#399

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

backend/AGENTS.md

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

backend/app/controllers/materials_controller.rb

@@ -89,15 +89,13 @@ class MaterialsController < ApplicationController
 
     begin
       Material.transaction do
-        tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
-        tag = tag_name.tag
-        tag = Tag.create!(tag_name:, category: :material) unless tag
-
+        tag = resolve_material_tag!(tag_name_raw)
         material = Material.new(tag:, url:,
                                 created_by_user: current_user,
                                 updated_by_user: current_user)
         material.file.attach(uploaded_blob) if uploaded_blob
         material.save!
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :create,
                                         created_by_user: current_user)
@@ -139,10 +137,7 @@ class MaterialsController < ApplicationController
     begin
       Material.transaction do
         MaterialVersionRecorder.ensure_snapshot!(material, created_by_user: current_user)
-        tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
-        tag = tag_name.tag
-        tag = Tag.create!(tag_name:, category: :material) unless tag
-
+        tag = resolve_material_tag!(tag_name_raw)
         material.assign_attributes(tag:, url:, updated_by_user: current_user)
         if uploaded_blob
           material.file.attach(uploaded_blob)
@@ -150,6 +145,7 @@ class MaterialsController < ApplicationController
           material.file.detach
         end
         material.save!
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :update,
                                         created_by_user: current_user)
@@ -240,6 +236,12 @@ class MaterialsController < ApplicationController
     nil
   end
 
+  def resolve_material_tag! tag_name_raw
+    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
+    tag = tag_name.tag
+    tag || Tag.create!(tag_name:, category: :material)
+  end
+
   def material_index_needs_tag_name? filters
     filters[:q].present? || filters[:sort] == 'tag_name'
   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
     ;
@@ -114,6 +115,77 @@ 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
@@ -142,48 +214,51 @@ class PostsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    # TODO: サイトに応じて thumbnail_base 設定
-    title = params[:title].presence
-    url = params[:url]
-    thumbnail = params[:thumbnail]
-    tag_names = params[:tags].to_s.split
-    original_created_from = params[:original_created_from]
-    original_created_before = params[:original_created_before]
-    parent_post_ids = parse_parent_post_ids
-    resized_thumbnail = thumbnail.present? ? Post.resized_thumbnail_attachment(thumbnail) : nil
-
-    post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
-                    original_created_from:, original_created_before:)
-    post.thumbnail.attach(resized_thumbnail) if resized_thumbnail
-
-    ApplicationRecord.transaction do
-      post.save!
-
-      Tag.normalise_tags!(tag_names, deny_deprecated: true, with_sections: true) =>
-          { tags:, sections: }
-      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
-
-      tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
-      post.video_ms = normalise_video_ms(tags)
-      validate_video_sections!(post.video_ms, sections)
-      post.save!
-      sync_post_tags!(post, tags, sections)
-
-      sync_parent_posts!(post, parent_post_ids)
-
-      PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
+    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: post_create_attributes.merge(
+                               preflight.slice(
+                                   :url,
+                                   :title,
+                                   :thumbnail_base,
+                                   :tags,
+                                   :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
     render_unprocessable_entity '廃止済みタグは付与できません．', field: :tags
   rescue Tag::SectionLiteralParseError
     render_validation_error fields: { tags: ['タグ区間の記法が不正です．'] }
-  rescue VideoMsParseError
+  rescue PostCreator::VideoMsParseError
     render_validation_error fields: { video_ms: ['動画時間の記法が不正です．'] }
+  rescue 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
@@ -192,6 +267,25 @@ 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
 
@@ -486,6 +580,79 @@ 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．'
@@ -565,6 +732,7 @@ 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: }
@@ -602,6 +770,23 @@ 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

@@ -1,50 +1,55 @@
 class PreviewController < ApplicationController
+  before_action :require_member!
+
   def title
-    # TODO: # 既知サイトなら決まったフォーマットで title 取得するやぅに．
-    return head :unauthorized unless current_user
+    return render_bad_request('URL は必須です．') if params[:url].blank?
 
-    url = params[:url]
-    return render_bad_request('URL は必須です．') unless url.present?
-
-    unless url.start_with?(/http(s)?:\/\//)
-      url = 'http://' + url
-    end
-
-    html = URI.open(url, open_timeout: 5, read_timeout: 5).read
-    doc = Nokogiri::HTML.parse(html)
-    title = doc.at('title')&.text&.strip
-
-    render json: { title: title }
-  rescue => e
+    render json: { title: Preview::ThumbnailFetcher.title(params[:url]) }
+  rescue Preview::UrlSafety::UnsafeUrl => e
     render_bad_request(e.message)
+  rescue Preview::HttpFetcher::FetchTimeout => e
+    render_preview_error(e.message, :gateway_timeout)
+  rescue Preview::HttpFetcher::ResponseTooLarge => e
+    render_preview_error(e.message, :payload_too_large)
+  rescue Preview::HttpFetcher::FetchFailed => e
+    render_preview_error(e.message, :bad_gateway)
   end
 
   def thumbnail
-    # TODO: 既知ドメインであれば指定のアドレスからサムネールを取得するやぅにする．
+    return render_bad_request('URL は必須です．') if params[:url].blank?
 
+    attachment =
+        Post.resized_thumbnail_attachment(
+            StringIO.new(Preview::ThumbnailFetcher.fetch(params[:url])))
+    send_data attachment[:io].read,
+              type: attachment[:content_type],
+              disposition: 'inline'
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    render_bad_request(e.message)
+  rescue Preview::HttpFetcher::FetchTimeout => e
+    render_preview_error(e.message, :gateway_timeout)
+  rescue Preview::HttpFetcher::ResponseTooLarge => e
+    render_preview_error(e.message, :payload_too_large)
+  rescue Preview::HttpFetcher::FetchFailed => e
+    render_preview_error(e.message, :bad_gateway)
+  rescue Preview::ThumbnailFetcher::GenerationFailed, MiniMagick::Error => e
+    render_unprocessable_entity(e.message)
+  end
+
+  private
+
+  def require_member!
     return head :unauthorized unless current_user
+    return if current_user.gte_member?
 
-    url = params[:url]
-    return render_bad_request('URL は必須です．') if url.blank?
+    head :forbidden
+  end
 
-    unless url.start_with?(/http(s)?:\/\//)
-      url = 'http://' + url
-    end
-
-    path = Rails.root.join('tmp', "thumb_#{ SecureRandom.hex }.png")
-    system("node #{ Rails.root }/lib/screenshot.js #{ Shellwords.escape(url) } #{ path }")
-
-    if File.exist?(path)
-      image = MiniMagick::Image.open(path)
-      image.resize '180x180'
-      File.delete(path) rescue nil
-      send_file image.path, type: 'image/png', disposition: 'inline'
-    else
-      render json: { type: 'internal_server_error',
-                     message: 'サムネールを生成できませんでした．',
-                     errors: { },
-                     base_errors: ['サムネールを生成できませんでした．'] },
-             status: :internal_server_error
-    end
+  def render_preview_error(message, status)
+    render json: { type: status.to_s,
+                   message:,
+                   errors: { },
+                   base_errors: [message] },
+           status:
   end
 end

backend/app/controllers/user_settings_controller.rb

@@ -0,0 +1,61 @@
+class UserSettingsController < ApplicationController
+  wrap_parameters false
+
+  def show
+    return head :unauthorized unless current_user
+
+    render json: current_setting.serializable_hash
+  end
+
+  def update
+    return head :unauthorized unless current_user
+
+    raw_attributes = editable_raw_attributes
+    field_errors = validate_raw_attributes(raw_attributes)
+    return render_validation_error fields: field_errors if field_errors.present?
+
+    setting = current_setting
+    setting.assign_attributes(raw_attributes)
+
+    if setting.save
+      render json: setting.serializable_hash, status: :ok
+    else
+      render_validation_error setting
+    end
+  end
+
+  private
+
+  def current_setting
+    Setting.find_or_create_by!(user: current_user) do |setting|
+      setting.assign_attributes(Setting.defaults)
+    end
+  rescue ActiveRecord::RecordNotUnique
+    Setting.find_by!(user: current_user)
+  end
+
+  def editable_raw_attributes
+    request.request_parameters.slice(*Setting::EDITABLE_ATTRIBUTES)
+  end
+
+  def validate_raw_attributes raw_attributes
+    raw_attributes.each_with_object({ }) do |(key, value), errors|
+      next if value_matches_type?(key, value)
+
+      errors[key.to_sym] = ['値の型が不正です．']
+    end
+  end
+
+  def value_matches_type? key, value
+    case Setting::TYPE_BY_ATTRIBUTE.fetch(key)
+    when :string
+      value.is_a?(String)
+    when :integer
+      value.is_a?(Integer)
+    when :boolean
+      value == true || value == false
+    else
+      false
+    end
+  end
+end

backend/app/controllers/user_theme_slots_controller.rb

@@ -0,0 +1,38 @@
+class UserThemeSlotsController < ApplicationController
+  wrap_parameters false
+
+  def index
+    return head :unauthorized unless current_user
+
+    render json: current_user
+                 .theme_slots
+                 .order(:base_theme, :slot_no)
+                 .map { |slot| slot.serializable_hash }
+  end
+
+  def update
+    return head :unauthorized unless current_user
+
+    base_theme = params[:base_theme].to_s
+    slot_no = params[:slot_no].to_i
+    tokens = params[:tokens]
+
+    unless UserThemeSlot::BASE_THEMES.include?(base_theme)
+      return render_validation_error fields: { base_theme: ['値が不正です．'] }
+    end
+    unless UserThemeSlot::SLOT_NOS.include?(slot_no)
+      return render_validation_error fields: { slot_no: ['値が不正です．'] }
+    end
+    unless tokens.is_a?(ActionController::Parameters) || tokens.is_a?(Hash)
+      return render_validation_error fields: { tokens: ['JSON object で指定してください．'] }
+    end
+
+    slot = UserThemeSlot.find_or_initialize_by(user: current_user,
+                                               base_theme:,
+                                               slot_no:)
+    slot.tokens = tokens.is_a?(ActionController::Parameters) ? tokens.to_unsafe_h : tokens
+    slot.save!
+
+    render json: slot.serializable_hash, status: :ok
+  end
+end

backend/app/models/post.rb

@@ -1,20 +1,57 @@
 class Post < ApplicationRecord
+  require 'date'
   require 'mini_magick'
+  require 'nokogiri'
   require 'stringio'
+  require 'timeout'
 
-  def self.resized_thumbnail_attachment(upload)
+  class RemoteThumbnailFetchFailed < StandardError; end
+
+  ORIGINAL_CREATED_INVALID_MESSAGE = 'オリジナルの作成日時の形式が不正です．'.freeze
+  ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE =
+      'オリジナルの作成日時は分単位で入力してください．'.freeze
+  ORIGINAL_CREATED_ORDER_MESSAGE = 'オリジナルの作成日時の順番がをかしぃです．'.freeze
+  ORIGINAL_CREATED_MINIMUM_RANGE_MESSAGE =
+      'オリジナルの作成日時の範囲は1分以上必要です．'.freeze
+  REMOTE_SVG_CONTENT_TYPE = 'image/svg+xml'.freeze
+  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)
-    image.resize '180x180'
-    image.format 'jpg'
+    bytes = upload.read
+    blob = Timeout.timeout(THUMBNAIL_PROCESS_TIMEOUT) do
+      image = image_for_thumbnail_upload(bytes, content_type:)
+      image.auto_orient
+      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
@@ -57,9 +94,9 @@ class Post < ApplicationRecord
 
   attribute :version_no, :integer, default: 1
 
-  before_validation :normalise_url
+  before_validation :normalise_url, if: :will_save_change_to_url?
 
-  validates :url, presence: true, uniqueness: true
+  validates :url, presence: true, uniqueness: true, length: { maximum: 768 }
   validates :video_ms, numericality: { only_integer: true, greater_than: 0 }, allow_nil: true
 
   validate :validate_original_created_range
@@ -101,7 +138,10 @@ class Post < ApplicationRecord
   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
@@ -118,7 +158,11 @@ class Post < ApplicationRecord
           '%d:%02d' % [min, s]
         end
 
-    remainder_ms.positive? ? "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }" : base
+    if remainder_ms.positive?
+      "#{ base }.#{ remainder_ms.to_s.rjust(3, '0') }"
+    else
+      base
+    end
   end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
@@ -140,19 +184,26 @@ class Post < ApplicationRecord
     thumbnail.attach(self.class.resized_thumbnail_attachment(StringIO.new(thumbnail.download)))
   end
 
+  def attach_thumbnail_from_url! raw_url
+    thumbnail.attach(self.class.remote_thumbnail_attachment(raw_url))
+  end
+
   private
 
   def validate_original_created_range
-    f = original_created_from
-    b = original_created_before
-    return if f.blank? || b.blank?
+    return if skip_original_created_validation?
 
-    f = Time.zone.parse(f) if String === f
-    b = Time.zone.parse(b) if String === b
-    return if !(f) || !(b)
+    f = parse_original_created_value(:original_created_from)
+    b = parse_original_created_value(:original_created_before)
+    return if f.nil? || b.nil?
 
-    if f >= b
-      errors.add :original_created_at, 'オリジナルの作成日時の順番がをかしぃです．'
+    if b <= f
+      errors.add :original_created_at, ORIGINAL_CREATED_ORDER_MESSAGE
+      return
+    end
+
+    if b - f < 1.minute
+      errors.add :original_created_at, ORIGINAL_CREATED_MINIMUM_RANGE_MESSAGE
     end
   end
 
@@ -173,15 +224,307 @@ class Post < ApplicationRecord
   def normalise_url
     return if url.blank?
 
-    self.url = url.strip
+    self.url = PostUrlNormaliser.normalise(url) || url.strip
+  end
 
-    u = URI.parse(url)
-    return unless u in URI::HTTP
+  def 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
 
-    u.host = u.host.downcase if u.host
-    u.path = u.path.sub(/\/\Z/, '') if u.path.present?
-    self.url = u.to_s
-  rescue URI::InvalidURIError
-    ;
+    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)
+    return nil if raw_value.blank? && value.blank?
+
+    time =
+        case raw_value
+        when String
+          parse_original_created_string(raw_value)
+        when Time, ActiveSupport::TimeWithZone
+          raw_value.in_time_zone
+        else
+          value&.in_time_zone
+        end
+    if time.nil?
+      errors.add field, ORIGINAL_CREATED_INVALID_MESSAGE
+      return nil
+    end
+    unless minute_precision_time?(time)
+      errors.add field, ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE
+      return nil
+    end
+    time
+  end
+
+  def parse_original_created_string raw_value
+    value = raw_value.to_s.strip
+    return nil if value.blank?
+
+    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
+      hour = match[4].to_i
+      minute = match[5].to_i
+      return nil unless valid_original_created_components?(year, month, day, hour, minute, 0)
+
+      return Time.zone.local(year, month, day, hour, minute)
+    end
+
+    match =
+        value.match(
+            /
+              \A(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2})
+              (?::(\d{2})(?:\.(\d+))?)?
+              (Z|[+-]\d{2}:?\d{2})?
+              \z
+            /x)
+    return nil if match.nil?
+
+    year = match[1].to_i
+    month = match[2].to_i
+    day = match[3].to_i
+    hour = match[4].to_i
+    minute = match[5].to_i
+    second = match[6]&.to_i || 0
+    fraction = match[7]
+    offset = match[8]
+    return nil unless valid_original_created_components?(year, month, day, hour, minute, second)
+    return nil if offset.present? && !(valid_original_created_offset?(offset))
+
+    if offset.present?
+      return Time.new(
+          year,
+          month,
+          day,
+          hour,
+          minute,
+          second + Rational(parse_original_created_nanoseconds(fraction), 1_000_000_000),
+          normalise_original_created_offset(offset)).in_time_zone
+    end
+
+    Time.zone.local(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second).change(nsec: parse_original_created_nanoseconds(fraction))
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def minute_precision_time? value
+    value.sec.zero? && value.nsec.zero?
+  end
+
+  def valid_original_created_components? year, month, day, hour, minute, second
+    return false unless Date.valid_date?(year, month, day)
+    return false unless hour.between?(0, 23)
+    return false unless minute.between?(0, 59)
+    return false unless second.between?(0, 59)
+
+    true
+  end
+
+  def valid_original_created_offset? value
+    match = value.match(/\A([+-])(\d{2}):?(\d{2})\z/)
+    return true if value == 'Z'
+    return false if match.nil?
+
+    hours = match[2].to_i
+    minutes = match[3].to_i
+    hours.between?(0, 23) && minutes.between?(0, 59)
+  end
+
+  def parse_original_created_nanoseconds value
+    return 0 if value.blank?
+
+    digits = value[0, 9].ljust(9, '0')
+    Integer(digits, 10)
+  end
+
+  def normalise_original_created_offset value
+    return '+00:00' if value == 'Z'
+
+    value.match?(/\A[+-]\d{2}:\d{2}\z/) ? value : "#{ value[0, 3] }:#{ value[3, 2] }"
+  end
+
+  def skip_original_created_validation?
+    return false if new_record?
+    return false if will_save_change_to_original_created_from?
+    return false if will_save_change_to_original_created_before?
+
+    true
   end
 end

backend/app/models/post_url_sanitisation_rule.rb

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

backend/app/models/setting.rb

@@ -1,7 +1,52 @@
 class Setting < ApplicationRecord
+  THEMES = ['system', 'light', 'dark'].freeze
+
+  # These remain in the typed settings schema to preserve existing backend
+  # work. The common `/users/settings` page currently surfaces only `theme`.
+  AUTO_FETCH_MODES = ['auto', 'manual', 'off'].freeze
+  WIKI_EDITOR_MODES = ['split', 'write', 'preview'].freeze
+
+  STRING_ATTRIBUTES = [
+    'theme',
+    'auto_fetch_title',
+    'auto_fetch_thumbnail',
+    'wiki_editor_mode',
+  ].freeze
+  INTEGER_ATTRIBUTES = [].freeze
+  BOOLEAN_ATTRIBUTES = [].freeze
+  EDITABLE_ATTRIBUTES =
+      (STRING_ATTRIBUTES + INTEGER_ATTRIBUTES + BOOLEAN_ATTRIBUTES).freeze
+  TYPE_BY_ATTRIBUTE = {
+    'theme' => :string,
+    'auto_fetch_title' => :string,
+    'auto_fetch_thumbnail' => :string,
+    'wiki_editor_mode' => :string,
+  }.freeze
+
   belongs_to :user
 
   validates :user_id, presence: true
-  validates :key, presence: true, length: { maximum: 255 }
-  validates :value, presence: true
+  validates :user_id, uniqueness: true
+
+  validates :theme, inclusion: { in: THEMES }
+  validates :auto_fetch_title, inclusion: { in: AUTO_FETCH_MODES }
+  validates :auto_fetch_thumbnail, inclusion: { in: AUTO_FETCH_MODES }
+  validates :wiki_editor_mode, inclusion: { in: WIKI_EDITOR_MODES }
+
+  def self.defaults
+    {
+      theme: 'system',
+      auto_fetch_title: 'manual',
+      auto_fetch_thumbnail: 'manual',
+      wiki_editor_mode: 'split',
+    }
+  end
+
+  def self.serializable_attributes
+    EDITABLE_ATTRIBUTES.map(&:to_sym)
+  end
+
+  def serializable_hash(options = nil)
+    super({ only: self.class.serializable_attributes }.merge(options || { }))
+  end
 end

backend/app/models/user.rb

@@ -7,7 +7,8 @@ class User < ApplicationRecord
 
   has_many :created_posts,
            class_name: 'Post', foreign_key: :uploaded_user_id, dependent: :nullify
-  has_many :settings
+  has_one :setting, dependent: :destroy
+  has_many :theme_slots, class_name: 'UserThemeSlot', dependent: :destroy
   has_many :user_ips, dependent: :destroy
   has_many :ip_addresses, through: :user_ips
   has_many :user_post_views, dependent: :destroy

backend/app/models/user_theme_slot.rb

@@ -0,0 +1,27 @@
+class UserThemeSlot < ApplicationRecord
+  BASE_THEMES = ['light', 'dark'].freeze
+  SLOT_NOS = [1, 2, 3].freeze
+
+  belongs_to :user
+
+  validates :user_id, presence: true
+  validates :base_theme, presence: true, inclusion: { in: BASE_THEMES }
+  validates :slot_no, presence: true, inclusion: { in: SLOT_NOS }
+  validates :tokens, presence: true
+  validates :user_id, uniqueness: { scope: [:base_theme, :slot_no] }
+
+  validate :tokens_must_be_object
+
+  def serializable_hash(options = nil)
+    hash = { only: [:base_theme, :slot_no, :tokens, :created_at, :updated_at] }
+    super(hash.merge(options || {}))
+  end
+
+  private
+
+  def tokens_must_be_object
+    return if tokens.is_a?(Hash)
+
+    errors.add(:tokens, 'は JSON object で指定してください．')
+  end
+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
-    json = common(post)
+  def base post, current_user = nil, host: nil
+    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
@@ -26,31 +31,59 @@ module PostRepr
   end
 
   def detail post, current_user = nil, parent_posts: [], child_posts: [],
-             sibling_posts: { }, related: []
-    base(post, current_user).merge(
-        'parent_posts' => cards(parent_posts),
-        'child_posts' => cards(child_posts),
-        'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
-          cards(posts)
-        },
-        'related' => cards(related))
+             sibling_posts: { }, related: [], host: nil
+    if host.present?
+      base(post, current_user, host:).merge(
+          'parent_posts' => cards(parent_posts, host:),
+          'child_posts' => cards(child_posts, host:),
+          'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
+            cards(posts, host:)
+          },
+          '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
-    common(post).merge('parent_posts' => [], 'child_posts' => [])
+  def card post, host: nil
+    if host.present?
+      common(post, host:).merge('parent_posts' => [], 'child_posts' => [])
+    else
+      common(post).merge('parent_posts' => [], 'child_posts' => [])
+    end
   end
 
-  def cards posts
-    posts.map { |post| card(post) }
+  def cards posts, host: nil
+    if host.present?
+      posts.map { |post| card(post, host:) }
+    else
+      posts.map { |post| card(post) }
+    end
   end
 
-  def many posts, current_user = nil
-    posts.map { |p| base(p, current_user) }
+  def many posts, current_user = nil, host: nil
+    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
@@ -65,11 +98,22 @@ module PostRepr
     }
   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)
-  rescue
+    options = { only_path: false }
+    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

@@ -0,0 +1,154 @@
+class PostCreator
+  class VideoMsParseError < ArgumentError; end
+
+  attr_reader :field_warnings
+
+  def initialize actor:, attributes:
+    @actor = actor
+    @attributes = attributes.symbolize_keys
+    @field_warnings = { }
+  end
+
+  def create!
+    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)
+
+    ApplicationRecord.transaction do
+      post.save!
+      post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
+      snapshot_tags = planned_snapshot_tags
+      post_tags = planned_post_tags
+      sections = planned_sections
+      TagVersioning.record_tag_snapshots!(snapshot_tags, created_by_user: @actor)
+      post.video_ms = planned_video_ms
+      post.save!
+      sync_post_tags!(post, post_tags, sections)
+      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 prepare_thumbnail_attachment
+    PostThumbnailAttachmentBuilder.build(
+        thumbnail: @attributes[:thumbnail],
+        thumbnail_base: @attributes[:thumbnail_base].presence)
+  end
+
+  def planned_snapshot_tags = planned_create_attributes[:snapshot_tags]
+
+  def planned_post_tags = planned_create_attributes[:post_tags]
+
+  def planned_sections = planned_create_attributes[:tag_sections]
+
+  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
+
+  def planned_video_ms
+    planned_create_attributes[:video_ms]
+  end
+
+  def planned_create_attributes
+    @planned_create_attributes ||= begin
+      if @attributes.key?(:snapshot_tag_specs)
+        snapshot_tags = materialise_tags(@attributes[:snapshot_tag_specs] || [])
+        post_tags = materialise_tags(@attributes[:post_tag_specs] || [])
+        {
+            snapshot_tags: snapshot_tags,
+            post_tags: post_tags,
+            tag_sections: materialise_sections(
+                @attributes[:tag_sections] || { },
+                snapshot_tags,
+                post_tags),
+            normalised_parent_post_ids: @attributes[:normalised_parent_post_ids] || [],
+            video_ms: @attributes[:video_ms] }
+      else
+        build_materialised_plan
+      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|
+        PostTagSection.create!(post_id: post.id,
+                               tag_id:,
+                               begin_ms:,
+                               end_ms:)
+      end
+    end
+    PostTag.where(post_id: post.id,
+                  tag_id: (current_ids - desired_ids).to_a).kept.find_each do |post_tag|
+      post_tag.discard_by!(@actor)
+    end
+  end
+
+  def sync_parent_posts! post, ids
+    if ids.include?(post.id)
+      post.errors.add :parent_post_ids, '自分自身を親投稿にはできません．'
+      raise ActiveRecord::RecordInvalid, post
+    end
+    missing = ids - Post.where(id: ids).pluck(:id)
+    if missing.present?
+      post.errors.add :parent_post_ids, "存在しない親投稿 Id. があります: #{ missing.join(' ') }"
+      raise ActiveRecord::RecordInvalid, post
+    end
+    ids.each { |parent_post_id| PostImplication.create_or_find_by!(post:, parent_post_id:) }
+  end
+end

