#416

Reviewed-on: #417
Co-authored-by: miteruzo <miteruzo@naver.com>

AGENTS.md

@@ -124,7 +124,7 @@ npm run preview
 - 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.
+  elements 4 spaces deeper than the statement's base indentation.
 
 ### Ruby delimiter and wrapping rules
 
@@ -140,6 +140,32 @@ npm run preview
   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。
+- Ruby では、行末の `\` を用途を問はず一切使用しない。
+- Ruby では、文字列連結、logger message、method call、条件式、SQL 断片、
+  正規表現その他すべての式で、行末バックスラッシュによる継続を禁止する。
+- Ruby の block body は、その基準位置から 2 空白深くする。
+- Ruby の wrapped expression、method argument、array element、hash pair などの
+  continuation indentation は、その statement の基準位置から 4 空白深くする。
+- Ruby の continuation indentation を、行頭からの絶対空白数として扱はない。
+- Ruby では、暗黙的に継続可能な構文を優先し、method call、array、Hash 及び
+  括弧内ではバックスラッシュなしで改行する。
+- Ruby では、行長制限を守るために行末バックスラッシュを導入してはならない。
+- Ruby で行末バックスラッシュが必要に見える場合は、括弧内で自然に改行する、
+  一つの文字列補間へまとめる、中間変数へ分ける、`format` を使ふ、heredoc を
+  使ふ、array 又は Hash を組み立ててから処理する、条件式全体を括弧で囲む、
+  method へ抽出する、のいづれかへ書き換へる。
+- Ruby では、一つの文字列を、改行をまたいだ隣接文字列 literal として記述しない。
+- Ruby では、method argument 内でも、複数の文字列 literal を区切りなしで縦に
+  並べない。
+- RSpec の `describe`、`context`、`it` 等の description が長い場合は、意味を
+  保ったまま一行へ収まる文言へ短縮する。
+- 文字列を短縮できない場合は、用途に応じて `format`、heredoc 又は中間変数を
+  検討する。
+- ただし RSpec description では、原則として簡潔な一行の文字列を使ふ。
+- formatter 又は自動修正にも、Ruby の行末バックスラッシュを生成させない。
+- 新規 code だけでなく、今回触れる Ruby code にも行末バックスラッシュを残さない。
+- 例へば class body 内の array は、class body の 2 空白を基準に、更に 4 空白
+  深くするため、結果として行頭から 6 空白になる。
 
 Bad:
 
@@ -191,6 +217,63 @@ end
 
 Bad:
 
+```rb
+Rails.logger.info(
+    "post_import_metadata_fetch_failure "\
+    "#{ payload.to_json }")
+```
+
+Good:
+
+```rb
+payload = {
+    error: e.class.name,
+    message: e.message }
+
+Rails.logger.info(
+    "post_import_metadata_fetch_failure #{ payload.to_json }")
+```
+
+Bad:
+
+```rb
+message = "first "\
+          "second"
+```
+
+Good:
+
+```rb
+message = format(
+    '%<first>s %<second>s',
+    first: 'first',
+    second: 'second')
+```
+
+Bad:
+
+```rb
+result = first_value + \
+         second_value
+```
+
+Bad:
+
+```rb
+it(
+    'returns 409 when stale changes '
+    'do not conflict'
+) do
+```
+
+Good:
+
+```rb
+it 'returns mergeable 409 for stale non-conflicting changes' do
+```
+
+Bad:
+
 ```rb
 records.each {
   do_work(_1) }
@@ -225,20 +308,37 @@ records.each {
   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
+  stage ternaries use explicit parentheses, and TypeScript / TSX indentation
-  of 8 spaces are compressed to tabs.
+  and alignment whitespace compress every complete run of 8 spaces 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.
+- In TypeScript and TSX, first determine visible indentation using 2-space
-- First determine visible indentation using 2-space block indentation and
+  block indentation and 4-space continuation indentation, then compress every
-  4-space continuation indentation, then compress only complete leading runs
+  complete run of 8 spaces used for indentation or column alignment to tabs.
-  of 8 spaces into tabs.
+- In TypeScript and TSX, 8-space compression is mandatory, not optional.
-- Tabs are only for leading indentation, never for spaces after non-space
+- In TypeScript and TSX, this applies both to leading indentation and to
-  text.
+  alignment whitespace after non-space text, such as aligned inline type
-- Keep residual leading 2, 4, or 6 spaces after any tab compression.
+  columns.
+- In TypeScript and TSX, keep residual 2, 4, or 6 spaces after each tab
+  compression.
+- In TypeScript and TSX, do not treat a tab as one logical indentation level.
+- In TypeScript and TSX, do not alter string literals, template-literal
+  contents, regular expressions, or user-facing text merely to apply 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.
+  tab + 4 spaces, 14 columns = 1 tab + 6 spaces, 16 columns = 2 tabs.
+- When TypeScript or TSX code already uses column alignment, apply the same
+  8-space compression rule to that alignment whitespace.
+- Example:
+
+```ts
+type Props = {
+    row:	      PostImportRow
+    displayNumber?:   number
+    onEdit?:	  () => void
+    onRetry?:	  () => void
+    onToggleSkip?:    (checked: boolean) => void }
+```
 - 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.
@@ -285,6 +385,13 @@ case 'no':
   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 JavaScript, JSX, TypeScript, and TSX, use `cn` from `@/lib/utils`
+  whenever `className` combines multiple values, conditional classes, or a
+  caller-provided `className` prop.
+- Do not construct `className` with template literals, `${ ... }`, string
+  concatenation, arrays joined with spaces, or feature-local class-merging
+  helpers.
+- A static `className="..."` containing only fixed classes does not need `cn`.
 - 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
@@ -460,9 +567,39 @@ and layout reuse, follow `frontend/AGENTS.md`.
   structure, control flow, or variable mutability unless the requested style
   explicitly requires it.
 - Do not add production dependencies without explicit approval.
+- Do not add user-facing copy, helper text, descriptions, notes, tooltips,
+  placeholders, empty-state messages, loading messages, or explanatory text
+  unless the user explicitly specified the wording.
+- When new user-facing wording appears necessary, ask the user for the exact
+  wording and placement before implementing it.
+- Do not invent replacement copy when removing unrequested wording.
 - Do not create, modify, or run tests unless the user explicitly asks for
-  test work. When the user asks for tests, keep working and rerun them until
+  test work. When the user asks for tests, keep working within the permitted
-  they pass or the remaining failure is clearly blocked.
+  test-file scope and rerun them until they pass or the remaining failure is
+  clearly blocked.
+- Test-only work includes adding, updating, deleting, reorganising, or fixing
+  SyntaxError in tests. During test-only work, do not modify production code.
+- During test-only work, do not change production constants, behaviour, API
+  contracts, validation, routes, authentication, permissions, UI, copy,
+  dependencies, limits, thresholds, defaults, migrations, schema, or
+  environment settings to satisfy tests.
+- Do not make production code match failing tests, mock assumptions, fixtures,
+  snapshots, old expectations, or stale setup. This includes changing
+  production constants merely because a test expects a different value.
+- If test work reveals a production bug, spec mismatch, or missing behaviour,
+  stop without modifying production code and report: the failing test or
+  discovered issue, the related production file, the actual behaviour, the
+  expected behaviour, and why a production change appears necessary.
+- Modify production code for test failures only when the user explicitly asks
+  for that production change. Do not expand a test task into a production task
+  on your own authority.
+- If the user explicitly asks for both production implementation and test
+  updates, implement production code to the confirmed specification first,
+  then add or update tests to verify that specification. Never roll production
+  behaviour back to satisfy old tests.
+- If it is unclear whether the test or the production implementation is stale,
+  or a test cannot be corrected without changing production code, ask the user
+  instead of guessing.
 
 ## Backend rules
 
@@ -516,6 +653,11 @@ and layout reuse, follow `frontend/AGENTS.md`.
 - Mobile UI must be checked as a first-class layout. Avoid wide fixed content,
   make dense controls wrap or scroll intentionally, and keep tag/filter
   controls usable without horizontal page overflow.
+- Frontend のスマホ／PC表示境界は原則 `md` とする。
+- button stack、footer action、dialogue action は `md` 未満で縦並び、
+  `md` 以上で横並びとする。
+- 同じ画面内で `sm` と `md` を混在させて中間 layout を作らない。
+- 明確に別の responsive 要件がある component だけを例外とする。
 - For mobile horizontal scrollers, make the scroll direction and item sizing
   explicit, and ensure chip text remains readable in both light and dark modes.
 - In TypeScript and TSX, prefer direct comparison operators such as `===` and
@@ -580,10 +722,10 @@ and layout reuse, follow `frontend/AGENTS.md`.
   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 block indentation uses
+- The TypeScript/TSX self-review must confirm block indentation uses 2 spaces
-  2 spaces per level, wrapped continuations use the repository's 4-space
+  per level, wrapped continuations use the repository's 4-space continuation
-  continuation alignment, and complete leading runs of 8 spaces may be
+  alignment, and every complete run of 8 spaces used for indentation or
-  compressed to tabs.
+  alignment has been 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.
@@ -596,9 +738,18 @@ and layout reuse, follow `frontend/AGENTS.md`.
 - 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
+- In TypeScript and TSX, convert every complete run of 8 spaces used for
-  tab character.
+  indentation or alignment to a tab character.
-- A leading tab is exactly equivalent to 8 leading spaces.
+- In TypeScript and TSX, a tab is exactly equivalent to 8 columns, whether it
+  appears at the beginning of a line or in alignment whitespace after
+  non-space text.
+- In TSX, JSX nesting uses 2-space block indentation and wrapped JSX
+  attributes use 4-space continuation indentation; after visible columns are
+  determined, compress every complete run of 8 spaces in the resulting
+  indentation or alignment to tabs.
+- In TSX, do not leave JSX subtree indentation at 8, 10, 12, 14, or 16
+  columns as spaces alone; convert each complete run of 8 spaces to tabs and
+  keep only the residual 2, 4, or 6 spaces.
 - In TypeScript and TSX function declarations, including `const` arrow
   function declarations, classify the parameter list before placing the closing
   `)`.
@@ -1241,9 +1392,9 @@ 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 block indentation uses 2 spaces per level, wrapped continuations
+9. Block indentation uses 2 spaces per level, wrapped continuations use the
-   use the repository's 4-space continuation alignment, and complete leading
+   repository's 4-space continuation alignment, and every complete run of 8
-   runs of 8 spaces may be compressed to tabs.
+   spaces used for indentation or alignment has been compressed to tabs.
 10. No line has trailing whitespace.
 
 Preferred:

backend/app/controllers/application_controller.rb

@@ -85,4 +85,11 @@ class ApplicationController < ActionController::API
                    base_errors: },
            status:
   end
+
+  def normalise_json value
+    return nil if value.nil?
+    return JSON.parse(value) if value.is_a?(String)
+
+    value
+  end
 end

backend/app/controllers/materials_controller.rb

@@ -237,7 +237,7 @@ class MaterialsController < ApplicationController
   end
 
   def resolve_material_tag! tag_name_raw
-    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
+    tag_name = TagName.find_or_create_by!(name: tag_name_raw)
     tag = tag_name.tag
     tag || Tag.create!(tag_name:, category: :material)
   end

backend/app/controllers/post_imports_controller.rb

@@ -1,44 +0,0 @@
-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/post_versions_controller.rb

@@ -1,7 +1,7 @@
 class PostVersionsController < ApplicationController
   def index
     post_id = params[:post].presence
-    tag_id = params[:tag].presence
+    tag_id = params[:tag].presence&.to_i
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -10,12 +10,6 @@ class PostVersionsController < ApplicationController
 
     offset = (page - 1) * limit
 
-    tag_name =
-        if tag_id
-          TagName.joins(:tag).find_by(tag: { id: tag_id })
-        end
-    return render json: { versions: [], count: 0 } if tag_id && tag_name.blank?
-
     q = PostVersion.joins(<<~SQL.squish)
           LEFT JOIN
             post_versions prev
@@ -23,17 +17,18 @@ class PostVersionsController < ApplicationController
               prev.post_id = post_versions.post_id
               AND prev.version_no = post_versions.version_no - 1
         SQL
-        .select('post_versions.*', 'prev.title AS prev_title', 'prev.url AS prev_url',
+        .select('post_versions.*',
-                'prev.thumbnail_base AS prev_thumbnail_base', 'prev.tags AS prev_tags',
+                'prev.title AS prev_title',
+                'prev.url AS prev_url',
+                'prev.thumbnail_base AS prev_thumbnail_base',
+                'prev.tags_json AS prev_tags_json',
                 'prev.video_ms AS prev_video_ms',
                 'prev.original_created_from AS prev_original_created_from',
                 'prev.original_created_before AS prev_original_created_before')
     q = q.where('post_versions.post_id = ?', post_id) if post_id
-    if tag_name
+    if tag_id
-      escaped = ActiveRecord::Base.sanitize_sql_like(tag_name.name)
+      q = q.where("JSON_CONTAINS(post_versions.tags_json, JSON_OBJECT('id', #{ tag_id })) " +
-      q = q.where(("CONCAT(' ', post_versions.tags, ' ') LIKE :kw " +
+                  "OR JSON_CONTAINS(prev.tags_json, JSON_OBJECT('id', #{ tag_id }))")
-                   "OR CONCAT(' ', prev.tags, ' ') LIKE :kw"),
-                  kw: "% #{ escaped } %")
     end
 
     count = q.except(:select, :order, :limit, :offset).count
@@ -52,51 +47,69 @@ class PostVersionsController < ApplicationController
     users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
 
     rows.map do |row|
-      cur_tags = split_tags(row.tags)
+      cur_tags =
-      prev_tags = split_tags(row.attributes['prev_tags'])
+          normalise_json(row.tags_json)
+          .sort_by { [(case _1.fetch('category')
+                       when 'deerjikist'
+                         0
+                       when 'meme'
+                         1
+                       when 'character'
+                         2
+                       when 'general'
+                         3
+                       when 'material'
+                         4
+                       when 'meta'
+                         5
+                       else
+                         6
+                       end),
+                      _1.fetch('name').downcase] }
+          .map { Post.tag_snapshot_literal(_1) }
+      prev_tags =
+          (normalise_json(row.attributes['prev_tags_json']) || [])
+          .sort_by { [(case _1.fetch('category')
+                       when 'deerjikist'
+                         0
+                       when 'meme'
+                         1
+                       when 'character'
+                         2
+                       when 'general'
+                         3
+                       when 'material'
+                         4
+                       when 'meta'
+                         5
+                       else
+                         6
+                       end),
+                      _1.fetch('name').downcase] }
+          .map { Post.tag_snapshot_literal(_1) }
 
-      {
+      { post_id: row.post_id,
-        post_id: row.post_id,
         version_no: row.version_no,
         event_type: row.event_type,
-        title: {
+        title: { current: row.title, prev: row.attributes['prev_title'] },
-          current: row.title,
+        url: { current: row.url, prev: row.attributes['prev_url'] },
-          prev: row.attributes['prev_title']
+        thumbnail: { current: nil, prev: nil },
-        },
+        thumbnail_base: { current: row.thumbnail_base,
-        url: {
+                          prev: row.attributes['prev_thumbnail_base'] },
-          current: row.url,
+        video_ms: { current: row.video_ms, prev: row.attributes['prev_video_ms'] },
-          prev: row.attributes['prev_url']
-        },
-        thumbnail: {
-          current: nil,
-          prev: nil
-        },
-        thumbnail_base: {
-          current: row.thumbnail_base,
-          prev: row.attributes['prev_thumbnail_base']
-        },
-        video_ms: {
-          current: row.video_ms,
-          prev: row.attributes['prev_video_ms']
-        },
         tags: build_version_tags(cur_tags, prev_tags),
         original_created_from: {
-          current: row.original_created_from&.iso8601,
+            current: row.original_created_from&.iso8601,
-          prev: row.attributes['prev_original_created_from']&.iso8601
+            prev: row.attributes['prev_original_created_from']&.iso8601 },
-        },
         original_created_before: {
-          current: row.original_created_before&.iso8601,
+            current: row.original_created_before&.iso8601,
-          prev: row.attributes['prev_original_created_before']&.iso8601
+            prev: row.attributes['prev_original_created_before']&.iso8601 },
-        },
         created_at: row.created_at.iso8601,
         created_by_user:
-          if row.created_by_user_id
+            if row.created_by_user_id
-            {
+              { id: row.created_by_user_id,
-              id: row.created_by_user_id,
+                name: users_by_id[row.created_by_user_id] }
-              name: users_by_id[row.created_by_user_id]
+            end }
-            }
-          end
-      }
     end
   end
 
@@ -117,8 +130,4 @@ class PostVersionsController < ApplicationController
       }
     end
   end
-
-  def split_tags(tags)
-    tags.to_s.split(/\s+/).reject(&:blank?)
-  end
 end

backend/app/controllers/posts_controller.rb

@@ -1,5 +1,6 @@
 class PostsController < ApplicationController
   Event = Struct.new(:post, :tag, :user, :change_type, :timestamp, keyword_init: true)
+  MAX_BULK_REQUEST_BYTES = 40 * 1024 * 1024
 
   class VideoMsParseError < ArgumentError
     ;
@@ -35,8 +36,8 @@ class PostsController < ApplicationController
     offset = (page - 1) * limit
 
     pt_max_sql =
-        PostTag
+        PostVersion
-        .select('post_id, MAX(updated_at) AS max_updated_at')
+        .select('post_id, MAX(created_at) AS max_updated_at')
         .group('post_id')
         .to_sql
 
@@ -49,9 +50,8 @@ class PostsController < ApplicationController
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
         .preload(:uploaded_user, :parents, :children,
-                 active_post_tags: [:sections,
+                 post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                    { tag: [:deerjikists, :materials,
+                                                { tag_name: :wiki_page }] }])
-                                            { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -103,9 +103,8 @@ class PostsController < ApplicationController
 
   def random
     post = filtered_posts.preload(:uploaded_user, :parents, :children,
-                                  active_post_tags: [:sections,
+                                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                     { tag: [:deerjikists, :materials,
+                                                                 { tag_name: :wiki_page }] }])
-                                                             { tag_name: :wiki_page }] }])
                          .with_attached_thumbnail
                          .order('RAND()')
                          .first
@@ -114,13 +113,83 @@ class PostsController < ApplicationController
     render json: PostRepr.base(post, current_user)
   end
 
+  def metadata
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+    return render_bad_request('URL は必須です．') if params[:url].blank?
+
+    normal_url = PostUrlNormaliser.normalise(params[:url].to_s)
+    return render_validation_error(fields: { url: ['URL が不正です．'] }) if normal_url.blank?
+
+    Preview::UrlSafety.validate(normal_url)
+    existing_post = Post.with_attached_thumbnail.find_by(url: normal_url)
+    if existing_post.present?
+      return render json: {
+          url: normal_url,
+          title: nil,
+          thumbnail_base: nil,
+          tags: nil,
+          display_tags: [],
+          original_created_from: nil,
+          original_created_before: nil,
+          duration: nil,
+          video_ms: nil,
+          field_warnings: { },
+          base_warnings: [],
+          existing_post_id: existing_post.id,
+          existing_post: compact_post(existing_post.id) }
+    end
+
+    metadata = PostMetadataFetcher.fetch(normal_url)
+    field_warnings = { }
+    field_warnings[:title] = ['タイトルを取得できませんでした．'] if metadata[:title].blank?
+    if metadata[:thumbnail_base].blank?
+      field_warnings[:thumbnail_base] = ['サムネールを取得できませんでした．']
+    end
+
+    render json: {
+        url: normal_url,
+        title: metadata[:title],
+        thumbnail_base: metadata[:thumbnail_base],
+        tags: metadata[:tags],
+        display_tags: metadata[:display_tags],
+        original_created_from: metadata[:original_created_from],
+        original_created_before: metadata[:original_created_before],
+        duration: metadata[:duration],
+        video_ms: metadata[:video_ms],
+        field_warnings: field_warnings,
+        base_warnings: [],
+        existing_post_id: nil,
+        existing_post: nil }
+  rescue ArgumentError => e
+    render_bad_request e.message
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    render_validation_error fields: { url: [e.message] }
+  rescue Preview::HttpFetcher::FetchFailed,
+         Preview::HttpFetcher::FetchTimeout,
+         Preview::HttpFetcher::ResponseTooLarge
+    render json: {
+        url: normal_url,
+        title: nil,
+        thumbnail_base: nil,
+        tags: nil,
+        display_tags: [],
+        original_created_from: nil,
+        original_created_before: nil,
+        duration: nil,
+        video_ms: nil,
+        field_warnings: { url: ['自動取得に失敗しました．'] },
+        base_warnings: [],
+        existing_post_id: nil,
+        existing_post: nil }
+  end
+
   def show
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
-                  active_post_tags: [:sections,
+                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                     { tag: [:deerjikists, :materials,
+                                                 { tag_name: :wiki_page }] }])
-                                             { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -142,17 +211,41 @@ class PostsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    preflight = PostCreatePreflight.new(
+        attributes: post_create_attributes,
+        thumbnail: params[:thumbnail],
+        host: request.base_url).run
+    return render json: dry_run_json(preflight) if bool?(:dry)
+    if preflight[:existing_post_id].present?
+      post = Post.new(url: preflight[:url])
+      post.errors.add :url, :taken
+      return render_post_form_record_invalid post
+    end
+
     post = PostCreator.new(actor: current_user,
-                           attributes: { title: params[:title], url: params[:url],
+                           attributes: post_create_attributes.merge(
-                                         thumbnail: params[:thumbnail], tags: params[:tags],
+                               preflight.slice(
-                                         original_created_from: params[:original_created_from],
+                                   :url,
-                                         original_created_before: params[:original_created_before],
+                                   :title,
-                                         parent_post_ids: parse_parent_post_ids,
+                                   :thumbnail_base,
-                                         video_ms: params[:video_ms],
+                                   :tags,
-                                         duration: params[:duration] }).create!
+                                   :parent_post_ids,
+                                   :original_created_from,
+                                   :original_created_before,
+                                   :duration,
+                                   :video_ms,
+                                   :direct_tag_specs,
+                                   :default_tag_specs,
+                                   :snapshot_tag_specs,
+                                   :post_tag_specs,
+                                   :tag_sections,
+                                   :normalised_parent_post_ids).symbolize_keys).merge(
+                               thumbnail: params[:thumbnail])).create!
 
     post.reload
     render json: PostRepr.base(post), status: :created
+  rescue PostCreatePreflight::ValidationFailed => e
+    render_validation_error fields: e.fields, base: e.base_errors
   rescue Tag::NicoTagNormalisationError
     render_validation_error fields: { tags: 'ニコニコ・タグは直接指定できません．' }
   rescue Tag::DeprecatedTagNormalisationError
@@ -161,6 +254,8 @@ class PostsController < ApplicationController
     render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
   rescue PostCreator::VideoMsParseError
     render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
+  rescue Post::RemoteThumbnailFetchFailed
+    render_validation_error fields: { thumbnail_base: ['サムネイル画像の取得に失敗しました．'] }
   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．'] }
   rescue ArgumentError => e
@@ -169,6 +264,25 @@ class PostsController < ApplicationController
     render_post_form_record_invalid e.record
   end
 
+  def bulk
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+    return head :unsupported_media_type unless request.content_mime_type == Mime[:multipart_form]
+    return head :payload_too_large if request.content_length.to_i > MAX_BULK_REQUEST_BYTES
+    posts = parse_bulk_posts_manifest
+    thumbnails = parse_bulk_thumbnails(posts.length)
+    result = PostBulkCreator.new(
+        actor: current_user,
+        posts:,
+        thumbnails:,
+        host: request.base_url).run
+    render json: result
+  rescue JSON::ParserError
+    render_bad_request 'posts manifest の JSON が不正です．'
+  rescue ArgumentError => e
+    render_validation_error base: [e.message]
+  end
+
   def viewed
     return head :unauthorized unless current_user
 
@@ -267,50 +381,6 @@ class PostsController < ApplicationController
     render_post_form_record_invalid e.record
   end
 
-  def changes
-    id = params[:id].presence
-    tag_id = params[:tag].presence
-    page = (params[:page].presence || 1).to_i
-    limit = (params[:limit].presence || 20).to_i
-
-    page = 1 if page < 1
-    limit = 1 if limit < 1
-
-    offset = (page - 1) * limit
-
-    pts = PostTag.with_discarded
-    pts = pts.where(post_id: id) if id.present?
-    pts = pts.where(tag_id:) if tag_id.present?
-    pts = pts.includes(:post, :created_user, :deleted_user,
-                       tag: [:deerjikists, :materials, { tag_name: :wiki_page }])
-
-    events = []
-    pts.each do |pt|
-      tag = TagRepr.base(pt.tag)
-      post = pt.post
-
-      events << Event.new(
-          post:,
-          tag:,
-          user: pt.created_user && { id: pt.created_user.id, name: pt.created_user.name },
-          change_type: 'add',
-          timestamp: pt.created_at)
-
-      if pt.discarded_at
-        events << Event.new(
-            post:,
-            tag:,
-            user: pt.deleted_user && { id: pt.deleted_user.id, name: pt.deleted_user.name },
-            change_type: 'remove',
-            timestamp: pt.discarded_at)
-      end
-    end
-    events.sort_by!(&:timestamp)
-    events.reverse!
-
-    render json: { changes: (events.slice(offset, limit) || []).as_json, count: events.size }
-  end
-
   private
 
   def filtered_posts
@@ -385,13 +455,13 @@ class PostsController < ApplicationController
       end
     end
 
-    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
-      pt.discard_by!(current_user)
+      pt.destroy!
     end
   end
 
   def build_tag_tree_for post
-    post_tags = post.active_post_tags.reject { |post_tag| post_tag.tag.deprecated? }
+    post_tags = post.post_tags.reject { |post_tag| post_tag.tag.deprecated? }
     tags = post_tags.map(&:tag)
     tag_ids = tags.map(&:id)
 
@@ -463,6 +533,79 @@ class PostsController < ApplicationController
     }.uniq
   end
 
+  def post_create_attributes
+    { title: params[:title],
+      url: params[:url],
+      thumbnail_base: params[:thumbnail_base],
+      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] }
+  end
+
+  def parse_bulk_posts_manifest
+    manifest = params[:posts]
+    raise ArgumentError, 'posts は必須です．' if manifest.blank?
+    raise ArgumentError, 'posts は JSON 文字列で指定してください．' unless manifest.is_a?(String)
+
+    posts = JSON.parse(manifest)
+    raise ArgumentError, 'posts は配列で指定してください．' unless posts.is_a?(Array)
+    raise ArgumentError, '投稿件数は 1 件以上必要です．' if posts.empty?
+    raise ArgumentError, '投稿件数が多すぎます．' if posts.length > 100
+    raise ArgumentError, 'posts 要素の形式が不正です．' unless posts.all? { _1.is_a?(Hash) }
+
+    posts
+  end
+
+  def parse_bulk_thumbnails post_count
+    thumbnails = { }
+    raw = params[:thumbnails]
+    return thumbnails if raw.blank?
+    raise ArgumentError, 'thumbnail key が不正です．' unless raw.respond_to?(:to_unsafe_h)
+
+    raw.to_unsafe_h.each do |key, value|
+      raise ArgumentError, 'thumbnail key が不正です．' unless key.to_s.match?(/\A\d+\z/)
+
+      index = Integer(key, 10)
+      raise ArgumentError, 'thumbnail index が範囲外です．' if index.negative? || index >= post_count
+      raise ArgumentError, 'thumbnail index が重複しています．' if thumbnails.key?(index)
+      unless value.is_a?(ActionDispatch::Http::UploadedFile)
+        raise ArgumentError, 'thumbnail upload が不正です．'
+      end
+
+      thumbnails[index] = value
+    end
+
+    thumbnails
+  end
+
+  def compact_post post_id
+    return nil if post_id.blank?
+
+    post = Post.with_attached_thumbnail.find_by(id: post_id)
+    PostCompactRepr.base(post, host: request.base_url)
+  end
+
+  def dry_run_json preflight
+    preflight.slice(
+        :url,
+        :title,
+        :thumbnail_base,
+        :tags,
+        :display_tags,
+        :parent_post_ids,
+        :original_created_from,
+        :original_created_before,
+        :duration,
+        :video_ms,
+        :field_warnings,
+        :base_warnings,
+        :existing_post_id,
+        :existing_post)
+  end
+
   def sync_parent_posts! post, parent_post_ids
     if parent_post_ids.include?(post.id)
       post.errors.add :parent_post_ids, '自分自身を親投稿にはできません．'
@@ -509,7 +652,10 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_version version
-    version.tags.to_s.split.reject { |name| name.downcase.start_with?('nico:') }.sort
+    version.tags_json
+        .reject { _1.fetch('category') == 'nico' }
+        .map { Post.tag_snapshot_literal(_1) }
+        .sort
   end
 
   def post_snapshot_from_record post
@@ -524,7 +670,6 @@ class PostsController < ApplicationController
   def editable_tag_names_from_post post
     post
         .post_tags
-        .kept
         .joins(tag: :tag_name)
         .merge(Tag.not_nico)
         .merge(Tag.where(deprecated_at: nil))
@@ -542,6 +687,7 @@ class PostsController < ApplicationController
 
   def post_incoming_snapshot title:, original_created_from:, original_created_before:,
                              tag_names:, video_ms_param:, duration_param:, parent_post_ids:
+    validate_original_created_values!(original_created_from, original_created_before)
     Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
                                         with_sections: true) =>
         { tags:, sections: }
@@ -579,6 +725,23 @@ class PostsController < ApplicationController
     value.to_s
   end
 
+  def validate_original_created_values! original_created_from, original_created_before
+    candidate = Post.new(
+        url: 'https://example.invalid/original-created-validation',
+        original_created_from:,
+        original_created_before:)
+    candidate.valid?
+    fields = [:original_created_from, :original_created_before, :original_created_at]
+    relevant_errors = candidate.errors.select { fields.include?(_1.attribute) }
+    return if relevant_errors.empty?
+
+    invalid_post = Post.new
+    relevant_errors.each { |error|
+      invalid_post.errors.add(error.attribute, error.message)
+    }
+    raise ActiveRecord::RecordInvalid, invalid_post
+  end
+
   def section_literal section
     "[#{ Post.ms_to_time(section[0]) }-#{ section[1] ? Post.ms_to_time(section[1]) : '' }]"
   end

backend/app/controllers/preview_controller.rb

@@ -18,14 +18,12 @@ class PreviewController < ApplicationController
   def thumbnail
     return render_bad_request('URL は必須です．') if params[:url].blank?
 
-    image = MiniMagick::Image.read(Preview::ThumbnailFetcher.fetch(params[:url]))
+    attachment =
-    image.auto_orient
+        Post.resized_thumbnail_attachment(
-    image.resize '180x180>'
+            StringIO.new(Preview::ThumbnailFetcher.fetch(params[:url])))
-    image.format 'png'
+    send_data attachment[:io].read,
-    width, height = image.dimensions
+              type: attachment[:content_type],
-    raise Preview::ThumbnailFetcher::GenerationFailed, 'サムネール画像の変換に失敗しました．' if width > 180 || height > 180
+              disposition: 'inline'
-
-    send_data image.to_blob, type: 'image/png', disposition: 'inline'
   rescue Preview::UrlSafety::UnsafeUrl => e
     render_bad_request(e.message)
   rescue Preview::HttpFetcher::FetchTimeout => e

backend/app/controllers/tags_controller.rb

@@ -200,14 +200,45 @@ class TagsController < ApplicationController
              .find_by(id: params[:id])
     return head :not_found unless tag
 
+    rows = normalise_deerjikist_rows(tag)
+    return if performed?
+
     ApplicationRecord.transaction do
-      tag.deerjikists = []
+      tag.lock!
-      params[:_json].each.with_index do |item, i|
+
-        platform = item[:platform]
+      requested_keys = rows.map { |row| [row[:platform], row[:code]] }.uniq
-        code = normalise_deerjikist_code(platform, item[:code])
+      row_indexes_by_key = rows_by_key(rows)
-        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
+      locked_deerjikists = lock_deerjikists_for_tag_update(tag.id, requested_keys)
-        deerjikist.tag = tag
+      current_deerjikists = locked_deerjikists.filter { |deerjikist|
-        render_deerjikist_form_record_invalid(deerjikist, i) unless deerjikist.save
+        deerjikist.tag_id == tag.id
+      }
+      requested_deerjikists = locked_deerjikists.filter { |deerjikist|
+        row_indexes_by_key.key?([deerjikist.platform, deerjikist.code])
+      }
+
+      render_deerjikist_conflicts(requested_deerjikists, row_indexes_by_key, tag)
+      raise ActiveRecord::Rollback if performed?
+
+      requested_keys_set = requested_keys.to_set
+      current_deerjikists.each do |deerjikist|
+        key = [deerjikist.platform, deerjikist.code]
+        deerjikist.destroy! unless requested_keys_set.include?(key)
+      end
+
+      existing_keys = requested_deerjikists.to_h { |deerjikist|
+        [[deerjikist.platform, deerjikist.code], true]
+      }
+      requested_keys.each do |platform, code|
+        next if existing_keys[[platform, code]]
+
+        deerjikist = Deerjikist.new(platform:, code:, tag:)
+        row_index = row_indexes_by_key[[platform, code]].first
+        begin
+          render_deerjikist_form_record_invalid(deerjikist, row_index) unless deerjikist.save
+        rescue ActiveRecord::RecordNotUnique
+          conflicts = lock_deerjikists_for_tag_update(tag.id, [[platform, code]])
+          render_deerjikist_conflicts(conflicts, row_indexes_by_key, tag)
+        end
         raise ActiveRecord::Rollback if performed?
       end
     end
@@ -542,7 +573,7 @@ class TagsController < ApplicationController
       return false
     end
 
-    target_tag_name = TagName.with_discarded.find_by(name:)
+    target_tag_name = TagName.find_by(name:)
     return true if target_tag_name.nil?
     return true if target_tag_name.canonical_id?
 
@@ -554,17 +585,14 @@ class TagsController < ApplicationController
     return if name == tag.name
 
     current_tag_name = tag.tag_name
-    target_tag_name = TagName.with_discarded.find_by(name:)
+    target_tag_name = TagName.find_by(name:)
 
     if target_tag_name.nil?
       current_tag_name.update!(name:)
       return
     end
 
-    promote_tag_alias!(
+    promote_tag_alias!(tag, current_tag_name:, promoted_tag_name: target_tag_name)
-        tag,
-        current_tag_name:,
-        promoted_tag_name: target_tag_name)
   end
 
   def promote_tag_alias! tag, current_tag_name:, promoted_tag_name:
@@ -574,11 +602,9 @@ class TagsController < ApplicationController
       TagVersioning.ensure_snapshot!(old_owner_tag, created_by_user: current_user)
     end
 
-    promoted_tag_name.undiscard! if promoted_tag_name.discarded?
     promoted_tag_name.update!(canonical: nil)
 
-    TagName.with_discarded
+    TagName.where(canonical_id: current_tag_name.id)
-           .where(canonical_id: current_tag_name.id)
            .where.not(id: promoted_tag_name.id)
            .find_each do |alias_tag_name|
       alias_tag_name.update!(canonical: promoted_tag_name)
@@ -609,7 +635,7 @@ class TagsController < ApplicationController
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      alias_tag_name = TagName.find_or_create_by!(name: alias_name)
       affected_tags << alias_tag_name.canonical&.tag
     end
 
@@ -624,7 +650,7 @@ class TagsController < ApplicationController
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      alias_tag_name = TagName.find_or_create_by!(name: alias_name)
       alias_tag_name.update!(canonical: tag.tag_name)
     end
 
@@ -653,6 +679,7 @@ class TagsController < ApplicationController
   end
 
   def normalise_deerjikist_code platform, code
+    code = code.to_s
     return code if platform != 'youtube' || code[0] != '@'
 
     url = "https://www.youtube.com/#{ code }"
@@ -669,6 +696,82 @@ class TagsController < ApplicationController
     nil
   end
 
+  def normalise_deerjikist_rows tag
+    rows = []
+
+    params[:_json].each.with_index do |item, index|
+      platform = item[:platform]
+      unless Deerjikist.platforms.key?(platform)
+        render_deerjikist_platform_invalid(index)
+        return rows
+      end
+
+      code = normalise_deerjikist_code(platform, item[:code])
+      deerjikist = Deerjikist.new(platform:, code:, tag:)
+      unless deerjikist.valid?
