backend/app/controllers/materials_controller.rb

@@ -70,7 +70,10 @@ class MaterialsController < ApplicationController
         .find_by(id: params[:id])
     return head :not_found unless material
 
-    wiki_page_body = material.tag&.tag_name('ja')&.wiki_page&.current_revision&.body
+    wiki_page_body =
+        TagDescription
+        .find_by(tag_id: material.tag_id, language_code: locale.language_code)
+        &.body
 
     render json: MaterialRepr.base(material, host: request.base_url,
                                    language_code: locale.language_code).merge(wiki_page_body:)

backend/app/controllers/nico_tags_controller.rb

@@ -26,7 +26,7 @@ class NicoTagsController < ApplicationController
         ExternalTag
         .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
                'ON post_tag_max.external_tag_id = external_tags.id')
-        .includes(linked_tags: { tag_names: :wiki_page })
+        .includes(linked_tags: [:tag_names, :tag_descriptions])
     if name
       q = q.where(('external_tags.name LIKE ? ' +
                    "OR CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?"),

backend/app/controllers/posts_controller.rb

@@ -53,7 +53,7 @@ class PostsController < ApplicationController
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
         .preload(:external_tags, :uploaded_user, :parents, :children,
                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_names: :wiki_page }] }])
+                                                :tag_names, :tag_descriptions] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -111,7 +111,7 @@ class PostsController < ApplicationController
         filtered_posts(locale)
         .preload(:uploaded_user, :parents, :children,
                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_names: :wiki_page }] }])
+                                                :tag_names, :tag_descriptions] }])
         .with_attached_thumbnail
         .order('RAND()')
         .first
@@ -198,7 +198,7 @@ class PostsController < ApplicationController
         Post
         .includes(:uploaded_user, :parents, :children,
                   post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                 { tag_names: :wiki_page }] }])
+                                                 :tag_names, :tag_descriptions] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post

backend/app/controllers/tag_versions_controller.rb

@@ -51,7 +51,7 @@ class TagVersionsController < ApplicationController
 
       tags_by_id =
           Tag
-          .includes(:tag_names, :materials, tag_names: :wiki_page)
+          .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
           .where(id: all_parent_tag_ids)
           .index_by(&:id)
 

backend/app/controllers/tags_controller.rb

@@ -175,7 +175,7 @@ class TagsController < ApplicationController
     tags_by_id =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
         .where(tag_names: { language_code: locale.language_code, primary_flg: true },
                id: tag_ids)
         .index_by(&:id)
@@ -238,7 +238,7 @@ class TagsController < ApplicationController
     base =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
         .where(tag_names: { language_code: locale.language_code, primary_flg: true },
                deprecated_at: nil)
     base = base.where('tags.post_count > 0') if present_only
@@ -282,7 +282,7 @@ class TagsController < ApplicationController
     tag =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
         .find_by(id: params[:id],
                  tag_names: { language_code: locale.language_code, primary_flg: true })
     return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
@@ -302,7 +302,7 @@ class TagsController < ApplicationController
     tag =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
         .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
     return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
 
@@ -320,7 +320,7 @@ class TagsController < ApplicationController
 
     tag = 
         Tag.joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
+        .includes(:tag_names, :tag_descriptions, parents: :tag_descriptions)
         .find_by(id: params[:id],
                  tag_names: { language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
@@ -340,7 +340,7 @@ class TagsController < ApplicationController
     tag =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
+        .includes(:tag_names, :tag_descriptions, parents: :tag_descriptions)
         .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 
@@ -359,7 +359,7 @@ class TagsController < ApplicationController
     tag =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
+        .includes(:tag_names, :tag_descriptions, parents: :tag_descriptions)
         .find_by(id: params[:id],
                  tag_names: { language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
@@ -424,7 +424,7 @@ class TagsController < ApplicationController
     tag =
         Tag
         .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
+        .includes(:tag_names, :materials, :tag_descriptions, parents: :tag_descriptions)
         .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
     return head :not_found unless tag
 

backend/app/controllers/wiki_pages_controller.rb

@@ -8,9 +8,9 @@ class WikiPagesController < ApplicationController
     descriptions =
         TagDescription.where(language_code: 'ja')
         .includes(tag: :tag_names)
-    pages = unmigrated_wiki_pages.includes(tag_name: :tag)
 
-    tag_groups = TagGroup.all
+    descriptions = descriptions.order(updated_at: :desc, id: :asc)
+    tag_groups = TagGroup.order(updated_at: :desc, id: :asc)
     if title.present?
       pattern = "%#{ ApplicationRecord.sanitize_sql_like(title) }%"
       descriptions =
@@ -19,12 +19,13 @@ class WikiPagesController < ApplicationController
           .where('tag_names.name LIKE ?', pattern).limit(20)
       tag_groups = tag_groups.where(
           'CONCAT(?, name) LIKE ?', TagGroupRepr::PREFIX, pattern).limit(20)
-      pages = pages.where('tag_names.name LIKE ?', pattern).limit(20)
     end
 
     json = descriptions.map { |description| WikiPageRepr.tag_description(description) }
     json.concat(tag_groups.map { WikiPageRepr.tag_group(_1) })
-    json.concat(WikiPageRepr.base(pages))
+    json.sort_by! do |row|
+      [-row['updated_at'].to_f, row.fetch('resource_type'), row.fetch('id')]
+    end
     json = json.first(20) if title.present?
     render json:
   end
@@ -37,11 +38,7 @@ class WikiPagesController < ApplicationController
     tag_group = TagGroup.find_by(id: params[:id])
     return render_tag_group tag_group if tag_group
 
-    page = WikiPage.joins(:tag_name)
+    render_wiki_page_or_404 nil
-                   .includes(tag_name: :tag)
-                   .find_by(id: params[:id])
-
-    render_wiki_page_or_404 page
   end
 
   def show_by_title
@@ -58,20 +55,14 @@ class WikiPagesController < ApplicationController
 
     return render_wiki_page_by_tag_description tag_description if tag_description
 
-    page =
+    render_wiki_page_or_404 nil
-        WikiPage
-        .joins(:tag_name)
-        .includes(tag_name: :tag)
-        .find_by(tag_name: { name: title })
-
-    render_wiki_page_or_404 page
   end
 
   def exists
     return head :no_content if TagDescription.exists?(id: params[:id])
     return head :no_content if TagGroup.exists?(id: params[:id])
 
-    head WikiPage.exists?(id: params[:id]) ? :no_content : :not_found
+    head :not_found
   end
 
   def exists_by_title
@@ -82,8 +73,7 @@ class WikiPagesController < ApplicationController
     end
     return head :no_content if tag_description_by_title(title)
 
-    exists = WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
+    head :not_found
-    head exists ? :no_content : :not_found
   end
 
   def diff
@@ -112,15 +102,7 @@ class WikiPagesController < ApplicationController
                      'title' => "#{ TagGroupRepr::PREFIX }#{ tag_group.name }",
                      'deprecated_at' => nil }
       else
-        page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
+        return head :not_found
-        from_rev = from && page.wiki_revisions.find(from)
-        to_rev = to ? page.wiki_revisions.find(to) : page.current_revision
-        if ((from_rev && !from_rev.content?) || !to_rev&.content?)
-          return render_unprocessable_entity('差分を表示できない版です．')
-        end
-        from_body = from_rev&.body
-        to_body = to_rev.body
-        resource = WikiPageRepr.base(page)
       end
     end
 
@@ -160,17 +142,9 @@ class WikiPagesController < ApplicationController
                                          status: :created)
     end
 
-    page = if title.include?(':')
+    page =
-      ApplicationRecord.transaction do
+        if title.include?(':')
-        tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
+          return render_unprocessable_entity field: :title
-          name.script_code = 'Jpan'
-          name.primary_flg = true
-          name.auto_generated = false
-        end
-
-        Wiki::Commit.create_legacy_content!(
-            tag_name:, body:, created_by_user: current_user, message:)
-      end
         else
           tag_name = TagName.find_by(language_code: 'ja', name: title)
           return render_unprocessable_entity field: :title unless tag_name&.tag
@@ -179,7 +153,8 @@ class WikiPagesController < ApplicationController
               tag: tag_name.tag, body:, created_by_user: current_user, message:)
         end
 
-    render json: WikiPageRepr.base(page), status: :created
+    description = TagDescription.find_by!(tag_id: page.tag_name.tag_id, language_code: 'ja')
+    render json: WikiPageRepr.tag_description(description), status: :created
   rescue ActiveRecord::RecordInvalid => e
     render_validation_error e.record
   rescue ActiveRecord::RecordNotUnique
@@ -209,44 +184,34 @@ class WikiPagesController < ApplicationController
       return head :ok
     end
 
-    page = WikiPage.find_by(id: params[:id])
+    return render_unprocessable_entity field: :title if title.include?(':')
-    if legacy_group_page?(page)
+    description = TagDescription.find_by(id: params[:id])
+    unless description
+      return render_unprocessable_entity field: :title if group || WikiPage.exists?(id: params[:id])
+      return head :not_found
+    end
+    tag = description.tag
+    tag_name = TagDescriptionOperation.compatibility_tag_name(tag)
+    if tag_name.name.include?(':') || (group && title != tag_name.name)
       return render_unprocessable_entity field: :title
     end
-    if group && !legacy_update_identified?(page, title, group)
-      return render_unprocessable_entity field: :title
-    end
-    return head :not_found unless page
 
     base_revision_id = params[:base_revision_id].presence
 
     ApplicationRecord.transaction do
-      page.lock!
+      tag.lock!
-
+      old_title = tag_name.name
-      old_title = page.title
+      if title != old_title
-
-      tag = page.tag_name.tag
-
-      if tag && title != old_title
         TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
       end
 
-      page.tag_name.update!(name: title) if title != old_title
+      tag_name.update!(name: title) if title != old_title
 
       message = params[:message].presence
-      description = TagDescription.find_by(id: page.id)
+      TagDescriptionOperation.update!(tag:, body:, updated_by_user: current_user,
-      description_page = description && (
-          tag&.id == description.tag_id ||
-          (tag.nil? && !old_title.include?(':')))
-      if description && !description_page
-        Wiki::Commit.legacy_content!(page:, body:, created_user: current_user,
                                       message:, base_revision_id:)
-      else
-        Wiki::Commit.content!(page:, body:, created_user: current_user,
-                              message:, base_revision_id:)
-      end
 
-      if tag && title != old_title
+      if title != old_title
         tag.reload
         TagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
       end
@@ -273,23 +238,7 @@ class WikiPagesController < ApplicationController
       return render json: tag_group_changes(TagGroupVersion.where(tag_group_id: tag_group.id))
     end
 
-    pages = id ? WikiPage.where(id:) : unmigrated_wiki_pages
+    json = []
-    revisions = WikiRevision.joins(wiki_page: :tag_name)
-        .where(wiki_page_id: pages.select(:id))
-        .includes(:created_user, wiki_page: { tag_name: :tag })
-        .order(id: :desc).limit(200)
-    json = revisions.map { |rev|
-      { revision_id: rev.id,
-        pred: rev.base_revision_id,
-        succ: nil,
-        wiki_page: { id: rev.wiki_page_id,
-                     title: rev.wiki_page.title,
-                     deprecated_at: rev.wiki_page.deprecated_at },
-        user: rev.created_user && { id: rev.created_user.id, name: rev.created_user.name },
-        kind: rev.kind,
-        message: rev.message,
-        timestamp: rev.created_at }
-    }
     unless id
       json.concat(tag_group_changes(TagGroupVersion.all))
       json.concat(description_changes(TagDescription.where(language_code: 'ja')))
@@ -351,6 +300,7 @@ class WikiPagesController < ApplicationController
     updated_at = version.created_at
     render json: {
         'id' => version.tag_group_id,
+        'resource_type' => 'tag_group',
         'title' => "#{ TagGroupRepr::PREFIX }#{ representation.fetch('name') }",
         'deprecated_at' => nil,
         'body' => body,
@@ -453,16 +403,6 @@ class WikiPagesController < ApplicationController
         .find_by(language_code: 'ja', tag_names: { language_code: 'ja', name: title })
   end
 
-  def unmigrated_wiki_pages
-    descriptions = TagDescription.where(language_code: 'ja')
-
-    WikiPage
-        .joins(:tag_name)
-        .where.not('tag_names.name LIKE ?', "#{ TagGroupRepr::PREFIX }%")
-        .where('tag_names.tag_id IS NULL OR tag_names.tag_id NOT IN (?)',
-               descriptions.select(:tag_id))
-  end
-
   def description_changes descriptions
     versions = TagDescriptionVersion.where(language_code: 'ja',
                                            tag_id: descriptions.select(:tag_id))

backend/app/models/external_tag.rb

@@ -1,4 +1,6 @@
 class ExternalTag < ApplicationRecord
+  before_create { SharedResourceIdAllocator.assign!(self) }
+
   enum :platform, nico: 'nico'
   validates :platform, presence: true, inclusion: { in: ExternalTag.platforms.keys }
 

backend/app/models/tag.rb

@@ -2,6 +2,8 @@ require 'set'
 
 
 class Tag < ApplicationRecord
+  before_create { SharedResourceIdAllocator.assign!(self) }
+
   class NicoTagNormalisationError < ArgumentError
     ;
   end
@@ -51,6 +53,7 @@ class Tag < ApplicationRecord
   has_many :tag_versions
 
   has_many :tag_names
+  has_many :tag_descriptions
 
   attribute :version_no, :integer, default: 1
 
@@ -96,7 +99,13 @@ class Tag < ApplicationRecord
 
   def deprecated? = deprecated_at?
 
-  def has_wiki = wiki_page.present?
+  def has_description? language_code:
+    if tag_descriptions.loaded?
+      tag_descriptions.any? { _1.language_code == language_code }
+    else
+      tag_descriptions.exists?(language_code:)
+    end
+  end
 
   def material_id = materials.first&.id
 

backend/app/models/tag_description.rb

@@ -1,3 +1,5 @@
 class TagDescription < ApplicationRecord
+  before_create { SharedResourceIdAllocator.assign!(self) }
+
   belongs_to :tag
 end

backend/app/models/tag_group.rb

@@ -1,4 +1,6 @@
 class TagGroup < ApplicationRecord
+  before_create { SharedResourceIdAllocator.assign!(self) }
+
   belongs_to :created_by_user, class_name: 'User', optional: true
   belongs_to :updated_by_user, class_name: 'User', optional: true
 

backend/app/representations/tag_repr.rb

@@ -3,21 +3,28 @@
 
 module TagRepr
   BASE = { only: [:id, :category, :post_count, :created_at, :updated_at, :deprecated_at],
-           methods: [:has_wiki, :material_id, :has_deerjikists] }.freeze
+           methods: [:material_id, :has_deerjikists] }.freeze
 
   module_function
 
   def base tag, language_code: 'ja'
-    tag.as_json(BASE).merge(name: name_for(tag, language_code),
+    tag.as_json(BASE).merge('has_wiki' => tag.has_description?(language_code:),
+                            name: name_for(tag, language_code),
                             aliases: tag.snapshot_aliases(language_code),
                             parents: tag.parents.map { inline(_1, language_code:) })
   end
 
   def inline tag, language_code: 'ja'
-    tag.as_json(BASE).merge(name: name_for(tag, language_code), aliases: [], parents: [])
+    tag.as_json(BASE).merge('has_wiki' => tag.has_description?(language_code:),
+                            name: name_for(tag, language_code), aliases: [], parents: [])
   end
 
-  def many(tags, language_code: 'ja') = tags.map { |tag| base(tag, language_code:) }
+  def many tags, language_code: 'ja'
+    records = tags.to_a
+    ActiveRecord::Associations::Preloader.new(
+        records:, associations: [:tag_descriptions, { parents: :tag_descriptions }]).call
+    records.map { |tag| base(tag, language_code:) }
+  end
 
   def name_for tag, language_code
     tag.name(language_code) || (tag.system? ? tag.name('ja') : nil)

backend/app/representations/wiki_page_repr.rb

@@ -13,6 +13,7 @@ module WikiPageRepr
   def tag_description description
     tag = description.tag
     { 'id' => description.id,
+      'resource_type' => 'tag_description',
       'tag_name_id' => tag.tag_name('ja')&.id,
       'body' => description.body,
       'created_user_id' => description.created_by_user_id,
@@ -26,7 +27,7 @@ module WikiPageRepr
   end
 
   def tag_group tag_group
-    TagGroupRepr.tag_group(tag_group)
+    TagGroupRepr.tag_group(tag_group).merge('resource_type' => 'tag_group')
   end
 
   def many wiki_pages

backend/app/services/shared_resource_id_allocator.rb

@@ -0,0 +1,56 @@
+require 'digest'
+
+
+class SharedResourceIdAllocator
+  SPACES = {
+      'tags' => ['tags', 'external_tags'],
+      'wiki' => ['tag_descriptions', 'tag_groups'] }.freeze
+  LOCK_TIMEOUT = 10
+
+  def self.assign! record
+    space, tables = SPACES.find { |_name, names| names.include?(record.class.table_name) }
+    raise ArgumentError, 'Unknown shared ID resource' unless tables
+
+    connection = record.class.connection
+    transaction = record.class.current_transaction
+    raise ActiveRecord::ActiveRecordError, 'Shared ID requires a transaction' unless transaction.open?
+
+    database = connection.pool.db_config.database
+    name = "btrc:ids:#{ Digest::SHA256.hexdigest(database)[0, 16] }:#{ space }"
+    quoted_name = connection.quote(name)
+    acquired = record.class.uncached do
+      connection.select_value("SELECT GET_LOCK(#{ quoted_name }, #{ LOCK_TIMEOUT })")
+    end
+    unless acquired.to_i == 1
+      raise ActiveRecord::LockWaitTimeout, "Shared ID lock unavailable: #{ space }"
+    end
+
+    release = lambda do
+      result = record.class.uncached do
+        connection.select_value("SELECT RELEASE_LOCK(#{ quoted_name })")
+      end
+      unless result.to_i == 1
+        raise ActiveRecord::ActiveRecordError, "Shared ID lock release failed: #{ space }"
+      end
+    end
+    begin
+      transaction.after_commit(&release)
+      transaction.after_rollback(&release)
+    rescue StandardError
+      release.call
+      raise
+    end
+
+    return if record.id.present?
+
+    # Locking reads see committed maxima even after earlier repeatable reads.
+    maxima = record.class.uncached do
+      tables.map do |table|
+        quoted_table = connection.quote_table_name(table)
+        connection.select_value(
+            "SELECT id FROM #{ quoted_table } ORDER BY id DESC LIMIT 1 FOR UPDATE").to_i
+      end
+    end
+    record.id = maxima.max + 1
+  end
+end

backend/app/services/tag_description_operation.rb

@@ -8,9 +8,9 @@ class TagDescriptionOperation
           tag_id: tag.id, language_code: LANGUAGE_CODE)
 
       page = Wiki::CompatibilityWriter.create!(
-          tag_name: tag.tag_name(LANGUAGE_CODE), body:, created_by_user:, message:)
+          tag_name: compatibility_tag_name(tag), body:, created_by_user:, message:)
       revision = page.wiki_revisions.order(id: :desc).first
-      record_version!(tag:, revision:, body:, user: created_by_user,
+      record_version!(tag:, revision:, body: revision.body, user: created_by_user,
                       description: nil)
       page
     end
@@ -22,7 +22,20 @@ class TagDescriptionOperation
       tag.lock!
       description = TagDescription.lock.find_by!(
           tag_id: tag.id, language_code: LANGUAGE_CODE)
-      page = WikiPage.lock.find(description.id)
+      tag_name = compatibility_tag_name(tag)
+      page = WikiPage.lock.find_by(tag_name_id: tag_name.id)
+      unless page
+        versions = TagDescriptionVersion.where(tag_id: tag.id, language_code: LANGUAGE_CODE)
+        if base_revision_id.present? && versions.maximum(:id) != base_revision_id.to_i
+          raise Wiki::Commit::Conflict, '競合が発生してゐます．'
+        end
+        page = Wiki::CompatibilityWriter.create!(
+            tag_name:, body:, created_by_user: updated_by_user, message:)
+        revision = page.current_revision
+        record_version!(tag:, revision:, body: revision.body,
+                        user: updated_by_user, description:)
+        next revision
+      end
       revision = Wiki::CompatibilityWriter.update!(
           page:, body:, updated_by_user:, message:,
           base_revision_id:)
@@ -34,6 +47,11 @@ class TagDescriptionOperation
     end
   end
 
+  def self.compatibility_tag_name tag
+    tag.tag_name(LANGUAGE_CODE) || TagName.find_by!(id: tag.tag_name_id,
+                                                  language_code: LANGUAGE_CODE)
+  end
+
   def self.record_version! tag:, revision:, body:, user:, description:
     version_no = description ? description.version_no + 1 : 1
     TagDescriptionVersion.create!(
@@ -44,7 +62,7 @@ class TagDescriptionOperation
       description.update!(body:, version_no:, updated_by_user_id: user.id)
     else
       TagDescription.create!(
-          id: revision.wiki_page_id, tag_id: tag.id,
+          tag_id: tag.id,
           language_code: LANGUAGE_CODE, version_no:, body:,
           created_by_user_id: user.id, updated_by_user_id: user.id)
     end

backend/app/services/tag_group_operation.rb

@@ -349,7 +349,7 @@ class TagGroupOperation
       tag_name.primary_flg = true
       tag_name.auto_generated = false
       tag_name.save!
-      Wiki::Commit.create_legacy_content!(tag_name:, body:, created_by_user: actor)
+      Wiki::CompatibilityWriter.create!(tag_name:, body:, created_by_user: actor)
     end
     nil
   end

backend/app/services/wiki/commit.rb

@@ -8,12 +8,13 @@ module Wiki
     end
 
     def self.create_content! tag_name:, body:, created_by_user:, message: nil
-      if tag_name.tag && tag_name.language_code == 'ja'
+      if tag_name.tag && tag_name.language_code == 'ja' && !tag_name.name.include?(':')
         return TagDescriptionOperation.create!(
             tag: tag_name.tag, body:, created_by_user:, message:)
       end
 
-      create_legacy_content!(tag_name:, body:, created_by_user:, message:)
+      tag_name.errors.add(:base, :invalid)
+      raise ActiveRecord::RecordInvalid, tag_name
     end
 
     def self.create_legacy_content! tag_name:, body:, created_by_user:, message: nil
@@ -42,14 +43,17 @@ module Wiki
     end
 
     def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
-      description = TagDescription.find_by(id: page.id)
+      description = TagDescription.find_by(tag_id: page.tag_name.tag_id, language_code: 'ja')
-      if description
+      description ||= TagDescription.joins(:tag).find_by(
+          tags: { tag_name_id: page.tag_name_id }, language_code: 'ja')
+      if description && !page.title.include?(':')
         return TagDescriptionOperation.update!(
             tag: description.tag, body:, updated_by_user: created_user,
             message:, base_revision_id:)
       end
 
-      legacy_content!(page:, body:, created_user:, message:, base_revision_id:)
+      page.errors.add(:base, :invalid)
+      raise ActiveRecord::RecordInvalid, page
     end
 
     def self.legacy_content! page:, body:, created_user:, message: nil,

backend/app/services/wiki/compatibility_writer.rb

@@ -1,8 +1,16 @@
 module Wiki
   class CompatibilityWriter
     def self.create! tag_name:, body:, created_by_user:, message: nil
-      Commit.create_legacy_content!(
+      ApplicationRecord.transaction do
-          tag_name:, body:, created_by_user:, message:)
+        tag_name.lock!
+        page = WikiPage.lock.find_by(tag_name_id: tag_name.id)
+        if page
+          update!(page:, body:, updated_by_user: created_by_user, message:)
+          page
+        else
+          Commit.create_legacy_content!(tag_name:, body:, created_by_user:, message:)
+        end
+      end
     end
 
     def self.update! page:, body:, updated_by_user:, message: nil,
@@ -23,7 +31,9 @@ module Wiki
         end
       end
 
-      return if Commit.normalise_body(page.body) == normalised
+      if Commit.normalise_body(page.body) == normalised && page.wiki_revisions.exists?
+        return
+      end
 
       Commit.legacy_content!(
           page:, body: normalised, created_user: updated_by_user, message:,

backend/lib/tasks/migrate_help_pages.rake

@@ -0,0 +1,51 @@
+namespace :help do
+  desc 'ヘルプ移行'
+  task migrate: :environment do
+    help_path = ENV.fetch('BTRC_HUB_HELP_PATH')
+    abort 'ヘルプ置場指定してね．' if help_path.blank?
+
+    # ファイルがすでに存在する場合は通さなぃ．
+    abort 'ファイル消してね．' if Dir.glob("#{ help_path }/*").present?
+
+    # 現状物理削除はなぃはず
+    pages = 
+        WikiPage
+        .joins(:tag_name)
+        .where(tag_names: { tag_id: nil, language_code: 'ja' })
+        .where.not("tag_names.name LIKE 'タググループ:%'")
+
+    puts "移行対象: #{pages.count} 件"
+    abort '移行対象がありません．' if pages.empty?
+
+    pages.find_each do |page|
+      puts page.body
+      puts page.title
+
+      puts 'この identifier は何にする?'
+      identifier = $stdin.gets.chomp
+      Dir.mkdir "#{ help_path }/#{ identifier }"
+      Dir.mkdir "#{ help_path }/#{ identifier }/editions"
+      Dir.mkdir "#{ help_path }/#{ identifier }/editions/ja"
+
+      last_file_name = ''
+      WikiVersion.where(wiki_page_id: page.id).order(:version_no).each do |ver|
+        last_file_name, last_file_name_no = last_file_name.split('.')
+
+        file_name = ver.created_at.strftime('%Y-%m-%d')
+        if file_name == last_file_name
+          file_name += ".#{ (last_file_name_no || 1).to_i + 1 }"
+        end
+
+        body = "# #{ ver.title.sub(/^ヘルプ:/, '') }\n\n#{ ver.body }"
+        File.write "#{ help_path }/#{ identifier }/editions/ja/#{ file_name }.mdx", body
+
+        last_file_name = file_name
+      end
+
+      article_meta = { 'identifier' => identifier,
+                       'canonical_language' => 'ja',
+                       'languages' => { 'ja' => { 'current_edition' => last_file_name } } }
+      File.write "#{ help_path }/#{ identifier }/article.yml", article_meta.to_yaml
+    end
+  end
+end

backend/spec/db/tag_description_migration_spec.rb

@@ -5,11 +5,11 @@ RSpec.describe 'Tag description migration identity' do
   it 'preserves every revision ID and repeated body in an independent sequence' do
     user = create_member_user!
     tag_name = create(:tag_name, name: 'description_migration')
-    page = Wiki::Commit.create_content!(
+    page = Wiki::Commit.create_legacy_content!(
         tag_name:, body: 'A', created_by_user: user)
     revisions = [page.current_revision]
     ['A', 'B', 'B', 'A'].each do |body|
-      revisions << Wiki::Commit.content!(
+      revisions << Wiki::Commit.legacy_content!(
           page:, body:, created_user: user, base_revision_id: revisions.last.id)
     end
     tag = create(:tag, primary_tag_name: tag_name)