backend/app/services/post_import_previewer.rb

@@ -0,0 +1,522 @@
+require 'time'
+require 'timeout'
+
+class PostImportPreviewer
+  FIELDS = [
+      'title',
+      'thumbnail_base',
+      'original_created_from',
+      'original_created_before',
+      'video_ms',
+      'duration',
+      'tags',
+      'parent_post_ids'].freeze
+  FETCH_WARNING_FIELDS = ['url', 'title', 'thumbnail_base'].freeze
+  TITLE_FETCH_WARNING = 'タイトルを取得できませんでした．'.freeze
+  THUMBNAIL_FETCH_WARNING = 'サムネールを取得できませんでした．'.freeze
+  METADATA_FETCH_WARNING = '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) }
+    url_counts = prepared_rows.filter_map { _1[:normal_url] }.tally
+    existing_posts =
+        Post.where(url: prepared_rows.map { _1[:normal_url] }.compact.uniq).index_by(&:url)
+    existing_parent_ids = preload_parent_ids(prepared_rows)
+    preload_metadata!(
+        prepared_rows,
+        fetch_metadata,
+        metadata_cache,
+        existing_posts,
+        url_counts)
+    known_tags =
+        preload_known_tags(
+            prepared_rows,
+            fetch_metadata,
+            metadata_cache,
+            existing_posts,
+            url_counts)
+    prepared_rows.map { |row|
+      preview_row(row,
+                  fetch_metadata:,
+                  metadata_cache:,
+                  existing_posts:,
+                  url_counts:,
+                  known_tags:,
+                  existing_parent_ids:)
+    }
+  end
+
+  def normalised_url value
+    PostUrlNormaliser.normalise(value)
+  end
+
+  private
+
+  def prepare_row row
+    source = row.symbolize_keys
+    url = source[:url].to_s.strip
+    normal_url = normalised_url(url)
+    source.merge(url_text: url, normal_url:, url_error: validate_url_safety(normal_url))
+  end
+
+  def preview_row row,
+                  fetch_metadata:,
+                  metadata_cache:,
+                  existing_posts:,
+                  url_counts:,
+                  known_tags:,
+                  existing_parent_ids:
+    attributes = initial_attributes(row)
+    provenance = initial_provenance(row)
+    tag_sources = initial_tag_sources(row, attributes, provenance)
+    field_warnings = initial_field_warnings(row)
+    base_warnings = initial_base_warnings(row)
+    url = row[:url_text]
+    provenance['url'] = 'manual'
+    normal_url = row[:normal_url]
+    url_for_metadata = normal_url || url
+    existing_post = normal_url.present? ? existing_posts[normal_url] : nil
+
+    validation_errors = {}
+    validation_errors[:url] = ['URL が不正です．'] if normal_url.blank?
+    if row[:url_error].present?
+      validation_errors[:url] = [row[:url_error]]
+    end
+    if normal_url.present? && url_counts[normal_url].to_i > 1
+      validation_errors[:url] = ['URL が重複しています．']
+    end
+
+    if row[:metadata_url].present? && row[:metadata_url] != url_for_metadata
+      clear_automatic_values!(attributes, provenance, tag_sources)
+      field_warnings = { }
+      base_warnings = [ ]
+    end
+
+    if validation_errors.blank? && normal_url.present? && existing_post
+      attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+      warnings_present = field_warnings.values.any?(&:present?) || base_warnings.present?
+      return { source_row: row[:source_row],
+               url: normal_url,
+               attributes:,
+               provenance:,
+               tag_sources:,
+               metadata_url: url_for_metadata,
+               skip_reason: 'existing',
+               existing_post_id: existing_post.id,
+               field_warnings:,
+               base_warnings:,
+               validation_errors:,
+               status: warnings_present ? 'warning' : 'ready' }
+    end
+
+    should_fetch = validation_errors.blank?
+    should_fetch &&= should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+    if should_fetch
+      clear_fetch_warnings!(field_warnings)
+      metadata = metadata_for(url_for_metadata, metadata_cache)
+      if metadata[:validation_errors].present?
+        validation_errors.merge!(metadata[:validation_errors])
+      else
+        apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
+        apply_fetch_warnings!(field_warnings, metadata[:warnings])
+      end
+    end
+
+    attributes['url'] = url
+    validate_basic_data(attributes, validation_errors)
+    validate_preview_tags(merged_tags(tag_sources, provenance['tags']),
+                          validation_errors,
+                          known_tags)
+    validate_parents(attributes['parent_post_ids'], validation_errors, existing_parent_ids)
+    attributes.delete('url')
+    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+
+    warnings_present = field_warnings.values.any?(&:present?) || base_warnings.present?
+    { source_row: row[:source_row],
+      url: validation_errors[:url].present? ? url : (normal_url || url),
+      attributes:,
+      provenance:,
+      tag_sources:,
+      metadata_url: url_for_metadata,
+      skip_reason: nil,
+      existing_post_id: nil,
+      field_warnings:,
+      base_warnings:,
+      validation_errors:,
+      status: validation_errors.present? ? 'error' : (warnings_present ? 'warning' : 'ready') }
+  end
+
+  def should_fetch_metadata? fetch_metadata, source_row
+    case fetch_metadata
+    when true then true
+    when Integer then fetch_metadata == source_row
+    when false, nil then false
+    else raise ArgumentError, '取得対象が不正です．'
+    end
+  end
+
+  def initial_attributes row
+    attributes = row[:attributes]&.stringify_keys || { }
+    FIELDS.to_h { |field|
+      value = attributes[field]
+      normalised =
+          if field == 'duration'
+            normalise_duration_attribute(value)
+          elsif field == 'video_ms'
+            value.nil? ? '' : value.to_s
+          else
+            value.to_s
+          end
+      [field, normalised] }
+  end
+
+  def initial_provenance row
+    provenance = row[:provenance]&.stringify_keys || { }
+    FIELDS.to_h { |field| [field, provenance[field].presence || 'automatic'] }
+      .merge('url' => 'manual')
+  end
+
+  def initial_tag_sources row, attributes, provenance
+    sources = row[:tag_sources]&.stringify_keys || { 'automatic' => '', 'manual' => '' }
+    sources['automatic'] = sources['automatic'].to_s
+    sources['manual'] =
+      provenance['tags'] == 'manual' ? attributes['tags'].to_s : sources['manual'].to_s
+    sources
+  end
+
+  def initial_field_warnings row
+    (row[:field_warnings] || { })
+      .stringify_keys
+      .transform_values { |value| Array(value).map(&:to_s) }
+  end
+
+  def initial_base_warnings row
+    Array(row[:base_warnings]).map(&:to_s)
+  end
+
+  def clear_automatic_values! attributes, provenance, tag_sources
+    ['title', 'thumbnail_base', 'original_created_from',
+     'original_created_before', 'video_ms', 'duration'].each do |field|
+      attributes[field] = '' if provenance[field] == 'automatic'
+    end
+    tag_sources['automatic'] = ''
+    attributes['tags'] = merged_tags(tag_sources, provenance['tags'])
+  end
+
+  def clear_fetch_warnings! field_warnings
+    FETCH_WARNING_FIELDS.each do |field|
+      field_warnings.delete(field)
+    end
+  end
+
+  def metadata_for url, cache
+    cache[url] ||= fetch_metadata(url)
+  end
+
+  def fetch_metadata url
+    return { data: { }, warnings: { 'url' => ['URL が空です．'] },
+             validation_errors: { } } if url.blank?
+
+    data = sanitise_metadata(PostMetadataFetcher.fetch(url).stringify_keys.compact)
+    warnings = { }
+    add_field_warning!(warnings, 'title', TITLE_FETCH_WARNING) if data['title'].blank?
+    if data['thumbnail_base'].blank?
+      add_field_warning!(warnings, 'thumbnail_base', THUMBNAIL_FETCH_WARNING)
+    end
+    { data:, warnings:, validation_errors: { } }
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
+    Rails.logger.info(
+        "post_import_metadata_fetch_unsafe_url #{ payload.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 #{ payload.to_json }")
+    { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
+  end
+
+  def sanitise_metadata metadata
+    {
+        'title' => sanitise_metadata_title(metadata['title']),
+        'thumbnail_base' => sanitise_metadata_url(metadata['thumbnail_base']),
+        'original_created_from' => sanitise_metadata_time(metadata['original_created_from']),
+        'original_created_before' => sanitise_metadata_time(metadata['original_created_before']),
+        'duration' => sanitise_metadata_duration(metadata['duration']),
+        'tags' => metadata['tags'].to_s.presence }.compact
+  end
+
+  def sanitise_metadata_title value
+    value.is_a?(String) ? value.presence : nil
+  end
+
+  def sanitise_metadata_url value
+    return nil unless value.is_a?(String)
+
+    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
+    return nil unless value.is_a?(String)
+
+    Time.iso8601(value).in_time_zone.change(sec: 0, nsec: 0).iso8601
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def sanitise_metadata_duration value
+    return nil unless value.is_a?(String)
+
+    value.presence
+  end
+
+  def normalise_duration_attribute value
+    return '' if value.nil?
+    return value if value.is_a?(String)
+
+    milliseconds = Integer(value, exception: false)
+    return value.to_s if milliseconds.nil? || milliseconds <= 0
+
+    seconds_string = (milliseconds / 1_000.0).to_s
+    seconds_string.end_with?('.0') ? seconds_string.delete_suffix('.0') : seconds_string
+  end
+
+  def preload_metadata! prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+    urls = prepared_rows.filter_map { |row|
+      next unless row[:normal_url].present?
+      next if row[:url_error].present?
+      next unless should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+      next if url_counts[row[:normal_url]].to_i > 1
+      next if existing_posts.key?(row[:normal_url])
+
+      row[:normal_url]
+    }.uniq
+    urls = urls.reject { metadata_cache.key?(_1) }
+    return if urls.empty?
+
+    url_queue = Queue.new
+    result_queue = Queue.new
+    urls.each { url_queue << _1 }
+    workers = [urls.length, 4].min.times.map {
+      Thread.new {
+        Rails.application.executor.wrap do
+          loop do
+            url = url_queue.pop(true)
+            result_queue << [url, safe_fetch_metadata(url)]
+          rescue ThreadError
+            break
+          end
+        end
+      }
+    }
+    Timeout.timeout(15) { workers.each(&:join) }
+  rescue Timeout::Error
+    workers&.each(&:kill)
+  ensure
+    workers&.each(&:join)
+    while result_queue&.size.to_i.positive?
+      url, result = result_queue.pop
+      metadata_cache[url] = result
+    end
+    urls&.each do |url|
+      metadata_cache[url] ||= { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] } }
+    end
+  end
+
+  def safe_fetch_metadata url
+    fetch_metadata(url)
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    payload = { error: e.class.name, message: e.message }
+    Rails.logger.info(
+        "post_import_metadata_fetch_unsafe_url #{ payload.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 #{ payload.to_json }")
+    { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
+  end
+
+  def preload_known_tags prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+    names = prepared_rows.flat_map { |row|
+      attributes = initial_attributes(row)
+      provenance = initial_provenance(row)
+      tag_sources = initial_tag_sources(row, attributes, provenance)
+      if metadata_url_changed?(row)
+        clear_automatic_values!(attributes, provenance, tag_sources)
+      end
+      if should_apply_metadata_to_row?(row, fetch_metadata, existing_posts, url_counts)
+        metadata = metadata_for(row[:normal_url], metadata_cache)
+        apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
+      end
+      preview_tag_names(merged_tags(tag_sources, provenance['tags']))
+    }.compact.uniq
+    return { } if names.empty?
+
+    Tag.joins(:tag_name)
+      .where(tag_names: { name: names })
+      .includes(:tag_name)
+      .to_a
+      .index_by(&:name)
+  end
+
+  def preload_parent_ids prepared_rows
+    ids = prepared_rows.flat_map { |row|
+      attributes = initial_attributes(row)
+      preview_parent_ids(attributes['parent_post_ids'])
+    }.uniq
+    return { } if ids.empty?
+
+    Post.where(id: ids).pluck(:id).to_h { [_1, true] }
+  end
+
+  def metadata_url_changed? row
+    row[:metadata_url].present? && row[:metadata_url] != (row[:normal_url] || row[:url_text])
+  end
+
+  def should_apply_metadata_to_row? row, fetch_metadata, existing_posts, url_counts
+    normal_url = row[:normal_url]
+    return false if normal_url.blank?
+    return false if row[:url_error].present?
+    return false if url_counts[normal_url].to_i > 1
+    return false if existing_posts.key?(normal_url)
+
+    should_fetch_metadata?(fetch_metadata, row[:source_row].to_i)
+  end
+
+  def validate_url_safety normal_url
+    return nil if normal_url.blank?
+
+    Preview::UrlSafety.validate(normal_url)
+    nil
+  rescue Preview::UrlSafety::UnsafeUrl => e
+    e.message
+  end
+
+  def apply_metadata! attributes, provenance, tag_sources, metadata
+    metadata.each do |field, value|
+      if field == 'tags'
+        next if provenance['tags'] == 'manual'
+
+        tag_sources['automatic'] = value.to_s
+        attributes['tags'] = merged_tags(tag_sources)
+        next
+      end
+      next unless provenance[field] == 'automatic'
+
+      attributes[field] = value
+      provenance[field] = 'automatic'
+    end
+  end
+
+  def apply_fetch_warnings! field_warnings, warnings
+    warnings.each do |field, values|
+      values.each do |value|
+        add_field_warning!(field_warnings, field, value)
+      end
+    end
+  end
+
+  def add_field_warning! field_warnings, field, message
+    field_warnings[field] ||= []
+    field_warnings[field] << message unless field_warnings[field].include?(message)
+  end
+
+  def merged_tags sources, origin = nil
+    return sources['manual'].to_s if origin == 'manual'
+
+    sources['automatic'].to_s
+  end
+
+  def preview_tag_names raw
+    names = raw.to_s.split
+    return [] if names.empty?
+    if names.any? { _1.downcase.start_with?('nico:') }
+      return []
+    end
+
+    names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+  rescue Tag::SectionLiteralParseError
+    []
+  end
+
+  def validate_preview_tags raw, errors, known_tags
+    names = raw.to_s.split
+    return if names.empty?
+    if names.any? { _1.downcase.start_with?('nico:') }
+      errors[:tags] = ['ニコニコ・タグは直接指定できません．']
+      return
+    end
+
+    parsed = names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
+    existing = parsed.filter_map { known_tags[_1] }
+    deprecated = existing.select(&:deprecated?).map(&:name)
+    errors[:tags] = ["廃止済みタグがあります: #{ deprecated.join(' ') }"] if deprecated.present?
+  rescue Tag::SectionLiteralParseError
+    errors[:tags] = ['タグ区間の記法が不正です．']
+  end
+
+  def validate_basic_data attributes, errors
+    post = Post.new(title: attributes['title'].presence,
+                    url: attributes['url'],
+                    thumbnail_base: attributes['thumbnail_base'].presence,
+                    original_created_from: attributes['original_created_from'].presence,
+                    original_created_before: attributes['original_created_before'].presence,
+                    video_ms: parse_video_ms(attributes, errors))
+    post.valid?
+    post.errors.each do |error|
+      next if error.attribute == :url && error.type == :taken
+
+      (errors[error.attribute] ||= []) << error.message
+    end
+  end
+
+  def parse_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')
+  rescue Tag::SectionLiteralParseError
+    errors[:video_ms] = ['動画時間の記法が不正です．']
+    nil
+  end
+
+  def preview_parent_ids raw
+    raw.to_s.split.map { Integer(_1, exception: false) }.compact
+  end
+
+  def validate_parents raw, errors, existing_parent_ids
+    ids = raw.to_s.split.map { Integer(_1, exception: false) }
+    return if ids.compact.empty? && raw.to_s.blank?
+
+    if ids.any? { _1.nil? || _1 <= 0 }
+      errors[:parent_post_ids] = ['親投稿 Id. が不正です．']
+      return
+    end
+    if ids.uniq.any? { !existing_parent_ids[_1] }
+      errors[:parent_post_ids] = ['存在しない親投稿 Id. があります．']
+    end
+  end
+end

backend/app/services/post_metadata_fetcher.rb

@@ -0,0 +1,198 @@
+require 'time'
+require 'date'
+
+class PostMetadataFetcher
+  TIMESTAMP_PATTERN =
+      /\A(\d{4})-(\d{2})-(\d{2})T(\d{2})
+        (?::(\d{2})(?::(\d{2})(?:\.(\d+))?)?)?
+        (Z|[+-]\d{2}:?\d{2})?\z/x
+
+  def self.fetch raw_url
+    uri, = Preview::UrlSafety.validate(raw_url)
+    response = Preview::HttpFetcher.fetch(
+        uri.to_s,
+        max_bytes: Preview::ThumbnailFetcher::HTML_MAX_BYTES)
+    metadata = Preview::HtmlMetadataExtractor.extract(response)
+    document = Nokogiri::HTML.parse(response.body)
+    content = lambda { |name|
+      document
+        .at_css("meta[property='#{ name }'], meta[name='#{ name }']")
+        &.[]('content')
+        &.strip
+        &.presence
+    }
+    duration = content.call('og:video:duration') || content.call('video:duration')
+    published = content.call('article:published_time') || content.call('date')
+    created_range = original_created_range(published)
+    platform_tags = platform_tags(uri)
+    { title: metadata[:title],
+      thumbnail_base:
+          Preview::KnownSiteExtractor.thumbnail_url(uri) || metadata[:image_url],
+      original_created_from: serialise_time(created_range&.first),
+      original_created_before: serialise_time(created_range&.last),
+      duration: serialise_duration(duration),
+      display_tags: display_tags(platform_tags),
+      tags: platform_tags.join(' ') }
+  end
+
+  def self.platform_tags uri
+    return ['動画', 'YouTube'] if Preview::KnownSiteExtractor.youtube_video_id(uri)
+    return ['動画', 'ニコニコ'] if Preview::KnownSiteExtractor.niconico_video_id(uri)
+
+    []
+  end
+
+  def self.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?
+
+    raw = value.to_s.strip
+    from, before =
+        case raw
+        when /\A(\d{4})\z/
+          year = Regexp.last_match(1).to_i
+          from = Time.zone.local(year, 1, 1)
+          [from, from + 1.year]
+        when /\A(\d{4})-(\d{2})\z/
+          year = Regexp.last_match(1).to_i
+          month = Regexp.last_match(2).to_i
+          return nil unless month.between?(1, 12)
+
+          from = Time.zone.local(year, month, 1)
+          [from, from + 1.month]
+        when /\A(\d{4})-(\d{2})-(\d{2})\z/
+          year = Regexp.last_match(1).to_i
+          month = Regexp.last_match(2).to_i
+          day = Regexp.last_match(3).to_i
+          return nil unless Date.valid_date?(year, month, day)
+
+          from = Time.zone.local(year, month, day)
+          [from, from + 1.day]
+        else
+          parse_timestamp_range(raw)
+        end
+    return nil if from.nil? || before.nil?
+
+    [from, before]
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def self.parse_timestamp_range raw
+    match = raw.match(TIMESTAMP_PATTERN)
+    return nil unless match
+
+    year = match[1].to_i
+    month = match[2].to_i
+    day = match[3].to_i
+    hour = match[4].to_i
+    minute = match[5]&.to_i || 0
+    second = match[6]&.to_i || 0
+    fraction = match[7]
+    offset = match[8]
+    return nil unless valid_timestamp_components?(year, month, day, hour, minute, second)
+    return nil unless valid_offset?(offset)
+
+    nanoseconds = parse_nanoseconds(fraction)
+    timestamp =
+        if offset.present?
+          Time.new(
+              year,
+              month,
+              day,
+              hour,
+              minute,
+              second + Rational(nanoseconds, 1_000_000_000),
+              parse_offset(offset)).in_time_zone
+        else
+          Time.zone.local(year, month, day, hour, minute, second).change(nsec: nanoseconds)
+        end
+
+    from = timestamp.change(sec: 0, nsec: 0)
+    before =
+        if match[5].nil?
+          from + 1.hour
+        else
+          from + 1.minute
+        end
+    [from, before]
+  end
+
+  def self.parse_nanoseconds value
+    return 0 if value.blank?
+
+    digits = value[0, 9].ljust(9, '0')
+    Integer(digits, 10)
+  end
+
+  def self.parse_offset value
+    return '+00:00' if value == 'Z'
+
+    value.match?(/\A[+-]\d{2}:\d{2}\z/) ? value : "#{ value[0, 3] }:#{ value[3, 2] }"
+  end
+
+  def self.serialise_duration value
+    seconds = Float(value)
+    return nil unless seconds.positive?
+
+    milliseconds = (seconds * 1_000).round
+    seconds_string = (milliseconds / 1_000.0).to_s
+    seconds_string.end_with?('.0') ? seconds_string.delete_suffix('.0') : seconds_string
+  rescue ArgumentError, TypeError
+    nil
+  end
+
+  def self.valid_timestamp_components? year, month, day, hour, minute, second
+    return false unless Date.valid_date?(year, month, day)
+    return false unless hour.between?(0, 23)
+    return false unless minute.between?(0, 59)
+    return false unless second.between?(0, 59)
+
+    true
+  end
+
+  def self.valid_offset? value
+    return true if value.nil? || value == 'Z'
+
+    match = value.match(/\A([+-])(\d{2}):?(\d{2})\z/)
+    return false if match.nil?
+
+    hours = match[2].to_i
+    minutes = match[3].to_i
+    hours.between?(0, 23) && minutes.between?(0, 59)
+  end
+
+  def self.serialise_time value
+    return nil if value.nil?
+
+    value.nsec.zero? ? value.iso8601 : value.iso8601(9)
+  end
+
+  private_class_method :platform_tags,
+                       :display_tags,
+                       :original_created_range,
+                       :parse_timestamp_range,
+                       :parse_nanoseconds,
+                       :parse_offset,
+                       :serialise_duration,
+                       :valid_timestamp_components?,
+                       :valid_offset?,
+                       :serialise_time
+end

backend/app/services/post_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_url_normaliser.rb

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

backend/app/services/preview/html_metadata_extractor.rb

@@ -0,0 +1,21 @@
+module Preview
+  class HtmlMetadataExtractor
+    IMAGE_SELECTORS = [
+      'meta[property="og:image"]',
+      'meta[name="twitter:image"]',
+      'meta[name="thumbnail"]'
+    ].freeze
+
+    def self.extract(response)
+      document = Nokogiri::HTML.parse(response.body)
+      image_url = IMAGE_SELECTORS.filter_map {
+        document.at_css(_1)&.[]('content')&.strip.presence
+      }.first
+
+      { title: document.at_css('title')&.text&.strip,
+        image_url: image_url ? URI.join(response.url, image_url).to_s : nil }
+    rescue URI::InvalidURIError
+      { title: document.at_css('title')&.text&.strip, image_url: nil }
+    end
+  end
+end

backend/app/services/preview/http_fetcher.rb

@@ -0,0 +1,123 @@
+require 'net/http'
+require 'json'
+
+module Preview
+  class HttpFetcher
+    class FetchFailed < StandardError; end
+    class FetchTimeout < FetchFailed; end
+    class ResponseTooLarge < FetchFailed; end
+
+    MAX_REDIRECTS = 5
+    DEFAULT_MAX_BYTES = 5.megabytes
+
+    Response = Data.define(:body, :content_type, :url)
+
+    def self.fetch(raw_url, max_bytes: DEFAULT_MAX_BYTES, redirects: MAX_REDIRECTS)
+      uri, addresses = UrlSafety.validate(raw_url)
+      response = request(uri, addresses.first, max_bytes)
+
+      if response.is_a?(Net::HTTPRedirection)
+        location = response['location']
+        if redirects.zero?
+          log_failure(:redirect_limit,
+                      url: uri.to_s,
+                      redirects:,
+                      location:,
+                      content_type: response['content-type'],
+                      content_length: response['content-length'])
+          raise FetchFailed, 'redirect が多すぎます．'
+        end
+
+        if location.blank?
+          log_failure(:blank_redirect_location,
+                      url: uri.to_s,
+                      redirects:,
+                      content_type: response['content-type'],
+                      content_length: response['content-length'])
+          raise FetchFailed, 'redirect 先が不正です．'
+        end
+
+        redirect_url =
+            begin
+              URI.join(uri, location).to_s
+            rescue URI::InvalidURIError => e
+              log_failure(:invalid_redirect_location,
+                          url: uri.to_s,
+                          redirects:,
+                          location:,
+                          error: e.class.name,
+                          message: e.message)
+              raise FetchFailed, 'redirect 先が不正です．'
+            end
+
+        return fetch(redirect_url, max_bytes:, redirects: redirects - 1)
+      end
+
+      unless response.is_a?(Net::HTTPSuccess)
+        log_failure(:http_status,
+                    url: uri.to_s,
+                    code: response.code,
+                    content_type: response['content-type'],
+                    content_length: response['content-length'])
+        raise FetchFailed, "外部サーバーが HTTP #{ response.code } を返しました．"
+      end
+
+      Response.new(response.body, response['content-type'].to_s, uri.to_s)
+    rescue Net::OpenTimeout, Net::ReadTimeout, Timeout::Error => e
+      log_failure(:timeout, url: uri&.to_s || raw_url, error: e.class.name, message: e.message)
+      raise FetchTimeout, e.message
+    rescue SocketError, SystemCallError, OpenSSL::SSL::SSLError, EOFError => e
+      log_failure(:network_error, url: uri&.to_s || raw_url, error: e.class.name,
+                  message: e.message)
+      raise FetchFailed, e.message
+    end
+
+    def self.request(uri, ip_address, max_bytes)
+      http = Net::HTTP.new(uri.host, uri.port)
+      http.ipaddr = ip_address
+      http.use_ssl = uri.scheme == 'https'
+      http.open_timeout = 5
+      http.read_timeout = 8
+      http.write_timeout = 5
+
+      request = Net::HTTP::Get.new(uri)
+      request['User-Agent'] = 'BTRC-Hub thumbnail preview'
+      request['Accept'] = 'text/html,image/*;q=0.9,*/*;q=0.1'
+
+      http.request(request) do |response|
+        length = response['content-length'].to_i
+        if length > max_bytes
+          log_failure(:response_too_large,
+                      url: uri.to_s,
+                      content_type: response['content-type'],
+                      content_length: response['content-length'],
+                      max_bytes:)
+          raise ResponseTooLarge, '外部データが大きすぎます．'
+        end
+
+        body = +''
+        response.read_body do |chunk|
+          body << chunk
+          next unless body.bytesize > max_bytes
+
+          log_failure(:response_too_large,
+                      url: uri.to_s,
+                      content_type: response['content-type'],
+                      content_length: response['content-length'],
+                      bytes_read: body.bytesize,
+                      max_bytes:)
+          raise ResponseTooLarge, '外部データが大きすぎます．'
+        end
+        response.instance_variable_set(:@body, body)
+        response.instance_variable_set(:@read, true)
+        return response
+      end
+    end
+
+    def self.log_failure(reason, **payload)
+      Rails.logger.warn("preview_http_fetcher_failure #{ { reason:, **payload }.to_json }")
+    end
+
+    private_class_method :request, :log_failure
+  end
+end

backend/app/services/preview/known_site_extractor.rb

@@ -0,0 +1,34 @@
+module Preview
+  class KnownSiteExtractor
+    def self.thumbnail_url(uri)
+      youtube_thumbnail(uri)
+    end
+
+    def self.youtube_video_id(uri)
+      case uri.host&.downcase
+      when 'youtu.be'
+        uri.path.split('/').reject(&:blank?).first
+      when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
+        uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
+      end&.then { _1 if _1.match?(/\A[A-Za-z0-9_-]{6,20}\z/) }
+    end
+
+    def self.niconico_video_id(uri)
+      case uri.host&.downcase
+      when 'www.nicovideo.jp', 'nicovideo.jp'
+        uri.path[%r{\A/watch/(sm\d+)\z}, 1]
+      when 'nico.ms'
+        uri.path[%r{\A/(sm\d+)\z}, 1]
+      end
+    end
+
+    def self.youtube_thumbnail(uri)
+      id = youtube_video_id(uri)
+      return unless id
+
+      "https://i.ytimg.com/vi/#{ id }/hqdefault.jpg"
+    end
+
+    private_class_method :youtube_thumbnail
+  end
+end

backend/app/services/preview/thumbnail_fetcher.rb

@@ -0,0 +1,102 @@
+module Preview
+  class ThumbnailFetcher
+    class GenerationFailed < StandardError; end
+    RASTER_IMAGE_CONTENT_TYPES = [
+      'image/jpeg', 'image/png', 'image/gif', 'image/webp'
+    ].freeze
+    HTML_MAX_BYTES = 1.megabyte
+    NICONICO_XML_MAX_BYTES = 256.kilobytes
+
+    def self.fetch(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+
+      known_url = KnownSiteExtractor.thumbnail_url(uri)
+      image = fetch_image_or_nil(known_url) if known_url
+      return image if image
+
+      niconico_url = niconico_thumbnail_url(uri)
+      image = fetch_image_or_nil(niconico_url) if niconico_url
+      return image if image
+
+      page = HttpFetcher.fetch(uri.to_s, max_bytes: HTML_MAX_BYTES)
+      metadata = HtmlMetadataExtractor.extract(page)
+      raise GenerationFailed, 'サムネール画像が見つかりませんでした．' if metadata[:image_url].blank?
+
+      fetch_image!(metadata[:image_url])
+    end
+
+    def self.fetch_image_response(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+      response = HttpFetcher.fetch(uri.to_s)
+      unless 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
+
+      response
+    rescue HttpFetcher::FetchTimeout
+      raise
+    rescue HttpFetcher::ResponseTooLarge
+      raise
+    rescue HttpFetcher::FetchFailed
+      raise GenerationFailed, 'サムネール画像を取得できませんでした．'
+    end
+
+    def self.title(raw_url)
+      uri, = UrlSafety.validate(raw_url)
+      HtmlMetadataExtractor.extract(
+          HttpFetcher.fetch(uri.to_s, max_bytes: HTML_MAX_BYTES))[:title]
+    end
+
+    def self.fetch_image_or_nil(url)
+      return nil if url.blank?
+
+      response = HttpFetcher.fetch(url)
+      return nil unless Post.remote_thumbnail_image_bytes?(
+                            response.body,
+                            content_type: response.content_type)
+
+      response.body
+    rescue HttpFetcher::FetchTimeout
+      raise
+    rescue HttpFetcher::FetchFailed
+      nil
+    end
+
+    def self.fetch_image!(url)
+      fetch_image_response(url).body
+    end
+
+    def self.niconico_thumbnail_url(uri)
+      video_id = KnownSiteExtractor.niconico_video_id(uri)
+      return nil if video_id.blank?
+
+      response = HttpFetcher.fetch("https://ext.nicovideo.jp/api/getthumbinfo/#{ video_id }",
+                                   max_bytes: NICONICO_XML_MAX_BYTES)
+      xml = Nokogiri::XML(response.body)
+      return nil unless xml.at_xpath('/nicovideo_thumb_response/@status')&.value == 'ok'
+
+      xml.at_xpath('//thumbnail_url')&.text&.strip.presence
+    rescue HttpFetcher::FetchFailed, HttpFetcher::FetchTimeout => e
+      payload = {
+          url: uri.to_s,
+          video_id:,
+          error: e.class.name,
+          message: e.message }
+      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ payload.to_json }")
+      nil
+    rescue Nokogiri::XML::SyntaxError => e
+      payload = {
+          url: uri.to_s,
+          video_id:,
+          error: e.class.name,
+          message: e.message }
+      Rails.logger.info("preview_niconico_getthumbinfo_fallback #{ payload.to_json }")
+      nil
+    end
+
+    private_class_method :fetch_image_or_nil, :fetch_image!,
+                         :niconico_thumbnail_url
+  end
+end

backend/app/services/preview/url_safety.rb

@@ -0,0 +1,55 @@
+require 'resolv'
+require 'ipaddr'
+require 'uri'
+
+module Preview
+  class UrlSafety
+    class UnsafeUrl < StandardError; end
+
+    FORBIDDEN_NETWORKS = [
+      '0.0.0.0/8', '10.0.0.0/8', '100.64.0.0/10', '127.0.0.0/8',
+      '169.254.0.0/16', '172.16.0.0/12', '192.0.0.0/24',
+      '192.0.2.0/24', '192.168.0.0/16', '198.18.0.0/15',
+      '198.51.100.0/24', '203.0.113.0/24', '224.0.0.0/4',
+      '240.0.0.0/4', '::/128', '::1/128', 'fc00::/7', 'fe80::/10',
+      'ff00::/8', '2001:db8::/32', '::ffff:0:0/96'
+    ].map { IPAddr.new(_1) }.freeze
+
+    def self.validate(raw_url)
+      value = raw_url.to_s.strip
+      if value.match?(/\A[a-z][a-z0-9+\-.]*:/i)
+        unless value.match?(/\Ahttps?:\/\//i)
+          raise UnsafeUrl, 'http または https の URL を指定してください．'
+        end
+      else
+        value = "http://#{ value }"
+      end
+      uri = URI.parse(value)
+
+      unless ['http', 'https'].include?(uri.scheme&.downcase) && uri.host.present?
+        raise UnsafeUrl, 'http または https の URL を指定してください．'
+      end
+      raise UnsafeUrl, 'userinfo つき URL は使用できません．' if uri.userinfo.present?
+
+      addresses = Resolv.getaddresses(uri.host)
+      raise UnsafeUrl, 'URL のホストを解決できません．' if addresses.empty?
+
+      parsed_addresses = addresses.map { IPAddr.new(_1) }
+      if parsed_addresses.any? { |address| forbidden?(address) }
+        raise UnsafeUrl, '安全でない接続先は使用できません．'
+      end
+
+      [uri, parsed_addresses.map(&:to_s)]
+    rescue Resolv::ResolvError
+      raise UnsafeUrl, 'URL のホストを解決できません．'
+    rescue URI::InvalidURIError, IPAddr::InvalidAddressError
+      raise UnsafeUrl, 'URL が不正です．'
+    end
+
+    def self.forbidden?(address)
+      FORBIDDEN_NETWORKS.any? { _1.include?(address) }
+    end
+
+    private_class_method :forbidden?
+  end
+end

backend/app/services/youtube/sync.rb

@@ -1,4 +1,3 @@
-require 'open-uri'
 require 'set'
 require 'time'
 
@@ -127,12 +126,12 @@ module Youtube
       return if post.thumbnail.attached?
       return if thumbnail_url.blank?
 