+        render_deerjikist_form_record_invalid(deerjikist, index)
+        return rows
+      end
+
+      rows << { index:, platform:, code: }
+    end
+
+    rows
+  end
+
+  def lock_deerjikists_for_tag_update tag_id, keys
+    clauses = ['tag_id = ?']
+    values = [tag_id]
+
+    keys.each do |platform, code|
+      clauses << '(platform = ? AND code = ?)'
+      values << platform << code
+    end
+
+    Deerjikist
+      .where(clauses.join(' OR '), *values)
+      .order(:platform, :code)
+      .lock
+      .to_a
+  end
+
+  def render_deerjikist_conflicts deerjikists, row_indexes_by_key, tag
+    conflicts = deerjikists.filter { |deerjikist| deerjikist.tag_id != tag.id }
+    return if conflicts.empty?
+
+    tag_names_by_id = Tag
+                      .joins(:tag_name)
+                      .where(id: conflicts.map(&:tag_id).uniq)
+                      .pluck('tags.id', 'tag_names.name')
+                      .to_h
+    fields = { }
+
+    conflicts.each do |deerjikist|
+      message = "この情報は既に「#{ tag_names_by_id[deerjikist.tag_id] }」に紐づいてゐます．"
+      row_indexes_by_key[[deerjikist.platform, deerjikist.code]].each do |index|
+        field = :"deerjikists.#{ index }.code"
+        fields[field] ||= []
+        fields[field] << message
+      end
+    end
+
+    render_validation_error fields:
+  end
+
+  def render_deerjikist_platform_invalid index
+    render_validation_error fields: {
+      :"deerjikists.#{ index }.platform" => ['値が不正です．'],
+    }
+  end
+
+  def rows_by_key rows
+    rows.each_with_object({ }) do |row, result|
+      key = [row[:platform], row[:code]]
+      result[key] ||= []
+      result[key] << row[:index]
+    end
+  end
+
   def render_deerjikist_form_record_invalid deerjikist, index
     fields = { }
 

backend/app/controllers/wiki_pages_controller.rb

@@ -94,7 +94,7 @@ class WikiPagesController < ApplicationController
     return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
-    tag_name = TagName.find_undiscard_or_create_by!(name: title)
+    tag_name = TagName.find_or_create_by!(name: title)
 
     page =
         Wiki::Commit.create_content!(

backend/app/models/post.rb

@@ -1,7 +1,9 @@
 class Post < ApplicationRecord
   require 'date'
   require 'mini_magick'
+  require 'nokogiri'
   require 'stringio'
+  require 'timeout'
 
   class RemoteThumbnailFetchFailed < StandardError; end
 
@@ -11,44 +13,69 @@ class Post < ApplicationRecord
   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
-
+  REMOTE_SVG_CONTENT_TYPE = 'image/svg+xml'.freeze
-  def self.resized_thumbnail_attachment(upload)
+  MAX_SVG_DIMENSION = 4_096
+  MAX_SVG_PIXELS = 16_777_216
+  THUMBNAIL_PROCESS_TIMEOUT = 5.seconds
+  def self.resized_thumbnail_attachment(upload, content_type: nil)
     upload.rewind
-    image = MiniMagick::Image.read(upload.read)
+    bytes = upload.read
-    image.resize '180x180^'
+    blob = Timeout.timeout(THUMBNAIL_PROCESS_TIMEOUT) do
-    image.gravity 'Center'
+      image = image_for_thumbnail_upload(bytes, content_type:)
-    image.extent '180x180'
+      image.auto_orient
-    image.format 'jpg'
+      image.resize '180x180'
+      image.format 'jpg'
+      image.to_blob
+    end
 
-    { io: StringIO.new(image.to_blob),
+    { io: StringIO.new(blob),
       filename: 'resized_thumbnail.jpg',
       content_type: 'image/jpeg' }
+  rescue Timeout::Error
+    raise MiniMagick::Error, 'サムネイル画像の変換に失敗しました．'
   ensure
     upload.rewind
   end
 
+  def self.remote_thumbnail_attachment(raw_url)
+    response = Preview::ThumbnailFetcher.fetch_image_response(raw_url)
+    resized_thumbnail_attachment(
+        StringIO.new(response.body),
+        content_type: response.content_type)
+  rescue Preview::UrlSafety::UnsafeUrl,
+         Preview::ThumbnailFetcher::GenerationFailed,
+         Preview::HttpFetcher::FetchFailed,
+         Preview::HttpFetcher::FetchTimeout,
+         Preview::HttpFetcher::ResponseTooLarge,
+         Timeout::Error,
+         MiniMagick::Error => e
+    raise RemoteThumbnailFetchFailed, e.message
+  end
+
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
-  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
+  has_many :tags, through: :post_tags
-  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
-  has_many :tags, through: :active_post_tags
   has_many :active_tags, -> { where(tags: { deprecated_at: nil }) },
-           through: :active_post_tags, source: :tag
+           through: :post_tags,
+           source: :tag
 
   has_many :user_post_views, dependent: :delete_all
   has_many :post_similarities, dependent: :delete_all
   has_many :post_versions
+
   has_many :gekanator_guessed_games,
            class_name: 'GekanatorGame',
            foreign_key: :guessed_post_id,
            dependent: :delete_all,
            inverse_of: :guessed_post
+
   has_many :gekanator_correct_games,
            class_name: 'GekanatorGame',
            foreign_key: :correct_post_id,
            dependent: :delete_all,
            inverse_of: :correct_post
+
   has_many :gekanator_question_examples, dependent: :delete_all
 
   has_many :parent_post_implications,
@@ -98,7 +125,6 @@ class Post < ApplicationRecord
 
   def snapshot_tag_names
     post_tags
-        .kept
         .joins(tag: :tag_name)
         .includes(:sections, tag: :tag_name)
         .order('tag_names.name')
@@ -112,8 +138,38 @@ class Post < ApplicationRecord
     end
   end
 
+  def self.tag_snapshot_literal tag
+    sections = tag.fetch('sections', []).map do |sec|
+      begin_ms = sec.fetch('begin_ms')
+      end_ms = sec['end_ms']
+
+      "[#{ Post.ms_to_time(begin_ms) }-#{ end_ms ? Post.ms_to_time(end_ms) : '' }]"
+    end
+
+    "#{ tag.fetch('name') }#{ sections.join }"
+  end
+
+  def snapshot_tags_json
+    post_tags
+        .joins(tag: :tag_name)
+        .includes(:sections, tag: :tag_name)
+        .order('tags.id')
+        .map do |pt|
+      { 'id' => pt.tag.id,
+        'version_no' => pt.tag.version_no,
+        'name' => pt.tag.name,
+        'category' => pt.tag.category,
+        'sections' => pt.sections.sort_by(&:begin_ms).map {
+          { 'begin_ms' => _1.begin_ms, 'end_ms' => _1.end_ms }
+        } }
+    end
+  end
+
   def self.section_literal section
-    "[#{ Post.ms_to_time(section.begin_ms) }-#{ section.end_ms ? Post.ms_to_time(section.end_ms) : '' }]"
+    end_ms =
+        section.end_ms ? Post.ms_to_time(section.end_ms) : ''
+
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ end_ms }]"
   end
 
   def self.ms_to_time ms
@@ -157,17 +213,7 @@ class Post < ApplicationRecord
   end
 
   def attach_thumbnail_from_url! raw_url
-    response = Preview::ThumbnailFetcher.fetch_image_response(raw_url)
+    thumbnail.attach(self.class.remote_thumbnail_attachment(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
@@ -209,6 +255,179 @@ class Post < ApplicationRecord
     self.url = PostUrlNormaliser.normalise(url) || url.strip
   end
 
+  def self.image_for_thumbnail_upload(bytes, content_type: nil)
+    if svg_content_type?(content_type) || svg_document_bytes?(bytes)
+      return decode_svg_thumbnail(bytes)
+    end
+
+    raise MiniMagick::Error, 'サムネイル画像の形式が不正です．' unless raster_thumbnail_bytes?(bytes)
+
+    decode_raster_thumbnail(bytes)
+  end
+
+  def self.raster_thumbnail_bytes?(bytes)
+    raster_thumbnail_format(bytes).present?
+  end
+
+  def self.remote_thumbnail_image_bytes?(bytes, content_type: nil)
+    return true if svg_content_type?(content_type) || svg_document_bytes?(bytes)
+
+    raster_thumbnail_bytes?(bytes)
+  end
+
+  def self.svg_content_type?(content_type)
+    content_type.to_s.split(';', 2).first.to_s.downcase.strip == REMOTE_SVG_CONTENT_TYPE
+  end
+
+  def self.svg_document_bytes?(bytes)
+    document = Nokogiri::XML(
+        bytes,
+        nil,
+        nil,
+        Nokogiri::XML::ParseOptions::STRICT |
+        Nokogiri::XML::ParseOptions::NONET)
+    document.root&.name == 'svg'
+  rescue Nokogiri::XML::SyntaxError
+    false
+  end
+
+  def self.decode_raster_thumbnail(bytes)
+    MiniMagick::Image.read(bytes)
+  end
+
+  def self.decode_svg_thumbnail(bytes)
+    MiniMagick::Image.read(sanitised_svg_bytes(bytes))
+  end
+
+  def self.raster_thumbnail_format(bytes)
+    binary = bytes.to_s.b
+    return 'jpeg' if binary.start_with?("\xFF\xD8\xFF".b)
+    return 'png' if binary.start_with?("\x89PNG\r\n\x1A\n".b)
+    return 'gif' if binary.start_with?('GIF87a'.b) || binary.start_with?('GIF89a'.b)
+    return 'webp' if binary.bytesize >= 12 &&
+                     binary.start_with?('RIFF'.b) &&
+                     binary.byteslice(8, 4) == 'WEBP'
+
+    nil
+  end
+
+  def self.sanitised_svg_bytes(bytes)
+    parse_options =
+        Nokogiri::XML::ParseOptions::STRICT |
+        Nokogiri::XML::ParseOptions::NONET
+    document = Nokogiri::XML(
+        bytes,
+        nil,
+        nil,
+        parse_options)
+    root = document.root
+    raise MiniMagick::Error, 'SVG が不正です．' if root == nil || root.name != 'svg'
+    raise MiniMagick::Error, 'SVG が不正です．' if document.internal_subset != nil
+    raise MiniMagick::Error, 'SVG が不正です．' if svg_uses_disallowed_features?(document)
+
+    width, height = svg_dimensions(root)
+    raise MiniMagick::Error, 'SVG が大きすぎます．' if width == nil || height == nil
+    if width > MAX_SVG_DIMENSION || height > MAX_SVG_DIMENSION || width * height > MAX_SVG_PIXELS
+      raise MiniMagick::Error, 'SVG が大きすぎます．'
+    end
+
+    document.to_xml
+  rescue Nokogiri::XML::SyntaxError
+    raise MiniMagick::Error, 'SVG が不正です．'
+  end
+
+  def self.svg_uses_disallowed_features?(document)
+    document.traverse.any? do |node|
+      next false unless node.element?
+
+      name = node.name.to_s.downcase
+      next true if name == 'script' || name == 'foreignobject'
+      next style_contains_disallowed_urls?(node.text.to_s) if name == 'style'
+
+      node.attribute_nodes.any? do |attribute|
+        attribute_name = attribute.name.to_s.downcase
+        attribute_value = attribute.value.to_s
+        attribute_name.start_with?('on') ||
+            external_svg_reference?(attribute_name, attribute_value)
+      end
+    end
+  end
+
+  def self.external_svg_reference?(attribute_name, attribute_value)
+    if ['href', 'xlink:href', 'src'].include?(attribute_name)
+      return external_svg_url?(attribute_value)
+    end
+    return style_contains_disallowed_urls?(attribute_value) if attribute_name == 'style'
+    return svg_url_function_disallowed?(attribute_value) if attribute_value.match?(/url\s*\(/i)
+
+    false
+  end
+
+  def self.external_svg_url?(value)
+    stripped = value.to_s.strip
+    return false if stripped.blank? || stripped.start_with?('#')
+
+    true
+  end
+
+  def self.style_contains_disallowed_urls?(value)
+    text = value.to_s
+    text.match?(/@import/i) || svg_url_function_disallowed?(text)
+  end
+
+  def self.svg_url_function_disallowed?(value)
+    value.to_s.scan(/url\s*\(([^)]*)\)/i).flatten.any? do |entry|
+      reference =
+          entry.to_s.strip
+               .delete_prefix("'")
+               .delete_prefix('"')
+               .delete_suffix("'")
+               .delete_suffix('"')
+      reference.present? && !(reference.start_with?('#'))
+    end
+  end
+
+  def self.svg_dimensions(root)
+    width = svg_length_to_pixels(root['width'])
+    height = svg_length_to_pixels(root['height'])
+    return [width, height] if width && height
+
+    view_box = root['viewBox'].to_s.strip.split(/\s+/).map { Float(_1) rescue nil }
+    return [nil, nil] if view_box.length != 4 || view_box.any?(&:nil?)
+    return [nil, nil] unless view_box[2].finite? && view_box[2].positive?
+    return [nil, nil] unless view_box[3].finite? && view_box[3].positive?
+
+    [view_box[2], view_box[3]]
+  end
+
+  def self.svg_length_to_pixels(value)
+    return nil if value.blank?
+
+    matched = /\A([0-9]+(?:\.[0-9]+)?)(px)?\z/i.match(value.to_s.strip)
+    return nil if matched == nil
+
+    pixels = Float(matched[1])
+    return nil unless pixels.finite? && pixels.positive?
+
+    pixels
+  rescue ArgumentError
+    nil
+  end
+
+  private_class_method :image_for_thumbnail_upload,
+                       :svg_content_type?,
+                       :decode_raster_thumbnail,
+                       :decode_svg_thumbnail,
+                       :raster_thumbnail_format,
+                       :sanitised_svg_bytes,
+                       :svg_uses_disallowed_features?,
+                       :external_svg_reference?,
+                       :external_svg_url?,
+                       :style_contains_disallowed_urls?,
+                       :svg_url_function_disallowed?,
+                       :svg_dimensions,
+                       :svg_length_to_pixels
+
   def parse_original_created_value field
     raw_value = public_send("#{ field }_before_type_cast")
     value = public_send(field)
@@ -238,7 +457,8 @@ class Post < ApplicationRecord
     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/))
+    match = value.match(/\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})\z/)
+    if match
       year = match[1].to_i
       month = match[2].to_i
       day = match[3].to_i
@@ -251,9 +471,12 @@ class Post < ApplicationRecord
 
     match =
         value.match(
-            /\A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})/ \
+            /
-            '(?::(\d{2})(?:\.(\d+))?)?' \
+              \A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})
-            '(Z|[+-]\d{2}:?\d{2})?\z/')
+              (?::(\d{2})(?:\.(\d+))?)?
+              (Z|[+-]\d{2}:?\d{2})?
+              \z
+            /x)
     return nil if match.nil?
 
     year = match[1].to_i

backend/app/models/post_tag.rb

@@ -1,14 +1,7 @@
 class PostTag < ApplicationRecord
-  include Discard::Model
-
-  before_destroy do
-    raise ActiveRecord::ReadOnlyRecord, '消さないでください．'
-  end
-
   belongs_to :post
   belongs_to :tag, counter_cache: :post_count
   belongs_to :created_user, class_name: 'User', optional: true
-  belongs_to :deleted_user, class_name: 'User', optional: true
 
   has_many :sections, -> { order(:begin_ms) }, class_name: 'PostTagSection',
                                                foreign_key: [:post_id, :tag_id],
@@ -18,18 +11,5 @@ class PostTag < ApplicationRecord
 
   validates :post_id, presence: true
   validates :tag_id, presence: true
-  validates :post_id, uniqueness: {
+  validates :post_id, uniqueness: { scope: :tag_id }
-      scope: :tag_id,
-      conditions: -> { where(discarded_at: nil) } }
-
-  def discard_by! deleted_user
-    return self if discarded?
-
-    transaction do
-      update!(discarded_at: Time.current, deleted_user:)
-      Tag.where(id: tag_id).update_all('post_count = GREATEST(post_count - 1, 0)')
-    end
-
-    self
-  end
 end

backend/app/models/post_tag_section.rb

@@ -4,10 +4,10 @@ class PostTagSection < ApplicationRecord
   belongs_to :post
   belongs_to :tag
 
-  belongs_to :post_tag, -> { kept }, foreign_key: [:post_id, :tag_id],
+  belongs_to :post_tag, foreign_key: [:post_id, :tag_id],
-                                     primary_key: [:post_id, :tag_id],
+                        primary_key: [:post_id, :tag_id],
-                                     inverse_of: :sections,
+                        inverse_of: :sections,
-                                     optional: true
+                        optional: true
 
   validates :post_id, presence: true
   validates :tag_id, presence: true

backend/app/models/tag.rb

@@ -2,8 +2,6 @@ require 'set'
 
 
 class Tag < ApplicationRecord
-  include MyDiscard
-
   class NicoTagNormalisationError < ArgumentError
     ;
   end
@@ -28,9 +26,7 @@ class Tag < ApplicationRecord
   end
 
   has_many :post_tags, inverse_of: :tag
-  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
+  has_many :posts, through: :post_tags
-  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
-  has_many :posts, through: :active_post_tags
 
   has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
   has_many :linked_tags, through: :nico_tag_relations, source: :tag
@@ -234,10 +230,10 @@ class Tag < ApplicationRecord
   end
 
   def self.find_or_create_by_tag_name! name, category:
-    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
+    tn = TagName.find_or_create_by!(name: name.to_s.strip)
     tn = tn.canonical if tn.canonical_id?
 
-    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) do |t|
+    Tag.find_or_create_by!(tag_name_id: tn.id) do |t|
       t.category = category
     end
   rescue ActiveRecord::RecordNotUnique
@@ -259,11 +255,11 @@ class Tag < ApplicationRecord
 
         TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
 
-        source_tag.post_tags.kept.find_each do |source_pt|
+        source_tag.post_tags.find_each do |source_pt|
           post_id = source_pt.post_id
           affected_post_ids << post_id
-          source_pt.discard_by!(created_by_user)
+          source_pt.destroy!
-          unless PostTag.kept.exists?(post_id:, tag: target_tag)
+          unless PostTag.exists?(post_id:, tag: target_tag)
             PostTag.create!(post_id:, tag: target_tag)
           end
         end
@@ -275,10 +271,10 @@ class Tag < ApplicationRecord
         end
 
         TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
-        source_tag.discard!
+        source_tag.destroy!
 
         if source_tag.nico?
-          source_tag_name.discard!
+          source_tag_name.destroy!
         else
           source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
                                          updated_at: Time.current)
@@ -293,13 +289,13 @@ class Tag < ApplicationRecord
       end
 
       # 投稿件数を再集計
-      target_tag.update_columns(post_count: PostTag.kept.where(tag: target_tag).count)
+      target_tag.update_columns(post_count: PostTag.where(tag: target_tag).count)
     end
 
     target_tag.reload
   end
 
-  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
+  def snapshot_aliases = tag_name.aliases.order(:name).pluck(:name)
 
   def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
 

backend/app/models/tag_name.rb

@@ -1,6 +1,4 @@
 class TagName < ApplicationRecord
-  include MyDiscard
-
   has_one :tag
   has_one :wiki_page
 

backend/app/models/tag_name_sanitisation_rule.rb

@@ -32,7 +32,7 @@ class TagNameSanitisationRule < ApplicationRecord
             elsif source_tag
               source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
             end
-            tn.discard!
+            tn.destroy!
 
             next
           end

backend/app/representations/post_compact_repr.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+
+module PostCompactRepr
+  module_function
+
+  def base post, host: nil
+    return nil if post.nil?
+
+    PostRepr
+        .common(post, host:)
+        .slice(
+            'id',
+            'title',
+            'url',
+            'thumbnail',
+            'thumbnail_base')
+  end
+end

backend/app/representations/post_repr.rb

@@ -17,8 +17,13 @@ module PostRepr
 
   module_function
 
-  def base post, current_user = nil
+  def base post, current_user = nil, host: nil
-    json = common(post)
+    json =
+        if host.present?
+          common(post, host:)
+        else
+          common(post)
+        end
     json['tags'] = tag_json(post)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
@@ -26,50 +31,89 @@ module PostRepr
   end
 
   def detail post, current_user = nil, parent_posts: [], child_posts: [],
-             sibling_posts: { }, related: []
+             sibling_posts: { }, related: [], host: nil
-    base(post, current_user).merge(
+    if host.present?
-        'parent_posts' => cards(parent_posts),
+      base(post, current_user, host:).merge(
-        'child_posts' => cards(child_posts),
+          'parent_posts' => cards(parent_posts, host:),
-        'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
+          'child_posts' => cards(child_posts, host:),
-          cards(posts)
+          'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
-        },
+            cards(posts, host:)
-        'related' => cards(related))
+          },
+          'related' => cards(related, host:))
+    else
+      base(post, current_user).merge(
+          'parent_posts' => cards(parent_posts),
+          'child_posts' => cards(child_posts),
+          'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
+            cards(posts)
+          },
+          'related' => cards(related))
+    end
   end
 
-  def card post
+  def card post, host: nil
-    common(post).merge('parent_posts' => [], 'child_posts' => [])
+    if host.present?
+      common(post, host:).merge('parent_posts' => [], 'child_posts' => [])
+    else
+      common(post).merge('parent_posts' => [], 'child_posts' => [])
+    end
   end
 
-  def cards posts
+  def cards posts, host: nil
-    posts.map { |post| card(post) }
+    if host.present?
+      posts.map { |post| card(post, host:) }
+    else
+      posts.map { |post| card(post) }
+    end
   end
 
-  def many posts, current_user = nil
+  def many posts, current_user = nil, host: nil
-    posts.map { |p| base(p, current_user) }
+    if host.present?
+      posts.map { |p| base(p, current_user, host:) }
+    else
+      posts.map { |p| base(p, current_user) }
+    end
   end
 
-  def common post
+  def common post, host: nil
     BASE_FIELDS.to_h { |field| [field.to_s, post.public_send(field)] }
-               .merge('thumbnail' => thumbnail_url(post))
+               .merge(
+                   'thumbnail' =>
+                       if host.present?
+                         thumbnail_url(post, host:)
+                       else
+                         thumbnail_url(post)
+                       end)
   end
 
   def tag_json post
     post
-        .active_post_tags
+        .post_tags
         .reject { _1.tag.deprecated? }
         .sort_by { _1.tag.name }
-        .map { |post_tag|
+        .map do |post_tag|
       TagRepr.inline(post_tag.tag).merge(
           'children' => [],
           'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
-    }
+    end
   end
 
-  def thumbnail_url post
+  def thumbnail_url post, host: nil
     return nil unless post.thumbnail.attached?
 
-    Rails.application.routes.url_helpers.rails_blob_url(post.thumbnail, only_path: false)
+    options = { only_path: false }
-  rescue
+    options[:host] = host if host.present?
+
+    Rails.application.routes.url_helpers.rails_storage_proxy_url(post.thumbnail, **options)
+  rescue ActionController::UrlGenerationError, ArgumentError, URI::InvalidURIError => e
+    payload = {
+        post_id: post.id,
+        attachment_id: post.thumbnail.attachment&.id,
+        blob_id: post.thumbnail.blob&.id,
+        error_class: e.class,
+        message: e.message }
+
+    Rails.logger.warn("PostRepr.thumbnail_url failed #{ payload.to_json }")
     nil
   end
 end

backend/app/services/post_bulk_creator.rb

@@ -0,0 +1,202 @@
+class PostBulkCreator
+  def initialize actor:, posts:, thumbnails:, host: nil
+    @actor_id = actor.id
+    @posts = posts
+    @thumbnails = thumbnails
+    @host = host
+  end
+
+  def run
+    results = Array.new(@posts.length)
+    mutex = Mutex.new
+    next_index = 0
+
+    workers = Array.new(2) do
+      Thread.new do
+        Rails.application.executor.wrap do
+          ActiveRecord::Base.connection_pool.with_connection do
+            actor = User.find(@actor_id)
+            loop do
+              index = nil
+              begin
+                index = mutex.synchronize do
+                  current = next_index
+                  next_index += 1
+                  current
+                end
+                break if index >= @posts.length
+
+                attributes = @posts[index]
+                results[index] = create_row(actor, attributes, index)
+              rescue StandardError => e
+                Rails.logger.error(
+                    "post_bulk_creator_worker_failure #{ { error: e.class.name,
+                                                          message: e.message,
+                                                          index: }.to_json }")
+                results[index] = {
+                    status: 'failed',
+                    recoverable: false,
+                    errors: { base: ['登録中にエラーが発生しました．'] },
+                    base_errors: [] }
+              end
+            end
+          end
+        end
+      end
+    end
+    workers.each(&:join)
+
+    results.each_index do |index|
+      next if results[index].present?
+
+      results[index] = {
+          status: 'failed',
+          recoverable: false,
+          errors: { base: ['登録中にエラーが発生しました．'] },
+          base_errors: [] }
+    end
+
+    { results: }
+  end
+
+  private
+
+  def create_row actor, attributes, index
+    preflight =
+        PostCreatePreflight.new(
+            attributes: attributes,
+            thumbnail: thumbnail_for(index, attributes),
+            host: @host).run
+    if preflight[:existing_post_id].present?
+      return {
+          status: 'skipped',
+          existing_post_id: preflight[:existing_post_id],
+          existing_post: preflight[:existing_post] }
+    end
+
+    post = PostCreator.new(
+        actor: actor,
+        attributes: normalised_attributes(attributes, preflight, index)).create!
+    result = {
+        status: 'created',
+        post: { id: post.id } }
+    result[:field_warnings] = preflight[:field_warnings] if preflight[:field_warnings].present?
+    result[:base_warnings] = preflight[:base_warnings] if preflight[:base_warnings].present?
+    result
+  rescue PostCreatePreflight::ValidationFailed => e
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: e.fields,
+        base_errors: e.base_errors }
+  rescue ActiveRecord::RecordInvalid => e
+    existing_post = existing_post_for_race(attributes, e.record)
+    if existing_post.present?
+      return {
+          status: 'skipped',
+          existing_post_id: existing_post[:id],
+          existing_post: existing_post }
+    end
+
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: e.record.errors.to_hash,
+        base_errors: e.record.errors[:base] }
+  rescue ActiveRecord::RecordNotUnique => e
+    if e.message.include?('index_posts_on_url')
+      existing_post = existing_post_for_race(attributes)
+      return {
+          status: 'skipped',
+          existing_post_id: existing_post[:id],
+          existing_post: existing_post } if existing_post.present?
+    end
+
+    Rails.logger.error(
+        "post_bulk_creator_record_not_unique #{ { error: e.class.name,
+                                                 message: e.message }.to_json }")
+    {
+        status: 'failed',
+        recoverable: false,
+        errors: { base: ['登録中にエラーが発生しました．'] },
+        base_errors: [] }
+  rescue Tag::NicoTagNormalisationError
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: { tags: ['ニコニコ・タグは直接指定できません．'] },
+        base_errors: [] }
+  rescue Tag::DeprecatedTagNormalisationError
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: { tags: ['廃止済みタグは付与できません．'] },
+        base_errors: [] }
+  rescue PostCreator::VideoMsParseError
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: { video_ms: ['動画時間の記法が不正です．'] },
+        base_errors: [] }
+  rescue Post::RemoteThumbnailFetchFailed
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: { thumbnail_base: ['サムネイル画像の取得に失敗しました．'] },
+        base_errors: [] }
+  rescue ArgumentError => e
+    {
+        status: 'failed',
+        recoverable: true,
+        errors: { base: [e.message] },
+        base_errors: [] }
+  rescue StandardError => e
+    Rails.logger.error(
+        "post_bulk_creator_failure #{ { error: e.class.name,
+                                        message: e.message }.to_json }")
+    {
+        status: 'failed',
+        recoverable: false,
+        errors: { base: ['登録中にエラーが発生しました．'] },
+        base_errors: [] }
+  end
+
+  def normalised_attributes attributes, preflight, index
+    {
+        url: preflight[:url],
+        title: preflight[:title],
+        thumbnail_base: preflight[:thumbnail_base],
+        thumbnail: thumbnail_for(index, attributes),
+        tags: preflight[:tags],
+        parent_post_ids: preflight[:parent_post_ids],
+        original_created_from: preflight[:original_created_from],
+        original_created_before: preflight[:original_created_before],
+        duration: preflight[:duration],
+        video_ms: preflight[:video_ms],
+        direct_tag_specs: preflight[:direct_tag_specs],
+        default_tag_specs: preflight[:default_tag_specs],
+        snapshot_tag_specs: preflight[:snapshot_tag_specs],
+        post_tag_specs: preflight[:post_tag_specs],
+        tag_sections: preflight[:tag_sections],
+        normalised_parent_post_ids: preflight[:normalised_parent_post_ids] }
+  end
+
+  def thumbnail_for index, attributes
+    return nil if attributes['thumbnail_base'].present? || attributes[:thumbnail_base].present?
+
+    @thumbnails[index]
+  end
+
+  def existing_post_for_race attributes, record = nil
+    return nil if record.present? && !(record.errors.of_kind?(:url, :taken))
+
+    normal_url = PostUrlNormaliser.normalise(attributes['url'] || attributes[:url])
+    return nil if normal_url.blank?
+
+    compact_existing_post(Post.with_attached_thumbnail.find_by(url: normal_url))
+  end
+
+  def compact_existing_post post
+    PostCompactRepr.base(post, host: @host)
+  end
+end

backend/app/services/post_create_plan.rb

@@ -0,0 +1,271 @@
+class PostCreatePlan
+  VIDEO_TAG_NAME = '動画'.freeze
+  TAGME_TAG_NAME = 'タグ希望'.freeze
+  NO_DEERJIKIST_TAG_NAME = 'ニジラー情報不詳'.freeze
+
+  def initialize attributes:
+    @attributes = attributes.symbolize_keys
+    @existing_tags_by_name = nil
+  end
+
+  def build!
+    direct_tag_specs, tag_sections = parse_direct_tag_specs
+    default_tag_specs = build_default_tag_specs(direct_tag_specs)
+    snapshot_tag_specs = merge_tag_specs(direct_tag_specs + default_tag_specs)
+    preload_existing_tags_by_name!(snapshot_tag_specs.map { _1[:name] })
+    validate_new_tag_specs!(snapshot_tag_specs)
+    post_tag_specs = expand_parent_tag_specs(snapshot_tag_specs)
+    video_ms = normalise_video_ms(snapshot_tag_specs)
+    validate_video_sections!(video_ms, tag_sections)
+    parent_post_ids = normalise_parent_post_ids
+    validate_parent_post_ids!(parent_post_ids)
+
+    {
+        url: @attributes[:url],
+        title: @attributes[:title].to_s,
+        thumbnail_base: @attributes[:thumbnail_base].presence,
+        original_created_from: @attributes[:original_created_from].presence,
+        original_created_before: @attributes[:original_created_before].presence,
+        tags: serialised_tags(direct_tag_specs, tag_sections),
+        display_tags: display_tags(direct_tag_specs, tag_sections),
+        duration: @attributes[:duration].to_s,
+        video_ms: video_ms,
+        parent_post_ids: parent_post_ids.join(' '),
+        direct_tag_specs: direct_tag_specs,
+        default_tag_specs: default_tag_specs,
+        snapshot_tag_specs: snapshot_tag_specs,
+        post_tag_specs: post_tag_specs,
+        tag_sections: tag_sections,
+        normalised_parent_post_ids: parent_post_ids }
+  end
+
+  private
+
+  def tag_names = @attributes[:tags].to_s.split
+
+  def parse_direct_tag_specs
+    tag_sections = { }
+    direct_tag_specs = []
+
+    tag_names.each do |raw_name|
+      tag_name, category, sections = parse_raw_tag_name(raw_name)
+      existing_tag = existing_tags_by_name[tag_name]
+      raise Tag::NicoTagNormalisationError if existing_tag&.nico?
+      raise Tag::DeprecatedTagNormalisationError, [existing_tag.name] if existing_tag&.deprecated?
+
+      direct_tag_specs << {
+          name: tag_name,
+          category: (category || existing_tag&.category || 'general').to_sym }
+      if sections.present?
+        tag_sections[tag_name] ||= []
+        tag_sections[tag_name].concat(sections)
+        tag_sections[tag_name] = Tag.merge_section_ranges(tag_sections[tag_name])
+        tag_sections.delete(tag_name) if tag_sections[tag_name] == [[0, nil]]
+      end
+    end
+
+    [merge_tag_specs(direct_tag_specs), tag_sections]
+  end
+
+  def parse_raw_tag_name raw_name
+    name = raw_name.to_s
+    prefix, category =
+        Tag::CATEGORY_PREFIXES.find {
+          name.downcase.start_with?(_1[0])
+        } || ['', nil]
+    name = name.sub(/\A#{ prefix }/i, '')
+
+    sections = []
+    while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
+      name = "#{ match[1] }#{ match[4] }"
+      next if match[2].empty? && match[3].empty?
+
+      sections << Tag.normalise_section_range!(
+          begin_raw: match[2],
+          end_raw: match[3],
+          tag_name: name)
+    end
+    if name.include?('[') || name.include?(']')
+      raise Tag::SectionLiteralParseError.new(raw_name, raw_name)
+    end
+
+    [resolved_tag_name(name), category&.to_sym, sections]
+  end
+
+  def build_default_tag_specs direct_tag_specs
+    default_tag_specs = []
+    if direct_tag_specs.length < 10 && direct_tag_specs.none? { _1[:name] == TAGME_TAG_NAME }
+      default_tag_specs << {
+          name: TAGME_TAG_NAME,
+          category: :meta }
+    end
+    if direct_tag_specs.none? { deerjikist_tag_spec?(_1) }
+      default_tag_specs << {
+          name: NO_DEERJIKIST_TAG_NAME,
+          category: :meta }
+    end
+
+    default_tag_specs
+  end
+
+  def validate_new_tag_specs! specs
+    Array(specs).each do |spec|
+      next if existing_tags_by_name.key?(spec[:name])
+
+      validate_new_tag_spec!(spec)
+    end
+  end
+
+  def validate_new_tag_spec! spec
+    tag_name = TagName.new(name: spec[:name])
+    tag = Tag.new(category: spec[:category], tag_name:)
+    return if tag_name.valid? && tag.valid?
+
+    post = Post.new
+    tag_name.errors[:name].each do |message|
+      post.errors.add :tags, "#{ spec[:name] }: #{ message }"
+    end
+    tag.errors.each do |error|
+      next if error.attribute == :tag_name
+
+      post.errors.add :tags, "#{ spec[:name] }: #{ error.message }"
+    end
+    raise ActiveRecord::RecordInvalid, post
+  end
+
+  def expand_parent_tag_specs snapshot_tag_specs
+    existing_snapshot_tags = snapshot_tag_specs.filter_map { existing_tags_by_name[_1[:name]] }
+    expanded_parent_specs =
+        Tag.expand_parent_tags(existing_snapshot_tags)
+           .reject(&:deprecated?)
+           .map { |tag|
+             {
+                 name: tag.name,
+                 category: tag.category.to_sym } }
+    merge_tag_specs(snapshot_tag_specs + expanded_parent_specs)
+  end
+
+  def merge_tag_specs specs
+    specs.each_with_object({ }) do |spec, merged|
+      merged[spec[:name]] =
+          if merged.key?(spec[:name]) && merged[spec[:name]][:category] != :general
+            merged[spec[:name]]
+          else
+            {
+                name: spec[:name],
+                category: spec[:category] }
+          end
+    end.values.sort_by { _1[:name] }
+  end
+
+  def existing_tags_by_name
+    @existing_tags_by_name ||= begin
+      names = tag_names.map { canonical_tag_name_without_sections(_1) }.uniq
+      Tag.joins(:tag_name).where(tag_names: { name: names }).index_by(&:name)
+    end
+  end
+
+  def preload_existing_tags_by_name! names
+    wanted_names = Array(names).map { _1.to_s }.reject(&:blank?).uniq
+    missing_names = wanted_names - existing_tags_by_name.keys
+    return if missing_names.empty?