backend/spec/models/shared_tag_ids_spec.rb

@@ -0,0 +1,84 @@
+require 'rails_helper'
+
+RSpec.describe 'Shared Tag and ExternalTag IDs', type: :model do
+  include TagGroupRecords
+  let(:user) { create_member_user! }
+
+  def create_resource resource
+    if resource == :tag
+      Tag.find_or_create_by_tag_name!(Locale.nipponese, 'shared_id_new', category: :general)
+    else
+      ExternalTag.create!(platform: :nico, name: 'shared_id_new')
+    end
+  end
+
+  [:tag, :external_tag].each do |resource|
+    it "starts #{ resource } at 1 when both tables are empty" do
+      expect(Tag.count).to eq(0)
+      expect(ExternalTag.count).to eq(0)
+      expect(create_resource(resource).id).to eq(1)
+    end
+
+    it "allocates #{ resource } above the other table's maximum" do
+      create(:tag, id: resource == :tag ? 1 : 20)
+      create(:external_tag, id: resource == :external_tag ? 1 : 20)
+
+      expect(create_resource(resource).id).to eq(21)
+    end
+
+    it "uses the current maximum after deleting earlier #{ resource } records" do
+      tag = create(:tag, id: 100)
+      TagName.where(tag_id: tag.id).update_all(tag_id: nil)
+      tag.destroy!
+      create(:external_tag, id: 200).destroy!
+      expect(Tag.unscoped.count).to eq(0)
+      expect(ExternalTag.unscoped.count).to eq(0)
+      expect(create_resource(resource).id).to eq(1)
+    end
+
+    it "preserves legacy overlaps and gaps when creating #{ resource }" do
+      [1, 2, 5].each { create(:tag, id: _1) }
+      [1, 3, 8].each { create(:external_tag, id: _1) }
+      tags = Tag.order(:id).map(&:attributes)
+      external_tags = ExternalTag.order(:id).map(&:attributes)
+
+      record = create_resource(resource)
+
+      aggregate_failures do
+        expect(record.id).to eq(9)
+        expect(Tag.where(id: [1, 2, 5]).order(:id).map(&:attributes)).to eq(tags)
+        expect(ExternalTag.where(id: [1, 3, 8]).order(:id).map(&:attributes)).to eq(external_tags)
+        expect(Tag.exists?(id: 3)).to be(false)
+        expect(ExternalTag.exists?(id: 2)).to be(false)
+      end
+    end
+
+    it "ignores the description and group ID space when creating #{ resource }" do
+      tag = create(:tag, id: 1)
+      create(:external_tag, id: 2)
+      TagDescription.create!(id: 100, tag:, language_code: 'ja', body: '', version_no: 1)
+      seed_group(name: 'separate_space', id: 200)
+
+      expect(create_resource(resource).id).to eq(3)
+    end
+  end
+
+  it 'preserves overlapping IDs during updates without rewriting the other resource' do
+    tag = create(:tag, id: 5)
+    external = create(:external_tag, id: 5)
+    tag.update!(category: :meta)
+    external.update!(name: 'updated_external')
+
+    expect(tag.reload.id).to eq(5)
+    expect(external.reload.id).to eq(5)
+    expect(tag.category).to eq('meta')
+    expect(external.name).to eq('updated_external')
+    expect(Tag.count).to eq(1)
+    expect(ExternalTag.count).to eq(1)
+  end
+
+  it 'allocates distinct IDs for successive creations across both tables' do
+    records = [:tag, :external_tag].map { create_resource(_1) }
+    expect(records.map(&:id)).to eq([1, 2])
+  end
+end

backend/spec/models/tag_repr_spec.rb

@@ -0,0 +1,50 @@
+require 'rails_helper'
+
+RSpec.describe TagRepr do
+  let(:tag) { create(:tag) }
+
+  def description_for record
+    TagDescription.create!(tag: record, language_code: 'ja', body: '', version_no: 1)
+  end
+
+  it 'keeps has_wiki boolean for the selected language in base and inline' do
+    description_for(tag)
+    [:base, :inline].each do |method|
+      expect(described_class.public_send(method, tag).as_json.fetch('has_wiki')).to be(true)
+      expect(described_class.public_send(method, tag, language_code: 'en')
+          .as_json.fetch('has_wiki')).to be(false)
+    end
+  end
+
+  it 'uses the same language for a tag and its parents' do
+    parent = create(:tag)
+    description_for(tag)
+    description_for(parent)
+    TagImplication.create!(tag:, parent_tag: parent)
+    ['ja', 'en'].each do |language_code|
+      row = described_class.base(tag, language_code:).as_json
+      expected = language_code == 'ja'
+      expect(row.fetch('has_wiki')).to be(expected)
+      expect(row.fetch('parents').sole.fetch('has_wiki')).to be(expected)
+    end
+  end
+
+  it 'preloads existence checks for many tags and their parents without Wiki reads' do
+    parent = create(:tag)
+    description_for(parent)
+    records = Array.new(3) do
+      create(:tag).tap { TagImplication.create!(tag: _1, parent_tag: parent) }
+    end
+    description_for(records.first)
+    queries = []
+    subscriber = ->(*args) { queries << args.last.fetch(:sql) }
+    rows = nil
+    ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+      rows = described_class.many(records).as_json
+    end
+    expect(rows.map { _1.fetch('has_wiki') }).to eq([true, false, false])
+    expect(rows.map { _1.fetch('parents').sole.fetch('has_wiki') }).to eq([true] * 3)
+    expect(queries.grep(/\bSELECT\b.*\btag_descriptions\b/im).size).to be <= 2
+    expect(queries.grep(/\bwiki_(pages|revisions|versions)\b/i)).to be_empty
+  end
+end

backend/spec/models/tag_spec.rb

@@ -1,6 +1,47 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
+  describe '#has_description?' do
+    let(:tag) { create(:tag) }
+
+    it 'checks the requested language and treats an empty description as present' do
+      TagDescription.create!(tag:, language_code: 'ja', body: '', version_no: 1)
+      expect(tag.has_description?(language_code: 'ja')).to be(true)
+      expect(tag.has_description?(language_code: 'en')).to be(false)
+    end
+
+    it 'returns false without a description' do
+      expect(tag.has_description?(language_code: 'ja')).to be(false)
+    end
+
+    it 'does not use a Wiki page as evidence of a description' do
+      user = create_member_user!
+      Wiki::Commit.create_legacy_content!(tag_name: tag.tag_name('ja'), body: 'legacy',
+                                          created_by_user: user)
+      expect(tag.has_description?(language_code: 'ja')).to be(false)
+    end
+
+    it 'reuses preloaded descriptions without reading Wiki or querying again' do
+      TagDescription.create!(tag:, language_code: 'ja', body: '', version_no: 1)
+      loaded = Tag.includes(:tag_descriptions).find(tag.id)
+      queries = []
+      subscriber = ->(*args) { queries << args.last.fetch(:sql) }
+      ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+        expect(loaded.has_description?(language_code: 'ja')).to be(true)
+        expect(loaded.has_description?(language_code: 'en')).to be(false)
+      end
+      expect(queries).to be_empty
+    end
+
+    it 'keeps language selection generic without enabling another Language record' do
+      tag.association(:tag_descriptions).target = [
+          TagDescription.new(tag:, language_code: 'en', body: '', version_no: 1)]
+      tag.association(:tag_descriptions).loaded!
+      expect(tag.has_description?(language_code: 'en')).to be(true)
+      expect(tag.has_description?(language_code: 'ja')).to be(false)
+    end
+  end
+
   describe 'external tag separation' do
     ['nico:reserved', 'NiCo:reserved'].each do |name|
       it "rejects the reserved prefix #{ name } for internal tags" do

backend/spec/requests/materials_spec.rb

@@ -178,6 +178,7 @@ RSpec.describe 'Materials API', type: :request do
   end
 
   describe 'GET /materials/:id' do
+    include WikiRecords
     let!(:tag) do
       create(:tag, primary_name: 'material_show', category: :material)
     end
@@ -205,6 +206,56 @@ RSpec.describe 'Materials API', type: :request do
       get '/materials/999999999'
       expect(response).to have_http_status(:not_found)
     end
+
+    def get_material_without_legacy_reads
+      queries = []
+      subscriber = lambda do |*args|
+        sql = args.last.fetch(:sql)
+        if sql.match?(/\bSELECT\b/i) && sql.match?(/\bwiki_(pages|revisions|versions)\b/i)
+          queries << sql
+        end
+      end
+      ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+        get "/materials/#{ material.id }"
+      end
+      expect(response).to have_http_status(:ok)
+      expect(queries).to be_empty
+    end
+
+    it 'reads the description even when the legacy revision has different content' do
+      page = seed_wiki_page(tag_name: tag.tag_name('ja'), body: 'legacy body',
+                            created_by_user: member_user)
+      TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
+          .update!(body: 'description body')
+      get_material_without_legacy_reads
+      expect(json.fetch('wiki_page_body')).to eq('description body')
+      expect(page.current_revision.body).to eq('legacy body')
+    end
+
+    it 'uses tag_id rather than description ID without a Wiki page or TagName' do
+      description = TagDescription.create!(id: tag.id + 1000, tag:, language_code: 'ja',
+                                           body: 'independent body', version_no: 1)
+      tag.tag_names.update_all(tag_id: nil)
+      get_material_without_legacy_reads
+      expect(description.id).not_to eq(tag.id)
+      expect(json.fetch('wiki_page_body')).to eq('independent body')
+      expect(json.fetch('tag').fetch('has_wiki')).to be(true)
+    end
+
+    it 'returns nil when only legacy Wiki content exists' do
+      seed_wiki_page(tag_name: tag.tag_name('ja'), body: 'legacy only',
+                     created_by_user: member_user)
+      TagDescription.where(tag_id: tag.id).delete_all
+      get_material_without_legacy_reads
+      expect(json.fetch('wiki_page_body')).to be_nil
+      expect(json.fetch('tag').fetch('has_wiki')).to be(false)
+    end
+
+    it 'returns nil for an untagged material' do
+      material.update!(tag: nil)
+      get_material_without_legacy_reads
+      expect(json.fetch('wiki_page_body')).to be_nil
+    end
   end
 
   describe 'POST /materials' do

backend/spec/requests/tag_description_wiki_spec.rb

@@ -1,16 +1,17 @@
 require 'rails_helper'
 
 RSpec.describe 'Tag description Wiki compatibility', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
   let!(:tag_name) { create(:tag_name, name: 'description_contract') }
   let!(:page) do
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name:, body: 'old-revision', created_by_user: user)
   end
   let!(:revisions) do
     first = page.current_revision
-    second = Wiki::Commit.content!(page:, body: 'old-second', created_user: user)
+    second = Wiki::Commit.legacy_content!(page:, body: 'old-second', created_user: user)
-    third = Wiki::Commit.content!(page:, body: 'old-third', created_user: user)
+    third = Wiki::Commit.legacy_content!(page:, body: 'old-third', created_user: user)
     [first, second, third]
   end
   let!(:tag) { create(:tag, primary_tag_name: tag_name) }
@@ -242,8 +243,8 @@ RSpec.describe 'Tag description Wiki compatibility', type: :request do
   end
 
   describe 'mixed changes' do
-    it 'includes unmigrated history and ignores migrated legacy-only revisions' do
+    it 'excludes unmigrated history and migrated legacy-only revisions' do
-      legacy_page = Wiki::Commit.create_content!(
+      legacy_page = seed_wiki_page(
           tag_name: create(:tag_name, name: 'Help_mixed'),
           body: 'help', created_by_user: user)
       legacy_revision = legacy_page.current_revision
@@ -256,7 +257,7 @@ RSpec.describe 'Tag description Wiki compatibility', type: :request do
       migrated = json.select { |row| row.fetch('wiki_page').fetch('id') == description.id }
       expect(migrated.map { |row| row.fetch('revision_id') }).to eq(versions.reverse.map(&:id))
       expect(json.map { |row| row.fetch('revision_id') }).not_to include(extra.id)
-      expect(json).to include(include(
+      expect(json).not_to include(include(
           'revision_id' => legacy_revision.id,
           'wiki_page' => include('id' => legacy_page.id, 'title' => 'Help_mixed')))
     end

backend/spec/requests/tag_description_wiki_write_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Tag description Wiki dual writes', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
   let!(:tag_name) { create(:tag_name, name: 'description_write') }
   let(:tag) { create(:tag, primary_tag_name: tag_name) }
@@ -31,7 +32,7 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
            headers: headers
     end
 
-    it 'creates both current records and histories with a shared revision ID' do
+    it 'creates a description with matching Wiki content and histories' do
       expect { create_description }
           .to change(WikiPage, :count).by(1)
           .and change(WikiRevision, :count).by(1)
@@ -39,17 +40,28 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
           .and change(TagDescription, :count).by(1)
           .and change(TagDescriptionVersion, :count).by(1)
       expect(response).to have_http_status(:created)
-
-      page = WikiPage.find(json.fetch('id'))
       description = TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
-      version = TagDescriptionVersion.find_by!(tag_id: tag.id, language_code: 'ja')
+      expect(description).to have_attributes(body: 'initial', version_no: 1)
-      expect(description).to have_attributes(id: page.id, body: 'initial', version_no: 1)
+      page = WikiPage.find_by!(tag_name:)
-      expect(version).to have_attributes(
-          id: page.current_revision.id, body: 'initial', version_no: 1,
-          event_type: 'create', created_by_user_id: user.id)
       expect(page.body).to eq(description.body)
-      expect(page.current_revision.body).to eq(version.body)
+      expect(page.current_revision.body).to eq(description.body)
-      expect(page.wiki_versions.last.body).to eq(version.body)
+      expect(page.wiki_versions.sole.body).to eq(description.body)
+      expect(json.fetch('id')).to eq(description.id)
+      expect(TagDescriptionVersion.find_by!(tag_id: tag.id, language_code: 'ja'))
+          .to have_attributes(body: 'initial', version_no: 1, created_by_user_id: user.id)
+    end
+
+    it 'reuses an existing compatibility page and synchronises its histories' do
+      page = Wiki::Commit.create_legacy_content!(
+          tag_name:, body: 'legacy', created_by_user: user)
+      expect { create_description }
+          .to change(WikiPage, :count).by(0)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+      expect(response).to have_http_status(:created)
+      description = TagDescription.find_by!(tag_id: tag.id)
+      expect(page.reload.body).to eq(description.body)
+      expect(TagDescriptionVersion.find(page.current_revision.id).body).to eq(page.body)
     end
 
     ['missing_description', 'orphan_description'].each do |title|
@@ -65,48 +77,19 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       end
     end
 
-    it 'creates a namespaced legacy Wiki resource without a Tag' do
+    [false, true].each do |linked|
-      expect do
+      it "rejects namespaced creation with Tag present: #{ linked }" do
-        post '/wiki', params: { title: 'Help:description_write', body: 'legacy' },
+        name = create(:tag_name, name: 'Help:frozen')
-             headers: headers
+        create(:tag, primary_tag_name: name) if linked
-      end.to change(WikiPage, :count).by(1)
+        before_state = stored_state
-          .and change(WikiRevision, :count).by(1)
+        post '/wiki', params: { title: name.name, body: 'legacy' }, headers: headers
-          .and change(WikiVersion, :count).by(1)
+        expect(response.status).to be_between(400, 499)
-          .and change(TagDescription, :count).by(0)
+        expect(stored_state).to eq(before_state)
-          .and change(TagDescriptionVersion, :count).by(0)
-
-      expect(response).to have_http_status(:created)
-      page = WikiPage.find(json.fetch('id'))
-      expect(page.tag_name.tag).to be_nil
-      expect(page.body).to eq('legacy')
-      expect(page.current_revision.body).to eq('legacy')
       end
-
-    it 'creates only legacy Wiki for a namespaced title with an existing Tag' do
-      namespaced_name = create(:tag_name, name: 'help:foo')
-      namespaced_tag = create(:tag, primary_tag_name: namespaced_name)
-
-      expect do
-        post '/wiki', params: { title: namespaced_name.name, body: 'legacy' },
-             headers: headers
-      end.to change(WikiPage, :count).by(1)
-          .and change(WikiRevision, :count).by(1)
-          .and change(WikiVersion, :count).by(1)
-          .and change(TagName, :count).by(0)
-          .and change(TagDescription, :count).by(0)
-          .and change(TagDescriptionVersion, :count).by(0)
-
-      expect(response).to have_http_status(:created)
-      page = WikiPage.find(json.fetch('id'))
-      expect(page).to have_attributes(tag_name_id: namespaced_name.id, body: 'legacy')
-      expect(page.tag_name.tag).to eq(namespaced_tag)
-      expect(page.current_revision.body).to eq('legacy')
-      expect(page.wiki_versions.last.body).to eq('legacy')
     end
 
     [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion].each do |model|
-      it "rolls back both systems when #{ model.name } persistence fails" do
+      it "rolls back new description creation when #{ model.name } persistence fails" do
-        tag_name
         before_state = stored_state
         aggregate_failures do
           fail_save(model) { create_description }
@@ -116,10 +99,32 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
     end
   end
 
+  it 'creates missing compatibility data without writing an ID-colliding Help page' do
+    description = TagDescription.create!(
+        id: 500, tag:, language_code: 'ja', body: 'before', version_no: 1)
+    help = WikiPage.create!(id: description.id,
+                            tag_name: create(:tag_name, name: 'Help:unrelated'),
+                            body: 'unrelated', created_user: user, updated_user: user)
+    Wiki::Commit.legacy_content!(page: help, body: help.body, created_user: user)
+    before_help = help.attributes
+    expect do
+      put "/wiki/#{ description.id }", params: { title: tag_name.name, body: 'after' },
+          headers: headers
+    end.to change(WikiPage, :count).by(1)
+        .and change(WikiRevision, :count).by(1)
+        .and change(WikiVersion, :count).by(1)
+    expect(response).to have_http_status(:ok)
+    expect(description.reload).to have_attributes(id: 500, body: 'after')
+    expect(help.reload.attributes).to eq(before_help)
+    compatibility = WikiPage.find_by!(tag_name:)
+    expect(compatibility.body).to eq(description.body)
+    expect(compatibility.current_revision.body).to eq(description.body)
+  end
+
   describe 'PUT /wiki/:id' do
     let!(:page) do
       tag
-      Wiki::Commit.create_content!(
+      seed_wiki_page(
           tag_name:, body: 'before', created_by_user: user)
     end
     let!(:first_revision) { page.current_revision }
@@ -138,7 +143,8 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       expect(page.reload.version_no).to eq(1)
       expect(description.version_no).to eq(1)
       expect { update_description }
-          .to change(WikiRevision, :count).by(1)
+          .to change(WikiPage, :count).by(0)
+          .and change(WikiRevision, :count).by(1)
           .and change(WikiVersion, :count).by(1)
           .and change(TagDescriptionVersion, :count).by(1)
       expect(response).to have_http_status(:ok)
@@ -157,7 +163,8 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       tag_name.update_columns(tag_id: nil)
 
       expect { update_description }
-          .to change(WikiRevision, :count).by(1)
+          .to change(WikiPage, :count).by(0)
+          .and change(WikiRevision, :count).by(1)
           .and change(WikiVersion, :count).by(1)
           .and change(TagDescriptionVersion, :count).by(1)
 
@@ -177,10 +184,10 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       page_state = page.attributes
       description_state = description.attributes
 
-      update_description(body: 'before', title: 'Help:description_renamed')
+      update_description(body: 'before', title: 'description_renamed')
 
       expect(response).to have_http_status(:ok)
-      expect(tag_name.reload.name).to eq('Help:description_renamed')
+      expect(tag_name.reload.name).to eq('description_renamed')
       expect(WikiRevision.count).to eq(revision_count)
       expect(WikiVersion.count).to eq(wiki_version_count)
       expect(TagDescriptionVersion.count).to eq(description_version_count)

backend/spec/requests/tag_descriptions_spec.rb

@@ -206,7 +206,13 @@ RSpec.describe 'Tag description native API', type: :request do
     context 'without an existing description' do
       before { tag }
 
-      it 'creates both current resources and histories with matching compatibility IDs' do
+      it 'creates a description with synchronised Wiki content and histories' do
+        unrelated = Wiki::Commit.create_legacy_content!(
+            tag_name: create(:tag_name, name: 'Help:unrelated_native_description'),
+            body: 'unrelated body', created_by_user: author)
+        unrelated_state = [unrelated.attributes,
+                           unrelated.wiki_revisions.map(&:attributes),
+                           unrelated.wiki_versions.map(&:attributes)]
         expect { native_write(body: 'created natively') }
             .to change(TagDescription, :count).by(1)
             .and change(TagDescriptionVersion, :count).by(1)
@@ -215,7 +221,7 @@ RSpec.describe 'Tag description native API', type: :request do
             .and change(WikiVersion, :count).by(1)
         expect(response).to have_http_status(:created)
         description = TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
-        page = WikiPage.find(description.id)
+        page = WikiPage.find_by!(tag_name: tag.tag_name('ja'))
         revision = page.current_revision
         version = TagDescriptionVersion.find(revision.id)
         expect(description).to have_attributes(
@@ -227,6 +233,9 @@ RSpec.describe 'Tag description native API', type: :request do
         expect(page).to have_attributes(tag_name_id: tag_name.id, body: description.body)
         expect(revision.body).to eq(version.body)
         expect(page.wiki_versions.last.body).to eq(version.body)
+        unrelated.reload
+        expect([unrelated.attributes, unrelated.wiki_revisions.map(&:attributes),
+                unrelated.wiki_versions.map(&:attributes)]).to eq(unrelated_state)
         expect_current(description)
 
         get "/wiki/#{ description.id }"

backend/spec/requests/tag_group_wiki_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Tag group Wiki facade reads', type: :request do
+  include WikiRecords
   include TagGroupRecords
 
   let!(:user) { create_member_user! }
@@ -69,34 +70,36 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
     end
   end
 
-  it 'combines Tag Groups, Help and Tag Descriptions in the unfiltered list' do
+  it 'combines Tag Groups and Tag Descriptions without Help in the unfiltered list' do
-    help = Wiki::Commit.create_legacy_content!(
+    help = seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:混在'), body: 'help', created_by_user: user)
     TagDescriptionOperation.create!(tag: new_tag, body: 'tag description', created_by_user: user)
     get '/wiki'
     expect(response).to have_http_status(:ok)
     expect(json.map { _1.fetch('title') }).to include(
-        'タググループ:読取り契約', help.title, '新タグ')
+        'タググループ:読取り契約', '新タグ')
+    expect(json.map { _1.fetch('title') }).not_to include(help.title)
   end
 
-  it 'keeps Help readable when its ID collides with a new group' do
+  it 'excludes Help when its ID collides with a new group' do
-    help = Wiki::Commit.create_legacy_content!(
+    help = seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:ID重複'), body: 'help body',
         created_by_user: user)
     seed_group(name: '別 ID重複', id: help.id, description: 'group body')
 
     get '/wiki'
     expect(response).to have_http_status(:ok)
-    expect(json.map { _1.fetch('title') }).to include(help.title, 'タググループ:別 ID重複')
+    expect(json.map { _1.fetch('title') }).to include('タググループ:別 ID重複')
+    expect(json.map { _1.fetch('title') }).not_to include(help.title)
 
     get "/wiki/title/#{ CGI.escapeURIComponent(help.title) }"
-    expect(response).to have_http_status(:ok)
+    expect(response).to have_http_status(:not_found)
-    expect(json.fetch('body')).to eq('help body')
 
     get '/wiki/changes'
     expect(response).to have_http_status(:ok)
     expect(json.map { _1.dig('wiki_page', 'title') }).to include(
-        help.title, 'タググループ:別 ID重複')
+        'タググループ:別 ID重複')
+    expect(json.map { _1.dig('wiki_page', 'title') }).not_to include(help.title)
   end
 
   it 'finds groups by a partial prefix of their displayed title' do
@@ -122,7 +125,7 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
   end
 
   it 'orders mixed resource history by timestamp rather than independent IDs' do
-    help = Wiki::Commit.create_legacy_content!(
+    help = seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:時系列'), body: 'help',
         created_by_user: user)
     TagDescriptionOperation.create!(tag: new_tag, body: 'description', created_by_user: user)
@@ -136,8 +139,8 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
     timestamps = json.map { Time.iso8601(_1.fetch('timestamp')) }
     expect(timestamps).to eq(timestamps.sort.reverse)
     titles = json.map { _1.dig('wiki_page', 'title') }
-    expect(titles.index('新タグ')).to be < titles.index(help.title)
+    expect(titles).not_to include(help.title)
-    expect(titles.index(help.title)).to be < titles.index('タググループ:読取り契約')
+    expect(titles.index('新タグ')).to be < titles.index('タググループ:読取り契約')
   end
 
   it 'renders nullable group editors without raising' do
@@ -166,16 +169,16 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
         'wiki_page' => include('id' => page.id, 'title' => 'タググループ:読取り契約'))
   end
 
-  it 'includes Help and group history but excludes legacy-only migrated revisions' do
+  it 'includes group history but excludes all legacy-only revisions' do
     extra = Wiki::Commit.legacy_content!(page:, body: 'legacy only', created_user: user)
-    help = Wiki::Commit.create_legacy_content!(
+    help = seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:変更一覧'), body: 'help', created_by_user: user)
     get '/wiki/changes'
     expect(response).to have_http_status(:ok)
     rows = json.select { _1.fetch('wiki_page').fetch('title') == 'タググループ:読取り契約' }
     expect(rows.map { _1.fetch('revision_id') }).to eq([last_revision.id, first_revision.id])
     expect(rows.map { _1.fetch('revision_id') }).not_to include(extra.id)
-    expect(json).to include(include(
+    expect(json).not_to include(include(
         'revision_id' => help.current_revision.id,
         'wiki_page' => include('title' => help.title)))
   end
@@ -214,7 +217,7 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
 
   context 'when Help, description and group share the same numeric ID' do
     let(:colliding_help) do
-      Wiki::Commit.create_legacy_content!(
+      seed_wiki_page(
           tag_name: create(:tag_name, name: 'Help:三者ID衝突'),
           body: 'help', created_by_user: user)
     end
@@ -239,13 +242,12 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
       colliding_description_version
     end
 
-    it 'lists all three resources without deduplicating their numeric ID' do
+    it 'lists both new resources sharing a numeric ID without legacy Help' do
       get '/wiki'
 
       expect(response).to have_http_status(:ok)
       rows = json.select { _1.fetch('id') == colliding_help.id }
       expect(rows.map { [_1.fetch('id'), _1.fetch('title')] }).to contain_exactly(
-          [colliding_help.id, colliding_help.title],
           [colliding_description.id, '新タグ'],
           [colliding_group_id, 'タググループ:三者ID衝突'])
     end
@@ -259,7 +261,6 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
         [row.fetch('revision_id'), row.fetch('wiki_page').fetch('title')]
       end
       expect(histories).to contain_exactly(
-          [colliding_help.current_revision.id, colliding_help.title],
           [colliding_description_version.id, '新タグ'],
           [group_version(colliding_group_id, 1).fetch('id'), 'タググループ:三者ID衝突'])
     end
@@ -285,8 +286,8 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
     end
   end
 
-  it 'resolves colliding group, Help and description IDs by title' do
+  it 'resolves new resources by title while excluding colliding legacy Help' do
-    help = Wiki::Commit.create_legacy_content!(
+    help = seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:ID衝突'), body: 'help', created_by_user: user)
     seed_group(name: 'ID衝突', id: help.id, description: 'group')
     TagDescription.create!(
@@ -294,11 +295,15 @@ RSpec.describe 'Tag group Wiki facade reads', type: :request do
     TagDescriptionVersion.create!(
         tag_id: new_tag.id, language_code: 'ja', version_no: 1,
         event_type: 'create', body: 'description', created_at: Time.current)
-    { 'タググループ:ID衝突' => 'group', 'Help:ID衝突' => 'help', '新タグ' => 'description' }
+    { 'タググループ:ID衝突' => 'group', '新タグ' => 'description' }
         .each do |title, body|
       get "/wiki/title/#{ CGI.escapeURIComponent(title) }"
       expect(response).to have_http_status(:ok)
       expect(json.fetch('body').strip).to eq(body)
     end
+    without_group_legacy_reads do
+      get "/wiki/title/#{ CGI.escapeURIComponent(help.title) }"
+    end
+    expect(response).to have_http_status(:not_found)
   end
 end

backend/spec/requests/tag_group_wiki_write_spec.rb

@@ -33,8 +33,11 @@ RSpec.describe 'Tag group Wiki facade writes', type: :request do
     end
   end
 
-  it 'creates the group, first snapshot and compatibility Wiki history' do
+  it 'creates the group, snapshot and matching compatibility histories' do
-    create_group
+    expect { create_group }
+        .to change(WikiPage, :count).by(1)
+        .and change(WikiRevision, :count).by(1)
+        .and change(WikiVersion, :count).by(1)
     expect(response).to have_http_status(:created)
     group = group_rows('tag_groups', name: '新規').sole
     expect(json).to include('id' => group.fetch('id'), 'title' => 'タググループ:新規')
@@ -43,10 +46,9 @@ RSpec.describe 'Tag group Wiki facade writes', type: :request do
     expect(version).to include('event_type' => 'create', 'created_by_user_id' => user.id)
     expect(group).to include('created_by_user_id' => user.id, 'updated_by_user_id' => user.id)
     page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:新規' })
-    expect(page.body.strip).to eq('- 洗澡鹿')
+    expect(page.body).to eq('- 洗澡鹿')
     expect(page.current_revision.body).to eq(page.body)
     expect(page.wiki_versions.sole.body).to eq(page.body)
-    # New IDs are independently allocated; no global identity assertion here.
   end
 
   it 'keeps repeated placements but only one membership and one snapshot member' do
@@ -293,8 +295,9 @@ RSpec.describe 'Tag group Wiki facade writes', type: :request do
         expect(group_state).to eq(before_state)
       end
 
-      (TagGroupRecords::GROUP_TABLES + ['wiki_pages', 'wiki_revisions', 'wiki_versions'])
+      tables = TagGroupRecords::GROUP_TABLES
-          .each do |table|
+      tables += ['wiki_pages', 'wiki_revisions', 'wiki_versions']
+      tables.each do |table|
         it "rolls back all writes after a real #{ table } write fails" do
           expect_atomic_group_write(table) { write_group(operation, headers) }
         end

backend/spec/requests/tag_group_write_integrity_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Tag group write integrity', type: :request do
+  include WikiRecords
   include TagGroupRecords
   include ActiveSupport::Testing::TimeHelpers
 
