration')).toBe ('2.5')
+    expect (formData.get ('tags')).toBe ('動画 tag1 tag2')
+    expect (formData.get ('original_created_from')).toBe (
+        toMinutePrecisionIsoUtc ('2024-01-01T12:34'))
+  })
+
+  it ('shows deduplicated original-created endpoint errors on the shared datetime field', async () => {
+    api.apiGet.mockResolvedValue ([])
+    api.isApiError.mockReturnValue (true)
+    api.apiPost.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type: 'validation_error',
+          errors: {
+            original_created_at: ['日時を確認してください．'],
+            original_created_from: ['日時を確認してください．'],
+            original_created_before: ['終了を確認してください．'] },
+        },
+      },
+    })
+
+    renderWithProviders (<PostNewPage user={buildUser ({ role: 'member' })}/>)
+
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+
+    expect (await screen.findByText ('日時を確認してください．')).toBeInTheDocument ()
+    expect (screen.getByText ('終了を確認してください．')).toBeInTheDocument ()
+    expect (screen.getAllByText ('日時を確認してください．')).toHaveLength (1)
   })
 })

frontend/src/pages/posts/PostNewPage.tsx

@@ -2,19 +2,20 @@ import { useCallback, useEffect, useMemo, useRef, useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useNavigate } from 'react-router-dom'
 
-import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import FieldError from '@/components/common/FieldError'
 import Form from '@/components/common/Form'
-import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import MainArea from '@/components/layout/MainArea'
+import PostDurationField from '@/components/posts/PostDurationField'
+import PostTagsField from '@/components/posts/PostTagsField'
+import PostTextField from '@/components/posts/PostTextField'
+import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
 import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiGet, apiPost } from '@/lib/api'
 import { canEditContent } from '@/lib/users'
-import { inputClass } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 import Forbidden from '@/pages/Forbidden'
 
@@ -25,7 +26,12 @@ import type { User } from '@/types'
 type Props = { user: User | null }
 
 type PostFormField =
-    'url' | 'title' | 'tags' | 'parentPostIds' | 'videoMs' | 'originalCreatedAt' | 'thumbnail'
+    'url' | 'title' | 'tags' | 'parentPostIds'
+    | 'videoMs' | 'originalCreatedAt' | 'originalCreatedFrom'
+    | 'originalCreatedBefore' | 'thumbnail'
+
+const groupedMessages = (...values: (string[] | undefined)[]): string[] =>
+    [...new Set (values.flatMap (value => value ?? []))]
 
 
 const PostNewPage: FC<Props> = ({ user }) => {
@@ -36,8 +42,10 @@ const PostNewPage: FC<Props> = ({ user }) => {
   const { baseErrors, fieldErrors, clearValidationErrors, applyValidationError } =
       useValidationErrors<PostFormField> ()
 
-  const [originalCreatedBefore, setOriginalCreatedBefore] = useState<string | null> (null)
-  const [originalCreatedFrom, setOriginalCreatedFrom] = useState<string | null> (null)
+  const [originalCreatedBefore, setOriginalCreatedBefore] =
+      useState<string | null> (null)
+  const [originalCreatedFrom, setOriginalCreatedFrom] =
+      useState<string | null> (null)
   const [parentPostIds, setParentPostIds] = useState ('')
   const [tags, setTags] = useState ('')
   const [duration, setDuration] = useState ('')
@@ -51,7 +59,7 @@ const PostNewPage: FC<Props> = ({ user }) => {
   const thumbnailPreviewRef = useRef ('')
   const videoFlg =
       useMemo (() => tags.split (/\s+/).some (tag => tag.replace (/\[.*\]$/, '') === '動画'),
-               [tags])
+	       [tags])
 
   const handleSubmit = async () => {
     clearValidationErrors ()
@@ -79,7 +87,7 @@ const PostNewPage: FC<Props> = ({ user }) => {
     catch (e)
     {
       applyValidationError (e)
-      toast ({ title: '投稿失敗', description: '入力を確認してください。' })
+      toast ({ title: '投稿失敗', description: '入力を確認してください．' })
     }
   }
 
@@ -105,7 +113,8 @@ const PostNewPage: FC<Props> = ({ user }) => {
     try
     {
       const data = await apiGet<Blob> ('/preview/thumbnail',
-				       { params: { url }, responseType: 'blob' })
+				       { params: { url },
+					 responseType: 'blob' })
       const imageURL = URL.createObjectURL (data)
       setThumbnailPreview (imageURL)
       setThumbnailFile (new File ([data],
@@ -134,30 +143,22 @@ const PostNewPage: FC<Props> = ({ user }) => {
 	  <PageTitle>広場に投稿を追加する</PageTitle>
 	  <FieldError messages={baseErrors}/>
 