+
+    existing_tags_by_name.merge!(
+        Tag.joins(:tag_name)
+           .where(tag_names: { name: missing_names })
+           .index_by(&:name))
+  end
+
+  def canonical_tag_name_without_sections raw_name
+    name, = parse_raw_tag_name(raw_name)
+    name
+  end
+
+  def deerjikist_tag_spec? spec
+    return true if spec[:category] == :deerjikist
+
+    existing_tags_by_name[spec[:name]]&.deerjikist?
+  end
+
+  def normalise_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.sort
+  end
+
+  def validate_parent_post_ids! ids
+    missing = ids - Post.where(id: ids).pluck(:id)
+    raise ArgumentError, "存在しない親投稿 Id. があります: #{ missing.join(' ') }" if missing.present?
+  end
+
+  def serialised_tags direct_tag_specs, tag_sections
+    direct_tag_specs.map { |spec|
+      "#{ spec[:name] }#{ tag_sections[spec[:name]].to_a.map { section_literal(_1) }.join }"
+    }.sort.join(' ')
+  end
+
+  def display_tags direct_tag_specs, tag_sections
+    direct_tag_specs.map { |spec|
+      {
+          name: spec[:name],
+          category: spec[:category].to_s,
+          section_literals: tag_sections[spec[:name]].to_a.map { section_literal(_1) } }
+    }.sort_by { _1[:name] }
+  end
+
+  def section_literal range
+    begin_ms, end_ms = range
+    "[#{ Post.ms_to_time(begin_ms) }-#{ end_ms ? Post.ms_to_time(end_ms) : '' }]"
+  end
+
+  def normalise_video_ms snapshot_tag_specs
+    return nil unless snapshot_tag_specs.any? { _1[:name] == VIDEO_TAG_NAME }
+
+    video_ms = @attributes[:video_ms]
+    if video_ms.present?
+      value = Integer(video_ms, exception: false)
+      raise PostCreator::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 PostCreator::VideoMsParseError unless value.positive?
+
+    value
+  rescue Tag::SectionLiteralParseError
+    raise PostCreator::VideoMsParseError
+  end
+
+  def validate_video_sections! video_ms, tag_sections
+    return unless video_ms
+
+    tag_sections.each_value do |ranges|
+      ranges.each do |begin_ms, end_ms|
+        if begin_ms >= video_ms
+          post = Post.new
+          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 = Post.new
+          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 resolved_tag_name name
+    tag_name = TagName.includes(:canonical).find_by(name:)
+    return name if tag_name.nil?
+
+    (tag_name.canonical || tag_name).name
+  end
+end

backend/app/services/post_create_preflight.rb

@@ -0,0 +1,141 @@
+class PostCreatePreflight
+  class ValidationFailed < StandardError
+    attr_reader :fields, :base_errors
+
+    def initialize fields: { }, base_errors: []
+      super('入力内容を確認してください．')
+      @fields = fields
+      @base_errors = base_errors
+    end
+  end
+
+  def initialize attributes:, thumbnail: nil, host: nil
+    @attributes = attributes.symbolize_keys
+    @thumbnail = thumbnail
+    @host = host
+  end
+
+  def run
+    preview = PostImportPreviewer.new.preview_rows(
+        rows: [preview_row],
+        fetch_metadata: false).first
+    if preview[:existing_post_id].present?
+      return {
+          url: preview[:url],
+          title: preview[:attributes]['title'],
+          thumbnail_base: preview[:attributes]['thumbnail_base'],
+          tags: preview[:attributes]['tags'],
+          parent_post_ids: preview[:attributes]['parent_post_ids'],
+          original_created_from: preview[:attributes]['original_created_from'],
+          original_created_before: preview[:attributes]['original_created_before'],
+          duration: preview[:attributes]['duration'],
+          video_ms: preview[:attributes]['video_ms'],
+          display_tags: preview[:display_tags] || [],
+          field_warnings: final_field_warnings(preview[:field_warnings] || { }),
+          base_warnings: preview[:base_warnings],
+          existing_post_id: preview[:existing_post_id],
+          existing_post: existing_post_compact(preview[:existing_post_id]) }
+    end
+
+    if preview[:validation_errors].present?
+      raise ValidationFailed.new(fields: preview[:validation_errors])
+    end
+
+    validate_thumbnail_upload!
+
+    plan = PostCreatePlan.new(
+        attributes: {
+            url: preview[:url],
+            title: preview[:attributes]['title'],
+            thumbnail_base: preview[:attributes]['thumbnail_base'],
+            tags: preview[:attributes]['tags'],
+            parent_post_ids: preview[:attributes]['parent_post_ids'],
+            original_created_from: preview[:attributes]['original_created_from'],
+            original_created_before: preview[:attributes]['original_created_before'],
+            duration: preview[:attributes]['duration'],
+            video_ms: preview[:attributes]['video_ms'] }).build!
+
+    {
+        url: plan[:url],
+        title: plan[:title],
+        thumbnail_base: plan[:thumbnail_base],
+        tags: plan[:tags],
+        parent_post_ids: plan[:parent_post_ids],
+        original_created_from: plan[:original_created_from],
+        original_created_before: plan[:original_created_before],
+        duration: plan[:duration],
+        video_ms: plan[:video_ms],
+        display_tags: plan[:display_tags],
+        direct_tag_specs: plan[:direct_tag_specs],
+        default_tag_specs: plan[:default_tag_specs],
+        snapshot_tag_specs: plan[:snapshot_tag_specs],
+        post_tag_specs: plan[:post_tag_specs],
+        tag_sections: plan[:tag_sections],
+        normalised_parent_post_ids: plan[:normalised_parent_post_ids],
+        field_warnings: final_field_warnings(preview[:field_warnings] || { }),
+        base_warnings: preview[:base_warnings],
+        existing_post_id: preview[:existing_post_id],
+        existing_post: existing_post_compact(preview[:existing_post_id]) }
+  end
+
+  private
+
+  def preview_row
+    {
+        source_row: 1,
+        url: @attributes[:url].to_s,
+        attributes: {
+            'title' => @attributes[:title].to_s,
+            'thumbnail_base' => @attributes[:thumbnail_base].to_s,
+            'original_created_from' => @attributes[:original_created_from].to_s,
+            'original_created_before' => @attributes[:original_created_before].to_s,
+            'duration' => @attributes[:duration].to_s,
+            'video_ms' => @attributes[:video_ms],
+            'tags' => @attributes[:tags].to_s,
+            'parent_post_ids' => parent_post_ids_text },
+        provenance: {
+            'url' => 'manual',
+            'title' => 'manual',
+            'thumbnail_base' => 'manual',
+            'original_created_from' => 'manual',
+            'original_created_before' => 'manual',
+            'duration' => 'manual',
+            'video_ms' => 'manual',
+            'tags' => 'manual',
+            'parent_post_ids' => 'manual' },
+        tag_sources: {
+            'automatic' => '',
+            'manual' => @attributes[:tags].to_s } }
+  end
+
+  def parent_post_ids_text
+    Array(@attributes[:parent_post_ids]).flat_map { _1.to_s.split }.join(' ')
+  end
+
+  def validate_thumbnail_upload!
+    return if @attributes[:thumbnail_base].present?
+    return if @thumbnail.blank?
+
+    PostThumbnailUploadValidator.validate!(@thumbnail)
+  rescue PostThumbnailUploadValidator::InvalidUpload => e
+    raise ValidationFailed.new(fields: { thumbnail: [e.message] })
+  end
+
+  def existing_post_compact post_id
+    return nil if post_id.blank?
+
+    post = Post.with_attached_thumbnail.find_by(id: post_id)
+    PostCompactRepr.base(post, host: @host)
+  end
+
+  def final_field_warnings field_warnings
+    thumbnail_warnings = (field_warnings['thumbnail_base'] || []).reject { _1 == 'サムネールなし' }
+    if @attributes[:thumbnail_base].blank? && @thumbnail.blank?
+      thumbnail_warnings = (thumbnail_warnings + ['サムネールなし']).uniq
+    end
+
+    next_warnings = field_warnings.except('thumbnail_base')
+    next_warnings['thumbnail_base'] = thumbnail_warnings if thumbnail_warnings.present?
+    next_warnings
+  end
+end

backend/app/services/post_creator.rb

@@ -10,103 +10,122 @@ class PostCreator
   end
 
   def create!
+    thumbnail_attachment = prepare_thumbnail_attachment
     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) =>
+      post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
-          { tags:, sections: }
+      snapshot_tags = planned_snapshot_tags
-      TagVersioning.record_tag_snapshots!(tags, created_by_user: @actor)
+      post_tags = planned_post_tags
-      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
+      sections = planned_sections
-      post.video_ms = normalise_video_ms(tags)
+      TagVersioning.record_tag_snapshots!(snapshot_tags, created_by_user: @actor)
-      validate_video_sections!(post.video_ms, sections)
+      post.video_ms = planned_video_ms
       post.save!
-      sync_post_tags!(post, tags, sections)
+      sync_post_tags!(post, post_tags, sections)
-      sync_parent_posts!(post, parent_post_ids)
+      sync_parent_posts!(post, planned_parent_post_ids)
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
     end
     post
+  rescue StandardError
+    post&.thumbnail&.purge if post&.thumbnail&.attached?
+    raise
   end
 
   private
 
-  def attach_thumbnail! post
+  def prepare_thumbnail_attachment
-    thumbnail = @attributes[:thumbnail]
+    PostThumbnailAttachmentBuilder.build(
-    if thumbnail.present?
+        thumbnail: @attributes[:thumbnail],
-      post.thumbnail.attach(Post.resized_thumbnail_attachment(thumbnail))
+        thumbnail_base: @attributes[:thumbnail_base].presence)
-      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 planned_snapshot_tags = planned_create_attributes[:snapshot_tags]
 
-  def parent_post_ids
+  def planned_post_tags = planned_create_attributes[:post_tags]
-    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
+  def planned_sections = planned_create_attributes[:tag_sections]
-    }.uniq
+
+  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
+
+  def planned_video_ms
+    planned_create_attributes[:video_ms]
   end
 
-  def normalise_video_ms tags
+  def planned_create_attributes
-    return nil unless tags.any? { _1.id == Tag.video.id }
+    @planned_create_attributes ||= begin
-
+      if @attributes.key?(:snapshot_tag_specs)
-    video_ms = @attributes[:video_ms]
+        snapshot_tags = materialise_tags(@attributes[:snapshot_tag_specs] || [])
-    if video_ms.present?
+        post_tags = materialise_tags(@attributes[:post_tag_specs] || [])
-      value = Integer(video_ms, exception: false)
+        {
-      raise VideoMsParseError unless value&.positive?
+            snapshot_tags: snapshot_tags,
-
+            post_tags: post_tags,
-      return value
+            tag_sections: materialise_sections(
-    end
+                @attributes[:tag_sections] || { },
-    duration = @attributes[:duration]
+                snapshot_tags,
-    return nil if duration.blank?
+                post_tags),
-
+            normalised_parent_post_ids: @attributes[:normalised_parent_post_ids] || [],
-    value = Tag.time_to_ms!(duration.to_s, tag_name: '動画時間')
+            video_ms: @attributes[:video_ms] }
-    raise VideoMsParseError unless value.positive?
+      else
-
+        build_materialised_plan
-    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 build_materialised_plan
+    plan = PostCreatePlan.new(attributes: @attributes).build!
+    snapshot_tags = materialise_tags(plan[:snapshot_tag_specs] || [])
+    post_tags = materialise_tags(plan[:post_tag_specs] || [])
+    {
+        snapshot_tags: snapshot_tags,
+        post_tags: post_tags,
+        tag_sections: materialise_sections(
+            plan[:tag_sections] || { },
+            snapshot_tags,
+            post_tags),
+        normalised_parent_post_ids: plan[:normalised_parent_post_ids] || [],
+        video_ms: plan[:video_ms] }
+  end
+
+  def materialise_tags specs
+    Array(specs).each_with_object({ }) do |spec, tags|
+      name = spec[:name] || spec['name']
+      category = spec[:category] || spec['category']
+      next if name.blank? || category.blank?
+
+      tag = Tag.find_or_create_by_tag_name!(name, category:)
+      tag.update!(category:) if tag.category.to_sym != category.to_sym
+      tags[name] ||= tag
+    end.values
+  end
+
+  def materialise_sections sections_by_name, snapshot_tags, post_tags
+    tags_by_name = post_tags.index_by(&:name)
+    snapshot_tags.each do |tag|
+      tags_by_name[tag.name] ||= tag
+    end
+
+    sections_by_name.each_with_object({ }) do |(tag_name, ranges), sections|
+      tag = tags_by_name[tag_name.to_s]
+      next if tag.nil?
+
+      sections[tag.id] = Array(ranges).map { |range| [range[0], range[1]] }
+    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|
@@ -116,10 +135,9 @@ class PostCreator
                                end_ms:)
       end
     end
+
     PostTag.where(post_id: post.id,
-                  tag_id: (current_ids - desired_ids).to_a).kept.find_each do |post_tag|
+                  tag_id: (current_ids - desired_ids).to_a).destroy_all
-      post_tag.discard_by!(@actor)
-    end
   end
 
   def sync_parent_posts! post, ids

backend/app/services/post_import_previewer.rb

@@ -3,17 +3,18 @@ require 'timeout'
 
 class PostImportPreviewer
   FIELDS = [
-    'title',
+      'title',
-    'thumbnail_base',
+      'thumbnail_base',
-    'original_created_from',
+      'original_created_from',
-    'original_created_before',
+      'original_created_before',
-    'duration',
+      'video_ms',
-    'tags',
+      'duration',
-    'parent_post_ids'].freeze
+      '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
+  METADATA_FETCH_WARNING = '自動取得に失敗しました．'.freeze
 
   def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
     prepared_rows = rows.map { prepare_row(_1) }
@@ -125,7 +126,6 @@ class PostImportPreviewer
     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')
@@ -151,7 +151,7 @@ class PostImportPreviewer
     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．'
+    else raise ArgumentError, '取得対象が不正です．'
     end
   end
 
@@ -162,6 +162,8 @@ class PostImportPreviewer
       normalised =
           if field == 'duration'
             normalise_duration_attribute(value)
+          elsif field == 'video_ms'
+            value.nil? ? '' : value.to_s
           else
             value.to_s
           end
@@ -194,7 +196,7 @@ class PostImportPreviewer
 
   def clear_automatic_values! attributes, provenance, tag_sources
     ['title', 'thumbnail_base', 'original_created_from',
-     'original_created_before', 'duration'].each do |field|
+     'original_created_before', 'video_ms', 'duration'].each do |field|
       attributes[field] = '' if provenance[field] == 'automatic'
     end
     tag_sources['automatic'] = ''
@@ -223,15 +225,15 @@ class PostImportPreviewer
     end
     { data:, warnings:, validation_errors: { } }
   rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_unsafe_url "\
+        "post_import_metadata_fetch_unsafe_url #{ payload.to_json }")
-        "#{ { error: e.class.name, message: e.message }.to_json }")
     { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
   rescue Preview::HttpFetcher::FetchFailed,
          Preview::HttpFetcher::ResponseTooLarge => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_failure "\
+        "post_import_metadata_fetch_failure #{ payload.to_json }")
-        "#{ { error: e.class.name, message: e.message }.to_json }")
     { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
   end
 
@@ -252,7 +254,15 @@ class PostImportPreviewer
   def sanitise_metadata_url value
     return nil unless value.is_a?(String)
 
-    PostUrlNormaliser.normalise(value)
+    stripped = value.strip
+    return nil if stripped.blank?
+
+    uri = URI.parse(stripped)
+    return nil unless uri.is_a?(URI::HTTP) && uri.host.present?
+
+    stripped
+  rescue URI::InvalidURIError
+    nil
   end
 
   def sanitise_metadata_time value
@@ -325,14 +335,14 @@ class PostImportPreviewer
   def safe_fetch_metadata url
     fetch_metadata(url)
   rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.info(
-        "post_import_metadata_fetch_unsafe_url "\
+        "post_import_metadata_fetch_unsafe_url #{ payload.to_json }")
-        "#{ { error: e.class.name, message: e.message }.to_json }")
     { data: { }, warnings: { }, validation_errors: { url: [e.message] } }
   rescue StandardError => e
+    payload = { error: e.class.name, message: e.message }
     Rails.logger.error(
-        "post_import_metadata_fetch_unexpected_failure "\
+        "post_import_metadata_fetch_unexpected_failure #{ payload.to_json }")
-        "#{ { error: e.class.name, message: e.message }.to_json }")
     { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
   end
 
@@ -439,7 +449,7 @@ class PostImportPreviewer
     []
   end
 
-  def validate_preview_tags raw, errors, field_warnings, known_tags
+  def validate_preview_tags raw, errors, known_tags
     names = raw.to_s.split
     return if names.empty?
     if names.any? { _1.downcase.start_with?('nico:') }
@@ -451,11 +461,6 @@ class PostImportPreviewer
     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
@@ -466,7 +471,7 @@ class PostImportPreviewer
                     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))
+                    video_ms: parse_video_ms(attributes, errors))
     post.valid?
     post.errors.each do |error|
       next if error.attribute == :url && error.type == :taken
@@ -475,7 +480,21 @@ class PostImportPreviewer
     end
   end
 
-  def parse_duration value, errors
+  def parse_video_ms attributes, errors
+    return nil unless attributes['tags'].to_s.split.include?('動画')
+
+    video_ms = attributes['video_ms']
+    if video_ms.present?
+      value = Integer(video_ms, exception: false)
+      if value&.positive?
+        return value
+      end
+
+      errors[:video_ms] = ['動画時間の記法が不正です．']
+      return nil
+    end
+
+    value = attributes['duration']
     return nil if value.blank?
 
     Tag.time_to_ms!(value.to_s, tag_name: '動画時間')

backend/app/services/post_import_row_normaliser.rb

@@ -1,190 +0,0 @@
-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

@@ -1,109 +0,0 @@
-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

@@ -1,25 +0,0 @@
-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

@@ -3,10 +3,9 @@ require 'date'
 
 class PostMetadataFetcher
   TIMESTAMP_PATTERN =
-      Regexp.new(
+      /\A(\d{4})-(\d{2})-(\d{2})T(\d{2})
-          '\A(\d{4})-(\d{2})-(\d{2})T(\d{2})' \
+        (?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?
-          '(?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?' \
+        (Z|[+-]\d{2}:?\d{2})?\z/x
-          '(Z|[+-]\d{2}:?\d{2})?\z')
 
   def self.fetch raw_url
     uri, = Preview::UrlSafety.validate(raw_url)
@@ -32,6 +31,7 @@ class PostMetadataFetcher
       original_created_from: serialise_time(created_range&.first),
       original_created_before: serialise_time(created_range&.last),
       duration: serialise_duration(duration),
+      display_tags: display_tags(platform_tags),
       tags: platform_tags.join(' ') }
   end
 
@@ -42,6 +42,24 @@ class PostMetadataFetcher
     []
   end
 
+  def self.display_tags names
+    return [] if names.blank?
+
+    existing_tags =
+        Tag
+        .joins(:tag_name)
+        .where(tag_names: { name: names })
+        .index_by(&:name)
+
+    names.map { |name|
+      tag = existing_tags[name]
+      {
+          name: name,
+          category: (tag&.category || 'meta'),
+          section_literals: [] }
+    }
+  end
+
   def self.original_created_range value
     return nil if value.blank?
 
@@ -168,6 +186,7 @@ class PostMetadataFetcher
   end
 
   private_class_method :platform_tags,
+                       :display_tags,
                        :original_created_range,
                        :parse_timestamp_range,
                        :parse_nanoseconds,

backend/app/services/post_thumbnail_attachment_builder.rb

@@ -0,0 +1,11 @@
+class PostThumbnailAttachmentBuilder
+  def self.build thumbnail:, thumbnail_base:
+    if thumbnail_base.present?
+      return Post.remote_thumbnail_attachment(thumbnail_base)
+    end
+
+    return nil if thumbnail.blank?
+
+    Post.resized_thumbnail_attachment(thumbnail)
+  end
+end

backend/app/services/post_thumbnail_upload_validator.rb

@@ -0,0 +1,34 @@
+class PostThumbnailUploadValidator
+  MAX_THUMBNAIL_BYTES = 20 * 1024 * 1024
+  ALLOWED_CONTENT_TYPES = Preview::ThumbnailFetcher::RASTER_IMAGE_CONTENT_TYPES.freeze
+
+  class InvalidUpload < StandardError; end
+
+  def self.validate! thumbnail
+    return if thumbnail.blank?
+    unless thumbnail.is_a?(ActionDispatch::Http::UploadedFile)
+      raise InvalidUpload, 'thumbnail upload が不正です．'
+    end
+    raise InvalidUpload, 'thumbnail file size が大きすぎます．' if thumbnail.size > MAX_THUMBNAIL_BYTES
+    raise InvalidUpload, 'サムネイル画像の形式が不正です．' unless allowed_content_type?(thumbnail.content_type)
+    bytes = thumbnail.read
+    raise InvalidUpload, 'サムネイル画像の形式が不正です．' if Post.svg_document_bytes?(bytes)
+    unless Post.raster_thumbnail_bytes?(bytes)
+      raise InvalidUpload, 'サムネイル画像の形式が不正です．'
+    end
+
+    attachment = Post.resized_thumbnail_attachment(
+        StringIO.new(bytes),
+        content_type: thumbnail.content_type)
+    attachment[:io].close if attachment[:io].respond_to?(:close)
+  rescue MiniMagick::Error, Timeout::Error
+    raise InvalidUpload, 'サムネイル画像の変換に失敗しました．'
+  ensure
+    thumbnail&.rewind if thumbnail.respond_to?(:rewind)
+  end
+
+  def self.allowed_content_type? content_type
+    mime_type = content_type.to_s.split(';', 2).first.to_s.downcase.strip
+    ALLOWED_CONTENT_TYPES.include?(mime_type)
+  end
+end

backend/app/services/post_version_recorder.rb

@@ -25,6 +25,7 @@ class PostVersionRecorder < VersionRecorder
       thumbnail_base: @record.thumbnail_base,
       video_ms: @record.video_ms,
       tags: @record.snapshot_tag_names.join(' '),
+      tags_json: @record.snapshot_tags_json,
       parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
       original_created_from: @record.original_created_from,
       original_created_before: @record.original_created_before }

backend/app/services/preview/thumbnail_fetcher.rb

@@ -1,7 +1,7 @@
 module Preview
   class ThumbnailFetcher
     class GenerationFailed < StandardError; end
-    ALLOWED_IMAGE_CONTENT_TYPES = [
+    RASTER_IMAGE_CONTENT_TYPES = [
       'image/jpeg', 'image/png', 'image/gif', 'image/webp'
     ].freeze
     HTML_MAX_BYTES = 1.megabyte
@@ -28,7 +28,9 @@ module Preview
     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)
+      unless Post.remote_thumbnail_image_bytes?(
+                 response.body,
+                 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
 
@@ -51,7 +53,9 @@ module Preview
       return nil if url.blank?
 
       response = HttpFetcher.fetch(url)
-      return nil unless allowed_image_content_type?(response.content_type)
+      return nil unless Post.remote_thumbnail_image_bytes?(
+                            response.body,
+                            content_type: response.content_type)
 
       response.body
     rescue HttpFetcher::FetchTimeout
@@ -92,13 +96,7 @@ module Preview
       nil
     end
 
-    def self.allowed_image_content_type?(content_type)
-      mime_type = content_type.to_s.split(';', 2).first.downcase.strip
-      ALLOWED_IMAGE_CONTENT_TYPES.include?(mime_type)
-    end
-
     private_class_method :fetch_image_or_nil, :fetch_image!,
-                         :niconico_thumbnail_url,
+                         :niconico_thumbnail_url
-                         :allowed_image_content_type?
   end
 end

backend/app/services/youtube/sync.rb

@@ -103,7 +103,7 @@ module Youtube
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -117,8 +117,8 @@ module Youtube
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
-        pt.discard_by!(nil)
+        pt.destroy!
       end
     end
 

backend/config/environments/development.rb

@@ -1,4 +1,4 @@
-require "active_support/core_ext/integer/time"
+require 'active_support/core_ext/integer/time'
 
 Rails.application.configure do
   # Settings specified here will take precedence over those in config/application.rb.
@@ -17,8 +17,8 @@ Rails.application.configure do
 
   # Enable/disable Action Controller caching. By default Action Controller caching is disabled.
   # Run rails dev:cache to toggle Action Controller caching.
-  if Rails.root.join("tmp/caching-dev.txt").exist?
+  if Rails.root.join('tmp/caching-dev.txt').exist?
-    config.public_file_server.headers = { "cache-control" => "public, max-age=#{2.days.to_i}" }
+    config.public_file_server.headers = { 'cache-control' => "public, max-age=#{2.days.to_i}" }
   else
     config.action_controller.perform_caching = false
   end
@@ -36,7 +36,11 @@ Rails.application.configure do
   config.action_mailer.perform_caching = false
 
   # Set localhost to be used by links generated in mailer templates.
-  config.action_mailer.default_url_options = { host: "localhost", port: 3000 }
+  config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }
+  Rails.application.routes.default_url_options.merge!(
+      host: 'localhost',
+      port: 3002,
+      protocol: 'http')
 
   # Print deprecation notices to the Rails logger.
   config.active_support.deprecation = :log

backend/config/routes.rb

@@ -33,12 +33,6 @@ 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
@@ -58,8 +52,9 @@ Rails.application.routes.draw do
 
   resources :posts, only: [:index, :show, :create, :update] do
     collection do
+      get :metadata
+      post :bulk
       get :random
-      get :changes
       get :versions, to: 'post_versions#index'
     end
 

backend/db/migrate/20260727123600_add_tags_json_to_post_versions.rb

@@ -0,0 +1,299 @@
+class AddTagsJsonToPostVersions < ActiveRecord::Migration[8.0]
+  RESOLUTION_GRACE = 1.second
+  SECTION_LITERAL_PATTERN = /\[[^\[\]\s]*-[^\[\]\s]*\]\z/
+
+  class MigrationPostVersion < ActiveRecord::Base
+    self.table_name = 'post_versions'
+  end
+
+  class MigrationTag < ActiveRecord::Base
+    self.table_name = 'tags'
+  end
+
+  class MigrationTagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  class MigrationTagVersion < ActiveRecord::Base
+    self.table_name = 'tag_versions'
+  end
+
+  class MigrationNicoTagVersion < ActiveRecord::Base
+    self.table_name = 'nico_tag_versions'
+  end
+
+  def up
+    add_column :post_versions, :tags_json, :json, after: :tags
+    MigrationPostVersion.reset_column_information
+
+    backfill_missing_initial_tag_versions!
+    intervals_by_name = build_intervals_by_name
+
+    say_with_time 'Backfilling post_versions.tags_json' do
+      MigrationPostVersion.where(tags_json: nil).find_each(batch_size: 500) do |version|
+        version.update_columns(tags_json: build_tags_json(version, intervals_by_name))
+      end
+    end
+
+    change_column_null :post_versions, :tags_json, false
+
+    schema = connection.quote(JSON.generate({
+        type: 'array',
+        items: { type: 'object',
+                 properties: { id: { type: 'integer', minimum: 1 },
+                               version_no: { type: 'integer', minimum: 1 },
+                               name: { type: 'string', minLength: 1 },
+                               category: { type: 'string', enum: ['deerjikist',
+                                                                  'meme',
+                                                                  'character',
+                                                                  'general',
+                                                                  'material',
+                                                                  'meta',
+                                                                  'nico'] },
+                               sections: { type: 'array',
+                                           items: { type: 'object',
+                                                    properties: { begin_ms: { type: 'integer',
+                                                                              minimum: 0 },
+                                                                  end_ms: { type: ['integer',
+                                                                                   'null'],
+                                                                            minimum: 0 } },
+                                                    required: ['begin_ms', 'end_ms'],
+                                                    additionalProperties: false } } },
+                 required: ['id', 'version_no', 'name', 'category', 'sections'],
+                 additionalProperties: false } }))
+
+    add_check_constraint :post_versions,
+                         "JSON_SCHEMA_VALID(#{ schema }, tags_json)",
+                         name: 'chk_post_versions_tags_json_schema'
+  end
+
+  def down
+    remove_check_constraint :post_versions, name: 'chk_post_versions_tags_json_schema'
+
+    remove_column :post_versions, :tags_json
+  end
+
+  private
+
+  def backfill_missing_initial_tag_versions!
+    say_with_time 'Backfilling missing initial tag versions' do
+      tag_rows = missing_initial_version_rows(MigrationTagVersion, nico: false)
+      nico_rows = missing_initial_version_rows(MigrationNicoTagVersion, nico: true)
+
+      MigrationTagVersion.insert_all!(tag_rows) if tag_rows.any?
+      MigrationNicoTagVersion.insert_all!(nico_rows) if nico_rows.any?
+
+      tag_rows.length + nico_rows.length
+    end
+  end
+
+  def missing_initial_version_rows version_class, nico:
+    first_versions =
+        version_class
+        .order(:tag_id, :version_no)
+        .to_a
+        .group_by(&:tag_id)
+        .transform_values(&:first)
+    rows = []
+
+    MigrationTag.find_each do |tag|
+      next if (tag.category == 'nico') != nico
+
+      first_version = first_versions[tag.id]
+      next unless first_version
+      next if valid_initial_version?(first_version)
+
+      assert_inferable_initial_version!(tag, first_version)
+      rows << initial_version_row(tag, first_version, nico:)
+    end
+
+    rows
+  end
+
+  def valid_initial_version? version
+    version.version_no == 1 && version.event_type == 'create'
+  end
+
+  def assert_inferable_initial_version! tag, version
+    inferable =
+        version.version_no == 2 &&
+        version.event_type == 'discard' &&
+        tag.created_at < version.created_at
+    return if inferable
+
+    details = [
+        "tag_id=#{ tag.id }",
+        "version_no=#{ version.version_no }",
+        "event_type=#{ version.event_type.inspect }",
+        "tag_created_at=#{ tag.created_at.iso8601(6) }",
+        "version_created_at=#{ version.created_at.iso8601(6) }"]
+
+    raise "Cannot infer initial tag version: #{ details.join(', ') }"
+  end
+
+  def initial_version_row tag, discard_version, nico:
+    row = {
+        tag_id: tag.id,
+        version_no: 1,
+        event_type: 'create',
+        name: discard_version.name,
+        created_at: tag.created_at,
+        created_by_user_id: nil }
+
+    if nico
+      return row.merge(linked_tags: discard_version.linked_tags)
+    end
+
+    row.merge(
+        category: discard_version.category,
+        aliases: discard_version.aliases,
+        parent_tag_ids: discard_version.parent_tag_ids,
+        deprecated_at: discard_version.deprecated_at)
+  end
+
+  def build_intervals_by_name
+    intervals_by_name = Hash.new { |hash, name| hash[name] = [] }
+    versions_by_kind = {
+        tag: versions_by_tag_id(MigrationTagVersion),
+        nico: versions_by_tag_id(MigrationNicoTagVersion) }
+    current_names = current_names_by_tag_id
+
+    MigrationTag.find_each do |tag|
+      nico = tag.category == 'nico'
+      kind = nico ? :nico : :tag
+      versions = versions_by_kind.fetch(kind).fetch(tag.id, [])
+
+      intervals_for(
+          tag,
+          versions,
+          current_name: current_names.fetch(tag.id),
+          nico:).each do |interval|
+        name = interval.delete(:name)
+        intervals_by_name[name] << interval
+      end
+    end
+
+    intervals_by_name
+  end
+
+  def versions_by_tag_id version_class
+    version_class
+        .order(:tag_id, :version_no)
+        .to_a
+        .group_by(&:tag_id)
+  end
+
+  def current_names_by_tag_id
+    MigrationTagName
+        .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+        .pluck('tags.id', 'tag_names.name')
+        .to_h
+  end
+
+  def intervals_for tag, versions, current_name:, nico:
+    if versions.empty?
+      return [{
+          name: current_name,
+          tag_id: tag.id,
+          version_no: tag.version_no,
+          category: nico ? 'nico' : tag.category,
+          from: tag.created_at,
+          to: tag.discarded_at }]
+    end
+
+    versions.each_with_index.filter_map do |version, index|
+      next if version.event_type == 'discard'
+
+      {
+          name: version.name,
+          tag_id: tag.id,
+          version_no: version.version_no,
+          category: nico ? 'nico' : version.category,
+          from: version.created_at,
+          to: versions[index + 1]&.created_at || tag.discarded_at }
+    end
+  end
+
+  def build_tags_json version, intervals_by_name
+    entries = version.tags.to_s.split.map do |literal|
+      name = tag_name_from_literal(literal)
+      interval = resolve_tag!(intervals_by_name.fetch(name, []), name:, version:)
+
+      { 'id' => interval.fetch(:tag_id),
+        'version_no' => interval.fetch(:version_no),
+        'name' => name,
+        'category' => interval.fetch(:category),
+        'sections' => [] }
+    end
+
+    assert_unique_tag_ids!(version, entries)
+
+    entries.sort_by { |entry| entry.fetch('id') }
+  end
+
+  def tag_name_from_literal literal
+    name = literal.dup
+    name.sub!(SECTION_LITERAL_PATTERN, '') while name.match?(
+        SECTION_LITERAL_PATTERN)
+
+    if name.empty? || name.include?('[') || name.include?(']')
+      raise "Invalid legacy tag literal: #{ literal.inspect }"
+    end
+
+    name
+  end
+
+  def resolve_tag! intervals, name:, version:
+    time = version.created_at
+    candidates = intervals.select do |interval|
+      interval.fetch(:from) <= time &&
+        (interval[:to].nil? || time < interval.fetch(:to))
+    end
+
+    candidates = future_candidates(intervals, time) if candidates.empty?
+
+    return candidates.first if candidates.one?
+
+    candidate_versions = candidates.map do |candidate|
+      [candidate.fetch(:tag_id), candidate.fetch(:version_no)]
+    end
+    details = [
+        "post_version_id=#{ version.id }",
+        "post_id=#{ version.post_id }",
+        "name=#{ name.inspect }",
+        "created_at=#{ time.iso8601(6) }",
+        "candidates=#{ candidate_versions.inspect }"].join(', ')
+
+    raise "Could not resolve tag snapshot: #{ details }"
+  end
+
+  def future_candidates intervals, time
+    candidates = intervals.select do |interval|
+      interval.fetch(:from) > time &&
+        interval.fetch(:from) <= time + RESOLUTION_GRACE
+    end
+    return [] if candidates.empty?
+
+    nearest_from = candidates.map { |interval| interval.fetch(:from) }.min
+
+    candidates.select do |interval|
+      interval.fetch(:from) == nearest_from
+    end
+  end
+
+  def assert_unique_tag_ids! version, entries
+    duplicate_tag_ids =
+        entries
+        .map { |entry| entry.fetch('id') }
+        .tally
+        .select { |_tag_id, count| count > 1 }
+        .keys
+    return if duplicate_tag_ids.empty?