-      post.thumbnail.attach(
-          io:           URI.open(thumbnail_url),
-          filename:     File.basename(URI.parse(thumbnail_url).path),
-          content_type: 'image/jpeg')
-
-      post.resized_thumbnail!
+      post.attach_thumbnail_from_url!(thumbnail_url)
+    rescue Post::RemoteThumbnailFetchFailed => e
+      Rails.logger.info("youtube_sync_thumbnail_fetch_failed #{ { post_id: post.id,
+                                                                  thumbnail_url:,
+                                                                  error: e.class.name,
+                                                                  message: e.message }.to_json }")
     end
 
     def youtube_url_regexp id

backend/config/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?
-    config.public_file_server.headers = { "cache-control" => "public, max-age=#{2.days.to_i}" }
+  if Rails.root.join('tmp/caching-dev.txt').exist?
+    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

@@ -52,6 +52,8 @@ 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'
@@ -81,6 +83,11 @@ Rails.application.routes.draw do
     end
   end
 
+  get 'users/settings', to: 'user_settings#show'
+  patch 'users/settings', to: 'user_settings#update'
+  get 'users/theme_slots', to: 'user_theme_slots#index'
+  put 'users/theme_slots/:base_theme/:slot_no', to: 'user_theme_slots#update'
+
   resources :users, only: [:create, :update] do
     collection do
       post :verify

backend/db/migrate/20260704000000_rebuild_settings_as_typed_user_settings.rb

@@ -0,0 +1,31 @@
+class RebuildSettingsAsTypedUserSettings < ActiveRecord::Migration[8.0]
+  def change
+    remove_foreign_key :settings, :users if foreign_key_exists?(:settings, :users)
+    remove_index :settings, :user_id if index_exists?(:settings, :user_id)
+
+    remove_column :settings, :key, :string if column_exists?(:settings, :key)
+    remove_column :settings, :value, :json if column_exists?(:settings, :value)
+
+    change_column_null :settings, :user_id, false
+
+    add_column :settings, :theme, :string, null: false, default: 'system'
+    add_column :settings,
+               :auto_fetch_title,
+               :string,
+               null: false,
+               default: 'manual'
+    add_column :settings,
+               :auto_fetch_thumbnail,
+               :string,
+               null: false,
+               default: 'manual'
+    add_column :settings,
+               :wiki_editor_mode,
+               :string,
+               null: false,
+               default: 'split'
+
+    add_index :settings, :user_id, unique: true
+    add_foreign_key :settings, :users
+  end
+end

backend/db/migrate/20260705000000_create_user_theme_slots.rb

@@ -0,0 +1,22 @@
+class CreateUserThemeSlots < ActiveRecord::Migration[8.0]
+  def change
+    create_table :user_theme_slots do |t|
+      t.references :user, null: false, foreign_key: true
+      t.string :base_theme, null: false
+      t.integer :slot_no, null: false
+      t.json :tokens, null: false
+      t.timestamps
+    end
+
+    add_index :user_theme_slots,
+              [:user_id, :base_theme, :slot_no],
+              unique: true,
+              name: 'index_user_theme_slots_on_user_theme_and_slot'
+    add_check_constraint :user_theme_slots,
+                         "base_theme IN ('light', 'dark')",
+                         name: 'user_theme_slots_base_theme_valid'
+    add_check_constraint :user_theme_slots,
+                         'slot_no BETWEEN 1 AND 3',
+                         name: 'user_theme_slots_slot_no_valid'
+  end
+end

backend/db/migrate/20260713000000_create_post_url_sanitisation_rules.rb

@@ -0,0 +1,61 @@
+class CreatePostUrlSanitisationRules < ActiveRecord::Migration[8.0]
+  class PostUrlSanitisationRule < ActiveRecord::Base
+    self.table_name = 'post_url_sanitisation_rules'
+  end
+
+  def up
+    create_table :post_url_sanitisation_rules, id: :integer, primary_key: :priority do |t|
+      t.string :source_pattern, null: false
+      t.string :replacement, null: false
+      t.timestamps
+      t.datetime :discarded_at
+
+      t.index :source_pattern, unique: true
+      t.index :discarded_at
+    end
+
+    now = Time.current
+
+    PostUrlSanitisationRule.insert_all!([
+        { priority: 10,
+          source_pattern: '\Ahttps?://youtu\.be/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 20,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/live/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 30,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/shorts/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 40,
+          source_pattern: '\Ahttps?://(?:www\.|m\.)?youtube\.com/embed/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 50,
+          source_pattern:
+              '\Ahttps?://(?:www\.|m\.)?youtube\.com/watch\?(?:[^#&]+&)*v=([^&#]+)(?:[&#].*)?\z',
+          replacement: 'https://www.youtube.com/watch?v=\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 60,
+          source_pattern: '\Ahttps?://nico\.ms/([^/?#]+)(?:[?#].*)?\z',
+          replacement: 'https://www.nicovideo.jp/watch/\1',
+          created_at: now,
+          updated_at: now },
+        { priority: 70,
+          source_pattern: '\Ahttps?://(?:www\.)?nicovideo\.jp/watch/([^?#/]+)(?:[?#].*)?\z',
+          replacement: 'https://www.nicovideo.jp/watch/\1',
+          created_at: now,
+          updated_at: now }])
+  end
+
+  def down
+    drop_table :post_url_sanitisation_rules
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
+ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -331,6 +331,16 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
+  create_table "post_url_sanitisation_rules", primary_key: "priority", id: :integer, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.string "source_pattern", null: false
+    t.string "replacement", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.datetime "discarded_at"
+    t.index ["discarded_at"], name: "index_post_url_sanitisation_rules_on_discarded_at"
+    t.index ["source_pattern"], name: "index_post_url_sanitisation_rules_on_source_pattern", unique: true
+  end
+
   create_table "post_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.integer "version_no", null: false
@@ -374,11 +384,26 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
 
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "user_id", null: false
-    t.string "key", null: false
-    t.json "value", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index ["user_id"], name: "index_settings_on_user_id"
+    t.string "theme", default: "system", null: false
+    t.string "auto_fetch_title", default: "manual", null: false
+    t.string "auto_fetch_thumbnail", default: "manual", null: false
+    t.string "wiki_editor_mode", default: "split", null: false
+    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|
@@ -426,9 +451,9 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.string "event_type", null: false
     t.string "name", null: false
     t.string "category", null: false
-    t.datetime "deprecated_at"
     t.text "aliases", null: false
     t.text "parent_tag_ids", null: false
+    t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_at"], name: "index_tag_versions_on_created_at"
@@ -441,10 +466,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_name_id", null: false
     t.string "category", default: "general", null: false
+    t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
-    t.datetime "deprecated_at"
     t.datetime "discarded_at"
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
@@ -566,6 +591,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
     t.index ["post_id"], name: "index_user_post_views_on_post_id"
   end
 
+  create_table "user_theme_slots", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "user_id", null: false
+    t.string "base_theme", null: false
+    t.integer "slot_no", null: false
+    t.json "tokens", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["user_id", "base_theme", "slot_no"], name: "index_user_theme_slots_on_user_theme_and_slot", unique: true
+    t.index ["user_id"], name: "index_user_theme_slots_on_user_id"
+    t.check_constraint "`base_theme` in (_utf8mb4'light',_utf8mb4'dark')", name: "user_theme_slots_base_theme_valid"
+    t.check_constraint "`slot_no` between 1 and 3", name: "user_theme_slots_slot_no_valid"
+  end
+
   create_table "users", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name"
     t.string "inheritance_code", limit: 64, null: false
@@ -576,19 +614,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) 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
@@ -738,6 +763,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_06_26_010000) do
   add_foreign_key "user_ips", "users"
   add_foreign_key "user_post_views", "posts"
   add_foreign_key "user_post_views", "users"
+  add_foreign_key "user_theme_slots", "users"
   add_foreign_key "wiki_assets", "users", column: "created_by_user_id"
   add_foreign_key "wiki_assets", "wiki_pages"
   add_foreign_key "wiki_pages", "tag_names"

backend/db/seeds.rb

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

backend/lib/package.json

@@ -1,15 +0,0 @@
-{
-  "name": "lib",
-  "version": "1.0.0",
-  "main": "screenshot.js",
-  "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
-  },
-  "keywords": [],
-  "author": "",
-  "license": "ISC",
-  "description": "",
-  "dependencies": {
-    "puppeteer": "^24.10.0"
-  }
-}

backend/lib/screenshot.js

@@ -1,18 +0,0 @@
-const puppeteer = require ('puppeteer')
-const fs = require ('fs')
-
-
-void (async () => {
-  const url = process.argv[2]
-  const output = process.argv[3]
-
-  const browser = await puppeteer.launch ({
-      args: ['--no-sandbox', '--disable-setuid-sandbox'] })
-
-  const page = await browser.newPage ()
-  await page.setViewport ({ width: 960, height: 960 })
-  await page.goto (url, { waitUntil: 'networkidle2', timeout: 15000 })
-
-  await page.screenshot ({ path: output })
-  await browser.close ()
-}) ()

backend/lib/tasks/sync_nico.rake

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

backend/spec/db/seeds_spec.rb

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

backend/spec/models/post_spec.rb

@@ -0,0 +1,361 @@
+require 'rails_helper'
+require 'tempfile'
+
+RSpec.describe Post, type: :model do
+  before do
+    PostUrlSanitisationRule.unscoped.delete_all
+  end
+
+  describe 'URL normalisation' do
+    it 'normalises the HTTP URL before applying sanitisation rules' do
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/videos/([^/]+)\\z',
+        replacement: 'https://example.com/watch/\\1'
+      )
+
+      post = described_class.create!(
+        title: 'normalised URL',
+        url: '  https://EXAMPLE.com/videos/123/  '
+      )
+
+      expect(post.url).to eq('https://example.com/watch/123')
+    end
+
+    it 'does not normalise an unchanged URL when another attribute changes' do
+      post = create(:post)
+      post.update_column(:url, 'https://EXAMPLE.com/unchanged/')
+
+      post.update!(title: 'updated title')
+
+      expect(post.reload.url).to eq('https://EXAMPLE.com/unchanged/')
+    end
+
+    it 'validates the sanitised URL length' do
+      path = 'a' * 375
+
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/(a+)\\z',
+        replacement: 'https://example.com/\\1\\1'
+      )
+
+      post = described_class.new(
+        title: 'long URL',
+        url: "https://example.com/#{ path }"
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors.details.fetch(:url)).to include(
+        error: :too_long,
+        count: 768
+      )
+    end
+
+    it 'validates uniqueness after sanitisation' do
+      PostUrlSanitisationRule.create!(
+        priority: 10,
+        source_pattern: '\\Ahttps://example\\.com/alias\\z',
+        replacement: 'https://example.com/canonical'
+      )
+      create(:post, url: 'https://example.com/canonical')
+
+      post = described_class.new(title: 'duplicate URL', url: 'https://example.com/alias')
+
+      expect(post).to be_invalid
+      expect(post.errors.details.fetch(:url)).to include(error: :taken, value: post.url)
+    end
+  end
+
+  describe 'thumbnail processing' do
+    def image_blob(width:, height:, background:, draw: nil)
+      Tempfile.create(['post-thumbnail', '.png']) do |file|
+        MiniMagick::Tool::Convert.new do |convert|
+          convert.size "#{ width }x#{ height }"
+          convert.xc background
+          draw&.call(convert)
+          convert << file.path
+        end
+        File.binread(file.path)
+      end
+    end
+
+    def upload_for(blob)
+      StringIO.new(blob).tap(&:rewind)
+    end
+
+    def read_image(attachment)
+      blob =
+          attachment.is_a?(Hash) ? attachment.fetch(:io).read : attachment.download
+      MiniMagick::Image.read(blob)
+    end
+
+    def colour_at(image, x, y)
+      image.get_pixels.fetch(y).fetch(x)
+    end
+
+    def expect_green(pixel)
+      expect(pixel[1]).to be > pixel[0] + 40
+      expect(pixel[1]).to be > pixel[2] + 40
+    end
+
+    def expect_red(pixel)
+      expect(pixel[0]).to be > pixel[1] + 40
+      expect(pixel[0]).to be > pixel[2] + 40
+    end
+
+    def expect_blue(pixel)
+      expect(pixel[2]).to be > pixel[0] + 40
+      expect(pixel[2]).to be > pixel[1] + 40
+    end
+
+    describe '.resized_thumbnail_attachment' do
+      it 'fits a wide image within 180x180 without distorting it' do
+        blob = image_blob(
+            width: 360,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 90,0 269,179'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([180, 90])
+        expect_red(colour_at(image, 0, 45))
+        expect_green(colour_at(image, 90, 45))
+        expect_red(colour_at(image, 179, 45))
+      end
+
+      it 'fits a tall image within 180x180 without distorting it' do
+        blob = image_blob(
+            width: 180,
+            height: 360,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 0,90 179,269'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([90, 180])
+        expect_red(colour_at(image, 45, 0))
+        expect_green(colour_at(image, 45, 90))
+        expect_red(colour_at(image, 45, 179))
+      end
+
+      it 'keeps a square image square without distortion' do
+        blob = image_blob(
+            width: 180,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'blue'
+              convert.draw 'rectangle 90,0 179,179'
+            })
+
+        resized = described_class.resized_thumbnail_attachment(upload_for(blob))
+        image = read_image(resized)
+
+        expect(image.dimensions).to eq([180, 180])
+        expect_red(colour_at(image, 20, 90))
+        expect_blue(colour_at(image, 160, 90))
+      end
+    end
+
+    describe '#attach_thumbnail_from_url!' do
+      it 'attaches a fetched remote image through the common resize path' do
+        blob = image_blob(
+            width: 240,
+            height: 180,
+            background: 'red',
+            draw: -> convert {
+              convert.fill 'green'
+              convert.draw 'rectangle 30,0 209,179'
+            })
+        response = Preview::HttpFetcher::Response.new(
+            blob,
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+
+        post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+        expect(post.thumbnail).to receive(:attach).once.and_call_original
+        post.attach_thumbnail_from_url!('https://example.com/thumb.png')
+
+        expect(post.thumbnail).to be_attached
+        image = read_image(post.thumbnail)
+        expect(image.dimensions).to eq([180, 135])
+      end
+
+      it 'does not attach anything when thumbnail conversion fails' do
+        response = Preview::HttpFetcher::Response.new(
+            'not-an-image',
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+        allow(described_class).to receive(:resized_thumbnail_attachment)
+            .and_raise(MiniMagick::Error, 'convert failed')
+
+        post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+        expect {
+          post.attach_thumbnail_from_url!('https://example.com/thumb.png')
+        }.to raise_error(Post::RemoteThumbnailFetchFailed, 'convert failed')
+
+        expect(post.thumbnail).not_to be_attached
+      end
+
+      it 'keeps an existing thumbnail when remote conversion fails' do
+        existing = described_class.create!(title: 'title', url: 'https://example.com/post')
+        existing.thumbnail.attach(
+            io: StringIO.new('existing'),
+            filename: 'existing.jpg',
+            content_type: 'image/jpeg')
+        blob_id = existing.thumbnail.blob.id
+        response = Preview::HttpFetcher::Response.new(
+            'not-an-image',
+            'image/png',
+            'https://example.com/thumb.png')
+        allow(Preview::ThumbnailFetcher).to receive(:fetch_image_response)
+            .with('https://example.com/thumb.png')
+            .and_return(response)
+        allow(described_class).to receive(:resized_thumbnail_attachment)
+            .and_raise(MiniMagick::Error, 'convert failed')
+
+        expect {
+          existing.attach_thumbnail_from_url!('https://example.com/thumb.png')
+        }.to raise_error(Post::RemoteThumbnailFetchFailed, 'convert failed')
+
+        existing.reload
+        expect(existing.thumbnail).to be_attached
+        expect(existing.thumbnail.blob.id).to eq(blob_id)
+      end
+    end
+  end
+
+  describe 'original created datetime validation' do
+    it 'allows unrelated updates on persisted posts with second-bearing datetimes' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+      post.update_columns(
+        original_created_from: Time.zone.parse('2024-01-01T12:34:30Z'),
+        original_created_before: Time.zone.parse('2024-01-01T12:35:30Z')
+      )
+
+      post.title = 'updated title'
+
+      expect(post).to be_valid
+      expect { post.save! }.not_to raise_error
+    end
+
+    it 'rejects second-bearing updates when the datetime field changes' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+
+      post.original_created_from = '2024-01-01T12:34:30Z'
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+    end
+
+    it 'accepts fixing persisted datetimes to minute precision' do
+      post = described_class.create!(title: 'title', url: 'https://example.com/post')
+      post.update_columns(
+        original_created_from: Time.zone.parse('2024-01-01T12:34:30Z'),
+        original_created_before: Time.zone.parse('2024-01-01T12:35:30Z')
+      )
+
+      post.original_created_from = '2024-01-01T12:34Z'
+      post.original_created_before = '2024-01-01T12:35Z'
+
+      expect(post).to be_valid
+      expect { post.save! }.not_to raise_error
+    end
+
+    it 'adds only the minute-precision error for second precision values' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34:30',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+      expect(post.errors[:original_created_at]).to be_empty
+    end
+
+    it 'adds only the minute-precision error for fractional-second values' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34:00.123',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_from]).to eq(
+        [described_class::ORIGINAL_CREATED_MINUTE_PRECISION_MESSAGE]
+      )
+      expect(post.errors[:original_created_at]).to be_empty
+    end
+
+    it 'checks range rules only for valid minute-precision endpoints' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34',
+        original_created_before: '2024-01-01T12:34'
+      )
+
+      expect(post).to be_invalid
+      expect(post.errors[:original_created_at]).to eq(
+        [described_class::ORIGINAL_CREATED_ORDER_MESSAGE]
+      )
+    end
+
+    it 'accepts a one-minute range at minute precision' do
+      post = described_class.new(
+        title: 'title',
+        url: 'https://example.com/post',
+        original_created_from: '2024-01-01T12:34',
+        original_created_before: '2024-01-01T12:35'
+      )
+
+      expect(post).to be_valid
+    end
+
+    it 'rejects invalid calendar dates and invalid hours' do
+      invalid_dates = [
+        '2024-02-31T12:00',
+        '2023-02-29T12:00',
+        '2024-02-29T24:00'
+      ]
+
+      invalid_dates.each do |value|
+        post = described_class.new(
+          title: 'title',
+          url: 'https://example.com/post',
+          original_created_from: value
+        )
+
+        expect(post).to be_invalid
+        expect(post.errors[:original_created_from]).to eq(
+          [described_class::ORIGINAL_CREATED_INVALID_MESSAGE]
+        )
+      end
+    end
+  end
+end

backend/spec/models/post_url_sanitisation_rule_spec.rb

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

backend/spec/models/setting_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+
+RSpec.describe Setting, type: :model do
+  it 'accepts the default typed user settings' do
+    setting = described_class.new({ user: create(:user) }.merge(described_class.defaults))
+
+    expect(setting).to be_valid
+  end
+
+  it 'requires one settings row per user' do
+    user = create(:user)
+    described_class.create!({ user: }.merge(described_class.defaults))
+
+    duplicate = described_class.new({ user: }.merge(described_class.defaults))
+
+    expect(duplicate).not_to be_valid
+    expect(duplicate.errors[:user_id]).to be_present
+  end
+
+  it 'validates enum-like settings columns' do
+    setting = described_class.new(
+        { user: create(:user),
+          theme: 'neon',
+          auto_fetch_title: 'sometimes',
+          auto_fetch_thumbnail: 'sometimes',
+          wiki_editor_mode: 'sideways' })
+
+    expect(setting).not_to be_valid
+    expect(setting.errors[:theme]).to be_present
+    expect(setting.errors[:auto_fetch_title]).to be_present
+    expect(setting.errors[:auto_fetch_thumbnail]).to be_present
+    expect(setting.errors[:wiki_editor_mode]).to be_present
+  end
+end

backend/spec/models/user_theme_slot_spec.rb

@@ -0,0 +1,40 @@
+require 'rails_helper'
+
+RSpec.describe UserThemeSlot, type: :model do
+  it 'accepts a theme slot for one user, base theme, and slot number' do
+    slot = described_class.new(user: create(:user),
+                               base_theme: 'light',
+                               slot_no: 1,
+                               tokens: { 'background' => '0 0% 100%' })
+
+    expect(slot).to be_valid
+  end
+
+  it 'requires unique slot numbers per user and base theme' do
+    user = create(:user)
+    described_class.create!(user:,
+                            base_theme: 'dark',
+                            slot_no: 2,
+                            tokens: { 'background' => '222.2 84% 4.9%' })
+
+    duplicate = described_class.new(user:,
+                                    base_theme: 'dark',
+                                    slot_no: 2,
+                                    tokens: { 'background' => '0 0% 100%' })
+
+    expect(duplicate).not_to be_valid
+    expect(duplicate.errors[:user_id]).to be_present
+  end
+
+  it 'validates base theme, slot number, and token object shape' do
+    slot = described_class.new(user: create(:user),
+                               base_theme: 'system',
+                               slot_no: 4,
+                               tokens: 'not-object')
+
+    expect(slot).not_to be_valid
+    expect(slot.errors[:base_theme]).to be_present
+    expect(slot.errors[:slot_no]).to be_present
+    expect(slot.errors[:tokens]).to be_present
+  end
+end

backend/spec/requests/materials_spec.rb

@@ -287,6 +287,25 @@ RSpec.describe 'Materials API', type: :request do
         expect(json.dig('export_paths', 'legacy_drive')).to eq('伊地知ニジカ/created.png')
       end
 
+      it 'creates a create tag_version for a newly created material tag' do
+        expect do
+          post '/materials', params: {
+            tag: 'material_create_versioned_tag',
+            file: dummy_upload(filename: 'created.png')
+          }
+        end.to change(TagVersion, :count).by(1)
+
+        expect(response).to have_http_status(:created)
+
+        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_create_versioned_tag' })
+        version = tag.tag_versions.order(:version_no).last
+
+        expect(version.event_type).to eq('create')
+        expect(version.name).to eq('material_create_versioned_tag')
+        expect(version.category).to eq('material')
+        expect(version.created_by_user).to eq(member_user)
+      end
+
       it 'snapshots attached file metadata and sha256' do
         post '/materials', params: {
           tag: 'material_create_file_version',
@@ -466,6 +485,73 @@ RSpec.describe 'Materials API', type: :request do
         expect(json.dig('tag', 'name')).to eq('material_update_new')
       end
 
+      it 'creates a create tag_version when update creates a new tag' do
+        expect do
+          put "/materials/#{ material.id }", params: {
+            tag: 'material_update_versioned_tag',
+            file: dummy_upload(filename: 'updated.png')
+          }
+        end.to change(Tag, :count).by(1)
+          .and change(TagName, :count).by(1)
+          .and change(TagVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_update_versioned_tag' })
+        version = tag.tag_versions.order(:version_no).last
+
+        expect(version.event_type).to eq('create')
+        expect(version.name).to eq('material_update_versioned_tag')
+        expect(version.category).to eq('material')
+        expect(version.created_by_user).to eq(member_user)
+      end
+
+      it 'backfills a create tag_version for an existing material tag without history' do
+        existing_tag =
+            Tag.create!(tag_name: TagName.create!(name: 'material_update_existing_no_history'),
+                        category: :material)
+
+        expect(existing_tag.tag_versions).to be_empty
+
+        expect do
+          put "/materials/#{ material.id }", params: {
+            tag: 'material_update_existing_no_history',
+            file: dummy_upload(filename: 'updated.png')
+          }
+        end.to change(TagVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        version = existing_tag.reload.tag_versions.order(:version_no).last
+        expect(version.event_type).to eq('create')
+        expect(version.name).to eq('material_update_existing_no_history')
+        expect(version.category).to eq('material')
+        expect(version.created_by_user).to eq(member_user)
+      end
+
+      it 'backfills a create tag_version for an existing character tag without history' do
+        existing_tag =
+            Tag.create!(tag_name: TagName.create!(name: 'material_update_character_no_history'),
+                        category: :character)
+
+        expect(existing_tag.tag_versions).to be_empty
+
+        expect do
+          put "/materials/#{ material.id }", params: {
+            tag: 'material_update_character_no_history',
+            file: dummy_upload(filename: 'updated.png')
+          }
+        end.to change(TagVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        version = existing_tag.reload.tag_versions.order(:version_no).last
+        expect(version.event_type).to eq('create')
+        expect(version.name).to eq('material_update_character_no_history')
+        expect(version.category).to eq('character')
+        expect(version.created_by_user).to eq(member_user)
+      end
+
       it 'detaches the existing file without purging blob when url replaces file' do
         old_blob_id = material.file.blob.id
 
@@ -494,6 +580,7 @@ RSpec.describe 'Materials API', type: :request do
       it 'does not increase version for the same snapshot update' do
         MaterialVersionRecorder.record!(material:, event_type: :create,
                                         created_by_user: member_user)
+        TagVersioning.ensure_snapshot!(tag, created_by_user: member_user)
 
         expect do
           put "/materials/#{ material.id }", params: {
@@ -501,6 +588,8 @@ RSpec.describe 'Materials API', type: :request do
           }
         end.not_to change(MaterialVersion, :count)
 
+        expect(tag.reload.tag_versions.count).to eq(1)
+
         expect(response).to have_http_status(:ok)
         expect(material.reload.version_no).to eq(1)
       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(
-      io: StringIO.new('dummy'),
-      filename: 'resized_thumbnail.jpg',
-      content_type: 'image/jpeg'
-    )
+    allow(Post).to receive(:resized_thumbnail_attachment) do
+      { io: StringIO.new('dummy'),
+        filename: 'resized_thumbnail.jpg',
+        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）
-    Rack::Test::UploadedFile.new(StringIO.new('dummy'), 'image/jpeg', original_filename: 'dummy.jpg')
+    real_thumbnail_upload
   end
 
   def real_thumbnail_upload
@@ -102,34 +101,34 @@ 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
-      get "/posts"
+    it 'returns posts with tag name in JSON' do
+      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
@@ -142,8 +141,8 @@ 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"] } }
-      expect(all_tag_names).to include("spec_tag")
+      all_tag_names = posts.flat_map { |p| p['tags'].map { |t| t['name'] } }
+      expect(all_tag_names).to include('spec_tag')
     end
 
     it 'keeps children and sections keys in non-detail tag responses' do
@@ -162,9 +161,9 @@ RSpec.describe 'Posts API', type: :request do
       ])
     end
 
-    context "when q is provided" do
-      it "filters posts by q (hit case)" do
-        get "/posts", params: { tags: "spec_tag" }
+    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 +181,8 @@ RSpec.describe 'Posts API', type: :request do
         end
       end
 
-      it "filters posts by q (hit case by alias)" do
-        get "/posts", params: { tags: "manko" }
+      it 'filters posts by q (hit case by alias)' do
+        get '/posts', params: { tags: 'manko' }
 
         expect(response).to have_http_status(:ok)
         posts = json.fetch('posts')
@@ -201,11 +200,11 @@ RSpec.describe 'Posts API', type: :request do
         end
       end
 
-      it "returns empty posts when nothing matches" do
-        get "/posts", params: { tags: "no_such_keyword_12345" }
+      it 'returns empty posts when nothing matches' do
+        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
@@ -693,6 +692,73 @@ 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 +778,46 @@ 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 +875,8 @@ 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 +934,7 @@ 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
 
@@ -1054,7 +1161,7 @@ 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_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
@@ -1251,6 +1358,47 @@ 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) }
 