@@ -24,7 +25,7 @@ RSpec.describe 'Tag group write integrity', type: :request do
   end
 
   def create_help body
-    Wiki::Commit.create_legacy_content!(
+    seed_wiki_page(
         tag_name: create(:tag_name, name: 'Help:既存'), body:, created_by_user: user)
   end
 
@@ -70,17 +71,16 @@ RSpec.describe 'Tag group write integrity', type: :request do
       expect(page.body).to eq('- 伊地知ニジカ')
     end
 
-    it 'updates Help with a colliding group ID without altering the group' do
+    it 'rejects a standalone Help update despite a colliding group ID' do
       page = create_help('Help body')
       id = seed_group(name: '別グループ', id: page.id, members:, placements:)
       group_before = TagGroup.find(id).attributes
       version_before = group_version(id, 1)
 
-      put_wiki(id, title: 'Help:改名', body: 'Help after')
+      expect_no_writes { put_wiki(id, title: 'Help:改名', body: 'Help after') }
 
-      expect(response).to have_http_status(:ok)
+      expect(page.reload.body).to eq('Help body')
-      expect(page.reload.body).to eq('Help after')
+      expect(page.title).to eq('Help:既存')
-      expect(page.title).to eq('Help:改名')
       expect(TagGroup.find(id).attributes).to eq(group_before)
       expect(group_version(id, 1)).to eq(version_before)
     end
@@ -98,7 +98,8 @@ RSpec.describe 'Tag group write integrity', type: :request do
     it 'keeps a description update separate from a colliding group' do
       page = Wiki::Commit.create_content!(
           tag_name: tag.tag_name('ja'), body: 'description before', created_by_user: user)
-      id = seed_group(name: '更新', id: page.id, members:, placements:)
+      description = TagDescription.find_by!(tag_id: tag.id)
+      id = seed_group(name: '更新', id: description.id, members:, placements:)
       group_before = TagGroup.find(id).attributes
 
       put_wiki(id, title: '洗澡鹿', body: 'description after')
@@ -115,18 +116,19 @@ RSpec.describe 'Tag group write integrity', type: :request do
       description = TagDescription.create!(
           id:, tag:, language_code: 'ja', version_no: 1, body: 'description')
 
-      put_wiki(id, title: 'Help:既存', body: 'Help after')
+      expect_no_writes { put_wiki(id, title: 'Help:既存', body: 'Help after') }
 
-      expect(response).to have_http_status(:ok)
+      expect(page.reload.body).to eq('Help before')
-      expect(page.reload.body).to eq('Help after')
       expect(description.reload.body).to eq('description')
       expect(TagGroup.find(id).version_no).to eq(1)
-      expect_no_writes { put_wiki(id, title: '洗澡鹿', body: 'description after') }
+      put_wiki(id, title: '洗澡鹿', body: 'description after')
+      expect(response).to have_http_status(:ok)
+      expect(description.reload.body).to eq('description after')
       put_wiki(id, title: 'タググループ:更新')
       expect(response).to have_http_status(:ok)
       expect(TagGroup.find(id).version_no).to eq(2)
-      expect(page.reload.body).to eq('Help after')
+      expect(page.reload.body).to eq('Help before')
-      expect(description.reload.body).to eq('description')
+      expect(description.reload.body).to eq('description after')
     end
   end
 
@@ -136,14 +138,14 @@ RSpec.describe 'Tag group write integrity', type: :request do
       id = seed_group(name: '更新', id: help.id, members:, placements:)
       help_before = help.attributes
 
+      expect do
         put "/tag_groups/#{ id }", params: native_payload(name: '改名'), headers:, as: :json
+      end.to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
 
       expect(response).to have_http_status(:ok)
-      page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:改名' })
+      expect(TagGroup.find(id).name).to eq('改名')
-      expect(page.id).not_to eq(help.id)
-      expect(page.body).to eq('- 洗澡鹿')
-      expect(page.current_revision.body).to eq(page.body)
-      expect(page.wiki_versions.sole.body).to eq(page.body)
       expect(help.reload.attributes).to eq(help_before)
     end
 

backend/spec/requests/tag_groups_spec.rb

@@ -391,6 +391,17 @@ RSpec.describe 'Tag group native API', type: :request do
         end
       end
 
+      it 'creates native state and its compatibility histories' do
+        expect { native_write(:create) }
+            .to change(WikiPage, :count).by(1)
+            .and change(WikiRevision, :count).by(1)
+            .and change(WikiVersion, :count).by(1)
+        expect(response).to have_http_status(:created)
+        expect_group_snapshot(
+            json.fetch('id'), number: 1, members: snapshot_members,
+            placements:, description: '全体の説明')
+      end
+
       [:create, :update].each do |operation|
         it "synchronises Wiki current state and histories on native #{ operation }" do
           native_write(operation)
@@ -418,19 +429,18 @@ RSpec.describe 'Tag group native API', type: :request do
         end
       end
 
-      it 'uses AUTO_INCREMENT for a new group instead of supplying a compatibility ID' do
+      it 'assigns the next group ID from the existing maximum' do
-        inserts = []
+        child_id
-        subscriber = lambda do |*args|
+        expected_id = [TagGroup.maximum(:id).to_i, TagDescription.maximum(:id).to_i].max + 1
-          sql = args.last.fetch(:sql)
-          inserts << sql if sql.match?(/\A\s*INSERT INTO `?tag_groups`?\s/i)
-        end
-        ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
         native_write(:create)
-        end
         expect(response).to have_http_status(:created)
-        expect(inserts.size).to eq(1)
+        expect(json.fetch('id')).to eq(expected_id)
-        columns = inserts.sole[/\((.*?)\)/, 1].split(',').map { _1.strip.delete('`') }
+      end
-        expect(columns).not_to include('id')
+
+      TagGroupRecords::GROUP_TABLES.each do |table|
+        it "rolls back native creation after #{ table } writes" do
+          expect_atomic_group_write(table) { native_write(:create) }
+        end
       end
 
       it 'updates a native group through Wiki and then reads structured current data' do

backend/spec/requests/tag_resource_ids_spec.rb

@@ -0,0 +1,101 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag resource ID allocation', type: :request do
+  include TagGroupRecords
+  include WikiRecords
+
+  let!(:user) { create_member_user! }
+  let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+
+  def seed_description id
+    tag = create(:tag, primary_name: "description_id_#{ id }")
+    TagDescription.create!(id:, tag:, language_code: 'ja', body: 'existing', version_no: 1)
+  end
+
+  def create_resource resource
+    if resource == :description
+      tag = create(:tag, primary_name: 'new_description')
+      post '/wiki', params: { title: tag.name('ja'), body: 'new description' }, headers: headers
+    else
+      post '/tag_groups', params: {
+          name: 'new_group', description: 'new group', members: [], placements: [] },
+          headers:, as: :json
+    end
+    expect(response).to have_http_status(:created)
+  end
+
+  [:description, :group].each do |resource|
+    it "keeps #{ resource } independent of the Tag and ExternalTag ID space" do
+      create(:tag, id: 100)
+      create(:external_tag, id: 200)
+      seed_description(1)
+      seed_group(name: 'shared_space', id: 2)
+
+      create_resource(resource)
+
+      expect(json.fetch('id')).to eq(3)
+    end
+
+    it "uses the other resource's larger maximum when allocating #{ resource }" do
+      seed_description(resource == :description ? 1 : 20)
+      seed_group(name: 'other_space', id: resource == :group ? 1 : 20)
+      create_resource(resource)
+      expect(json.fetch('id')).to eq(21)
+    end
+
+    it "starts #{ resource } at 1 even after previous allocated rows were removed" do
+      expect(TagDescription.count).to eq(0)
+      expect(TagGroup.count).to eq(0)
+      if resource == :description
+        seed_description(100).destroy!
+      else
+        id = seed_group(name: 'removed', id: 100)
+        TagGroup.find(id).destroy!
+      end
+      create_resource(resource)
+      expect(json.fetch('id')).to eq(1)
+    end
+
+    it "allocates #{ resource } above both maxima, preserving legacy overlaps and gaps" do
+      [1, 2, 5].each { seed_description(_1) }
+      [1, 3, 8].each { seed_group(name: "group_#{ _1 }", id: _1) }
+      descriptions = TagDescription.order(:id).map(&:attributes)
+      groups = TagGroup.order(:id).map(&:attributes)
+
+      create_resource(resource)
+
+      expect(json.fetch('id')).to eq(9)
+      expect(TagDescription.where(id: [1, 2, 5]).order(:id).map(&:attributes)).to eq(descriptions)
+      expect(TagGroup.where(id: [1, 3, 8]).order(:id).map(&:attributes)).to eq(groups)
+      expect(TagDescription.exists?(id: 3)).to be(false)
+      expect(TagGroup.exists?(id: 2)).to be(false)
+    end
+  end
+
+  it 'preserves group ID and unrelated rows on update' do
+    id = seed_group(name: 'existing', id: 5, description: 'before')
+    other_id = seed_group(name: 'other', id: 8, description: 'other')
+    other = TagGroup.find(other_id).attributes
+    put "/tag_groups/#{ id }", params: {
+        name: 'renamed', description: 'after', members: [], placements: [] }, headers:, as: :json
+    expect(response).to have_http_status(:ok)
+    expect(json.fetch('id')).to eq(id)
+    expect(TagGroup.find(id).description).to eq('after')
+    expect(TagGroup.find(other_id).attributes).to eq(other)
+    expect(TagGroup.count).to eq(2)
+  end
+
+  it 'preserves description identity on a compatibility update' do
+    tag = create(:tag, primary_name: 'existing_description')
+    page = seed_wiki_page(tag_name: tag.tag_name('ja'), body: 'before', created_by_user: user)
+    description = TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
+    id = description.id
+    put "/wiki/#{ id }", params: {
+        title: tag.name('ja'), body: 'after', base_revision_id: page.current_revision.id },
+        headers: headers
+    expect(response).to have_http_status(:ok)
+    expect(description.reload.id).to eq(id)
+    expect(description.body).to eq('after')
+    expect(TagDescription.count).to eq(1)
+  end
+end

backend/spec/requests/tag_wiki_history_integrity_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Tag and wiki history integrity', type: :request do
+  include WikiRecords
   let(:member_user) { create(:user, role: 'member') }
 
   def stub_current_user user
@@ -13,7 +14,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   def create_wiki_for_tag! tag:, body: 'wiki body', user: member_user
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name: primary_tag_name_for(tag, 'ja'),
         body:,
         created_by_user: user,

backend/spec/requests/tags_spec.rb

@@ -38,6 +38,22 @@ RSpec.describe 'Tags API', type: :request do
   end
 
   describe 'GET /tags' do
+    it 'serialises descriptions and parents without loading legacy Wiki pages' do
+      TagDescription.create!(tag:, language_code: 'ja', body: '', version_no: 1)
+      TagDescription.create!(tag: tag2, language_code: 'ja', body: '', version_no: 1)
+      TagImplication.create!(tag:, parent_tag: tag2)
+      queries = []
+      subscriber = ->(*args) { queries << args.last.fetch(:sql) }
+      ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+        get '/tags', params: { name: 'spec_tag' }
+      end
+      expect(response).to have_http_status(:ok)
+      row = response_tags.sole
+      expect(row.fetch('has_wiki')).to be(true)
+      expect(row.fetch('parents').sole.fetch('has_wiki')).to be(true)
+      expect(queries.grep(/\bSELECT\b.*\bwiki_(pages|revisions|versions)\b/im)).to be_empty
+    end
+
     it 'includes legacy external JSON alongside an internal tag with the same id' do
       external = create(:external_tag, id: tag.id, name: 'spec_external', post_count: 3)
 

backend/spec/requests/wiki_conflict_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Wiki conflict handling', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
 
   def auth_headers user
@@ -9,8 +10,8 @@ RSpec.describe 'Wiki conflict handling', type: :request do
 
   it 'returns 409 when base_revision_id is stale' do
     page =
-        Wiki::Commit.create_content!(
+        seed_wiki_page(
-            tag_name: create(:tag_name, name: 'wiki_conflict_request'),
+            tag_name: create(:tag, primary_name: 'wiki_conflict_request').tag_name('ja'),
             body: 'first',
             created_by_user: user,
             message: 'init')
@@ -25,12 +26,10 @@ RSpec.describe 'Wiki conflict handling', type: :request do
         base_revision_id: stale_id)
 
     put "/wiki/#{ page.id }",
-        params: {
+        params: { title: 'wiki_conflict_request',
-          title: 'wiki_conflict_request',
                   body: 'third',
                   message: 'stale',
-          base_revision_id: stale_id,
+                  base_revision_id: stale_id },
-        },
         headers: auth_headers(user)
 
     expect(response).to have_http_status(:conflict)

backend/spec/requests/wiki_creation_freeze_spec.rb

@@ -0,0 +1,63 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki creation freeze', type: :request do
+  include TagGroupRecords
+  include WikiRecords
+
+  let!(:user) { create_member_user! }
+  let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+
+  it 'creates missing compatibility history when updating an independent group' do
+    id = seed_group(name: 'independent', description: 'before')
+    expect do
+      put "/tag_groups/#{ id }", params: {
+          name: 'independent', description: 'after', members: [], placements: [] },
+          headers:, as: :json
+    end.to change(WikiPage, :count).by(1)
+        .and change(WikiRevision, :count).by(1)
+        .and change(WikiVersion, :count).by(1)
+    expect(response).to have_http_status(:ok)
+    expect(TagGroup.find(id).description).to eq('after')
+    page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:independent' })
+    expect(page.body).to include('after')
+    expect(page.current_revision.body).to eq(page.body)
+    expect(page.wiki_versions.sole.body).to eq(page.body)
+  end
+
+  context 'existing description write protection' do
+    let!(:tag) { create(:tag, primary_name: 'protected_description') }
+    let!(:page) do
+      seed_wiki_page(tag_name: tag.tag_name('ja'), body: 'before', created_by_user: user)
+    end
+
+    [nil, :guest, :banned].each do |role|
+      it "rejects #{ role || 'anonymous' } without changing either history" do
+        actor = role && create(:user, role == :banned ? :member : role)
+        actor.update!(banned_at: Time.current) if role == :banned
+        request_headers = actor ? { 'X-Transfer-Code' => actor.inheritance_code } : { }
+        before_state = group_state
+        put "/wiki/#{ page.id }", params: { title: tag.name('ja'), body: 'after' },
+            headers: request_headers
+        expect(response).to have_http_status(role ? :forbidden : :unauthorized)
+        expect(group_state).to eq(before_state)
+      end
+    end
+
+    it 'rejects banned IPs without writes' do
+      IpAddress.create!(ip_address: IPAddr.new('127.0.0.1').hton, banned_at: Time.current)
+      before_state = group_state
+      put "/wiki/#{ page.id }", params: { title: tag.name('ja'), body: 'after' }, headers: headers
+      expect(response).to have_http_status(:forbidden)
+      expect(group_state).to eq(before_state)
+    end
+
+    ['', "\r\n\r\n"].each do |body|
+      it "rejects invalid description body #{ body.inspect } atomically" do
+        before_state = group_state
+        put "/wiki/#{ page.id }", params: { title: tag.name('ja'), body: }, headers: headers
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(group_state).to eq(before_state)
+      end
+    end
+  end
+end

backend/spec/requests/wiki_history_integrity_spec.rb

@@ -2,6 +2,7 @@ require 'cgi'
 require 'rails_helper'
 
 RSpec.describe 'Wiki history integrity', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
 
   def auth_headers user
@@ -9,49 +10,22 @@ RSpec.describe 'Wiki history integrity', type: :request do
   end
 
   def create_wiki_page title:, body: 'body', message: 'init', user: self.user
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
-        tag_name: create(:tag_name, name: title),
+        tag_name: create(:tag, primary_name: title).tag_name('ja'),
         body:,
         created_by_user: user,
         message:)
   end
 
   describe 'POST /wiki' do
-    it 'creates wiki_page, wiki_revision, and wiki_version atomically' do
+    it 'rejects frozen creation without partial page or history' do
-      expect {
+      expect do
-        post '/wiki',
+        post '/wiki', params: { title: 'Help:wiki_history_create_atomic', body: 'initial' },
-             params: {
-               title: 'Help:wiki_history_create_atomic',
-               body: "a\nb\nc",
-               message: 'initial commit',
-             },
              headers: auth_headers(user)
-      }
+      end.to change(WikiPage, :count).by(0)
-          .to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(0)
-          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(0)
-          .and change(WikiVersion, :count).by(1)
+      expect(response.status).to be_between(400, 499)
-
-      expect(response).to have_http_status(:created)
-
-      page = WikiPage.find(json.fetch('id'))
-      revision = page.current_revision
-      version = page.wiki_versions.order(:version_no).last
-
-      expect(page.title).to eq('Help:wiki_history_create_atomic')
-      expect(page.body).to eq("a\nb\nc")
-
-      expect(revision).to be_content
-      expect(revision.message).to eq('initial commit')
-      expect(revision.lines_count).to eq(3)
-
-      expect(version).to have_attributes(
-        version_no: 1,
-        event_type: 'create',
-        title: 'Help:wiki_history_create_atomic',
-        body: "a\nb\nc",
-        reason: 'initial commit',
-        created_by_user_id: user.id
-      )
     end
 
     it 'returns 422 and creates nothing when normalised body is blank' do
@@ -71,21 +45,19 @@ RSpec.describe 'Wiki history integrity', type: :request do
           .where(tag_names: { name: 'Help:wiki_history_blank_body' })).not_to exist
     end
 
-    it 'returns 422 and creates no partial page when title already exists' do
+    it 'rejects frozen creation without modifying an existing page or history' do
       create_wiki_page(title: 'Help:wiki_history_duplicate_title', body: 'first')
 
-      expect {
+      expect do
         post '/wiki',
-             params: {
+             params: { title: 'Help:wiki_history_duplicate_title',
-               title: 'Help:wiki_history_duplicate_title',
+                       body: 'second', message: 'duplicate' },
-               body: 'second',
-               message: 'duplicate',
-             },
              headers: auth_headers(user)
-      }
+      end.to change(WikiPage, :count).by(0)
-          .not_to change(WikiPage, :count)
+          .and change(WikiRevision, :count).by(0)
+          .and change(WikiVersion, :count).by(0)
 
-      expect(response).to have_http_status(:unprocessable_entity)
+      expect(response.status).to be_between(400, 499)
       expect(WikiPage.joins(:tag_name)
           .where(tag_names: { name: 'Help:wiki_history_duplicate_title' }).count).to eq(1)
     end

backend/spec/requests/wiki_index_order_spec.rb

@@ -0,0 +1,42 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki resource ordering', type: :request do
+  include TagGroupRecords
+  let(:user) { create_member_user! }
+
+  it 'selects the latest twenty across both resources before applying the global limit' do
+    start = Time.utc(2026, 1, 1)
+    descriptions = 24.times.map do |index|
+      tag = create(:tag, primary_name: "rank_#{ index }")
+      TagDescription.create!(tag:, language_code: 'ja', body: 'current', version_no: 1,
+                             updated_at: start + index.hours)
+    end
+    groups = [24, 25].map do |hour|
+      group = TagGroup.find(seed_group(name: "rank_group_#{ hour }"))
+      group.update_columns(updated_at: start + hour.hours)
+      group
+    end
+
+    get '/wiki', params: { title: 'rank' }
+
+    expect(response).to have_http_status(:ok)
+    expected = groups.reverse.map { ['tag_group', _1.id] } +
+        descriptions.last(18).reverse.map { ['tag_description', _1.id] }
+    expect(json.map { [_1.fetch('resource_type'), _1.fetch('id')] }).to eq(expected)
+  end
+
+  it 'breaks timestamp ties by resource kind and ID while retaining legacy overlaps' do
+    time = Time.utc(2026, 1, 1)
+    tag = create(:tag, primary_name: 'tied')
+    TagDescription.create!(id: 51, tag:, language_code: 'ja', body: 'current',
+                           version_no: 1, updated_at: time)
+    group = TagGroup.find(seed_group(name: 'tied', id: 51))
+    group.update_columns(updated_at: time)
+
+    2.times do
+      get '/wiki', params: { title: 'tied' }
+      expect(json.map { [_1.fetch('resource_type'), _1.fetch('id')] })
+          .to eq([['tag_description', 51], ['tag_group', 51]])
+    end
+  end
+end

backend/spec/requests/wiki_spec.rb

@@ -4,6 +4,7 @@ require 'securerandom'
 
 
 RSpec.describe 'Wiki API', type: :request do
+  include WikiRecords
   def auth_headers(user)
     { 'X-Transfer-Code' => user.inheritance_code }
   end
@@ -18,7 +19,7 @@ RSpec.describe 'Wiki API', type: :request do
         deprecated_at: Time.zone.local(2026, 6, 1))
   end
   let!(:page) do
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name: tn,
         body: 'init',
         created_by_user: user,
@@ -108,94 +109,14 @@ RSpec.describe 'Wiki API', type: :request do
       end
     end
 
-    context 'when success' do
+    ['Help:TestPage', 'ヘルプ:ホーム'].each do |title|
-      it 'creates wiki_page and first content revision' do
+      it "rejects frozen creation of #{ title } without history writes" do
         expect do
-          post endpoint, params: { title: 'Help:TestPage', body: "a\nb\nc", message: 'init' },
+          post endpoint, params: { title:, body: 'initial' }, headers: auth_headers(member)
-                         headers: auth_headers(member)
+        end.to change(WikiPage, :count).by(0)
-        end
+            .and change(WikiRevision, :count).by(0)
-            .to change(WikiPage, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
-            .and change(WikiRevision, :count).by(1)
+        expect(response.status).to be_between(400, 499)
-            .and change(WikiVersion, :count).by(1)
-
-        expect(response).to have_http_status(:created)
-
-        page_id = json.fetch('id')
-        expect(json.fetch('title')).to eq('Help:TestPage')
-
-        created_page = WikiPage.find(page_id)
-        version = created_page.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          version_no: 1,
-          event_type: 'create',
-          title: 'Help:TestPage',
-          body: "a\nb\nc",
-          created_by_user_id: member.id
-        )
-
-        rev = created_page.current_revision
-        expect(rev).to be_present
-        expect(rev).to be_content
-        expect(rev.message).to eq('init')
-
-        expect(created_page.body).to eq("a\nb\nc")
-
-        expect(rev.lines_count).to eq(3)
-        expect(rev.wiki_revision_lines.order(:position).pluck(:position)).to eq([0, 1, 2])
-        expect(rev.wiki_lines.pluck(:body)).to match_array(['a', 'b', 'c'])
-      end
-
-      it 'reuses existing WikiLine rows by sha256' do
-        # 先に同じ行を作っておく
-        WikiLine.create!(sha256: Digest::SHA256.hexdigest('a'), body: 'a', created_at: Time.current, updated_at: Time.current)
-
-        post endpoint,
-             params: { title: 'Help:Reuse', body: "a\na" },
-             headers: auth_headers(member)
-
-        page = WikiPage.find(JSON.parse(response.body).fetch('id'))
-        rev = page.current_revision
-        expect(rev.lines_count).to eq(2)
-
-        # "a" の WikiLine が増殖しない（1行のはず）
-        expect(WikiLine.where(body: 'a').count).to eq(1)
-      end
-
-      it 'deduplicates duplicated new lines before upsert' do
-        duplicated = 'duplicated_line_for_wiki_line_upsert_spec'
-
-        post endpoint,
-             params: { title: 'Help:DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
-             headers: auth_headers(member)
-
-        expect(response).to have_http_status(:created)
-
-        page = WikiPage.find(json.fetch('id'))
-        rev = page.current_revision
-
-        expect(rev.lines_count).to eq(2)
-        expect(WikiLine.where(body: duplicated).count).to eq(1)
-        expect(rev.wiki_revision_lines.count).to eq(2)
-        expect(rev.wiki_revision_lines.pluck(:wiki_line_id).uniq.size).to eq(1)
-      end
-
-      it 'normalises CRLF and strips trailing newlines' do
-        post endpoint,
-             params: { title: 'Help:NormalisedBody',
-                       body: "a\r\nb\r\n\r\n", message: 'normalise' },
-             headers: auth_headers(member)
-
-        expect(response).to have_http_status(:created)
-
-        page = WikiPage.find(json.fetch('id'))
-        rev = page.current_revision
-        version = page.wiki_versions.order(:version_no).last
-
-        expect(page.body).to eq("a\nb")
-        expect(version.body).to eq("a\nb")
-        expect(rev.lines_count).to eq(2)
-        expect(rev.wiki_lines.order('wiki_revision_lines.position').map(&:body)).to eq(['a', 'b'])
       end
     end
   end
@@ -208,10 +129,10 @@ RSpec.describe 'Wiki API', type: :request do
       { 'X-Transfer-Code' => user.inheritance_code }
     end
 
-    let!(:test_tag_name) { create(:tag_name, name: 'TestPage') }
+    let!(:test_tag_name) { create(:tag, primary_name: 'TestPage').tag_name('ja') }
 
     let!(:page) do
-      Wiki::Commit.create_content!(
+      seed_wiki_page(
           tag_name: test_tag_name,
           body: "a\nb",
           created_by_user: member,
@@ -249,7 +170,8 @@ RSpec.describe 'Wiki API', type: :request do
 
         expect do
           put "/wiki/#{page.id}",
-              params: { title: 'TestPage', body: "x\ny", message: 'edit', base_revision_id: current_id },
+              params: { title: 'TestPage', body: "x\ny", message: 'edit',
+                        base_revision_id: current_id },
               headers: auth_headers(member)
         end
             .to change(WikiRevision, :count).by(1)
@@ -284,7 +206,7 @@ RSpec.describe 'Wiki API', type: :request do
             created_by_user: member)
 
         linked_page =
-            Wiki::Commit.create_content!(
+            seed_wiki_page(
                 tag_name: linked_tag_name,
                 body: 'before',
                 created_by_user: member,
@@ -358,13 +280,14 @@ RSpec.describe 'Wiki API', type: :request do
 
   describe 'GET /wiki/search' do
     before do
-      Wiki::Commit.create_content!(
+      search_tag = create(:tag, primary_name: 'spec_wiki_title_2')
-          tag_name: create(:tag_name, name: 'spec_wiki_title_2'),
+      seed_wiki_page(
+          tag_name: search_tag.tag_name('ja'),
           body: 'search body 2',
           created_by_user: user,
           message: 'init')
 
-      Wiki::Commit.create_content!(
+      seed_wiki_page(
           tag_name: create(:tag_name, name: 'unrelated_title'),
           body: 'unrelated body',
           created_by_user: user,
@@ -516,7 +439,7 @@ RSpec.describe 'Wiki API', type: :request do
     it 'raises because redirect revisions are deprecated' do
       target_tag_name = create(:tag_name, name: 'redirect_deprecated_target')
       target =
-          Wiki::Commit.create_content!(
+          seed_wiki_page(
               tag_name: target_tag_name,
               body: 'target',
               created_by_user: user,
@@ -539,7 +462,7 @@ RSpec.describe 'Wiki API', type: :request do
     linked_tag = create(:tag, primary_tag_name: linked_tag_name, category: :general)
 
     linked_page =
-        Wiki::Commit.create_content!(
+        seed_wiki_page(
             tag_name: linked_tag_name,
             body: 'before',
             created_by_user: user,

backend/spec/requests/wiki_title_collision_spec.rb

@@ -1,6 +1,7 @@
 require 'rails_helper'
 
 RSpec.describe 'Wiki title collision', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
 
   def auth_headers user
@@ -8,7 +9,7 @@ RSpec.describe 'Wiki title collision', type: :request do
   end
 
   def create_wiki_page title:, body:
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,
@@ -43,20 +44,18 @@ RSpec.describe 'Wiki title collision', type: :request do
     expect(source.wiki_versions.count).to eq(source_version_count)
   end
 
-  it 'returns 422 when creating wiki with existing title' do
+  it 'rejects frozen creation with an existing title without adding history' do
     create_wiki_page(title: 'Help:wiki_collision_create', body: 'already exists')
 
-    expect {
+    expect do
       post '/wiki',
-           params: {
+           params: { title: 'Help:wiki_collision_create', body: 'new body',
-             title: 'Help:wiki_collision_create',
+                     message: 'duplicate create' },
-             body: 'new body',
-             message: 'duplicate create',
-           },
            headers: auth_headers(user)
-    }
+    end.to change(WikiPage, :count).by(0)
-        .not_to change(WikiPage, :count)
+        .and change(WikiRevision, :count).by(0)
+        .and change(WikiVersion, :count).by(0)
 
-    expect(response).to have_http_status(:unprocessable_entity)
+    expect(response.status).to be_between(400, 499)
   end
 end

backend/spec/requests/wiki_unmigrated_contract_spec.rb

@@ -1,115 +1,78 @@
 require 'rails_helper'
 