+
+    details = [
+        "post_version_id=#{ version.id }",
+        "duplicate_tag_ids=#{ duplicate_tag_ids.inspect }"].join(', ')
+
+    raise "Duplicate tag IDs: #{ details }"
+  end
+end

backend/db/migrate/20260921000000_delete_inactive_records_from_post_tags.rb

@@ -0,0 +1,53 @@
+class DeleteInactiveRecordsFromPostTags < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        post_tags
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :post_tags, [:tag_id, :discarded_at]
+    remove_index :post_tags, [:post_id, :discarded_at]
+    remove_index :post_tags, name: 'idx_post_tags_active_unique'
+    remove_index :post_tags, :discarded_at
+
+    remove_foreign_key :post_tags, column: :deleted_user_id
+    remove_index :post_tags, :deleted_user_id
+
+    remove_column :post_tags, :active_unique_key
+    remove_column :post_tags, :is_active
+    remove_column :post_tags, :discarded_at
+    remove_column :post_tags, :deleted_user_id
+    remove_column :post_tags, :updated_at
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      MODIFY COLUMN
+        id BIGINT NOT NULL
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      DROP PRIMARY KEY
+    SQL
+
+    remove_column :post_tags, :id
+
+    execute <<~SQL
+      ALTER TABLE
+        post_tags
+      ADD PRIMARY KEY
+        (post_id, tag_id)
+    SQL
+
+    remove_index :post_tags, :post_id
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260921010000_add_foreign_key_on_post_id_and_tag_id_in_post_tag_sections.rb

@@ -0,0 +1,11 @@
+class AddForeignKeyOnPostIdAndTagIdInPostTagSections < ActiveRecord::Migration[8.0]
+  def change
+    remove_foreign_key :post_tag_sections, :posts, column: :post_id
+    remove_foreign_key :post_tag_sections, :tags, column: :tag_id
+
+    add_foreign_key :post_tag_sections, :post_tags,
+                    column: [:post_id, :tag_id],
+                    primary_key: [:post_id, :tag_id],
+                    on_delete: :cascade
+  end
+end

backend/db/migrate/20260921020000_delete_discarded_records_from_tags.rb

@@ -0,0 +1,46 @@
+class DeleteDiscardedRecordsFromTags < ActiveRecord::Migration[8.0]
+  def up
+    remove_foreign_key :tag_versions, :tags, column: :tag_id
+    remove_foreign_key :nico_tag_versions, :tags, column: :tag_id
+    remove_foreign_key :material_versions, :tags, column: :tag_id
+
+    execute <<~SQL
+      DELETE
+        ntr
+      FROM
+        nico_tag_relations ntr
+        INNER JOIN
+          tags t
+          ON
+            t.discarded_at IS NOT NULL
+            AND t.id IN (ntr.tag_id, ntr.nico_tag_id)
+    SQL
+
+    execute <<~SQL
+      DELETE
+        ti
+      FROM
+        tag_implications ti
+        INNER JOIN
+          tags t
+          ON
+            t.discarded_at IS NOT NULL
+            AND t.id IN (ti.tag_id, ti.parent_tag_id)
+    SQL
+
+    execute <<~SQL
+      DELETE
+      FROM
+        tags
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :tags, :discarded_at
+    remove_column :tags, :discarded_at
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+end

backend/db/migrate/20260921030000_delete_discarded_records_from_tag_names.rb

@@ -0,0 +1,18 @@
+class DeleteDiscardedRecordsFromTagNames < ActiveRecord::Migration[8.0]
+  def up
+    execute <<~SQL
+      DELETE
+      FROM
+        tag_names
+      WHERE
+        discarded_at IS NOT NULL
+    SQL
+
+    remove_index :tag_names, :discarded_at
+    remove_column :tag_names, :discarded_at
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  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_13_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) 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
@@ -311,23 +311,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
   end
 
-  create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "post_tags", primary_key: ["post_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
     t.bigint "created_user_id"
-    t.bigint "deleted_user_id"
     t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.datetime "discarded_at"
-    t.virtual "is_active", type: :boolean, as: "(`discarded_at` is null)", stored: true
-    t.virtual "active_unique_key", type: :string, as: "(case when (`discarded_at` is null) then concat(`post_id`,_utf8mb4':',`tag_id`) else NULL end)", stored: true
-    t.index ["active_unique_key"], name: "idx_post_tags_active_unique", unique: true
     t.index ["created_user_id"], name: "index_post_tags_on_created_user_id"
-    t.index ["deleted_user_id"], name: "index_post_tags_on_deleted_user_id"
-    t.index ["discarded_at"], name: "index_post_tags_on_discarded_at"
-    t.index ["post_id", "discarded_at"], name: "index_post_tags_on_post_id_and_discarded_at"
-    t.index ["post_id"], name: "index_post_tags_on_post_id"
-    t.index ["tag_id", "discarded_at"], name: "index_post_tags_on_tag_id_and_discarded_at"
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
@@ -349,6 +338,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
     t.text "tags", null: false
+    t.json "tags_json", null: false
     t.text "parent_post_ids", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
@@ -362,6 +352,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_post_versions_video_ms_positive"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
     t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"items\":{\"type\":\"object\",\"properties\":{\"id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1},\"name\":{\"type\":\"string\",\"minLength\":1},\"category\":{\"type\":\"string\",\"enum\":[\"deerjikist\",\"meme\",\"character\",\"general\",\"material\",\"meta\",\"nico\"]},\"sections\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"properties\":{\"begin_ms\":{\"type\":\"integer\",\"minimum\":0},\"end_ms\":{\"type\":[\"integer\",\"null\"],\"minimum\":0}},\"required\":[\"begin_ms\",\"end_ms\"],\"additionalProperties\":false}}},\"required\":[\"id\",\"version_no\",\"name\",\"category\",\"sections\"],\"additionalProperties\":false}}',`tags_json`)", name: "chk_post_versions_tags_json_schema"
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -393,19 +384,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["user_id"], name: "index_settings_on_user_id", unique: true
   end
 
-  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "wiki_page_id", null: false
-    t.integer "no", null: false
-    t.string "alt_text"
-    t.binary "sha256", limit: 32, null: false
-    t.bigint "created_by_user_id", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
-    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
-    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
-  end
-
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
@@ -431,9 +409,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.bigint "canonical_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.datetime "discarded_at"
     t.index ["canonical_id"], name: "index_tag_names_on_canonical_id"
-    t.index ["discarded_at"], name: "index_tag_names_on_discarded_at"
     t.index ["name"], name: "index_tag_names_on_name", unique: true
   end
 
@@ -470,10 +446,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
-    t.datetime "discarded_at"
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
-    t.index ["discarded_at"], name: "index_tags_on_discarded_at"
     t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
@@ -614,6 +588,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
     t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
+  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "no", null: false
+    t.string "alt_text"
+    t.binary "sha256", limit: 32, null: false
+    t.bigint "created_by_user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
+    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
+    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
+  end
+
   create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "sha256", limit: 64, null: false
     t.text "body", null: false
@@ -707,7 +694,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   add_foreign_key "material_sync_suppressions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "materials"
   add_foreign_key "material_versions", "materials", column: "parent_id"
-  add_foreign_key "material_versions", "tags"
   add_foreign_key "material_versions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "users", column: "updated_by_user_id"
   add_foreign_key "materials", "materials", column: "parent_id"
@@ -716,18 +702,15 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   add_foreign_key "materials", "users", column: "updated_by_user_id"
   add_foreign_key "nico_tag_relations", "tags"
   add_foreign_key "nico_tag_relations", "tags", column: "nico_tag_id"
-  add_foreign_key "nico_tag_versions", "tags"
   add_foreign_key "nico_tag_versions", "users", column: "created_by_user_id"
   add_foreign_key "post_implications", "posts"
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
-  add_foreign_key "post_tag_sections", "posts"
+  add_foreign_key "post_tag_sections", "post_tags", column: ["post_id", "tag_id"], primary_key: ["post_id", "tag_id"], on_delete: :cascade
-  add_foreign_key "post_tag_sections", "tags"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
-  add_foreign_key "post_tags", "users", column: "deleted_user_id"
   add_foreign_key "post_versions", "posts"
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
@@ -737,7 +720,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   add_foreign_key "tag_names", "tag_names", column: "canonical_id"
   add_foreign_key "tag_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
-  add_foreign_key "tag_versions", "tags"
   add_foreign_key "tag_versions", "users", column: "created_by_user_id"
   add_foreign_key "tags", "tag_names"
   add_foreign_key "theatre_comments", "theatres"

backend/lib/tasks/sync_nico.rake

@@ -16,7 +16,7 @@ namespace :nico do
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -30,8 +30,8 @@ namespace :nico do
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
-        pt.discard_by!(nil)
+        pt.destroy!
       end
     end
 

backend/spec/db/delete_discarded_tags_spec.rb

@@ -0,0 +1,123 @@
+require 'rails_helper'
+require_relative '../../db/migrate/20260921020000_delete_discarded_records_from_tags'
+require_relative '../../db/migrate/20260921030000_delete_discarded_records_from_tag_names'
+
+RSpec.describe 'discarded tag cleanup migrations' do
+  [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |migration_class|
+    it "rejects rollback of #{ migration_class.name }" do
+      expect { migration_class.new.down }
+          .to raise_error(ActiveRecord::IrreversibleMigration)
+    end
+  end
+
+  context 'with legacy records' do
+    self.use_transactional_tests = false
+
+    before do
+      record_class = Class.new(ActiveRecord::Base) do
+        self.abstract_class = true
+      end
+      stub_const('TagCleanupMigrationRecord', record_class)
+      config = ActiveRecord::Base.connection_db_config.configuration_hash
+      @database = "btrc_hub_test_tag_cleanup_#{ Process.pid }_#{ SecureRandom.hex(4) }"
+      record_class.establish_connection(config.merge(database: nil))
+      @connection = record_class.lease_connection
+      @connection.create_database(@database)
+      @database_created = true
+      @connection.execute("USE #{ @connection.quote_table_name(@database) }")
+    end
+
+    after do
+      @connection.drop_database(@database) if @database_created
+    ensure
+      TagCleanupMigrationRecord.remove_connection
+    end
+
+    before do
+      @connection.create_table(:tag_names) do |t|
+        t.string :name, null: false, index: { unique: true }
+        t.bigint :canonical_id
+        t.datetime :discarded_at, index: true
+      end
+      @connection.add_foreign_key(:tag_names, :tag_names, column: :canonical_id)
+      @connection.create_table(:tags) do |t|
+        t.references :tag_name, null: false, foreign_key: true, index: { unique: true }
+        t.datetime :discarded_at, index: true
+      end
+      @connection.create_table(:nico_tag_relations) do |t|
+        t.references :tag, null: false, foreign_key: true
+        t.references :nico_tag, null: false, foreign_key: { to_table: :tags }
+      end
+      @connection.create_table(:tag_implications) do |t|
+        t.references :tag, null: false, foreign_key: true
+        t.references :parent_tag, null: false, foreign_key: { to_table: :tags }
+      end
+      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
+        @connection.create_table(table) do |t|
+          t.references :tag, null: false, foreign_key: true
+        end
+      end
+
+      @connection.execute(<<~SQL)
+        INSERT INTO tag_names (id, name, canonical_id, discarded_at) VALUES
+          (1, 'kept', NULL, NULL),
+          (2, 'merged_alias', 1, NULL),
+          (3, 'nico:deleted', NULL, '2026-09-20'),
+          (4, 'nico:kept', NULL, NULL),
+          (5, 'deleted_name', NULL, '2026-09-20')
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO tags (id, tag_name_id, discarded_at) VALUES
+          (1, 1, NULL), (2, 2, '2026-09-20'),
+          (3, 3, '2026-09-20'), (4, 4, NULL)
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO nico_tag_relations (id, tag_id, nico_tag_id) VALUES
+          (1, 1, 4), (2, 2, 4), (3, 1, 3), (4, 2, 3)
+      SQL
+      @connection.execute(<<~SQL)
+        INSERT INTO tag_implications (id, tag_id, parent_tag_id) VALUES
+          (1, 1, 4), (2, 2, 1), (3, 1, 2), (4, 2, 3)
+      SQL
+      @connection.execute('INSERT INTO tag_versions (tag_id) VALUES (1), (2)')
+      @connection.execute('INSERT INTO nico_tag_versions (tag_id) VALUES (3), (4)')
+      @connection.execute('INSERT INTO material_versions (tag_id) VALUES (1), (2)')
+    end
+
+    it 'removes discarded records and their links while retaining aliases and history' do
+      [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |klass|
+        migration = klass.new
+        allow(migration).to receive(:connection).and_return(@connection)
+        migration.suppress_messages { migration.up }
+      end
+
+      expect(@connection.select_values('SELECT id FROM tags ORDER BY id')).to eq([1, 4])
+      expect(@connection.select_rows('SELECT id, canonical_id FROM tag_names ORDER BY id'))
+          .to eq([[1, nil], [2, 1], [4, nil]])
+      expect(@connection.select_values('SELECT id FROM nico_tag_relations')).to eq([1])
+      expect(@connection.select_values('SELECT id FROM tag_implications')).to eq([1])
+      expect(@connection.select_values('SELECT tag_id FROM tag_versions ORDER BY tag_id'))
+          .to eq([1, 2])
+      expect(@connection.select_values('SELECT tag_id FROM nico_tag_versions ORDER BY tag_id'))
+          .to eq([3, 4])
+      expect(@connection.select_values('SELECT tag_id FROM material_versions ORDER BY tag_id'))
+          .to eq([1, 2])
+
+      [:tags, :tag_names].each do |table|
+        expect(@connection.column_exists?(table, :discarded_at)).to be(false)
+        expect(@connection.index_exists?(table, :discarded_at)).to be(false)
+      end
+      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
+        expect(@connection.foreign_key_exists?(table, :tags, column: :tag_id)).to be(false)
+      end
+      expect(@connection.foreign_key_exists?(:tags, :tag_names)).to be(true)
+      expect(@connection.foreign_key_exists?(:tag_names, :tag_names, column: :canonical_id))
+          .to be(true)
+      expect(@connection.index_exists?(:tag_names, :name, unique: true)).to be(true)
+      expect(@connection.index_exists?(:tags, :tag_name_id, unique: true)).to be(true)
+      [:nico_tag_relations, :tag_implications].each do |table|
+        expect(@connection.foreign_keys(table).map(&:to_table)).to eq(['tags', 'tags'])
+      end
+    end
+  end
+end

backend/spec/models/post_spec.rb

@@ -110,7 +110,7 @@ RSpec.describe Post, type: :model do
     end
 
     describe '.resized_thumbnail_attachment' do
-      it 'centre-crops a wide image to 180x180 without distorting it' do
+      it 'fits a wide image within 180x180 without distorting it' do
         blob = image_blob(
             width: 360,
             height: 180,
@@ -123,13 +123,13 @@ RSpec.describe Post, type: :model do
         resized = described_class.resized_thumbnail_attachment(upload_for(blob))
         image = read_image(resized)
 
-        expect(image.dimensions).to eq([180, 180])
+        expect(image.dimensions).to eq([180, 90])
-        expect_green(colour_at(image, 0, 90))
+        expect_red(colour_at(image, 0, 45))
-        expect_green(colour_at(image, 90, 90))
+        expect_green(colour_at(image, 90, 45))
-        expect_green(colour_at(image, 179, 90))
+        expect_red(colour_at(image, 179, 45))
       end
 
-      it 'centre-crops a tall image to 180x180 without distorting it' do
+      it 'fits a tall image within 180x180 without distorting it' do
         blob = image_blob(
             width: 180,
             height: 360,
@@ -142,10 +142,10 @@ RSpec.describe Post, type: :model do
         resized = described_class.resized_thumbnail_attachment(upload_for(blob))
         image = read_image(resized)
 
-        expect(image.dimensions).to eq([180, 180])
+        expect(image.dimensions).to eq([90, 180])
-        expect_green(colour_at(image, 90, 0))
+        expect_red(colour_at(image, 45, 0))
-        expect_green(colour_at(image, 90, 90))
+        expect_green(colour_at(image, 45, 90))
-        expect_green(colour_at(image, 90, 179))
+        expect_red(colour_at(image, 45, 179))
       end
 
       it 'keeps a square image square without distortion' do
@@ -192,7 +192,7 @@ RSpec.describe Post, type: :model do
 
         expect(post.thumbnail).to be_attached
         image = read_image(post.thumbnail)
-        expect(image.dimensions).to eq([180, 180])
+        expect(image.dimensions).to eq([180, 135])
       end
 
       it 'does not attach anything when thumbnail conversion fails' do

backend/spec/models/post_tag_spec.rb

@@ -1,5 +1,73 @@
+require 'rails_helper'
+
 RSpec.describe PostTag, type: :model do
+  describe 'uniqueness' do
+    it 'rejects duplicate post and tag pairs but allows either to be reused' do
+      post_tag = create(:post_tag)
+      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect(duplicate).not_to be_valid
+      expect(duplicate.errors.of_kind?(:post_id, :taken)).to be(true)
+      expect(build(:post_tag, post: post_tag.post, tag: create(:tag))).to be_valid
+      expect(build(:post_tag, post: create(:post), tag: post_tag.tag)).to be_valid
+    end
+
+    it 'enforces uniqueness in the database when validation is bypassed' do
+      post_tag = create(:post_tag)
+      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect { duplicate.save!(validate: false) }
+          .to raise_error(ActiveRecord::RecordNotUnique)
+    end
+  end
+
+  describe '#destroy!' do
+    it 'deletes only the selected pair and its sections and updates the counter' do
+      post_tag = create(:post_tag)
+      same_post = create(:post_tag, post: post_tag.post)
+      same_tag = create(:post_tag, tag: post_tag.tag)
+      sections = [post_tag, same_post, same_tag].map do |link|
+        create(:post_tag_section, post: link.post, tag: link.tag,
+                                  begin_ms: 1000, end_ms: 2000)
+      end
+
+      expect { post_tag.destroy! }.to change(described_class, :count).by(-1)
+          .and change(PostTagSection, :count).by(-1)
+          .and change { post_tag.tag.reload.post_count }.from(2).to(1)
+
+      expect(described_class.exists?(post: post_tag.post, tag: post_tag.tag)).to be(false)
+      expect(same_post.reload).to be_persisted
+      expect(same_tag.reload).to be_persisted
+      expect(PostTagSection.all).to contain_exactly(*sections.drop(1))
+      expect(post_tag.post.reload.tags).to contain_exactly(same_post.tag)
+      expect(post_tag.tag.reload.posts).to contain_exactly(same_tag.post)
+    end
+
+    it 'allows a removed tag to be added again without restoring old sections' do
+      post_tag = create(:post_tag)
+      create(:post_tag_section, post: post_tag.post, tag: post_tag.tag,
+                                begin_ms: 1000, end_ms: 2000)
+      post_tag.destroy!
+
+      replacement = create(:post_tag, post: post_tag.post, tag: post_tag.tag)
+
+      expect(replacement.reload.sections).to be_empty
+      expect(replacement.tag.reload.post_count).to eq(1)
+    end
+  end
+
   describe '#sections' do
+    it 'loads the owning post_tag from a section using both keys' do
+      post_tag = create(:post_tag)
+      create(:post_tag, post: post_tag.post)
+      create(:post_tag, tag: post_tag.tag)
+      section = create(:post_tag_section, post: post_tag.post,
+                                         tag: post_tag.tag,
+                                         begin_ms: 1000, end_ms: 2000)
+
+      expect(section.reload.post_tag).to eq(post_tag)
+    end
+
     it 'loads sections by post_id and tag_id' do
       post_tag = create(:post_tag)
       section = create(:post_tag_section,
@@ -12,18 +80,25 @@ RSpec.describe PostTag, type: :model do
     end
 
     it 'does not load sections for another tag on the same post' do
-      post = create(:post)
+      post_tag = create(:post_tag)
-      tag = create(:tag)
+      post = post_tag.post
       other_tag = create(:tag)
 
-      post_tag = create(:post_tag, post:, tag:)
+      own_section = create(:post_tag_section,
+                           post:,
+                           tag: post_tag.tag,
+                           begin_ms: 1000,
+                           end_ms: 2000)
+
+      create(:post_tag, post:, tag: other_tag)
+
       create(:post_tag_section,
              post:,
              tag: other_tag,
              begin_ms: 1000,
              end_ms: 2000)
 
-      expect(post_tag.sections).to be_empty
+      expect(post_tag.reload.sections).to contain_exactly(own_section)
     end
 
     it 'allows open-ended sections' do

backend/spec/models/post_version_spec.rb

@@ -19,6 +19,7 @@ RSpec.describe PostVersion, type: :model do
       url: post_record.url,
       thumbnail_base: post_record.thumbnail_base,
       tags: post_record.snapshot_tag_names.join(' '),
+      tags_json: post_record.snapshot_tags_json,
       parent_post_ids: post_record.snapshot_parent_post_ids.join(' '),
       original_created_from: post_record.original_created_from,
       original_created_before: post_record.original_created_before,

backend/spec/models/tag_name_sanitisation_rule_spec.rb

@@ -57,7 +57,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
 
       it 'deletes the source tag_name' do
         described_class.apply!
-        expect(TagName.exists?(source.id)).to be(false)
+        expect(TagName.unscoped.exists?(source.id)).to be(false)
         expect(existing.reload.name).to eq('foobar')
       end
     end
@@ -75,7 +75,27 @@ RSpec.describe TagNameSanitisationRule, type: :model do
         described_class.apply!
         expected_tag_name_id = existing.canonical_id || existing.id
         expect(source_tag.reload.tag_name_id).to eq(expected_tag_name_id)
-        expect(TagName.exists?(source_tag_name_id)).to be(false)
+        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
+      end
+    end
+
+    context 'when the sanitised name is an alias of an existing tag' do
+      let!(:existing_tag) { create(:tag) }
+      let!(:alias_name) do
+        TagName.create!(name: 'foobar', canonical: existing_tag.tag_name)
+      end
+      let!(:source) do
+        TagName.create!(name: 'tmp').tap do |tn|
+          tn.update_columns(name: 'foo_bar', updated_at: Time.current)
+        end
+      end
+
+      it 'deletes only the source and preserves the alias and its canonical tag' do
+        described_class.apply!
+
+        expect(TagName.unscoped.exists?(source.id)).to be(false)
+        expect(alias_name.reload.canonical).to eq(existing_tag.tag_name)
+        expect(Tag.find(existing_tag.id)).to eq(existing_tag)
       end
     end
 
@@ -92,13 +112,15 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
 
       it 'merges the source tag into the existing tag and deletes the source tag_name' do
-        expect(TagName.find_by(name: 'foobar')&.tag&.id).to eq(existing_tag.id)
+        post = create(:post)
-        expect(TagName.find_by(name: 'foo_bar')&.tag&.id).to eq(source_tag.id)
+        PostTag.create!(post:, tag: source_tag)
 
         described_class.apply!
 
-        expect(Tag.exists?(source_tag.id)).to be(false)
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(TagName.exists?(source_tag.tag_name_id)).to be(false)
+        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
+        expect(post.reload.tags).to contain_exactly(existing_tag)
+        expect(existing_tag.reload.name).to eq('foobar')
       end
     end
   end

backend/spec/models/tag_spec.rb

@@ -173,6 +173,47 @@ RSpec.describe Tag, type: :model do
     end
   end
 
+  describe '.find_or_create_by_tag_name!' do
+    it 'creates a tag and name with the requested category after stripping whitespace' do
+      tag = nil
+
+      expect {
+        tag = described_class.find_or_create_by_tag_name!(
+            '  lookup_new  ', category: :character)
+      }.to change(Tag, :count).by(1).and change(TagName, :count).by(1)
+
+      expect(tag.name).to eq('lookup_new')
+      expect(tag.category).to eq('character')
+    end
+
+    it 'reuses the canonical tag for an alias without changing its category' do
+      tag = create(:tag, category: :character)
+      alias_name = TagName.create!(name: 'lookup_alias', canonical: tag.tag_name)
+      found = nil
+
+      expect {
+        found = described_class.find_or_create_by_tag_name!(
+            alias_name.name, category: :general)
+      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
+
+      expect(found).to eq(tag)
+      expect(found.category).to eq('character')
+    end
+
+    it 'creates a tag for an existing canonical name reached through an alias' do
+      canonical = create(:tag_name)
+      alias_name = TagName.create!(name: 'lookup_alias', canonical:)
+      tag = nil
+
+      expect {
+        tag = described_class.find_or_create_by_tag_name!(
+            alias_name.name, category: :general)
+      }.to change(Tag, :count).by(1).and change(TagName, :count).by(0)
+
+      expect(tag.tag_name).to eq(canonical)
+    end
+  end
+
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
@@ -185,18 +226,14 @@ RSpec.describe Tag, type: :model do
     context 'when merging a simple source tag' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'discards the source post_tag, creates an active target post_tag, discards the source tag, and aliases the source tag_name' do
+      it 'deletes the source tag, moves its post link, and keeps its name as an alias' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
 
-        expect(source_pt.discarded_at).to be_present
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(target_link).to be_present
-        expect(active_target).to be_present
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
         expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
@@ -206,38 +243,101 @@ RSpec.describe Tag, type: :model do
       let!(:target_post_tag) { PostTag.create!(post: post_record, tag: target_tag) }
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'discards the source post_tag, keeps one active target post_tag, discards the source tag, and aliases the source tag_name' do
+      it 'deletes the source link and preserves the existing target link' do
+        create(:post_tag_section, post: post_record, tag: source_tag,
+                                  begin_ms: 1000, end_ms: 2000)
+        target_section = create(:post_tag_section, post: post_record,
+                                                   tag: target_tag,
+                                                   begin_ms: 3000, end_ms: nil)
+
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        target_links = PostTag.where(post: post_record, tag: target_tag)
-        active = PostTag.kept.where(post_id: post_record.id, tag_id: target_tag.id)
 
-        expect(source_pt.discarded_at).to be_present
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(target_links).to contain_exactly(target_post_tag)
-        expect(active.count).to eq(1)
+        expect(PostTagSection.where(post: post_record, tag: source_tag)).to be_empty
-        expect(active.first.id).to eq(target_post_tag.id)
+        expect(target_post_tag.reload.sections).to contain_exactly(target_section)
 
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
         expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
 
+    it 'keeps source history and records the new target alias after deleting the source' do
+      user = create_member_user!
+      source_name = source_tag.name
+      source_alias = TagName.create!(name: 'merge_alias', canonical: source_tag_name)
+      TagVersioning.ensure_snapshot!(source_tag, created_by_user: user)
+      original_version = source_tag.tag_versions.first
+
+      described_class.merge_tags!(target_tag, [source_tag], created_by_user: user)
+
+      versions = TagVersion.where(tag_id: source_tag.id).order(:version_no)
+      expect(versions.pluck(:version_no, :event_type))
+          .to eq([[1, 'create'], [2, 'discard']])
+      expect(versions.first).to eq(original_version)
+      expect(versions.last).to have_attributes(
+          name: source_name, aliases: source_alias.name, created_by_user: user)
+      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+
+      target_versions = target_tag.tag_versions.order(:version_no)
+      expect(target_versions.pluck(:event_type)).to eq(['create', 'update'])
+      expect(target_versions.last.aliases.split).to eq([source_name])
+    end
+
+    it 'deletes source relationships while preserving unrelated relationships' do
+      parent = create(:tag)
+      child = create(:tag)
+      nico_tag = create(:tag, :nico)
+      TagImplication.create!(tag: source_tag, parent_tag: parent)
+      TagImplication.create!(tag: child, parent_tag: source_tag)
+      kept_implication = TagImplication.create!(tag: target_tag, parent_tag: parent)
+      NicoTagRelation.create!(tag: source_tag, nico_tag:)
+      kept_relation = NicoTagRelation.create!(tag: target_tag, nico_tag:)
+      TagSimilarity.create!(tag: source_tag, target_tag:, cos: 0.5)
+      TagSimilarity.create!(tag: target_tag, target_tag: source_tag, cos: 0.5)
+      kept_similarity = TagSimilarity.create!(tag: target_tag, target_tag: parent,
+                                               cos: 0.5)
+
+      described_class.merge_tags!(target_tag, [source_tag])
+
+      expect(TagImplication.all).to contain_exactly(kept_implication)
+      expect(NicoTagRelation.all).to contain_exactly(kept_relation)
+      expect(TagSimilarity.all).to contain_exactly(kept_similarity)
+      expect(TagVersion.where(tag_id: source_tag.id).order(:version_no).last.parent_tag_ids)
+          .to eq(parent.id.to_s)
+    end
+
+    it 'preserves material history referencing the deleted source tag' do
+      source_tag.update!(category: :material)
+      target_tag.update!(category: :material)
+      material = Material.create!(tag: source_tag, url: 'https://example.com/material')
+      version = MaterialVersionRecorder.record!(
+          material:, event_type: :create, created_by_user: nil)
+      material.update!(tag: target_tag)
+
+      described_class.merge_tags!(target_tag, [source_tag])
+
+      expect(version.reload).to have_attributes(
+          tag_id: source_tag.id, tag_name: source_tag_name.name, tag_category: 'material')
+      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+      expect(material.reload.tag).to eq(target_tag)
+    end
+
     context 'when source_tags includes the target itself' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'ignores the target in source_tags while still merging the source tag' do
         described_class.merge_tags!(target_tag, [source_tag, target_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
 
         expect(Tag.find(target_tag.id)).to be_present
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_pt.discarded_at).to be_present
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(target_link).to be_present
-        expect(active_target).to be_present
         expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
@@ -260,18 +360,16 @@ RSpec.describe Tag, type: :model do
         )
       end
 
-      it 'still merges, but discards the source tag_name instead of aliasing it' do
+      it 'still merges and keeps the source name as an alias without validating it' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        target_link = PostTag.find_by(post: post_record, tag: target_tag)
-        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
-        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name.id)
 
-        expect(source_pt.discarded_at).to be_present
+        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(target_link).to be_present
-        expect(active_target).to be_present
 
-        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -288,36 +386,72 @@ RSpec.describe Tag, type: :model do
             message: 'init')
       end
 
-      it 'rolls back the transaction' do
+      it 'rolls back earlier deletions, links, and history when a later source has a wiki' do
+        earlier_source = create(:tag)
+        earlier_name = earlier_source.tag_name
+        source_section = create(:post_tag_section, post: post_record,
+                                                   tag: source_tag,
+                                                   begin_ms: 1000, end_ms: 2000)
+
         expect {
-          described_class.merge_tags!(target_tag, [source_tag])
+          described_class.merge_tags!(target_tag, [earlier_source, source_tag])
         }.to raise_error(ActiveRecord::RecordInvalid)
 
-        expect(Tag.with_discarded.find(source_tag.id)).not_to be_discarded
+        expect(Tag.unscoped.exists?(earlier_source.id)).to be(true)
-        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
+        expect(earlier_name.reload.canonical_id).to be_nil
-        expect(PostTag.kept.find(source_post_tag.id).tag_id).to eq(source_tag.id)
+        expect(TagVersion.where(tag_id: [earlier_source.id, source_tag.id, target_tag.id]))
-        expect(PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)).to be_nil
+            .to be_empty
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(true)
+        expect(TagName.unscoped.exists?(source_tag_name.id)).to be(true)
+        expect(source_post_tag.reload.tag_id).to eq(source_tag.id)
+        expect(source_post_tag.sections).to contain_exactly(source_section)
+        expect(PostTag.find_by(post: post_record, tag: target_tag)).to be_nil
+        expect(source_tag.reload.post_count).to eq(1)
         expect(source_tag_name.reload.canonical_id).to be_nil
         expect(target_tag.reload.post_count).to eq(0)
       end
     end
 
     context 'when merging a nico source tag' do
-      let!(:target_tag) { create(:tag, category: :nico, name: 'nico:foo') }
+      let!(:target_tag) do
-      let!(:source_tag) { create(:tag, category: :nico, name: 'nico:bar') }
+        create(:tag, category: :nico, tag_name: create(:tag_name, name: 'nico:foo'))
+      end
+      let!(:source_tag) do
+        create(:tag, category: :nico, tag_name: create(:tag_name, name: 'nico:bar'))
+      end
       let!(:source_tag_name_id) { source_tag.tag_name_id }
 
-      it 'discards the source tag_name instead of aliasing it' do
+      it 'deletes the source tag and name instead of keeping an alias' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        discarded_source_tag = Tag.with_discarded.find(source_tag.id)
+        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name_id)
+        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
-
-        expect(discarded_source_tag).to be_discarded
-        expect(discarded_source_tag_name).to be_discarded
-        expect(discarded_source_tag_name.canonical_id).to be_nil
         expect(target_tag.reload.post_count).to eq(0)
       end
+
+      it 'keeps nico history while deleting source links and allows recreating the name' do
+        linked_tag = create(:tag)
+        NicoTagRelation.create!(nico_tag: source_tag, tag: linked_tag)
+        kept_relation = NicoTagRelation.create!(nico_tag: target_tag, tag: linked_tag)
+        user = create_member_user!