@@ -1307,7 +1455,7 @@ 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_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
@@ -1564,7 +1712,7 @@ 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)
@@ -2206,6 +2354,91 @@ RSpec.describe 'Posts API', type: :request do
 
       expect(response).to have_http_status(:unprocessable_entity)
     end
+
+    it 'rejects second-bearing original created timestamps on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'invalid original created from',
+          url: 'https://example.com/invalid-original-created-from',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00:01Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_from' => ['オリジナルの作成日時は分単位で入力してください．']
+      )
+      expect(json.fetch('errors')).not_to have_key('original_created_at')
+    end
+
+    it 'rejects fractional-second original created timestamps on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'invalid original created before',
+          url: 'https://example.com/invalid-original-created-before',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_before: '2020-01-01T00:00:00.123Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_before' => ['オリジナルの作成日時は分単位で入力してください．']
+      )
+      expect(json.fetch('errors')).not_to have_key('original_created_at')
+    end
+
+    it 'rejects non-increasing original created ranges on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'non-increasing original created range',
+          url: 'https://example.com/non-increasing-original-created-range',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00Z',
+          original_created_before: '2020-01-01T00:00Z')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_at' => ['オリジナルの作成日時の順番がをかしぃです．']
+      )
+    end
+
+    it 'accepts original created ranges that are exactly one minute on POST /posts' do
+      sign_in_as(member)
+
+      post '/posts', params: post_write_params(
+          title: 'valid original created range',
+          url: 'https://example.com/valid-original-created-range',
+          tags: 'spec_tag',
+          thumbnail: dummy_upload,
+          original_created_from: '2020-01-01T00:00Z',
+          original_created_before: '2020-01-01T00:01Z')
+
+      expect(response).to have_http_status(:created)
+      expect(Time.iso8601(json.fetch('original_created_from')))
+          .to eq(Time.utc(2020, 1, 1, 0, 0))
+      expect(Time.iso8601(json.fetch('original_created_before')))
+          .to eq(Time.utc(2020, 1, 1, 0, 1))
+    end
+
+    it 'rejects unparseable original created timestamps on PUT /posts/:id' do
+      sign_in_as(member)
+      base_version = create_post_version_for!(post_record)
+
+      put "/posts/#{post_record.id}", params: post_write_params(
+          base_version_no: base_version.version_no,
+          title: 'updated title',
+          tags: 'spec_tag',
+          original_created_from: 'not-a-time')
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+        'original_created_from' => ['オリジナルの作成日時の形式が不正です．']
+      )
+    end
   end
 
   describe 'tag versioning from post write actions' do

backend/spec/requests/preview_spec.rb

@@ -1,28 +1,46 @@
-require "rails_helper"
+require 'rails_helper'
 
 
-RSpec.describe "Preview", type: :request do
-  describe "GET /preview/title" do
-    it "401 unless logged in" do
+RSpec.describe 'Preview', type: :request do
+  describe 'GET /preview/title' do
+    it '401 unless logged in' do
       sign_out
-      get "/preview/title", params: { url: "example.com" }
+      get '/preview/title', params: { url: 'example.com' }
       expect(response).to have_http_status(:unauthorized)
     end
 
-    it "400 when url blank" do
-      sign_in_as(create(:user))
-      get "/preview/title", params: { url: "" }
+    it '403 when logged in as guest' do
+      sign_in_as(create(:user, :guest))
+      get '/preview/title', params: { url: 'example.com' }
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it '400 when url blank' do
+      sign_in_as(create(:user, :member))
+      get '/preview/title', params: { url: '' }
       expect(response).to have_http_status(:bad_request)
     end
 
-    it "returns parsed title (stubbing URI.open)" do
-      sign_in_as(create(:user))
-      fake_html = "<html><head><title>  Hello  </title></head></html>"
-      allow(URI).to receive(:open).and_return(StringIO.new(fake_html))
+    it 'returns parsed title' do
+      sign_in_as(create(:user, :member))
+      allow(Preview::ThumbnailFetcher)
+          .to receive(:title)
+          .with('example.com')
+          .and_return('Hello')
 
-      get "/preview/title", params: { url: "example.com" }
+      get '/preview/title', params: { url: 'example.com' }
       expect(response).to have_http_status(:ok)
-      expect(json["title"]).to eq("Hello")
+      expect(json['title']).to eq('Hello')
+    end
+
+    it '413 when fetched response is too large' do
+      sign_in_as(create(:user, :member))
+      allow(Preview::ThumbnailFetcher)
+          .to receive(:title)
+          .and_raise(Preview::HttpFetcher::ResponseTooLarge, '外部データが大きすぎます．')
+
+      get '/preview/title', params: { url: 'example.com' }
+      expect(response).to have_http_status(:payload_too_large)
     end
   end
 end

backend/spec/requests/user_settings_spec.rb

@@ -0,0 +1,98 @@
+require 'rails_helper'
+
+RSpec.describe 'user settings', type: :request do
+  describe 'GET /users/settings' do
+    it 'requires a current user' do
+      sign_out
+
+      get '/users/settings'
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'returns defaults and creates a missing settings row' do
+      user = create(:user)
+      sign_in_as(user)
+
+      expect {
+        get '/users/settings'
+      }.to change(Setting, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to eq(
+          'theme' => 'system',
+          'auto_fetch_title' => 'manual',
+          'auto_fetch_thumbnail' => 'manual',
+          'wiki_editor_mode' => 'split')
+      expect(user.reload.setting).to be_present
+    end
+  end
+
+  describe 'PATCH /users/settings' do
+    it 'requires a current user' do
+      sign_out
+
+      patch '/users/settings', params: { theme: 'dark' }, as: :json
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'updates multiple typed settings at once' do
+      user = create(:user)
+      sign_in_as(user)
+
+      patch '/users/settings',
+            params: {
+              theme: 'dark',
+              auto_fetch_title: 'auto',
+              auto_fetch_thumbnail: 'off',
+              wiki_editor_mode: 'preview' },
+            as: :json
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'theme' => 'dark',
+          'auto_fetch_title' => 'auto',
+          'auto_fetch_thumbnail' => 'off',
+          'wiki_editor_mode' => 'preview')
+      expect(user.reload.setting).to have_attributes(
+          theme: 'dark',
+          auto_fetch_title: 'auto',
+          auto_fetch_thumbnail: 'off',
+          wiki_editor_mode: 'preview')
+    end
+
+    it 'does not treat Rails parameter wrapping as an editable setting' do
+      user = create(:user)
+      sign_in_as(user)
+
+      patch '/users/settings',
+            params: { theme: 'light', user_setting: { theme: 'dark' } },
+            as: :json
+
+      expect(response).to have_http_status(:ok)
+      expect(user.reload.setting.theme).to eq('light')
+    end
+
+    it 'returns validation_error for type mismatches' do
+      sign_in_as(create(:user))
+
+      patch '/users/settings', params: { theme: 1 }, as: :json
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include('type' => 'validation_error')
+      expect(json.fetch('errors')).to include(
+          'theme' => ['値の型が不正です．'])
+    end
+
+    it 'returns validation_error for invalid enum values' do
+      sign_in_as(create(:user))
+
+      patch '/users/settings', params: { theme: 'neon' }, as: :json
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include('type' => 'validation_error')
+      expect(json.fetch('errors').fetch('theme')).to be_present
+    end
+  end
+end

backend/spec/requests/user_theme_slots_spec.rb

@@ -0,0 +1,104 @@
+require 'rails_helper'
+
+RSpec.describe 'user theme slots', type: :request do
+  describe 'GET /users/theme_slots' do
+    it 'requires a current user' do
+      sign_out
+
+      get '/users/theme_slots'
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'returns only the current user slots in stable order' do
+      user = create(:user)
+      other_user = create(:user)
+      sign_in_as(user)
+      UserThemeSlot.create!(user:, base_theme: 'light', slot_no: 2, tokens: { 'a' => 1 })
+      UserThemeSlot.create!(user:, base_theme: 'dark', slot_no: 1, tokens: { 'b' => 2 })
+      UserThemeSlot.create!(user: other_user,
+                            base_theme: 'dark',
+                            slot_no: 3,
+                            tokens: { 'c' => 3 })
+
+      get '/users/theme_slots'
+
+      expect(response).to have_http_status(:ok)
+      expect(json.map { |slot| [slot.fetch('base_theme'), slot.fetch('slot_no')] }).to eq(
+          [['dark', 1], ['light', 2]])
+      expect(json.map { |slot| slot.fetch('tokens') }).to eq(
+          [{ 'b' => 2 }, { 'a' => 1 }])
+    end
+  end
+
+  describe 'PUT /users/theme_slots/:base_theme/:slot_no' do
+    it 'requires a current user' do
+      sign_out
+
+      put '/users/theme_slots/light/1',
+          params: { tokens: { background: '0 0% 100%' } },
+          as: :json
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'creates a theme slot' do
+      user = create(:user)
+      sign_in_as(user)
+
+      expect {
+        put '/users/theme_slots/light/1',
+            params: { tokens: { background: '0 0% 100%', tagColours: { nico: '#ffffff' } } },
+            as: :json
+      }.to change(UserThemeSlot, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('base_theme' => 'light', 'slot_no' => 1)
+      expect(json.fetch('tokens')).to include(
+          'background' => '0 0% 100%',
+          'tagColours' => { 'nico' => '#ffffff' })
+      expect(user.theme_slots.find_by!(base_theme: 'light', slot_no: 1).tokens).to include(
+          'background' => '0 0% 100%')
+    end
+
+    it 'updates an existing theme slot instead of creating a duplicate' do
+      user = create(:user)
+      sign_in_as(user)
+      UserThemeSlot.create!(user:, base_theme: 'dark', slot_no: 2, tokens: { 'old' => true })
+
+      expect {
+        put '/users/theme_slots/dark/2',
+            params: { tokens: { background: '222.2 84% 4.9%' } },
+            as: :json
+      }.not_to change(UserThemeSlot, :count)
+
+      expect(response).to have_http_status(:ok)
+      expect(user.theme_slots.find_by!(base_theme: 'dark', slot_no: 2).tokens).to eq(
+          'background' => '222.2 84% 4.9%')
+    end
+
+    it 'rejects invalid path parameters and token shapes' do
+      sign_in_as(create(:user))
+
+      put '/users/theme_slots/system/4',
+          params: { tokens: 'not-object' },
+          as: :json
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'base_theme' => ['値が不正です．'])
+    end
+
+    it 'rejects non-object tokens for valid slots' do
+      sign_in_as(create(:user))
+
+      put '/users/theme_slots/light/1',
+          params: { tokens: 'not-object' },
+          as: :json
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'tokens' => ['JSON object で指定してください．'])
+    end
+  end
+end

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

@@ -0,0 +1,78 @@
+require 'rails_helper'
+require 'base64'
+
+RSpec.describe PostCreator do
+  let(:actor) { create(:user, :member) }
+
+  def real_thumbnail_upload
+    gif = Base64.decode64('R0lGODdhAQABAIABAP///wAAACwAAAAAAQABAAACAkQBADs=')
+
+    Rack::Test::UploadedFile.new(
+        StringIO.new(gif),
+        'image/gif',
+        original_filename: 'thumbnail.gif')
+  end
+
+  before do
+    allow(Tag).to receive(:normalise_tags!).and_return({ tags: [], sections: {} })
+    allow(TagVersioning).to receive(:record_tag_snapshots!)
+    allow(Tag).to receive(:expand_parent_tags).and_return([])
+    allow(PostVersionRecorder).to receive(:record!)
+  end
+
+  it 'prefers thumbnail_base over an explicit upload' do
+    expect(Post).not_to receive(:resized_thumbnail_attachment)
+    allow(Post).to receive(:remote_thumbnail_attachment).and_return(
+        io: StringIO.new('remote'),
+        filename: 'resized_thumbnail.jpg',
+        content_type: 'image/jpeg')
+
+    post = described_class.new(
+        actor:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail: real_thumbnail_upload,
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' }).create!
+
+    expect(post.thumbnail).to be_attached
+    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+  end
+
+  it 'uses the common remote thumbnail attach path when thumbnail_base is given' do
+    expect(Post).to receive(:remote_thumbnail_attachment)
+        .with('https://example.com/thumb.jpg')
+        .and_return(
+            io: StringIO.new('thumbnail'),
+            filename: 'thumbnail.jpg',
+            content_type: 'image/jpeg')
+
+    post = described_class.new(
+        actor:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' }).create!
+
+    expect(post.thumbnail_base).to eq('https://example.com/thumb.jpg')
+    expect(post.thumbnail).to be_attached
+  end
+
+  it 'does not create a post when remote thumbnail fetch fails' do
+    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:,
+        attributes: {
+          title: 'title',
+          url: 'https://example.com/post',
+          thumbnail_base: 'https://example.com/thumb.jpg',
+          tags: '' })
+
+    post_count = Post.count
+    expect { creator.create! }.to raise_error(Post::RemoteThumbnailFetchFailed)
+    expect(Post.count).to eq(post_count)
+  end
+end

backend/spec/services/post_import_previewer_spec.rb

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

backend/spec/services/post_metadata_fetcher_spec.rb

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

backend/spec/services/post_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/post_url_normaliser_spec.rb

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

backend/spec/services/preview/http_fetcher_spec.rb

@@ -0,0 +1,23 @@
+require 'rails_helper'
+
+RSpec.describe Preview::HttpFetcher do
+  describe '.fetch' do
+    it 'raises FetchFailed when redirect location is invalid' do
+      redirect = Net::HTTPFound.new('1.1', '302', 'Found')
+      redirect['location'] = 'http://[invalid'
+
+      allow(Preview::UrlSafety).to receive(:validate)
+          .with('https://example.com/page')
+          .and_return([URI.parse('https://example.com/page'), ['203.0.113.10']])
+      allow(described_class).to receive(:request)
+          .and_return(redirect)
+      allow(Rails.logger).to receive(:warn)
+
+      expect {
+        described_class.fetch('https://example.com/page')
+      }.to raise_error(Preview::HttpFetcher::FetchFailed)
+      expect(Rails.logger).to have_received(:warn)
+          .with(/invalid_redirect_location/)
+    end
+  end
+end

backend/spec/services/preview/thumbnail_fetcher_spec.rb

@@ -0,0 +1,104 @@
+require 'rails_helper'
+
+RSpec.describe Preview::ThumbnailFetcher do
+  describe '.fetch' 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',
+          'https://example.com/page')
+      svg = Preview::HttpFetcher::Response.new(
+          '<svg></svg>',
+          'image/svg+xml',
+          'https://example.com/thumb.svg')
+
+      allow(Preview::UrlSafety).to receive(:validate) do |url|
+        [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)
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.svg')
+          .and_return(svg)
+
+      expect(described_class.fetch('https://example.com/page')).to eq('<svg></svg>')
+    end
+
+    it 'accepts allowed image content type with parameters' do
+      page = Preview::HttpFetcher::Response.new(
+          '<meta property="og:image" content="https://example.com/thumb.jpg">',
+          'text/html',
+          'https://example.com/page')
+      image = Preview::HttpFetcher::Response.new(
+          "\xFF\xD8\xFFjpeg-bytes".b,
+          'image/jpeg; charset=binary',
+          'https://example.com/thumb.jpg')
+
+      allow(Preview::UrlSafety).to receive(:validate) do |url|
+        [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)
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_return(image)
+
+      expect(described_class.fetch('https://example.com/page'))
+          .to eq("\xFF\xD8\xFFjpeg-bytes".b)
+    end
+  end
+
+  describe '.fetch_image_response' do
+    it 'rejects an unsafe input URL before HTTP fetch' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+      expect(Preview::HttpFetcher).not_to receive(:fetch)
+
+      expect {
+        described_class.fetch_image_response('https://unsafe.example.com/thumb.jpg')
+      }.to raise_error(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+    end
+
+    it 'rejects an unsafe redirect target' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_raise(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::UrlSafety::UnsafeUrl, '安全でない接続先は使用できません．')
+    end
+
+    it 'rejects an oversized image response' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_raise(Preview::HttpFetcher::ResponseTooLarge, 'too large')
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::HttpFetcher::ResponseTooLarge)
+    end
+
+    it 'rejects a non-image content type' do
+      allow(Preview::UrlSafety).to receive(:validate)
+          .and_return([URI.parse('https://example.com/thumb.jpg'), ['8.8.8.8']])
+      allow(Preview::HttpFetcher).to receive(:fetch)
+          .with('https://example.com/thumb.jpg')
+          .and_return(
+              Preview::HttpFetcher::Response.new(
+                  '<html></html>',
+                  'text/html',
+                  'https://example.com/thumb.jpg'))
+
+      expect {
+        described_class.fetch_image_response('https://example.com/thumb.jpg')
+      }.to raise_error(Preview::ThumbnailFetcher::GenerationFailed)
+    end
+  end
+end

backend/spec/services/preview/url_safety_spec.rb

@@ -0,0 +1,15 @@
+require 'rails_helper'
+
+RSpec.describe Preview::UrlSafety do
+  describe '.validate' do
+    it 'raises UnsafeUrl when DNS resolution fails' do
+      allow(Resolv).to receive(:getaddresses)
+          .with('missing.example')
+          .and_raise(Resolv::ResolvError)
+
+      expect {
+        described_class.validate('https://missing.example')
+      }.to raise_error(Preview::UrlSafety::UnsafeUrl)
+    end
+  end
+end

backend/spec/services/youtube/sync_spec.rb

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

backend/spec/tasks/nico_export_spec.rb

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

backend/spec/tasks/nico_sync_spec.rb

@@ -1,10 +1,10 @@
-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:)
@@ -16,17 +16,21 @@ RSpec.describe "nico:sync" do
     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", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+    post = Post.create!(
+      title: 'old',
+      url: 'https://www.nicovideo.jp/watch/sm9',
+      uploaded_user: nil
+    )
 
     # 既存の非nicoタグ（kept_non_nico_ids）
-    kept_general = create_tag!("spec_kept", category: "general")
+    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")
-    nico = create_tag!("nico:AAA", category: "nico")
+    linked = create_tag!('spec_linked', category: 'general')
+    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）
@@ -42,43 +46,91 @@ 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("nico:AAA")
-    expect(active_tag_names).to include("spec_linked")
+    expect(active_tag_names).to include('spec_kept')
+    expect(active_tag_names).to include('nico:AAA')
+    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 にあった古い nico tag は active から外され、履歴として discard される" do
-    post = Post.create!(title: "old", url: "https://www.nicovideo.jp/watch/sm9", uploaded_user: nil)
+  it '既存 post のサムネール取得に共通 attach 経路を使ふ' do
+    post = Post.create!(
+        title: 'old',
+        url: 'https://www.nicovideo.jp/watch/sm9',
+        uploaded_user: nil)
+    Tag.bot
+    Tag.tagme
+
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
+    allow(URI).to receive(:open) do
+      StringIO.new(
+          '<meta name="thumbnail" content="https://example.com/thumb.jpg">')
+    end
+    expect_any_instance_of(Post).to receive(:attach_thumbnail_from_url!)
+        .with('https://example.com/thumb.jpg')
+
+    run_rake_task('nico:sync')
+  end
+
+  it 'サムネール取得失敗後も次回同期で再試行できる' do
+    post = Post.create!(
+        title: 'old',
+        url: 'https://www.nicovideo.jp/watch/sm9',
+        uploaded_user: nil)
+    Tag.bot
+    Tag.tagme
+
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => [] }])
+    allow(URI).to receive(:open) do
+      StringIO.new(
+          '<meta name="thumbnail" content="https://example.com/thumb.jpg">')
+    end
+    calls = 0
+    allow_any_instance_of(Post).to receive(:attach_thumbnail_from_url!) do
+      calls += 1
+      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
+    post = Post.create!(
+      title: 'old',
+      url: 'https://www.nicovideo.jp/watch/sm9',
+      uploaded_user: nil
+    )
 
     # 旧nicoタグ（今回の同期結果に含まれない）
-    old_nico = create_tag!("nico:OLD", category: "nico")
+    old_nico = create_tag!('nico:OLD', category: 'nico')
     old_pt = PostTag.create!(post: post, tag: old_nico)
     expect(old_pt.discarded_at).to be_nil
 
     # 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"] }])
-    allow(URI).to receive(:open).and_return(StringIO.new("<html></html>"))
+    stub_python([{ 'code' => 'sm9', 'title' => 't', 'tags' => ['NEW'] }])
+    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）
     old_pts = PostTag.where(post_id: post.id, tag_id: old_nico.id).order(:id).to_a
@@ -86,9 +138,9 @@ RSpec.describe "nico:sync" do
 
     # NEW は active にいる
     post.reload
-    active_names = post.tags.joins(:tag_name).pluck("tag_names.name")
-    expect(active_names).to include("nico:NEW")
-    expect(active_names).not_to include("nico:OLD")
+    active_names = post.tags.joins(:tag_name).pluck('tag_names.name')
+    expect(active_names).to include('nico:NEW')
+    expect(active_names).not_to include('nico:OLD')
   end
 
   def snapshot_tags(post)

frontend/AGENTS.md

@@ -50,16 +50,27 @@ pass or the remaining failure is clearly blocked.
 - Prefer single quotes for strings unless interpolation or escaping makes double quotes better.
 - Never write a TypeScript or TSX line longer than 99 characters.
 - Aim to keep TypeScript and TSX lines within 79 characters where practical.
-- Use 4-space logical indentation in TypeScript and TSX.
+- Use 2-space block indentation in TypeScript and TSX.
+- Use 4-space continuation indentation for wrapped expressions, arguments,
+  ternary branches, method chains, object pairs, arrays, and JSX attributes.
+- Treat the user's `PostImportSourcePage.tsx` and
+  `PostImportReviewPage.tsx` formatting as the local reference shape.
 - For arrays, never put whitespace or a line break immediately before `]`.
 - Keep the first element on the same line as `[` by default.
 - If an array would exceed the line limit, break after `[` and indent
   elements by 4 spaces.
-- In TypeScript and TSX only, replace every leading run of 8 spaces with a tab
-  to reduce bytes.
+- In TypeScript and TSX only, use tabs for leading 8-column compression only.
+- A tab does not represent one indentation level.
+- Determine visible indentation with 2-space block indentation and 4-space
+  continuation indentation first, then compress only complete leading runs of
+  8 spaces into tabs.
 - Treat one leading tab as exactly equivalent to 8 leading spaces.
 - Use tabs only for leading indentation. Never replace spaces that occur after
   a non-space character on the same line.
+- Keep residual leading 2, 4, or 6 spaces after any tab compression.
+- Examples: 2 columns = 2 spaces, 4 columns = 4 spaces, 6 columns = 6
+  spaces, 8 columns = 1 tab, 10 columns = 1 tab + 2 spaces, 12 columns = 1
+  tab + 4 spaces.
 
 ## React
 
@@ -97,17 +108,35 @@ pass or the remaining failure is clearly blocked.
   third-party request outside the Rails API.
 - For blob responses, pass `responseType: 'blob'` so the wrapper does not camelCase the body.
 
+## Dialogues
+
+- Dialogue work follows the shared-frontend reuse rules below.
+
 ## Imports and aliases
 
 - The `@` alias points to `frontend/src`.
 - Prefer `@/...` imports for app code instead of long relative paths.
 - Keep type imports separate with `import type`.
-- Match existing import grouping: external packages, app modules, then type imports.
+- Do not mix runtime values and `type` specifiers in one named import
+  declaration.
+- Do not write `import { value, type TypeName } from ...`.
+- Keep short value imports from one module on one line when they fit within
+  99 characters.
+- Order imports as four groups with a blank line between groups: external
+  value imports, `@/...` value imports, external type imports, `@/...`
+  type imports.
 
 ## Tailwind and UI
 
 - 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.
@@ -118,23 +147,816 @@ 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.
-- When adding dynamic tag color classes, update `tailwind.config.js` safelist
+- 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.
 
-## TSX formatting
+## TypeScript and TSX formatting
 
+- The delimiter-placement and line-breaking rules in this section apply to
+  both plain TypeScript `.ts` and TSX `.tsx`, unless a bullet explicitly says
+  it is JSX- or React-specific.
 - Preserve compact TSX expression shapes such as inline ternary branches and
   closing `</div>)` forms when nearby code uses them.
+- Block bodies for components, functions, callbacks, `if`, `try`, `catch`,
+  `finally`, loops, and JSX nesting use 2 spaces per level.
+- Put the opening brace of `try`, `catch`, and `finally` blocks on the next
+  line at the same indentation as the keyword.
+- Do not indent the opening `{` one level deeper than `try`, `catch`, or
+  `finally`.
+- Indent the block body 2 spaces deeper than the keyword and opening brace.
+- Put the closing `}` on its own line at the same indentation as the keyword.
+- Do not write `try {`, `catch {`, or `finally {`.
+- Wrapped expressions, arguments, ternary branches, method chains, and object
+  pairs use 4-space continuation indentation relative to the owning
+  expression. Do not confuse this with 2-space block indentation.
+- Tabs are leading 8-column compression only. They do not represent one
+  nesting level. Decide visible indentation first, then compress only
+  complete leading runs of 8 spaces into tabs.
+- Do not add braces around a single-line `if` body merely for formatting.
+- Use braces for multi-line `if`, `else`, and loop bodies.
+- Multi-stage ternary expressions must use explicit parentheses for each
+  condition group and nested branch. Do not rely on indentation alone to show
+  `?` / `:` pairing.
+- Keep short inline props types local when they remain readable and within the
+  line limit; do not mechanically extract a named type with no reuse benefit.
+- In JavaScript, JSX, TypeScript, and TSX, never use `_1`, `_2`, or similar
+  Ruby-style numbered parameter names. Reserve numbered parameters for Ruby.
+  Use a meaningful callback parameter name such as `row`, `item`, `value`,
+  `entry`, or `result`.
+- In multi-line object literals, keep the opening `{` with the first pair when
+  the line length allows it; do not mechanically explode short objects into
+  Prettier-style vertical blocks.
+- Method chains should align as a continuation under the receiver expression;
+  do not indent chains more deeply than the normal continuation depth.
+- `PostImportSourcePage.tsx` and `PostImportReviewPage.tsx` are the current
+  canonical examples for block indentation, continuation indentation, import
+  grouping, ternary grouping, method-chain placement, and local inline props
+  types.
+- Treat TypeScript and TSX formatting rules as hard constraints, not
+  preferences. Before finishing a TypeScript or TSX edit, inspect the edited
+  hunks for closing `)`, `]`, and `}` placement and fix violations instead of
+  relying on formatter defaults.
+- After every TypeScript or TSX edit, perform a style-only self-review of the
+  edited hunks before running verification or reporting completion. The task is
+  not complete while any edited TypeScript or TSX hunk violates these local
+  formatting rules.
+- The TypeScript/TSX self-review must classify every edited leading or trailing
+  `)`, `]`, and `}` by syntax role before deciding whether it is valid. Do not
+  apply a rule by glyph alone. A closing `)` for a function parameter list is
+  different from a closing `)` for a function call. A closing `}` for a block
+  is different from a closing `}` for an object, type literal, import list, or
+  destructuring pattern.
+- The TSX-specific self-review must confirm there are no common Prettier-style
+  React component declarations with a multi-line destructured parameter.
+- The TypeScript/TSX self-review must confirm multi-line function declaration
+  parameter `)` placement follows the detailed parameter-list rules below.
+- The TypeScript/TSX self-review must confirm call-expression `)` is never at
+  the beginning of a line.
+- The TypeScript/TSX self-review must confirm
+  object/type/import/destructuring `}` is not at the beginning of a line.
+- The TypeScript/TSX self-review must confirm multi-line
+  function/lambda/callback/block `}` is on its own line and never at the end
+  of the previous line.
+- The TypeScript/TSX self-review must confirm array `]` is not at the
+  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
+  2 spaces per level, wrapped continuations use the repository's 4-space
+  continuation alignment, and complete leading runs of 8 spaces may be
+  compressed to tabs.
 - For long Tailwind `className` strings, wrap across lines only when needed.
-- Keep continuation indentation aligned with the 4-space logical indentation
-  rule, using tabs only as leading 8-space compression.
+- Keep continuation indentation aligned with the repository's 4-space
+  continuation rule while keeping block indentation at 2 spaces.
+- Keep short value imports from one module on one line when they fit within
+  99 characters.
+- In TypeScript and TSX function declarations, including `const` arrow
+  function declarations, classify the parameter list before placing the closing
+  `)`.
+- Block indentation example:
+
+```ts
+const Component = () => {
+  const value = loadValue ()
+
+  useEffect (() => {
+    if (value != null)
+      useValue (value)
+  }, [value])
+}
+```
+
+- `try` / `catch` / `finally` brace placement example:
+
+```ts
+try
+{
+  doWork ()
+}
+catch
+{
+  recover ()
+}
+finally
+{
+  cleanUp ()
+}
+```
+
+- Continuation indentation example:
+
+```ts
+const editingRow =
+    Number.isFinite (editingSourceRow)
+    ? rows.find (row => row.sourceRow === editingSourceRow) ?? null
+    : null
+```
+
+- Import grouping example:
+
+```ts
+import { useNavigate, useParams, useSearchParams } from 'react-router-dom'
+
+import { loadPostImportSession } from '@/lib/postImportSession'
+
+import type { FC } from 'react'
+
+import type { PostImportRow } from '@/lib/postImportSession'
+```
+
+- Inline props type example:
+
+```ts
+const Footer = (
+    { loading,
+      onSubmit }: { loading:  boolean
+		    onSubmit: () => void },
+) => null
+```
+
+- Ternary grouping example:
+
+```ts
+const rows =
+    repairMode === 'failed'
+    ? (
+	[...source].sort ((a, b) => {
+	  const aFailed = a.failed ? 0 : 1
+	  const bFailed = b.failed ? 0 : 1
+	  return aFailed - bFailed
+	}))
+    : source
+```
+
+- If the parameter list itself is given its own multi-line block after the
+  function's opening `(`, put the closing parameter `)` at the beginning of its
+  own line before the return type or `=>`.
+- If the only line break is inside a parameter's inline type, object type, or
+  destructuring shape, and the parameter list itself is not split as a separate
+  block, keep the closing parameter `)` on the same line as that parameter's
+  final `}`. In this case, moving `)` to a new line is wrong.
+- Do not write React component declarations in the common Prettier form
+  `const Component = ({ ... }) => (` when the destructured parameter spans
+  multiple lines. Use the project form with the opening `(` after `=`, the
+  destructured object as the argument, and the closing parameter `)` on its own
+  line before `=>`.
+- In TypeScript and TSX, never place a closing parenthesis at the beginning of
+  a line except for a multi-line function declaration parameter list.
+- Never place a closing square bracket at the beginning of a line.
+- For object literals, type literals, import/export named bindings, destructuring
+  patterns, and other associative-array-style braces, do not place the closing
+  brace at the beginning of a line. Keep `}` on the same line as the final
+  property, binding, or specifier unless that would violate the line limit.
+  Function, lambda, callback, and block closing braces are exempt and should
+  stay on their own line when that fits the local style. When a function,
+  lambda, callback, or block body spans multiple lines, do not put its closing
+  `}` at the end of the previous line.
+- For arrays and tuple-like lists, do not place the closing `]` at the
+  beginning of a line. Keep `]` on the same line as the final element unless
+  that would violate the line limit.
+- For function and method calls, do not place the closing `)` at the beginning
+  of a line. The only TypeScript/TSX exception is the closing parameter `)` of a
+  multi-line function declaration.
 - Do not add braces around `if`, `else`, or `for` bodies when the body is a
   single physical line.
 - Always add braces around `if`, `else`, or `for` bodies when the body spans
   two or more physical lines, even if it is one statement.
+- Use correct British English spelling for new identifiers, filenames,
+  component names, helper names, comments, and developer-facing prose unless
+  editing an already established American-English API that must keep its
+  existing spelling for compatibility.
+- Prefer British English spellings such as `behaviour`, `colour`, `realise`,
+  `theatre`, `centre`, `favourite`, `optimise`, and `catalogue`.
+- Avoid American or Canadian spellings such as `behavior`, `color`, `realize`,
+  `theater`, `center`, `favorite`, `optimize`, and `catalog`.
+- Even when an external library or API uses the wrong spelling, prefer to
+  correct it at the local boundary and use proper British English names in this
+  frontend codebase. For example, prefer
+  `import { color: colour } from '@external-lib'` over spreading `color`
+  through local code.
+- Apply the same boundary correction to object destructuring, wrapper helpers,
+  adapter layers, and local variable names when doing so does not break the
+  external contract.
+- In this frontend, prefer names such as `BehaviourSettingsSection.tsx`, not
+  `BehaviorSettingsSection.tsx`.
 - Avoid reformatting unrelated JSX.
 