 RSpec.describe 'Unmigrated Wiki compatibility', type: :request do
+  include WikiRecords
   let!(:user) { create_member_user! }
   let!(:tag_name) { create(:tag_name, name: 'Help_contract') }
   let!(:page) do
-    Wiki::Commit.create_content!(tag_name:, body: 'before', created_by_user: user)
+    seed_wiki_page(tag_name:, body: 'before', created_by_user: user)
   end
   let!(:first_revision) { page.current_revision }
   let!(:last_revision) do
-    Wiki::Commit.content!(page:, body: 'after', created_user: user,
+    Wiki::Commit.legacy_content!(page:, body: 'after', created_user: user,
                                  message: 'legacy edit', base_revision_id: first_revision.id)
   end
 
   before { expect(TagDescription.exists?(id: page.id)).to be(false) }
 
-  it 'keeps a Tag-linked legacy page in the legacy domain when its title changes' do
+  it 'rejects standalone updates even after a Tag is linked to the legacy page' do
     create(:tag, primary_tag_name: tag_name)
+    original = page.reload.attributes
 
     expect do
       put "/wiki/#{ page.id }",
           params: { title: 'legacy_tag_renamed', body: 'changed legacy body',
                     message: 'legacy rename', base_revision_id: last_revision.id },
           headers: { 'X-Transfer-Code' => user.inheritance_code }
-    end.to change(WikiRevision, :count).by(1)
+    end.to change(WikiRevision, :count).by(0)
-        .and change(WikiVersion, :count).by(1)
+        .and change(WikiVersion, :count).by(0)
         .and change(TagDescription, :count).by(0)
         .and change(TagDescriptionVersion, :count).by(0)
 
-    expect(response).to have_http_status(:ok)
+    expect(response).to have_http_status(:unprocessable_entity)
-    expect(page.reload).to have_attributes(body: 'changed legacy body')
+    expect(page.reload.attributes).to eq(original)
-    expect(page.title).to eq('legacy_tag_renamed')
+    expect(page.current_revision).to have_attributes(message: 'legacy edit')
-    expect(page.current_revision).to have_attributes(message: 'legacy rename')
   end
 
-  it 'shows legacy current and historical content by ID' do
+  include TagGroupRecords
-    get "/wiki/#{ page.id }"
-    expect(response).to have_http_status(:ok)
-    expect(json).to include('body' => 'after', 'revision_id' => last_revision.id,
-                           'pred' => first_revision.id, 'succ' => nil)
-    get "/wiki/#{ page.id }", params: { version: first_revision.id }
-    expect(response).to have_http_status(:ok)
-    expect(json).to include('body' => 'before', 'revision_id' => first_revision.id,
-                           'pred' => nil, 'succ' => last_revision.id)
-  end
 
-  it 'shows legacy current and historical content by title' do
+  [:id, :title].each do |lookup|
-    get "/wiki/title/#{ tag_name.name }"
+    [nil, :historical].each do |edition|
-    expect(response).to have_http_status(:ok)
+      it "rejects legacy #{ lookup } #{ edition || 'current' } without legacy SELECTs" do
-    expect(json).to include('body' => 'after', 'revision_id' => last_revision.id)
+        path = lookup == :id ? "/wiki/#{ page.id }" : "/wiki/title/#{ tag_name.name }"
-    get "/wiki/title/#{ tag_name.name }", params: { version: first_revision.id }
+        params = edition ? { version: first_revision.id } : { }
-    expect(response).to have_http_status(:ok)
+        without_group_legacy_reads { get path, params: }
-    expect(json).to include('body' => 'before', 'revision_id' => first_revision.id)
-  end
-
-  it 'recognises legacy IDs' do
-    get "/wiki/#{ page.id }/exists"
-    expect(response).to have_http_status(:no_content)
-  end
-
-  it 'recognises legacy titles' do
-    get "/wiki/title/#{ tag_name.name }/exists"
-    expect(response).to have_http_status(:no_content)
-  end
-
-  it 'diffs legacy revisions with explicit and current target' do
-    [last_revision.id, nil].each do |to|
-      get "/wiki/#{ page.id }/diff", params: { from: first_revision.id, to: }
-      expect(response).to have_http_status(:ok)
-      expect(json).to include(
-          'wiki_page_id' => page.id, 'title' => tag_name.name,
-          'older_revision_id' => first_revision.id, 'newer_revision_id' => last_revision.id,
-          'diff' => [{ 'type' => 'removed', 'content' => 'before' },
-                     { 'type' => 'added', 'content' => 'after' }])
-    end
-  end
-
-  describe 'revision resource scope' do
-    let!(:other_page) do
-      Wiki::Commit.create_content!(
-          tag_name: create(:tag_name, name: 'Help_other_contract'),
-          body: 'other page history', created_by_user: user)
-    end
-    let(:other_revision) { other_page.current_revision }
-
-    it 'returns 404 when show specifies another page revision' do
-      get "/wiki/#{ page.id }", params: { version: other_revision.id }
-      expect(response).to have_http_status(:not_found)
-    end
-
-    it 'returns 404 when diff from belongs to another page' do
-      get "/wiki/#{ page.id }/diff",
-          params: { from: other_revision.id, to: last_revision.id }
-      expect(response).to have_http_status(:not_found)
-    end
-
-    it 'returns 404 when diff to belongs to another page' do
-      get "/wiki/#{ page.id }/diff",
-          params: { from: first_revision.id, to: other_revision.id }
         expect(response).to have_http_status(:not_found)
       end
     end
 
-  it 'retains legacy history metadata and ordering' do
+    it "does not recognise legacy #{ lookup } existence" do
-    get '/wiki/changes', params: { id: page.id }
+      path = lookup == :id ? "/wiki/#{ page.id }" : "/wiki/title/#{ tag_name.name }"
+      without_group_legacy_reads { get "#{ path }/exists" }
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  ['/wiki', '/wiki/search', '/wiki/changes'].each do |path|
+    it "excludes unmigrated content from #{ path } without legacy SELECTs" do
+      without_group_legacy_reads { get path }
       expect(response).to have_http_status(:ok)
-    expect(json.map { |row| row.fetch('revision_id') }).to eq(
+      expect(json).to eq([])
-        [last_revision.id, first_revision.id])
+    end
-    expect(json.first).to include(
+  end
-        'pred' => first_revision.id, 'succ' => nil, 'kind' => 'content',
+
-        'message' => 'legacy edit', 'timestamp' => last_revision.created_at.iso8601(3),
+  it 'returns empty scoped history without legacy SELECTs' do
-        'wiki_page' => { 'id' => page.id, 'title' => tag_name.name, 'deprecated_at' => nil },
+    without_group_legacy_reads { get '/wiki/changes', params: { id: page.id } }
-        'user' => { 'id' => user.id, 'name' => user.name })
+    expect(response).to have_http_status(:ok)
+    expect(json).to eq([])
+  end
+
+  [false, true].each do |explicit|
+    it "rejects legacy diff with #{ explicit ? 'explicit' : 'current' } target" do
+      params = { from: first_revision.id }
+      params[:to] = last_revision.id if explicit
+      without_group_legacy_reads { get "/wiki/#{ page.id }/diff", params: }
+      expect(response).to have_http_status(:not_found)
+    end
   end
 end

backend/spec/services/shared_resource_id_allocator_mysql_spec.rb

@@ -0,0 +1,143 @@
+require 'rails_helper'
+require 'timeout'
+
+RSpec.describe 'Shared resource IDs across MySQL connections', type: :model do
+  self.use_transactional_tests = false
+
+  before do
+    expect(Rails.env.test?).to be(true)
+    expect(ApplicationRecord.connection.adapter_name).to match(/mysql/i)
+    expect(ApplicationRecord.connection_pool.size).to be >= 3
+    @prefix = "shared_ids_#{ SecureRandom.hex(8) }"
+    @names = [0, 1].map { create(:tag_name, name: "#{ @prefix }_#{ _1 }") }
+    @tag = Tag.create!(tag_name_id: @names.first.id, category: :general)
+    @names.first.update!(tag_id: @tag.id)
+    @threads = []
+    @release = Queue.new
+  end
+
+  after do
+    @release << true if @release
+    begin
+      Array(@threads).each do |thread|
+        raise 'Shared ID worker did not finish' unless thread.join(15)
+      end
+    ensure
+      if @prefix
+        ExternalTag.where(name: "#{ @prefix }_external").delete_all
+        TagGroup.where(name: "#{ @prefix }_group").delete_all
+      end
+      TagDescription.where(tag_id: @tag.id).delete_all if @tag
+      if @names
+        ids = @names.map(&:id)
+        TagName.where(id: ids).update_all(tag_id: nil)
+        Tag.where(tag_name_id: ids).delete_all
+        TagName.where(id: ids).delete_all
+      end
+    end
+  end
+
+  def await_queue queue
+    Timeout.timeout(15) { queue.pop }
+  end
+
+  def worker &block
+    Thread.new do
+      Thread.current.report_on_exception = false
+      ApplicationRecord.connection_pool.with_connection(&block)
+    end.tap { @threads << _1 }
+  end
+
+  def create_resource kind
+    case kind
+    when :tag
+      Tag.create!(tag_name_id: @names.last.id, category: :general)
+    when :external
+      ExternalTag.create!(platform: :nico, name: "#{ @prefix }_external")
+    when :description
+      TagDescription.create!(tag: @tag, language_code: 'ja', body: '', version_no: 1)
+    when :group
+      TagGroup.create!(name: "#{ @prefix }_group", version_no: 1)
+    end
+  end
+
+  def hold_creation kind, rollback: false
+    ready = Queue.new
+    thread = worker do |connection|
+      id = nil
+      connection.transaction do
+        lock_name = nil
+        subscriber = lambda do |*args|
+          match = args.last.fetch(:sql).match(/GET_LOCK\('([^']+)'/)
+          lock_name = match[1] if match
+        end
+        ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+          id = create_resource(kind).id
+        end
+        ready << [id, connection.select_value('SELECT CONNECTION_ID()').to_i, lock_name]
+        await_queue(@release)
+        raise ActiveRecord::Rollback if rollback
+      end
+      id
+    end
+    [thread, await_queue(ready)]
+  end
+
+  def result thread
+    raise 'Shared ID worker did not finish' unless thread.join(15)
+    thread.value
+  end
+
+  { tags: [:external, :tag], wiki: [:description, :group] }.each do |space, kinds|
+    [false, true].each do |rollback|
+      it "serialises #{ space } inserts through #{ rollback ? 'rollback' : 'commit' }" do
+        tables = SharedResourceIdAllocator::SPACES.fetch(space.to_s)
+        maxima = tables.map do |table|
+          ApplicationRecord.connection.select_value("SELECT MAX(id) FROM #{ table }").to_i
+        end
+        first, (first_id, connection_id, lock_name) = hold_creation(kinds.first, rollback:)
+        expect(first_id).to eq(maxima.max + 1)
+        connection = ApplicationRecord.connection
+        quoted_lock = connection.quote(lock_name)
+        expect(connection.select_value("SELECT IS_USED_LOCK(#{ quoted_lock })").to_i)
+            .to eq(connection_id)
+
+        started = Queue.new
+        second = worker do |other|
+          started << other.select_value('SELECT CONNECTION_ID()').to_i
+          create_resource(kinds.last).id
+        end
+        expect(await_queue(started)).not_to eq(connection_id)
+        @release << true
+        expect(result(first)).to eq(first_id)
+        expect(result(second)).to eq(rollback ? first_id : first_id + 1)
+        expect(connection.select_value("SELECT IS_FREE_LOCK(#{ quoted_lock })").to_i).to eq(1)
+      end
+    end
+  end
+
+  it 'allows the other ID space to commit while the first space remains locked' do
+    first, (_id, connection_id, lock_name) = hold_creation(:external)
+    second = worker { create_resource(:group).id }
+    expect(result(second)).to be_positive
+    connection = ApplicationRecord.connection
+    quoted_lock = connection.quote(lock_name)
+    expect(connection.select_value("SELECT IS_USED_LOCK(#{ quoted_lock })").to_i)
+        .to eq(connection_id)
+    @release << true
+    result(first)
+  end
+
+  it 'raises on a real lock acquisition failure without inserting a record' do
+    first, (_id, _connection_id, lock_name) = hold_creation(:external, rollback: true)
+    stub_const('SharedResourceIdAllocator::LOCK_TIMEOUT', 0)
+    expect { create_resource(:external) }.to raise_error(ActiveRecord::LockWaitTimeout)
+    expect(ExternalTag.where(name: "#{ @prefix }_external")).not_to exist
+    @release << true
+    result(first)
+    connection = ApplicationRecord.connection
+    quoted_lock = connection.quote(lock_name)
+    expect(connection.select_value("SELECT IS_FREE_LOCK(#{ quoted_lock })").to_i)
+        .to eq(1)
+  end
+end

backend/spec/services/shared_resource_id_allocator_spec.rb

@@ -0,0 +1,88 @@
+require 'rails_helper'
+
+RSpec.describe SharedResourceIdAllocator do
+  let(:record) { build(:external_tag) }
+  let(:connection) { double('connection') }
+  let(:transaction) { double('transaction', open?: true) }
+  let(:callbacks) { { } }
+  let(:sql) { [] }
+
+  before do
+    config = double('config', database: 'test_shared_ids')
+    allow(connection).to receive_message_chain(:pool, :db_config).and_return(config)
+    allow(connection).to receive(:quote) { "'#{ _1 }'" }
+    allow(connection).to receive(:quote_table_name) { "`#{ _1 }`" }
+    allow(connection).to receive(:select_value) do |statement|
+      sql << statement
+      if statement.include?('GET_LOCK') || statement.include?('RELEASE_LOCK')
+        1
+      elsif statement.include?('`tags`')
+        8
+      else
+        3
+      end
+    end
+    allow(ExternalTag).to receive(:connection).and_return(connection)
+    allow(ExternalTag).to receive(:current_transaction).and_return(transaction)
+    allow(ExternalTag).to receive(:uncached).and_yield
+    [:after_commit, :after_rollback].each do |event|
+      allow(transaction).to receive(event) { |&callback| callbacks[event] = callback }
+    end
+  end
+
+  [:after_commit, :after_rollback].each do |event|
+    it "holds the shared lock until #{ event }" do
+      described_class.assign!(record)
+      expect(record.id).to eq(9)
+      expect(sql.grep(/RELEASE_LOCK/)).to be_empty
+      expect(sql.grep(/FOR UPDATE/).size).to eq(2)
+      callbacks.fetch(event).call
+      expect(sql.grep(/RELEASE_LOCK/).size).to eq(1)
+    end
+  end
+
+  it 'does not silently proceed after an acquisition timeout' do
+    allow(connection).to receive(:select_value).and_return(0)
+    expect { described_class.assign!(record) }.to raise_error(ActiveRecord::LockWaitTimeout)
+    expect(record.id).to be_nil
+    expect(callbacks).to be_empty
+  end
+
+  it 'releases a successfully acquired lock when allocation fails and rolls back' do
+    allow(connection).to receive(:select_value).with(/FOR UPDATE/).and_raise('query failed')
+    expect { described_class.assign!(record) }.to raise_error(RuntimeError, 'query failed')
+    callbacks.fetch(:after_rollback).call
+    expect(sql.grep(/RELEASE_LOCK/).size).to eq(1)
+  end
+
+  it 'preserves explicitly supplied historical IDs' do
+    record.id = 5
+    described_class.assign!(record)
+    expect(record.id).to eq(5)
+    expect(sql.grep(/FOR UPDATE/)).to be_empty
+    callbacks.fetch(:after_commit).call
+  end
+
+  it 'uses the same named lock within each space and different locks between spaces' do
+    locks = [Tag, ExternalTag, TagDescription, TagGroup].map do |model|
+      allow(model).to receive(:connection).and_return(connection)
+      allow(model).to receive(:current_transaction).and_return(transaction)
+      allow(model).to receive(:uncached).and_yield
+      record = model.new(id: 50)
+      described_class.assign!(record)
+      statement = sql.grep(/GET_LOCK/).last
+      callbacks.fetch(:after_commit).call
+      statement
+    end
+    expect(locks[0]).to eq(locks[1])
+    expect(locks[2]).to eq(locks[3])
+    expect(locks[0]).not_to eq(locks[2])
+  end
+
+  it 'reports lock release failures' do
+    described_class.assign!(record)
+    allow(connection).to receive(:select_value).with(/RELEASE_LOCK/).and_return(nil)
+    expect { callbacks.fetch(:after_commit).call }
+        .to raise_error(ActiveRecord::ActiveRecordError, /lock release failed/)
+  end
+end

backend/spec/services/wiki/commit_integrity_spec.rb

@@ -2,41 +2,42 @@ require 'digest'
 require 'rails_helper'
 
 RSpec.describe Wiki::Commit do
+  include WikiRecords
   let(:user) { create_member_user! }
 
   def create_page title:, body: 'initial body'
-    described_class.create_content!(
+    seed_wiki_page(
-        tag_name: create(:tag_name, name: title),
+        tag_name: create(:tag, primary_name: title).tag_name('ja'),
         body:,
         created_by_user: user,
         message: 'init')
   end
 
   describe '.create_content!' do
-    it 'creates page, revision, and version with normalised body' do
+    it 'rejects standalone Help creation without adding page or history' do
-      expect {
+      name = create(:tag_name, name: 'Help:frozen_service')
-        described_class.create_content!(
+      counts = [WikiPage.count, WikiRevision.count, WikiVersion.count]
-            tag_name: create(:tag_name, name: 'commit_integrity_create'),
+      expect do
-            body: "a\r\nb\r\n\r\n",
+        described_class.create_content!(tag_name: name, body: 'initial', created_by_user: user)
-            created_by_user: user,
+      end.to raise_error(ActiveRecord::RecordInvalid)
-            message: 'init')
+      expect([WikiPage.count, WikiRevision.count, WikiVersion.count]).to eq(counts)
-      }
+    end
-          .to change(WikiPage, :count).by(1)
+
+    it 'keeps the internal compatibility writer available' do
+      name = create(:tag_name, name: 'タググループ:compatibility_service')
+      page = nil
+      expect do
+        page = described_class.create_legacy_content!(
+            tag_name: name, body: 'initial', created_by_user: user)
+      end.to change(WikiPage, :count).by(1)
           .and change(WikiRevision, :count).by(1)
           .and change(WikiVersion, :count).by(1)
-
+      expect(page.current_revision.body).to eq('initial')
-      page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'commit_integrity_create' })
+      expect(page.wiki_versions.sole.body).to eq('initial')
-      revision = page.current_revision
-      version = page.wiki_versions.order(:version_no).last
-
-      expect(page.body).to eq("a\nb")
-      expect(revision.lines_count).to eq(2)
-      expect(version.body).to eq("a\nb")
-      expect(version.reason).to eq('init')
     end
 
     it 'rejects body that becomes blank after normalisation' do
-      tag_name = create(:tag_name, name: 'commit_integrity_blank')
+      tag_name = create(:tag, primary_name: 'commit_integrity_blank').tag_name('ja')
 
       expect {
         described_class.create_content!(
@@ -52,6 +53,17 @@ RSpec.describe Wiki::Commit do
   end
 
   describe '.content!' do
+    it 'rejects standalone Help updates without modifying histories' do
+      page = seed_wiki_page(tag_name: create(:tag_name, name: 'Help:standalone'),
+                            body: 'before', created_by_user: user)
+      counts = [WikiRevision.count, WikiVersion.count]
+      expect do
+        described_class.content!(page:, body: 'after', created_user: user)
+      end.to raise_error(ActiveRecord::RecordInvalid)
+      expect(page.reload.body).to eq('before')
+      expect([WikiRevision.count, WikiVersion.count]).to eq(counts)
+    end
+
     it 'updates page body, revision, and version' do
       page = create_page(title: 'commit_integrity_update', body: 'before')
       current_id = page.current_revision.id
@@ -80,7 +92,7 @@ RSpec.describe Wiki::Commit do
       tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
-          described_class.create_content!(
+          seed_wiki_page(
               tag_name:,
               body: 'before',
               created_by_user: user,

backend/spec/services/wiki/commit_spec.rb

@@ -1,12 +1,13 @@
 require 'rails_helper'
 
 RSpec.describe Wiki::Commit do
+  include WikiRecords
   let(:user) { create_member_user! }
 
   def create_page(title: 'commit_spec_page', body: 'initial body')
-    tag_name = create(:tag_name, name: title)
+    tag_name = create(:tag, primary_name: title).tag_name('ja')
 
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name:,
         body:,
         created_by_user: user,
@@ -84,7 +85,7 @@ RSpec.describe Wiki::Commit do
       tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
-          described_class.create_content!(
+          seed_wiki_page(
               tag_name:,
               body: 'before',
               created_by_user: user,
@@ -111,7 +112,7 @@ RSpec.describe Wiki::Commit do
       tag = create(:tag, primary_tag_name: tag_name, category: :general)
 
       page =
-          described_class.create_content!(
+          seed_wiki_page(
               tag_name:,
               body: 'before',
               created_by_user: user,

backend/spec/services/wiki_version_recorder_spec.rb

@@ -1,10 +1,11 @@
 require 'rails_helper'
 
 RSpec.describe WikiVersionRecorder do
+  include WikiRecords
   let(:user) { create_member_user! }
 
   def create_page title:, body: 'body'
-    Wiki::Commit.create_content!(
+    seed_wiki_page(
         tag_name: create(:tag_name, name: title),
         body:,
         created_by_user: user,

backend/spec/support/wiki_records.rb

@@ -0,0 +1,20 @@
+# Historical records must remain seedable after application creation is frozen.
+module WikiRecords
+  def seed_wiki_page(tag_name:, body:, created_by_user:, message: nil)
+    page = WikiPage.create!(tag_name:, body:,
+                            created_user: created_by_user, updated_user: created_by_user)
+    revision = Wiki::Commit.legacy_content!(
+        page:, body:, created_user: created_by_user, message:)
+    if tag_name.tag && tag_name.language_code == 'ja'
+      TagDescription.create!(
+          id: page.id, tag: tag_name.tag, language_code: 'ja', body: page.reload.body,
+          version_no: 1, created_by_user_id: created_by_user.id,
+          updated_by_user_id: created_by_user.id)
+      TagDescriptionVersion.create!(
+          id: revision.id, tag_id: tag_name.tag_id, language_code: 'ja',
+          version_no: 1, event_type: 'create', body: page.body,
+          created_by_user_id: created_by_user.id, created_at: revision.created_at)
+    end
+    page
+  end
+end

frontend/.gitignore

@@ -22,3 +22,5 @@ dist-ssr
 *.njsproj
 *.sln
 *.sw?
+
+/help

frontend/package-lock.json

@@ -38,6 +38,7 @@
         "remark-gfm": "^4.0.1",
         "tailwind-merge": "^3.3.0",
         "unist-util-visit-parents": "^6.0.1",
+        "yaml": "^2.9.1",
         "zustand": "^5.0.8"
       },
       "devDependencies": {
@@ -2060,9 +2061,6 @@
         "arm"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2077,9 +2075,6 @@
         "arm"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2094,9 +2089,6 @@
         "arm64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2111,9 +2103,6 @@
         "arm64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2128,9 +2117,6 @@
         "loong64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2145,9 +2131,6 @@
         "loong64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2162,9 +2145,6 @@
         "ppc64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2179,9 +2159,6 @@
         "ppc64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2196,9 +2173,6 @@
         "riscv64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2213,9 +2187,6 @@
         "riscv64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2230,9 +2201,6 @@
         "s390x"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2247,9 +2215,6 @@
         "x64"
       ],
       "dev": true,
-      "libc": [
-        "glibc"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -2264,9 +2229,6 @@
         "x64"
       ],
       "dev": true,
-      "libc": [
-        "musl"
-      ],
       "license": "MIT",
       "optional": true,
       "os": [
@@ -9114,10 +9076,9 @@
       "license": "ISC"
     },
     "node_modules/yaml": {
-      "version": "2.8.3",
+      "version": "2.9.1",
-      "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.8.3.tgz",
+      "resolved": "https://registry.npmjs.org/yaml/-/yaml-2.9.1.tgz",
-      "integrity": "sha512-AvbaCLOO2Otw/lW5bmh9d/WEdcDFdQp2Z2ZUH3pX9U2ihyUY0nvLv7J6TrWowklRGPYbB/IuIMfYgxaCPg5Bpg==",
+      "integrity": "sha512-3NxN8+78OdzbT7C/WjGsyfPAtJaN3FNDsWxv7Y7mcDsT/oOmgW8BpyQQFFBnvZE3j9Y2Sdz1ULFLezL7Eb2yFw==",
-      "dev": true,
       "license": "ISC",
       "bin": {
         "yaml": "bin.mjs"

frontend/package.json

@@ -42,6 +42,7 @@
     "remark-gfm": "^4.0.1",
     "tailwind-merge": "^3.3.0",
     "unist-util-visit-parents": "^6.0.1",
+    "yaml": "^2.9.1",
     "zustand": "^5.0.8"
   },
   "devDependencies": {

frontend/scripts/help-assets.test.ts

@@ -0,0 +1,112 @@
+import { mkdir, mkdtemp, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import path from 'node:path'
+import { afterAll, afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { generateHelpAssets } from './help-assets'
+
+import type { ArticleMeta, HelpChange, HelpSearchEntry, HelpTitleIndex } from '@/lib/help'
+
+vi.hoisted (() => {
+  vi.stubGlobal ('Uint8Array', Object.getPrototypeOf (new TextEncoder ().encode ('')).constructor)
+})
+afterAll (() => vi.unstubAllGlobals ())
+
+
+const readAsset = <T,> (modules: Map<string, string>, name: string): T => {
+  const source = modules.get (`virtual:help/${ name }`)!
+  const argument = source.slice ('export default JSON.parse('.length, -1)
+  return JSON.parse (JSON.parse (argument))
+}
+
+
+describe ('Build-time Help assets', () => {
+  let root: string
+
+  beforeEach (async () => {
+    root = await mkdtemp (path.join (tmpdir (), 'btrc-help-assets-'))
+  })
+
+  afterEach (async () => {
+    await rm (root, { recursive: true, force: true })
+  })
+
+  const writeArticle = async (
+      identifier: string,
+      editions: Record<string, string>,
+      current = '2026-10-02.10',
+  ) => {
+    const articleRoot = path.join (root, identifier)
+    const editionRoot = path.join (articleRoot, 'editions', 'ja')
+    await mkdir (editionRoot, { recursive: true })
+    await writeFile (path.join (articleRoot, 'article.yml'), [
+	`identifier: ${ identifier }`, 'canonical_language: ja', 'title: stale YAML title',
+	'languages:', '  ja:', `    current_edition: ${ current }`].join ('\n'))
+    await Promise.all (Object.entries (editions).map (([edition, source]) =>
+	writeFile (path.join (editionRoot, `${ edition }.mdx`), source)))
+  }
+
+  it ('generates current search and ordered published history from each edition H1', async () => {
+    await writeArticle ('guide', {
+	'2026-10-01': '# 旧ホーム\n\n過去本文',
+	'2026-10-02': '# ホーム\n\n最初の同日版',
+	'2026-10-02.2': '# ホーム\n\n第二版',
+	'2026-10-02.3': '# ホーム\n\n第三版',
+	'2026-10-02.10': '\uFEFF# 最新ホーム\r\n\r\n現在本文\r\n# 別見出し',
+	'2026-10-02.11': '# 未公開\n\n検索に含めない' })
+    const { modules } = await generateHelpAssets (root)
+    const articles = readAsset<Record<string, ArticleMeta>> (modules, 'articles')
+    expect (articles.guide.languages.ja).toEqual ({
+	currentEdition: '2026-10-02.10', publishedEditions: [
+	    '2026-10-01', '2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10'] })
+    expect (readAsset<Record<string, HelpSearchEntry[]>> (modules, 'search').ja).toEqual ([{
+	identifier: 'guide', edition: '2026-10-02.10', title: '最新ホーム',
+	body: '\r\n現在本文\r\n# 別見出し' }])
+    const changes = readAsset<Record<string, HelpChange[]>> (modules, 'changes').ja
+    expect (changes.map (row => [row.edition, row.title, row.pred, row.change, row.date]))
+	.toEqual ([
+	    ['2026-10-02.10', '最新ホーム', '2026-10-02.3', 'update', '2026-10-02'],
+	    ['2026-10-02.3', 'ホーム', '2026-10-02.2', 'update', '2026-10-02'],
+	    ['2026-10-02.2', 'ホーム', '2026-10-02', 'update', '2026-10-02'],
+	    ['2026-10-02', 'ホーム', '2026-10-01', 'update', '2026-10-02'],
+	    ['2026-10-01', '旧ホーム', null, 'new', '2026-10-01']])
+    const titles = readAsset<Record<string, HelpTitleIndex>> (modules, 'titles').ja
+    expect (titles).toEqual ({ '旧ホーム': ['guide'], 'ホーム': ['guide'],
+	'最新ホーム': ['guide'] })
+    expect (modules.get ('virtual:help/loaders')).not.toContain ('2026-10-02.11')
+    expect (modules.get ('virtual:help/loaders')).toContain ('2026-10-02.10.mdx?raw')
+    expect (modules.get ('virtual:help/search')).not.toContain ('import(')
+  })
+
+  it ('retains ambiguous title identifiers and normalises width and case', async () => {
+    await writeArticle ('alpha', { '2026-10-02': '# ＨＯＭＥ\n本文' }, '2026-10-02')
+    await writeArticle ('beta', { '2026-10-02': '# Home\n本文' }, '2026-10-02')
+    const { modules } = await generateHelpAssets (root)
+    expect (readAsset<Record<string, HelpTitleIndex>> (modules, 'titles').ja.home)
+	.toEqual (['alpha', 'beta'])
+    expect (readAsset<Record<string, HelpChange[]>> (modules, 'changes').ja
+	.map (row => row.identifier)).toEqual (['alpha', 'beta'])
+  })
+
+  it ('rejects missing current files during generation', async () => {
+    await writeArticle ('guide', { '2026-10-02': '# ホーム' })
+    await expect (generateHelpAssets (root)).rejects.toThrow ('Missing current Help edition')
+  })
+
+  it.each (['本文\n# 遅い見出し', '#   \n本文']) (
+      'rejects missing leading H1 at build time: %s', async source => {
+	await writeArticle ('guide', { '2026-10-02.10': source })
+	await expect (generateHelpAssets (root)).rejects.toThrow ('Missing leading Help H1')
+      })
+
+  it ('rejects absent canonical metadata instead of generating incomplete assets', async () => {
+    await writeArticle ('guide', { '2026-10-02.10': '# ホーム' })
+    await writeFile (path.join (root, 'guide', 'article.yml'),
+	'identifier: guide\nlanguages:\n  ja:\n    current_edition: 2026-10-02.10')
+    await expect (generateHelpAssets (root)).rejects.toThrow ('Invalid Help metadata')
+  })
+
+  it ('rejects an empty Help checkout', async () => {
+    await expect (generateHelpAssets (root)).rejects.toThrow ('No Help articles found')
+  })
+})