+        source_name = source_tag.name
+
+        described_class.merge_tags!(target_tag, [source_tag], created_by_user: user)
+
+        expect(NicoTagRelation.all).to contain_exactly(kept_relation)
+        versions = NicoTagVersion.where(tag_id: source_tag.id).order(:version_no)
+        expect(versions.pluck(:version_no, :event_type))
+            .to eq([[1, 'create'], [2, 'discard']])
+        expect(versions.last).to have_attributes(
+            name: source_name, linked_tags: linked_tag.name, created_by_user: user)
+
+        recreated = described_class.find_or_create_by_tag_name!(source_name, category: :nico)
+
+        expect(recreated.id).not_to eq(source_tag.id)
+        expect(recreated.tag_name_id).not_to eq(source_tag_name_id)
+        expect(recreated.nico_tag_versions).to be_empty
+        expect(versions.reload.size).to eq(2)
+      end
     end
 
     def snapshot_tags(post)
@@ -333,6 +467,7 @@ RSpec.describe Tag, type: :model do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
+        tags_json: post.snapshot_tags_json,
         parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
@@ -364,12 +499,15 @@ RSpec.describe Tag, type: :model do
         expect(latest.event_type).to eq('update')
         expect(latest.created_by_user).to be_nil
         expect(latest.tags).to eq(snapshot_tags(post_record.reload))
+        expect(latest.tags_json.map { |item| item.fetch('id') }).to eq([target_tag.id])
+        expect(affected_versions.first.tags_json.map { |item| item.fetch('id') })
+            .to eq([source_tag.id])
 
         expect(unaffected_post.reload.post_versions.count).to eq(1)
       end
     end
 
-    context 'when the source tag has no active post_tags' do
+    context 'when the source tag has no post_tags' do
       let!(:another_post) do
         Post.create!(url: 'https://example.com/posts/3', title: 'another post')
       end

backend/spec/requests/post_imports_spec.rb

@@ -1,184 +0,0 @@
-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

@@ -9,11 +9,11 @@ RSpec.describe 'Posts API', type: :request do
   # resized_thumbnail! が MiniMagick 依存でコケやすいので request spec ではスタブしとくのが無難。
   before do
     allow_any_instance_of(Post).to receive(:resized_thumbnail!).and_return(true)
-    allow(Post).to receive(:resized_thumbnail_attachment).and_return(
+    allow(Post).to receive(:resized_thumbnail_attachment) do
-      io: StringIO.new('dummy'),
+      { io: StringIO.new('dummy'),
-      filename: 'resized_thumbnail.jpg',
+        filename: 'resized_thumbnail.jpg',
-      content_type: 'image/jpeg'
+        content_type: 'image/jpeg' }
-    )
+    end
   end
 
   def create_nico_tag!(name)
@@ -21,8 +21,7 @@ RSpec.describe 'Posts API', type: :request do
   end
 
   def dummy_upload
-    # 中身は何でもいい（加工処理はスタブしてる）
+    real_thumbnail_upload
-    Rack::Test::UploadedFile.new(StringIO.new('dummy'), 'image/jpeg', original_filename: 'dummy.jpg')
   end
 
   def real_thumbnail_upload
@@ -56,6 +55,7 @@ RSpec.describe 'Posts API', type: :request do
             thumbnail_base: post.thumbnail_base,
             video_ms: post.video_ms,
             tags: post.snapshot_tag_names.join(' '),
+            tags_json: post.snapshot_tags_json,
             parent_post_ids: post.snapshot_parent_post_ids.join(' '),
             original_created_from: post.original_created_from,
             original_created_before: post.original_created_before,
@@ -102,34 +102,34 @@ RSpec.describe 'Posts API', type: :request do
     end
   end
 
-  describe "GET /posts" do
+  describe 'GET /posts' do
     let!(:user) { create_member_user! }
 
-    let!(:tag_name) { TagName.create!(name: "spec_tag") }
+    let!(:tag_name) { TagName.create!(name: 'spec_tag') }
     let!(:tag) { Tag.create!(tag_name:, category: :general) }
     let!(:tag_name2) { TagName.create!(name: 'unko') }
     let!(:tag2) { Tag.create!(tag_name: tag_name2, category: :deerjikist) }
     let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     let!(:hit_post) do
-      Post.create!(uploaded_user: user, title: "hello spec world",
+      Post.create!(uploaded_user: user, title: 'hello spec world',
                    url: 'https://example.com/spec2').tap do |p|
         PostTag.create!(post: p, tag:)
       end
     end
 
     let!(:miss_post) do
-      Post.create!(uploaded_user: user, title: "unrelated title",
+      Post.create!(uploaded_user: user, title: 'unrelated title',
                    url: 'https://example.com/spec3').tap do |p|
         PostTag.create!(post: p, tag: tag2)
       end
     end
 
-    it "returns posts with tag name in JSON" do
+    it 'returns posts with tag name in JSON' do
-      get "/posts"
+      get '/posts'
 
       expect(response).to have_http_status(:ok)
-      posts = json.fetch("posts")
+      posts = json.fetch('posts')
 
       # 全postの全tagが name を含むこと
       expect(posts).not_to be_empty
@@ -142,18 +142,21 @@ RSpec.describe 'Posts API', type: :request do
       expect(json['count']).to be_an(Integer)
 
       # spec_tag を含む投稿が存在すること
-      all_tag_names = posts.flat_map { |p| p["tags"].map { |t| t["name"] } }
+      all_tag_names = posts.flat_map { |p| p['tags'].map { |t| t['name'] } }
-      expect(all_tag_names).to include("spec_tag")
+      expect(all_tag_names).to include('spec_tag')
     end
 
     it 'keeps children and sections keys in non-detail tag responses' do
       PostTagSection.create!(post: hit_post, tag:, begin_ms: 1_000, end_ms: nil)
+      deprecated_tag = create(:tag, deprecated_at: Time.current)
+      create(:post_tag, post: hit_post, tag: deprecated_tag)
 
       get '/posts'
 
       expect(response).to have_http_status(:ok)
 
       hit_json = json.fetch('posts').find { |post| post['id'] == hit_post.id }
+      expect(hit_json.fetch('tags').map { |item| item.fetch('id') }).to eq([tag.id])
       tag_json = hit_json.fetch('tags').find { |item| item['name'] == 'spec_tag' }
 
       expect(tag_json.fetch('children')).to eq([])
@@ -162,9 +165,29 @@ RSpec.describe 'Posts API', type: :request do
       ])
     end
 
-    context "when q is provided" do
+    it 'preloads tag details and sections as the number of posts grows' do
-      it "filters posts by q (hit case)" do
+      5.times do
-        get "/posts", params: { tags: "spec_tag" }
+        link = create(:post_tag, post: create(:post, uploaded_user: user))
+        create(:post_tag_section, post: link.post, tag: link.tag,
+                                  begin_ms: 1000, end_ms: 2000)
+      end
+      get '/posts', params: { limit: 1 }
+
+      one_post_queries = count_sql_queries do
+        get '/posts', params: { limit: 1 }
+      end
+      many_post_queries = count_sql_queries do
+        get '/posts', params: { limit: 20 }
+      end
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('posts').size).to eq(8)
+      expect(many_post_queries).to be <= one_post_queries
+    end
+
+    context 'when q is provided' do
+      it 'filters posts by q (hit case)' do
+        get '/posts', params: { tags: 'spec_tag' }
 
         expect(response).to have_http_status(:ok)
         posts = json.fetch('posts')
@@ -182,8 +205,8 @@ RSpec.describe 'Posts API', type: :request do
         end
       end
 
-      it "filters posts by q (hit case by alias)" do
+      it 'filters posts by q (hit case by alias)' do
-        get "/posts", params: { tags: "manko" }
+        get '/posts', params: { tags: 'manko' }
 
         expect(response).to have_http_status(:ok)
         posts = json.fetch('posts')
@@ -201,11 +224,11 @@ RSpec.describe 'Posts API', type: :request do
         end
       end
 
-      it "returns empty posts when nothing matches" do
+      it 'returns empty posts when nothing matches' do
-        get "/posts", params: { tags: "no_such_keyword_12345" }
+        get '/posts', params: { tags: 'no_such_keyword_12345' }
 
         expect(response).to have_http_status(:ok)
-        expect(json.fetch("posts")).to eq([])
+        expect(json.fetch('posts')).to eq([])
         expect(json.fetch('count')).to eq(0)
       end
     end
@@ -460,6 +483,71 @@ RSpec.describe 'Posts API', type: :request do
       end
     end
 
+    context 'when update times include version history' do
+      let(:t0) { Time.zone.parse('2020-01-01 12:00:00') }
+      let(:t1) { t0 + 1.day }
+      let(:t2) { t0 + 2.days }
+      let(:t3) { t0 + 3.days }
+      let!(:history_post) do
+        create(:post, url: 'https://example.com/version-time/history',
+                      created_at: t0, updated_at: t0)
+      end
+      let!(:plain_post) do
+        create(:post, url: 'https://example.com/version-time/plain',
+                      created_at: t1, updated_at: t1)
+      end
+      let!(:newer_post) do
+        create(:post, url: 'https://example.com/version-time/newer',
+                      created_at: t0, updated_at: t3)
+      end
+
+      before do
+        link = create(:post_tag, post: history_post, tag:)
+        travel_to(t0) do
+          PostVersionRecorder.record!(post: history_post,
+                                      event_type: :create, created_by_user: nil)
+          PostVersionRecorder.record!(post: newer_post,
+                                      event_type: :create, created_by_user: nil)
+        end
+        travel_to(t2) do
+          link.destroy!
+          PostVersionRecorder.record!(post: history_post,
+                                      event_type: :update, created_by_user: nil)
+        end
+        create(:post_tag, post: plain_post, tag:, created_at: t3)
+      end
+
+      ['asc', 'desc'].each do |direction|
+        it "sorts by the later of post update and latest version time (#{ direction })" do
+          get '/posts', params: { url: '/version-time/', order: "updated_at:#{ direction }" }
+
+          expect(response).to have_http_status(:ok)
+          expected_ids = [plain_post.id, history_post.id, newer_post.id]
+          expected_ids.reverse! if direction == 'desc'
+          expect(json.fetch('posts').map { |item| item.fetch('id') }).to eq(expected_ids)
+          expect(json.fetch('count')).to eq(3)
+
+          times = json.fetch('posts').to_h do |item|
+            [item.fetch('id'), Time.zone.parse(item.fetch('updated_at'))]
+          end
+          expect(times).to eq({ plain_post.id => t1,
+                               history_post.id => t2,
+                               newer_post.id => t3 })
+          expect(history_post.reload.updated_at).to eq(t0)
+        end
+      end
+
+      it 'filters inclusively by the latest version time after a tag is deleted' do
+        get '/posts', params: { url: '/version-time/',
+                               updated_from: t2.iso8601,
+                               updated_to: t2.iso8601 }
+
+        expect(response).to have_http_status(:ok)
+        expect(json.fetch('posts').map { |item| item.fetch('id') }).to eq([history_post.id])
+        expect(json.fetch('count')).to eq(1)
+      end
+    end
+
     context 'when original_created_from/original_created_to are provided' do
       # 注意: controller の現状ロジックに合わせてる
       # original_created_from は `original_created_before > ?`
@@ -693,6 +781,73 @@ RSpec.describe 'Posts API', type: :request do
     end
   end
 
+  describe 'GET /posts/metadata' do
+    let(:member) { create(:user, :member) }
+
+    it 'returns compact existing post data without fetching external metadata' do
+      sign_in_as(member)
+      existing = create(
+          :post,
+          title: 'existing post',
+          url: 'https://example.com/existing')
+      existing.thumbnail.attach(
+          io: StringIO.new('thumbnail'),
+          filename: 'thumbnail.jpg',
+          content_type: 'image/jpeg')
+      expect(PostMetadataFetcher).not_to receive(:fetch)
+
+      get '/posts/metadata', params: { url: 'https://example.com/existing' }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'url' => existing.url,
+          'existing_post_id' => existing.id,
+          'field_warnings' => { })
+      expect(json.fetch('existing_post')).to include(
+          'id' => existing.id,
+          'title' => existing.title,
+          'url' => existing.url,
+          'thumbnail_base' => existing.thumbnail_base)
+      expect(json.dig('existing_post', 'thumbnail'))
+          .to include('/rails/active_storage/blobs/proxy/')
+    end
+
+    it 'returns fetched metadata and structured display tags' do
+      sign_in_as(member)
+      allow(Preview::UrlSafety).to receive(:validate)
+      allow(PostMetadataFetcher).to receive(:fetch).and_return(
+          title: 'fetched title',
+          thumbnail_base: 'https://example.com/thumbnail.jpg',
+          tags: 'character:虹夏',
+          display_tags: [{ name: '虹夏', category: 'character' }],
+          original_created_from: nil,
+          original_created_before: nil,
+          duration: '1:00',
+          video_ms: 60_000)
+
+      get '/posts/metadata', params: { url: 'https://example.com/new' }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'url' => 'https://example.com/new',
+          'title' => 'fetched title',
+          'duration' => '1:00',
+          'video_ms' => 60_000,
+          'field_warnings' => { })
+      expect(json.fetch('display_tags')).to eq(
+          [{ 'name' => '虹夏', 'category' => 'character' }])
+    end
+
+    it 'returns URL validation errors as 422' do
+      sign_in_as(member)
+
+      get '/posts/metadata', params: { url: 'file:///etc/passwd' }
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to have_key('url')
+    end
+  end
+
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
     let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
@@ -712,6 +867,46 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:forbidden)
     end
 
+    it 'dry-runs without persisting posts or new tags' do
+      sign_in_as(member)
+      counts = [Post.count, Tag.count, TagName.count]
+
+      post '/posts?dry=1', params: post_write_params(
+          title: 'dry-run post',
+          url: 'https://example.com/dry-run',
+          tags: 'character:new_dry_run_tag')
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'url' => 'https://example.com/dry-run',
+          'tags' => 'new_dry_run_tag',
+          'existing_post_id' => nil)
+      expect(json.fetch('display_tags')).to eq(
+          [{ 'name' => 'new_dry_run_tag',
+             'category' => 'character',
+             'section_literals' => [] }])
+      expect([Post.count, Tag.count, TagName.count]).to eq(counts)
+    end
+
+    it 'dry-runs an existing URL without validating its upload' do
+      sign_in_as(member)
+      existing = create(:post, url: 'https://example.com/dry-existing')
+      invalid_upload = Rack::Test::UploadedFile.new(
+          StringIO.new('<svg></svg>'),
+          'image/png',
+          original_filename: 'thumbnail.png')
+
+      post '/posts?dry=1', params: post_write_params(
+          title: '',
+          url: existing.url,
+          tags: '',
+          thumbnail: invalid_upload)
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('existing_post_id' => existing.id)
+      expect(json.fetch('field_warnings')).not_to have_key('thumbnail_base')
+    end
+
     it '201 and creates post + tags when member' do
       sign_in_as(member)
 
@@ -769,7 +964,8 @@ RSpec.describe 'Posts API', type: :request do
       )
 
       expect(response).to have_http_status(:created)
-      expect(open_transactions).to eq([baseline_open_transactions])
+      expect(open_transactions).to eq(
+          [baseline_open_transactions, baseline_open_transactions])
     end
 
     it 'returns 422 and does not create a post when thumbnail resize fails' do
@@ -827,7 +1023,7 @@ RSpec.describe 'Posts API', type: :request do
 
       expect(response).to have_http_status(:unprocessable_entity)
       expect(json.fetch('errors')).to include(
-        'tags' => ['廃止済みタグは付与できません．']
+        'tags' => ['廃止済みタグがあります: deprecated_direct_tag']
       )
     end
 
@@ -1054,11 +1250,9 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
-    context "when nico tag already exists in tags" do
+    context 'when nico tag already exists in tags' do
       before do
-        Tag.find_undiscard_or_create_by!(
+        Tag.find_or_create_by_tag_name!('nico:nico_tag', category: :nico)
-            tag_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
-            category: :nico)
       end
 
       it 'returns 422 with tag field errors' do
@@ -1251,6 +1445,47 @@ RSpec.describe 'Posts API', type: :request do
     end
   end
 
+  describe 'POST /posts/bulk' do
+    let(:member) { create(:user, :member) }
+
+    it 'parses the manifest and indexed thumbnail parts' do
+      sign_in_as(member)
+      manifest = [{ 'url' => 'https://example.com/bulk',
+                    'title' => 'bulk post',
+                    'tags' => 'spec_tag',
+                    'parent_post_ids' => '' }]
+      creator = instance_double(
+          PostBulkCreator,
+          run: { results: [{ status: 'created', post: { id: 123 } }] })
+      allow(PostBulkCreator).to receive(:new).and_return(creator)
+
+      post '/posts/bulk', params: {
+          posts: JSON.generate(manifest),
+          thumbnails: { '0' => real_thumbnail_upload } }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('results')).to eq(
+          [{ 'status' => 'created', 'post' => { 'id' => 123 } }])
+      expect(PostBulkCreator).to have_received(:new) do |arguments|
+        expect(arguments[:actor]).to eq(member)
+        expect(arguments[:posts]).to eq(manifest)
+        expect(arguments[:thumbnails].keys).to eq([0])
+        expect(arguments[:host]).to eq('http://www.example.com')
+      end
+    end
+
+    it 'rejects malformed manifests as a request-level error' do
+      sign_in_as(member)
+
+      post '/posts/bulk', params: {
+          posts: '{',
+          thumbnails: { '0' => real_thumbnail_upload } }
+
+      expect(response).to have_http_status(:bad_request)
+      expect(json.fetch('message')).to eq('posts manifest の JSON が不正です．')
+    end
+  end
+
   describe 'PUT /posts/:id' do
     let(:member) { create(:user, :member) }
 
@@ -1270,9 +1505,11 @@ RSpec.describe 'Posts API', type: :request do
 
     it '200 and updates title + resync tags when member' do
       sign_in_as(member)
+      create(:post_tag_section, post: post_record, tag:,
+                                begin_ms: 1000, end_ms: 2000)
 
       tn2 = TagName.create!(name: 'spec_tag_2')
-      Tag.create!(tag_name: tn2, category: :general)
+      replacement_tag = Tag.create!(tag_name: tn2, category: :general)
 
       put "/posts/#{post_record.id}", params: post_update_params(
           post_record,
@@ -1285,6 +1522,38 @@ RSpec.describe 'Posts API', type: :request do
 
       names = json['tags'].map { |n| n['name'] }
       expect(names).to include('spec_tag_2')
+      expect(names).not_to include('spec_tag')
+      expect(PostTag.exists?(post: post_record, tag:)).to be(false)
+      expect(PostTagSection.exists?(post: post_record, tag:)).to be(false)
+      expect(tag.reload.post_count).to eq(0)
+      expect(replacement_tag.reload.post_count).to eq(1)
+
+      versions = post_record.post_versions.order(:version_no)
+      expect(versions.first.tags_json).to include(
+          a_hash_including('id' => tag.id,
+                           'sections' => [{ 'begin_ms' => 1000, 'end_ms' => 2000 }]))
+      expect(versions.last.tags_json.map { |item| item.fetch('id') })
+          .not_to include(tag.id)
+    end
+
+    it 'can add a removed tag again and records both changes' do
+      sign_in_as(member)
+
+      put "/posts/#{ post_record.id }", params: post_update_params(post_record, tags: '')
+      expect(response).to have_http_status(:ok)
+      expect(PostTag.exists?(post: post_record, tag:)).to be(false)
+
+      put "/posts/#{ post_record.id }", params: post_update_params(
+          post_record, tags: 'spec_tag')
+
+      expect(response).to have_http_status(:ok)
+      expect(PostTag.where(post: post_record, tag:).count).to eq(1)
+      expect(PostTag.find_by!(post: post_record, tag:).created_user).to eq(member)
+      expect(tag.reload.post_count).to eq(1)
+      snapshots = post_record.post_versions.order(:version_no).map do |version|
+        version.tags_json.map { |item| item.fetch('id') }
+      end
+      expect(snapshots.map { |ids| ids.include?(tag.id) }).to eq([true, false, true])
     end
 
     it 'rejects a deprecated tag specified directly' do
@@ -1307,11 +1576,9 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
-    context "when nico tag already exists in tags" do
+    context 'when nico tag already exists in tags' do
       before do
-        Tag.find_undiscard_or_create_by!(
+        Tag.find_or_create_by_tag_name!('nico:nico_tag', category: :nico)
-            tag_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
-            category: :nico)
       end
 
       it 'returns 422 with tag field errors' do
@@ -1564,7 +1831,7 @@ RSpec.describe 'Posts API', type: :request do
         expect(post_record.reload.title).to eq('updated by other user')
       end
 
-      it 'returns 409 with mergeable true when stale tag changes do not conflict but merge is not requested' do
+      it 'returns mergeable 409 for stale non-conflicting tag changes without merge' do
         sign_in_as(member)
 
         base_version = create_post_version_for!(post_record.reload)
@@ -1730,123 +1997,29 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:not_found)
     end
 
-    it '200 and returns viewed boolean' do
+    it 'returns viewed state and current tags with their sections' do
+      create(:post_tag_section, post: post_record, tag:,
+                                begin_ms: 1000, end_ms: nil)
+      deprecated_tag = create(:tag, deprecated_at: Time.current)
+      create(:post_tag, post: post_record, tag: deprecated_tag)
+
       get '/posts/random'
+
       expect(response).to have_http_status(:ok)
       expect(json).to have_key('viewed')
       expect([true, false]).to include(json['viewed'])
+      expect(json.fetch('tags')).to contain_exactly(
+          a_hash_including('id' => tag.id,
+                           'children' => [],
+                           'sections' => [{ 'begin_ms' => 1000, 'end_ms' => nil }]))
     end
   end
 
   describe 'GET /posts/changes' do
-    let(:member) { create(:user, :member) }
+    it 'returns 404 for the retired history endpoint' do
+      get '/posts/changes'
 
-    it 'returns add/remove events (history) for a post' do
+      expect(response).to have_http_status(:not_found)
-      # add
-      tn2 = TagName.create!(name: 'spec_tag2')
-      tag2 = Tag.create!(tag_name: tn2, category: :general)
-      pt = PostTag.create!(post: post_record, tag: tag2, created_user: member)
-
-      # remove (discard)
-      pt.discard_by!(member)
-
-      get '/posts/changes', params: { id: post_record.id }
-
-      expect(response).to have_http_status(:ok)
-      expect(json).to include('changes', 'count')
-      expect(json['changes']).to be_an(Array)
-      expect(json['count']).to be >= 2
-
-      types = json['changes'].map { |e| e['change_type'] }.uniq
-      expect(types).to include('add')
-      expect(types).to include('remove')
-    end
-
-    it 'filters history by tag' do
-      tn2 = TagName.create!(name: 'history_tag_hit')
-      tag2 = Tag.create!(tag_name: tn2, category: :general)
-
-      tn3 = TagName.create!(name: 'history_tag_miss')
-      tag3 = Tag.create!(tag_name: tn3, category: :general)
-
-      other_post = Post.create!(
-        title: 'other post',
-        url: 'https://example.com/history-other'
-      )
-
-      # hit: add
-      PostTag.create!(post: post_record, tag: tag2, created_user: member)
-
-      # hit: add + remove
-      pt2 = PostTag.create!(post: other_post, tag: tag2, created_user: member)
-      pt2.discard_by!(member)
-
-      # miss: add + remove
-      pt3 = PostTag.create!(post: post_record, tag: tag3, created_user: member)
-      pt3.discard_by!(member)
-
-      get '/posts/changes', params: { tag: tag2.id }
-
-      expect(response).to have_http_status(:ok)
-      expect(json).to include('changes', 'count')
-      expect(json['count']).to eq(3)
-
-      changes = json.fetch('changes')
-
-      expect(changes.map { |e| e.dig('tag', 'id') }.uniq).to eq([tag2.id])
-      expect(changes.map { |e| e['change_type'] }).to match_array(%w[add add remove])
-      expect(changes.map { |e| e.dig('post', 'id') }).to match_array([
-        post_record.id,
-        other_post.id,
-        other_post.id
-      ])
-    end
-
-    it 'filters history by post and tag together' do
-      tn2 = TagName.create!(name: 'history_tag_combo_hit')
-      tag2 = Tag.create!(tag_name: tn2, category: :general)
-
-      tn3 = TagName.create!(name: 'history_tag_combo_miss')
-      tag3 = Tag.create!(tag_name: tn3, category: :general)
-
-      other_post = Post.create!(
-        title: 'other combo post',
-        url: 'https://example.com/history-combo-other'
-      )
-
-      # hit
-      PostTag.create!(post: post_record, tag: tag2, created_user: member)
-
-      # miss by post
-      pt2 = PostTag.create!(post: other_post, tag: tag2, created_user: member)
-      pt2.discard_by!(member)
-
-      # miss by tag
-      pt3 = PostTag.create!(post: post_record, tag: tag3, created_user: member)
-      pt3.discard_by!(member)
-
-      get '/posts/changes', params: { id: post_record.id, tag: tag2.id }
-
-      expect(response).to have_http_status(:ok)
-      expect(json).to include('changes', 'count')
-      expect(json['count']).to eq(1)
-
-      changes = json.fetch('changes')
-      expect(changes.size).to eq(1)
-      expect(changes[0]['change_type']).to eq('add')
-      expect(changes[0].dig('post', 'id')).to eq(post_record.id)
-      expect(changes[0].dig('tag', 'id')).to eq(tag2.id)
-    end
-
-    it 'returns empty history when tag does not match' do
-      tn2 = TagName.create!(name: 'history_tag_no_hit')
-      tag2 = Tag.create!(tag_name: tn2, category: :general)
-
-      get '/posts/changes', params: { tag: tag2.id }
-
-      expect(response).to have_http_status(:ok)
-      expect(json.fetch('changes')).to eq([])
-      expect(json.fetch('count')).to eq(0)
     end
   end
 
@@ -1876,6 +2049,7 @@ RSpec.describe 'Posts API', type: :request do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
+        tags_json: post.snapshot_tags_json,
         parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
@@ -1897,7 +2071,7 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     let!(:v2) do
-      post_record.post_tags.kept.find_by!(tag: tag).discard_by!(member)
+      post_record.post_tags.find_by!(tag: tag).destroy!
       PostTag.create!(post: post_record, tag: tag2, created_user: member)
       post_record.update!(
         title: 'updated spec post',
@@ -2271,9 +2445,9 @@ RSpec.describe 'Posts API', type: :request do
 
       expect(response).to have_http_status(:created)
       expect(Time.iso8601(json.fetch('original_created_from')))
-          .to eq(Time.iso8601('2020-01-01T00:00Z'))
+          .to eq(Time.utc(2020, 1, 1, 0, 0))
       expect(Time.iso8601(json.fetch('original_created_before')))
-          .to eq(Time.iso8601('2020-01-01T00:01Z'))
+          .to eq(Time.utc(2020, 1, 1, 0, 1))
     end
 
     it 'rejects unparseable original created timestamps on PUT /posts/:id' do

backend/spec/requests/tags_deerjikists_spec.rb

@@ -226,6 +226,14 @@ RSpec.describe 'Tags deerjikists API', type: :request do
               [platform2, code2],
             )
         end
+
+        it 'locks the tag before replacing the complete list' do
+          expect_any_instance_of(Tag).to receive(:lock!).and_call_original
+
+          do_request
+
+          expect(response).to have_http_status(:ok)
+        end
       end
 
       context 'when tag already has deerjikists' do
@@ -299,6 +307,81 @@ RSpec.describe 'Tags deerjikists API', type: :request do
         end
       end
 
+      context 'when platform is outside the enum' do
+        let(:payload) do
+          [
+            { platform: 'invalid', code: code1 },
+          ]
+        end
+
+        it 'returns 422 with an indexed platform error without changing the list' do
+          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+
+          expect {
+            do_request
+          }.not_to change { Deerjikist.where(tag: tag).map { |d| [d.platform, d.code] } }
+
+          expect(response).to have_http_status(:unprocessable_entity)
+          expect(json.fetch('errors')).to include(
+            'deerjikists.0.platform' => [be_present],
+          )
+        end
+      end
+
+      context 'when a requested deerjikist belongs to another tag' do
+        let!(:other_tag) { create(:tag, category: :deerjikist) }
+        let!(:owned_deerjikist) do
+          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+        end
+        let!(:conflicting_deerjikist) do
+          Deerjikist.create!(platform: platform2, code: code2, tag: other_tag)
+        end
+        let(:payload) do
+          [
+            { platform: 'nico', code: 'new-code' },
+            { platform: platform2, code: code2 },
+          ]
+        end
+
+        before do
+          other_tag.tag_name.update!(name: 'existing-deerjikist')
+        end
+
+        it 'returns an indexed 422 error and rolls back the complete replacement' do
+          expect {
+            do_request
+          }.not_to change { Deerjikist.order(:platform, :code).pluck(:platform, :code, :tag_id) }
+
+          expect(response).to have_http_status(:unprocessable_entity)
+          expect(json.fetch('errors')).to include(
+            'deerjikists.1.code' => [include('existing-deerjikist')],
+          )
+          expect(owned_deerjikist.reload.tag_id).to eq(tag.id)
+          expect(conflicting_deerjikist.reload.tag_id).to eq(other_tag.id)
+        end
+      end
+
+      context 'when a requested deerjikist already belongs to the same tag' do
+        let!(:existing_deerjikist) do
+          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+        end
+        let(:payload) do
+          [
+            { platform: platform1, code: code1 },
+          ]
+        end
+
+        it 'keeps the existing row' do
+          expect {
+            do_request
+          }.not_to change { existing_deerjikist.reload.created_at }
+
+          expect(response).to have_http_status(:ok)
+          expect(Deerjikist.where(tag: tag).pluck(:platform, :code))
+            .to eq([[platform1, code1]])
+        end
+      end
+
       context 'when youtube code is handle' do
         let(:channel_id) { 'UCabcdefghijklmnopqrstuv' }
         let(:payload) do

backend/spec/requests/wiki_body_search_pending_spec.rb

@@ -1,27 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe 'Wiki body search', type: :request do
-  let!(:user) { create_member_user! }
-
-  it 'searches wiki pages by body text' do
-    pending '#336 で対応予定'
-
-    Wiki::Commit.create_content!(
-        tag_name: TagName.create!(name: 'wiki_body_search_hit'),
-        body: 'unique body keyword for wiki search',
-        created_by_user: user,
-        message: 'init')
-
-    Wiki::Commit.create_content!(
-        tag_name: TagName.create!(name: 'wiki_body_search_miss'),
-        body: 'ordinary body',
-        created_by_user: user,
-        message: 'init')
-
-    get '/wiki/search', params: { body: 'unique body keyword' }
-
-    expect(response).to have_http_status(:ok)
-    expect(json.map { |page| page['title'] }).to include('wiki_body_search_hit')
-    expect(json.map { |page| page['title'] }).not_to include('wiki_body_search_miss')
-  end
-end

backend/spec/requests/wiki_restore_pending_spec.rb

@@ -1,37 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe 'Wiki restore', type: :request do
-  let!(:user) { create_member_user! }
-
-  def auth_headers user
-    { 'X-Transfer-Code' => user.inheritance_code }
-  end
-
-  it 'restores wiki page to previous version' do
-    pending '#337 で対応予定'
-
-    page =
-        Wiki::Commit.create_content!(
-            tag_name: TagName.create!(name: 'wiki_restore_page'),
-            body: 'v1',
-            created_by_user: user,
-            message: 'init')
-
-    v1 = page.wiki_versions.order(:version_no).last
-
-    Wiki::Commit.content!(
-        page:,
-        body: 'v2',
-        created_user: user,
-        message: 'edit',
-        base_revision_id: page.current_revision.id)
-
-    post "/wiki/#{ page.id }/restore",
-         params: { version_no: v1.version_no },
-         headers: auth_headers(user)
-
-    expect(response).to have_http_status(:ok)
-    expect(page.reload.body).to eq('v1')
-    expect(page.wiki_versions.order(:version_no).last.event_type).to eq('restore')
-  end
-end

backend/spec/services/post_bulk_creator_spec.rb

@@ -0,0 +1,59 @@
+require 'rails_helper'
+
+RSpec.describe PostBulkCreator do
+  it 'limits workers to two and keeps failures in their request slots' do
+    actor = instance_double(User, id: 123)
+    allow(User).to receive(:find).with(123) {
+      instance_double(User, id: 123)
+    }
+    mutex = Mutex.new
+    active = 0
+    maximum_active = 0
+
+    allow(PostCreatePreflight).to receive(:new) do |attributes:, **|
+      preflight = instance_double(PostCreatePreflight)
+      allow(preflight).to receive(:run) do
+        mutex.synchronize do
+          active += 1
+          maximum_active = [maximum_active, active].max
+        end
+        sleep 0.02
+        mutex.synchronize { active -= 1 }
+        attributes.symbolize_keys.merge(
+            existing_post_id: nil,
+            field_warnings: { },
+            base_warnings: [])
+      end
+      preflight
+    end
+    allow(PostCreator).to receive(:new) do |attributes:, **|
+      creator = instance_double(PostCreator)
+      if attributes[:title] == 'broken'
+        allow(creator).to receive(:create!).and_raise(StandardError, 'broken')
+      else
+        post = instance_double(Post, id: attributes[:title].delete_prefix('post ').to_i)
+        allow(creator).to receive(:create!).and_return(post)
+      end
+      creator
+    end
+    posts = [
+        { 'title' => 'post 1', 'url' => 'https://example.com/1' },
+        { 'title' => 'broken', 'url' => 'https://example.com/2' },
+        { 'title' => 'post 3', 'url' => 'https://example.com/3' },
+        { 'title' => 'post 4', 'url' => 'https://example.com/4' }]
+
+    results = described_class.new(
+        actor:,
+        posts:,
+        thumbnails: { }).run.fetch(:results)
+
+    expect(maximum_active).to eq(2)
+    expect(results.length).to eq(posts.length)
+    expect(results.map { _1[:status] }).to eq(
+        ['created', 'failed', 'created', 'created'])
+    expect(results[0].dig(:post, :id)).to eq(1)
+    expect(results[1]).to include(status: 'failed', recoverable: false)
+    expect(results[2].dig(:post, :id)).to eq(3)
+    expect(results[3].dig(:post, :id)).to eq(4)
+  end
+end

backend/spec/services/post_create_plan_spec.rb

@@ -0,0 +1,82 @@
+require 'rails_helper'
+
+RSpec.describe PostCreatePlan do
+  def create_tag! name, category
+    Tag.create!(name:, category:)
+  end
+
+  before do
+    create_tag!('タグ希望', :meta)
+    create_tag!('ニジラー情報不詳', :meta)
+  end
+
+  it 'plans direct and existing default tags without persisting records' do
+    counts = [TagName.count, Tag.count]
+
+    plan = described_class.new(
+        attributes: {
+            url: 'https://example.com/post',
+            title: 'title',
+            tags: 'character:new_character',
+            parent_post_ids: '' }).build!
+
+    expect(plan[:tags]).to eq('new_character')
+    expect(plan[:direct_tag_specs]).to eq(
+        [{ name: 'new_character', category: :character }])
+    expect(plan[:default_tag_specs]).to include(
+        { name: 'タグ希望', category: :meta },
+        { name: 'ニジラー情報不詳', category: :meta })
+    expect([TagName.count, Tag.count]).to eq(counts)
+  end
+
+  it 'resolves aliases and keeps tag sections separate from canonical names' do
+    canonical = create_tag!('虹夏', :character)
+    TagName.create!(name: 'にじか', canonical: canonical.tag_name)
+    create_tag!('動画', :meta)
+
+    plan = described_class.new(
+        attributes: {
+            url: 'https://example.com/video',
+            title: 'video',
+            tags: '動画 にじか[0:10-0:20]',
+            duration: '1:00',
+            parent_post_ids: '' }).build!
+
+    expect(plan[:tags].split).to include('動画', '虹夏[0:10-0:20]')
+    expect(plan[:display_tags]).to include(
+        { name: '虹夏',
+          category: 'character',
+          section_literals: ['[0:10-0:20]'] })
+    expect(plan[:video_ms]).to eq(60_000)
+  end
+
+  it 'validates a new tag name without persisting it' do
+    long_name = 'a' * 256
+    counts = [TagName.count, Tag.count]
+
+    expect {
+      described_class.new(
+          attributes: {
+              url: 'https://example.com/post',
+              title: 'title',
+              tags: long_name,
+              parent_post_ids: '' }).build!
+    }.to raise_error(ActiveRecord::RecordInvalid) { |error|
+      expect(error.record.errors[:tags]).not_to be_empty
+    }
+    expect([TagName.count, Tag.count]).to eq(counts)
+  end
+
+  it 'ignores duration when the planned tags do not include video' do
+    plan = described_class.new(
+        attributes: {
+            url: 'https://example.com/post',
+            title: 'title',
+            tags: 'ordinary_tag',
+            duration: 'invalid',
+            parent_post_ids: '' }).build!
+
+    expect(plan[:duration]).to eq('invalid')
+    expect(plan[:video_ms]).to be_nil
+  end
+end

backend/spec/services/post_creator_spec.rb

@@ -20,12 +20,12 @@ RSpec.describe PostCreator do
     allow(PostVersionRecorder).to receive(:record!)
   end
 
-  it 'prefers an explicit upload over thumbnail_base' do
+  it 'prefers thumbnail_base over an explicit upload' do
-    allow(Post).to receive(:resized_thumbnail_attachment).and_return(
+    expect(Post).not_to receive(:resized_thumbnail_attachment)
-        io: StringIO.new('upload'),
+    allow(Post).to receive(:remote_thumbnail_attachment).and_return(
+        io: StringIO.new('remote'),
         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:,
@@ -41,13 +41,12 @@ RSpec.describe PostCreator do
   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!)
+    expect(Post).to receive(:remote_thumbnail_attachment)
-        .with('https://example.com/thumb.jpg') do |post, _url|
+        .with('https://example.com/thumb.jpg')
-      post.thumbnail.attach(
+        .and_return(
-          io: StringIO.new('thumbnail'),
+            io: StringIO.new('thumbnail'),
-          filename: 'thumbnail.jpg',
+            filename: 'thumbnail.jpg',
-          content_type: 'image/jpeg')
+            content_type: 'image/jpeg')
-    end
 
     post = described_class.new(
         actor:,
@@ -61,8 +60,8 @@ RSpec.describe PostCreator do
     expect(post.thumbnail).to be_attached
   end
 
-  it 'keeps creating the post and records a warning when remote thumbnail fetch fails' do
+  it 'does not create a post when remote thumbnail fetch fails' do
-    allow_any_instance_of(Post).to receive(:attach_thumbnail_from_url!)
+    allow(Post).to receive(:remote_thumbnail_attachment)
         .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:,
@@ -72,11 +71,8 @@ RSpec.describe PostCreator do
           thumbnail_base: 'https://example.com/thumb.jpg',
           tags: '' })
 
-    post = creator.create!
+    post_count = Post.count
-
+    expect { creator.create! }.to raise_error(Post::RemoteThumbnailFetchFailed)
-    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+    expect(Post.count).to eq(post_count)
-    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_row_normaliser_spec.rb

@@ -1,77 +0,0 @@
-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

@@ -1,152 +0,0 @@
-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

@@ -1,40 +0,0 @@
-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_thumbnail_upload_validator_spec.rb

@@ -0,0 +1,52 @@
+require 'rails_helper'
+require 'base64'
+require 'tempfile'
+
+RSpec.describe PostThumbnailUploadValidator do
+  def with_upload bytes, content_type:, filename:
+    tempfile = Tempfile.new(['thumbnail-upload', File.extname(filename)])
+    tempfile.binmode
+    tempfile.write(bytes)
+    tempfile.rewind
+    upload = ActionDispatch::Http::UploadedFile.new(
+        tempfile:,
+        filename:,
+        type: content_type)
+    yield upload
+  ensure
+    tempfile&.close!