+## Shared frontend systems
+
+Before creating a new component, hook, helper, store, context, or other
+frontend abstraction, search at least:
+
+- `src/components/common`
+- `src/components/layout`
+- `src/components/ui`
+- `src/components/dialogues`
+- `src/lib`
+- `src/lib/dialogues`
+- `src/stores`
+- `src/types.ts`
+
+Also inspect the existing pages and components in the same feature.
+
+Search by responsibility, not by filename alone. Check display, interaction,
+state, communication, validation, and permission behaviour before deciding that
+an existing implementation is unsuitable.
+
+### Component placement and reuse order
+
+When adding UI, use this order:
+
+1. reuse an existing feature component
+2. reuse an existing component from `components/common`
+3. reuse an existing layout component from `components/layout`
+4. use an existing primitive from `components/ui` through the established
+   common API
+5. extend an existing component minimally
+6. add a feature-local component in the feature area
+7. add a new common component only when multiple features clearly share a
+   stable visual contract
+
+Do not place a one-screen component in a common directory merely because its
+name starts with `Common`.
+
+### Low-level primitives
+
+Treat `components/ui` as low-level primitives. If a higher-level common API
+already exists for dialogues, toast, form validation, navigation, or similar
+behaviour, feature code must use that API instead of assembling primitives
+directly.
+
+Examples of existing preferred entrypoints include:
+
+- dialogue: `@/lib/dialogues/useDialogue`
+- toast: the existing toast API
+- internal navigation: `PrefetchLink`
+- form errors: `FieldError`, `FieldWarning`, `FormField`
+- buttons: `Button`
+- conditional class merge: `cn`
+
+Do not evade the rule with aliases or thin wrappers around the low-level
+primitive.
+
+### Dialogues
+
+Feature-facing dialogue work must use `@/lib/dialogues/useDialogue`.
+
+Reuse the existing common dialogue API and common dialogue component. Do not
+import `@/components/ui/dialog` directly in feature code to assemble bespoke
+dialogue shells, and do not evade this rule with aliases such as
+`Dialog as Dialogue`.
+
+Do not reimplement overlay, portal, close button, header, footer, focus
+handling, Escape handling, outside-click handling, or confirmation flow in
+feature code.
+
+Keep business-specific form content in feature code, and keep the visual and
+behavioural dialogue shell in common code.
+
+Use British spelling `Dialogue` for project-defined dialogue identifiers. Keep
+exact third-party spellings only at the external boundary where compatibility
+requires them.
+
+### API calls
+
+Rails API calls must use `src/lib/api.ts`.
+
+Do not create feature-local Axios instances, fetch wrappers, header injectors,
+camelCase converters, or generic error converters. If blob or other special
+transport behaviour is already supported by the common API, use the existing
+options instead of bypassing the wrapper.
+
+### Query keys, server state, and prefetch
+
+Before adding query state, inspect:
+
+- `src/lib/queryKeys.ts`
+- existing domain helpers
+- existing prefetchers
+- the root query-key hierarchy
+- current mutation invalidation patterns
+- the app-wide `QueryClient`
+
+Do not write ad hoc query-key arrays in feature code. Do not duplicate fetcher,
+prefetcher, or invalidation helpers for the same resource.
+
+### Domain helpers
+
+For posts, tags, wiki, materials, and other domain work, inspect the existing
+helpers in `src/lib/*.ts` before adding logic to a page component.
+
+Do not accumulate these in page components when an existing helper layer should
+own them:
+
+- API request construction
+- response-shape conversion
+- query-key construction
+- canonical URL generation
+- permission calculation
+- storage serialisation
+- domain-specific parsing
+
+Keep purely local one-screen display shaping local when that is the clearest
+place for it.
+
+### Permission helpers
+
+Use the existing permission helpers such as `src/lib/users.ts` when deciding
+editability, role checks, admin/member visibility, and similar UI behaviour.
+
+Do not scatter `user?.role`, numeric role comparisons, or string comparisons
+through components. Frontend visibility control should be consistent even though
+backend authorization remains the final gate.
+
+### Validation errors
+
+Before adding feature-local validation-error handling, inspect:
+
+- `useValidationErrors`
+- `apiErrors`
+- `FieldError`
+- `FieldWarning`
+- `FormField`
+- `inputClass`
+
+Do not create a new generic hook, field-error state shape, or error-rendering
+component for a pattern the shared error stack already covers. Keep only
+genuinely feature-specific business errors local.
+
+### Forms and fields
+
+Before creating a new input, textarea, date/time field, tag input, label, or
+error layout, inspect at least:
+
+- `Form`
+- `FormField`
+- `FieldError`
+- `FieldWarning`
+- `DateTimeField`
+- `TagInput`
+- `TextArea`
+- `Label`
+- `Button`
+
+Do not create a same-function field component merely because the spacing or
+surface styling is slightly different. Prefer feature-level composition over
+bloated common-field option lists.
+
+### Navigation and prefetch
+
+Use `PrefetchLink` and existing router helpers for internal navigation. Do not
+introduce feature-local `<a>`, `window.location`, or custom prefetch logic for
+internal routes. Keep path-segment encoding aligned with the existing rules.
+
+### State management
+
+Before adding state, decide whether the source of truth should be:
+
+- component-local state
+- URL search params
+- TanStack Query server state
+- an existing Zustand store
+- an existing event bus
+- an existing storage helper
+
+Do not create a new global store, context, or event bus for one screen when
+local state or an existing mechanism is enough. Do not create a second store
+for the same responsibility.
+
+### Storage and settings
+
+When touching localStorage, sessionStorage, or user settings, inspect existing
+settings helpers, storage helpers, expiry handling, versioning, and sanitisers.
+
+Do not reimplement per-component key naming, JSON parsing and serialisation,
+expiry, or schema checks when a shared helper already owns the pattern.
+
+### Hooks
+
+Before creating a custom hook, search existing `src/lib/use*.ts` and
+`src/lib/use*.tsx`.
+
+Hooks are for shared stateful behaviour or React lifecycle integration. Do not
+turn a pure function, one-off helper, or mere re-export shim into `useFoo`.
+
+### Stores, contexts, and event buses
+
+Add a new store, context, or event bus only when the current mechanisms cannot
+express the requirement and there are multiple genuinely separate consumers.
+
+Do not hold the same information redundantly across URL state, query cache,
+local component state, Zustand, and an event bus. Keep one source of truth.
+
+### Types
+
+If a domain type already exists in `src/types.ts` or a domain helper, reuse it
+instead of redefining the same shape in a feature file.
+
+Small local props and draft types may stay local. Do not create giant
+catch-all type files such as `CommonTypes.ts`.
+
+### Styling utilities
+
+Use existing styling utilities such as `cn` and `inputClass`.
+
+Do not add feature-local class-merge helpers, generic status-colour mappers, or
+responsive wrapper helpers when a shared utility already exists. Keep common
+tone names visual only; feature-specific state names stay in feature code.
+
+### Layout
+
+Before adding page shells, padding rules, viewport-height handling, sidebar
+offsets, or footer offsets, inspect existing layout components such as
+`MainArea`, top navigation, sidebar, page title, and section-title patterns.
+
+Do not create a second layout shell before checking whether the current layout
+can be reused or minimally extended.
+
+- 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
+more authoritative than formatter habit. Unless a subsection explicitly
+mentions JSX, it applies equally to `.ts` and `.tsx`.
+
+#### Import and export named bindings
+
+Bad:
+
+```ts
+import {
+    Button,
+    Card,
+} from '@/components/ui'
+```
+
+Good:
+
+```ts
+import { Button,
+	 Card } from '@/components/ui'
+```
+
+Also acceptable when short:
+
+```ts
+import { Button, Card } from '@/components/ui'
+```
+
+Rule: named-binding `}` is associative-array-style syntax. It must not be alone
+at the beginning of a line. Prefer keeping `{` with the first binding and `}`
+with the final binding when this fits the line limit.
+
+#### Type literals
+
+Bad:
+
+```ts
+type Props = {
+    open: boolean
+    onOpenChange: (open: boolean) => void
+}
+```
+
+Good:
+
+```ts
+type Props = {
+    open: boolean
+    onOpenChange: (open: boolean) => void }
+```
+
+Rule: type-literal `}` is not a block close. It must stay on the same line as
+the final property unless that would break the hard line limit.
+
+#### Object literals
+
+Bad:
+
+```ts
+const value = {
+    open,
+    activeScope,
+}
+```
+
+Good:
+
+```ts
+const value = {
+    open,
+    activeScope }
+```
+
+Bad:
+
+```ts
+const value = useMemo (() => ({
+    open,
+    activeScope,
+}), [open, activeScope])
+```
+
+Good:
+
+```ts
+const value = useMemo (() => ({
+    open,
+    activeScope }), [open, activeScope])
+```
+
+Rule: object-literal `}` is associative-array-style syntax. It must not be on a
+line by itself. Keep it with the final property, and keep call `)` off the
+beginning of a line.
+
+#### Destructuring parameters
+
+Bad:
+
+```tsx
+const Component: FC<Props> = ({
+    open,
+    onOpenChange,
+}) => {
+  return null
+}
+```
+
+Good:
+
+```tsx
+const Component: FC<Props> = (
+    { open,
+      onOpenChange },
+) => {
+  return null
+}
+```
+
+Rule: when a React component or helper takes a destructured object parameter
+that spans multiple lines, do not use the Prettier-style `= ({ ... }) =>`
+shape. Put the function parameter list on its own lines. The destructuring `}`
+stays with the final binding. The parameter-list `)` is then allowed and
+required at the beginning of its own line.
+
+#### Inline typed destructuring parameter
+
+Good:
+
+```ts
+const RouteTransitionWrapper = ({ user, setUser }: {
+    user:     User | null
+    setUser:  Dispatch<SetStateAction<User | null>> }) => {
+  return null
+}
+```
+
+Bad:
+
+```ts
+const RouteTransitionWrapper = ({ user, setUser }: {
+    user:     User | null
+    setUser:  Dispatch<SetStateAction<User | null>>
+}) => {
+  return null
+}
+```
+
+Rule: this is not a separately split parameter-list block. The line break is
+inside the inline type. Keep the type-literal `}` and parameter-list `)` on the
+same line as the final type property.
+
+#### Multi-line normal parameter list
+
+Bad:
+
+```ts
+const updateDraft = <Key extends keyof Settings,> (
+    key: Key,
+    value: Settings[Key]) => {
+  return null
+}
+```
+
+Good:
+
+```ts
+const updateDraft = <Key extends keyof Settings,> (
+    key:    Key,
+    value:  Settings[Key],
+) => {
+  return null
+}
+```
+
+Rule: when the parameter list itself is split across multiple parameter lines,
+the closing parameter `)` goes at the beginning of its own line before `=>` or
+the return type.
+
+#### Function and callback blocks
+
+Bad:
+
+```ts
+const handleSave = () => { save ()
+}
+```
+
+Bad:
+
+```ts
+const handleSave = () => {
+  save () }
+```
+
+Good:
+
+```ts
+const handleSave = () => {
+  save ()
+}
+```
+
+Rule: block `}` closes executable code, not associative data. Multi-line
+function, lambda, callback, `if`, `for`, `switch`, and similar block braces
+belong on their own line.
+
+#### Function and method calls
+
+Bad:
+
+```ts
+const value = compute (
+    first,
+    second
+)
+```
+
+Good:
+
+```ts
+const value = compute (
+    first,
+    second)
+```
+
+Rule: call-expression `)` must not be at the beginning of a line. The exception
+for leading `)` applies only to function declaration parameter lists, never to
+calls.
+
+#### JSX closing markers
+
+Bad:
+
+```tsx
+<Button
+    type="button"
+    onClick={handleSave}
+>
+  保存
+</Button>
+)
+```
+
+Good:
+
+```tsx
+<Button
+    type="button"
+    onClick={handleSave}>
+  保存
+</Button>)
+```
+
+Bad:
+
+```tsx
+<Input
+    value={value}
+    onChange={handleChange}
+/>
+```
+
+Good:
+
+```tsx
+<Input
+    value={value}
+    onChange={handleChange}/>
+```
+
+Rule: keep `>` or `/>` with the final prop, and keep JSX closing parentheses in
+the local compact form such as `</div>)`.
+
+#### Arrays and tuples
+
+Bad:
+
+```ts
+const items = [
+    first,
+    second,
+]
+```
+
+Good:
+
+```ts
+const items = [
+    first,
+    second]
+```
+
+Good when short:
+
+```ts
+const items = [first, second]
+```
+
+Rule: array and tuple `]` must not be at the beginning of a line. Keep it with
+the final element unless that would break the hard line limit.
+
+#### Single-line braces
+
+Good:
+
+```ts
+const next = { ...current, enabled: true }
+const tag = { id, name }
+```
+
+Bad:
+
+```tsx
+<Component prop={ value }/>
+```
+
+Good:
+
+```tsx
+<Component prop={value}/>
+```
+
+Rule: JavaScript object braces on one line get one inner space. JSX expression
+braces do not get inner spaces.
+
+#### Final TSX self-review checklist
+
+Before reporting completion after a TypeScript or TSX edit, check the edited
+hunks line by line:
+
+1. No import/export/type/object/destructuring `}` appears alone at the beginning
+   of a line.
+2. No call-expression `)` appears at the beginning of a line.
+3. Any leading `)` is definitely closing a function declaration parameter list,
+   not a call.
+4. Any parameter-list `)` at the end of a line is valid because the parameter
+   list itself was not split, only an inline type or destructuring shape was.
+5. No array or tuple `]` appears at the beginning of a line.
+6. Multi-line executable block `}` is on its own line.
+7. JSX `>` and `/>` stay with the final prop unless nearby code proves
+   otherwise.
+8. JSX closing parentheses keep the compact local style.
+9. Leading block indentation uses 2 spaces per level, wrapped continuations
+   use the repository's 4-space continuation alignment, and complete leading
+   runs of 8 spaces may be compressed to tabs.
+10. No line has trailing whitespace.
+
 ## Lint and build constraints
 
 - ESLint uses `@eslint/js`, `typescript-eslint`, `eslint-plugin-react-hooks`,

frontend/src/App.tsx

@@ -1,8 +1,9 @@
-import { AnimatePresence, LayoutGroup, motion } from 'framer-motion'
-import { useEffect, useState } from 'react'
-import { BrowserRouter,
+import { AnimatePresence, LayoutGroup, MotionConfig, motion } from 'framer-motion'
+import { Fragment, useEffect, useMemo, useState } from 'react'
+import { createBrowserRouter,
 	 Navigate,
 	 Route,
+	 RouterProvider,
 	 Routes,
 	 useLocation } from 'react-router-dom'
 
@@ -12,6 +13,20 @@ import TopNav from '@/components/TopNav'
 import DialogueProvider from '@/components/dialogues/DialogueProvider'
 import { Toaster } from '@/components/ui/toaster'
 import { apiPost, isApiError } from '@/lib/api'
+import { applyClientAnimationMode,
+	 applyClientAppearance,
+	 type ClientAnimationMode,
+	 fetchUserThemeSlots,
+	 fetchUserSettings,
+	 getClientThemeMode,
+	 hasStoredClientThemeSelection,
+	 normaliseUserThemeSlots,
+	 setCachedUserThemeSlots,
+	 seedClientThemeMode } from '@/lib/settings'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { UnsavedChangesGuardProvider } from '@/lib/useUnsavedChangesGuard'
+
+import { KeyboardShortcutsProvider } from '@/lib/useKeyboardShortcuts'
 import DeerjikistDetailPage from '@/pages/deerjikists/DeerjikistDetailPage'
 import MaterialBasePage from '@/pages/materials/MaterialBasePage'
 import MaterialDetailPage from '@/pages/materials/MaterialDetailPage'
@@ -27,8 +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 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'
@@ -48,11 +63,51 @@ import type { Dispatch, FC, SetStateAction } from 'react'
 import type { User } from '@/types'
 
 
-const RouteTransitionWrapper = ({ user, setUser }: {
+const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
+    animationMode: ClientAnimationMode
     user:     User | null
     setUser:  Dispatch<SetStateAction<User | null>> }) => {
   const location = useLocation ()
 
+  if (animationMode === 'off')
+    {
+      return (
+	  <Routes location={location}>
+	    <Route path="/" element={<Navigate to="/posts" replace/>}/>
+	    <Route path="/posts" element={<PostListPage/>}/>
+	    <Route path="/posts/new" element={<PostNewPage user={user}/>}/>
+	    <Route path="/posts/search" element={<PostSearchPage/>}/>
+	    <Route path="/posts/:id" element={<PostDetailRoute user={user}/>}/>
+	    <Route path="/posts/changes" element={<PostHistoryPage/>}/>
+	    <Route path="/tags" element={<TagListPage/>}/>
+	    <Route path="/tags/:id" element={<TagDetailPage/>}/>
+	    <Route path="/tags/:id/deerjikists" element={<DeerjikistDetailPage/>}/>
+	    <Route path="/tags/nico" element={<NicoTagListPage user={user}/>}/>
+	    <Route path="/nico/tags" element={<NicoTagListPage user={user}/>}/>
+	    <Route path="/tags/changes" element={<TagHistoryPage/>}/>
+	    <Route path="/theatres/:id" element={<TheatreDetailPage user={user}/>}/>
+	    <Route path="/materials" element={<MaterialBasePage/>}>
+	      <Route index element={<MaterialListPage/>}/>
+	      <Route path="changes" element={<MaterialHistoryPage/>}/>
+	      <Route path="new" element={<MaterialNewPage/>}/>
+	      <Route path="suppressions" element={<MaterialSyncSuppressionsPage/>}/>
+	      <Route path=":id" element ={<MaterialDetailPage/>}/>
+	    </Route>
+	    <Route path="/wiki" element={<WikiSearchPage/>}/>
+	    <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+	    <Route path="/wiki/new" element={<WikiNewPage user={user}/>}/>
+	    <Route path="/wiki/:id/edit" element={<WikiEditPage user={user}/>}/>
+	    <Route path="/wiki/:id/diff" element={<WikiDiffPage/>}/>
+	    <Route path="/wiki/changes" element={<WikiHistoryPage/>}/>
+	    <Route path="/users/settings" element={<SettingPage user={user} setUser={setUser}/>}/>
+	    <Route path="/settings" element={<Navigate to="/users/settings" replace/>}/>
+	    <Route path="/tos" element={<TOSPage/>}/>
+	    <Route path="/gekanator" element={<GekanatorPage user={user}/>}/>
+	    <Route path="/more" element={<MorePage/>}/>
+	    <Route path="*" element={<NotFound/>}/>
+	  </Routes>)
+    }
+
   return (
       <AnimatePresence mode="wait">
 	<Routes location={location}>
@@ -100,9 +155,40 @@ 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 ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const LayoutWrapper = animationMode === 'off' ? Fragment : LayoutGroup
+
+  const appLayoutTransition = useMemo (
+      () => (
+	  animationMode === 'off'
+	  ? { duration: 0 }
+	  : animationMode === 'reduced'
+	    ? { duration: .08, ease: 'linear' as const }
+	    : { duration: .2, ease: 'easeOut' as const }
+      ),
+      [animationMode],
+  )
+
+  useEffect (() => {
+    applyClientAppearance ()
+
+    const mediaQuery = window.matchMedia ('(prefers-color-scheme: dark)')
+    const handleThemeChange = () => {
+      if (getClientThemeMode () === 'system')
+	applyClientAppearance ()
+    }
+
+    mediaQuery.addEventListener ('change', handleThemeChange)
+    return () => mediaQuery.removeEventListener ('change', handleThemeChange)
+  }, [])
+
+  useEffect (() => {
+    applyClientAnimationMode (animationMode)
+  }, [animationMode])
 
   useEffect (() => {
     const createUser = async () => {
@@ -137,6 +223,30 @@ const App: FC = () => {
       createUser ()
   }, [])
 
+  useEffect (() => {
+    if (!(user))
+      return
+
+    void (async () => {
+	try
+	{
+	  const [settings, themeSlots] = await Promise.all ([
+	      fetchUserSettings (),
+	      fetchUserThemeSlots (),
+	  ])
+	  const storedThemeSlots = normaliseUserThemeSlots (themeSlots)
+	  setCachedUserThemeSlots (storedThemeSlots)
+	  if (!(hasStoredClientThemeSelection ()))
+	    seedClientThemeMode (settings.theme)
+	  applyClientAppearance ()
+	}
+      catch
+      {
+	return
+      }
+    }) ()
+  }, [user])
+
   switch (status)
   {
   case 503:
@@ -144,26 +254,46 @@ const App: FC = () => {
   }
 
   return (
-      <>
-	<RouteBlockerOverlay/>
-	{import.meta.env.DEV && <DevModeWatermark/>}
-
-	<BrowserRouter>
-	  <DialogueProvider>
-	    <LayoutGroup>
+      <DialogueProvider>
+	<UnsavedChangesGuardProvider>
+	  <KeyboardShortcutsProvider>
+	  <MotionConfig
+	      reducedMotion={
+		  animationMode === 'normal'
+		  ? 'never'
+		  : animationMode === 'reduced'
+		    ? 'user'
+		    : 'always'
+	      }>
+	    <LayoutWrapper>
 	      <motion.div
-		  layout="position"
-		  transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-		  className="relative flex flex-col h-dvh w-full overflow-y-hidden">
+		  layout={animationMode === 'off' ? false : 'position'}
+		  transition={{ layout: appLayoutTransition }}
+		  className="relative flex h-dvh w-full flex-col overflow-y-hidden">
 		<TopNav user={user}/>
-		<RouteTransitionWrapper user={user} setUser={setUser}/>
+		<RouteTransitionWrapper
+		    animationMode={animationMode}
+		    user={user}
+		    setUser={setUser}/>
 	      </motion.div>
-	    </LayoutGroup>
+	    </LayoutWrapper>
+	  </MotionConfig>
 
-	    <Toaster/>
-	  </DialogueProvider>
-	</BrowserRouter>
-      </>)
+	  <Toaster/>
+	  </KeyboardShortcutsProvider>
+	</UnsavedChangesGuardProvider>
+      </DialogueProvider>)
 }
 
+const router = createBrowserRouter ([{
+    path: '*',
+    element: <RoutedApp/> }])
+
+const App: FC = () => (
+    <>
+      <RouteBlockerOverlay/>
+      {import.meta.env.DEV && <DevModeWatermark/>}
+      <RouterProvider router={router}/>
+    </>)
+
 export default App

frontend/src/components/DraggableDroppableTagRow.test.tsx

@@ -0,0 +1,75 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import DraggableDroppableTagRow from '@/components/DraggableDroppableTagRow'
+import { buildTag } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+const dndKit = vi.hoisted (() => ({
+  useDraggable: vi.fn (),
+  useDroppable: vi.fn (),
+}))
+
+vi.mock ('@dnd-kit/core', () => dndKit)
+
+const tag = buildTag ({ id: 7, name: 'ドラッグ元', postCount: 3 })
+
+const renderRow = (activeDndId?: string) => {
+  renderWithProviders (
+      <DraggableDroppableTagRow
+          activeDndId={activeDndId}
+          tag={tag}
+          nestLevel={2}
+          pathKey="cat-general-7"
+          suppressClickRef={{ current: false }}/>,
+  )
+}
+
+const tagBody = (): HTMLElement => {
+  const link = document.querySelector<HTMLElement> ('a[title="ドラッグ元"]')
+
+  if (link == null)
+    throw new Error ('tag link not found')
+
+  const body = link.closest ('div')
+
+  if (body == null)
+    throw new Error ('tag body not found')
+
+  return body
+}
+
+describe ('DraggableDroppableTagRow', () => {
+  beforeEach (() => {
+    vi.clearAllMocks ()
+    dndKit.useDraggable.mockReturnValue ({
+        attributes: { 'aria-describedby': 'drag-source' },
+        listeners:  { onPointerDown: vi.fn () },
+        setNodeRef: vi.fn (),
+        transform:  null })
+    dndKit.useDroppable.mockReturnValue ({
+        isOver:     false,
+        setNodeRef: vi.fn () })
+  })
+
+  it ('passes dndId through draggable data for active-row tracking', () => {
+    renderRow ()
+
+    expect (dndKit.useDraggable).toHaveBeenCalledWith (
+        expect.objectContaining ({
+            id:   'tag-node:cat-general-7',
+            data: expect.objectContaining ({
+                dndId:     'tag-node:cat-general-7',
+                nestLevel: 2,
+                tagId:     7 }) }))
+  })
+
+  it ('hides only the active drag source from the explicit active dnd id', () => {
+    renderRow ('tag-node:cat-general-7')
+    expect (tagBody ()).toHaveStyle ({ visibility: 'hidden' })
+  })
+
+  it ('keeps inactive tag rows visible while another tag is dragged', () => {
+    renderRow ('tag-node:other')
+    expect (tagBody ()).toHaveStyle ({ visibility: 'visible' })
+  })
+})

frontend/src/components/DraggableDroppableTagRow.tsx

@@ -4,6 +4,8 @@ import { motion } from 'framer-motion'
 import { useRef } from 'react'
 
 import TagLink from '@/components/TagLink'
+import { clientAnimationTransition } from '@/lib/clientAnimation'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { cn } from '@/lib/utils'
 
 import type { CSSProperties, FC, MutableRefObject } from 'react'
@@ -11,6 +13,7 @@ import type { CSSProperties, FC, MutableRefObject } from 'react'
 import type { Tag } from '@/types'
 
 type Props = {
+    activeDndId?:      string
     tag:              Tag
     nestLevel:        number
     pathKey:          string
@@ -19,7 +22,21 @@ type Props = {
     sp?:              boolean }
 
 
-const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTagId, suppressClickRef, sp }) => {
+const DraggableDroppableTagRow: FC<Props> = ({
+    activeDndId,
+    tag,
+    nestLevel,
+    pathKey,
+    parentTagId,
+    suppressClickRef,
+    sp,
+}) => {
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const layoutTransition = clientAnimationTransition (
+      animationMode,
+      { normal: { duration: .2, ease: 'easeOut' as const } },
+  )
   const dndId = `tag-node:${ pathKey }`
 
   const downPosRef = useRef<{ x: number; y: number } | null> (null)
@@ -45,18 +62,23 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
   const { attributes,
 	  listeners,
 	  setNodeRef: setDragRef,
-	  transform,
-	  isDragging: dragging } = useDraggable ({ id:    dndId,
-						   data:  { kind:   'tag',
-							    tagId:  tag.id,
-							    parentTagId } })
+	  transform } = useDraggable ({ id:    dndId,
+					data:  { kind:   'tag',
+						 dndId,
+						 tagId:  tag.id,
+						 parentTagId,
+						 nestLevel } })
 
   const { setNodeRef: setDropRef, isOver: over } = useDroppable ({
       id:   dndId,
       data: { kind: 'tag', tagId: tag.id } })
 