frontend/scripts/help-assets.ts

@@ -0,0 +1,192 @@
+import { readFile, readdir } from 'node:fs/promises'
+import path from 'node:path'
+import { normalizePath as normalisePath } from 'vite'
+import { parse as parseYAML } from 'yaml'
+
+import type { Plugin } from 'vite'
+
+type Language = { currentEdition: string; publishedEditions: string[] }
+type Article = {
+    identifier: string
+    canonicalLanguage: string
+    languages: Record<string, Language> }
+type Text = { title: string; body: string }
+type SearchEntry = Text & { identifier: string; edition: string }
+type Change = {
+    identifier: string
+    edition: string
+    title: string
+    pred: string | null
+    change: 'new' | 'update'
+    date: string }
+type RawArticle = {
+    identifier: string
+    canonical_language: string
+    languages: Record<string, { current_edition: string }> }
+
+const prefix = 'virtual:help/'
+
+
+const compareEditions = (a: string, b: string): number => {
+  const [dateA, revisionA = '1'] = a.split ('.')
+  const [dateB, revisionB = '1'] = b.split ('.')
+  return dateA.localeCompare (dateB) || Number (revisionA) - Number (revisionB)
+}
+
+
+const validateEdition = (edition: string): void => {
+  const [date, revision = '1'] = edition.split ('.')
+  if (!(/^\d{4}-\d{2}-\d{2}(?:\.[1-9]\d*)?$/.test (edition))
+      || new Date (date).toISOString ().slice (0, 10) !== date
+      || !(Number.isSafeInteger (Number (revision))))
+    throw new Error (`Invalid Help edition: ${ edition }`)
+}
+
+
+export const generateHelpAssets = async (
+    root: string,
+): Promise<{ modules: Map<string, string>; files: string[] }> => {
+  const modules = new Map<string, string> ()
+  const files: string[] = [root]
+  const articles: Record<string, Article> = Object.create (null)
+  const search: Record<string, SearchEntry[]> = Object.create (null)
+  const changes: Record<string, Change[]> = Object.create (null)
+  const titles: Record<string, Record<string, string[]>> = Object.create (null)
+  const components: string[] = []
+  const sources: string[] = []
+  const texts: string[] = []
+  const directories = (await readdir (root, { withFileTypes: true }))
+      .filter (entry => entry.isDirectory () && !(entry.name.startsWith ('.')))
+      .sort ((a, b) => a.name.localeCompare (b.name))
+
+  for (const directory of directories)
+  {
+    const articlePath = path.join (root, directory.name, 'article.yml')
+    files.push (articlePath)
+    const raw = parseYAML (await readFile (articlePath, 'utf8')) as RawArticle | null
+    if (raw == null || raw.identifier !== directory.name
+	|| typeof raw.canonical_language !== 'string'
+	|| raw.languages == null || typeof raw.languages !== 'object'
+	|| !(Object.hasOwn (raw.languages, raw.canonical_language)))
+      throw new Error (`Invalid Help metadata: ${ articlePath }`)
+
+    const article: Article = {
+	identifier: raw.identifier,
+	canonicalLanguage: raw.canonical_language,
+	languages: Object.create (null) }
+    articles[raw.identifier] = article
+
+    for (const [language, metadata] of Object.entries (raw.languages))
+    {
+      if (!(/^[a-zA-Z0-9-]+$/.test (language))
+	  || typeof metadata?.current_edition !== 'string')
+	throw new Error (`Invalid Help language: ${ articlePath }/${ language }`)
+
+      const currentEdition = metadata.current_edition
+      validateEdition (currentEdition)
+      const editionRoot = path.join (root, directory.name, 'editions', language)
+      files.push (editionRoot)
+      const editions = (await readdir (editionRoot)).filter (name => name.endsWith ('.mdx'))
+	  .map (name => name.slice (0, -4))
+      editions.forEach (validateEdition)
+      if (!(editions.includes (currentEdition)))
+	throw new Error (`Missing current Help edition: ${ editionRoot }/${ currentEdition }`)
+
+      const publishedEditions = editions
+	  .filter (edition => compareEditions (edition, currentEdition) <= 0)
+	  .sort (compareEditions)
+      article.languages[language] = { currentEdition, publishedEditions }
+      search[language] ??= []
+      changes[language] ??= []
+      titles[language] ??= Object.create (null)
+
+      for (const [index, edition] of publishedEditions.entries ())
+      {
+	const sourcePath = path.join (editionRoot, `${ edition }.mdx`)
+	files.push (sourcePath)
+	const mdx = (await readFile (sourcePath, 'utf8')).replace (/^\uFEFF/, '')
+	const heading = mdx.match (/^# +([^\r\n]+)(?:\r?\n|$)/)
+	if (heading == null || !(heading[1].trim ()))
+	  throw new Error (`Missing leading Help H1: ${ sourcePath }`)
+
+	const text = { title: heading[1].trim (), body: mdx.slice (heading[0].length) }
+	const key = JSON.stringify (`${ raw.identifier }/${ language }/${ edition }`)
+	const textId = `${ prefix }text/${ raw.identifier }/${ language }/${ edition }`
+	const componentId = JSON.stringify (normalisePath (sourcePath))
+	const sourceId = JSON.stringify (normalisePath (sourcePath) + '?raw')
+	modules.set (textId, `export default ${ JSON.stringify (text) }`)
+	texts.push (`${ key }: () => import(${ JSON.stringify (textId) })`)
+	components.push (`${ key }: () => import(${ componentId })`)
+	sources.push (`${ key }: () => import(${ sourceId })`)
+
+	if (edition === currentEdition)
+	  search[language].push ({ identifier: raw.identifier, edition, ...text })
+	changes[language].push ({ identifier: raw.identifier, edition, title: text.title,
+	    pred: publishedEditions[index - 1] ?? null,
+	    change: index === 0 ? 'new' : 'update', date: edition.split ('.')[0] })
+	const title = text.title.trim ().normalize ('NFKC').toLowerCase ()
+	const identifiers = titles[language][title] ??= []
+	if (!(identifiers.includes (raw.identifier)))
+	  identifiers.push (raw.identifier)
+      }
+    }
+  }
+
+  if (Object.keys (articles).length === 0)
+    throw new Error (`No Help articles found: ${ root }`)
+
+  Object.values (changes).forEach (rows => rows.sort ((a, b) =>
+      compareEditions (b.edition, a.edition) || a.identifier.localeCompare (b.identifier)))
+  for (const [name, data] of Object.entries ({ articles, search, changes, titles }))
+  {
+    modules.set (`${ prefix }${ name }`,
+	`export default JSON.parse(${ JSON.stringify (JSON.stringify (data)) })`)
+  }
+  modules.set (`${ prefix }loaders`, [
+      `export const components = { ${ components.join (',\n') } };`,
+      `export const sources = { ${ sources.join (',\n') } };`,
+      `export const texts = { ${ texts.join (',\n') } };`].join ('\n'))
+  return { modules, files }
+}
+
+
+export const helpAssets = (): Plugin => {
+  const state: { root: string; data?: ReturnType<typeof generateHelpAssets> } = { root: '' }
+  const data = () => state.data ??= generateHelpAssets (state.root)
+
+  return {
+      name: 'help-assets',
+      configResolved (config) {
+	state.root = path.resolve (config.root, 'help')
+      },
+      async buildStart () {
+	state.data = generateHelpAssets (state.root)
+	const generated = await data ()
+	generated.files.forEach (file => this.addWatchFile (file))
+      },
+      resolveId (id) {
+	return id.startsWith (prefix) ? `\0${ id }` : null
+      },
+      async load (id) {
+	if (!(id.startsWith (`\0${ prefix }`)))
+	  return null
+	const source = (await data ()).modules.get (id.slice (1))
+	if (source == null)
+	  throw new Error (`Unknown Help asset: ${ id.slice (1) }`)
+	return source
+      },
+      configureServer (server) {
+	server.watcher.add (state.root)
+	server.watcher.on ('all', (_event, file) => {
+	  if (!(file.startsWith (state.root + path.sep)) || !(/\.(mdx|yml)$/.test (file)))
+	    return
+	  state.data = undefined
+	  for (const module of server.moduleGraph.idToModuleMap.values ())
+	  {
+	    if (module.id?.startsWith (`\0${ prefix }`))
+	      server.moduleGraph.invalidateModule (module)
+	  }
+	  server.ws.send ({ type: 'full-reload' })
+	})
+      } }
+}

frontend/src/App.tsx

@@ -15,7 +15,6 @@ import { Toaster } from '@/components/ui/toaster'
 import { apiPost, isApiError } from '@/lib/api'
 import { applyClientAnimationMode,
 	 applyClientAppearance,
-	 type ClientAnimationMode,
 	 fetchUserThemeSlots,
 	 fetchUserSettings,
 	 getClientThemeMode,
@@ -25,7 +24,6 @@ import { applyClientAnimationMode,
 	 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'
@@ -34,12 +32,15 @@ import MaterialHistoryPage from '@/pages/materials/MaterialHistoryPage'
 import MaterialListPage from '@/pages/materials/MaterialListPage'
 import MaterialNewPage from '@/pages/materials/MaterialNewPage'
 import MaterialSyncSuppressionsPage from '@/pages/materials/MaterialSyncSuppressionsPage'
-// import MaterialSearchPage from '@/pages/materials/MaterialSearchPage'
 import MorePage from '@/pages/MorePage'
 import GekanatorPage from '@/pages/GekanatorPage'
 import NicoTagListPage from '@/pages/tags/NicoTagListPage'
 import NotFound from '@/pages/NotFound'
 import TOSPage from '@/pages/TOSPage.mdx'
+import HelpDetailPage from '@/pages/help/HelpDetailPage'
+import HelpChangesPage from '@/pages/help/HelpChangesPage'
+import HelpDiffPage from '@/pages/help/HelpDiffPage'
+import HelpListPage from '@/pages/help/HelpListPage'
 import PostDetailPage from '@/pages/posts/PostDetailPage'
 import PostHistoryPage from '@/pages/posts/PostHistoryPage'
 import PostNewPage from '@/pages/posts/PostNewPage'
@@ -60,6 +61,7 @@ import WikiSearchPage from '@/pages/wiki/WikiSearchPage'
 
 import type { Dispatch, FC, SetStateAction } from 'react'
 
+import type { ClientAnimationMode } from '@/lib/settings'
 import type { User } from '@/types'
 
 
@@ -69,9 +71,7 @@ const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
     setUser:        Dispatch<SetStateAction<User | null>> }) => {
   const location = useLocation ()
 
-  if (animationMode === 'off')
+  const routes = (
-    {
-      return (
       <Routes location={location}>
 	<Route path="/" element={<Navigate to="/posts" replace/>}/>
 	<Route path="/posts" element={<PostListPage/>}/>
@@ -99,6 +99,10 @@ const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
 	<Route path="/wiki/:id/edit" element={<WikiEditPage user={user}/>}/>
 	<Route path="/wiki/:id/diff" element={<WikiDiffPage/>}/>
 	<Route path="/wiki/changes" element={<WikiHistoryPage/>}/>
+	<Route path="/help" element={<HelpListPage/>}/>
+	<Route path="/help/changes" element={<HelpChangesPage/>}/>
+	<Route path="/help/:identifier/diff" element={<HelpDiffPage/>}/>
+	<Route path="/help/:identifier" element={<HelpDetailPage/>}/>
 	<Route path="/users/settings" element={<SettingPage user={user} setUser={setUser}/>}/>
 	<Route path="/settings" element={<Navigate to="/users/settings" replace/>}/>
 	<Route path="/tos" element={<TOSPage/>}/>
@@ -106,44 +110,13 @@ const RouteTransitionWrapper = ({ animationMode, user, setUser }: {
 	<Route path="/more" element={<MorePage/>}/>
 	<Route path="*" element={<NotFound/>}/>
       </Routes>)
-    }
+
+  if (animationMode === 'off')
+    return routes
 
   return (
       <AnimatePresence mode="wait">
-	<Routes location={location}>
+	{routes}
-	  <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>
       </AnimatePresence>)
 }
 
@@ -166,9 +139,9 @@ const RoutedApp: FC = () => {
       () => (
 	  animationMode === 'off'
 	  ? { duration: 0 }
-	  : animationMode === 'reduced'
+	  : (animationMode === 'reduced'
 	     ? { duration: .08, ease: 'linear' as const }
-	    : { duration: .2, ease: 'easeOut' as const }
+	     : { duration: .2, ease: 'easeOut' as const })
       ),
       [animationMode],
   )
@@ -285,10 +258,12 @@ const RoutedApp: FC = () => {
       </DialogueProvider>)
 }
 
+
 const router = createBrowserRouter ([{
     path: '*',
     element: <RoutedApp/> }])
 
+
 const App: FC = () => (
     <>
       <RouteBlockerOverlay/>
@@ -296,4 +271,5 @@ const App: FC = () => (
       <RouterProvider router={router}/>
     </>)
 
+
 export default App

frontend/src/components/TopNav.tsx

@@ -20,6 +20,7 @@ import type { FC, MouseEvent } from 'react'
 import type { Material, Menu, MenuVisibleItem, Tag, User } from '@/types'
 
 type Props = { user: User | null }
+type NavDensity = 'auto' | 'comfortable' | 'compact'
 
 
 export const menuOutline = (
@@ -40,6 +41,9 @@ export const menuOutline = (
 
   const materialFlg = /^\/materials\/\d+/.test (pathName)
 
+  const helpVsbl = /\/help\/((?!changes)[^\/?]+)/.test (pathName)
+  const helpIdentifier = pathName.split ('/')[2] ?? ''
+
   return [
       { name: '広場', to: '/posts', subMenu: [
 	  { name: '一覧', to: '/posts' },
@@ -71,7 +75,7 @@ export const menuOutline = (
 	    visible: materialFlg && Boolean (material?.tag) },
 	  { name: '履歴', to: `/materials/changes?material_id=${ material?.id }`,
 	    visible: materialFlg }] },
-      { name: 'Wiki', to: '/wiki/ヘルプ:ホーム', base: '/wiki', subMenu: [
+      { name: 'Wiki', to: '/wiki', subMenu: [
 	  { name: '検索', to: '/wiki' },
 	  { name: '新規', to: '/wiki/new', visible: editable },
 	  { name: '全体履歴', to: '/wiki/changes' },
@@ -82,6 +86,13 @@ export const menuOutline = (
 	  { name: '履歴', to: `/wiki/changes?id=${ wikiId }`, visible: wikiPageFlg },
 	  { name: '編輯', to: `/wiki/${ wikiId || wikiTitle }/edit`,
 	    visible: wikiPageFlg && editable }] },
+      { name: 'ヘルプ', to: '/help/home', base: '/help', subMenu: [
+	  { name: '検索', to: '/help' },
+	  { name: '全体履歴', to: '/help/changes' },
+	  { component: <Separator/>, visible: helpVsbl },
+	  { name: '履歴',
+	    to: `/help/changes?identifier=${ helpIdentifier }`,
+	    visible: helpVsbl }] },
       { 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' }] },
@@ -104,6 +115,8 @@ const TopNav: FC<Props> = ({ user }) => {
   const dirRef = useRef<(-1) | 1> (1)
   const itemsRef = useRef<(HTMLAnchorElement | null)[]> ([])
   const navRef = useRef<HTMLDivElement | null> (null)
+  const layoutRef = useRef<HTMLDivElement | null> (null)
+  const barRef = useRef<HTMLElement | null> (null)
 
   const measure = (idx: number) => {
     const nav = navRef.current
@@ -128,6 +141,8 @@ const TopNav: FC<Props> = ({ user }) => {
       width:    0,
       visible:  false })
   const [menuOpen, setMenuOpen] = useState (false)
+  const [desktop, setDesktop] = useState (false)
+  const [density, setDensity] = useState<NavDensity> ('auto')
   const [moreVsbl, setMoreVsbl] = useState (false)
   const [openItemIdx, setOpenItemIdx] = useState (-1)
   const [wikiId, setWikiId] = useState<number | null> (WikiIdBus.get ())
@@ -194,15 +209,81 @@ const TopNav: FC<Props> = ({ user }) => {
   const dir = dirRef.current
 
   useLayoutEffect (() => {
-    const raf = requestAnimationFrame (() => measure (moreVsbl ? -1 : activeIdx))
+    const layout = layoutRef.current
-    const onResize = () => requestAnimationFrame (() => measure (moreVsbl ? -1 : activeIdx))
+    const bar = barRef.current
+    const primary = bar?.querySelector<HTMLElement> ('.top-nav-primary')
+    if (layout == null || bar == null || primary == null)
+      return
 
-    addEventListener ('resize', onResize)
+    const userLink = bar.querySelector<HTMLElement> ('.top-nav-user-desktop')
-    return () => {
+    let raf = 0
-      cancelAnimationFrame (raf)
+    let active = true
-      removeEventListener ('resize', onResize)
+
+    const update = () => {
+      if (!(window.matchMedia ('(min-width: 768px)').matches))
+      {
+	setDesktop (false)
+	setDensity ('auto')
+	return
       }
-  })
+
+      // Measure the same desktop elements while the mobile layout is active.
+      layout.setAttribute ('data-measuring', '')
+      const previousDensity = layout.getAttribute ('data-density') ?? 'auto'
+      const fittingDensity = (() => {
+	try
+	{
+	  for (const candidate of ['auto', 'comfortable', 'compact'] as const)
+	  {
+	    layout.setAttribute ('data-density', candidate)
+	    const style = getComputedStyle (bar)
+	    const required = primary.getBoundingClientRect ().width
+		+ (userLink?.getBoundingClientRect ().width ?? 0)
+		+ parseFloat (style.paddingLeft) + parseFloat (style.paddingRight)
+		+ (userLink == null ? 0 : parseFloat (style.columnGap))
+	    if (required <= bar.clientWidth)
+	      return candidate
+	  }
+	  return null
+	}
+	finally
+	{
+	  layout.setAttribute ('data-density', previousDensity)
+	  layout.removeAttribute ('data-measuring')
+	}
+      }) ()
+      setDensity (fittingDensity ?? 'compact')
+      setDesktop (fittingDensity != null)
+      if (fittingDensity != null)
+	measure (moreVsbl ? -1 : activeIdx)
+    }
+
+    const schedule = () => {
+      if (!(active))
+	return
+      cancelAnimationFrame (raf)
+      raf = requestAnimationFrame (update)
+    }
+
+    const observer =
+	typeof ResizeObserver === 'undefined' ? null : new ResizeObserver (schedule)
+    observer?.observe (bar)
+    observer?.observe (primary)
+    if (userLink != null)
+      observer?.observe (userLink)
+    update ()
+    addEventListener ('resize', schedule)
+    document.fonts?.addEventListener ('loadingdone', schedule)
+    void document.fonts?.ready.then (schedule)
+
+    return () => {
+      active = false
+      cancelAnimationFrame (raf)
+      observer?.disconnect ()
+      removeEventListener ('resize', schedule)
+      document.fonts?.removeEventListener ('loadingdone', schedule)
+    }
+  }, [activeIdx, moreVsbl, desktop, density, user?.name])
 
   useEffect (() => {
     const unsubscribe = WikiIdBus.subscribe (setWikiId)
@@ -215,19 +296,22 @@ const TopNav: FC<Props> = ({ user }) => {
   }, [activeIdx, location])
 
   return (
-      <>
+      <div ref={layoutRef} className="top-nav-layout w-full min-w-0 shrink-0"
-	<nav className="top-nav-root px-3 flex justify-between items-center w-full">
+	  data-desktop={desktop} data-density={density}>
-	  <div className="flex items-center gap-2 h-12">
+	<nav ref={barRef}
+	    className="top-nav-root top-nav-bar flex justify-between items-center w-full">
+	  <div className="top-nav-primary flex shrink-0 items-center h-12">
 	    <PrefetchLink
 		to="/posts"
-		className="top-nav-brand-link mx-4 text-xl font-bold"
+		className="top-nav-brand-link shrink-0 whitespace-nowrap font-bold"
 		onClick={() => {
 		  scroll (0, 0)
 		}}>
 	      ぼざクリ タグ広場
 	    </PrefetchLink>
 
-	    <div ref={navRef} className="relative hidden md:flex h-12 items-center">
+	    <div ref={navRef}
+		className="top-nav-desktop-menu relative shrink-0 h-12 items-center">
 	      <div aria-hidden
 		   className={cn ('absolute inset-y-0 h-12',
 				  'top-nav-highlight',
@@ -239,6 +323,7 @@ const TopNav: FC<Props> = ({ user }) => {
 	      {visibleMenu.map ((item, i) => (
 		  <motion.div
 		      key={item.to}
+		      className="shrink-0 whitespace-nowrap"
 		      {...(animationsOff
 			   ? { }
 			   : { layoutId: `menu-${ item.name }` })}
@@ -252,7 +337,7 @@ const TopNav: FC<Props> = ({ user }) => {
 			ref={(el: (HTMLAnchorElement | null)) => {
 			  itemsRef.current[i] = el
 			}}
-			className={cn ('top-nav-menu-link relative z-10 flex h-full items-center px-5',
+			className={cn ('top-nav-menu-link relative z-10 flex h-full items-center',
 				       (i === openItemIdx) && 'font-bold')}>
 		      {item.name}
 		    </PrefetchLink>
@@ -267,7 +352,8 @@ const TopNav: FC<Props> = ({ user }) => {
 		    setMoreVsbl (true)
 		    measure (-1)
 		  }}
-		  className={cn ('top-nav-menu-link relative z-10 flex h-full items-center px-5',
+		  className={cn ('top-nav-menu-link relative z-10 flex h-full items-center',
+				 'shrink-0 whitespace-nowrap',
 				 (openItemIdx < 0 || moreVsbl) && 'font-bold')}>
 		その他 &raquo;
 	      </PrefetchLink>
@@ -278,7 +364,8 @@ const TopNav: FC<Props> = ({ user }) => {
 
 	  <button
 	     type="button"
-	     className="top-nav-mobile-toggle md:hidden ml-auto border-0 bg-transparent pr-4"
+	     className="top-nav-mobile-toggle shrink-0 whitespace-nowrap
+			ml-auto border-0 bg-transparent pr-4"
 	     onClick={() => {
 	       setMenuOpen (!(menuOpen))
 	     }}>
@@ -291,7 +378,8 @@ const TopNav: FC<Props> = ({ user }) => {
 	      key="submenu-shell"
 	      {...(animationsOff ? { }
 		   : { layout: true })}
-	      className="relative z-20 hidden md:block overflow-hidden top-nav-submenu"
+	      className="top-nav-desktop-submenu relative z-20 shrink-0
+			 overflow-hidden top-nav-submenu"
 	      animate={{ height: submenuHeight }}
 	      onMouseLeave={() => {
 		if (moreVsbl)
@@ -305,7 +393,8 @@ const TopNav: FC<Props> = ({ user }) => {
 	   ? (
 	      moreMenu.map ((item, i) => (
 		  <div key={i} className="relative h-[40px]">
-		    <div className="absolute inset-0 flex items-center px-3">
+		    <div className="absolute inset-0 flex items-center px-3
+				    overflow-x-auto whitespace-nowrap">
 		      <motion.div
 			  transition={topNavTransition}
 			  {...(animationsOff
@@ -315,7 +404,7 @@ const TopNav: FC<Props> = ({ user }) => {
 			       : { initial: { x: 40, y: -40, opacity: 0 },
 				   animate: { x: 0, y: 0, opacity: 1 },
 				   exit: { x: 40, y: -40, opacity: 0 } }))}
-			  className="z-10 h-full flex items-center px-3 font-bold w-28">
+			  className="z-10 h-full flex shrink-0 items-center px-3 font-bold w-28">
 			<h2>{item.name}</h2>
 		      </motion.div>
 		      {item.subMenu
@@ -363,7 +452,8 @@ const TopNav: FC<Props> = ({ user }) => {
 		  <div className="relative h-[40px]">
 		    {animationsOff
 		     ? (
-			 <div className="absolute inset-0 flex items-center px-3">
+			 <div className="absolute inset-0 flex items-center px-3
+					 overflow-x-auto whitespace-nowrap">
 			   {(visibleMenu[activeIdx]?.subMenu ?? [])
 			    .filter (item => item.visible ?? true)
 			    .map ((item, i) => (
@@ -392,7 +482,8 @@ const TopNav: FC<Props> = ({ user }) => {
 			       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"
+			       className="absolute inset-0 flex items-center px-3
+					  overflow-x-auto whitespace-nowrap"
 			       initial="enter"
 			       animate="centre"
 			       exit="exit"
@@ -432,7 +523,7 @@ const TopNav: FC<Props> = ({ user }) => {
 	 ? (
 	     menuOpen && (
 		 <div
-		     className={cn ('top-nav-root top-nav-mobile-menu flex flex-col md:hidden',
+		     className={cn ('top-nav-root top-nav-mobile-menu flex flex-col',
 				    'items-start')}>
 		   <Separator/>
 		   {visibleMenu.map ((item, i) => (
@@ -476,9 +567,6 @@ const TopNav: FC<Props> = ({ user }) => {
 		       </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'))}>
@@ -492,7 +580,7 @@ const TopNav: FC<Props> = ({ user }) => {
 	       {menuOpen && (
 		   <motion.div
 		       key="spmenu"
-		       className={cn ('top-nav-root top-nav-mobile-menu flex flex-col md:hidden',
+		       className={cn ('top-nav-root top-nav-mobile-menu flex flex-col',
 				      'items-start')}
 		       variants={{ closed: { clipPath: 'inset(0 0 100% 0)',
 					     height:   0 },
@@ -558,9 +646,6 @@ const TopNav: FC<Props> = ({ user }) => {
 			 </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'))}>
@@ -570,7 +655,7 @@ const TopNav: FC<Props> = ({ user }) => {
 		     <Separator/>
 		   </motion.div>)}
 	     </AnimatePresence>)}
-      </>)
+      </div>)
 }
 
 export default TopNav

frontend/src/components/TopNavUser.tsx

@@ -15,8 +15,8 @@ const TopNavUser: FC<Props> = ({ user, sp }) => {
     return
 
   const className = cn ((sp
-			 ? 'md:hidden w-full min-h-[40px] flex items-center pl-8'
+			 ? 'top-nav-user-mobile w-full min-h-[40px] flex items-center pl-8'
-			 : 'hidden md:block ml-auto pr-4'),
+			 : 'top-nav-user-desktop shrink-0 whitespace-nowrap ml-auto'),
 		        'font-bold text-red-600 hover:text-red-400',
 		        'dark:text-yellow-400 dark:hover:text-yellow-200')
 