+  end
+
+  it 'accepts a raster upload after decoding and rewinds it' do
+    gif = Base64.decode64('R0lGODdhAQABAIABAP///wAAACwAAAAAAQABAAACAkQBADs=')
+
+    with_upload(gif, content_type: 'image/gif', filename: 'thumbnail.gif') do |upload|
+      expect { described_class.validate!(upload) }.not_to raise_error
+      expect(upload.read(6)).to eq('GIF87a')
+    end
+  end
+
+  it 'rejects SVG content disguised as a raster MIME type' do
+    with_upload(
+        '<svg width="10" height="10"></svg>',
+        content_type: 'image/png',
+        filename: 'thumbnail.png') do |upload|
+      expect { described_class.validate!(upload) }
+          .to raise_error(
+              described_class::InvalidUpload,
+              'サムネイル画像の形式が不正です．')
+    end
+  end
+
+  it 'rejects non-raster content disguised as an image' do
+    with_upload(
+        '%PDF-1.7',
+        content_type: 'image/png',
+        filename: 'thumbnail.png') do |upload|
+      expect { described_class.validate!(upload) }
+          .to raise_error(
+              described_class::InvalidUpload,
+              'サムネイル画像の形式が不正です．')
+    end
+  end
+end

backend/spec/services/preview/thumbnail_fetcher_spec.rb

@@ -2,7 +2,7 @@ require 'rails_helper'
 
 RSpec.describe Preview::ThumbnailFetcher do
   describe '.fetch' do
-    it 'rejects svg thumbnails' do
+    it 'accepts svg thumbnails for the common safe rasterisation path' do
       page = Preview::HttpFetcher::Response.new(
           '<meta property="og:image" content="https://example.com/thumb.svg">',
           'text/html',
@@ -12,8 +12,9 @@ RSpec.describe Preview::ThumbnailFetcher do
           'image/svg+xml',
           'https://example.com/thumb.svg')
 
-      allow(Preview::UrlSafety).to receive(:validate)
+      allow(Preview::UrlSafety).to receive(:validate) do |url|
-          .and_return([URI.parse('https://example.com/page'), ['203.0.113.10']])
+        [URI.parse(url), ['203.0.113.10']]
+      end
       allow(Preview::HttpFetcher).to receive(:fetch)
           .with('https://example.com/page', max_bytes: described_class::HTML_MAX_BYTES)
           .and_return(page)
@@ -21,9 +22,7 @@ RSpec.describe Preview::ThumbnailFetcher do
           .with('https://example.com/thumb.svg')
           .and_return(svg)
 
-      expect {
+      expect(described_class.fetch('https://example.com/page')).to eq('<svg></svg>')
-        described_class.fetch('https://example.com/page')
-      }.to raise_error(Preview::ThumbnailFetcher::GenerationFailed)
     end
 
     it 'accepts allowed image content type with parameters' do
@@ -32,12 +31,13 @@ RSpec.describe Preview::ThumbnailFetcher do
           'text/html',
           'https://example.com/page')
       image = Preview::HttpFetcher::Response.new(
-          'jpeg-bytes',
+          "\xFF\xD8\xFFjpeg-bytes".b,
           'image/jpeg; charset=binary',
           'https://example.com/thumb.jpg')
 
-      allow(Preview::UrlSafety).to receive(:validate)
+      allow(Preview::UrlSafety).to receive(:validate) do |url|
-          .and_return([URI.parse('https://example.com/page'), ['203.0.113.10']])
+        [URI.parse(url), ['203.0.113.10']]
+      end
       allow(Preview::HttpFetcher).to receive(:fetch)
           .with('https://example.com/page', max_bytes: described_class::HTML_MAX_BYTES)
           .and_return(page)
@@ -45,7 +45,8 @@ RSpec.describe Preview::ThumbnailFetcher do
           .with('https://example.com/thumb.jpg')
           .and_return(image)
 
-      expect(described_class.fetch('https://example.com/page')).to eq('jpeg-bytes')
+      expect(described_class.fetch('https://example.com/page'))
+          .to eq("\xFF\xD8\xFFjpeg-bytes".b)
     end
   end
 

backend/spec/services/youtube/sync_spec.rb

@@ -268,6 +268,10 @@ RSpec.describe Youtube::Sync do
       expect(tag_ids).to include(deerjikist_tag.id)
       expect(tag_ids).not_to include(Tag.no_deerjikist.id)
 
+      expect(PostTag.exists?(post:, tag: Tag.no_deerjikist)).to be(false)
+      expect(Tag.no_deerjikist.reload.post_count).to eq(0)
+      expect(deerjikist_tag.reload.post_count).to eq(1)
+
       expect(PostVersionRecorder).to have_received(:ensure_snapshot!).with(
         post,
         created_by_user: nil

backend/spec/tasks/nico_sync_spec.rb

@@ -1,36 +1,35 @@
-require "rails_helper"
+require 'rails_helper'
 
 
-RSpec.describe "nico:sync" do
+RSpec.describe 'nico:sync' do
   def stub_python(json_array)
     status = instance_double(Process::Status, success?: true)
-    allow(Open3).to receive(:capture3).and_return([json_array.to_json, "", status])
+    allow(Open3).to receive(:capture3).and_return([json_array.to_json, '', status])
   end
 
   def create_tag!(name, category:)
-    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
+    Tag.find_or_create_by_tag_name!(name, category:)
-    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) { |t| t.category = category }
   end
 
   def link_nico_to_tag!(nico_tag, tag)
     NicoTagRelation.create!(nico_tag_id: nico_tag.id, tag_id: tag.id)
   end
 
-  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
+  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",
+      title: 'old',
-      url: "https://www.nicovideo.jp/watch/sm9",
+      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")
+    kept_general = create_tag!('spec_kept', category: 'general')
     PostTag.create!(post: post, tag: kept_general)
 
     # 追加される linked tag を準備（nico tag に紐付く一般タグ）
-    linked = create_tag!("spec_linked", category: "general")
+    linked = create_tag!('spec_linked', category: 'general')
-    nico = create_tag!("nico:AAA", category: "nico")
+    nico = create_tag!('nico:AAA', category: 'nico')
     link_nico_to_tag!(nico, linked)
 
     # bot / tagme は task 内で使うので作っておく（Tag.bot/tagme がある前提）
@@ -46,22 +45,22 @@ RSpec.describe "nico:sync" do
         'deleted_at' => '2026-01-31 00:00:00' }])
 
     # 外部HTTPは今回「既存 post なので呼ばれない」はずだが、念のため塞ぐ
-    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
+    allow(URI).to receive(:open).and_return(StringIO.new('<html></html>'))
 
-    run_rake_task("nico:sync")
+    run_rake_task('nico:sync')
 
     post.reload
-    active_tag_names = post.tags.joins(:tag_name).pluck("tag_names.name")
+    active_tag_names = post.tags.joins(:tag_name).pluck('tag_names.name')
 
-    expect(active_tag_names).to include("spec_kept")
+    expect(active_tag_names).to include('spec_kept')
-    expect(active_tag_names).to include("nico:AAA")
+    expect(active_tag_names).to include('nico:AAA')
-    expect(active_tag_names).to include("spec_linked")
+    expect(active_tag_names).to include('spec_linked')
 
     expect(post.original_created_from).to eq(Time.iso8601('2026-01-01T03:34:00Z'))
     expect(post.original_created_before).to eq(Time.iso8601('2026-01-01T03:35:00Z'))
 
     # 差分が出るので bot が付く（kept_non_nico_ids != desired_non_nico_ids）
-    expect(active_tag_names).to include("bot操作")
+    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
@@ -73,11 +72,11 @@ RSpec.describe "nico:sync" do
     Tag.tagme
 
     stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
-    allow(URI).to receive(:open)
+    allow(URI).to receive(:open) do
-        .and_return(
+      StringIO.new(
-            StringIO.new(
+          '<meta name="thumbnail" content="https://example.com/thumb.jpg">')
-                '<meta name="thumbnail" content="https://example.com/thumb.jpg">'))
+    end
-    expect(post).to receive(:attach_thumbnail_from_url!)
+    expect_any_instance_of(Post).to receive(:attach_thumbnail_from_url!)
         .with('https://example.com/thumb.jpg')
 
     run_rake_task('nico:sync')
@@ -92,53 +91,63 @@ RSpec.describe "nico:sync" do
     Tag.tagme
 
     stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
-    allow(URI).to receive(:open)
+    allow(URI).to receive(:open) do
-        .and_return(
+      StringIO.new(
-            StringIO.new(
+          '<meta name="thumbnail" content="https://example.com/thumb.jpg">')
-                '<meta name="thumbnail" content="https://example.com/thumb.jpg">'))
+    end
-    expect(post).to receive(:attach_thumbnail_from_url!)
+    calls = 0
-        .with('https://example.com/thumb.jpg')
+    allow_any_instance_of(Post).to receive(:attach_thumbnail_from_url!) do
-        .twice
+      calls += 1
-        .and_raise(Post::RemoteThumbnailFetchFailed, 'failed')
+      raise Post::RemoteThumbnailFetchFailed, 'failed'
+    end
 
     2.times do
       run_rake_task('nico:sync')
     end
+    expect(calls).to eq(2)
   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
+  it '古い nico tag の関連を物理削除し、変更前後の履歴を version に残す' do
     post = Post.create!(
-      title: "old",
+      title: 'old',
-      url: "https://www.nicovideo.jp/watch/sm9",
+      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")
+    old_nico = create_tag!('nico:OLD', category: 'nico')
-    old_pt = PostTag.create!(post: post, tag: old_nico)
+    PostTag.create!(post:, tag: old_nico)
-    expect(old_pt.discarded_at).to be_nil
+    create_post_version_for!(post)
 
     # 今回は NEW のみ欲しい
-    new_nico = create_tag!("nico:NEW", category: "nico")
+    new_nico = create_tag!('nico:NEW', category: 'nico')
 
     # bot/tagme 念のため
     Tag.bot
     Tag.tagme
 
-    stub_python([{ "code" => "sm9", "title" => "t", "tags" => ["NEW"] }])
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => ['NEW'] }])
-    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
+    allow(URI).to receive(:open).and_return(StringIO.new('<html></html>'))
 
-    run_rake_task("nico:sync")
+    run_rake_task('nico:sync')
 
-    # OLD は active から外れる（discarded_at が入る）
+    expect(PostTag.exists?(post:, tag: old_nico)).to be(false)
-    old_pts = PostTag.where(post_id: post.id, tag_id: old_nico.id).order(:id).to_a
+    expect(old_nico.reload.post_count).to eq(0)
-    expect(old_pts.last.discarded_at).to be_present
+    expect(new_nico.reload.post_count).to eq(1)
+
+    versions = post.post_versions.order(:version_no)
+    expect(versions.first.tags_json.map { |item| item.fetch('id') })
+        .to include(old_nico.id)
+    expect(versions.last.tags_json.map { |item| item.fetch('id') })
+        .to include(new_nico.id)
+    expect(versions.last.tags_json.map { |item| item.fetch('id') })
+        .not_to include(old_nico.id)
 
     # NEW は active にいる
     post.reload
-    active_names = post.tags.joins(:tag_name).pluck("tag_names.name")
+    active_names = post.tags.joins(:tag_name).pluck('tag_names.name')
-    expect(active_names).to include("nico:NEW")
+    expect(active_names).to include('nico:NEW')
-    expect(active_names).not_to include("nico:OLD")
+    expect(active_names).not_to include('nico:OLD')
   end
 
   def snapshot_tags(post)
@@ -154,6 +163,7 @@ RSpec.describe "nico:sync" do
       url: post.url,
       thumbnail_base: post.thumbnail_base,
       tags: snapshot_tags(post),
+      tags_json: post.snapshot_tags_json,
       parent_post_ids: post.snapshot_parent_post_ids.join(' '),
       original_created_from: post.original_created_from,
       original_created_before: post.original_created_before,

frontend/AGENTS.md

@@ -130,6 +130,13 @@ pass or the remaining failure is clearly blocked.
 
 - Tailwind scans `src/**/*.{html,js,ts,jsx,tsx,mdx}`.
 - Use `cn` from `src/lib/utils.ts` for conditional class names and class merging.
+- In JavaScript, JSX, TypeScript, and TSX, use `cn` from `@/lib/utils`
+  whenever `className` combines multiple values, conditional classes, or a
+  caller-provided `className` prop.
+- Do not construct `className` with template literals, `${ ... }`, string
+  concatenation, arrays joined with spaces, or feature-local class-merging
+  helpers.
+- A static `className="..."` containing only fixed classes does not need `cn`.
 - Reuse components from `src/components/common`, `src/components/layout`, and
   `src/components/ui` before adding new primitives.
 - Keep Tailwind classes consistent with nearby components.
@@ -140,6 +147,15 @@ pass or the remaining failure is clearly blocked.
   short Japanese labels that fit the control.
 - Preserve existing Japanese tone and orthography in nearby UI text, including
   old-kana wording where the file already uses it.
+- Do not add user-facing copy, helper text, descriptions, notes, tooltips,
+  placeholders, empty-state messages, loading messages, or explanatory text
+  unless the user explicitly specified the wording.
+- When new user-facing wording appears necessary, ask the user for the exact
+  wording and placement before implementing it.
+- Do not invent replacement copy when removing unrequested wording.
+- Do not use `タグなし` as user-facing copy for an empty tag state. When the
+  tag state is empty, show no copy. If actual data contains the tag name
+  `タグなし`, treat it as ordinary data and display it normally.
 - When adding dynamic tag colour classes, update `tailwind.config.js` safelist
   if the class cannot be statically detected.
 - Do not introduce new UI libraries or production dependencies without approval.
@@ -586,6 +602,12 @@ offsets, or footer offsets, inspect existing layout components such as
 Do not create a second layout shell before checking whether the current layout
 can be reused or minimally extended.
 
+- Frontend のスマホ／PC表示境界は原則 `md` とする。
+- button stack、footer action、dialogue action は `md` 未満で縦並び、
+  `md` 以上で横並びとする。
+- 同じ画面内で `sm` と `md` を混在させて中間 layout を作らない。
+- 明確に別の responsive 要件がある component だけを例外とする。
+
 ### Delimiter decision table
 
 Use this table before accepting any edited TypeScript or TSX hunk. The table is

frontend/src/App.tsx

@@ -1,8 +1,9 @@
 import { AnimatePresence, LayoutGroup, MotionConfig, motion } from 'framer-motion'
 import { Fragment, useEffect, useMemo, useState } from 'react'
-import { BrowserRouter,
+import { createBrowserRouter,
 	 Navigate,
 	 Route,
+	 RouterProvider,
 	 Routes,
 	 useLocation } from 'react-router-dom'
 
@@ -41,11 +42,8 @@ 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 PostListPage from '@/pages/posts/PostListPage'
 import PostSearchPage from '@/pages/posts/PostSearchPage'
 import ServiceUnavailable from '@/pages/ServiceUnavailable'
 import SettingPage from '@/pages/users/SettingPage'
@@ -78,9 +76,6 @@ 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/>}/>
@@ -119,9 +114,6 @@ 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/>}/>
@@ -163,7 +155,7 @@ const PostDetailRoute = ({ user }: { user: User | null }) => {
 }
 
 
-const App: FC = () => {
+const RoutedApp: FC = () => {
   const [user, setUser] = useState<User | null> (null)
   const [status, setStatus] = useState (200)
   const behaviourSettings = useClientBehaviourSettings ()
@@ -262,42 +254,46 @@ const App: FC = () => {
   }
 
   return (
-      <>
+      <DialogueProvider>
-	<RouteBlockerOverlay/>
+	<UnsavedChangesGuardProvider>
-	{import.meta.env.DEV && <DevModeWatermark/>}
+	  <KeyboardShortcutsProvider>
+	  <MotionConfig
+	      reducedMotion={
+		  animationMode === 'normal'
+		  ? 'never'
+		  : animationMode === 'reduced'
+		    ? 'user'
+		    : 'always'
+	      }>
+	    <LayoutWrapper>
+	      <motion.div
+		  layout={animationMode === 'off' ? false : 'position'}
+		  transition={{ layout: appLayoutTransition }}
+		  className="relative flex h-dvh w-full flex-col overflow-y-hidden">
+		<TopNav user={user}/>
+		<RouteTransitionWrapper
+		    animationMode={animationMode}
+		    user={user}
+		    setUser={setUser}/>
+	      </motion.div>
+	    </LayoutWrapper>
+	  </MotionConfig>
 
-	<BrowserRouter>
+	  <Toaster/>
-	  <DialogueProvider>
+	  </KeyboardShortcutsProvider>
-	    <UnsavedChangesGuardProvider>
+	</UnsavedChangesGuardProvider>
-	      <KeyboardShortcutsProvider>
+      </DialogueProvider>)
-	      <MotionConfig
-		  reducedMotion={
-		      animationMode === 'normal'
-		      ? 'never'
-		      : animationMode === 'reduced'
-			? 'user'
-			: 'always'
-		  }>
-		<LayoutWrapper>
-		  <motion.div
-		      layout={animationMode === 'off' ? false : 'position'}
-		      transition={{ layout: appLayoutTransition }}
-		      className="relative flex flex-col h-dvh w-full overflow-y-hidden">
-		    <TopNav user={user}/>
-		    <RouteTransitionWrapper
-			animationMode={animationMode}
-			user={user}
-			setUser={setUser}/>
-		  </motion.div>
-		</LayoutWrapper>
-	      </MotionConfig>
-
-	      <Toaster/>
-	      </KeyboardShortcutsProvider>
-	    </UnsavedChangesGuardProvider>
-	  </DialogueProvider>
-	</BrowserRouter>
-      </>)
 }
 
+const router = createBrowserRouter ([{
+    path: '*',
+    element: <RoutedApp/> }])
+
+const App: FC = () => (
+    <>
+      <RouteBlockerOverlay/>
+      {import.meta.env.DEV && <DevModeWatermark/>}
+      <RouterProvider router={router}/>
+    </>)
+
 export default App

frontend/src/components/PostEditForm.test.tsx

@@ -78,19 +78,23 @@ describe ('PostEditForm', () => {
 
     render (<PostEditForm post={post} onSave={vi.fn ()}/>)
 
-    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('180.5')
+    expect (screen.getByText ('動画時間').parentElement?.querySelector ('input'))
+	.toHaveValue ('180.5')
 
     const tags = screen.getAllByRole ('textbox')[2]
     fireEvent.change (tags, { target: { value: 'general-tag' } })
-    expect (screen.queryByPlaceholderText ('例: 2 / 2.5 / 1:23')).not.toBeInTheDocument ()
+    expect (screen.queryByText ('動画時間')).not.toBeInTheDocument ()
 
     fireEvent.change (tags, {
       target: { value: '動画 general-tag' },
     })
-    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('180.5')
+    expect (screen.getByText ('動画時間').parentElement?.querySelector ('input'))
+	.toHaveValue ('180.5')
   })
 
-  it ('shows deduplicated original-created endpoint errors on the shared datetime field', async () => {
+  it (
+      'shows deduplicated original-created endpoint errors on the shared datetime field',
+      async () => {
     const post = buildPost ()
     api.isApiError.mockReturnValue (true)
     postsApi.updatePost.mockRejectedValueOnce ({
@@ -112,5 +116,5 @@ describe ('PostEditForm', () => {
     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/PostOriginalCreatedTimeField.test.tsx

@@ -73,7 +73,7 @@ describe ('PostOriginalCreatedTimeField', () => {
             setOriginalCreatedBefore={vi.fn ()}/>,
     )
 
-    const input = screen.getDisplayValue ('2024-01-01T12:34')
+    const input = screen.getByDisplayValue ('2024-01-01T12:34')
     fireEvent.change (input, { target: { value: '2024-01-01T12:35' } })
 
     expect (setFrom).toHaveBeenCalledWith ('2024-01-01T03:35Z')

frontend/src/components/PostOriginalCreatedTimeField.tsx

@@ -24,10 +24,10 @@ const PostOriginalCreatedTimeField: FC<Props> = (
       <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="my-1 flex">
-		  <div className="min-w-0 flex-1">
+		  <div className="w-80">
 		    <DateTimeField
-			className="w-full"
+			className="mr-2"
 			disabled={disabled ?? false}
 			aria-describedby={describedBy}
 			aria-invalid={invalid}
@@ -61,10 +61,10 @@ const PostOriginalCreatedTimeField: FC<Props> = (
 		  </div>
 		</div>
 
-		<div className="my-1 flex flex-col gap-2 sm:flex-row sm:items-start">
+		<div className="my-1 flex">
-		  <div className="min-w-0 flex-1">
+		  <div className="w-80">
 		    <DateTimeField
-			className="w-full"
+			className="mr-2"
 			disabled={disabled}
 			aria-describedby={describedBy}
 			aria-invalid={invalid}

frontend/src/components/PrefetchLink.tsx

@@ -6,7 +6,6 @@ import { createPath, useNavigate } from 'react-router-dom'
 import { useOverlayStore } from '@/components/RouteBlockerOverlay'
 import { prefetchForURL } from '@/lib/prefetchers'
 import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
-import { useUnsavedChangesGuard } from '@/lib/useUnsavedChangesGuard'
 import { cn } from '@/lib/utils'
 
 import type { AnchorHTMLAttributes, MouseEvent, TouchEvent } from 'react'
@@ -36,7 +35,6 @@ export default forwardRef<HTMLAnchorElement, Props> (({
   const navigate = useNavigate ()
   const qc = useQueryClient ()
   const behaviourSettings = useClientBehaviourSettings ()
-  const { confirmDiscardNavigation } = useUnsavedChangesGuard ()
   const linkPreloadMode = behaviourSettings.linkPreload ?? 'intent'
   const path = useMemo (
       () => typeof to === 'string' ? to : createPath (to),
@@ -45,10 +43,6 @@ export default forwardRef<HTMLAnchorElement, Props> (({
   const url = useMemo (() => {
     return (new URL (path, window.location.origin)).toString ()
   }, [path])
-  const nextPathname = useMemo (
-      () => (new URL (path, window.location.origin)).pathname,
-      [path],
-  )
   const setOverlay = useOverlayStore (s => s.setActive)
 
   const doPrefetch = async () => {
@@ -93,13 +87,6 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
       ev.preventDefault ()
 
-      if (nextPathname !== window.location.pathname)
-	{
-	  const confirmed = await confirmDiscardNavigation ()
-	  if (!(confirmed))
-	    return
-	}
-
       flushSync (() => {
 	setOverlay (true)
       })

frontend/src/components/TagLink.tsx

@@ -4,9 +4,13 @@ import { cn } from '@/lib/utils'
 
 import type { ComponentProps, CSSProperties, FC, HTMLAttributes } from 'react'
 
-import type { Tag } from '@/types'
+import type { Category, Tag } from '@/types'
 
-type CommonProps = { 
+type LightweightTag = {
+    name:     string
+    category: Category }
+
+type FullCommonProps = {
     tag:        Tag
     nestLevel?: number
     truncateOnMobile?: boolean
@@ -14,18 +18,43 @@ type CommonProps = {
     withCount?: boolean }
 
 type PropsWithLink =
-    & CommonProps
+    & FullCommonProps
     & { linkFlg?: true }
     & Partial<ComponentProps<typeof PrefetchLink>>
 
 type PropsWithoutLink =
-    & CommonProps
+    & FullCommonProps
     & { linkFlg: false }
     & Partial<HTMLAttributes<HTMLSpanElement>>
 
+type LightweightPropsWithLink =
+    & {
+	tag:              LightweightTag
+	nestLevel?:       number
+	truncateOnMobile?: boolean
+	withWiki:         false
+	withCount:        false
+	linkFlg?:         true }
+    & Partial<ComponentProps<typeof PrefetchLink>>
+
+type LightweightPropsWithoutLink =
+    & {
+	tag:              LightweightTag
+	nestLevel?:       number
+	truncateOnMobile?: boolean
+	withWiki:         false
+	withCount:        false
+	linkFlg:          false }
+    & Partial<HTMLAttributes<HTMLSpanElement>>
+
 type Props =
     | PropsWithLink
     | PropsWithoutLink
+    | LightweightPropsWithLink
+    | LightweightPropsWithoutLink
+
+const isFullTag = (tag: Tag | LightweightTag): tag is Tag =>
+    'id' in tag
 
 
 const TagLink: FC<Props> = ({ tag,
@@ -46,16 +75,18 @@ const TagLink: FC<Props> = ({ tag,
   const spanClass = 'tag-link-colour'
   const linkClass = 'tag-link-colour tag-link-hover-colour'
   const textClass = 'group min-w-0 max-w-full overflow-hidden align-bottom'
-  const rootClass =
-      'inline-flex min-w-0 max-w-full flex-nowrap items-stretch align-baseline gap-x-1 md:items-baseline'
   const markerWrapClass = 'shrink-0 self-start md:self-auto'
   const countClass = 'shrink-0 self-end md:self-auto'
+  const matchedAlias = isFullTag (tag) ? tag.matchedAlias : null
   const textTitle = title
-      ?? (tag.matchedAlias == null ? tag.name : `${ tag.matchedAlias } → ${ tag.name }`)
+      ?? (matchedAlias == null ? tag.name : `${ matchedAlias } → ${ tag.name }`)
 
   return (
-      <span className={rootClass}>
+      <span
-	{(linkFlg && withWiki) && (
+	  className={cn (
+	      'inline-flex min-w-0 max-w-full flex-nowrap items-stretch align-baseline',
+	      'gap-x-1 md:items-baseline')}>
+	{(linkFlg && withWiki && isFullTag (tag)) && (
 	    <span className={markerWrapClass}>
 	      {(tag.materialId != null || tag.hasWiki || tag.hasDeerjikists)
 	       ? (
@@ -118,7 +149,7 @@ const TagLink: FC<Props> = ({ tag,
 		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
 	      ↳
 	    </span>)}
-	{tag.matchedAlias != null && (
+	{matchedAlias != null && (
 	    <>
 	      <span
 		  title={textTitle}
@@ -126,7 +157,7 @@ const TagLink: FC<Props> = ({ tag,
 		  style={colourStyle}
 		  {...props}>
 		<ResponsiveMarqueeText
-		    text={tag.matchedAlias}
+		    text={matchedAlias}
 		    title={textTitle}
 		    truncateOnMobile={truncateOnMobile}/>
 	      </span>
@@ -156,7 +187,7 @@ const TagLink: FC<Props> = ({ tag,
 		  title={textTitle}
 		  truncateOnMobile={truncateOnMobile}/>
 	    </span>)}
-	{withCount && (
+	{(withCount && isFullTag (tag)) && (
 	    <span className={countClass}>{tag.postCount}</span>)}
       </span>)
 }

frontend/src/components/TopNav.test.tsx

@@ -17,19 +17,21 @@ describe ('menuOutline', () => {
     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 ('uses /posts/new as the post creation entrypoint', () => {
+    expect (submenuItem ('member', '広場', '追加')?.to).toBe ('/posts/new')
+  })
+
   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

@@ -45,7 +45,6 @@ export const menuOutline = (
 	  { name: '一覧', to: '/posts' },
 	  { name: '検索', to: '/posts/search' },
 	  { 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: [

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

@@ -80,7 +80,9 @@ describe ('DialogueProvider', () => {
     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')
+    expect (screen.getByRole ('button', { name: '左操作' })).toHaveClass (
+	'w-full',
+	'md:w-auto')
     fireEvent.click (screen.getByRole ('button', { name: '左操作' }))
 
     await waitFor (() => expect (action).toHaveBeenCalledTimes (1))

frontend/src/components/dialogues/DialogueProvider.tsx

@@ -215,12 +215,12 @@ const DialogueProvider: FC<Props> = ({ children }) => {
 
 		       <DialogFooter
 			   className="shrink-0 flex-col gap-2 pt-4
-				      sm:flex-row sm:justify-between sm:gap-0 sm:space-x-0">
+				      md:flex-row md:justify-between md:gap-0 md:space-x-0">
-			 <div className="flex w-full flex-col gap-2 sm:w-auto sm:flex-row">
+			 <div className="flex w-full flex-col gap-2 md:w-auto md:flex-row">
 			   {startActions.map (action => (
 			       <Button
 				   key={action.label}
-				   className="w-full sm:w-auto"
+				   className="w-full md:w-auto"
 				   variant={action.variant === 'danger'
 				       ? 'destructive'
 				       : 'default'}
@@ -232,9 +232,9 @@ const DialogueProvider: FC<Props> = ({ children }) => {
 			       </Button>))}
 			 </div>
 
-			 <div className="flex w-full flex-col gap-2 sm:w-auto sm:flex-row">
+			 <div className="flex w-full flex-col gap-2 md:w-auto md:flex-row">
 			   <Button
-			       className="w-full sm:w-auto"
+			       className="w-full md:w-auto"
 			       variant="outline"
 			       onClick={() => closeRequest (active.id)}
 			       disabled={pendingIds.includes (active.id)
@@ -245,7 +245,7 @@ const DialogueProvider: FC<Props> = ({ children }) => {
 			   {endActions.map (action => (
 			       <Button
 				   key={action.label}
-				   className="w-full sm:w-auto"
+				   className="w-full md:w-auto"
 				   variant={action.variant === 'danger'
 				       ? 'destructive'
 				       : 'default'}

frontend/src/components/posts/PostCoreDataFields.tsx

@@ -0,0 +1,94 @@
+import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
+import PostTagsField from '@/components/posts/PostTagsField'
+import PostTextField from '@/components/posts/PostTextField'
+
+import type { FC, ReactNode } from 'react'
+
+type TextMessages = string[] | undefined
+
+type CoreField = {
+  value:    string
+  onChange: (value: string) => void
+  errors?:  TextMessages
+  warnings?: TextMessages
+  disabled?: boolean }
+
+type OriginalCreatedField = {
+  originalCreatedAt?:     TextMessages
+  originalCreatedFrom?:   TextMessages
+  originalCreatedBefore?: TextMessages }
+
+type PostCoreDataFieldsProps = {
+  title: {
+    value:     string
+    onChange:  (value: string) => void
+    errors?:   TextMessages
+    warnings?: TextMessages
+    disabled?: boolean
+    after?:    ReactNode }
+  originalCreated: {
+    disabled?:                boolean
+    originalCreatedFrom:      string | null
+    setOriginalCreatedFrom:   (value: string | null) => void
+    originalCreatedBefore:    string | null
+    setOriginalCreatedBefore: (value: string | null) => void
+    errors?:                  OriginalCreatedField }
+  tags: {
+    value:     string
+    onChange:  (value: string) => void
+    errors?:   TextMessages
+    warnings?: TextMessages
+    disabled?: boolean
+    rows?:     number }
+  parentPostIds: CoreField }
+
+const groupedMessages = (...values: (TextMessages | null | undefined)[]): string[] =>
+    [...new Set (values.flatMap (value => value ?? []))]
+
+
+const PostCoreDataFields: FC<PostCoreDataFieldsProps> = (
+    { title,
+      originalCreated,
+      tags,
+      parentPostIds },
+) => (
+    <>
+      <PostTextField
+          label="タイトル"
+          value={title.value}
+          disabled={title.disabled}
+          warnings={title.warnings}
+          errors={title.errors}
+          after={title.after}
+          onChange={title.onChange}/>
+
+      <PostOriginalCreatedTimeField
+          disabled={originalCreated.disabled}
+          originalCreatedFrom={originalCreated.originalCreatedFrom}
+          setOriginalCreatedFrom={originalCreated.setOriginalCreatedFrom}
+          originalCreatedBefore={originalCreated.originalCreatedBefore}
+          setOriginalCreatedBefore={originalCreated.setOriginalCreatedBefore}
+          errors={groupedMessages (
+              originalCreated.errors?.originalCreatedAt,
+              originalCreated.errors?.originalCreatedFrom,
+              originalCreated.errors?.originalCreatedBefore)}/>
+
+      <PostTagsField
+          tags={tags.value}
+          disabled={tags.disabled}
+          setTags={tags.onChange}
+          warnings={tags.warnings}
+          errors={tags.errors}
+          rows={tags.rows}/>
+
+      <PostTextField
+          label="親投稿"
+          value={parentPostIds.value}
+          disabled={parentPostIds.disabled}
+          warnings={parentPostIds.warnings}
+          errors={parentPostIds.errors}
+          onChange={parentPostIds.onChange}/>
+    </>)
+
+export default PostCoreDataFields
+export type { PostCoreDataFieldsProps }

frontend/src/components/posts/PostCreationDataFields.tsx

@@ -0,0 +1,48 @@
+import PostCoreDataFields from '@/components/posts/PostCoreDataFields'
+import PostTextField from '@/components/posts/PostTextField'
+
+import type { FC, ReactNode } from 'react'
+
+import type { PostCoreDataFieldsProps } from '@/components/posts/PostCoreDataFields'
+
+type TextMessages = string[] | undefined
+
+type Props = {
+  url: {
+    value:       string
+    onChange:    (value: string) => void
+    errors?:     TextMessages
+    warnings?:   TextMessages
+    disabled?:   boolean
+    type?:       string
+    placeholder?: string }
+  thumbnailField: ReactNode
+  core:           PostCoreDataFieldsProps
+  extraFields?:   ReactNode }
+
+
+const PostCreationDataFields: FC<Props> = (
+    { url,
+      thumbnailField,
+      core,
+      extraFields },
+) => (
+    <>
+      <PostTextField
+          label="URL"
+          type={url.type}
+          value={url.value}
+          disabled={url.disabled}
+          warnings={url.warnings}
+          errors={url.errors}
+          placeholder={url.placeholder}
+          onChange={url.onChange}/>
+
+      {thumbnailField}
+
+      <PostCoreDataFields {...core}/>
+
+      {extraFields}
+    </>)
+
+export default PostCreationDataFields

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

@@ -0,0 +1,31 @@
+import { render, screen } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import { buildPostImportRow } from '@/test/postImportFactories'
+
+import type { DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+const sharedFieldsSpy = vi.hoisted (() => vi.fn (() => <div data-testid="shared-fields"/>))
+
+vi.mock ('@/components/posts/PostCreationDataFields', () => ({
+  default: sharedFieldsSpy,
+}))
+
+describe ('PostCreationDataFields usage', () => {
+  it ('is used by PostImportRowForm', async () => {
+    const { default: PostImportRowForm } = await import (
+        '@/components/posts/import/PostImportRowForm')
+
+    render (
+        <PostImportRowForm
+            row={buildPostImportRow ()}
+            controls={{
+              close: vi.fn (),
+              confirm: vi.fn (),
+              setActions: vi.fn (),
+            } as DialogueFormControls}
+            onSave={vi.fn ()}/>)
+
+    expect (screen.getByTestId ('shared-fields')).toBeInTheDocument ()
+  })
+})

frontend/src/components/posts/PostDurationField.tsx

@@ -21,8 +21,7 @@ const PostDurationField: FC<Props> = (
         onChange={onChange}
         errors={errors}
         disabled={disabled}
-        type="text"
+        type="text"/>
-        placeholder="例: 2 / 2.5 / 1:23"/>
 )
 
 export default PostDurationField

frontend/src/components/posts/PostTextField.tsx

@@ -14,7 +14,8 @@ type Props = {
   type?:        string
   placeholder?: string
   className?:   string
-  after?:       ReactNode }
+  after?:       ReactNode
+  onBlur?:      () => void }
 
 
 const PostTextField: FC<Props> = (
@@ -27,7 +28,8 @@ const PostTextField: FC<Props> = (
       type = 'text',
       placeholder,
       className,
-      after },
+      after,
+      onBlur },
 ) => (
     <FormField label={label} messages={errors}>
       {({ describedBy, invalid }) => (
@@ -37,6 +39,7 @@ const PostTextField: FC<Props> = (
                 value={value}
                 disabled={disabled}
                 placeholder={placeholder}
+                onBlur={onBlur}
                 onChange={ev => onChange (ev.target.value)}
                 aria-describedby={describedBy}
                 aria-invalid={invalid}

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

@@ -1,4 +1,4 @@
-import { render, screen } from '@testing-library/react'
+import { fireEvent, render, screen } from '@testing-library/react'
 import { describe, expect, it } from 'vitest'
 
 import PostThumbnailPreview from '@/components/posts/PostThumbnailPreview'
@@ -9,4 +9,28 @@ describe ('PostThumbnailPreview', () => {
 
     expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
   })
+
+  it ('renders an empty thumbnail frame without text when the URL is empty', () => {
+    const { container } = render (
+        <PostThumbnailPreview url="" className="h-10 w-10"/>)
+
+    expect (screen.queryByRole ('img')).toBeNull ()
+    expect (screen.queryByText ('サムネールを表示できません')).toBeNull ()
+    expect (screen.queryByText ('なし')).toBeNull ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
+  })
+
+  it ('renders an empty thumbnail frame without text when image loading fails', () => {
+    const { container } = render (
+        <PostThumbnailPreview url="blob:preview" className="h-10 w-10"/>)
+
+    fireEvent.error (screen.getByRole ('img'))