-	  {/* URL */}
-	  <FormField label="URL" messages={fieldErrors.url}>
-	    {({ describedBy, invalid }) => (
-		<input type="url"
-		       placeholder="例：https://www.nicovideo.jp/watch/..."
-		       value={url}
-		       onChange={e => setURL (e.target.value)}
-		       aria-describedby={describedBy}
-		       aria-invalid={invalid}
-		       className={inputClass (invalid)}/>)}
-	  </FormField>
+	  <PostTextField
+	      label="URL"
+	      type="url"
+	      value={url}
+	      errors={fieldErrors.url}
+	      placeholder="例：https://www.nicovideo.jp/watch/..."
+	      onChange={setURL}/>
 
-	  {/* タイトル */}
-	  <FormField label="タイトル" messages={fieldErrors.title}>
-	    {({ describedBy, invalid }) => (
-		<div className="space-y-2">
-		  <input type="text"
-			 aria-describedby={describedBy}
-			 aria-invalid={invalid}
-			 className={inputClass (invalid)}
-			 value={title}
-			 placeholder={titleLoading ? 'Loading...' : ''}
-			 onChange={ev => setTitle (ev.target.value)}
-			 disabled={titleLoading}/>
+	  <PostTextField
+	      label="タイトル"
+	      value={title}
+	      errors={fieldErrors.title}
+	      disabled={titleLoading}
+	      placeholder={titleLoading ? 'Loading...' : undefined}
+	      onChange={setTitle}
+	      after={
 		  <div className="flex flex-wrap items-center gap-2 text-sm">
 		    <span>必要なタイミングで URL から取得できます．</span>
 		    <Button
@@ -167,59 +168,51 @@ const PostNewPage: FC<Props> = ({ user }) => {
 			disabled={!(url) || titleLoading}>
 		      取得
 		    </Button>
-		  </div>
-		</div>)}
-	  </FormField>
+		  </div>}/>
 
-	  {/* サムネール */}
-	  <FormField label="サムネール" messages={fieldErrors.thumbnail}>
-	    {({ describedBy, invalid }) => (
-		<>
-		  <div className="mb-2 flex flex-wrap items-center gap-2 text-sm">
-		    <span>必要なタイミングで URL から取得できます．</span>
-		    <Button
-			type="button"
-			variant="outline"
-			onClick={() => void fetchThumbnail ()}
-			disabled={!(url) || thumbnailLoading}>
-		      取得
-		    </Button>
-		  </div>
-		  {thumbnailLoading && (
-		      <p className="text-gray-500 text-sm">Loading...</p>)}
-		  <input type="file"
-			 accept="image/*"
-			 aria-describedby={describedBy}
-			 aria-invalid={invalid}
-			 onChange={e => {
-			   const file = e.target.files?.[0]
-			   if (file)
-			     {
-			       setThumbnailFile (file)
-			       setThumbnailPreview (URL.createObjectURL (file))
-			     }
-			 }}/>
-		  {thumbnailPreview && (
-		      <img src={thumbnailPreview}
-			   alt="preview"
-			   className="mt-2 max-h-48 rounded border"/>)}
-		</>)}
-	  </FormField>
+	  <div className="space-y-2">
+	    <div className="flex flex-wrap items-center gap-2 text-sm">
+	      <span>必要なタイミングで URL から取得できます．</span>
+	      <Button
+		  type="button"
+		  variant="outline"
+		  onClick={() => void fetchThumbnail ()}
+		  disabled={!(url) || thumbnailLoading}>
+		取得
+	      </Button>
+	    </div>
+	    {thumbnailLoading && (
+		<p className="text-gray-500 text-sm">Loading...</p>)}
+	    <PostTextField
+		label="サムネール"
+		value={thumbnailFile?.name ?? ''}
+		errors={fieldErrors.thumbnail}
+		disabled
+		onChange={() => {}}/>
+	    <input
+		type="file"
+		accept="image/*"
+		onChange={e => {
+		  const file = e.target.files?.[0]
+		  if (file)
+		    {
+		      setThumbnailFile (file)
+		      setThumbnailPreview (URL.createObjectURL (file))
+		    }
+		}}/>
+	    <PostThumbnailPreview
+		url={thumbnailPreview}
+		alt="preview"
+		className="h-28 w-28"/>
+	  </div>
 