frontend/src/index.css

@@ -197,12 +197,244 @@ body
   background: var(--top-nav-root-bg-mobile);
 }
 
+.top-nav-bar
+{
+  padding-inline: 8px;
+  column-gap: 4px;
+}
+
+.top-nav-primary
+{
+  column-gap: 4px;
+}
+
+.top-nav-layout .top-nav-brand-link
+{
+  margin-inline: 4px;
+  font-size: 1rem;
+}
+
+.top-nav-desktop-menu,
+.top-nav-desktop-submenu,
+.top-nav-user-desktop
+{
+  display: none;
+}
+
+.top-nav-desktop-menu
+{
+  font-size: .875rem;
+}
+
+.top-nav-desktop-menu .top-nav-menu-link
+{
+  padding-inline: 8px;
+}
+
+.top-nav-user-desktop
+{
+  padding-right: 4px;
+  font-size: .875rem;
+}
+
+.top-nav-user-mobile
+{
+  overflow-wrap: anywhere;
+}
+
 @media (min-width: 768px)
 {
-  .top-nav-root
+  .top-nav-layout .top-nav-brand-link
+  {
+    font-size: 1.125rem;
+  }
+
+  .top-nav-layout[data-desktop='true'] .top-nav-root
   {
     background: var(--top-nav-root-bg-desktop);
   }
+
+  .top-nav-layout[data-desktop='true'] .top-nav-desktop-menu,
+  .top-nav-layout[data-measuring] .top-nav-desktop-menu
+  {
+    display: flex;
+  }
+
+  .top-nav-layout[data-desktop='true'] .top-nav-user-desktop,
+  .top-nav-layout[data-measuring] .top-nav-user-desktop,
+  .top-nav-layout[data-desktop='true'] .top-nav-desktop-submenu
+  {
+    display: block;
+  }
+
+  .top-nav-layout[data-desktop='true'] .top-nav-mobile-toggle,
+  .top-nav-layout[data-measuring] .top-nav-mobile-toggle,
+  .top-nav-layout[data-desktop='true'] .top-nav-mobile-menu,
+  .top-nav-layout[data-desktop='true'] .top-nav-user-mobile
+  {
+    display: none;
+  }
+
+  .top-nav-layout[data-measuring]
+  {
+    visibility: hidden;
+  }
+}
+
+@media (min-width: 1024px)
+{
+  .top-nav-bar
+  {
+    padding-inline: 12px;
+    column-gap: 8px;
+  }
+
+  .top-nav-primary
+  {
+    column-gap: 6px;
+  }
+
+  .top-nav-layout .top-nav-brand-link
+  {
+    margin-inline: 8px;
+    font-size: 1.25rem;
+  }
+
+  .top-nav-desktop-menu
+  {
+    column-gap: 2px;
+  }
+
+  .top-nav-desktop-menu,
+  .top-nav-user-desktop
+  {
+    font-size: .9375rem;
+  }
+
+  .top-nav-desktop-menu .top-nav-menu-link
+  {
+    padding-inline: 12px;
+  }
+
+  .top-nav-user-desktop
+  {
+    padding-right: 8px;
+  }
+}
+
+@media (min-width: 1280px)
+{
+  .top-nav-bar
+  {
+    column-gap: 12px;
+  }
+
+  .top-nav-primary
+  {
+    column-gap: 8px;
+  }
+
+  .top-nav-layout .top-nav-brand-link
+  {
+    margin-inline: 16px;
+  }
+
+  .top-nav-desktop-menu
+  {
+    column-gap: 4px;
+  }
+
+  .top-nav-desktop-menu,
+  .top-nav-user-desktop
+  {
+    font-size: 1rem;
+  }
+
+  .top-nav-desktop-menu .top-nav-menu-link
+  {
+    padding-inline: 20px;
+  }
+
+  .top-nav-user-desktop
+  {
+    padding-right: 16px;
+  }
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-bar
+{
+  padding-inline: 12px;
+  column-gap: 8px;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-primary
+{
+  column-gap: 6px;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-brand-link
+{
+  margin-inline: 8px;
+  font-size: 1.25rem;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-desktop-menu
+{
+  column-gap: 2px;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-desktop-menu,
+.top-nav-layout[data-density='comfortable'] .top-nav-user-desktop
+{
+  font-size: .9375rem;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-desktop-menu .top-nav-menu-link
+{
+  padding-inline: 12px;
+}
+
+.top-nav-layout[data-density='comfortable'] .top-nav-user-desktop
+{
+  padding-right: 8px;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-bar
+{
+  padding-inline: 8px;
+  column-gap: 4px;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-primary
+{
+  column-gap: 4px;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-brand-link
+{
+  margin-inline: 4px;
+  font-size: 1.125rem;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-desktop-menu
+{
+  column-gap: 0;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-desktop-menu,
+.top-nav-layout[data-density='compact'] .top-nav-user-desktop
+{
+  font-size: .875rem;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-desktop-menu .top-nav-menu-link
+{
+  padding-inline: 8px;
+}
+
+.top-nav-layout[data-density='compact'] .top-nav-user-desktop
+{
+  padding-right: 4px;
 }
 
 .top-nav-brand-link,

frontend/src/lib/help.test.ts

@@ -0,0 +1,130 @@
+import { describe, expect, it } from 'vitest'
+
+import { createHelpFixture } from '@/test/helpFixtures'
+
+
+describe ('Help file catalogue', () => {
+  it.each ([['Éclair', 'eclair'], ['home', 'HOME'], ['e\u0301clair', 'Éclair']]) (
+      'compares title %s and %s equally at primary strength', (a, b) => {
+	const { api } = createHelpFixture ()
+	expect (api.compareHelpTitles (a, b)).toBe (0)
+      })
+
+  it ('orders distinct Latin titles in both directions', () => {
+    const { api } = createHelpFixture ()
+    expect (api.compareHelpTitles ('Apple', 'Zebra')).toBeLessThan (0)
+    expect (api.compareHelpTitles ('Zebra', 'Apple')).toBeGreaterThan (0)
+  })
+
+  it.each ([['ほーむ', 'ホーム'], ['ホーム', 'ほーむ'], ['ﾎｰﾑ', 'ホーム'],
+      ['ＡＢＣ', 'abc'], ['ｶﾞｲﾄﾞ', 'がいど']]) (
+      'normalises search text %s and %s identically', (query, text) => {
+	const { api } = createHelpFixture ()
+	expect (api.normaliseHelpSearchText (query)).toBe (api.normaliseHelpSearchText (text))
+      })
+
+  it.each ([['2026-10-02', null], ['2026-10-02.2', 2],
+      ['2026-10-02.3', 3], ['2026-10-02.10', 10]] as const) (
+      'separates the date and revision of %s', (edition, revision) => {
+	const { api } = createHelpFixture ()
+	expect (api.parseHelpEdition (edition)).toEqual ({ date: '2026-10-02', revision })
+	const date = api.helpEditionDate (edition)!
+	expect ([date.getFullYear (), date.getMonth (), date.getDate ()]).toEqual ([2026, 9, 2])
+      })
+
+  it.each (['missing', '2026-02-30', '2026-10-02.0', '2026-10-02.2.extra',
+      '2026-10-02.9007199254740992']) ('rejects invalid edition %s', edition => {
+    const { api } = createHelpFixture ()
+    expect (api.parseHelpEdition (edition)).toBeNull ()
+    expect (api.helpEditionDate (edition)).toBeNull ()
+  })
+
+  it ('compares numeric revision suffixes without losing the edition identifiers', () => {
+    const { api } = createHelpFixture ()
+    expect (['2026-10-02.10', '2026-10-02.3', '2026-10-02', '2026-10-02.2']
+	.sort (api.compareHelpEditions)).toEqual ([
+	'2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10'])
+  })
+
+  it ('uses current_edition rather than the newest file, without YAML titles', async () => {
+    const { api } = createHelpFixture ()
+    expect ((await api.getHelpArticle ('guide'))?.languages.ja.currentEdition)
+	.toBe ('2026-10-02.10')
+    expect (await api.getHelpSearchEntries ('ja')).toEqual ([
+	{ identifier: 'guide', edition: '2026-10-02.10',
+	  title: 'ホーム第十版', body: '\nタグを検索する 第十版本文' },
+	{ identifier: '設定 手順', edition: '2026-10-03',
+	  title: '設定', body: '\nタグを設定する' }])
+  })
+
+  it ('orders published editions numerically and separates languages', async () => {
+    const { api } = createHelpFixture ()
+    expect (await api.getHelpEditions ('guide', 'ja')).toEqual ([
+	'2026-10-01', '2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10'])
+    expect (await api.getHelpEditions ('guide', 'en')).toEqual (['2026-10-02'])
+    expect (await api.getHelpPublishedEditions ('guide', 'ja'))
+	.not.toContain ('2026-10-02.11')
+  })
+
+  it ('uses generated edition titles without reparsing raw sources', async () => {
+    const { api, raw } = createHelpFixture ()
+    expect (await api.getHelpEditionText ('guide', 'ja', '2026-10-01'))
+	.toEqual ({ title: '旧ホーム', body: '\n過去限定本文' })
+    raw['../../help/guide/editions/ja/2026-10-02.mdx']
+	.mockResolvedValue ('\uFEFF# 改題\r\n\r\n本文\r\n# 別見出し')
+    expect (await api.getHelpEditionText ('guide', 'ja', '2026-10-02'))
+	.toEqual ({ title: 'ホーム', body: '\nタグを検索する' })
+    expect (raw['../../help/guide/editions/ja/2026-10-02.mdx']).not.toHaveBeenCalled ()
+    expect ((await api.getHelpEditionSource ('guide', 'ja', '2026-10-02'))?.source)
+	.toBe ('\uFEFF# 改題\r\n\r\n本文\r\n# 別見出し')
+  })
+
+  it ('returns missing resources without substituting another edition', async () => {
+    const { api } = createHelpFixture ()
+    expect (await api.getHelpArticle ('absent')).toBeNull ()
+    expect (await api.getHelpEditions ('absent', 'ja')).toEqual ([])
+    expect (await api.getHelpEdition ('guide', 'ja', 'missing')).toBeNull ()
+    expect (await api.getHelpEditionText ('guide', 'fr', '2026-10-02')).toBeNull ()
+  })
+
+  it ('reports generated search asset failures instead of hiding articles', async () => {
+    const { api, loads } = createHelpFixture ()
+    loads.search.mockImplementationOnce (() => { throw new Error ('asset failure') })
+    await expect (api.getHelpSearchEntries ('ja')).rejects.toThrow ('asset failure')
+  })
+
+  it ('reports raw loading failures and excludes unpublished editions', async () => {
+    const { api, raw } = createHelpFixture ()
+    const loader = raw['../../help/guide/editions/ja/2026-10-02.mdx']
+    loader.mockRejectedValueOnce (new Error ('fixture failure'))
+    await expect (api.getHelpEditionSource ('guide', 'ja', '2026-10-02'))
+	.rejects.toThrow ('fixture failure')
+    expect (await api.getHelpEdition ('guide', 'ja', '2026-10-02.11')).toBeNull ()
+    expect (await api.getHelpEditionSource ('guide', 'ja', '2026-10-02.11')).toBeNull ()
+  })
+
+  it ('compares raw H1 and body lines in the requested direction', async () => {
+    const { api } = createHelpFixture ()
+    const forward = await api.getHelpDiff ('guide', 'ja', '2026-10-01', '2026-10-02.10')
+    expect (forward?.from.title).toBe ('旧ホーム')
+    expect (forward?.to.title).toBe ('ホーム第十版')
+    expect (forward?.lines).toEqual (expect.arrayContaining ([
+	{ type: 'removed', content: '# 旧ホーム\n' },
+	{ type: 'added', content: '# ホーム第十版\n' },
+	{ type: 'unchanged', content: '\n' }]))
+    const reverse = await api.getHelpDiff ('guide', 'ja', '2026-10-02.10', '2026-10-01')
+    expect (reverse?.lines).toEqual (expect.arrayContaining ([
+	{ type: 'added', content: '# 旧ホーム\n' },
+	{ type: 'removed', content: '# ホーム第十版\n' }]))
+  })
+
+  it.each ([['missing', 'ja', '2026-10-01', '2026-10-02.10'],
+      ['guide', 'ja', '2026-10-01', '2026-10-02.11'],
+      ['guide', 'en', '2026-10-01', '2026-10-02']]) (
+      'rejects invalid diff editions for %s/%s without reading sources',
+      async (id, language, from, to) => {
+	const { api, raw } = createHelpFixture ()
+	expect (await api.getHelpDiff (id, language, from, to)).toBeNull ()
+	Object.values (raw).forEach (load => expect (load).not.toHaveBeenCalled ())
+      })
+})

frontend/src/lib/help.ts

@@ -0,0 +1,237 @@
+import type { ComponentType } from 'react'
+
+type ArticleLanguage = { currentEdition: string; publishedEditions: string[] }
+
+export type ArticleMeta = {
+    identifier: string
+    canonicalLanguage: string
+    languages:  Record<string, ArticleLanguage> }
+
+export type HelpEditionText = {
+    title: string
+    body:  string }
+
+export type HelpSearchEntry = HelpEditionText & {
+    identifier: string
+    edition:    string }
+
+export type HelpEditionContent = HelpEditionText & { content: ComponentType }
+
+export type HelpEditionSource = HelpEditionText & { source: string }
+export type HelpChange = Pick<HelpSearchEntry, 'identifier' | 'edition' | 'title'> & {
+    pred: string | null
+    change: 'new' | 'update'
+    date: string }
+export type HelpTitleIndex = Record<string, string[]>
+export type HelpDiffLine = {
+    type: 'added' | 'removed' | 'unchanged'
+    content: string }
+export type HelpDiff = {
+    from: HelpEditionSource
+    to: HelpEditionSource
+    lines: HelpDiffLine[] }
+
+export type HelpEditionIdentifier = { date: string; revision: number | null }
+
+// Fix the locale and primary strength; ICU versions still differ from MySQL UCA 9.0.
+const helpTitleCollator = new Intl.Collator ('en', {
+    usage: 'sort', sensitivity: 'base', ignorePunctuation: false, numeric: false })
+
+
+export const compareHelpTitles = (a: string, b: string): number =>
+    helpTitleCollator.compare (a, b)
+
+
+export const normaliseHelpSearchText = (value: string): string =>
+    value.normalize ('NFKC').toLowerCase ().replace (/[ァ-ヶヽヾ]/g,
+	character => String.fromCodePoint (character.codePointAt (0)! - 0x60))
+
+
+export const parseHelpEdition = (edition: string): HelpEditionIdentifier | null => {
+  const matched = edition.match (/^(\d{4}-\d{2}-\d{2})(?:\.([1-9]\d*))?$/)
+  if (matched == null)
+    return null
+  const date = new Date (matched[1])
+  const revision = matched[2] == null ? null : Number (matched[2])
+  if (Number.isNaN (date.getTime ()) || date.toISOString ().slice (0, 10) !== matched[1]
+      || (revision != null && !(Number.isSafeInteger (revision))))
+    return null
+  return { date: matched[1], revision }
+}
+
+
+export const compareHelpEditions = (a: string, b: string): number => {
+  const before = parseHelpEdition (a)
+  const after = parseHelpEdition (b)
+  if (before == null || after == null)
+    return a.localeCompare (b)
+  return before.date.localeCompare (after.date)
+      || (before.revision ?? 1) - (after.revision ?? 1)
+}
+
+
+export const helpEditionDate = (edition: string): Date | null => {
+  const parsed = parseHelpEdition (edition)
+  return parsed == null ? null : new Date (`${ parsed.date }T00:00:00`)
+}
+
+
+export const getHelpArticle = async (identifier: string): Promise<ArticleMeta | null> => {
+  const { default: articles } = await import ('virtual:help/articles')
+  return Object.hasOwn (articles, identifier) ? articles[identifier] : null
+}
+
+
+export const getHelpEditions = async (
+    identifier: string,
+    language: string,
+): Promise<string[]> => {
+  const article = await getHelpArticle (identifier)
+  return article?.languages[language]?.publishedEditions ?? []
+}
+
+
+export const getHelpPublishedEditions = async (
+    identifier: string,
+    language: string,
+): Promise<string[]> => await getHelpEditions (identifier, language)
+
+
+export const getHelpEdition = async (
+    identifier: string,
+    language: string,
+    edition: string,
+): Promise<ComponentType | null> => {
+  const { components } = await import ('virtual:help/loaders')
+  const loader = components[`${ identifier }/${ language }/${ edition }`]
+
+  if (!(loader))
+    return null
+
+  return (await loader ()).default
+}
+
+
+export const getHelpEditionSource = async (
+    identifier: string,
+    language: string,
+    edition: string,
+): Promise<HelpEditionSource | null> => {
+  const { sources } = await import ('virtual:help/loaders')
+  const loader = sources[`${ identifier }/${ language }/${ edition }`]
+
+  if (!(loader))
+    return null
+
+  const [source, text] = await Promise.all ([
+      loader (), getHelpEditionText (identifier, language, edition)])
+  return text == null ? null : { source: source.default, ...text }
+}
+
+
+export const getHelpEditionText = async (
+    identifier: string,
+    language: string,
+    edition: string,
+): Promise<HelpEditionText | null> => {
+  const { texts } = await import ('virtual:help/loaders')
+  const loader = texts[`${ identifier }/${ language }/${ edition }`]
+  return loader == null ? null : (await loader ()).default
+}
+
+
+export const getHelpSearchEntries = async (
+    language: string,
+): Promise<HelpSearchEntry[]> => {
+  const { default: search } = await import ('virtual:help/search')
+  return search[language] ?? []
+}
+
+
+export const getHelpEditionContent = async (
+    identifier: string,
+    language: string,
+    edition: string,
+): Promise<HelpEditionContent | null> => {
+  const [content, text] = await Promise.all ([
+      getHelpEdition (identifier, language, edition),
+      getHelpEditionText (identifier, language, edition)])
+
+  return content != null && text != null ? { content, ...text } : null
+}
+
+
+export const getHelpChanges = async (language: string): Promise<HelpChange[]> => {
+  const { default: changes } = await import ('virtual:help/changes')
+  return changes[language] ?? []
+}
+
+
+export const getHelpTitleIndex = async (language: string): Promise<HelpTitleIndex> => {
+  const { default: titles } = await import ('virtual:help/titles')
+  return titles[language] ?? { }
+}
+
+
+const diffHelpLines = (from: string, to: string): HelpDiffLine[] => {
+  const before = from.match (/[^\n]*\n|[^\n]+$/g) ?? []
+  const after = to.match (/[^\n]*\n|[^\n]+$/g) ?? []
+  const lengths = Array.from ({ length: before.length + 1 },
+      () => new Uint32Array (after.length + 1))
+
+  for (let i = before.length - 1; i >= 0; --i)
+  {
+    for (let j = after.length - 1; j >= 0; --j)
+    {
+      lengths[i][j] =
+	  before[i] === after[j]
+	  ? lengths[i + 1][j + 1] + 1
+	  : Math.max (lengths[i + 1][j], lengths[i][j + 1])
+    }
+  }
+
+  const lines: HelpDiffLine[] = []
+  let i = 0
+  let j = 0
+  while (i < before.length || j < after.length)
+  {
+    if (i < before.length && j < after.length && before[i] === after[j])
+    {
+      lines.push ({ type: 'unchanged', content: before[i] })
+      ++i
+      ++j
+    }
+    else if (i < before.length
+	     && (j === after.length || lengths[i + 1][j] >= lengths[i][j + 1]))
+    {
+      lines.push ({ type: 'removed', content: before[i] })
+      ++i
+    }
+    else
+    {
+      lines.push ({ type: 'added', content: after[j] })
+      ++j
+    }
+  }
+  return lines
+}
+
+
+export const getHelpDiff = async (
+    identifier: string,
+    language: string,
+    from: string,
+    to: string,
+): Promise<HelpDiff | null> => {
+  const editions = await getHelpPublishedEditions (identifier, language)
+  if (!(editions.includes (from)) || !(editions.includes (to)))
+    return null
+
+  const [before, after] = await Promise.all ([
+      getHelpEditionSource (identifier, language, from),
+      getHelpEditionSource (identifier, language, to)])
+  if (before == null || after == null)
+    return null
+
+  return { from: before, to: after, lines: diffHelpLines (before.source, after.source) }
+}

frontend/src/lib/helpPrefetch.test.tsx

@@ -0,0 +1,126 @@
+import { QueryClient } from '@tanstack/react-query'
+import { fireEvent, screen, waitFor } from '@testing-library/react'
+import { Route, Routes, useLocation } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import * as prefetchers from '@/lib/prefetchers'
+import HelpDetailPage from '@/pages/help/HelpDetailPage'
+import HelpDiffPage from '@/pages/help/HelpDiffPage'
+import { helpFixture } from '@/test/helpFixtures'
+import { renderWithProviders } from '@/test/render'
+
+const settings = vi.hoisted (() => ({ linkPreload: 'intent' }))
+vi.mock ('@/lib/useClientBehaviourSettings', () => ({
+    useClientBehaviourSettings: () => settings }))
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+
+
+const Location = () => {
+  const location = useLocation ()
+  return <output data-testid="location">{location.pathname}</output>
+}
+
+
+describe ('Help prefetch integration', () => {
+  beforeEach (() => {
+    helpFixture.reset ()
+    settings.linkPreload = 'intent'
+    vi.clearAllMocks ()
+  })
+
+  it.each (['/help', '/help?title=ホーム&text=検索&page=2', '/help/guide', '/help/changes',
+      '/help/guide/diff?from=2026-10-01&to=2026-10-02.10',
+      '/help/%E8%A8%AD%E5%AE%9A%20%E6%89%8B%E9%A0%86?edition=2026-10-03']) (
+      'registers a unique prefetcher for %s', path => {
+	const url = new URL (path, window.location.origin)
+	expect (prefetchers.routePrefetchers.filter (entry => entry.test (url))).toHaveLength (1)
+      })
+
+  it ('loads and reuses the same MDX module for repeated prefetch and display', async () => {
+    const { queryClient } = renderWithProviders (
+	<>
+	  <PrefetchLink to="/help/guide">Help</PrefetchLink>
+	  <Routes>
+	    <Route path="/" element={null}/>
+	    <Route path="/help/:identifier" element={<HelpDetailPage/>}/>
+	  </Routes>
+	</>)
+    const loader = helpFixture.moduleLoads['../../help/guide/editions/ja/2026-10-02.10.mdx']
+    await Promise.all ([
+	prefetchers.prefetchForURL (queryClient, '/help/guide'),
+	prefetchers.prefetchForURL (queryClient, '/help/guide')])
+    expect (loader).toHaveBeenCalledTimes (1)
+    fireEvent.click (screen.getByRole ('link', { name: 'Help' }))
+    await screen.findByRole ('heading', { name: 'ホーム第十版' })
+    expect (loader).toHaveBeenCalledTimes (1)
+  })
+
+  it ('prefetches the requested identifier and edition independently', async () => {
+    const client = new QueryClient ()
+    await prefetchers.prefetchForURL (client, '/help/guide?edition=2026-10-02.3')
+    await prefetchers.prefetchForURL (client, `/help/${encodeURIComponent ('設定 手順')}`)
+    expect (helpFixture.modules['../../help/guide/editions/ja/2026-10-02.3.mdx'])
+	.toHaveBeenCalledTimes (1)
+    expect (helpFixture.modules['../../help/設定 手順/editions/ja/2026-10-03.mdx'])
+	.toHaveBeenCalledTimes (1)
+    expect (helpFixture.modules['../../help/guide/editions/en/2026-10-02.mdx'])
+	.not.toHaveBeenCalled ()
+  })
+
+  it ('loads history editions without treating changes as an article', async () => {
+    const article = vi.spyOn (helpFixture.api, 'getHelpArticle')
+    await prefetchers.prefetchForURL (new QueryClient (), '/help/changes')
+    expect (article).not.toHaveBeenCalledWith ('changes')
+    expect (helpFixture.loads.changes).toHaveBeenCalledTimes (1)
+    Object.values (helpFixture.raw).forEach (load => expect (load).not.toHaveBeenCalled ())
+    Object.values (helpFixture.modules).forEach (load => expect (load).not.toHaveBeenCalled ())
+  })
+
+  it ('reuses two prefetched raw editions when displaying their diff', async () => {
+    const path = '/help/guide/diff?from=2026-10-01&to=2026-10-02.10'
+    const { queryClient } = renderWithProviders (
+	<>
+	  <PrefetchLink to={path}>diff</PrefetchLink>
+	  <Routes>
+	    <Route path="/" element={null}/>
+	    <Route path="/help/:identifier/diff" element={<HelpDiffPage/>}/>
+	  </Routes>
+	</>)
+    await Promise.all ([prefetchers.prefetchForURL (queryClient, path),
+	prefetchers.prefetchForURL (queryClient, path)])
+    fireEvent.click (screen.getByRole ('link', { name: 'diff' }))
+    expect (await screen.findByRole ('link', { name: '旧ホーム (2026-10-01)' }))
+	.toHaveAttribute ('href', '/help/guide?edition=2026-10-01')
+    expect (screen.getByText ('+ # ホーム第十版')).toBeInTheDocument ()
+    Object.entries (helpFixture.raw).forEach (([name, load]) => {
+      const expected = /\/ja\/(2026-10-01|2026-10-02\.10)\.mdx$/.test (name) ? 1 : 0
+      expect (load).toHaveBeenCalledTimes (expected)
+    })
+    Object.values (helpFixture.modules).forEach (load => expect (load).not.toHaveBeenCalled ())
+  })
+
+  it.each (['intent', 'off']) ('respects %s intent settings and still prefetches clicks',
+      async mode => {
+	settings.linkPreload = mode
+	const run = vi.spyOn (prefetchers, 'prefetchForURL').mockResolvedValue ()
+	renderWithProviders (<><Location/><PrefetchLink to="/help/guide">Help</PrefetchLink></>)
+	const link = screen.getByRole ('link', { name: 'Help' })
+	fireEvent.mouseEnter (link)
+	fireEvent.touchStart (link)
+	expect (run).toHaveBeenCalledTimes (mode === 'intent' ? 2 : 0)
+	fireEvent.click (link)
+	await waitFor (() => expect (screen.getByTestId ('location'))
+	    .toHaveTextContent ('/help/guide'))
+	expect (run).toHaveBeenCalledTimes (mode === 'intent' ? 3 : 1)
+      })
+
+  it ('continues navigation after prefetch failure', async () => {
+    vi.spyOn (console, 'error').mockImplementation (() => {})
+    vi.spyOn (prefetchers, 'prefetchForURL').mockRejectedValue (new Error ('offline'))
+    renderWithProviders (<><Location/><PrefetchLink to="/help/guide">Help</PrefetchLink></>)
+    fireEvent.click (screen.getByRole ('link', { name: 'Help' }))
+    await waitFor (() => expect (screen.getByTestId ('location'))
+	.toHaveTextContent ('/help/guide'))
+  })
+})

frontend/src/lib/prefetchers.ts

@@ -1,8 +1,13 @@
 import { QueryClient } from '@tanstack/react-query'
 import { match } from 'path-to-regexp'
 
+import { getHelpArticle,
+	 getHelpChanges,
+	 getHelpDiff,
+	 getHelpEditionContent,
+	 getHelpSearchEntries } from '@/lib/help'
 import { fetchPost, fetchPosts, fetchPostChanges } from '@/lib/posts'
-import { postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
+import { helpKeys, postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
 import { fetchNicoTags, fetchTagByName, fetchTag, fetchTagChanges, fetchTags } from '@/lib/tags'
 import { fetchWikiPage,
 	 fetchWikiPageByTitle,
@@ -15,12 +20,69 @@ type Prefetcher = (qc: QueryClient, url: URL) => Promise<void>
 const mPost = match<{ id: string }> ('/posts/:id')
 const mWiki = match<{ title: string }> ('/wiki/:title')
 const mTag = match<{ id: string }> ('/tags/:id')
+const mHelp = match<{ identifier: string }> ('/help/:identifier')
+const mHelpDiff = match<{ identifier: string }> ('/help/:identifier/diff')
 
 
 const boolFromQuery = (value: string | null): boolean =>
     ['1', 'true', 'on', 'yes', ''].includes ((value ?? '').toLowerCase ())
 