+
+    expect (screen.queryByRole ('img')).toBeNull ()
+    expect (screen.queryByText ('サムネールを表示できません')).toBeNull ()
+    expect (screen.queryByText ('なし')).toBeNull ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
+  })
 })

frontend/src/components/posts/PostThumbnailPreview.tsx

@@ -1,49 +1,63 @@
 import { useEffect, useState } from 'react'
 
+import { cn } from '@/lib/utils'
+
 import type { FC } from 'react'
 
 type Props = {
   url:        string
+  file?:      File
   alt?:       string
-  className?: string }
+  className?: string
+  referrerPolicy?: 'no-referrer' }
 
 
 const PostThumbnailPreview: FC<Props> = (
-    { url, alt = 'サムネール', className = 'h-16 w-16' },
+    { url,
+      file,
+      alt = 'サムネール',
+      className = 'h-16 w-16',
+      referrerPolicy },
 ) => {
   const [failed, setFailed] = useState (false)
+  const [fileUrl, setFileUrl] = useState<string | null> (null)
 
   useEffect (() => {
     setFailed (false)
-  }, [url])
+  }, [file, url])
 
-  if (!(url))
+  useEffect (() => {
-    {
+    if (file == null)
-      return (
+      {
-          <div
+        setFileUrl (null)
-              className={`${ className } flex items-center justify-center rounded border
+        return
-                          border-border bg-muted text-xs text-muted-foreground`}>
+      }
-            なし
+
-          </div>)
+    const nextUrl = URL.createObjectURL (file)
+    setFileUrl (nextUrl)
+
+    return () => {
+      URL.revokeObjectURL (nextUrl)
     }
+  }, [file])
 
-  if (failed)
+  const resolvedUrl = url.trim () !== '' ? url : (fileUrl ?? '')
+
+  if (resolvedUrl === '' || failed)
     {
       return (
           <div
-              className={`${ className } flex items-center justify-center rounded border
+              className={cn (
-                          border-amber-300 bg-amber-50 p-2 text-center text-xs
+                  className,
-                          text-amber-700 dark:border-amber-900 dark:bg-amber-950
+                  'rounded border border-border bg-muted')}/>)
-                          dark:text-amber-200`}>
-            サムネールを表示できません
-          </div>)
     }
 
   return (
       <img
-          src={url}
+          src={resolvedUrl}
           alt={alt}
-          className={`${ className } rounded border border-border object-cover`}
+          referrerPolicy={referrerPolicy}
+          className={cn (className, 'rounded border border-border object-cover')}
           onError={() => setFailed (true)}/>)
 }
 

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

@@ -85,7 +85,7 @@ describe ('PostImportRowForm', () => {
   it ('marks edited fields and areas invalid from field errors', () => {
     const row = buildPostImportRow ({
       validationErrors: { url: ['URL error'], tags: ['tag error'] },
-      importErrors: { duration: ['duration error'] },
+      importErrors: { title: ['title error'] },
       fieldWarnings: { title: ['title warning'] } })
 
     render (
@@ -96,7 +96,7 @@ describe ('PostImportRowForm', () => {
 
     expect (screen.getByText ('URL error')).toBeInTheDocument ()
     expect (screen.getByText ('tag error')).toBeInTheDocument ()
-    expect (screen.getByText ('duration error')).toBeInTheDocument ()
+    expect (screen.getByText ('title error')).toBeInTheDocument ()
     expect (screen.getByText ('title warning')).toBeInTheDocument ()
     expect (screen.getAllByRole ('textbox').filter (
 	textbox => textbox.getAttribute ('aria-invalid') === 'true')).toHaveLength (3)
@@ -134,7 +134,9 @@ describe ('PostImportRowForm', () => {
       resetRequested: false })
   })
 
-  it ('keeps the shared duration and tags string contract without leaking file upload UI', async () => {
+  it (
+      'shows upload input only when the thumbnail URL is blank',
+      async () => {
     let actions: DialogueFormAction[] = []
     const controls: DialogueFormControls = {
       close: vi.fn (),
@@ -152,8 +154,20 @@ describe ('PostImportRowForm', () => {
             onSave={onSave}/>)
     await waitFor (() => expect (actions.length).toBe (2))
 
-    expect (container.querySelector ('input[type="file"]')).toBeNull ()
+    const labels = Array.from (container.querySelectorAll ('label'))
-    expect (screen.getByPlaceholderText ('例: 2 / 2.5 / 1:23')).toHaveValue ('2')
+        .map (node => node.textContent?.trim ())
+
+    expect (labels.slice (0, 6)).toEqual ([
+      'URL',
+      'サムネール',
+      'タイトル',
+      'オリジナルの作成日時',
+      'タグ',
+      '親投稿'])
+    expect (container.querySelector ('input[type="file"]')).toHaveAttribute (
+	'accept',
+	'image/*')
+    expect (screen.queryByPlaceholderText ('例: 2 / 2.5 / 1:23')).not.toBeInTheDocument ()
     expect (screen.getByDisplayValue ('tag1')).toBeInTheDocument ()
 
     await act (async () => {
@@ -162,10 +176,9 @@ describe ('PostImportRowForm', () => {
 
     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 ({
@@ -178,7 +191,6 @@ describe ('PostImportRowForm', () => {
           thumbnailBase: '',
           originalCreatedFrom: '',
           originalCreatedBefore: '',
-          duration: '',
           tags: '',
           parentPostIds: '' },
         provenance: {
@@ -187,7 +199,6 @@ describe ('PostImportRowForm', () => {
           thumbnailBase: 'automatic',
           originalCreatedFrom: 'automatic',
           originalCreatedBefore: 'automatic',
-          duration: 'automatic',
           tags: 'automatic',
           parentPostIds: 'automatic' },
         tagSources: { automatic: '', manual: '' },
@@ -210,7 +221,9 @@ describe ('PostImportRowForm', () => {
     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 () => {
+  it (
+      'disables every field while save validation is pending and re-enables them afterwards',
+      async () => {
     let actions: DialogueFormAction[] = []
     let resolveSave:
         ((value: { saved: boolean
@@ -234,8 +247,9 @@ describe ('PostImportRowForm', () => {
             onSave={onSave}/>)
     await waitFor (() => expect (actions.length).toBe (2))
 
+    let savePromise: Promise<boolean | void> | undefined
     await act (async () => {
-      await actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
+      savePromise = actions.find (action => action.label === '編輯内容を保存')?.onSelect ()
     })
 
     await waitFor (() => {
@@ -249,6 +263,9 @@ describe ('PostImportRowForm', () => {
       row: buildPostImportRow ({
         attributes: { title: 'draft title' },
         validationErrors: { title: ['タイトルを確認してください．'] } }) })
+    await act (async () => {
+      await savePromise
+    })
 
     await waitFor (() => {
       screen.getAllByRole ('textbox').forEach (textbox => {
@@ -257,5 +274,5 @@ describe ('PostImportRowForm', () => {
     })
     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

@@ -1,17 +1,17 @@
 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 PostCreationDataFields from '@/components/posts/PostCreationDataFields'
 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 { hasThumbnailBaseValue, hasVideoTag } from '@/lib/postImportRows'
 
 import type { FC } from 'react'
 
-import type { PostImportEditableDraft, PostImportRow } from '@/lib/postImportSession'
 import type { DialogueFormControls } from '@/lib/dialogues/useDialogue'
+import type { PostImportEditableDraft, PostImportRow } from '@/lib/postImportTypes'
 
 type Draft = PostImportEditableDraft
 
@@ -23,15 +23,18 @@ type Props = {
 			     saved: boolean
 			     row:   PostImportRow | null }> }
 
+const THUMBNAIL_MISSING_WARNING = 'サムネールなし'
+
 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 ?? '') })
+    parentPostIds: String (row.attributes.parentPostIds ?? ''),
+    duration: String (row.attributes.duration ?? ''),
+    thumbnailFile: row.thumbnailFile })
 
 const buildResetDraft = (row: PostImportRow): Draft => ({
     url: row.resetSnapshot.url,
@@ -39,9 +42,10 @@ const buildResetDraft = (row: PostImportRow): Draft => ({
     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 ?? '') })
+    parentPostIds: String (row.resetSnapshot.attributes.parentPostIds ?? ''),
+    duration: String (row.resetSnapshot.attributes.duration ?? ''),
+    thumbnailFile: undefined })
 
 const groupedMessages = (...values: (string[] | undefined)[]): string[] =>
     [...new Set (values.flatMap (value => value ?? []))]
@@ -52,9 +56,10 @@ const sameDraft = (left:  Draft, right: Draft): boolean =>
     && left.thumbnailBase === right.thumbnailBase
     && left.originalCreatedFrom === right.originalCreatedFrom
     && left.originalCreatedBefore === right.originalCreatedBefore
-    && left.duration === right.duration
     && left.tags === right.tags
     && left.parentPostIds === right.parentPostIds
+    && left.duration === right.duration
+    && left.thumbnailFile === right.thumbnailFile
 
 const sameProvenance = (
     current: PostImportRow['provenance'],
@@ -69,6 +74,24 @@ const sameTagSources = (
     (current?.automatic ?? '') === reset.automatic
     && (current?.manual ?? '') === reset.manual
 
+const sameWarnings = (
+    current: PostImportRow,
+    reset:   PostImportRow['resetSnapshot'],
+): boolean =>
+    JSON.stringify (current.fieldWarnings) === JSON.stringify (reset.fieldWarnings)
+    && JSON.stringify (current.baseWarnings) === JSON.stringify (reset.baseWarnings)
+
+const thumbnailWarnings = (
+    messages:       string[] | undefined,
+    thumbnailBase:  string,
+    thumbnailFile:  File | undefined,
+): string[] => {
+  const others = (messages ?? []).filter (message => message !== THUMBNAIL_MISSING_WARNING)
+  return hasThumbnailBaseValue (thumbnailBase) || thumbnailFile != null
+      ? others
+      : [...new Set ([...others, THUMBNAIL_MISSING_WARNING])]
+}
+
 
 const PostImportRowForm: FC<Props> = (
     { row,
@@ -79,24 +102,33 @@ const PostImportRowForm: FC<Props> = (
   const [messageRow, setMessageRow] = useState<PostImportRow | null> (null)
   const [saving, setSaving] = useState (false)
   const [resetRequested, setResetRequested] = useState (false)
+  const [committedThumbnailBase, setCommittedThumbnailBase] = useState (
+      () => String (row.attributes.thumbnailBase ?? ''))
 
   useEffect (() => {
     const nextDraft = buildDraft (row)
     setDraft (nextDraft)
     setMessageRow (null)
     setResetRequested (false)
+    setCommittedThumbnailBase (String (row.attributes.thumbnailBase ?? ''))
   }, [row])
 
   const displayRow = messageRow ?? row
   const resetDraft = useMemo (
       () => buildResetDraft (row),
       [row])
+  const durationVisible = hasVideoTag (draft.tags)
+  const currentThumbnailWarnings = thumbnailWarnings (
+      displayRow.fieldWarnings.thumbnailBase,
+      draft.thumbnailBase,
+      draft.thumbnailFile)
   const resetDisabled =
       saving
       || (sameDraft (draft, resetDraft)
           && sameProvenance (row.provenance, row.resetSnapshot.provenance)
           && sameTagSources (row.tagSources, row.resetSnapshot.tagSources)
-          && row.metadataUrl === row.resetSnapshot.metadataUrl)
+          && row.metadataUrl === row.resetSnapshot.metadataUrl
+          && sameWarnings (displayRow, row.resetSnapshot))
 
   const update = <Key extends keyof Draft,> (
       key:   Key,
@@ -113,7 +145,6 @@ const PostImportRowForm: FC<Props> = (
 
     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' })
@@ -123,6 +154,7 @@ const PostImportRowForm: FC<Props> = (
     setDraft (resetDraft)
     setResetRequested (true)
     setMessageRow (null)
+    setCommittedThumbnailBase (resetDraft.thumbnailBase)
     return false
   }, [controls, resetDisabled, resetDraft])
 
@@ -164,77 +196,103 @@ const PostImportRowForm: FC<Props> = (
 	    <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}
+		    url={committedThumbnailBase}
+		    file={
+			hasThumbnailBaseValue (committedThumbnailBase)
+			? undefined
+			: draft.thumbnailFile}
 		    className="h-28 w-28"/>
 	      </div>
 
 	      <div className="space-y-4">
-		<PostTextField
+		<PostCreationDataFields
-		    label="URL"
+		    url={{
-		    value={draft.url}
+			value: draft.url,
-		    disabled={saving}
+			onChange: value => update ('url', value),
-		    warnings={displayRow.fieldWarnings.url}
+			disabled: saving,
-		    errors={groupedMessages (
+			warnings: displayRow.fieldWarnings.url,
-			displayRow.validationErrors.url,
+			errors: groupedMessages (
-			displayRow.importErrors?.url)}
+			    displayRow.validationErrors.url,
-		    onChange={value => update ('url', value)}/>
+			    displayRow.importErrors?.url) }}
-		<PostTextField
+		    thumbnailField={
-		    label="タイトル"
+			<>
-		    value={draft.title}
+			  <PostTextField
-		    disabled={saving}
+			      label="サムネール"
-		    warnings={displayRow.fieldWarnings.title}
+			      value={draft.thumbnailBase}
-		    errors={groupedMessages (
+			      disabled={saving}
-			displayRow.validationErrors.title,
+			      warnings={currentThumbnailWarnings}
-			displayRow.importErrors?.title)}
+			      errors={groupedMessages (
-		    onChange={value => update ('title', value)}/>
+				  displayRow.validationErrors.thumbnailBase,
-		<PostTextField
+				  displayRow.importErrors?.thumbnailBase)}
-		    label="サムネール基底 URL"
+			      onBlur={() => {
-		    value={draft.thumbnailBase}
+				if (draft.thumbnailBase.trim () !== committedThumbnailBase.trim ())
-		    disabled={saving}
+				  setCommittedThumbnailBase (draft.thumbnailBase)
-		    warnings={displayRow.fieldWarnings.thumbnailBase}
+			      }}
-		    errors={groupedMessages (
+			      onChange={value => update ('thumbnailBase', value)}/>
-			displayRow.validationErrors.thumbnailBase,
+			  {!(hasThumbnailBaseValue (draft.thumbnailBase)) && (
-			displayRow.importErrors?.thumbnailBase)}
+			      <input
-		    onChange={value => update ('thumbnailBase', value)}/>
+				  type="file"
-		<PostOriginalCreatedTimeField
+				  accept="image/*"
-		    disabled={saving}
+				  disabled={saving}
-		    originalCreatedFrom={draft.originalCreatedFrom || null}
+				  onChange={event => {
-		    setOriginalCreatedFrom={value => update ('originalCreatedFrom', value ?? '')}
+				    const file = event.target.files?.[0]
-		    originalCreatedBefore={draft.originalCreatedBefore || null}
+				    update ('thumbnailFile', file)
-		    setOriginalCreatedBefore={value => update ('originalCreatedBefore', value ?? '')}
+				  }}/>)}
-		    errors={groupedMessages (
+			</>}
-			displayRow.validationErrors.originalCreatedAt,
+		    core={{
-			displayRow.validationErrors.originalCreatedFrom,
+			title: {
-			displayRow.validationErrors.originalCreatedBefore,
+			    value: draft.title,
-			displayRow.importErrors?.originalCreatedAt,
+			    onChange: value => update ('title', value),
-			displayRow.importErrors?.originalCreatedFrom,
+			    disabled: saving,
-			displayRow.importErrors?.originalCreatedBefore)}/>
+			    warnings: displayRow.fieldWarnings.title,
-		<PostDurationField
+			    errors: groupedMessages (
-		    value={draft.duration}
+				displayRow.validationErrors.title,
-		    disabled={saving}
+				displayRow.importErrors?.title) },
-		    errors={groupedMessages (
+			originalCreated: {
-			displayRow.validationErrors.duration,
+			    disabled: saving,
-			displayRow.validationErrors.videoMs,
+			    originalCreatedFrom: draft.originalCreatedFrom || null,
-			displayRow.importErrors?.duration,
+			    setOriginalCreatedFrom: value =>
-			displayRow.importErrors?.videoMs)}
+				update ('originalCreatedFrom', value ?? ''),
-		    onChange={value => update ('duration', value)}/>
+			    originalCreatedBefore: draft.originalCreatedBefore || null,
-		<PostTagsField
+			    setOriginalCreatedBefore: value =>
-		    tags={draft.tags}
+				update ('originalCreatedBefore', value ?? ''),
-		    disabled={saving}
+			    errors: {
-		    setTags={value => update ('tags', value)}
+				originalCreatedAt: groupedMessages (
-		    warnings={displayRow.fieldWarnings.tags}
+				    displayRow.validationErrors.originalCreatedAt,
-		    errors={groupedMessages (
+				    displayRow.importErrors?.originalCreatedAt),
-			displayRow.validationErrors.tags,
+				originalCreatedFrom: groupedMessages (
-			displayRow.importErrors?.tags)}
+				    displayRow.validationErrors.originalCreatedFrom,
-		    rows={4}/>
+				    displayRow.importErrors?.originalCreatedFrom),
-		<PostTextField
+				originalCreatedBefore: groupedMessages (
-		    label="親投稿"
+				    displayRow.validationErrors.originalCreatedBefore,
-		    value={draft.parentPostIds}
+				    displayRow.importErrors?.originalCreatedBefore) } },
-		    disabled={saving}
+			tags: {
-		    errors={groupedMessages (
+			    value: draft.tags,
-			displayRow.validationErrors.parentPostIds,
+			    onChange: value => update ('tags', value),
-			displayRow.importErrors?.parentPostIds)}
+			    disabled: saving,
-		    onChange={value => update ('parentPostIds', value)}/>
+			    warnings: displayRow.fieldWarnings.tags,
+			    errors: groupedMessages (
+				displayRow.validationErrors.tags,
+				displayRow.importErrors?.tags),
+			    rows: 4 },
+			parentPostIds: {
+			    value: draft.parentPostIds,
+			    onChange: value => update ('parentPostIds', value),
+			    disabled: saving,
+			    errors: groupedMessages (
+				displayRow.validationErrors.parentPostIds,
+				displayRow.importErrors?.parentPostIds) } }}
+		    extraFields={
+			durationVisible
+			? (
+			    <PostDurationField
+				value={draft.duration}
+				onChange={value => update ('duration', value)}
+				disabled={saving}
+				errors={groupedMessages (
+				    displayRow.validationErrors.videoMs,
+				    displayRow.importErrors?.videoMs)}/>)
+			: null}/>
 		<FieldWarning messages={displayRow.baseWarnings}/>
 		<FieldError messages={displayRow.validationErrors.base}/>
 		<FieldError messages={displayRow.importErrors?.base}/>

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

@@ -1,18 +1,32 @@
+import FieldError from '@/components/common/FieldError'
+import PostImportTagLinks from '@/components/posts/import/PostImportTagLinks'
 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 {
+    canEditReviewRow,
+    canRetryResultRow,
+    hasVideoTag,
+} from '@/lib/postImportRows'
 import { cn, originalCreatedAtString } from '@/lib/utils'
 
 import type { FC } from 'react'
 
-import type { PostImportRow } from '@/lib/postImportSession'
+import type { PostImportRow } from '@/lib/postImportTypes'
 
 type Props = {
-    row:           PostImportRow
+    row:	      PostImportRow
-    onEdit:        () => void
+    displayNumber?:   number
-    editDisabled?: boolean }
+    onEdit?:	      () => void
+    onRetry?:	      () => void
+    onToggleSkip?:    (checked: boolean) => void
+    rowMessages?:     string[]
+    editDisabled?:    boolean
+    retryDisabled?:   boolean
+    skipDisabled?:    boolean
+    showActions?:     boolean
+    showSkipToggle?:  boolean }
 
 const summaryWarning = (row: PostImportRow): string | null =>
     Object.values (row.fieldWarnings ?? { }).flat ()[0]
@@ -25,95 +39,159 @@ const summaryDate = (row: PostImportRow): string =>
 	row.attributes.originalCreatedBefore?.toString () ?? null)
 
 
-const PostImportRowSummary: FC<Props> = ({ row, onEdit, editDisabled }) => {
+const PostImportRowSummary: FC<Props> = (
+    { row,
+      displayNumber,
+      onEdit,
+      onRetry,
+      onToggleSkip,
+      rowMessages,
+      editDisabled,
+      retryDisabled,
+      skipDisabled,
+      showActions = true,
+      showSkipToggle = false },
+) => {
   const warning = summaryWarning (row)
   const displayStatus = displayPostImportStatus (row)
+  const editVisible = onEdit != null
+  const editAllowed = editVisible && canEditReviewRow (row)
+  const retryAllowed = onRetry != null && canRetryResultRow (row)
+  const skipChecked = row.skipReason === 'manual'
+  const rowNumber = displayNumber ?? row.sourceRow
+  const duration = String (row.attributes.duration ?? '')
+  const showDuration = hasVideoTag (row.attributes.tags) && duration !== ''
+  const skipControl = showSkipToggle
+      ? (
+	  <label className="flex items-center gap-2 text-sm">
+	    <input
+		type="checkbox"
+		checked={skipChecked}
+		onChange={event => onToggleSkip?.(event.target.checked)}
+		disabled={skipDisabled === true}/>
+	    <span>スキップ</span>
+	  </label>)
+      : null
 
   return (
       <>
-        <div
+	<div
-            className={cn (
+	    className={cn (
-                'hidden items-center gap-4 rounded-lg border p-4 md:grid',
+		'hidden items-center gap-4 rounded-lg border p-4 md:grid',
-                'md:grid-cols-[4rem_5rem_minmax(0,1fr)_auto_auto]',
+		'md:grid-cols-[4rem_5rem_minmax(0,1fr)_auto_auto]',
-                'transition-shadow hover:shadow-sm')}>
+		'transition-shadow hover:shadow-sm')}>
-          <div className="space-y-1">
+	  <div className="space-y-1">
-            <div className="text-sm font-medium">#{row.sourceRow}</div>
+	    <div className="text-sm font-medium">#{rowNumber}</div>
-          </div>
+	  </div>
-          <PostImportThumbnailPreview
+	  <PostImportThumbnailPreview
-              url={String (row.attributes.thumbnailBase ?? '')}
+	      url={String (row.attributes.thumbnailBase ?? '')}
-              className="h-16 w-16"/>
+	      file={row.thumbnailFile}
-          <div className="min-w-0 space-y-1">
+	      className="h-16 w-16"/>
-            <div className="line-clamp-2 text-sm font-medium">
+	  <div className="min-w-0 space-y-1">
-              {String (row.attributes.title ?? '') || '（タイトル未取得）'}
+	    <div className="line-clamp-2 text-sm font-medium">
-            </div>
+	      {String (row.attributes.title ?? '')}
-            <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
+	    </div>
-              {row.url}
+	    <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
-            </div>
+	      {row.url}
-            <div className="truncate text-xs text-neutral-500 dark:text-neutral-400">
+	    </div>
-              {String (row.attributes.tags ?? '') || 'タグなし'}
+	    <PostImportTagLinks tags={row.displayTags}/>
-            </div>
+	    <div className="text-xs text-neutral-500 dark:text-neutral-400">
-            <div className="text-xs text-neutral-500 dark:text-neutral-400">
+	      {summaryDate (row)}
-              {summaryDate (row)}
+	    </div>
-              {row.attributes.duration ? ` / ${ row.attributes.duration }` : ''}
+	    {showDuration && (
-            </div>
+		<div className="text-xs text-neutral-500 dark:text-neutral-400">
-            {warning && (
+		  動画時間 {duration}
-                <div className="text-xs text-amber-700 dark:text-amber-200">
+		</div>)}
-                  {warning}
+	    {warning && (
-                </div>)}
+		<div className="text-xs text-amber-700 dark:text-amber-200">
-          </div>
+		  {warning}
-          <div className="space-y-1">
+		</div>)}
-            {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
+	    <FieldError messages={rowMessages}/>
-          </div>
+	  </div>
-          <div className="flex justify-end">
+	  <div className="space-y-1">
-            <Button
+	    {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
-                type="button"
+	  </div>
-                variant="outline"
+	  <div className="flex justify-end">
-                onClick={onEdit}
+	    <div className="flex items-center gap-2">
-                disabled={!(canEditReviewRow (row)) || editDisabled === true}>
+	      {skipControl}
-              編輯
+	      {showActions && editVisible && (
-            </Button>
+		  <Button
-          </div>
+		      type="button"
-        </div>
+		      variant="outline"
+		      onClick={onEdit}
+		      disabled={editDisabled === true || !(editAllowed)}>
+		    編輯
+		  </Button>)}
+	      {showActions && retryAllowed && (
+		  <Button
+		      type="button"
+		      variant="outline"
+		      onClick={onRetry}
+		      disabled={retryDisabled === true}>
+		    再試行
+		  </Button>)}
+	    </div>
+	  </div>
+	</div>
 
-        <div
+	<div
-            className={cn (
+	    className={cn (
-                'space-y-3 rounded-lg border p-4 md:hidden',
+		'space-y-3 rounded-lg border p-4 md:hidden',
-                'transition-shadow hover:shadow-sm')}>
+		'transition-shadow hover:shadow-sm')}>
-          <div className="flex items-start gap-3">
+	  <div className="text-sm font-medium">#{rowNumber}</div>
-            <PostImportThumbnailPreview
+	  <div className="flex items-start gap-3">
-                url={String (row.attributes.thumbnailBase ?? '')}
+	    <PostImportThumbnailPreview
-                className="h-20 w-20 shrink-0"/>
+		url={String (row.attributes.thumbnailBase ?? '')}
-            <div className="min-w-0 flex-1 space-y-2">
+		file={row.thumbnailFile}
-              <div className="line-clamp-2 text-sm font-medium">
+		className="h-20 w-20 shrink-0"/>
-                {String (row.attributes.title ?? '') || '（タイトル未取得）'}
+	    <div className="min-w-0 flex-1 space-y-2">
-              </div>
+	      <div className="line-clamp-2 text-sm font-medium">
-              <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
+		{String (row.attributes.title ?? '')}
-                {row.url}
+	      </div>
-              </div>
+	      <div className="truncate text-xs text-neutral-600 dark:text-neutral-300">
-              <div className="flex flex-wrap gap-2">
+		{row.url}
-                {displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
+	      </div>
-              </div>
+	      <div className="flex flex-wrap gap-2">
-              <div className="text-xs text-neutral-500 dark:text-neutral-400">
+		{displayStatus != null && <PostImportStatusBadge value={displayStatus}/>}
-                {String (row.attributes.tags ?? '') || 'タグなし'}
+	      </div>
-              </div>
+	      <PostImportTagLinks tags={row.displayTags}/>
-              <div className="text-xs text-neutral-500 dark:text-neutral-400">
+	      <div className="text-xs text-neutral-500 dark:text-neutral-400">
-                {summaryDate (row)}
+		{summaryDate (row)}
-                {row.attributes.duration ? ` / ${ row.attributes.duration }` : ''}
+	      </div>
-              </div>
+	      {showDuration && (
-              {warning && (
+		  <div className="text-xs text-neutral-500 dark:text-neutral-400">
-                  <div className="text-xs text-amber-700 dark:text-amber-200">
+		    動画時間 {duration}
-                    {warning}
+		  </div>)}
-                  </div>)}
+	      {warning && (
-            </div>
+		  <div className="text-xs text-amber-700 dark:text-amber-200">
-          </div>
+		    {warning}
-          <Button
+		  </div>)}
-              type="button"
+	      <FieldError messages={rowMessages}/>
-              variant="outline"
+	      {skipControl}
-              onClick={onEdit}
+	    </div>
-              disabled={!(canEditReviewRow (row)) || editDisabled === true}>
+	  </div>
-            編輯
+	  {showActions && (editVisible || retryAllowed) && (
-          </Button>
+	      <div className="flex flex-col gap-2 md:flex-row">
-        </div>
+		{editVisible && (
+		    <Button
+			type="button"
+			className="w-full md:w-auto"
+			variant="outline"
+			onClick={onEdit}
+			disabled={editDisabled === true || !(editAllowed)}>
+		      編輯
+		    </Button>)}
+		{retryAllowed && (
+		    <Button
+			type="button"
+			className="w-full md:w-auto"
+			variant="outline"
+			onClick={onRetry}
+			disabled={retryDisabled === true}>
+		      再試行
+		    </Button>)}
+	      </div>)}
+	</div>
       </>)
 }
 

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

@@ -10,13 +10,19 @@ type Props = {
 
 const LABELS: Record<PostImportBadgeValue, string> = {
     ready: '登録可能',
+    error: '登録不可',
     warning: '警告',
-    skipped: 'スキップ' }
+    skipped: 'スキップ',
+    created: '登録済み',
+    failed: '登録失敗' }
 
 const TONES: Record<PostImportBadgeValue, StatusBadgeTone> = {
     ready: 'success',
+    error: 'warning',
     warning: 'warning',
-    skipped: 'neutral' }
+    skipped: 'neutral',
+    created: 'success',
+    failed: 'warning' }
 
 
 const PostImportStatusBadge: FC<Props> = ({ value }) => (

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

@@ -0,0 +1,36 @@
+import TagLink from '@/components/TagLink'
+
+import type { FC } from 'react'
+
+import type { PostImportDisplayTag } from '@/lib/postImportTypes'
+
+type Props = {
+  tags: PostImportDisplayTag[] | undefined }
+
+const PostImportTagLinks: FC<Props> = ({ tags }) => {
+  if (tags == null || tags.length === 0)
+    return null
+
+  return (
+      <div className="flex flex-wrap text-xs gap-x-1">
+	{tags.map (tag => {
+	  const key = `${ tag.category }:${ tag.name }:${ tag.sectionLiterals?.join ('|') ?? '' }`
+	  return (
+	      <span key={key} className="inline-flex flex-nowrap items-baseline gap-1">
+		<TagLink
+		    tag={{
+			name: tag.name,
+			category: tag.category }}
+		    linkFlg={false}
+		    withWiki={false}
+		    withCount={false}/>
+		{tag.sectionLiterals?.map (literal => (
+		    <span key={literal} className="text-xs text-neutral-500 dark:text-neutral-400">
+		      {literal}
+		    </span>))}
+	      </span>)
+	})}
+      </div>)
+}
+
+export default PostImportTagLinks

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

@@ -1,14 +1,8 @@
-import { render, screen, waitFor } from '@testing-library/react'
+import { fireEvent, render, screen } 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 ()
@@ -16,63 +10,50 @@ describe ('PostImportThumbnailPreview', () => {
     globalThis.URL.revokeObjectURL = vi.fn ()
   })
 
-  it ('uses a backend-fetched blob URL instead of the external thumbnail URL directly', async () => {
+  it ('renders the remote URL directly without a backend proxy', () => {
-    api.apiGet.mockResolvedValueOnce (new Blob (['img'], { type: 'image/png' }))
-
     render (
-        <PostImportThumbnailPreview
+	<PostImportThumbnailPreview
-            url="https://example.com/thumbnail.jpg"
+	    url="https://example.com/thumbnail.jpg"
-            className="h-10 w-10"/>)
+	    className="h-10 w-10"/>)
 
-    await waitFor (() => {
+    expect (screen.getByRole ('img')).toHaveAttribute (
-      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
+	'src',
-    })
+	'https://example.com/thumbnail.jpg')
-    expect (screen.getByRole ('img')).not.toHaveAttribute (
+    expect (screen.getByRole ('img')).toHaveAttribute (
-        'src',
+	'referrerpolicy',
-        'https://example.com/thumbnail.jpg')
+	'no-referrer')
-    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 () => {
+  it ('shows the empty frame after the remote image fails', () => {
-    api.apiGet.mockRejectedValueOnce (new Error ('unsafe'))
+    const { container } = render (
+	<PostImportThumbnailPreview
+	    url="https://example.com/missing.jpg"
+	    className="h-10 w-10"/>)
 
-    render (
+    fireEvent.error (screen.getByRole ('img'))
-        <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 ()
+    expect (container.querySelector ('div.rounded.border.bg-muted')).not.toBeNull ()
+    expect (container.textContent).toBe ('')
   })
 
-  it ('revokes the old object URL when the source URL changes', async () => {
+  it ('uses and revokes an object URL only when the remote URL is blank', () => {
-    const createObjectUrlMock =
+    const file = new File (['image'], 'thumbnail.png', { type: 'image/png' })
-        globalThis.URL.createObjectURL as unknown as ReturnType<typeof vi.fn>
+    const { rerender, unmount } = render (
-    createObjectUrlMock
+	<PostImportThumbnailPreview url="" file={file} className="h-10 w-10"/>)
-        .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 (
+    expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:preview')
-        <PostImportThumbnailPreview
-            url="https://example.com/first.jpg"
-            className="h-10 w-10"/>)
-    await waitFor (() => {
-      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:first')
-    })
 
     rerender (
-        <PostImportThumbnailPreview
+	<PostImportThumbnailPreview
-            url="https://example.com/second.jpg"
+	    url="https://example.com/remote.jpg"
-            className="h-10 w-10"/>)
+	    file={file}
+	    className="h-10 w-10"/>)
+    expect (screen.getByRole ('img')).toHaveAttribute (
+	'src',
+	'https://example.com/remote.jpg')
 
-    await waitFor (() => {
+    unmount ()
-      expect (screen.getByRole ('img')).toHaveAttribute ('src', 'blob:second')
+    expect (globalThis.URL.revokeObjectURL).toHaveBeenCalledWith ('blob:preview')
-    })
-    expect (globalThis.URL.revokeObjectURL).toHaveBeenCalledWith ('blob:first')
   })
 })

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

@@ -1,89 +1,25 @@
-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
+  file?:      File
   alt?:       string
   className?: string }
 
 
 const PostImportThumbnailPreview: FC<Props> = (
     { url,
+      file,
       alt = 'サムネール',
       className = 'h-16 w-16' },
-) => {
+) => (
-  const [previewUrl, setPreviewUrl] = useState ('')
+    <PostThumbnailPreview
-  const [unavailable, setUnavailable] = useState (false)
+        url={url}
-  const previewUrlRef = useRef ('')
+        file={file}
-
+        alt={alt}
-  useEffect (() => {
+        className={className}
-    if (previewUrlRef.current)
+        referrerPolicy="no-referrer"/>)
-      {
-        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

@@ -12,16 +12,18 @@ describe ('displayPostImportStatus', () => {
     expect (displayPostImportStatus (buildPostImportRow ({
       skipReason: 'existing',
       existingPostId: 2 }))).toBe ('skipped')
+    expect (displayPostImportStatus (buildPostImportRow ({
+      skipReason: 'manual' }))).toBe ('skipped')
   })
 
-  it ('does not expose validation, failure, or created states as badges', () => {
+  it ('distinguishes validation, failure, and created states', () => {
     expect (displayPostImportStatus (buildPostImportRow ({
       status: 'error',
-      validationErrors: { title: ['invalid'] } }))).toBeNull ()
+      validationErrors: { title: ['invalid'] } }))).toBe ('error')
     expect (displayPostImportStatus (buildPostImportRow ({
-      importStatus: 'failed' }))).toBeNull ()
+      importStatus: 'failed' }))).toBe ('failed')
     expect (displayPostImportStatus (buildPostImportRow ({
       importStatus: 'created',
-      createdPostId: 3 }))).toBeNull ()
+      createdPostId: 3 }))).toBe ('created')
   })
 })

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

@@ -1,6 +1,12 @@
-import type { PostImportRow } from '@/lib/postImportSession'
+import type { PostImportRow } from '@/lib/postImportTypes'
 
-export type PostImportDisplayStatus = 'ready' | 'skipped' | 'warning'
+export type PostImportDisplayStatus =
+    'ready'