-	  {/* 親投稿 */}
-	  <FormField label="親投稿" messages={fieldErrors.parentPostIds}>
-	    {({ describedBy, invalid }) => (
-		<input
-		    type="text"
-		    value={parentPostIds}
-		    onChange={e => setParentPostIds (e.target.value)}
-		    aria-describedby={describedBy}
-		    aria-invalid={invalid}
-		    className={inputClass (invalid)}/>)}
-	  </FormField>
+	  <PostTextField
+	      label="親投稿"
+	      value={parentPostIds}
+	      errors={fieldErrors.parentPostIds}
+	      onChange={setParentPostIds}/>
 
-	  {/* タグ */}
-	  <PostFormTagsArea tags={tags} setTags={setTags} errors={fieldErrors.tags}/>
+	  <PostTagsField tags={tags} setTags={setTags} errors={fieldErrors.tags}/>
 
 	  {/* オリジナルの作成日時 */}
 	  <PostOriginalCreatedTimeField
@@ -227,21 +220,16 @@ const PostNewPage: FC<Props> = ({ user }) => {
 	      setOriginalCreatedFrom={setOriginalCreatedFrom}
 	      originalCreatedBefore={originalCreatedBefore}
 	      setOriginalCreatedBefore={setOriginalCreatedBefore}
-	      errors={fieldErrors.originalCreatedAt}/>
+	      errors={groupedMessages (
+		  fieldErrors.originalCreatedAt,
+		  fieldErrors.originalCreatedFrom,
+		  fieldErrors.originalCreatedBefore)}/>
 
-	  {/* 動画時間 */}
-	  {(videoFlg &&
-	      <FormField label="動画時間" messages={fieldErrors.videoMs}>
-		{({ invalid }) => (
-		    <input
-			type="number"
-			min="0.001"
-			step="0.001"
-			value={duration}
-			onChange={e => setDuration (e.target.value)}
-			aria-invalid={invalid}
-			className={inputClass (invalid)}/>)}
-	      </FormField>)}
+	  {videoFlg && (
+	      <PostDurationField
+		  value={duration}
+		  errors={fieldErrors.videoMs}
+		  onChange={setDuration}/>)}
 
 	  {/* 送信 */}
 	  <Button onClick={handleSubmit}

frontend/src/test/postImportFactories.ts

@@ -0,0 +1,53 @@
+import type { PostImportRow } from '@/lib/postImportSession'
+
+export const buildPostImportRow = (
+    overrides: Partial<PostImportRow> = {},
+): PostImportRow => {
+  const attributes = {
+    title: '',
+    thumbnailBase: '',
+    originalCreatedFrom: '',
+    originalCreatedBefore: '',
+    duration: '',
+    tags: '',
+    parentPostIds: '',
+    ...overrides.attributes }
+  const provenance = {
+    url: 'manual' as const,
+    title: 'automatic' as const,
+    thumbnailBase: 'automatic' as const,
+    originalCreatedFrom: 'automatic' as const,
+    originalCreatedBefore: 'automatic' as const,
+    duration: 'automatic' as const,
+    tags: 'automatic' as const,
+    parentPostIds: 'automatic' as const,
+    ...overrides.provenance }
+  const fieldWarnings = { ...overrides.fieldWarnings }
+  const baseWarnings = [...(overrides.baseWarnings ?? [])]
+  const tagSources = {
+    automatic: overrides.tagSources?.automatic ?? '',
+    manual: overrides.tagSources?.manual ?? '' }
+  const url = overrides.url ?? 'https://example.com/post'
+
+  return {
+    ...overrides,
+    sourceRow: overrides.sourceRow ?? 1,
+    url,
+    attributes,
+    fieldWarnings,
+    baseWarnings,
+    validationErrors: overrides.validationErrors ?? {},
+    provenance,
+    tagSources,
+    status: overrides.status ?? 'ready',
+    recoverable: overrides.recoverable,
+    resetSnapshot: overrides.resetSnapshot ?? {
+	url,
+	attributes: { ...attributes },
+	provenance: { ...provenance },
+	tagSources: { ...tagSources },
+	fieldWarnings: Object.fromEntries (
+	    Object.entries (fieldWarnings).map (([key, values]) => [key, [...values]])),
+	baseWarnings: [...baseWarnings],
+	metadataUrl: overrides.metadataUrl } }
+}