 
+const prefetchHelpIndex: Prefetcher = async qc => {
+  await qc.prefetchQuery ({
+      queryKey: helpKeys.index ('ja'),
+      queryFn: () => getHelpSearchEntries ('ja'),
+      staleTime: Infinity })
+}
+
+
+const prefetchHelpShow: Prefetcher = async (qc, url) => {
+  const matched = mHelp (url.pathname)
+  if (!(matched))
+    return
+
+  const { identifier } = matched.params
+  const language = 'ja'
+  const article = await qc.fetchQuery ({
+      queryKey: helpKeys.article (identifier),
+      queryFn: () => getHelpArticle (identifier),
+      staleTime: Infinity })
+  const edition = url.searchParams.get ('edition') ?? article?.languages[language]?.currentEdition
+  if (edition == null)
+    return
+
+  await qc.prefetchQuery ({
+      queryKey: helpKeys.edition (identifier, language, edition),
+      queryFn: () => getHelpEditionContent (identifier, language, edition),
+      staleTime: Infinity })
+}
+
+
+const prefetchHelpChanges: Prefetcher = async qc => {
+  await qc.prefetchQuery ({
+      queryKey: helpKeys.changes ('ja'),
+      queryFn: () => getHelpChanges ('ja'),
+      staleTime: Infinity })
+}
+
+
+const prefetchHelpDiff: Prefetcher = async (qc, url) => {
+  const matched = mHelpDiff (url.pathname)
+  const fromValues = url.searchParams.getAll ('from')
+  const toValues = url.searchParams.getAll ('to')
+  const [from] = fromValues
+  const [to] = toValues
+  if (!(matched) || fromValues.length !== 1 || toValues.length !== 1 || !(from) || !(to))
+    return
+
+  const { identifier } = matched.params
+  await qc.prefetchQuery ({
+      queryKey: helpKeys.diff (identifier, 'ja', from, to),
+      queryFn: () => getHelpDiff (identifier, 'ja', from, to),
+      staleTime: Infinity })
+}
+
+
 const prefetchWikiPagesIndex: Prefetcher = async (qc, url) => {
   const title = url.searchParams.get ('title') ?? ''
 
@@ -223,6 +285,13 @@ const prefetchTagChanges: Prefetcher = async (qc, url) => {
 
 
 export const routePrefetchers: { test: (u: URL) => boolean; run: Prefetcher }[] = [
+    { test: u => /^\/help\/?$/.test (u.pathname), run: prefetchHelpIndex },
+    { test: u => /^\/help\/changes\/?$/.test (u.pathname), run: prefetchHelpChanges },
+    { test: u => Boolean (mHelpDiff (u.pathname)), run: prefetchHelpDiff },
+    { test: u => {
+	const matched = mHelp (u.pathname)
+	return Boolean (matched && matched.params.identifier !== 'changes')
+      }, run: prefetchHelpShow },
     { test: u => ['/', '/posts', '/posts/search'].includes (u.pathname),
       run: prefetchPostsIndex },
     { test: u => (!(['/posts/new', '/posts/changes', '/posts/search'].includes (u.pathname))

frontend/src/lib/queryKeys.ts

@@ -61,3 +61,14 @@ export const wikiKeys = {
     root:   ['wiki'] as const,
     index:  (p: { title?: string }) => ['wiki', 'index', p] as const,
     show:   (title: string, p: { version?: string }) => ['wiki', title, p] as const }
+
+export const helpKeys = {
+    root:    ['help'] as const,
+    index:   (language: string) => ['help', 'index', language] as const,
+    titles:  (language: string) => ['help', 'titles', language] as const,
+    article: (identifier: string) => ['help', 'article', identifier] as const,
+    edition: (identifier: string, language: string, edition: string) =>
+	     ['help', 'edition', identifier, language, edition] as const,
+    diff: (identifier: string, language: string, from: string, to: string) =>
+	  ['help', 'diff', identifier, language, from, to] as const,
+    changes: (language: string) => ['help', 'changes', language] as const }

frontend/src/lib/tags.test.ts

@@ -72,11 +72,25 @@ describe ('tags API functions', () => {
     )
   })
 
-  it ('returns null when tag fetches fail', async () => {
+  it ('returns null for a missing named tag while retaining the ID helper contract', async () => {
-    api.apiGet.mockRejectedValueOnce (new Error ('missing'))
     api.apiGet.mockRejectedValueOnce (new Error ('missing'))
+    api.apiGet.mockRejectedValueOnce ({ isAxiosError: true, response: { status: 404 } })
 
     await expect (fetchTag ('1')).resolves.toBeNull ()
     await expect (fetchTagByName ('unknown')).resolves.toBeNull ()
   })
+
+  it.each ([403, 500]) ('propagates named tag HTTP %s', async status => {
+    const error = { isAxiosError: true, response: { status } }
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchTagByName ('ホーム')).rejects.toBe (error)
+  })
+
+  it ('propagates named tag network failures and encodes the name', async () => {
+    const error = new Error ('offline')
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchTagByName ('名前/#%')).rejects.toBe (error)
+    expect (api.apiGet).toHaveBeenLastCalledWith (
+	`/tags/name/${ encodeURIComponent ('名前/#%') }`)
+  })
 })

frontend/src/lib/tags.ts

@@ -1,3 +1,5 @@
+import { isAxiosError } from 'axios'
+
 import { apiGet } from '@/lib/api'
 
 import type { Deerjikist,
@@ -68,11 +70,13 @@ export const fetchExternalTag = async (id: string): Promise<Tag | null> => {
 export const fetchTagByName = async (name: string): Promise<Tag | null> => {
   try
   {
-    return await apiGet (`/tags/name/${ name }`)
+    return await apiGet (`/tags/name/${ encodeURIComponent (name) }`)
   }
-  catch
+  catch (error)
   {
+    if (isAxiosError (error) && error.response?.status === 404)
       return null
+    throw error
   }
 }
 

frontend/src/lib/wiki.test.ts

@@ -2,9 +2,7 @@ import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { fetchWikiPage, fetchWikiPageByTitle, fetchWikiPages } from '@/lib/wiki'
 
-const api = vi.hoisted (() => ({
+const api = vi.hoisted (() => ({ apiGet: vi.fn () }))
-  apiGet: vi.fn (),
-}))
 
 vi.mock ('@/lib/api', () => api)
 
@@ -23,26 +21,35 @@ describe ('wiki API functions', () => {
     expect (api.apiGet).toHaveBeenNthCalledWith (
 	1,
 	'/wiki',
-        { params: { title: '虹' } },
+	{ params: { title: '虹' } })
-    )
     expect (api.apiGet).toHaveBeenNthCalledWith (
 	2,
 	'/wiki/1',
-        { params: { version: '3' } },
+	{ params: { version: '3' } })
-    )
   })
 
   it ('encodes title path segments and returns null on misses', async () => {
     api.apiGet.mockResolvedValueOnce ({ id: 2 })
-    api.apiGet.mockRejectedValueOnce (new Error ('missing'))
+    api.apiGet.mockRejectedValueOnce ({ isAxiosError: true, response: { status: 404 } })
 
     await fetchWikiPageByTitle ('a/b c', { version: undefined })
-    await expect (fetchWikiPageByTitle ('missing', {})).resolves.toBeNull ()
+    await expect (fetchWikiPageByTitle ('missing', { })).resolves.toBeNull ()
 
     expect (api.apiGet).toHaveBeenNthCalledWith (
 	1,
 	'/wiki/title/a%2Fb%20c',
-        { params: { version: undefined } },
+	{ params: { version: undefined } })
-    )
+  })
+
+  it.each ([403, 500]) ('preserves HTTP %s errors', async status => {
+    const error = { isAxiosError: true, response: { status } }
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchWikiPageByTitle ('ホーム', { })).rejects.toBe (error)
+  })
+
+  it ('preserves network failures for callers', async () => {
+    const error = new Error ('network failure')
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchWikiPageByTitle ('ホーム', { })).rejects.toBe (error)
   })
 })

frontend/src/lib/wiki.ts

@@ -1,3 +1,5 @@
+import { isAxiosError } from 'axios'
+
 import { apiGet } from '@/lib/api'
 
 import type { WikiPage } from '@/types'
@@ -21,8 +23,10 @@ export const fetchWikiPageByTitle = async (
   {
     return await apiGet (`/wiki/title/${ encodeURIComponent (title) }`, { params: { version } })
   }
-  catch
+  catch (error)
   {
+    if (isAxiosError (error) && error.response?.status === 404)
       return null
+    throw error
   }
 }

frontend/src/mdx-components.test.tsx

@@ -0,0 +1,77 @@
+import { fireEvent, screen, within } from '@testing-library/react'
+import { afterAll, beforeEach, describe, expect, it, vi } from 'vitest'
+import { Route, Routes } from 'react-router-dom'
+
+import HelpDetailPage from '@/pages/help/HelpDetailPage'
+import { compileMdx, transformMdx } from '@/test/compileMdx'
+import { helpFixture } from '@/test/helpFixtures'
+import { renderWithProviders } from '@/test/render'
+
+const prefetch = vi.hoisted (() => vi.fn (async () => {}))
+vi.hoisted (() => {
+  vi.stubGlobal ('Uint8Array', Object.getPrototypeOf (new TextEncoder ().encode ('')).constructor)
+})
+afterAll (() => vi.unstubAllGlobals ())
+vi.mock ('@/lib/prefetchers', () => ({ prefetchForURL: prefetch }))
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+
+const tableSource = [
+    '# 表のある記事', '', '| 項目 | 説明 |', '| --- | --- |',
+    '| [ヘルプ](/help/guide) | **強調** |', '| 通常 | 本文 |'].join ('\n')
+
+
+describe ('Help MDX with the application compiler', () => {
+  beforeEach (() => helpFixture.reset ())
+
+  it ('compiles GFM table structure, links and emphasis', async () => {
+    const Content = await compileMdx (tableSource)
+    renderWithProviders (<Content/>)
+    const table = screen.getByRole ('table')
+    expect (table.querySelector ('thead')).not.toBeNull ()
+    expect (table.querySelector ('tbody')).not.toBeNull ()
+    expect (within (table).getAllByRole ('columnheader')).toHaveLength (2)
+    expect (within (table).getAllByRole ('cell')).toHaveLength (4)
+    expect (within (table).getByRole ('link', { name: 'ヘルプ' }))
+	.toHaveAttribute ('href', '/help/guide')
+    expect (table.querySelector ('strong')).toHaveTextContent ('強調')
+  })
+
+  it ('retains headings, paragraphs and lists', async () => {
+    const Content = await compileMdx ('# 見出し\n\n本文\n\n- 第一\n- 第二')
+    renderWithProviders (<Content/>)
+    expect (screen.getByRole ('heading', { level: 1 })).toHaveTextContent ('見出し')
+    expect (screen.getByText ('本文').tagName).toBe ('P')
+    expect (screen.getAllByRole ('listitem')).toHaveLength (2)
+  })
+
+  it ('keeps tables inside the Help dark-mode typography container', async () => {
+    const Content = await compileMdx (tableSource)
+    helpFixture.modules['../../help/guide/editions/ja/2026-10-02.10.mdx']
+	.mockResolvedValue ({ default: Content })
+    renderWithProviders (
+	<Routes><Route path="/help/:identifier" element={<HelpDetailPage/>}/></Routes>,
+	{ route: '/help/guide' })
+    const table = await screen.findByRole ('table')
+    expect (table.closest ('article')).toHaveClass ('prose', 'dark:prose-invert')
+  })
+
+  it ('preserves long cell contents when rendering a wide table', async () => {
+    const cell = 'wide'.repeat (100)
+    const Content = await compileMdx (`| 項目 |\n| --- |\n| ${ cell } |`)
+    renderWithProviders (<Content/>)
+    expect (screen.getByRole ('cell')).toHaveTextContent (cell)
+  })
+
+  it.each (['.mdx?raw', '.mdx?url']) ('preserves the %s transform bypass', async suffix => {
+    expect (await transformMdx (tableSource, suffix)).toBeNull ()
+  })
+
+  it ('uses the common PrefetchLink interaction for internal MDX links', async () => {
+    prefetch.mockClear ()
+    const Content = await compileMdx ('[内部リンク](/help/guide)')
+    renderWithProviders (<Content/>)
+    fireEvent.mouseEnter (screen.getByRole ('link', { name: '内部リンク' }))
+    expect (prefetch).toHaveBeenCalledWith (expect.anything (),
+	new URL ('/help/guide', window.location.origin).href)
+  })
+})

frontend/src/mdx-components.tsx

@@ -1,4 +1,52 @@
+import { useMemo } from 'react'
+import { useLocation } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+
 import type { MDXComponents } from 'mdx/types'
+import type { ComponentProps } from 'react'
 
 
-export const useMDXComponents = (): MDXComponents => ({ })
+const MDXLink = (
+    { href, children, ...props }: ComponentProps<'a'>,
+) => {
+  const location = useLocation ()
+  const url = useMemo (() => {
+    try
+    {
+      const base = new URL (location.pathname + location.search, window.location.origin)
+      return href ? new URL (href, base) : null
+    }
+    catch
+    {
+      return null
+    }
+  }, [href, location.pathname, location.search])
+  const internal = url != null
+      && url.origin === window.location.origin
+      && (url.protocol === 'http:' || url.protocol === 'https:')
+  const anchor = href?.startsWith ('#')
+      || (url?.pathname === location.pathname
+	  && url.search === location.search && Boolean (url.hash))
+  const external = url != null && !(internal)
+      && (url.protocol === 'http:' || url.protocol === 'https:')
+
+  if (internal && !(anchor) && props.download == null)
+  {
+    return (
+	<PrefetchLink to={url.pathname + url.search + url.hash} {...props}>
+	  {children}
+	</PrefetchLink>)
+  }
+
+  return (
+      <a href={href}
+	 {...props}
+	 target={external ? props.target ?? '_blank' : props.target}
+	 rel={props.rel ?? 'noopener noreferrer'}>
+	{children}
+      </a>)
+}
+
+
+export const useMDXComponents = (): MDXComponents => ({ a: MDXLink })

frontend/src/pages/help/HelpChangesPage.test.tsx

@@ -0,0 +1,55 @@
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { render, screen } from '@testing-library/react'
+import { HelmetProvider } from 'react-helmet-async'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { apiGet } from '@/lib/api'
+import App from '@/App'
+import { helpFixture } from '@/test/helpFixtures'
+
+vi.hoisted (() => {
+  window.history.replaceState (null, '', '/help/changes')
+})
+
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+vi.mock ('@/lib/api', () => ({ apiGet: vi.fn (), apiPost: async () => ({}),
+			    isApiError: () => false }))
+vi.mock ('@/components/TopNav', () => ({ default: () => null }))
+vi.mock ('@/components/DevModeWatermark', () => ({ default: () => null }))
+vi.mock ('@/lib/useClientBehaviourSettings', () => ({
+    useClientBehaviourSettings: () => ({ animation: 'off', linkPreload: 'off' }) }))
+
+
+describe ('Help global edition history', () => {
+  beforeEach (() => helpFixture.reset ())
+
+  it ('routes /help/changes to published editions in date and numeric order', async () => {
+    const client = new QueryClient ({ defaultOptions: { queries: { retry: false } } })
+    const { container } = render (
+	<QueryClientProvider client={client}>
+	  <HelmetProvider><App/></HelmetProvider>
+	</QueryClientProvider>)
+    const links = await screen.findAllByRole ('link')
+    const editions = links.map (link => link.getAttribute ('href'))
+	.filter (href => href?.startsWith ('/help/') && href.includes ('edition='))
+    expect (editions).toEqual ([
+	`/help/${encodeURIComponent ('設定 手順')}?edition=2026-10-03`,
+	'/help/guide?edition=2026-10-02.10', '/help/guide?edition=2026-10-02.3',
+	'/help/guide?edition=2026-10-02.2', '/help/guide?edition=2026-10-02',
+	'/help/guide?edition=2026-10-01'])
+    expect (container).toHaveTextContent ('旧ホーム')
+    expect (screen.getAllByRole ('columnheader').map (cell => cell.textContent))
+	.toEqual (['差分', 'タイトル', '有効開始年月日'])
+    expect (container).not.toHaveTextContent ('未公開ホーム')
+    expect (container).not.toHaveTextContent ('Invalid Date')
+    expect (container.textContent).not.toMatch (/\d{1,2}:\d{2}/)
+    expect (screen.getAllByRole ('link', { name: '差分' }).map (link =>
+	link.getAttribute ('href'))).toEqual ([
+	'/help/guide/diff?from=2026-10-02.3&to=2026-10-02.10',
+	'/help/guide/diff?from=2026-10-02.2&to=2026-10-02.3',
+	'/help/guide/diff?from=2026-10-02&to=2026-10-02.2',
+	'/help/guide/diff?from=2026-10-01&to=2026-10-02'])
+    expect (apiGet).not.toHaveBeenCalled ()
+    expect (window.location.pathname).toBe ('/help/changes')
+  })
+})

frontend/src/pages/help/HelpChangesPage.tsx

@@ -0,0 +1,119 @@
+import { useQuery } from '@tanstack/react-query'
+import { useMemo } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useSearchParams } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import PageTitle from '@/components/common/PageTitle'
+import Pagination from '@/components/common/Pagination'
+import MainArea from '@/components/layout/MainArea'
+import { SITE_TITLE } from '@/config'
+import { getHelpChanges, helpEditionDate } from '@/lib/help'
+import { helpKeys } from '@/lib/queryKeys'
+import { LIST_LIMIT_OPTIONS } from '@/lib/settings'
+import { dateString } from '@/lib/utils'
+
+import type { FC } from 'react'
+
+
+const HelpChangesPage: FC = () => {
+  const [searchParams, setSearchParams] = useSearchParams ()
+  const identifier = searchParams.get ('identifier') ?? ''
+  const pageValue = searchParams.get ('page') ?? '1'
+  const pageNumber = Number (pageValue)
+  const requestedPage =
+      (/^[1-9]\d*$/.test (pageValue) && Number.isSafeInteger (pageNumber))
+      ? pageNumber : 1
+  const limit = LIST_LIMIT_OPTIONS.find (
+      value => String (value) === searchParams.get ('limit')) ?? 20
+  const { data: changes = [], isLoading, error } = useQuery ({
+      queryKey: helpKeys.changes ('ja'),
+      queryFn: () => getHelpChanges ('ja'),
+      staleTime: Infinity })
+
+  const results = useMemo (() => identifier
+      ? changes.filter (entry => entry.identifier === identifier)
+      : changes, [changes, identifier])
+  const totalPages = Math.ceil (results.length / limit)
+  const page = requestedPage <= Math.max (1, totalPages) ? requestedPage : 1
+  const pageResults = results.slice ((page - 1) * limit, page * limit)
+
+  const handleLimit = (value: string) => {
+    const next = new URLSearchParams (searchParams)
+    next.set ('limit', value)
+    next.set ('page', '1')
+    setSearchParams (next)
+  }
+
+  return (
+      <MainArea className="min-w-0 max-w-full">
+	<Helmet>
+	  <title>{`ヘルプ改定履歴 | ${ SITE_TITLE }`}</title>
+	</Helmet>
+	<div className="flex flex-wrap items-center justify-between gap-3">
+	  <PageTitle>ヘルプ改定履歴</PageTitle>
+	  <label className="flex items-center gap-2 text-xs text-muted-foreground">
+	    <span>件数</span>
+	    <select value={limit} onChange={ev => handleLimit (ev.target.value)}
+		className="rounded border border-border bg-background px-2 py-1 text-sm
+			   text-foreground">
+	      {LIST_LIMIT_OPTIONS.map (value => (
+		  <option key={value} value={value}>{value}</option>))}
+	    </select>
+	  </label>
+	</div>
+
+	{isLoading
+	 ? <p className="mt-4">読み込み中...</p>
+	 : (error
+	    ? <p className="mt-4 text-red-600" role="alert">{error.message}</p>
+	    : (
+		<div className="mt-4">
+		  <div className="min-w-0 max-w-full overflow-x-auto">
+		    <table className="table-auto w-full min-w-[900px] whitespace-nowrap
+				      border-collapse">
+		      <thead className="border-b-2 border-black dark:border-white">
+			<tr>
+			  <th className="p-2 text-left">差分</th>
+			  <th className="p-2 text-left">タイトル</th>
+			  <th className="p-2 text-left">有効開始年月日</th>
+			</tr>
+		      </thead>
+		      <tbody>
+			{pageResults.map (entry => {
+			  const path = `/help/${ encodeURIComponent (entry.identifier) }`
+			  const diffQuery = new URLSearchParams ({
+			      from: entry.pred ?? '', to: entry.edition })
+			  const diffTo = `${ path }/diff?${ diffQuery.toString () }`
+			  const updatedAt = helpEditionDate (entry.edition)
+
+			  return (
+			      <tr key={`${ entry.identifier }/${ entry.edition }`}
+				  className="even:bg-gray-100 text-gray-900
+					     dark:even:bg-gray-700 dark:text-gray-100">
+				<td className="p-2">
+				  {entry.pred != null && (
+				      <PrefetchLink to={diffTo}>
+					差分
+				      </PrefetchLink>)}
+				</td>
+				<td className="p-2">
+				  <PrefetchLink to={`${ path }?edition=${ entry.edition }`}>
+				    {entry.title}
+				  </PrefetchLink>
+				</td>
+				<td className="p-2">
+				  {updatedAt != null && dateString (updatedAt, 'hour')}
+				</td>
+			      </tr>)
+			})}
+		      </tbody>
+		    </table>
+		  </div>
+		  {totalPages > 0 && <Pagination page={page} totalPages={totalPages}/>}
+		</div>))}
+      </MainArea>)
+}
+
+
+export default HelpChangesPage

frontend/src/pages/help/HelpDetailPage.test.tsx

@@ -0,0 +1,128 @@
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
+import { Route, Routes, useLocation, useNavigate } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import HelpDetailPage from '@/pages/help/HelpDetailPage'
+import { helpFixture } from '@/test/helpFixtures'
+import { renderWithProviders } from '@/test/render'
+
+import type { ReactElement } from 'react'
+
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+
+
+const Navigation = () => {
+  const navigate = useNavigate ()
+  const location = useLocation ()
+  return (
+      <>
+	<output data-testid="location">{location.pathname}{location.search}</output>
+	<button onClick={() => navigate ('/help/設定%20手順')}>switch article</button>
+	<button onClick={() => navigate ('/help/guide?edition=2026-10-02.3')}>
+	  switch edition
+	</button>
+      </>)
+}
+
+
+const renderDetail = (route = '/help/guide') => renderWithProviders (
+    <>
+      <Navigation/>
+      <Routes>
+	<Route path="/help/:identifier" element={<HelpDetailPage/>}/>
+      </Routes>
+    </>, { route })
+
+
+describe ('Help details', () => {
+  beforeEach (() => helpFixture.reset ())
+
+  it.each (['2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10']) (
+      'displays a date without inventing a time for edition %s', async edition => {
+	const { container } = renderDetail (`/help/guide?edition=${ edition }`)
+	await screen.findByRole ('heading')
+	expect (container).toHaveTextContent ('10月2日')
+	expect (container).not.toHaveTextContent ('Invalid Date')
+	expect (container.textContent).not.toMatch (/\d{1,2}:\d{2}/)
+	const revision = edition.split ('.')[1]
+	if (revision != null)
+	  expect (container).toHaveTextContent (` .${ revision }`)
+	expect (helpFixture.modules[`../../help/guide/editions/ja/${ edition }.mdx`])
+	    .toHaveBeenCalled ()
+      })
+
+  it ('displays current_edition H1 and body even when newer files exist', async () => {
+    renderDetail ()
+    expect (await screen.findByRole ('heading', { name: 'ホーム第十版' }))
+	.toBeInTheDocument ()
+    expect (screen.getByText ('タグを検索する 第十版本文')).toBeInTheDocument ()
+    expect (screen.queryByText ('未公開限定本文')).not.toBeInTheDocument ()
+    await waitFor (() => expect (document.title).toContain ('ホーム第十版 ヘルプ'))
+  })
+
+  it ('uses the historical H1 in both page and document titles', async () => {
+    renderDetail ('/help/guide?edition=2026-10-01')
+    expect (await screen.findByRole ('heading', { name: '旧ホーム' })).toBeInTheDocument ()
+    expect (screen.getByText ('過去限定本文')).toBeInTheDocument ()
+    await waitFor (() => expect (document.title).toContain ('旧ホーム ヘルプ'))
+    expect (screen.getByText ('(最古)')).toBeInTheDocument ()
+    expect (screen.getByRole ('link', { name: '新 >' }))
+	.toHaveAttribute ('href', '/help/guide?edition=2026-10-02')
+  })
+
+  it ('navigates .2, .3 and .10 in numeric edition order', async () => {
+    renderDetail ('/help/guide?edition=2026-10-02.3')
+    await screen.findByRole ('heading', { name: 'ホーム第三版' })
+    expect (screen.getByRole ('link', { name: '< 古' }))
+	.toHaveAttribute ('href', '/help/guide?edition=2026-10-02.2')
+    const next = screen.getByRole ('link', { name: '新 >' })
+    expect (next).toHaveAttribute ('href', '/help/guide?edition=2026-10-02.10')
+    fireEvent.click (next)
+    await screen.findByRole ('heading', { name: 'ホーム第十版' })
+    expect (screen.getByText ('(最新)')).toBeInTheDocument ()
+    expect (screen.queryByText ('第三版本文')).not.toBeInTheDocument ()
+  })
+
+  it.each (['/help/missing', '/help/guide?edition=missing',
+      '/help/guide?edition=2026-02-30', '/help/guide?edition=2026-10-02.2.extra',
+      '/help/guide?edition=2026-10-02.11']) (
+      'shows NotFound without redirecting %s', async route => {
+	renderDetail (route)
+	expect (await screen.findByText ('404')).toBeInTheDocument ()
+	expect (screen.getByTestId ('location')).toHaveTextContent (route)
+      })
+
+  it ('hides the old body and title immediately while another article loads', async () => {
+    let finish!: (value: { default: () => ReactElement }) => void
+    const pending = new Promise<{ default: () => ReactElement }> (resolve => {
+      finish = resolve
+    })
+    helpFixture.modules['../../help/設定 手順/editions/ja/2026-10-03.mdx']
+	.mockReturnValueOnce (pending)
+    renderDetail ()
+    await screen.findByRole ('heading', { name: 'ホーム第十版' })
+    fireEvent.click (screen.getByRole ('button', { name: 'switch article' }))
+    expect (screen.queryByText ('タグを検索する 第十版本文')).not.toBeInTheDocument ()
+    await waitFor (() => expect (document.title).not.toContain ('ホーム'))
+    await act (async () => finish ({ default: () => <h1>設定</h1> }))
+    await screen.findByRole ('heading', { name: '設定' })
+    await waitFor (() => expect (document.title).toContain ('設定 ヘルプ'))
+  })
+
+  it ('ignores a late response for the previous edition', async () => {
+    let finish!: (value: { default: () => ReactElement }) => void
+    const pending = new Promise<{ default: () => ReactElement }> (resolve => {
+      finish = resolve
+    })
+    const loader = helpFixture.modules['../../help/guide/editions/ja/2026-10-02.10.mdx']
+    loader.mockReturnValueOnce (pending)
+    renderDetail ()
+    await waitFor (() => expect (loader).toHaveBeenCalled ())
+    fireEvent.click (screen.getByRole ('button', { name: 'switch edition' }))
+    await screen.findByRole ('heading', { name: 'ホーム第三版' })
+    await act (async () => finish ({ default: () => <h1>遅延した旧本文</h1> }))
+    expect (screen.queryByText ('遅延した旧本文')).not.toBeInTheDocument ()
+    expect (screen.getByRole ('heading', { name: 'ホーム第三版' })).toBeInTheDocument ()
+    await waitFor (() => expect (document.title).toContain ('ホーム第三版 ヘルプ'))
+  })
+})