+  const activeDragging = activeDndId === dndId
   const style: CSSProperties = { transform:   CSS.Translate.toString (transform),
-				 visibility:  dragging ? 'hidden' : 'visible' }
+				 visibility:  activeDragging ? 'hidden' : 'visible' }
+  const innerClassName = cn (
+      'inline-flex min-w-0 max-w-full items-baseline overflow-hidden',
+      sp && 'touch-pan-y')
 
   return (
       <div
@@ -69,12 +91,16 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
 	      return
 	    const dx = e.clientX - p.x
 	    const dy = e.clientY - p.y
+
 	    if (dx * dx + dy * dy >= 9)
 	      armEatNextClick ()
 	  }}
 	  onPointerUpCapture={() => {
 	    downPosRef.current = null
 	  }}
+	  onPointerCancelCapture={() => {
+	    downPosRef.current = null
+	  }}
 	  onClickCapture={e => {
 	    if (suppressClickRef.current)
 	      {
@@ -82,22 +108,35 @@ const DraggableDroppableTagRow: FC<Props> = ({ tag, nestLevel, pathKey, parentTa
 		e.stopPropagation ()
 	      }
 	  }}
-	  ref={node => {
-	    setDragRef (node)
-	    setDropRef (node)
-	  }}
-	  style={style}
+	  ref={setDropRef}
 	  className={cn (
 	      'min-w-0 max-w-full overflow-hidden rounded select-none',
+	      sp && 'touch-pan-y',
 	      over && 'ring-2 ring-offset-2')}
-	  {...attributes}
-	  {...listeners}>
-	<motion.div
-	    className="flex min-w-0 max-w-full items-baseline overflow-hidden"
-	    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-	    layoutId={`tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
-	  <TagLink tag={tag} nestLevel={nestLevel}/>
-	</motion.div>
+	  >
+	{activeDragging
+	 ? (
+	    <div
+		ref={setDragRef}
+		style={style}
+		className={innerClassName}
+		{...attributes}
+		{...listeners}>
+	      <TagLink tag={tag} nestLevel={nestLevel}/>
+	    </div>)
+	 : (
+	    <motion.div
+		ref={setDragRef}
+		style={style}
+		className={innerClassName}
+		{...attributes}
+		{...listeners}
+		transition={{ layout: layoutTransition }}
+		layoutId={animationMode === 'off'
+		    ? undefined
+		    : `tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
+	      <TagLink tag={tag} nestLevel={nestLevel}/>
+	    </motion.div>)}
       </div>)
 }
 

frontend/src/components/MaterialSidebar.tsx

@@ -488,25 +488,23 @@ const MaterialSidebar: FC = () => {
 	  </div>
 	</div>
 
-	<div className="hidden md:block">
-	  <SidebarComponent>
-	    <div className="space-y-4">
-	      <MaterialFilterButtons
-		  materialFilter={materialFilter}
-		  onChange={handleFilterChange}/>
-	      {isLoading && (
-		  <p className="text-sm text-neutral-500 dark:text-stone-400">読込中……</p>)}
-	      {isError && (
-		  <p className="text-sm text-red-600 dark:text-red-300">
-		    タグ一覧の取得に失敗しました．
-		  </p>)}
-	      {(!isLoading && !isError) && (
-		  <ul>
-		    {renderDesktopTree (visibleRootTags)}
-		  </ul>)}
-	    </div>
-	  </SidebarComponent>
-	</div>
+	<SidebarComponent sidebarKey="materials" className="hidden md:block">
+	  <div className="space-y-4">
+	    <MaterialFilterButtons
+		materialFilter={materialFilter}
+		onChange={handleFilterChange}/>
+	    {isLoading && (
+		<p className="text-sm text-neutral-500 dark:text-stone-400">読込中……</p>)}
+	    {isError && (
+		<p className="text-sm text-red-600 dark:text-red-300">
+		  タグ一覧の取得に失敗しました．
+		</p>)}
+	    {(!isLoading && !isError) && (
+		<ul>
+		  {renderDesktopTree (visibleRootTags)}
+		</ul>)}
+	  </div>
+	</SidebarComponent>
       </>)
 }
 

frontend/src/components/PostEditForm.test.tsx

@@ -19,8 +19,8 @@ const toastApi = vi.hoisted (() => ({
 vi.mock ('@/lib/posts', () => postsApi)
 vi.mock ('@/lib/api', () => api)
 vi.mock ('@/components/ui/use-toast', () => toastApi)
-vi.mock ('@/components/dialogues/DialogueProvider', () => ({
-  useDialogue: () => ({
+vi.mock ('@/lib/dialogues/useDialogue', () => ({
+  default: () => ({
     choice: vi.fn (),
   }),
 }))
@@ -78,15 +78,43 @@ describe ('PostEditForm', () => {
 
     render (<PostEditForm post={post} onSave={vi.fn ()}/>)
 
-    expect (screen.getByRole ('spinbutton')).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.queryByRole ('spinbutton')).not.toBeInTheDocument ()
+    expect (screen.queryByText ('動画時間')).not.toBeInTheDocument ()
 
     fireEvent.change (tags, {
       target: { value: '動画 general-tag' },
     })
-    expect (screen.getByRole ('spinbutton')).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 () => {
+    const post = buildPost ()
+    api.isApiError.mockReturnValue (true)
+    postsApi.updatePost.mockRejectedValueOnce ({
+      response: {
+        status: 422,
+        data:   {
+          type: 'validation_error',
+          errors: {
+            original_created_at: ['日時を確認してください．'],
+            original_created_from: ['日時を確認してください．'],
+            original_created_before: ['終了を確認してください．'] },
+        },
+      },
+    })
+
+    render (<PostEditForm post={post} onSave={vi.fn ()}/>)
+    fireEvent.submit (screen.getByRole ('button', { name: '更新' }).closest ('form')!)
+
+    expect (await screen.findByText ('日時を確認してください．')).toBeInTheDocument ()
+    expect (screen.getByText ('終了を確認してください．')).toBeInTheDocument ()
+    expect (screen.getAllByText ('日時を確認してください．')).toHaveLength (1)
+      })
 })

frontend/src/components/PostEditForm.tsx

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

frontend/src/components/PostEmbed.tsx

@@ -4,6 +4,8 @@ import YoutubeEmbed from 'react-youtube'
 import NicoViewer from '@/components/NicoViewer'
 import TwitterEmbed from '@/components/TwitterEmbed'
 import { useDialogue } from '@/components/dialogues/DialogueProvider'
+import { Button } from '@/components/ui/button'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 
 import type { FC, RefObject } from 'react'
 
@@ -24,16 +26,19 @@ type Props = {
     onError?:           (data: unknown) => void }
 
 
-const PostEmbed: FC<Props> = ({
-    ref,
-    post,
-    onLoadComplete,
-    onMetadataChange,
-    onVideoReady,
-    onPlaybackChange,
-    onError,
-}) => {
+const PostEmbed: FC<Props> = (
+    { ref,
+      post,
+      onLoadComplete,
+      onMetadataChange,
+      onVideoReady,
+      onPlaybackChange,
+      onError },
+) => {
   const dialogue = useDialogue ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const embedAutoLoadMode = behaviourSettings.embedAutoLoad ?? 'auto'
+  const [manualLoadRequested, setManualLoadRequested] = useState (false)
   const [framed, setFramed] = useState (false)
   const [youtubePlayer, setYoutubePlayer] = useState<YouTubePlayer | null> (null)
   const niconicoVideoReadyRef = useRef (false)
@@ -105,6 +110,10 @@ const PostEmbed: FC<Props> = ({
     niconicoVideoReadyRef.current = false
   }, [post.url])
 
+  useEffect (() => {
+    setManualLoadRequested (false)
+  }, [embedAutoLoadMode, post.url])
+
   useEffect (() => {
     if (!(youtubePlayer) || !(onPlaybackChange))
       return
@@ -117,6 +126,28 @@ const PostEmbed: FC<Props> = ({
   }, [onPlaybackChange, reportYoutubePlayback, youtubePlayer])
 
   const url = new URL (post.url)
+  const shouldLoadEmbed =
+      embedAutoLoadMode === 'auto'
+      || (
+	  embedAutoLoadMode === 'manual'
+	  && manualLoadRequested
+      )
+
+  const externalLink = (
+      <a href={post.url} target="_blank" rel="noreferrer">
+	外部ページを開く
+      </a>)
+
+  const manualLoadControl = (
+      <div className="flex flex-wrap items-center gap-3">
+	<Button
+	    type="button"
+	    variant="outline"
+	    onClick={() => setManualLoadRequested (true)}>
+	  埋め込みを読込
+	</Button>
+	{externalLink}
+      </div>)
 
   switch (url.hostname.split ('.').slice (-2).join ('.'))
   {
@@ -128,6 +159,11 @@ const PostEmbed: FC<Props> = ({
 
       const [videoId] = mVideoId
 
+      if (embedAutoLoadMode === 'off')
+	return externalLink
+      if (shouldLoadEmbed === false)
+	return manualLoadControl
+
       return (
 	  <NicoViewer
 	      ref={ref}
@@ -150,6 +186,11 @@ const PostEmbed: FC<Props> = ({
       const [userId] = mUserId
       const [statusId] = mStatusId
 
+      if (embedAutoLoadMode === 'off')
+	return externalLink
+      if (shouldLoadEmbed === false)
+	return manualLoadControl
+
       return <TwitterEmbed userId={userId} statusId={statusId}/>
     }
 
@@ -159,6 +200,11 @@ const PostEmbed: FC<Props> = ({
       if (!(videoId))
 	break
 
+      if (embedAutoLoadMode === 'off')
+	return externalLink
+      if (shouldLoadEmbed === false)
+	return manualLoadControl
+
       return (
 	  <YoutubeEmbed videoId={videoId} opts={{ playerVars: {
 	      playsinline:  1,
@@ -184,6 +230,11 @@ const PostEmbed: FC<Props> = ({
 		height={360}/>)
 	 : (
 	    <div>
+	      {embedAutoLoadMode === 'off'
+	       ? externalLink
+	       : embedAutoLoadMode === 'manual' && shouldLoadEmbed === false
+		 ? manualLoadControl
+		 : (
 	      <a href="#" onClick={async e => {
 		e.preventDefault ()
 
@@ -197,7 +248,7 @@ const PostEmbed: FC<Props> = ({
 		    confirmText: '表示' }))
 	      }}>
 		外部ページを表示
-	      </a>
+	      </a>)}
 	    </div>)}
       </>)
 }

frontend/src/components/PostFormTagsArea.tsx

@@ -68,9 +68,12 @@ const PostFormTagsArea: FC<Props> = ({ tags, setTags, errors, ...rest }) => {
 
     setBounds ({ start, end })
 
-    const data = await apiGet<Tag[]> ('/tags/autocomplete', { params: { q: token, nico: '0' } })
-    setSuggestions (data.filter (t => t.postCount > 0))
-    setSuggestionsVsbl (suggestions.length > 0)
+    const data = await apiGet<Tag[]> ('/tags/autocomplete', { params: {
+	q: token,
+	nico: '0' } })
+    const nextSuggestions = data.filter (t => t.postCount > 0)
+    setSuggestions (nextSuggestions)
+    setSuggestionsVsbl (nextSuggestions.length > 0)
   }
 
   return (

frontend/src/components/PostList.tsx

@@ -3,6 +3,7 @@ import { useRef } from 'react'
 import { useLocation } from 'react-router-dom'
 
 import PrefetchLink from '@/components/PrefetchLink'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { cn } from '@/lib/utils'
 import { useSharedTransitionStore } from '@/stores/sharedTransitionStore'
 
@@ -16,6 +17,15 @@ type Props = { posts:     Post[]
 
 const PostList: FC<Props> = ({ posts, onClick }) => {
   const location = useLocation ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const thumbnailMode = behaviourSettings.thumbnailMode ?? 'normal'
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const cardLayoutTransition =
+      animationMode === 'off'
+      ? { duration: 0 }
+      : animationMode === 'reduced'
+	? { duration: .08, ease: 'linear' as const }
+	: { duration: .2, ease: 'easeOut' as const }
 
   const setForLocationKey = useSharedTransitionStore (s => s.setForLocationKey)
 
@@ -39,7 +49,8 @@ const PostList: FC<Props> = ({ posts, onClick }) => {
 		  }}>
 		<motion.div
 		    ref={cardRef}
-		    layoutId={layoutId}
+		    layout={animationMode === 'off' ? false : true}
+		    layoutId={animationMode === 'off' ? undefined : layoutId}
 		    className={cn ('w-full h-full overflow-hidden rounded-xl shadow',
 				   'transform-gpu will-change-transform',
 				   (post.childPosts ?? []).length > 0 && 'ring-4 ring-green-500',
@@ -54,22 +65,36 @@ const PostList: FC<Props> = ({ posts, onClick }) => {
 		    }}
 		    onLayoutAnimationComplete={() => {
 		      if (!(cardRef.current))
-			return 
+			return
 
 		      cardRef.current.style.zIndex = ''
 		      cardRef.current.style.position = ''
 		    }}
-		    transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
-		  <img src={post.thumbnail || post.thumbnailBase || undefined}
-		       alt={post.title || post.url}
-		       title={post.title || post.url || undefined}
-		       loading={i < 12 ? 'eager' : 'lazy'}
-		       decoding="async"
-		       className="object-cover w-full h-full"/>
+		    transition={{ layout: cardLayoutTransition }}>
+		  {thumbnailMode === 'off'
+		   ? (
+		      <div className="flex h-full w-full items-center justify-center
+				      bg-muted text-center text-xs text-muted-foreground">
+			サムネイルなし
+		      </div>)
+		   : (
+		      <img
+			  src={post.thumbnail || post.thumbnailBase || undefined}
+			  alt={post.title || post.url}
+			  title={post.title || post.url || undefined}
+			  loading={
+			      thumbnailMode === 'light'
+			      ? 'lazy'
+			      : i < 12
+				? 'eager'
+				: 'lazy'
+			  }
+			  decoding="async"
+			  className="object-cover w-full h-full"/>)}
 		</motion.div>
 	      </PrefetchLink>)
 	})}
       </div>)
 }
 
-export default PostList
+export default PostList

frontend/src/components/PostOriginalCreatedTimeField.test.tsx

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

frontend/src/components/PostOriginalCreatedTimeField.tsx

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

frontend/src/components/PrefetchLink.tsx

@@ -5,6 +5,7 @@ import { createPath, useNavigate } from 'react-router-dom'
 
 import { useOverlayStore } from '@/components/RouteBlockerOverlay'
 import { prefetchForURL } from '@/lib/prefetchers'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { cn } from '@/lib/utils'
 
 import type { AnchorHTMLAttributes, MouseEvent, TouchEvent } from 'react'
@@ -33,10 +34,15 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
   const navigate = useNavigate ()
   const qc = useQueryClient ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const linkPreloadMode = behaviourSettings.linkPreload ?? 'intent'
+  const path = useMemo (
+      () => typeof to === 'string' ? to : createPath (to),
+      [to],
+  )
   const url = useMemo (() => {
-    const path = (typeof to === 'string') ? to : createPath (to)
-    return (new URL (path, location.origin)).toString ()
-  }, [to])
+    return (new URL (path, window.location.origin)).toString ()
+  }, [path])
   const setOverlay = useOverlayStore (s => s.setActive)
 
   const doPrefetch = async () => {
@@ -54,11 +60,15 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
   const handleMouseEnter = async (ev: MouseEvent<HTMLAnchorElement>) => {
     onMouseEnter?.(ev)
+    if (ev.defaultPrevented || linkPreloadMode !== 'intent')
+      return
     await doPrefetch ()
   }
 
   const handleTouchStart = async (ev: TouchEvent<HTMLAnchorElement>) => {
     onTouchStart?.(ev)
+    if (ev.defaultPrevented || linkPreloadMode !== 'intent')
+      return
     await doPrefetch ()
   }
 
@@ -99,7 +109,7 @@ export default forwardRef<HTMLAnchorElement, Props> (({
 
   return (
       <a ref={ref}
-	 href={typeof to === 'string' ? to : createPath (to)}
+	 href={path}
 	 onMouseEnter={handleMouseEnter}
 	 onTouchStart={handleTouchStart}
 	 onClick={handleClick}

frontend/src/components/ResponsiveMarqueeText.tsx

@@ -1,3 +1,4 @@
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { cn } from '@/lib/utils'
 import { useEffect, useRef, useState } from 'react'
 
@@ -20,6 +21,8 @@ const MIN_MARQUEE_OVERFLOW_PX = 1
 const ResponsiveMarqueeText: FC<Props> = (
     { text, className, truncateOnMobile = false, title },
 ) => {
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
   const outerRef = useRef<HTMLSpanElement | null> (null)
   const staticRef = useRef<HTMLSpanElement | null> (null)
   const animatedRef = useRef<HTMLSpanElement | null> (null)
@@ -98,6 +101,7 @@ const ResponsiveMarqueeText: FC<Props> = (
     const animated = animatedRef.current
     const canMarquee = (
         active
+        && animationMode !== 'off'
         && desktopMarqueeEnabled
         && overflowPx >= MIN_MARQUEE_OVERFLOW_PX
         && animated != null)
@@ -207,7 +211,7 @@ const ResponsiveMarqueeText: FC<Props> = (
       resetAnimated ()
       setMarqueeVisible (false)
     }
-  }, [active, desktopMarqueeEnabled, overflowPx, text])
+  }, [active, animationMode, desktopMarqueeEnabled, overflowPx, text])
 
   return (
       <span

frontend/src/components/TagDetailSidebar.tsx

@@ -1,11 +1,13 @@
 import { DndContext,
 	 DragOverlay,
+	 MeasuringStrategy,
 	 MouseSensor,
 	 TouchSensor,
+	 pointerWithin,
 	 useDroppable,
 	 useSensor,
 	 useSensors } from '@dnd-kit/core'
-import { restrictToWindowEdges } from '@dnd-kit/modifiers'
+import { restrictToWindowEdges, snapCenterToCursor } from '@dnd-kit/modifiers'
 import { useQueryClient } from '@tanstack/react-query'
 import { motion } from 'framer-motion'
 import { useEffect, useMemo, useRef, useState } from 'react'
@@ -20,18 +22,28 @@ import SidebarComponent from '@/components/layout/SidebarComponent'
 import { toast } from '@/components/ui/use-toast'
 import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
 import { apiDelete, apiGet, apiPatch, apiPost } from '@/lib/api'
+import { clientAnimationTransition } from '@/lib/clientAnimation'
 import { postsKeys, tagsKeys } from '@/lib/queryKeys'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { dateString, originalCreatedAtString } from '@/lib/utils'
 
-import type { DragEndEvent } from '@dnd-kit/core'
+import type { CollisionDetection, DragEndEvent } from '@dnd-kit/core'
 import type { FC, MutableRefObject, ReactNode } from 'react'
 
 import type { Category, Post, TagWithSections } from '@/types'
 
 type TagByCategory = { [key in Category]: TagWithSections[] }
 
+const tagCollisionDetection: CollisionDetection = args => {
+  return pointerWithin (args)
+}
+
+const alwaysMeasureDroppables = {
+    droppable: { strategy: MeasuringStrategy.Always } } as const
+
 
 const renderTagTree = (
+    activeDndId:       string | undefined,
     tag:              TagWithSections,
     nestLevel:        number,
     path:             string,
@@ -43,6 +55,7 @@ const renderTagTree = (
   const self = (
       <li key={key} className="mb-1">
 	<DraggableDroppableTagRow
+	    activeDndId={activeDndId}
 	    tag={tag}
 	    nestLevel={nestLevel}
 	    pathKey={key}
@@ -56,11 +69,17 @@ const renderTagTree = (
       ...((tag.children
 	   ?.sort ((a, b) => a.name < b.name ? -1 : 1)
 	   .flatMap (child =>
-	      renderTagTree (child, nestLevel + 1, key, suppressClickRef, tag.id, sp)))
+	      renderTagTree (
+		  activeDndId,
+		  child,
+		  nestLevel + 1,
+		  key,
+		  suppressClickRef,
+		  tag.id,
+		  sp)))
 	  ?? [])]
 }
 
-
 const isDescendant = (
     root:     TagWithSections,
     targetId: number,
@@ -127,6 +146,37 @@ const buildTagByCategory = (post: Post): TagByCategory => {
 }
 
 
+const buildFlatTagByCategory = (
+    byCategory: TagByCategory,
+): TagByCategory => {
+  const tagsTmp = { } as TagByCategory
+  const seen = new Set<number> ()
+
+  for (const category of CATEGORIES)
+    tagsTmp[category] = []
+
+  const visit = (tag: TagWithSections) => {
+    if (seen.has (tag.id))
+      return
+
+    seen.add (tag.id)
+    tagsTmp[tag.category].push ({ ...tag, children: [] })
+
+    for (const child of tag.children ?? [])
+      visit (child)
+  }
+
+  for (const category of CATEGORIES)
+    for (const tag of byCategory[category] ?? [])
+      visit (tag)
+
+  for (const category of CATEGORIES)
+    tagsTmp[category].sort ((tagA, tagB) => tagA.name < tagB.name ? -1 : 1)
+
+  return tagsTmp
+}
+
+
 const changeCategory = async (
     tagId:    number,
     category: Category): Promise<void> => {
@@ -145,14 +195,47 @@ const DropSlot = ({ cat }: { cat: Category }) => {
       </li>)
 }
 
+const EmptyCategoryDropSection = (
+    { cat, children }: { cat: Category
+			 children: ReactNode }) => {
+  const { setNodeRef, isOver: over } = useDroppable ({
+      id:   `slot:${ cat }`,
+      data: { kind: 'slot', cat } })
 
-type Props = { post: Post; sp?: boolean }
+  return (
+      <div ref={setNodeRef} className="my-3">
+	{children}
+	<ul>
+	  <li className="h-1">
+	    {over && <div className="h-0.5 w-full rounded bg-sky-400"/>}
+	  </li>
+	</ul>
+      </div>)
+}
 
 
-const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
+type Props = {
+    className?: string
+    post:       Post
+    sp?:        boolean }
+
+type ActiveTagDrag = {
+    dndId:       string
+    tagId:      number
+    nestLevel:  number }
+
+
+const TagDetailSidebar: FC<Props> = ({ className, post, sp }) => {
   sp = Boolean (sp)
 
   const qc = useQueryClient ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const tagRelationDisplay = behaviourSettings.tagRelationDisplay ?? 'grouped'
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const layoutTransition = clientAnimationTransition (
+      animationMode,
+      { normal: { duration: .2, ease: 'easeOut' as const } },
+  )
 
   const baseTags = useMemo<TagByCategory> (() => {
     const tagsTmp = { } as TagByCategory
@@ -170,10 +253,15 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
     return tagsTmp
   }, [post])
 
-  const [activeTagId, setActiveTagId] = useState<number | null> (null)
+  const [activeTagDrag, setActiveTagDrag] = useState<ActiveTagDrag | null> (null)
   const [dragging, setDragging] = useState (false)
   const [saving, setSaving] = useState (false)
   const [tags, setTags] = useState (baseTags)
+  const flatTagsByCategory = useMemo<TagByCategory> (
+      () => buildFlatTagByCategory (tags),
+      [tags],
+  )
+  const activeDndId = activeTagDrag?.dndId
 
   const suppressClickRef = useRef (false)
 
@@ -278,13 +366,23 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
   }, [baseTags])
 
   return (
-      <SidebarComponent>
+      <SidebarComponent sidebarKey="post-detail-tags" className={className}>
 	<TagSearch/>
 	<DndContext
 	    sensors={sensors}
+	    collisionDetection={tagCollisionDetection}
+	    measuring={alwaysMeasureDroppables}
 	    onDragStart={e => {
 	      if (e.active.data.current?.kind === 'tag')
-		setActiveTagId (e.active.data.current?.tagId ?? null)
+		{
+		  const tagId = e.active.data.current?.tagId
+		  const nestLevel = e.active.data.current?.nestLevel
+		  const dndId = e.active.data.current?.dndId
+		  setActiveTagDrag (
+		      tagId == null || nestLevel == null || dndId == null
+		      ? null
+		      : { dndId, tagId, nestLevel })
+		}
 	      setDragging (true)
 	      suppressClickRef.current = true
 	      document.body.style.userSelect = 'none'
@@ -295,38 +393,80 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
 		suppressClickRef.current = false}, { capture: true, once: true })
 	    }}
 	    onDragCancel={() => {
-	      setActiveTagId (null)
+	      setActiveTagDrag (null)
 	      setDragging (false)
 	      document.body.style.userSelect = ''
 	      suppressClickRef.current = false
 	    }}
 	    onDragEnd={async e => {
-	      setActiveTagId (null)
+	      setActiveTagDrag (null)
 	      setDragging (false)
 	      await onDragEnd (e)
 	      document.body.style.userSelect = ''
 	    }}
 	    modifiers={[restrictToWindowEdges]}>
-	  {CATEGORIES.map ((cat: Category) => ((tags[cat] ?? []).length > 0 || dragging) && (
-	      <div className="my-3" key={cat}>
+	  {CATEGORIES.map ((cat: Category) => {
+	    const categoryTags =
+		tagRelationDisplay === 'grouped'
+		? (tags[cat] ?? [])
+		: (flatTagsByCategory[cat] ?? [])
+
+	    if (!(categoryTags.length > 0 || dragging))
+	      return null
+
+	    const sectionTitle = (
 		<SubsectionTitle>
 		  <motion.div
-		      layoutId={`tag-${ sp ? 'sp-' : '' }${ cat }`}
-		      transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
+		      layoutId={animationMode === 'off'
+			  ? undefined
+			  : `tag-${ sp ? 'sp-' : '' }${ cat }`}
+		      transition={{ layout: layoutTransition }}>
 		    {CATEGORY_NAMES[cat]}
 		  </motion.div>
-		</SubsectionTitle>
+		</SubsectionTitle>)
 
-		<ul>
-		  {(tags[cat] ?? []).flatMap (tag => (
-		      renderTagTree (tag, 0, `cat-${ cat }`, suppressClickRef, undefined, sp)))}
-		  <DropSlot cat={cat}/>
-		</ul>
-	      </div>))}
+	    if (!(categoryTags.length > 0))
+	      return (
+		  <EmptyCategoryDropSection cat={cat} key={cat}>
+		    {sectionTitle}
+		  </EmptyCategoryDropSection>)
+
+	    return (
+		<div className="my-3" key={cat}>
+		  {sectionTitle}
+		  <ul>
+		    {(tagRelationDisplay === 'grouped'
+		      ? (tags[cat] ?? []).flatMap (tag =>
+			    renderTagTree (
+				activeDndId,
+				tag,
+				0,
+				`cat-${ cat }`,
+				suppressClickRef,
+				undefined,
+				sp,
+			    ),
+			)
+		      : (flatTagsByCategory[cat] ?? []).map (tag => (
+			  <li key={`flat-${ cat }-${ tag.id }`} className="mb-1">
+			    <DraggableDroppableTagRow
+				activeDndId={activeDndId}
+				tag={tag}
+				nestLevel={0}
+				pathKey={`flat-${ cat }-${ tag.id }`}
+				suppressClickRef={suppressClickRef}
+				sp={sp}/>
+			  </li>)))}
+		    <DropSlot cat={cat}/>
+		  </ul>
+		</div>)
+	  })}
 	  {post && (
 	      <motion.div
-		  layoutId={`post-info-${ sp }`}
-		  transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
+		  layoutId={animationMode === 'off'
+		      ? undefined
+		      : `post-info-${ sp }`}
+		  transition={{ layout: layoutTransition }}>
 		<SectionTitle>情報</SectionTitle>
 		<ul>
 		  <li>Id.: {post.id}</li>
@@ -363,11 +503,14 @@ const TagDetailSidebar: FC<Props> = ({ post, sp }) => {
 		</ul>
 	      </motion.div>)}
 
-	  <DragOverlay adjustScale={false}>
+	  <DragOverlay
+	      adjustScale={false}
+	      modifiers={[snapCenterToCursor]}
+	      dropAnimation={animationMode === 'off' ? null : undefined}>
 	    <div className="pointer-events-none">
-	      {activeTagId != null && (() => {
-		const tag = findTag (tags, activeTagId)
-		return tag && <TagLink tag={tag}/>
+	      {activeTagDrag != null && (() => {
+		const tag = findTag (tags, activeTagDrag.tagId)
+		return tag && <TagLink tag={tag} nestLevel={activeTagDrag.nestLevel}/>
 	      }) ()}
 	    </div>
 	  </DragOverlay>

frontend/src/components/TagLink.tsx

@@ -1,13 +1,16 @@
 import PrefetchLink from '@/components/PrefetchLink'
 import ResponsiveMarqueeText from '@/components/ResponsiveMarqueeText'
-import { LIGHT_COLOUR_SHADE, DARK_COLOUR_SHADE, TAG_COLOUR } from '@/consts'
 import { cn } from '@/lib/utils'
 