+    | 'error'
+    | 'skipped'
+    | 'warning'
+    | 'created'
+    | 'failed'
 
 export type PostImportBadgeValue = PostImportDisplayStatus
 
@@ -11,12 +17,18 @@ const hasWarnings = (row: PostImportRow): boolean =>
 export const displayPostImportStatus = (
     row: PostImportRow,
 ): PostImportDisplayStatus | null =>
-    (row.skipReason === 'existing' || row.importStatus === 'skipped')
+    row.status === 'pending'
+    ? null
+    : (row.importStatus === 'failed')
+    ? 'failed'
+    : (row.skipReason != null || row.importStatus === 'skipped')
     ? 'skipped'
-    : ((Object.keys (row.validationErrors ?? { }).length > 0
+    : (row.importStatus === 'created')
-	|| row.importStatus === 'failed'
+      ? 'created'
-	|| row.importStatus === 'created')
+      : (row.status === 'error')
-       ? null
+      ? 'error'
-       : ((hasWarnings (row) || row.status === 'warning')
+      : (Object.values (row.validationErrors ?? { }).some (messages => messages.length > 0))
-	  ? 'warning'
+      ? 'error'
-	  : 'ready'))
+      : ((hasWarnings (row) || row.status === 'warning')
+	 ? 'warning'
+	 : 'ready')

frontend/src/components/ui/dialog.tsx

@@ -1,10 +1,10 @@
-"use client"
+'use client'
 
-import * as React from "react"
+import * as DialogPrimitive from '@radix-ui/react-dialog'
-import * as DialogPrimitive from "@radix-ui/react-dialog"
+import { X } from 'lucide-react'
-import { X } from "lucide-react"
+import * as React from 'react'
 
-import { cn } from "@/lib/utils"
+import { cn } from '@/lib/utils'
 
 const Dialog = DialogPrimitive.Root
 
@@ -15,111 +15,109 @@ const DialogPortal = DialogPrimitive.Portal
 const DialogClose = DialogPrimitive.Close
 
 const DialogOverlay = React.forwardRef<
-  React.ElementRef<typeof DialogPrimitive.Overlay>,
+    React.ElementRef<typeof DialogPrimitive.Overlay>,
-  React.ComponentPropsWithoutRef<typeof DialogPrimitive.Overlay>
+    React.ComponentPropsWithoutRef<typeof DialogPrimitive.Overlay>
->(({ className, ...props }, ref) => (
+>(
-  <DialogPrimitive.Overlay
+    ({ className, ...props }, ref) => (
-    ref={ref}
+	<DialogPrimitive.Overlay
-    className={cn(
+	    ref={ref}
-      "fixed inset-0 z-50 bg-black/80 data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0",
+	    className={cn (
-      className)}
+		'fixed inset-0 z-50 bg-black/80',
-    {...props}
+		'data-[state=open]:animate-in data-[state=closed]:animate-out',
-  />))
+		'data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0',
+		className)}
+	    {...props}/>))
 DialogOverlay.displayName = DialogPrimitive.Overlay.displayName
 
 const DialogContent = React.forwardRef<
-  React.ElementRef<typeof DialogPrimitive.Content>,
+    React.ElementRef<typeof DialogPrimitive.Content>,
-  React.ComponentPropsWithoutRef<typeof DialogPrimitive.Content>
+    React.ComponentPropsWithoutRef<typeof DialogPrimitive.Content>
->(({ className, children, ...props }, ref) => (
+>(
-  <DialogPortal>
+    ({ className, children, ...props }, ref) => (
-    <DialogOverlay />
+	<DialogPortal>
-    <DialogPrimitive.Content
+	  <DialogOverlay />
-      ref={ref}
+	  <DialogPrimitive.Content
-      className={cn (
+	      ref={ref}
-	  'fixed left-[50%] top-[50%] z-50 grid w-[calc(100%-2rem)] max-w-lg',
+	      className={cn (
-	  'translate-x-[-50%] translate-y-[-50%]',
+		  'fixed left-[50%] top-[50%] z-50 grid w-[calc(100%-2rem)] max-w-lg',
-	  'gap-5 rounded-2xl border border-border',
+		  'translate-x-[-50%] translate-y-[-50%]',
-	  'bg-background p-6 text-foreground shadow-2xl',
+		  'gap-5 rounded-2xl border border-border',
-	  'duration-200',
+		  'bg-background p-6 text-foreground shadow-2xl',
-	  'data-[state=open]:animate-in data-[state=closed]:animate-out',
+		  'duration-200',
-	  'data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0',
+		  'data-[state=open]:animate-in data-[state=closed]:animate-out',
-	  'data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95',
+		  'data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0',
-	  className)}
+		  'data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95',
-      {...props}
+		  className)}
-    >
+	      {...props}>
-      {children}
+	    {children}
 
-      <DialogPrimitive.Close
+	    <DialogPrimitive.Close
-	  className={cn (
+		className={cn (
-	      'absolute left-4 top-4 rounded-full p-1',
+		    'absolute left-4 top-4 rounded-full p-1',
-	      'text-slate-500 transition-colors',
+		    'text-slate-500 transition-colors',
-	      'hover:bg-slate-200 hover:text-slate-900',
+		    'hover:bg-slate-200 hover:text-slate-900',
-	      'dark:text-slate-400 dark:hover:bg-slate-700 dark:hover:text-slate-50',
+		    'dark:text-slate-400 dark:hover:bg-slate-700 dark:hover:text-slate-50',
-	      'focus:outline-none focus:ring-2 focus:ring-slate-400')}>
+		    'focus:outline-none focus:ring-2 focus:ring-slate-400')}>
-	<X className="h-4 w-4"/>
+	      <X className="h-4 w-4"/>
-	<span className="sr-only">閉ぢる</span>
+	      <span className="sr-only">閉ぢる</span>
-      </DialogPrimitive.Close>
+	    </DialogPrimitive.Close>
-    </DialogPrimitive.Content>
+	  </DialogPrimitive.Content>
-  </DialogPortal>))
+	</DialogPortal>))
 DialogContent.displayName = DialogPrimitive.Content.displayName
 
-const DialogHeader = ({
+const DialogHeader = (
-  className,
+    { className, ...props }: React.HTMLAttributes<HTMLDivElement>,
-  ...props
+) => (
-}: React.HTMLAttributes<HTMLDivElement>) => (
+    <div
-  <div
+	className={cn (
-    className={cn(
+	    'flex flex-col space-y-1.5 text-center md:text-left',
-      "flex flex-col space-y-1.5 text-center sm:text-left",
+	    className)}
-      className)}
+	{...props}/>)
-    {...props}
+DialogHeader.displayName = 'DialogHeader'
-  />)
-DialogHeader.displayName = "DialogHeader"
 
-const DialogFooter = ({
+const DialogFooter = (
-  className,
+    { className, ...props }: React.HTMLAttributes<HTMLDivElement>,
-  ...props
+) => (
-}: React.HTMLAttributes<HTMLDivElement>) => (
+    <div
-  <div
+	className={cn (
-    className={cn(
+	    'flex flex-col-reverse md:flex-row md:justify-end md:space-x-2',
-      "flex flex-col-reverse sm:flex-row sm:justify-end sm:space-x-2",
+	    className)}
-      className)}
+	{...props}/>)
-    {...props}
+DialogFooter.displayName = 'DialogFooter'
-  />)
-DialogFooter.displayName = "DialogFooter"
 
 const DialogTitle = React.forwardRef<
-  React.ElementRef<typeof DialogPrimitive.Title>,
+    React.ElementRef<typeof DialogPrimitive.Title>,
-  React.ComponentPropsWithoutRef<typeof DialogPrimitive.Title>
+    React.ComponentPropsWithoutRef<typeof DialogPrimitive.Title>
->(({ className, ...props }, ref) => (
+>(
-  <DialogPrimitive.Title
+    ({ className, ...props }, ref) => (
-    ref={ref}
+	<DialogPrimitive.Title
-    className={cn(
+	    ref={ref}
-      "text-lg font-semibold leading-none tracking-tight",
+	    className={cn (
-      className)}
+		'text-lg font-semibold leading-none tracking-tight',
-    {...props}
+		className)}
-  />))
+	    {...props}/>))
 DialogTitle.displayName = DialogPrimitive.Title.displayName
 
 const DialogDescription = React.forwardRef<
-  React.ElementRef<typeof DialogPrimitive.Description>,
+    React.ElementRef<typeof DialogPrimitive.Description>,
-  React.ComponentPropsWithoutRef<typeof DialogPrimitive.Description>
+    React.ComponentPropsWithoutRef<typeof DialogPrimitive.Description>
->(({ className, ...props }, ref) => (
+>(
-  <DialogPrimitive.Description
+    ({ className, ...props }, ref) => (
-    ref={ref}
+	<DialogPrimitive.Description
-    className={cn("text-sm text-muted-foreground", className)}
+	    ref={ref}
-    {...props}
+	    className={cn ('text-sm text-muted-foreground', className)}
-  />))
+	    {...props}/>))
 DialogDescription.displayName = DialogPrimitive.Description.displayName
 
 export {
-  Dialog,
+    Dialog,
-  DialogPortal,
+    DialogPortal,
-  DialogOverlay,
+    DialogOverlay,
-  DialogClose,
+    DialogClose,
-  DialogTrigger,
+    DialogTrigger,
-  DialogContent,
+    DialogContent,
-  DialogHeader,
+    DialogHeader,
-  DialogFooter,
+    DialogFooter,
-  DialogTitle,
+    DialogTitle,
-  DialogDescription,
+    DialogDescription,
 }

frontend/src/lib/api.ts

@@ -8,6 +8,7 @@ import type { AxiosError, AxiosRequestConfig } from 'axios'
 type Opt = {
     params?:        AxiosRequestConfig['params']
     headers?:       Record<string, string>
+    signal?:        AbortSignal
     responseType?:  'blob' }
 
 const client = axios.create ({ baseURL: API_BASE_URL })

frontend/src/lib/postImportRows.test.ts

@@ -16,7 +16,7 @@ import { creatableImportRows,
 	 resultRowMessages,
 	 resultSummaryCounts,
 	 retryImportRow,
-	 reviewSummaryCounts } from '@/lib/postImportSession'
+	 reviewSummaryCounts } from '@/lib/postImportRows'
 import { buildPostImportRow } from '@/test/postImportFactories'
 
 describe ('post import row state', () => {
@@ -26,22 +26,26 @@ describe ('post import row state', () => {
       sourceRow: 2,
       skipReason: 'existing',
       existingPostId: 20 })
-    const invalid = buildPostImportRow ({
+    const manual = buildPostImportRow ({
       sourceRow: 3,
+      skipReason: 'manual' })
+    const invalid = buildPostImportRow ({
+      sourceRow: 4,
       status: 'error',
       validationErrors: { url: ['invalid'] } })
     const created = buildPostImportRow ({
-      sourceRow: 4,
+      sourceRow: 5,
       importStatus: 'created',
       createdPostId: 40 })
-    const rows = [ready, existing, invalid, created]
+    const rows = [ready, existing, manual, invalid, created]
 
-    expect (processableImportRows (rows)).toEqual ([ready, existing])
+    expect (processableImportRows (rows)).toEqual ([ready])
     expect (creatableImportRows (rows)).toEqual ([ready])
     expect (reviewSummaryCounts (rows)).toEqual ({
-      total: 4,
+      creatable: 1,
-      submittable: 1,
+      manualSkipped: 1,
-      skipPlanned: 1 })
+      existingSkipped: 1,
+      pendingOrError: 1 })
   })
 
   it ('preserves terminal rows while merging validation results', () => {
@@ -270,7 +274,7 @@ describe ('post import row state', () => {
           thumbnailBase: '',
           originalCreatedFrom: '',
           originalCreatedBefore: '',
-          duration: '2.5',
+          duration: '2',
           tags: 'edited-tag',
           parentPostIds: '' },
         true)
@@ -279,7 +283,7 @@ describe ('post import row state', () => {
     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.duration).toBe ('2')
     expect (nextRow.attributes.tags).toBe ('edited-tag')
     expect (nextRow.provenance.title).toBe ('manual')
     expect (nextRow.provenance.url).toBe ('manual')

frontend/src/lib/postImportRows.ts

@@ -2,11 +2,41 @@ import type { PostImportEditableDraft,
 	      PostImportResultRow,
 	      PostImportRow } from '@/lib/postImportTypes'
 
-const hasSkipReason = (row: PostImportRow): boolean =>
+const THUMBNAIL_MISSING_WARNING = 'サムネールなし'
+
+export const hasThumbnailBaseValue = (value: unknown): boolean =>
+    typeof value === 'string' && value.trim () !== ''
+
+export const hasVideoTag = (value: unknown): boolean =>
+    typeof value === 'string'
+    && value.split (/\s+/).includes ('動画')
+
+export const isExistingSkipRow = (row: PostImportRow): boolean =>
     row.skipReason === 'existing'
 
+
+export const isManualSkipRow = (row: PostImportRow): boolean =>
+    row.skipReason === 'manual'
+
+
+const hasSkipReason = (row: PostImportRow): boolean =>
+    row.skipReason != null
+
+export const compactMessageRecord = (
+    messages: Record<string, string[]>,
+): Record<string, string[]> =>
+    Object.fromEntries (
+	Object.entries (messages).filter (([, values]) => values.length > 0))
+
+
+export const hasErrorMessages = (
+    messages: Record<string, string[]>,
+): boolean =>
+    Object.values (messages).some (values => values.length > 0)
+
+
 const hasValidationErrors = (row: PostImportRow): boolean =>
-    Object.keys (row.validationErrors ?? { }).length > 0
+    hasErrorMessages (row.validationErrors ?? { })
 
 const isRecoverableRow = (row: PostImportRow): boolean =>
     row.recoverable === true
@@ -15,9 +45,33 @@ const isRepairableImportStatus = (row: PostImportRow): boolean =>
     isRecoverableRow (row)
     && (row.importStatus === 'failed' || row.importStatus === 'pending')
 
+
+export const isNonRecoverableFailedRow = (row: PostImportRow): boolean =>
+    row.importStatus === 'failed' && row.recoverable !== true
+
+
+export const isTerminalRow = (row: PostImportRow): boolean =>
+    row.importStatus === 'created'
+    || row.importStatus === 'skipped'
+    || isNonRecoverableFailedRow (row)
+
+
+export const isCompletedReviewRow = (row: PostImportRow): boolean =>
+    row.importStatus === 'created'
+    || row.importStatus === 'skipped'
+    || hasSkipReason (row)
+
+
+export const validatableImportRows = (rows: PostImportRow[]): PostImportRow[] =>
+    rows.filter (row => !(hasSkipReason (row)) && !(isTerminalRow (row)))
+
 const buildResetSnapshot = (row: PostImportRow) => ({
     url: row.url,
     attributes: { ...row.attributes },
+    displayTags: row.displayTags?.map (tag => ({
+	name: tag.name,
+	category: tag.category,
+	sectionLiterals: tag.sectionLiterals == null ? undefined : [...tag.sectionLiterals] })) ?? [],
     provenance: { ...row.provenance },
     tagSources: {
 	automatic: row.tagSources?.automatic ?? '',
@@ -27,9 +81,34 @@ const buildResetSnapshot = (row: PostImportRow) => ({
     baseWarnings: [...row.baseWarnings],
     metadataUrl: row.metadataUrl })
 
+const deduped = (values: string[]): string[] =>
+    [...new Set (values)]
+
+
+const thumbnailWarnings = (row: PostImportRow): string[] => {
+    const current = row.fieldWarnings.thumbnailBase ?? []
+    const others = current.filter (message => message !== THUMBNAIL_MISSING_WARNING)
+    return hasThumbnailBaseValue (row.attributes.thumbnailBase) || row.thumbnailFile != null
+        ? others
+        : deduped ([...others, THUMBNAIL_MISSING_WARNING])
+}
+
+
+export const applyThumbnailWarning = (row: PostImportRow): PostImportRow => ({
+    ...row,
+    fieldWarnings: compactMessageRecord ({
+	...row.fieldWarnings,
+	thumbnailBase: thumbnailWarnings (row) }) })
+
+
+export const applyThumbnailWarnings = (rows: PostImportRow[]): PostImportRow[] =>
+    rows.map (row => applyThumbnailWarning (row))
+
 
 export const processableImportRows = (rows: PostImportRow[]): PostImportRow[] =>
-    rows.filter (row => {
+    validatableImportRows (rows).filter (row => {
+      if (row.status === 'pending')
+        return false
       if (row.importStatus === 'created')
         return false
       if (row.importStatus === 'skipped')
@@ -46,13 +125,12 @@ export const creatableImportRows = (rows: PostImportRow[]): PostImportRow[] =>
 
 
 export const reviewSummaryCounts = (rows: PostImportRow[]) => ({
-    total: rows.length,
+    creatable: rows.filter (row => creatableImportRows ([row]).length > 0).length,
-    submittable: rows.filter (row =>
+    manualSkipped: rows.filter (row => isManualSkipRow (row)).length,
-        creatableImportRows ([row]).length > 0
+    existingSkipped: rows.filter (row => isExistingSkipRow (row)).length,
-        && !(hasValidationErrors (row))).length,
+    pendingOrError: rows.filter (row =>
-    skipPlanned: rows.filter (row =>
+        !(isCompletedReviewRow (row))
-        processableImportRows ([row]).length > 0
+        && creatableImportRows ([row]).length === 0).length })
-        && hasSkipReason (row)).length })
 
 
 export const resultSummaryCounts = (rows: PostImportRow[]) =>
@@ -85,19 +163,22 @@ export const resultRepairMode = (
 
 
 export const canEditReviewRow = (row: PostImportRow): boolean =>
-    !(row.importStatus === 'created'
+    !(hasSkipReason (row)
+      || row.importStatus === 'created'
       || row.importStatus === 'skipped'
       || (row.importStatus === 'failed' && row.recoverable !== true))
 
 
 export const canEditResultRow = (row: PostImportRow): boolean =>
-    row.recoverable === true
+    row.skipReason == null
+    && row.recoverable === true
     && (row.importStatus === 'failed'
         || (row.importStatus === 'pending' && hasValidationErrors (row)))
 
 
 export const canRetryResultRow = (row: PostImportRow): boolean =>
-    row.recoverable === true
+    row.skipReason == null
+    && row.recoverable === true
     && (row.importStatus === 'failed'
         || (row.importStatus === 'pending' && !(hasValidationErrors (row))))
 
@@ -113,6 +194,14 @@ export const resultRowWarnings = (row: PostImportRow): string[] =>
         ...Object.values (row.fieldWarnings ?? { }).flat (),
         ...row.baseWarnings])]
 
+
+const isManualChange = (
+    current: unknown,
+    next:    string,
+): boolean =>
+    next !== String (current ?? '')
+
+
 export const buildNextEditedRow = (
     editingRow:  PostImportRow,
     draft:       PostImportEditableDraft,
@@ -133,12 +222,12 @@ export const buildNextEditedRow = (
     draftFields.forEach (([field, value]) => {
 	nextAttributes[field] = value
 	nextProvenance[field] =
-	    value !== String (editingRow.attributes[field] ?? '')
+	    isManualChange (editingRow.attributes[field], value)
 	    ? 'manual'
 	    : (editingRow.provenance[field] ?? 'automatic')
     })
     nextAttributes.tags = draft.tags
-    if (draft.tags !== String (editingRow.attributes.tags ?? ''))
+    if (isManualChange (editingRow.attributes.tags, draft.tags))
       {
 	nextProvenance.tags = 'manual'
 	nextTagSources.manual = draft.tags
@@ -153,6 +242,12 @@ export const buildNextEditedRow = (
 	...editingRow,
 	url: draft.url,
 	attributes: nextAttributes,
+	displayTags:
+	    editingRow.displayTags?.map (tag => ({
+		name: tag.name,
+		category: tag.category,
+		sectionLiterals: tag.sectionLiterals == null ? undefined : [...tag.sectionLiterals] })),
+	thumbnailFile: draft.thumbnailFile,
 	provenance: {
 	    ...nextProvenance,
 	    url: urlChanged ? 'manual' : (editingRow.provenance.url ?? 'manual') },
@@ -212,7 +307,7 @@ export const mergeValidatedImportRows = (
         return previous
 
       const fieldWarnings =
-          Object.keys (row.fieldWarnings).length > 0 || row.metadataUrl !== previous.metadataUrl
+          hasErrorMessages (row.fieldWarnings) || row.metadataUrl !== previous.metadataUrl
           ? { ...row.fieldWarnings }
           : { ...previous.fieldWarnings }
       for (const [field, origin] of Object.entries (row.provenance))
@@ -225,10 +320,17 @@ export const mergeValidatedImportRows = (
           ...previous,
           url: row.url,
           attributes: row.attributes,
+          displayTags:
+              row.displayTags?.map (tag => ({
+                  name: tag.name,
+                  category: tag.category,
+                  sectionLiterals:
+                      tag.sectionLiterals == null ? undefined : [...tag.sectionLiterals] })),
           provenance: row.provenance,
           tagSources: row.tagSources,
           skipReason: row.skipReason,
           existingPostId: row.existingPostId,
+          existingPost: row.existingPost,
           fieldWarnings,
           baseWarnings:
               row.baseWarnings.length > 0 || row.metadataUrl !== previous.metadataUrl
@@ -265,9 +367,11 @@ export const mergeImportResults = (
               skipReason: undefined,
               createdPostId: result.post.id,
               existingPostId: undefined,
-              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              existingPost: undefined,
+              fieldWarnings: compactMessageRecord (
+		  result.fieldWarnings ?? row.fieldWarnings),
               baseWarnings: result.baseWarnings ?? row.baseWarnings,
-              importErrors: result.errors }
+              importErrors: compactMessageRecord (result.errors ?? { }) }
         case 'skipped':
           return {
               ...row,
@@ -276,9 +380,11 @@ export const mergeImportResults = (
               skipReason: 'existing',
               createdPostId: undefined,
               existingPostId: result.existingPostId,
-              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              existingPost: result.existingPost ?? row.existingPost,
+              fieldWarnings: compactMessageRecord (
+		  result.fieldWarnings ?? row.fieldWarnings),
               baseWarnings: result.baseWarnings ?? row.baseWarnings,
-              importErrors: result.errors }
+              importErrors: compactMessageRecord (result.errors ?? { }) }
         case 'failed':
           return {
               ...row,
@@ -287,9 +393,11 @@ export const mergeImportResults = (
               skipReason: undefined,
               createdPostId: undefined,
               existingPostId: undefined,
-              fieldWarnings: result.fieldWarnings ?? row.fieldWarnings,
+              existingPost: undefined,
+              fieldWarnings: compactMessageRecord (
+		  result.fieldWarnings ?? row.fieldWarnings),
               baseWarnings: result.baseWarnings ?? row.baseWarnings,
-              importErrors: result.errors }
+              importErrors: compactMessageRecord (result.errors ?? { }) }
         }
     })
 }
@@ -307,6 +415,7 @@ export const retryImportRow = (
         : row)
 
 export const initialisePreviewRows = (rows: PostImportRow[]): PostImportRow[] =>
-    rows.map (row => ({
+    applyThumbnailWarnings (
-        ...row,
+	rows.map (row => ({
-        resetSnapshot: buildResetSnapshot (row) }))
+	    ...row,
+	    resetSnapshot: buildResetSnapshot (row) })))

frontend/src/lib/postImportSession.ts

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

frontend/src/lib/postImportSourceValidation.test.ts

@@ -1,6 +1,9 @@
 import { describe, expect, it } from 'vitest'
 
-import { countImportSourceLines, validateImportSource } from '@/lib/postImportSession'
+import {
+    countImportSourceLines,
+    validateImportSource,
+} from '@/lib/postImportSourceValidation'
 
 describe ('post import source validation', () => {
   it ('counts trimmed non-empty CRLF and LF rows', () => {

frontend/src/lib/postImportSourceValidation.ts

@@ -12,23 +12,14 @@ const bytesize = (value: string): number =>
     new TextEncoder ().encode (value).length
 
 
-const normaliseImportUrl = (value: string): string | null => {
+const parseImportUrl = (value: string): URL | null => {
     const trimmed = value.trim ()
     if (!(trimmed))
       return null
 
     try
     {
-      const url = new URL (trimmed)
+      return 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
     {
@@ -37,12 +28,23 @@ const normaliseImportUrl = (value: string): string | null => {
 }
 
 
-export const countImportSourceLines = (source: string): number =>
+const normaliseImportUrl = (url: URL): string => {
+  url.hostname = url.hostname.toLowerCase ()
+  if (url.pathname.endsWith ('/'))
+    url.pathname = url.pathname.replace (/\/+$/, '')
+  return url.toString ()
+}
+
+
+export const extractImportSourceUrls = (source: string): string[] =>
     source
         .split (/\r\n|\n|\r/)
         .map (line => line.trim ())
         .filter (line => line !== '')
-        .length
+
+
+export const countImportSourceLines = (source: string): number =>
+    extractImportSourceUrls (source).length
 
 
 export const validateImportSource = (
@@ -61,7 +63,6 @@ export const validateImportSource = (
       ++count
       const sourceRow = index + 1
       const displayUrl = truncateUrl (value)
-      const normalised = normaliseImportUrl (value)
       if (count > MAX_ROWS)
         {
           issues.push ({
@@ -70,14 +71,6 @@ export const validateImportSource = (
               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 ({
@@ -86,7 +79,8 @@ export const validateImportSource = (
               url: displayUrl })
           return
         }
-      if (normalised == null)
+      const parsed = parseImportUrl (value)
+      if (parsed == null)
         {
           issues.push ({
               sourceRow,
@@ -94,6 +88,23 @@ export const validateImportSource = (
               url: displayUrl })
           return
         }
+      if (!(parsed.protocol === 'http:' || parsed.protocol === 'https:'))
+        {
+          issues.push ({
+              sourceRow,
+              message: 'HTTP または HTTPS の URL ではありません．',
+              url: displayUrl })
+          return
+        }
+      if (!(parsed.host))
+        {
+          issues.push ({
+              sourceRow,
+              message: 'URL の形式が不正です．',
+              url: displayUrl })
+          return
+        }
+      const normalised = normaliseImportUrl (parsed)
       const duplicateRow = seen.get (normalised)
       if (duplicateRow != null)
         {

frontend/src/lib/postImportStorage.test.ts

@@ -1,117 +1,31 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
-import { cleanupExpiredPostImportSessions,
+import {
-	 clearPostImportSourceDraft,
+    clearPostImportSourceDraft,
-	 loadPostImportSession,
+    loadPostImportSourceDraft,
-	 loadPostImportSourceDraft,
+    savePostImportSourceDraft,
-	 savePostImportSession,
+} from '@/lib/postImportStorage'
-	 savePostImportSourceDraft } from '@/lib/postImportSession'
-import { buildPostImportRow } from '@/test/postImportFactories'
 
-describe ('post import storage', () => {
+describe ('post import source draft storage', () => {
   beforeEach (() => {
     sessionStorage.clear ()
-    vi.useRealTimers ()
+    vi.restoreAllMocks ()
   })
 
-  it ('round-trips a valid session and source draft', () => {
+  it ('round-trips and clears the URL list 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' })
+    expect (loadPostImportSourceDraft ()).toEqual ({
+	source: 'https://example.com' })
+
     clearPostImportSourceDraft ()
+
     expect (loadPostImportSourceDraft ()).toEqual ({ source: '' })
   })
 
-  it ('rejects inconsistent post IDs and terminal statuses', () => {
+  it ('ignores malformed stored drafts', () => {
-    const session = {
+    sessionStorage.setItem ('post-import-source-draft', '{')
-      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 ())
+    expect (loadPostImportSourceDraft ()).toEqual ({ source: '' })
-      {
-	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', () => {

frontend/src/lib/postImportStorage.ts

@@ -1,52 +1,24 @@
-import type { PostImportOrigin,
+import type { StorageErrorHandler } from '@/lib/postImportTypes'
-	      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')
+  if (typeof window === 'undefined')
-      return null
+    return null
 
-    try
+  try
-    {
+  {
-      return sessionStorage.getItem (key)
+    return sessionStorage.getItem (key)
-    }
+  }
-    catch
+  catch
-    {
+  {
-      onError?.('保存済みデータを読み込めませんでした．')
+    onError?.('保存済みデータを読み込めませんでした．')
-      return null
+    return null
-    }
+  }
 }
 
 
@@ -55,19 +27,19 @@ const writeStorage = (
     value:     string,
     onError?:  StorageErrorHandler,
 ): boolean => {
-    if (typeof window === 'undefined')
+  if (typeof window === 'undefined')
-      return false
+    return false
 
-    try
+  try
-    {
+  {
-      sessionStorage.setItem (key, value)
+    sessionStorage.setItem (key, value)
-      return true
+    return true
-    }
+  }
-    catch
+  catch
-    {
+  {
-      onError?.('ブラウザへ保存できませんでした．')
+    onError?.('ブラウザへ保存できませんでした．')
-      return false
+    return false
-    }
+  }
 }
 
 
@@ -75,281 +47,36 @@ const removeStorage = (
     key:       string,
     onError?:  StorageErrorHandler,
 ) => {
-    if (typeof window === 'undefined')
+  if (typeof window === 'undefined')
-      return
+    return
 
-    try
+  try
-    {
+  {
-      sessionStorage.removeItem (key)
+    sessionStorage.removeItem (key)
-    }
+  }
-    catch
+  catch
-    {
+  {
-      onError?.('保存済みデータを削除できませんでした．')
+    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)
+  const raw = readStorage (SOURCE_DRAFT_KEY, onError)
-    if (raw == null)
+  if (raw == null)
-      return { source: '' }
+    return { source: '' }
 
-    try
+  try
-    {
+  {
-      const value = JSON.parse (raw) as { source?: string }
+    const value = JSON.parse (raw) as { source?: string }
-      return { source: typeof value.source === 'string' ? value.source : '' }
+    return { source: typeof value.source === 'string' ? value.source : '' }
-    }
+  }
-    catch
+  catch
-    {
+  {
-      return { source: '' }
+    return { source: '' }
-    }
+  }
 }
 
 
@@ -363,56 +90,5 @@ export const savePostImportSourceDraft = (
 export const clearPostImportSourceDraft = (
     onError?: StorageErrorHandler,
 ) => {
-    removeStorage (SOURCE_DRAFT_KEY, onError)
+  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

@@ -1,3 +1,5 @@
+import type { Category } from '@/types'
+
 export type PostImportOrigin = 'automatic' | 'manual'
 export type PostImportRepairMode = 'all' | 'failed'
 export type PostImportStatus =
@@ -5,19 +7,32 @@ export type PostImportStatus =
     | 'created'
     | 'skipped'
     | 'failed'
-export type PostImportSkipReason = 'existing'
+export type PostImportSkipReason = 'existing' | 'manual'
 export type PostImportResultStatus = 'created' | 'skipped' | 'failed'
 export type PostImportAttributeValue = string | number
 
+export type PostImportDisplayTag = {
+    name:            string
+    category:        Category
+    sectionLiterals?: string[] }
+
 export type PostImportResetSnapshot = {
     url:         string
     attributes:  Record<string, PostImportAttributeValue>
+    displayTags: PostImportDisplayTag[]
     provenance:  Record<string, PostImportOrigin>
     tagSources:  Record<PostImportOrigin, string>
     fieldWarnings: Record<string, string[]>
     baseWarnings: string[]
     metadataUrl?: string }
 
+export type PostImportExistingPost = {
+    id:            number
+    title:         string
+    url:           string
+    thumbnail?:    string | null
+    thumbnailBase?: string | null }
+
 export type PostImportRow = {
     sourceRow:         number
     url:               string
@@ -28,14 +43,17 @@ export type PostImportRow = {
     importErrors?:     Record<string, string[]>
     provenance:        Record<string, PostImportOrigin>
     tagSources?:       Record<PostImportOrigin, string>
-    status:            'ready' | 'warning' | 'error'
+    status:            'pending' | 'ready' | 'warning' | 'error'
     skipReason?:       PostImportSkipReason
     existingPostId?:   number
+    existingPost?:     PostImportExistingPost
     metadataUrl?:      string
+    displayTags?:      PostImportDisplayTag[]
     resetSnapshot:     PostImportResetSnapshot
     createdPostId?:    number
     importStatus?:     PostImportStatus
-    recoverable?:      boolean }
+    recoverable?:      boolean
+    thumbnailFile?:    File }
 
 export type PostImportResultRow =
     | {
@@ -49,6 +67,7 @@ export type PostImportResultRow =
 	sourceRow:      number
 	status:         'skipped'
 	existingPostId: number
+	existingPost?:  PostImportExistingPost
 	fieldWarnings?: Record<string, string[]>
 	baseWarnings?:  string[]
 	errors?:        Record<string, string[]> }
@@ -60,13 +79,6 @@ export type PostImportResultRow =
 	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
@@ -80,6 +92,7 @@ export type PostImportEditableDraft = {
     originalCreatedBefore: string
     duration:              string
     tags:                  string
-    parentPostIds:         string }
+    parentPostIds:         string
+    thumbnailFile?:        File }
 
 export type StorageErrorHandler = (message: string) => void

frontend/src/lib/postNewQueryState.test.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from 'vitest'
+
+import {
+    buildPostNewReviewPath,
+    hasPostNewReviewState,
+    isPostNewReviewPathWithinLimit,
+    parsePostNewReviewUrls,
+    postNewReviewPathByteLength,
+} from '@/lib/postNewQueryState'
+
+describe ('post new review URL state', () => {
+  it ('encodes each URL separately and preserves literal plus signs', () => {
+    const urls = [
+	'https://example.com/one+a',
+	'https://example.com/two?value=b+c']
+
+    const path = buildPostNewReviewPath (urls)
+
+    expect (path).toBe (
+	'/posts/new?urls=https%3A%2F%2Fexample.com%2Fone%2Ba'
+	+ '+https%3A%2F%2Fexample.com%2Ftwo%3Fvalue%3Db%2Bc')
+    expect (parsePostNewReviewUrls (path.slice ('/posts/new'.length))).toEqual (urls)
+  })
+
+  it ('uses only the raw urls parameter as review state', () => {
+    expect (hasPostNewReviewState ('?session_id=old&meta=old')).toBe (false)
+    expect (hasPostNewReviewState ('?unknown=value&urls=')).toBe (true)
+    expect (parsePostNewReviewUrls ('?unknown=value&urls=one+two&meta=old'))
+	.toEqual (['one', 'two'])
+  })
+
+  it ('allows at most a 6 143 byte request target', () => {
+    const baseUrl = 'https://example.com/'
+    const baseLength = postNewReviewPathByteLength ([baseUrl])
+    const allowed = `${ baseUrl }${ 'a'.repeat (6_143 - baseLength) }`
+    const denied = `${ allowed }a`
+
+    expect (postNewReviewPathByteLength ([allowed])).toBe (6_143)
+    expect (isPostNewReviewPathWithinLimit ([allowed])).toBe (true)
+    expect (postNewReviewPathByteLength ([denied])).toBe (6_144)
+    expect (isPostNewReviewPathWithinLimit ([denied])).toBe (false)
+  })
+})

frontend/src/lib/postNewQueryState.ts

@@ -0,0 +1,58 @@
+const POST_NEW_REVIEW_PATH_PREFIX = '/posts/new?urls='
+const MAX_POST_NEW_REVIEW_TARGET_BYTES = 6_144
+
+const textEncoder = new TextEncoder ()
+
+
+const rawUrlsParam = (search: string): string | null => {
+  const query = search.startsWith ('?') ? search.slice (1) : search
+  if (query === '')
+    return null
+
+  for (const segment of query.split ('&'))
+    {
+      if (segment === 'urls')
+        return ''
+      if (segment.startsWith ('urls='))
+        return segment.slice ('urls='.length)
+    }
+
+  return null
+}
+
+
+export const buildPostNewReviewPath = (urls: string[]): string =>
+    `${ POST_NEW_REVIEW_PATH_PREFIX }${ urls.map (url => encodeURIComponent (url)).join ('+') }`
+
+
+export const postNewReviewPathByteLength = (urls: string[]): number =>
+    textEncoder.encode (buildPostNewReviewPath (urls)).byteLength
+
+
+export const isPostNewReviewPathWithinLimit = (urls: string[]): boolean =>
+    postNewReviewPathByteLength (urls) < MAX_POST_NEW_REVIEW_TARGET_BYTES
+
+
+export const parsePostNewReviewUrls = (search: string): string[] => {
+  const raw = rawUrlsParam (search)
+  if (raw == null)
+    return []
+
+  return raw
+      .split ('+')
+      .filter (segment => segment !== '')
+      .map (segment => {
+        try
+        {
+          return decodeURIComponent (segment)
+        }
+        catch
+        {
+          return segment
+        }
+      })
+}
+
+
+export const hasPostNewReviewState = (search: string): boolean =>
+    rawUrlsParam (search) != null