-import type { ComponentProps, FC, HTMLAttributes } from 'react'
+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
@@ -15,18 +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,
@@ -36,26 +64,29 @@ const TagLink: FC<Props> = ({ tag,
 			      withWiki  = true,
 			      withCount = true,
 			      className,
+			      style,
 			      title,
 			      ...props }) => {
-  const spanClass = cn (
-      `text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE }`,
-      `dark:text-${ TAG_COLOUR[tag.category] }-${ DARK_COLOUR_SHADE }`)
-  const linkClass = cn (
-      spanClass,
-      `hover:text-${ TAG_COLOUR[tag.category] }-${ LIGHT_COLOUR_SHADE - 200 }`,
-      `dark:hover:text-${ TAG_COLOUR[tag.category] }-${ DARK_COLOUR_SHADE - 200 }`)
+  const colourStyle = {
+      '--tag-link-colour': `var(--tag-colour-${ tag.category })`,
+      '--tag-link-hover-colour': `var(--tag-colour-${ tag.category }-hover)`,
+      ...style,
+  } as CSSProperties
+  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}>
-	{(linkFlg && withWiki) && (
+      <span
+	  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)
 	       ? (
@@ -63,7 +94,8 @@ const TagLink: FC<Props> = ({ tag,
 		  ? (
 		      <PrefetchLink
 			  to={`/wiki/${ encodeURIComponent (tag.name) }`}
-			  className={linkClass}>
+			  className={linkClass}
+			  style={colourStyle}>
 			?
 		      </PrefetchLink>)
 		  : (
@@ -71,13 +103,15 @@ const TagLink: FC<Props> = ({ tag,
 		      ? (
 			  <PrefetchLink
 			      to={`/materials/${ tag.materialId }`}
-			      className={linkClass}>
+			      className={linkClass}
+			      style={colourStyle}>
 			    ?
 			  </PrefetchLink>)
 		      : (
 			  <PrefetchLink
 			      to={`/tags/${ tag.id }/deerjikists`}
-			      className={linkClass}>
+			      className={linkClass}
+			      style={colourStyle}>
 			    ?
 			  </PrefetchLink>)))
 	       : (
@@ -115,14 +149,15 @@ const TagLink: FC<Props> = ({ tag,
 		style={{ paddingLeft: `${ (nestLevel - 1) }rem` }}>
 	      ↳
 	    </span>)}
-	{tag.matchedAlias != null && (
+	{matchedAlias != null && (
 	    <>
 	      <span
 		  title={textTitle}
 		  className={cn (spanClass, textClass, className)}
+		  style={colourStyle}
 		  {...props}>
 		<ResponsiveMarqueeText
-		    text={tag.matchedAlias}
+		    text={matchedAlias}
 		    title={textTitle}
 		    truncateOnMobile={truncateOnMobile}/>
 	      </span>
@@ -134,6 +169,7 @@ const TagLink: FC<Props> = ({ tag,
 		to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}
 		title={textTitle}
 		className={cn (linkClass, textClass, className)}
+		style={colourStyle}
 		{...props}>
 	      <ResponsiveMarqueeText
 		  text={tag.name}
@@ -144,13 +180,14 @@ const TagLink: FC<Props> = ({ tag,
 	    <span
 		  title={textTitle}
 		  className={cn (spanClass, textClass, className)}
+		  style={colourStyle}
 		  {...props}>
 	      <ResponsiveMarqueeText
 		  text={tag.name}
 		  title={textTitle}
 		  truncateOnMobile={truncateOnMobile}/>
 	    </span>)}
-	{withCount && (
+	{(withCount && isFullTag (tag)) && (
 	    <span className={countClass}>{tag.postCount}</span>)}
       </span>)
 }

frontend/src/components/TagSearch.tsx

@@ -105,6 +105,7 @@ const TagSearch: FC = () => {
   return (
       <div className="relative w-full">
 	<input type="text"
+	       data-shortcut-focus-search="true"
 	       placeholder="タグ検索..."
 	       value={search}
 	       onChange={whenChanged}

frontend/src/components/TagSidebar.tsx

@@ -8,6 +8,8 @@ import SectionTitle from '@/components/common/SectionTitle'
 import SidebarComponent from '@/components/layout/SidebarComponent'
 import { CATEGORIES } from '@/consts'
 import { apiGet } from '@/lib/api'
+import { clientAnimationTransition } from '@/lib/clientAnimation'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 
 import type { FC, MouseEvent } from 'react'
 
@@ -21,6 +23,13 @@ type Props = { posts:     Post[]
 
 const TagSidebar: FC<Props> = ({ posts, onClick }) => {
   const navigate = useNavigate ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const animationsOff = animationMode === 'off'
+  const layoutTransition = clientAnimationTransition (
+      animationMode,
+      { normal: { duration: .2, ease: 'easeOut' as const } },
+  )
 
   const [tagsVsbl, setTagsVsbl] = useState (false)
   const [tags, setTags] = useState<TagByCategory> ({ })
@@ -65,12 +74,18 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
 	  {CATEGORIES.flatMap (cat => cat in tags ? (
 	      tags[cat].map (tag => (
 		  <li key={tag.id} className="mb-1 min-w-0 max-w-full overflow-hidden">
-		    <motion.div
-			className="flex min-w-0 max-w-full items-baseline overflow-hidden"
-			transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-			layoutId={`tag-${ tag.id }`}>
-		      <TagLink tag={tag} onClick={onClick}/>
-		    </motion.div>
+		    {animationsOff
+		     ? (
+			 <div className="flex min-w-0 max-w-full items-baseline overflow-hidden">
+			   <TagLink tag={tag} onClick={onClick}/>
+			 </div>)
+		     : (
+			 <motion.div
+			     className="flex min-w-0 max-w-full items-baseline overflow-hidden"
+			     transition={{ layout: layoutTransition }}
+			     layoutId={`tag-${ tag.id }`}>
+			   <TagLink tag={tag} onClick={onClick}/>
+			 </motion.div>)}
 		  </li>))) : [])}
 	</ul>
 	<SectionTitle>関聯</SectionTitle>
@@ -96,25 +111,32 @@ const TagSidebar: FC<Props> = ({ posts, onClick }) => {
       </>)
 
   return (
-      <SidebarComponent>
+      <SidebarComponent sidebarKey="posts-index-tags">
 	<TagSearch/>
 
 	<div className="hidden md:block mt-4">
 	  {posts.length > 0 && TagBlock}
 	</div>
 
-	<AnimatePresence initial={false}>
-	  {tagsVsbl && (
-	      <motion.div
-		  key="sptags"
-		  className="md:hidden overflow-hidden"
-		  initial={{ height: 0 }}
-		  animate={{ height: 'auto' }}
-		  exit={{ height: 0 }}
-		  transition={{ duration: .2, ease: 'easeOut' }}>
-		{posts.length > 0 && TagBlock}
-	      </motion.div>)}
-	</AnimatePresence>
+	{animationsOff
+	 ? (
+	     tagsVsbl && (
+		 <div className="md:hidden overflow-hidden">
+		   {posts.length > 0 && TagBlock}
+		 </div>))
+	 : (
+	     <AnimatePresence initial={false}>
+	       {tagsVsbl && (
+		   <motion.div
+		       key="sptags"
+		       className="md:hidden overflow-hidden"
+		       initial={{ height: 0 }}
+		       animate={{ height: 'auto' }}
+		       exit={{ height: 0 }}
+		       transition={layoutTransition}>
+		     {posts.length > 0 && TagBlock}
+		   </motion.div>)}
+	     </AnimatePresence>)}
 
 	<a href="#"
 	   className="md:hidden block my-2 text-center text-sm

frontend/src/components/TopNav.test.tsx

@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest'
+
+import { menuOutline } from '@/components/TopNav'
+import { buildUser } from '@/test/factories'
+
+const submenuItem = (role: 'guest' | 'member' | 'admin', section: string, item: string) => {
+  const menu = menuOutline ({
+    user: buildUser ({ role }),
+    wikiId: section === 'Wiki' ? 10 : null,
+    pathName: section === 'Wiki' ? '/wiki/page' : '/posts' })
+  return menu.find (entry => entry.name === section)?.subMenu.find (
+      subMenuItem => subMenuItem.name === item)
+}
+
+describe ('menuOutline', () => {
+  it ('uses content-edit permission for post, material, and Wiki actions', () => {
+    for (const role of ['member', 'admin'] as const)
+      {
+	expect (submenuItem (role, '広場', '追加')?.visible).toBe (true)
+	expect (submenuItem (role, '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', '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

@@ -8,6 +8,8 @@ import PrefetchLink from '@/components/PrefetchLink'
 import TopNavUser from '@/components/TopNavUser'
 import { WikiIdBus } from '@/lib/eventBus/WikiIdBus'
 import { materialsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { canEditContent } from '@/lib/users'
 import { fetchTag, fetchTagByName } from '@/lib/tags'
 import { fetchMaterial } from '@/lib/materials'
 import { cn } from '@/lib/utils'
@@ -25,10 +27,11 @@ export const menuOutline = (
 	tag?: Tag | null
 	material?: Material | null
 	wikiId: number | null
-	user: User | null,
+	user: User | null
 	pathName: string },
 ): Menu => {
   const postCount = tag?.postCount ?? material?.tag?.postCount ?? 0
+  const editable = canEditContent (user)
 
   const wikiPageFlg = Boolean (/^\/wiki\/(?!new|changes)[^/]+/.test (pathName) && wikiId)
   const wikiTitle = pathName.split ('/')[2] ?? ''
@@ -41,7 +44,7 @@ export const menuOutline = (
       { name: '広場', to: '/posts', subMenu: [
 	  { name: '一覧', to: '/posts' },
 	  { name: '検索', to: '/posts/search' },
-	  { name: '追加', to: '/posts/new' },
+	  { name: '追加', to: '/posts/new', visible: editable },
 	  { name: '全体履歴', to: '/posts/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:広場' }] },
       { name: 'タグ', to: '/tags', subMenu: [
@@ -57,8 +60,9 @@ export const menuOutline = (
 	    visible: tagFlg && tag?.category !== 'nico' }] },
       { name: '素材', to: '/materials', visible: true, subMenu: [
 	  { name: '一覧', to: '/materials' },
-	  { name: '追加', to: '/materials/new' },
-	  { name: '抑止', to: '/materials/suppressions' },
+	  { name: '追加', to: '/materials/new', visible: editable },
+	  { name: '抑止', to: '/materials/suppressions',
+	    visible: user?.role === 'admin' },
 	  { name: '全体履歴', to: '/materials/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:素材管理' },
 	  { component: <Separator/>, visible: materialFlg },
@@ -69,14 +73,15 @@ export const menuOutline = (
 	    visible: materialFlg }] },
       { name: 'Wiki', to: '/wiki/ヘルプ:ホーム', base: '/wiki', subMenu: [
 	  { name: '検索', to: '/wiki' },
-	  { name: '新規', to: '/wiki/new' },
+	  { name: '新規', to: '/wiki/new', visible: editable },
 	  { name: '全体履歴', to: '/wiki/changes' },
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:Wiki' },
 	  { component: <Separator/>, visible: wikiPageFlg },
 	  { name: `広場 (${ postCount || 0 })`, to: `/posts?tags=${ wikiTitle }`,
 	    visible: wikiPageFlg },
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
-	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`, visible: wikiPageFlg }] },
+	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`,
+	    visible: wikiPageFlg && editable }] },
       { name: 'おたのしみ', visible: false, subMenu: [
 	  { name: '上映会 (β)', to: '/theatres/1' },
 	  { name: 'グカネータ (β)', to: '/gekanator' }] },
@@ -91,6 +96,10 @@ export const menuOutline = (
 
 const TopNav: FC<Props> = ({ user }) => {
   const location = useLocation ()
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const animationsOff = animationMode === 'off'
+  const reducedAnimations = animationMode === 'reduced'
 
   const dirRef = useRef<(-1) | 1> (1)
   const itemsRef = useRef<(HTMLAnchorElement | null)[]> ([])
@@ -155,6 +164,24 @@ const TopNav: FC<Props> = ({ user }) => {
   const activeIdx =
       visibleMenu.findIndex (item => location.pathname.startsWith (item.base || item.to))
   const submenuHeight = moreVsbl ? 40 * moreMenu.length : (activeIdx < 0 ? 0 : 40)
+  const topNavTransition =
+      animationsOff
+      ? { duration: 0 }
+      : reducedAnimations
+	? { duration: .08, ease: 'linear' as const }
+	: { duration: .2, ease: 'easeOut' as const }
+  const opacityTransition =
+      animationsOff
+      ? { duration: 0 }
+      : reducedAnimations
+	? { duration: .08 }
+	: { duration: .12 }
+  const highlightTransitionClass =
+      animationsOff
+      ? undefined
+      : reducedAnimations
+	? 'transition-[transform,width] duration-75 ease-linear'
+	: 'transition-[transform,width] duration-200 ease-out'
 
   const prevActiveIdxRef = useRef<number> (activeIdx)
 
@@ -189,13 +216,11 @@ const TopNav: FC<Props> = ({ user }) => {
 
   return (
       <>
-	<nav className="px-3 flex justify-between items-center w-full
-			bg-yellow-200 dark:bg-red-975 md:bg-yellow-50">
+	<nav className="top-nav-root px-3 flex justify-between items-center w-full">
 	  <div className="flex items-center gap-2 h-12">
 	    <PrefetchLink
 		to="/posts"
-		className="mx-4 text-xl font-bold text-pink-600 hover:text-pink-400
-			   dark:text-pink-300 dark:hover:text-pink-100"
+		className="top-nav-brand-link mx-4 text-xl font-bold"
 		onClick={() => {
 		  scroll (0, 0)
 		}}>
@@ -205,8 +230,8 @@ const TopNav: FC<Props> = ({ user }) => {
 	    <div ref={navRef} className="relative hidden md:flex h-12 items-center">
 	      <div aria-hidden
 		   className={cn ('absolute inset-y-0 h-12',
-				  'bg-yellow-200 dark:bg-red-950',
-				  'transition-[transform,width] duration-200 ease-out')}
+				  'top-nav-highlight',
+				  highlightTransitionClass)}
 		   style={{ width:      hl.width,
 			    transform:  `translateX(${ hl.left }px)`,
 			    opacity:    hl.visible ? 1 : 0 }}/>
@@ -214,10 +239,12 @@ const TopNav: FC<Props> = ({ user }) => {
 	      {visibleMenu.map ((item, i) => (
 		  <motion.div
 		      key={item.to}
-		      layoutId={`menu-${ item.name }`}
+		      {...(animationsOff
+			   ? { }
+			   : { layoutId: `menu-${ item.name }` })}
 		      animate={{ opacity: moreVsbl ? 0 : 1 }}
-		      transition={{ opacity: { duration: .12 },
-				    layout: { duration: .2, ease: 'easeOut' } }}
+		      transition={{ opacity: opacityTransition,
+				    layout: topNavTransition }}
 		      style={{ pointerEvents: moreVsbl ? 'none' : 'auto' }}
 		      onMouseEnter={() => setMoreVsbl (false)}>
 		    <PrefetchLink
@@ -225,7 +252,7 @@ const TopNav: FC<Props> = ({ user }) => {
 			ref={(el: (HTMLAnchorElement | null)) => {
 			  itemsRef.current[i] = el
 			}}
-			className={cn ('relative z-10 flex h-full items-center px-5',
+			className={cn ('top-nav-menu-link relative z-10 flex h-full items-center px-5',
 				       (i === openItemIdx) && 'font-bold')}>
 		      {item.name}
 		    </PrefetchLink>
@@ -240,7 +267,7 @@ const TopNav: FC<Props> = ({ user }) => {
 		    setMoreVsbl (true)
 		    measure (-1)
 		  }}
-		  className={cn ('relative z-10 flex h-full items-center px-5',
+		  className={cn ('top-nav-menu-link relative z-10 flex h-full items-center px-5',
 				 (openItemIdx < 0 || moreVsbl) && 'font-bold')}>
 		その他 &raquo;
 	      </PrefetchLink>
@@ -249,30 +276,28 @@ const TopNav: FC<Props> = ({ user }) => {
 
 	  <TopNavUser user={user}/>
 
-	  <a href="#"
-	     className="md:hidden ml-auto pr-4
-			text-pink-600 hover:text-pink-400
-			dark:text-pink-300 dark:hover:text-pink-100"
-	     onClick={ev => {
-	       ev.preventDefault ()
+	  <button
+	     type="button"
+	     className="top-nav-mobile-toggle md:hidden ml-auto border-0 bg-transparent pr-4"
+	     onClick={() => {
 	       setMenuOpen (!(menuOpen))
 	     }}>
 	    {menuOpen ? '×' : 'Menu'}
-	  </a>
+	  </button>
 	</nav>
 
 	<AnimatePresence initial={false}>
 	  <motion.div
 	      key="submenu-shell"
-	      layout
-	      className="relative z-20 hidden md:block overflow-hidden
-			 bg-yellow-200 dark:bg-red-950"
+	      {...(animationsOff ? { }
+		   : { layout: true })}
+	      className="relative z-20 hidden md:block overflow-hidden top-nav-submenu"
 	      animate={{ height: submenuHeight }}
 	      onMouseLeave={() => {
 		if (moreVsbl)
 		  setMoreVsbl (false)
 	      }}
-	      transition={{ layout: { duration: .2, ease: 'easeOut' } }}
+	      transition={{ layout: topNavTransition }}
 	      onAnimationComplete={() => {
 		measure (moreVsbl ? -1 : activeIdx)
 	      }}>
@@ -282,12 +307,14 @@ const TopNav: FC<Props> = ({ user }) => {
 		  <div key={i} className="relative h-[40px]">
 		    <div className="absolute inset-0 flex items-center px-3">
 		      <motion.div
-			  transition={{ duration: .2, ease: 'easeOut' }}
-			  {...((item.visible ?? true)
+			  transition={topNavTransition}
+			  {...(animationsOff
+			       ? { }
+			       : ((item.visible ?? true)
 			       ? { layoutId: `menu-${ item.name }` }
 			       : { initial: { x: 40, y: -40, opacity: 0 },
 				   animate: { x: 0, y: 0, opacity: 1 },
-				   exit: { x: 40, y: -40, opacity: 0 } })}
+				   exit: { x: 40, y: -40, opacity: 0 } }))}
 			  className="z-10 h-full flex items-center px-3 font-bold w-28">
 			<h2>{item.name}</h2>
 		      </motion.div>
@@ -298,30 +325,34 @@ const TopNav: FC<Props> = ({ user }) => {
 			  ? (
 			      <motion.div
 				  key={`c-${ i }-${ j }`}
-				  transition={{ duration: .2, ease: 'easeOut' }}
-				  {...((visibleMenu[activeIdx]?.name
+				  transition={topNavTransition}
+				  {...(animationsOff
+				       ? { }
+				       : ((visibleMenu[activeIdx]?.name
 					=== item.name)
 				       ? { layoutId: `submenu-${ item.name }-${ j }` }
 				       : { initial: { y: -40, opacity: 0 },
 					   animate: { y: 0, opacity: 1 },
-					   exit: { y: -40, opacity: 0 } })}>
+					   exit: { y: -40, opacity: 0 } }))}>
 				{subItem.component}
 			      </motion.div>)
 			  : (
 			      <motion.div
 				  key={`l-${ i }-${ j }`}
-				  transition={{ duration: .2, ease: 'easeOut' }}
-				  {...((visibleMenu[activeIdx]?.name
+				  transition={topNavTransition}
+				  {...(animationsOff
+				       ? { }
+				       : ((visibleMenu[activeIdx]?.name
 					=== item.name)
 				       ? { layoutId: `submenu-${ item.name }-${ j }` }
 				       : { initial: { y: -40, opacity: 0 },
 					   animate: { y: 0, opacity: 1 },
-					   exit: { y: -40, opacity: 0 } })}>
+					   exit: { y: -40, opacity: 0 } }))}>
 				<PrefetchLink
 				    to={subItem.to}
 				    target={subItem.to.slice (0, 2) === '//' ? '_blank' : undefined}
 				    onClick={() => setMoreVsbl (false)}
-				    className="h-full flex items-center px-3">
+				    className="top-nav-menu-link h-full flex items-center px-3">
 				  {subItem.name}
 				</PrefetchLink>
 			      </motion.div>)))}
@@ -330,129 +361,215 @@ const TopNav: FC<Props> = ({ user }) => {
 	   : ((visibleMenu[activeIdx]?.subMenu ?? []).length > 0
 	      && (
 		  <div className="relative h-[40px]">
-		    <AnimatePresence initial={false} custom={dir}>
-		      <motion.div
-			  key={activeIdx}
-			  custom={dir}
-			  variants={{ enter: (d: -1 | 1) => ({ y: d * 24, opacity: 0 }),
-				      centre: { y: 0, opacity: 1 },
-				      exit: (d: -1 | 1) => ({ y: (-d) * 24, opacity: 0 }) }}
-			  className="absolute inset-0 flex items-center px-3"
-			  initial="enter"
-			  animate="centre"
-			  exit="exit"
-			  transition={{ duration: .2, ease: 'easeOut' }}>
-			{(visibleMenu[activeIdx]?.subMenu ?? [])
-			 .filter (item => item.visible ?? true)
-			 .map ((item, i) => (
-			    'component' in item
-			    ? (
-				<motion.div
-				    key={`c-${ i }`}
-				    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-				    layoutId={`submenu-${ visibleMenu[activeIdx].name }-${ i }`}>
-				  {item.component}
-				</motion.div>)
-			    : (
-				<motion.div
-				    key={`l-${ i }`}
-				    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-				    layoutId={`submenu-${ visibleMenu[activeIdx].name }-${ i }`}>
-				  <PrefetchLink
-				      to={item.to}
-				      target={item.to.slice (0, 2) === '//' ? '_blank' : undefined}
-				      className="h-full flex items-center px-3">
-				    {item.name}
-				  </PrefetchLink>
-				</motion.div>)))}
-		      </motion.div>
-		    </AnimatePresence>
+		    {animationsOff
+		     ? (
+			 <div className="absolute inset-0 flex items-center px-3">
+			   {(visibleMenu[activeIdx]?.subMenu ?? [])
+			    .filter (item => item.visible ?? true)
+			    .map ((item, i) => (
+			       'component' in item
+			       ? (
+				   <div key={`c-${ i }`}>
+				     {item.component}
+				   </div>)
+			       : (
+				   <div key={`l-${ i }`}>
+				     <PrefetchLink
+					 to={item.to}
+					 target={item.to.slice (0, 2) === '//'
+						 ? '_blank'
+						 : undefined}
+					 className="top-nav-menu-link h-full flex items-center px-3">
+				       {item.name}
+				     </PrefetchLink>
+				   </div>)))}
+			 </div>)
+		     : (
+			 <AnimatePresence initial={false} custom={dir}>
+			   <motion.div
+			       key={activeIdx}
+			       custom={dir}
+			       variants={{ enter: (d: -1 | 1) => ({ y: d * 24, opacity: 0 }),
+					   centre: { y: 0, opacity: 1 },
+					   exit: (d: -1 | 1) => ({ y: (-d) * 24, opacity: 0 }) }}
+			       className="absolute inset-0 flex items-center px-3"
+			       initial="enter"
+			       animate="centre"
+			       exit="exit"
+			       transition={topNavTransition}>
+			     {(visibleMenu[activeIdx]?.subMenu ?? [])
+			      .filter (item => item.visible ?? true)
+			      .map ((item, i) => (
+				 'component' in item
+				 ? (
+				     <motion.div
+					 key={`c-${ i }`}
+					 transition={{ layout: topNavTransition }}
+					 layoutId={`submenu-${ visibleMenu[activeIdx].name }-${ i }`}>
+				       {item.component}
+				     </motion.div>)
+				 : (
+				     <motion.div
+					 key={`l-${ i }`}
+					 transition={{ layout: topNavTransition }}
+					 layoutId={`submenu-${ visibleMenu[activeIdx].name }-${ i }`}>
+				       <PrefetchLink
+					   to={item.to}
+					   target={item.to.slice (0, 2) === '//'
+						   ? '_blank'
+						   : undefined}
+					   className="top-nav-menu-link h-full flex items-center px-3">
+					 {item.name}
+				       </PrefetchLink>
+				     </motion.div>)))}
+			   </motion.div>
+			 </AnimatePresence>)}
 		  </div>))}
 	  </motion.div>
 	</AnimatePresence>
 
-	<AnimatePresence initial={false}>
-	  {menuOpen && (
-	      <motion.div
-		  key="spmenu"
-		  className={cn ('flex flex-col md:hidden',
-				 'bg-yellow-200 dark:bg-red-975 items-start')}
-		  variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
-					height:   0 },
-			      open:   { clipPath: 'inset(0 0 0% 0)',
-					height:   'auto' } }}
-		  initial="closed"
-		  animate="open"
-		  exit="closed"
-		  transition={{ duration: .2, ease: 'easeOut' }}>
-		<Separator/>
-		{visibleMenu.map ((item, i) => (
-		    <Fragment key={i}>
-		      <PrefetchLink
-			  to={i === openItemIdx ? item.to : '#'}
-			  className={cn ('w-full min-h-[40px] flex items-center pl-8',
-				     ((i === openItemIdx)
-				      && 'font-bold bg-yellow-50 dark:bg-red-950'))}
-			  onClick={(ev: MouseEvent<HTMLAnchorElement>) => {
-			    if (i !== openItemIdx)
-			      {
-				ev.preventDefault ()
-				setOpenItemIdx (i)
-			      }
-			  }}>
-			{item.name}
-		      </PrefetchLink>
+	{animationsOff
+	 ? (
+	     menuOpen && (
+		 <div
+		     className={cn ('top-nav-root top-nav-mobile-menu flex flex-col md:hidden',
+				    'items-start')}>
+		   <Separator/>
+		   {visibleMenu.map ((item, i) => (
+		       <Fragment key={i}>
+			 <PrefetchLink
+			     to={i === openItemIdx ? item.to : '#'}
+			     className={cn ('top-nav-mobile-row w-full min-h-[40px] flex items-center pl-8',
+					((i === openItemIdx)
+					 && 'top-nav-mobile-active font-bold'))}
+			     onClick={(ev: MouseEvent<HTMLAnchorElement>) => {
+			       if (i !== openItemIdx)
+				 {
+				   ev.preventDefault ()
+				   setOpenItemIdx (i)
+				 }
+			     }}>
+			   {item.name}
+			 </PrefetchLink>
 
-		      <AnimatePresence initial={false}>
-			{i === openItemIdx && (
-			    <motion.div
-				key={`sp-sub-${ i }`}
-				className="w-full bg-yellow-50 dark:bg-red-950"
-				variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
-						      height:   0,
-						      opacity:  0 },
-					    open:   { clipPath: 'inset(0 0 0% 0)',
-						      height:   'auto',
-						      opacity:  1 } }}
-				initial="closed"
-				animate="open"
-				exit="closed"
-				transition={{ duration: .2, ease: 'easeOut' }}>
-			      {item.subMenu
-			       .filter (subItem => subItem.visible ?? true)
-			       .map ((subItem, j) => (
-				  'component' in subItem
-				  ? (
-				      <Fragment key={`sp-c-${ i }-${ j }`}>
-					{subItem.component}
-				      </Fragment>)
-				  : (
-				      <PrefetchLink
-					  key={`sp-l-${ i }-${ j }`}
-					  to={subItem.to}
-					  target={subItem.to.slice (0, 2) === '//'
-						  ? '_blank'
-						  : undefined}
-					  className="w-full min-h-[36px] flex items-center pl-12">
-					{subItem.name}
-				      </PrefetchLink>)))}
-			    </motion.div>)}
-		      </AnimatePresence>
-		    </Fragment>))}
-		<PrefetchLink
-		    to="/more"
-		    ref={(el: (HTMLAnchorElement | null)) => {
-		      itemsRef.current[visibleMenu.length] = el
-		    }}
-		    className={cn ('w-full min-h-[40px] flex items-center pl-8',
-				   ((openItemIdx < 0)
-				    && 'font-bold bg-yellow-50 dark:bg-red-950'))}>
-		  その他 &raquo;
-		</PrefetchLink>
-		<TopNavUser user={user} sp/>
-		<Separator/>
-	      </motion.div>)}
-	</AnimatePresence>
+			 {i === openItemIdx && (
+			     <div className="top-nav-submenu w-full">
+			       {item.subMenu
+				.filter (subItem => subItem.visible ?? true)
+				.map ((subItem, j) => (
+				   'component' in subItem
+				   ? (
+				       <Fragment key={`sp-c-${ i }-${ j }`}>
+					 {subItem.component}
+				       </Fragment>)
+				   : (
+				       <PrefetchLink
+					   key={`sp-l-${ i }-${ j }`}
+					   to={subItem.to}
+					   target={subItem.to.slice (0, 2) === '//'
+						   ? '_blank'
+						   : undefined}
+					   className="top-nav-mobile-row w-full min-h-[36px] flex items-center pl-12">
+					 {subItem.name}
+				       </PrefetchLink>)))}
+			     </div>)}
+		       </Fragment>))}
+		   <PrefetchLink
+		       to="/more"
+		       ref={(el: (HTMLAnchorElement | null)) => {
+			 itemsRef.current[visibleMenu.length] = el
+		       }}
+		       className={cn ('top-nav-mobile-row w-full min-h-[40px] flex items-center pl-8',
+				      ((openItemIdx < 0)
+				       && 'top-nav-mobile-active font-bold'))}>
+		     その他 &raquo;
+		   </PrefetchLink>
+		   <TopNavUser user={user} sp/>
+		   <Separator/>
+		 </div>))
+	 : (
+	     <AnimatePresence initial={false}>
+	       {menuOpen && (
+		   <motion.div
+		       key="spmenu"
+		       className={cn ('top-nav-root top-nav-mobile-menu flex flex-col md:hidden',
+				      'items-start')}
+		       variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
+					     height:   0 },
+				   open:   { clipPath: 'inset(0 0 0% 0)',
+					     height:   'auto' } }}
+		       initial="closed"
+		       animate="open"
+		       exit="closed"
+		       transition={topNavTransition}>
+		     <Separator/>
+		     {visibleMenu.map ((item, i) => (
+			 <Fragment key={i}>
+			   <PrefetchLink
+			       to={i === openItemIdx ? item.to : '#'}
+			       className={cn ('top-nav-mobile-row w-full min-h-[40px] flex items-center pl-8',
+					  ((i === openItemIdx)
+					   && 'top-nav-mobile-active font-bold'))}
+			       onClick={(ev: MouseEvent<HTMLAnchorElement>) => {
+				 if (i !== openItemIdx)
+				   {
+				     ev.preventDefault ()
+				     setOpenItemIdx (i)
+				   }
+			       }}>
+			     {item.name}
+			   </PrefetchLink>
+
+			   <AnimatePresence initial={false}>
+			     {i === openItemIdx && (
+				 <motion.div
+				     key={`sp-sub-${ i }`}
+				     className="top-nav-submenu w-full"
+				     variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
+							   height:   0,
+							   opacity:  0 },
+						 open:   { clipPath: 'inset(0 0 0% 0)',
+							   height:   'auto',
+							   opacity:  1 } }}
+				     initial="closed"
+				     animate="open"
+				     exit="closed"
+				     transition={topNavTransition}>
+				   {item.subMenu
+				    .filter (subItem => subItem.visible ?? true)
+				    .map ((subItem, j) => (
+				       'component' in subItem
+				       ? (
+					   <Fragment key={`sp-c-${ i }-${ j }`}>
+					     {subItem.component}
+					   </Fragment>)
+				       : (
+					   <PrefetchLink
+					       key={`sp-l-${ i }-${ j }`}
+					       to={subItem.to}
+					       target={subItem.to.slice (0, 2) === '//'
+						       ? '_blank'
+						       : undefined}
+					       className="top-nav-mobile-row w-full min-h-[36px] flex items-center pl-12">
+					     {subItem.name}
+					   </PrefetchLink>)))}
+				 </motion.div>)}
+			   </AnimatePresence>
+			 </Fragment>))}
+		     <PrefetchLink
+			 to="/more"
+			 ref={(el: (HTMLAnchorElement | null)) => {
+			   itemsRef.current[visibleMenu.length] = el
+			 }}
+			 className={cn ('top-nav-mobile-row w-full min-h-[40px] flex items-center pl-8',
+					((openItemIdx < 0)
+					 && 'top-nav-mobile-active font-bold'))}>
+		       その他 &raquo;
+		     </PrefetchLink>
+		     <TopNavUser user={user} sp/>
+		     <Separator/>
+		   </motion.div>)}
+	     </AnimatePresence>)}
       </>)
 }
 

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

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

frontend/src/components/common/DateTimeField.tsx

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

frontend/src/components/common/FieldWarning.tsx

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

frontend/src/components/common/Form.tsx

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

frontend/src/components/common/StatusBadge.tsx

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

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

@@ -20,4 +20,16 @@ describe ('TabGroup', () => {
     expect (screen.getByText ('Alpha')).toBeInTheDocument ()
     expect (screen.queryByText ('Beta')).not.toBeInTheDocument ()
   })
+
+  it ('renders tabs as buttons and shows the right addon', () => {
+    render (
+        <TabGroup rightAddon={<span>件数 20</span>}>
+          <Tab name="広場">Plaza</Tab>
+        </TabGroup>,
+    )
+
+    expect (screen.getByRole ('button', { name: '広場' })).toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '広場' })).not.toBeInTheDocument ()
+    expect (screen.getByText ('件数 20')).toBeInTheDocument ()
+  })
 })

frontend/src/components/common/TabGroup.tsx

@@ -7,12 +7,15 @@ type TabProps = { name:     string
 		  init?:    boolean
 		  children: React.ReactNode }
 
-type Props = { children: React.ReactNode }
+type Props = {
+    children:    React.ReactNode
+    rightAddon?: React.ReactNode
+}
 
 export const Tab = ({ children }: TabProps) => <>{children}</>
 
 
-const TabGroup: FC<Props> = ({ children }) => {
+const TabGroup: FC<Props> = ({ children, rightAddon }) => {
   const tabs = React.Children.toArray (children) as React.ReactElement<TabProps>[]
 
   const [current, setCurrent] = useState<number> (() => {
@@ -22,17 +25,27 @@ const TabGroup: FC<Props> = ({ children }) => {
 
   return (
       <div className="mt-4">
-	<div className="flex gap-4">
-	  {tabs.map ((tab, i) => (
-	      <a key={i}
-		 href="#"
-		 className={cn (i === current && 'font-bold')}
-		 onClick={ev => {
-		   ev.preventDefault ()
-		   setCurrent (i)
-		 }}>
-		{tab.props.name}
-	      </a>))}
+	<div className="flex items-center justify-between gap-4">
+	  <div className="flex min-w-0 gap-4">
+	    {tabs.map ((tab, i) => (
+		<button
+		   key={i}
+		   type="button"
+		   className={cn (
+		       'bg-transparent p-0 text-left text-[hsl(var(--theme-link))] hover:opacity-85',
+		       'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring',
+		       i === current && 'font-bold',
+		   )}
+		   onClick={() => {
+		     setCurrent (i)
+		   }}>
+		  {tab.props.name}
+		</button>))}
+	  </div>
+	  {rightAddon && (
+	      <div className="shrink-0">
+		{rightAddon}
+	      </div>)}
 	</div>
 	<div className="mt-2">
 	  {tabs[current]}

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

@@ -26,7 +26,7 @@ describe ('TagInput', () => {
     await waitFor (() => {
       expect (api.apiGet).toHaveBeenCalledWith (
           '/tags/autocomplete',
-          { params: { q: '虹夏' } },
+          { params: { q: '虹夏', nico: '0' } },
       )
     })
     expect (setValue).toHaveBeenCalledWith ('ぼっち 虹夏')
@@ -41,4 +41,20 @@ describe ('TagInput', () => {
     expect (api.apiGet).not.toHaveBeenCalled ()
     expect (setValue).toHaveBeenCalledWith (' ')
   })
+
+  it ('sends nico=1 only when includeNico is true', async () => {
+    const setValue = vi.fn ()
+    api.apiGet.mockResolvedValueOnce ([buildTag ({ name: '虹夏', postCount: 2 })])
+
+    render (<TagInput value="" setValue={setValue} includeNico={true}/>)
+
+    fireEvent.change (screen.getByRole ('textbox'), { target: { value: '虹夏' } })
+
+    await waitFor (() => {
+      expect (api.apiGet).toHaveBeenCalledWith (
+          '/tags/autocomplete',
+          { params: { q: '虹夏', nico: '1' } },
+      )
+    })
+  })
 })

frontend/src/components/common/TagInput.tsx

@@ -10,13 +10,20 @@ import type { Tag } from '@/types'
 
 
 type Props = {
+    includeNico?:   boolean
     describedBy?:  string
     invalid?:      boolean
     value:         string
     setValue:      (value: string) => void }
 
 
-const TagInput: FC<Props> = ({ describedBy, invalid, value, setValue }) => {
+const TagInput: FC<Props> = ({
+    includeNico = false,
+    describedBy,
+    invalid,
+    value,
+    setValue,
+}) => {
   const [activeIndex, setActiveIndex] = useState (-1)
   const [suggestions, setSuggestions] = useState<Tag[]> ([])
   const [suggestionsVsbl, setSuggestionsVsbl] = useState (false)
@@ -32,10 +39,12 @@ const TagInput: FC<Props> = ({ describedBy, invalid, value, setValue }) => {
 	return
       }
 
-    const data = await apiGet<Tag[]> ('/tags/autocomplete', { params: { q } })
-    setSuggestions (data.filter (t => t.postCount > 0))
-    if (suggestions.length > 0)
-      setSuggestionsVsbl (true)
+    const data = await apiGet<Tag[]> ('/tags/autocomplete', { params: {
+	q,
+	nico: includeNico ? '1' : '0' } })
+    const nextSuggestions = data.filter (t => t.postCount > 0)
+    setSuggestions (nextSuggestions)
+    setSuggestionsVsbl (nextSuggestions.length > 0)
   }
 
   // TODO: TagSearch からのコピペのため，共通化を考へる．

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

@@ -0,0 +1,116 @@
+import { useCallback, useEffect } from 'react'
+import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import DialogueProvider from '@/components/dialogues/DialogueProvider'
+import useDialogue from '@/lib/dialogues/useDialogue'
+
+import type { DialogueFormControls } from '@/lib/dialogues/useDialogue'
+
+const FormBody = (
+    { controls,
+      onSelect }: { controls: DialogueFormControls
+		    onSelect: () => Promise<boolean> | boolean },
+) => {
+  useEffect (() => {
+    controls.setActions ([{
+      label: '左操作',
+      placement: 'start',
+      onSelect }, {
+      label: '保存',
+      onSelect: () => true }])
+  }, [controls, onSelect])
+
+  return <div>長いフォーム本文</div>
+}
+
+const NestedConfirmFormBody = ({ controls }: { controls: DialogueFormControls }) => {
+  const reset = useCallback (async () => {
+    await controls.confirm ({
+      title: '変更をリセットしますか?',
+      confirmText: 'リセット' })
+    return false
+  }, [controls])
+
+  return <FormBody controls={controls} onSelect={reset}/>
+}
+
+describe ('DialogueProvider', () => {
+  it ('keeps ordinary dialogues in FIFO order', async () => {
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => {
+		void dialogue.confirm ({ title: '一件目' })
+		void dialogue.confirm ({ title: '二件目' })
+	      }}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+
+    expect (screen.getByText ('一件目')).toBeInTheDocument ()
+    expect (screen.queryByText ('二件目')).not.toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: '確定' }))
+    expect (await screen.findByText ('二件目')).toBeInTheDocument ()
+  })
+
+  it ('keeps a large form open when an action returns false', async () => {
+    const action = vi.fn ().mockResolvedValue (false)
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => void dialogue.form ({
+		title: '投稿を編輯',
+		description: '説明',
+		size: 'large',
+		body: controls => <FormBody controls={controls} onSelect={action}/> })}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+
+    const dialogue = screen.getByRole ('dialog')
+    expect (dialogue).toHaveClass ('max-h-[calc(100dvh-1rem)]', 'flex-col', 'max-w-3xl')
+    await waitFor (() => expect (screen.getByRole ('button', { name: '左操作' }))
+	.toBeInTheDocument ())
+    expect (screen.getByRole ('button', { name: '左操作' })).toHaveClass (
+	'w-full',
+	'md:w-auto')
+    fireEvent.click (screen.getByRole ('button', { name: '左操作' }))
+
+    await waitFor (() => expect (action).toHaveBeenCalledTimes (1))
+    expect (screen.getByText ('投稿を編輯')).toBeInTheDocument ()
+  })
+
+  it ('opens a nested confirmation over a form and returns to the same form', async () => {
+    const Launcher = () => {
+      const dialogue = useDialogue ()
+      return (
+	  <button
+	      onClick={() => void dialogue.form ({
+		title: '投稿を編輯',
+		body: controls => <NestedConfirmFormBody controls={controls}/> })}>
+	    開く
+	  </button>)
+    }
+
+    render (<DialogueProvider><Launcher/></DialogueProvider>)
+    fireEvent.click (screen.getByRole ('button', { name: '開く' }))
+    const action = await screen.findByRole ('button', { name: '左操作' })
+    fireEvent.click (action)
+
+    expect (await screen.findByText ('変更をリセットしますか?')).toBeInTheDocument ()
+    fireEvent.click (screen.getByRole ('button', { name: 'リセット' }))
+    await waitFor (() => {
+      expect (screen.queryByText ('変更をリセットしますか?')).not.toBeInTheDocument ()
+    })
+    expect (screen.getByText ('投稿を編輯')).toBeInTheDocument ()
+  })
+})

frontend/src/components/dialogues/DialogueProvider.tsx

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

frontend/src/components/layout/MainArea.tsx

@@ -1,5 +1,7 @@
 import { motion } from 'framer-motion'
 
+import { clientAnimationTransition } from '@/lib/clientAnimation'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
 import { cn } from '@/lib/utils'
 
 import type { FC, ReactNode } from 'react'
@@ -9,12 +11,21 @@ type Props = {
     className?: string }
 
 
-const MainArea: FC<Props> = ({ children, className }) => (
-    <motion.main
-	transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-	className={cn ('flex-1 overflow-y-auto p-4', className)}
-	layout="position">
-      {children}
-    </motion.main>)
+const MainArea: FC<Props> = ({ children, className }) => {
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const layoutTransition = clientAnimationTransition (
+      animationMode,
+      { normal: { duration: .2, ease: 'easeOut' as const } },
+  )
 
-export default MainArea
+  return (
+      <motion.main
+	  transition={{ layout: layoutTransition }}
+	  className={cn ('flex-1 overflow-y-auto p-4', className)}
+	  layout={animationMode === 'off' ? false : 'position'}>
+	{children}
+      </motion.main>)
+}
+
+export default MainArea

frontend/src/components/layout/SidebarComponent.test.tsx

@@ -0,0 +1,124 @@
+import { fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { HelmetProvider } from 'react-helmet-async'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import SidebarComponent from '@/components/layout/SidebarComponent'
+
+
+const sidebarWidth = (element: Element | null): string =>
+    (element as HTMLElement).style.getPropertyValue ('--sidebar-width')
+
+
+const sidebarRoot = (container: HTMLElement): Element =>
+    container.querySelector ('[style*="--sidebar-width"]')!
+
+
+const sidebarTree = (props: Partial<Parameters<typeof SidebarComponent>[0]>) => (
+    <HelmetProvider>
+      <div data-sidebar-container>
+	<SidebarComponent sidebarKey="test-sidebar" {...props}>
+	  Sidebar body
+	</SidebarComponent>
+      </div>
+    </HelmetProvider>)
+
+
+const renderSidebar = (
+    props: Partial<Parameters<typeof SidebarComponent>[0]> = {},
+    containerWidth = 800,
+) => {
+  Object.defineProperty (HTMLElement.prototype, 'clientWidth', {
+      configurable: true,
+      get () {
+	return this.hasAttribute ('data-sidebar-container') ? containerWidth : 0
+      },
+  })
+
+  const rendered = render (sidebarTree (props))
+
+  return rendered
+}
+
+
+describe ('SidebarComponent', () => {
+  beforeEach (() => {
+    Object.defineProperty (window, 'innerWidth', {
+	configurable: true,
+	value:        1_000,
+    })
+
+    Object.defineProperty (HTMLElement.prototype, 'setPointerCapture', {
+	configurable: true,
+	value:        vi.fn (),
+    })
+    Object.defineProperty (HTMLElement.prototype, 'releasePointerCapture', {
+	configurable: true,
+	value:        vi.fn (),
+    })
+    Object.defineProperty (HTMLElement.prototype, 'hasPointerCapture', {
+	configurable: true,
+	value:        vi.fn (() => true),
+    })
+
+    vi.spyOn (HTMLElement.prototype, 'setPointerCapture').mockImplementation (() => {
+      ;
+    })
+    vi.spyOn (HTMLElement.prototype, 'releasePointerCapture').mockImplementation (() => {
+      ;
+    })
+    vi.spyOn (HTMLElement.prototype, 'hasPointerCapture').mockReturnValue (true)
+  })
+
+  it ('uses maxWidth without applying the container main-width reserve twice', async () => {
+    localStorage.setItem ('sidebar:test-sidebar:left:width', '700')
+    const onWidthChange = vi.fn ()
+
+    const { container } = renderSidebar ({ maxWidth: 700, onWidthChange }, 800)
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('700px')
+    })
+    expect (onWidthChange).toHaveBeenLastCalledWith (700)
+  })
+
+  it ('resets width and removes only its storage key on double click', async () => {
+    localStorage.setItem ('sidebar:test-sidebar:right:width', '420')
+    localStorage.setItem ('sidebar:other-sidebar:right:width', '480')
+
+    const { container } = renderSidebar ({ side: 'right' }, 900)
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('420px')
+    })
+
+    fireEvent.doubleClick (screen.getByRole ('separator', { name: 'サイドバー幅' }))
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('256px')
+    })
+    expect (localStorage.getItem ('sidebar:test-sidebar:right:width')).toBeNull ()
+    expect (localStorage.getItem ('sidebar:other-sidebar:right:width')).toBe ('480')
+  })
+
+  it ('clamps current width on maxWidth changes without re-reading storage', async () => {
+    localStorage.setItem ('sidebar:test-sidebar:left:width', '420')
+
+    const { container, rerender } = renderSidebar ({ maxWidth: 420 }, 900)
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('420px')
+    })
+
+    rerender (sidebarTree ({ maxWidth: 300 }))
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('300px')
+    })
+
+    rerender (sidebarTree ({ maxWidth: 500 }))
+
+    await waitFor (() => {
+      expect (sidebarWidth (sidebarRoot (container))).toBe ('300px')
+    })
+  })
+})

frontend/src/components/layout/SidebarComponent.tsx

@@ -1,19 +1,327 @@
 import { motion } from 'framer-motion'
 import { Helmet } from 'react-helmet-async'
 
-import type { FC, ReactNode } from 'react'
+import { clientAnimationTransition } from '@/lib/clientAnimation'
+import { useClientBehaviourSettings } from '@/lib/useClientBehaviourSettings'
+import { cn } from '@/lib/utils'
 
-type Props = { children: ReactNode }
+import type { CSSProperties, FC, MouseEvent, PointerEvent, ReactNode } from 'react'
+import { useCallback, useEffect, useRef, useState } from 'react'
+
+type SidebarSide = 'left' | 'right'
+
+type Props = {
+    children:      ReactNode
+    className?:    string
+    maxWidth?:     number
+    onWidthChange?: (width: number) => void
+    sidebarKey:    string
+    side?:         SidebarSide }
+
+type ResizeState = {
+    pointerId:  number
+    startWidth: number
+    startX:     number
+    side:       SidebarSide }
+
+type PendingPressState = ResizeState & { startY: number }
+
+const DEFAULT_SIDEBAR_WIDTH = 256
+const MIN_SIDEBAR_WIDTH = 192
+const MIN_MAIN_WIDTH = 360
+const MAX_VIEWPORT_WIDTH_RATIO = .8
+const LONG_PRESS_DELAY_MS = 350
+const TOUCH_MOVE_THRESHOLD_PX = 8
 
 
-const SidebarComponent: FC<Props> = ({ children }) => (
-    <motion.div
-	layout="position"
-	transition={{ layout: { duration: .2, ease: 'easeOut' } }}
-	className="p-4 w-full md:w-64 md:h-full md:overflow-y-auto sidebar">
-      <Helmet>
-	<style>
-	  {`
+const storageKeyForSidebar = (sidebarKey: string, side: SidebarSide): string =>
+    `sidebar:${ sidebarKey }:${ side }:width`
+
+
+const getSidebarMaxWidth = (containerWidth: number): number => {
+  const viewportWidth =
+      typeof window === 'undefined' ? containerWidth : window.innerWidth
+  const viewportMaxWidth = Math.floor (viewportWidth * MAX_VIEWPORT_WIDTH_RATIO)
+  const containerMaxWidth = Math.floor (containerWidth - MIN_MAIN_WIDTH)
+  const dynamicMaxWidth = Math.min (viewportMaxWidth, containerMaxWidth)
+
+  return Math.max (MIN_SIDEBAR_WIDTH, dynamicMaxWidth)
+}
+
+
+const readStoredSidebarWidth = (
+    sidebarKey: string,
+    side: SidebarSide): number => {
+  if (typeof window === 'undefined')
+    return DEFAULT_SIDEBAR_WIDTH
+
+  const value = window.localStorage.getItem (storageKeyForSidebar (sidebarKey, side))
+  const width = value == null ? Number.NaN : Number (value)
+
+  return Number.isFinite (width) ? width : DEFAULT_SIDEBAR_WIDTH
+}
+
+
+const SidebarComponent: FC<Props> = ({
+    children,
+    className,
+    maxWidth,
+    onWidthChange,
+    sidebarKey,
+    side = 'left',
+}) => {
+  const behaviourSettings = useClientBehaviourSettings ()
+  const animationMode = behaviourSettings.animation ?? 'normal'
+  const layoutTransition = clientAnimationTransition (
+      animationMode,
+      { normal: { duration: .2, ease: 'easeOut' as const } },
+  )
+  const rootRef = useRef<HTMLDivElement | null> (null)
+  const maxWidthRef = useRef (maxWidth)
+  const getContainerWidth = useCallback (() => {
+    const containerWidth = rootRef.current
+	?.closest ('[data-sidebar-container]')
+	?.clientWidth
+    ?? window.innerWidth
+    return containerWidth
+  }, [])
+  const getClampedWidth = useCallback ((
+      nextWidth: number,
+      containerWidth: number): number => {
+    const viewportWidth =
+	typeof window === 'undefined' ? containerWidth : window.innerWidth
+    const viewportMaxWidth = Math.floor (viewportWidth * MAX_VIEWPORT_WIDTH_RATIO)
+    const maxAllowedWidth =
+	maxWidthRef.current == null
+	? getSidebarMaxWidth (containerWidth)
+	: Math.max (
+	    MIN_SIDEBAR_WIDTH,
+	    Math.min (viewportMaxWidth, maxWidthRef.current))
+
+    return Math.min (maxAllowedWidth, Math.max (MIN_SIDEBAR_WIDTH, nextWidth))
+  }, [])
+
+  const [width, setWidth] = useState (() => (
+      typeof window === 'undefined'
+      ? DEFAULT_SIDEBAR_WIDTH
+      : getClampedWidth (
+	  readStoredSidebarWidth (sidebarKey, side),
+	  window.innerWidth)))
+  const [resizing, setResizing] = useState (false)
+  const widthRef = useRef (width)
+  const longPressTimerRef = useRef<ReturnType<typeof setTimeout> | null> (null)
+  const pendingPressRef = useRef<PendingPressState | null> (null)
+  const resizeRef = useRef<ResizeState | null> (null)
+  const bodyStyleRef = useRef<{ cursor: string, userSelect: string } | null> (null)
+
+  const clearLongPressTimer = useCallback (() => {
+    if (longPressTimerRef.current == null)
+      return
+
+    clearTimeout (longPressTimerRef.current)
+    longPressTimerRef.current = null
+  }, [])
+
+  const restoreBodyStyle = useCallback (() => {
+    if (bodyStyleRef.current == null)
+      return
+
+    document.body.style.cursor = bodyStyleRef.current.cursor
+    document.body.style.userSelect = bodyStyleRef.current.userSelect
+    bodyStyleRef.current = null
+  }, [])
+
+  const startResize = useCallback ((state: ResizeState) => {
+    clearLongPressTimer ()
+    pendingPressRef.current = null
+    resizeRef.current = state
+    setResizing (true)
+
+    if (bodyStyleRef.current == null)
+    {
+      bodyStyleRef.current = {
+	  cursor: document.body.style.cursor,
+	  userSelect: document.body.style.userSelect }
+    }
+
+    document.body.style.cursor = 'col-resize'
+    document.body.style.userSelect = 'none'
+  }, [clearLongPressTimer])
+
+  const finishResize = useCallback (() => {
+    clearLongPressTimer ()
+    pendingPressRef.current = null
+
+    const state = resizeRef.current
+    resizeRef.current = null
+
+    if (state != null)
+      window.localStorage.setItem (
+	  storageKeyForSidebar (sidebarKey, state.side),
+	  String (widthRef.current))
+
+    setResizing (false)
+    restoreBodyStyle ()
+  }, [clearLongPressTimer, restoreBodyStyle, sidebarKey])
+
+  const applyWidth = useCallback ((nextWidth: number) => {
+    if (nextWidth === widthRef.current)
+      return
+
+    widthRef.current = nextWidth
+    setWidth (nextWidth)
+  }, [])
+
+  useEffect (() => {
+    maxWidthRef.current = maxWidth
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (widthRef.current, containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth, maxWidth])
+
+  const updateWidth = useCallback ((clientX: number) => {
+    const state = resizeRef.current
+    if (state == null)
+      return
+
+    const containerWidth = getContainerWidth ()
+    const delta = state.side === 'left'
+		  ? clientX - state.startX
+		  : state.startX - clientX
+    const nextWidth = getClampedWidth (state.startWidth + delta, containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth])
+
+  const handlePointerDown = (ev: PointerEvent<HTMLDivElement>) => {
+    if (ev.pointerType !== 'mouse' && ev.pointerType !== 'touch')
+      return
+
+    if (ev.pointerType === 'mouse' && ev.button !== 0)
+      return
+
+    ev.preventDefault ()
+    ev.stopPropagation ()
+    ev.currentTarget.setPointerCapture (ev.pointerId)
+
+    const state = {
+	pointerId: ev.pointerId,
+	side,
+	startWidth: widthRef.current,
+	startX: ev.clientX }
+
+    if (ev.pointerType === 'mouse')
+    {
+      startResize (state)
+      return
+    }
+
+    pendingPressRef.current = { ...state, startY: ev.clientY }
+    clearLongPressTimer ()
+    longPressTimerRef.current = setTimeout (() => {
+      if (pendingPressRef.current != null)
+	startResize (pendingPressRef.current)
+    }, LONG_PRESS_DELAY_MS)
+  }
+
+  const handlePointerMove = (ev: PointerEvent<HTMLDivElement>) => {
+    ev.stopPropagation ()
+
+    if (resizeRef.current != null)
+    {
+      ev.preventDefault ()
+      updateWidth (ev.clientX)
+      return
+    }
+
+    const pendingPress = pendingPressRef.current
+    if (pendingPress == null || pendingPress.pointerId !== ev.pointerId)
+      return
+
+    const deltaX = ev.clientX - pendingPress.startX
+    const deltaY = ev.clientY - pendingPress.startY
+    const distance = Math.hypot (deltaX, deltaY)
+
+    if (distance >= TOUCH_MOVE_THRESHOLD_PX)
+    {
+      clearLongPressTimer ()
+      pendingPressRef.current = null
+    }
+  }
+
+  const handlePointerEnd = (ev: PointerEvent<HTMLDivElement>) => {
+    ev.stopPropagation ()
+
+    if (ev.currentTarget.hasPointerCapture (ev.pointerId))
+      ev.currentTarget.releasePointerCapture (ev.pointerId)
+
+    finishResize ()
+  }
+
+  const resetWidth = useCallback (() => {
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (DEFAULT_SIDEBAR_WIDTH, containerWidth)
+    applyWidth (nextWidth)
+    window.localStorage.removeItem (storageKeyForSidebar (sidebarKey, side))
+  }, [applyWidth, getClampedWidth, getContainerWidth, sidebarKey, side])
+
+  const handleDoubleClick = (ev: MouseEvent<HTMLDivElement>) => {
+    ev.preventDefault ()
+    ev.stopPropagation ()
+    resetWidth ()
+  }
+
+  useEffect (() => {
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (
+	readStoredSidebarWidth (sidebarKey, side),
+	containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth, sidebarKey, side])
+
+  useEffect (() => {
+    const containerWidth = getContainerWidth ()
+    const nextWidth = getClampedWidth (widthRef.current, containerWidth)
+    applyWidth (nextWidth)
+  }, [applyWidth, getClampedWidth, getContainerWidth])
+
+  useEffect (() => {
+    if (typeof window === 'undefined')
+      return
+
+    const handleResize = () => {
+      const containerWidth = getContainerWidth ()
+      const nextWidth = getClampedWidth (widthRef.current, containerWidth)
+      applyWidth (nextWidth)
+    }
+
+    window.addEventListener ('resize', handleResize)
+    return () => window.removeEventListener ('resize', handleResize)
+  }, [applyWidth, getClampedWidth, getContainerWidth])
+
+  useEffect (() => {
+    onWidthChange?.(width)
+  }, [onWidthChange, width])
+
+  useEffect (() => () => {
+    clearLongPressTimer ()
+    restoreBodyStyle ()
+  }, [clearLongPressTimer, restoreBodyStyle])
+
+  const style = {
+      '--sidebar-width': `${ width }px` } as CSSProperties
+
+  return (
+      <motion.div
+	  ref={rootRef}
+	  layout={animationMode === 'off' ? false : 'position'}
+	  transition={{ layout: layoutTransition }}
+	  style={style}
+	  className={cn (
+	      'relative w-full md:w-[var(--sidebar-width)] md:shrink-0 md:h-full',
+	      className)}>
+	<Helmet>
+	  <style>
+	    {`
 	      .sidebar
 	      {
 		direction: rtl;
@@ -23,10 +331,34 @@ const SidebarComponent: FC<Props> = ({ children }) => (
 	      {
 		direction: ltr;
 	      }`}
-	</style>
-      </Helmet>
+	  </style>
+	</Helmet>
 
-      {children}
-    </motion.div>)
+	<div className="h-full overflow-y-auto p-4 sidebar">
+	  {children}
+	</div>
 
-export default SidebarComponent
+	<div
+	    role="separator"
+	    aria-orientation="vertical"
+	    aria-label="サイドバー幅"
+	    onPointerDown={handlePointerDown}
+	    onPointerMove={handlePointerMove}
+	    onPointerUp={handlePointerEnd}
+	    onPointerCancel={handlePointerEnd}
+	    onDoubleClick={handleDoubleClick}
+	    className={cn (
+		'hidden md:block absolute top-0 bottom-0 z-20 w-4 cursor-col-resize',
+		'touch-none select-none',
+		side === 'left' ? '-right-2' : '-left-2',
+		'before:absolute before:top-0 before:bottom-0 before:w-px',
+		'before:bg-neutral-500/0 hover:before:bg-neutral-500/30',
+		'before:transition-colors before:duration-150',
+		side === 'left'
+		? 'before:left-1/2'
+		: 'before:right-1/2',
+		resizing && 'before:bg-neutral-500/40')}/>
+      </motion.div>)
+}
+
+export default SidebarComponent

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 }