frontend/src/pages/help/HelpDetailPage.tsx

@@ -0,0 +1,106 @@
+import { useQuery } from '@tanstack/react-query'
+import { Helmet } from 'react-helmet-async'
+import { useLocation, useParams } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import MainArea from '@/components/layout/MainArea'
+import { SITE_TITLE } from '@/config'
+import { getHelpArticle,
+	 getHelpEditionContent,
+	 helpEditionDate,
+	 parseHelpEdition } from '@/lib/help'
+import { dateString } from '@/lib/utils'
+import { helpKeys } from '@/lib/queryKeys'
+import NotFound from '@/pages/NotFound'
+
+import type { FC } from 'react'
+
+
+const HelpDetailPage: FC = () => {
+  const { identifier = '' } = useParams ()
+  const location = useLocation ()
+
+  // Locale 対応が入るまでは ja 固定
+  const language = 'ja'
+
+  const { data: article, isLoading: articleLoading } = useQuery ({
+      queryKey: helpKeys.article (identifier),
+      queryFn: () => getHelpArticle (identifier),
+      staleTime: Infinity })
+
+  const query = new URLSearchParams (location.search)
+  const requestedEdition = query.get ('edition')
+
+  const languageMeta = article?.languages[language]
+
+  const edition = requestedEdition ?? languageMeta?.currentEdition
+  const editionInfo = parseHelpEdition (edition ?? '')
+  const editionDate = helpEditionDate (edition ?? '')
+
+  const editions = languageMeta?.publishedEditions ?? []
+
+  const index = edition ? editions.indexOf (edition) : -1
+  const pred = index > 0 ? editions[index - 1] : undefined
+  const succ =
+      index >= 0 && index < editions.length - 1
+      ? editions[index + 1]
+      : undefined
+
+  const { data: current, isSuccess, isError } = useQuery ({
+      enabled: edition != null && editionInfo != null && editions.includes (edition),
+      queryKey: helpKeys.edition (identifier, language, edition ?? ''),
+      queryFn: () => getHelpEditionContent (identifier, language, edition ?? ''),
+      staleTime: Infinity })
+
+  if (!articleLoading
+      && (article == null
+	  || languageMeta == null
+	  || edition == null
+	  || editionInfo == null
+	  || !(editions.includes (edition))))
+    return <NotFound/>
+
+  if (isError || (isSuccess && current == null))
+    return <NotFound/>
+
+  const Content = current?.content
+
+  return (
+      <MainArea>
+	<Helmet>
+	  <title>{current?.title || identifier} ヘルプ | {SITE_TITLE}</title>
+	</Helmet>
+
+	{requestedEdition && (
+	    <div className="text-sm flex gap-3 items-center justify-center
+			    border border-gray-700 rounded px-2 py-1 mb-4">
+	      {pred
+	       ? (
+		  <PrefetchLink
+		      to={`/help/${ encodeURIComponent (identifier) }?edition=${ pred }`}>
+		    &lt; 古
+		  </PrefetchLink>)
+	       : '(最古)'}
+
+	      <span>
+		{editionDate != null && dateString (editionDate, 'hour')}
+		{editionInfo?.revision != null && ` .${ editionInfo.revision }`}
+	      </span>
+
+	      {succ
+	       ? (
+		  <PrefetchLink
+		      to={`/help/${ encodeURIComponent (identifier) }?edition=${ succ }`}>
+		    新 &gt;
+		  </PrefetchLink>)
+	       : '(最新)'}
+	    </div>)}
+
+	<article className="prose dark:prose-invert mx-auto p-4">
+	  {Content ? <Content/> : <div>Loading...</div>}
+	</article>
+      </MainArea>)
+}
+
+
+export default HelpDetailPage

frontend/src/pages/help/HelpDiffPage.tsx

@@ -0,0 +1,81 @@
+import { useQuery } from '@tanstack/react-query'
+import { Helmet } from 'react-helmet-async'
+import { useParams, useSearchParams } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import PageTitle from '@/components/common/PageTitle'
+import MainArea from '@/components/layout/MainArea'
+import { SITE_TITLE } from '@/config'
+import { getHelpDiff } from '@/lib/help'
+import { helpKeys } from '@/lib/queryKeys'
+import { cn } from '@/lib/utils'
+import NotFound from '@/pages/NotFound'
+
+import type { FC } from 'react'
+
+const markers = { added: '+ ', removed: '- ', unchanged: '  ' }
+
+
+const HelpDiffPage: FC = () => {
+  const { identifier = '' } = useParams ()
+  const [searchParams] = useSearchParams ()
+  const from = searchParams.get ('from') ?? ''
+  const to = searchParams.get ('to') ?? ''
+  const validParams = Boolean (identifier && from && to)
+      && searchParams.getAll ('from').length === 1
+      && searchParams.getAll ('to').length === 1
+  const { data: diff, isLoading, isError } = useQuery ({
+      enabled: validParams,
+      queryKey: helpKeys.diff (identifier, 'ja', from, to),
+      queryFn: () => getHelpDiff (identifier, 'ja', from, to),
+      staleTime: Infinity })
+
+  if (!(validParams) || isError || (!(isLoading) && diff == null))
+    return <NotFound/>
+
+  const title = `${ diff?.to.title ?? identifier } (${ from } → ${ to })`
+  const path = `/help/${ encodeURIComponent (identifier) }`
+
+  return (
+      <MainArea className="min-w-0 max-w-full">
+	<Helmet>
+	  <title>{`ヘルプ 差分: ${ title } | ${ SITE_TITLE }`}</title>
+	</Helmet>
+	<PageTitle>{title}</PageTitle>
+
+	{diff
+	 ? (
+	    <>
+	      <div className="flex flex-wrap items-center gap-3">
+		<PrefetchLink to={`${ path }?edition=${ encodeURIComponent (from) }`}>
+		  {diff.from.title} ({from})
+		</PrefetchLink>
+		<span>→</span>
+		<PrefetchLink to={`${ path }?edition=${ encodeURIComponent (to) }`}>
+		  {diff.to.title} ({to})
+		</PrefetchLink>
+	      </div>
+	      <pre className="mt-4 overflow-x-auto whitespace-pre">
+		<code>
+		  {diff.lines.map ((line, index) => {
+		    const colour = cn (
+			'block text-gray-900 dark:text-gray-100',
+			line.type === 'added' && 'bg-green-200 dark:bg-green-800',
+			line.type === 'added' && 'text-green-950 dark:text-green-50',
+			line.type === 'removed' && 'bg-red-200 dark:bg-red-800',
+			line.type === 'removed' && 'text-red-950 dark:text-red-50')
+
+		    return (
+			<span key={index} className={colour}>
+			  {markers[line.type]}{line.content.replace (/\r?\n$/, '')}
+			</span>)
+		  })}
+		</code>
+	      </pre>
+	    </>)
+	 : <div>Loading...</div>}
+      </MainArea>)
+}
+
+
+export default HelpDiffPage

frontend/src/pages/help/HelpListPage.test.tsx

@@ -0,0 +1,130 @@
+import { fireEvent, screen } from '@testing-library/react'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import HelpListPage from '@/pages/help/HelpListPage'
+import { helpFixture } from '@/test/helpFixtures'
+import { renderWithProviders } from '@/test/render'
+
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+
+
+describe ('Help search', () => {
+  beforeEach (() => helpFixture.reset ())
+
+  it ('initially lists each current article once with encoded detail links', async () => {
+    renderWithProviders (<HelpListPage/>, { route: '/help' })
+    expect (await screen.findByRole ('link', { name: 'ホーム第十版' }))
+	.toHaveAttribute ('href', '/help/guide')
+    expect (screen.getByRole ('link', { name: '設定' }))
+	.toHaveAttribute ('href', `/help/${encodeURIComponent ('設定 手順')}`)
+    expect (screen.getByText ('2 件')).toBeInTheDocument ()
+    expect (screen.queryByText ('旧ホーム')).not.toBeInTheDocument ()
+    expect (screen.queryByText ('未公開ホーム')).not.toBeInTheDocument ()
+  })
+
+  it.each ([
+      ['ホーム', '', ['ホーム第十版']],
+      ['', '検索', ['ホーム第十版']],
+      ['', 'タグ', ['設定', 'ホーム第十版']],
+      ['ホーム', '設定', []],
+      ['ホーム', '検索', ['ホーム第十版']],
+      ['旧ホーム', '', []],
+      ['', '過去限定本文', []]]) (
+      'searches title %s and body %s together', async (title, body, expected) => {
+	const { container } = renderWithProviders (<HelpListPage/>)
+	await screen.findByText ('2 件')
+	fireEvent.change (screen.getByRole ('textbox', { name: 'タイトル' }), {
+	    target: { value: title } })
+	fireEvent.change (screen.getByRole ('textbox', { name: '内容' }), {
+	    target: { value: body } })
+	fireEvent.click (screen.getByRole ('button', { name: '検索' }))
+	expect (Array.from (container.querySelectorAll ('tbody a'), link => link.textContent))
+	    .toEqual (expected)
+	if (expected.length === 0)
+	  expect (screen.getByText ('該当する記事がありません．')).toBeInTheDocument ()
+      })
+
+  it ('displays loading failures without stale results', async () => {
+    helpFixture.loads.search.mockImplementationOnce (() => {
+      throw new Error ('fixture loading failed')
+    })
+    renderWithProviders (<HelpListPage/>)
+    expect (await screen.findByRole ('alert')).toHaveTextContent ('fixture loading failed')
+    expect (screen.queryByRole ('link', { name: 'ホーム第十版' })).not.toBeInTheDocument ()
+  })
+
+  it ('sorts edition suffixes numerically and displays their date without a time', async () => {
+    const editions = ['2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10']
+    helpFixture.assets.search.default.ja = editions.map ((edition, index) => ({
+	identifier: `article-${ index }`, edition, title: `article-${ index }`, body: '' }))
+    const { container } = renderWithProviders (<HelpListPage/>, { route: '/help' })
+    await screen.findByText ('4 件')
+    expect (Array.from (container.querySelectorAll ('tbody a'), link => link.textContent))
+	.toEqual (['article-3', 'article-2', 'article-1', 'article-0'])
+    const dates = Array.from (container.querySelectorAll ('tbody tr'), row =>
+	row.children[1].textContent)
+    expect (dates).toHaveLength (4)
+    dates.forEach (date => {
+      expect (date).toContain ('10月2日')
+      expect (date).not.toContain ('Invalid Date')
+      expect (date).not.toMatch (/\d{1,2}:\d{2}/)
+    })
+  })
+
+  it.each ([['ホーム', 'ほーむ', '', true], ['ほーむ', 'ホーム', '', true],
+      ['ホーム', 'ﾎｰﾑ', '', true], ['ホーム', '', 'ホーム', true],
+      ['ホーム', 'ほーむ', 'ﾎｰﾑ', true], ['ホーム', 'ほーむ', '不一致', false]] as const) (
+      'searches title %s with %s and body with %s', async (title, query, text, found) => {
+	const entry = { identifier: 'guide', edition: '2026-10-02.10',
+	    title, body: 'ほーむの案内' }
+	helpFixture.assets.search.default.ja = [entry]
+	const params = new URLSearchParams ({ title: query, text })
+	renderWithProviders (<HelpListPage/>, { route: `/help?${ params }` })
+	await screen.findByText (`${ found ? 1 : 0 } 件`)
+	if (found)
+	  expect (screen.getByRole ('link', { name: title })).toHaveAttribute ('href', '/help/guide')
+	else
+	  expect (screen.queryByRole ('link', { name: title })).not.toBeInTheDocument ()
+	expect (entry).toEqual ({ identifier: 'guide', edition: '2026-10-02.10',
+	    title, body: 'ほーむの案内' })
+      })
+
+  // ai_ci equality is documented by MySQL; these are not captured DB sort results.
+  it.each (['asc', 'desc']) ('orders different titles before identifiers in order %s',
+      async direction => {
+	helpFixture.assets.search.default.ja = [
+	    { identifier: 'alpha', edition: '2026-10-02', title: 'Zebra', body: '' },
+	    { identifier: 'beta', edition: '2026-10-02', title: 'Apple', body: '' }]
+	const { container } = renderWithProviders (<HelpListPage/>, {
+	    route: `/help?order=title:${ direction }` })
+	await screen.findByText ('2 件')
+	const expected = direction === 'asc'
+	    ? ['/help/beta', '/help/alpha'] : ['/help/alpha', '/help/beta']
+	expect (Array.from (container.querySelectorAll ('tbody a'), link =>
+	    link.getAttribute ('href'))).toEqual (expected)
+      })
+
+  it.each (['asc', 'desc']) ('uses identifier ties for MySQL ai_ci title order %s',
+      async direction => {
+	helpFixture.assets.search.default.ja = [
+	    { identifier: 'alpha', edition: '2026-10-02', title: 'Éclair', body: '' },
+	    { identifier: 'beta', edition: '2026-10-02', title: 'eclair', body: '' }]
+	const { container } = renderWithProviders (<HelpListPage/>, {
+	    route: `/help?order=title:${ direction }` })
+	await screen.findByText ('2 件')
+	expect (Array.from (container.querySelectorAll ('tbody a'), link =>
+	    link.getAttribute ('href'))).toEqual (['/help/alpha', '/help/beta'])
+      })
+
+  it.each (['asc', 'desc']) ('ignores title case before identifier ties in order %s',
+      async direction => {
+	helpFixture.assets.search.default.ja = [
+	    { identifier: 'alpha', edition: '2026-10-02', title: 'home', body: '' },
+	    { identifier: 'beta', edition: '2026-10-02', title: 'HOME', body: '' }]
+	const { container } = renderWithProviders (<HelpListPage/>, {
+	    route: `/help?order=title:${ direction }` })
+	await screen.findByText ('2 件')
+	expect (Array.from (container.querySelectorAll ('tbody a'), link =>
+	    link.getAttribute ('href'))).toEqual (['/help/alpha', '/help/beta'])
+      })
+})

frontend/src/pages/help/HelpListPage.tsx

@@ -0,0 +1,212 @@
+import { useQuery } from '@tanstack/react-query'
+import { useEffect, useMemo, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useSearchParams } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import SortHeader from '@/components/SortHeader'
+import FormField from '@/components/common/FormField'
+import PageTitle from '@/components/common/PageTitle'
+import Pagination from '@/components/common/Pagination'
+import MainArea from '@/components/layout/MainArea'
+import { SITE_TITLE } from '@/config'
+import { compareHelpEditions,
+	 compareHelpTitles,
+	 getHelpSearchEntries,
+	 helpEditionDate,
+	 normaliseHelpSearchText } from '@/lib/help'
+import { helpKeys } from '@/lib/queryKeys'
+import { LIST_LIMIT_OPTIONS } from '@/lib/settings'
+import { dateString, inputClass } from '@/lib/utils'
+
+import type { FormEvent, FC } from 'react'
+
+type SearchConditions = { title: string; text: string }
+type HelpOrderField = 'title' | 'updated_at'
+type HelpOrder = `${ HelpOrderField }:${ 'asc' | 'desc' }`
+
+const defaultDirection: Record<HelpOrderField, 'asc' | 'desc'> = {
+    title: 'asc', updated_at: 'desc' }
+
+
+const HelpSearchPage: FC = () => {
+  const [searchParams, setSearchParams] = useSearchParams ()
+  const pageValue = searchParams.get ('page') ?? '1'
+  const pageNumber = Number (pageValue)
+  const requestedPage =
+      (/^[1-9]\d*$/.test (pageValue) && Number.isSafeInteger (pageNumber))
+      ? pageNumber : 1
+  const limit = LIST_LIMIT_OPTIONS.find (
+      value => String (value) === searchParams.get ('limit')) ?? 20
+  const requestedOrder = searchParams.get ('order') ?? 'updated_at:desc'
+  const order: HelpOrder =
+      ['title:asc', 'title:desc', 'updated_at:asc', 'updated_at:desc'].includes (requestedOrder)
+      ? requestedOrder as HelpOrder
+      : 'updated_at:desc'
+  const conditions = useMemo<SearchConditions> (() => ({
+      title: searchParams.get ('title') ?? '',
+      text: searchParams.get ('text') ?? '' }), [searchParams])
+  const [title, setTitle] = useState (conditions.title)
+  const [text, setText] = useState (conditions.text)
+  const { data: entries = [], isLoading: loading, error } = useQuery ({
+      queryKey: helpKeys.index ('ja'),
+      queryFn: () => getHelpSearchEntries ('ja'),
+      staleTime: Infinity })
+
+  useEffect (() => {
+    setTitle (conditions.title)
+    setText (conditions.text)
+  }, [conditions.title, conditions.text])
+
+  const results = useMemo (() => {
+    const titleQuery = normaliseHelpSearchText (conditions.title.trim ())
+    const textQuery = normaliseHelpSearchText (conditions.text.trim ())
+    const [field, direction] = order.split (':')
+
+    return (
+	entries.filter (entry => (
+	    (!(titleQuery)
+	     || normaliseHelpSearchText (entry.title).includes (titleQuery))
+	    && (!(textQuery)
+		|| normaliseHelpSearchText (entry.body).includes (textQuery))))
+	.sort ((a, b) => {
+	  const comparison = field === 'title'
+	      ? compareHelpTitles (a.title, b.title)
+	      : compareHelpEditions (a.edition, b.edition)
+
+	  return (direction === 'asc' ? comparison : -comparison)
+	      || a.identifier.localeCompare (b.identifier)
+	}))
+  }, [entries, conditions, order])
+
+  const totalPages = Math.ceil (results.length / limit)
+  const page = requestedPage <= Math.max (1, totalPages) ? requestedPage : 1
+  const pageResults = results.slice ((page - 1) * limit, page * limit)
+
+  const handleLimit = (value: string) => {
+    const next = new URLSearchParams (searchParams)
+    next.set ('limit', value)
+    next.set ('page', '1')
+    setSearchParams (next)
+  }
+
+  const handleSearch = (ev: FormEvent<HTMLFormElement>) => {
+    ev.preventDefault ()
+    const next = new URLSearchParams (searchParams)
+    if (title)
+      next.set ('title', title)
+    else
+      next.delete ('title')
+    if (text)
+      next.set ('text', text)
+    else
+      next.delete ('text')
+    next.set ('page', '1')
+    setSearchParams (next)
+  }
+
+  return (
+      <MainArea className="min-w-0 max-w-full">
+	<Helmet>
+	  <title>{`ヘルプ | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<div className="max-w-xl">
+	  <div className="flex flex-wrap items-center justify-between gap-3">
+	    <PageTitle>ヘルプ検索</PageTitle>
+	    <label className="flex items-center gap-2 text-xs text-muted-foreground">
+	      <span>件数</span>
+	      <select value={limit} onChange={ev => handleLimit (ev.target.value)}
+		  className="rounded border border-border bg-background px-2 py-1 text-sm
+			     text-foreground">
+		{LIST_LIMIT_OPTIONS.map (value => (
+		    <option key={value} value={value}>{value}</option>))}
+	      </select>
+	    </label>
+	  </div>
+	  <form onSubmit={handleSearch} className="space-y-2">
+	    <FormField label="タイトル">
+	      {({ invalid }) => (
+		  <input type="text"
+		      aria-label="タイトル"
+		      value={title}
+		      onChange={e => setTitle (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
+
+	    <FormField label="内容">
+	      {({ invalid }) => (
+		  <input type="text"
+		      aria-label="内容"
+		      value={text}
+		      onChange={e => setText (e.target.value)}
+		      className={inputClass (invalid)}/>)}
+	    </FormField>
+
+	    <div className="py-3">
+	      <button type="submit"
+		  className="bg-blue-500 text-white px-4 py-2 rounded">
+		検索
+	      </button>
+	    </div>
+	  </form>
+	</div>
+
+	{loading
+	 ? <p className="mt-4">読み込み中...</p>
+	 : (error
+	    ? <p className="mt-4 text-red-600" role="alert">{error.message}</p>
+	    : (
+		<div className="mt-4">
+		  <p className="mb-2 text-sm" aria-live="polite">{results.length} 件</p>
+		  <div className="min-w-0 max-w-full overflow-x-auto">
+		    <table className="table-auto w-full min-w-[640px] whitespace-nowrap
+				      border-collapse text-gray-900 dark:text-gray-100">
+		      <thead className="border-b-2 border-black dark:border-white">
+			<tr>
+			  <th className="p-2 text-left">
+			    <SortHeader<HelpOrderField>
+				by="title"
+				label="タイトル"
+				currentOrder={order}
+				defaultDirection={defaultDirection}/>
+			  </th>
+			  <th className="p-2 text-left">
+			    <SortHeader<HelpOrderField>
+				by="updated_at"
+				label="有効開始年月日"
+				currentOrder={order}
+				defaultDirection={defaultDirection}/>
+			  </th>
+			</tr>
+		      </thead>
+		      <tbody>
+			{pageResults.map (entry => {
+			  const updatedAt = helpEditionDate (entry.edition)
+
+			  return (
+			      <tr key={entry.identifier}
+				  className="even:bg-gray-100 text-gray-900
+					     dark:even:bg-gray-700 dark:text-gray-100">
+				<td className="p-2">
+				  <PrefetchLink
+				      to={`/help/${encodeURIComponent (entry.identifier)}`}>
+				    {entry.title}
+				  </PrefetchLink>
+				</td>
+				<td className="p-2">
+				  {updatedAt != null && dateString (updatedAt, 'hour')}
+				</td>
+			      </tr>)
+			})}
+		      </tbody>
+		    </table>
+		  </div>
+		  {totalPages > 0 && <Pagination page={page} totalPages={totalPages}/>}
+		  {results.length === 0 && <p className="mt-4">該当する記事がありません．</p>}
+		</div>))}
+      </MainArea>)
+}
+
+
+export default HelpSearchPage

frontend/src/pages/wiki/WikiDetailPage.test.tsx

@@ -1,14 +1,19 @@
-import { screen } from '@testing-library/react'
+import { act, fireEvent, screen, waitFor, within } from '@testing-library/react'
-import { Route, Routes } from 'react-router-dom'
+import { Route, Routes, useLocation } from 'react-router-dom'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
+import { apiPost } from '@/lib/api'
+import { getHelpTitleIndex } from '@/lib/help'
+import { tagsKeys, wikiKeys } from '@/lib/queryKeys'
 import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
-import { buildTag, buildWikiPage } from '@/test/factories'
+import WikiNewPage from '@/pages/wiki/WikiNewPage'
+import { buildTag, buildUser, buildWikiPage } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
 const wikiApi = vi.hoisted (() => ({
   fetchWikiPage:        vi.fn (),
   fetchWikiPageByTitle: vi.fn (),
+  fetchWikiPages:       vi.fn (),
 }))
 
 const tagsApi = vi.hoisted (() => ({
@@ -22,8 +27,140 @@ const postsApi = vi.hoisted (() => ({
 vi.mock ('@/lib/wiki', () => wikiApi)
 vi.mock ('@/lib/tags', () => tagsApi)
 vi.mock ('@/lib/posts', () => postsApi)
+vi.mock ('@/lib/help', () => ({ getHelpTitleIndex: vi.fn () }))
+vi.mock ('@/lib/api', async importOriginal => ({
+    ...await importOriginal<typeof import ('@/lib/api')> (), apiPost: vi.fn () }))
+vi.mock ('@/components/ui/use-toast', () => ({ toast: vi.fn () }))
+vi.mock ('react-markdown-editor-lite', () => ({
+    default: ({ value, onChange }: {
+	value: string
+	onChange: (event: { text: string }) => void }) => (
+	    <textarea aria-label="本文エディタ" value={value}
+		onChange={event => onChange ({ text: event.target.value })}/>) }))
+
+
+const Location = () => {
+  const location = useLocation ()
+  return <output data-testid="location">{location.pathname}{location.search}</output>
+}
+
 
 describe ('WikiDetailPage', () => {
+  beforeEach (() => {
+    wikiApi.fetchWikiPageByTitle.mockReset ().mockResolvedValue (null)
+    wikiApi.fetchWikiPages.mockReset ().mockResolvedValue ([])
+    tagsApi.fetchTagByName.mockReset ().mockResolvedValue (null)
+    postsApi.fetchPosts.mockReset ().mockResolvedValue ({ posts: [], count: 0 })
+    vi.mocked (getHelpTitleIndex).mockReset ().mockResolvedValue ({ })
+    vi.mocked (apiPost).mockReset ()
+  })
+
+  it ('offers creation for an existing tag after the Help lookup completes', async () => {
+    let finish!: (index: Record<string, string[]>) => void
+    const pending = new Promise<Record<string, string[]>> (resolve => {
+      finish = resolve
+    })
+    vi.mocked (getHelpTitleIndex).mockReturnValueOnce (pending)
+    tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: '既存タグ', hasWiki: false }))
+    renderWithProviders (
+	<Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	{ route: `/wiki/${ encodeURIComponent ('既存タグ') }` })
+    await waitFor (() => expect (getHelpTitleIndex).toHaveBeenCalled ())
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+    await act (async () => finish ({ }))
+    expect (await screen.findByRole ('link', { name: '新規作成してください' }))
+	.toHaveAttribute ('href', `/wiki/new?title=${ encodeURIComponent ('既存タグ') }`)
+  })
+
+  it ('creates a tag description through the existing form and displays its content', async () => {
+    const page = buildWikiPage ({ title: '既存タグ', body: '説明文',
+	resourceType: 'tag_description' })
+    tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: page.title, hasWiki: false }))
+    vi.mocked (apiPost).mockResolvedValueOnce (page)
+    const path = `/wiki/${ encodeURIComponent (page.title) }`
+    const { container, queryClient } = renderWithProviders (
+	<>
+	  <Location/>
+	  <Routes>
+	    <Route path="/wiki/new" element={<WikiNewPage user={buildUser ({ role: 'member' })}/>}/>
+	    <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+	  </Routes>
+	</>, { route: path })
+    fireEvent.click (await screen.findByRole ('link', { name: '新規作成してください' }))
+    await screen.findByRole ('heading', { name: '新規 Wiki ページ' })
+    expect (queryClient.getQueryData (wikiKeys.show (page.title, { }))).toBeNull ()
+    queryClient.setQueryData (wikiKeys.index ({ }), [])
+    wikiApi.fetchWikiPageByTitle.mockResolvedValue (page)
+    wikiApi.fetchWikiPages.mockResolvedValue ([page])
+    tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: page.title, hasWiki: true }))
+    expect (screen.getAllByRole ('textbox')[0]).toHaveValue (page.title)
+    fireEvent.change (screen.getByRole ('textbox', { name: '本文エディタ' }), {
+	target: { value: page.body } })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+    await screen.findByRole ('heading', { name: page.title })
+    expect (screen.getByTestId ('location')).toHaveTextContent (path)
+    expect (screen.queryByRole ('textbox', { name: '本文エディタ' })).not.toBeInTheDocument ()
+    expect (within (container.querySelector ('article')!).getByText (page.body))
+	.toBeInTheDocument ()
+    const form = vi.mocked (apiPost).mock.calls[0][1] as FormData
+    expect (form.get ('title')).toBe (page.title)
+    expect (form.get ('body')).toBe (page.body)
+    expect (apiPost).toHaveBeenCalledWith ('/wiki', form,
+	{ headers: { 'Content-Type': 'multipart/form-data' } })
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+    expect (queryClient.getQueryData (wikiKeys.show (page.title, { }))).toEqual (page)
+    await waitFor (() => expect (queryClient.getQueryData (wikiKeys.index ({ })))
+	.toEqual ([page]))
+    await waitFor (() => expect (queryClient.getQueryData (tagsKeys.show (page.title)))
+	.toMatchObject ({ hasWiki: true }))
+    expect (getHelpTitleIndex).toHaveBeenCalledTimes (1)
+  })
+
+  it ('keeps failed saves on the form without changing cached Wiki or tag state', async () => {
+    const title = '既存タグ'
+    const tag = buildTag ({ name: title, hasWiki: false })
+    const path = `/wiki/new?title=${ encodeURIComponent (title) }`
+    vi.mocked (apiPost).mockRejectedValueOnce (new Error ('save failed'))
+    const { queryClient } = renderWithProviders (
+	<><Location/><WikiNewPage user={buildUser ({ role: 'member' })}/></>, { route: path })
+    queryClient.setQueryData (wikiKeys.show (title, { }), null)
+    queryClient.setQueryData (wikiKeys.index ({ }), [])
+    queryClient.setQueryData (tagsKeys.show (title), tag)
+    fireEvent.change (screen.getByRole ('textbox', { name: '本文エディタ' }), {
+	target: { value: '保存しない本文' } })
+    await act (async () => fireEvent.click (screen.getByRole ('button', { name: '追加' })))
+    expect (apiPost).toHaveBeenCalledTimes (1)
+    expect (screen.getByTestId ('location')).toHaveTextContent (path)
+    expect (screen.getByRole ('heading', { name: '新規 Wiki ページ' })).toBeInTheDocument ()
+    expect (queryClient.getQueryData (wikiKeys.show (title, { }))).toBeNull ()
+    expect (queryClient.getQueryData (tagsKeys.show (title))).toEqual (tag)
+    expect (queryClient.getQueryState (wikiKeys.index ({ }))?.isInvalidated).toBe (false)
+  })
+
+  it ('shows NotFound when neither a tag nor a Help title exists', async () => {
+    renderWithProviders (
+	<Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	{ route: '/wiki/missing' })
+    expect (await screen.findByText ('404')).toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+  })
+
+  it.each (['403', '500', 'offline']) ('keeps Wiki error %s distinct from missing content',
+      async message => {
+	wikiApi.fetchWikiPageByTitle.mockRejectedValue (new Error (message))
+	tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: '既存タグ' }))
+	renderWithProviders (
+	    <Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	    { route: `/wiki/${ encodeURIComponent ('既存タグ') }` })
+	expect (await screen.findByRole ('alert')).toHaveTextContent (message)
+	expect (getHelpTitleIndex).not.toHaveBeenCalled ()
+	expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	    .not.toBeInTheDocument ()
+      })
+
   it ('renders deprecated state outside the wiki title link', async () => {
     wikiApi.fetchWikiPageByTitle.mockResolvedValueOnce (buildWikiPage ({
       title:        '旧タグ',

frontend/src/pages/wiki/WikiDetailPage.tsx

@@ -1,5 +1,3 @@
-import type { FC } from 'react'
-
 import { useQuery } from '@tanstack/react-query'
 import { useEffect, useMemo } from 'react'
 import { Helmet } from 'react-helmet-async'
@@ -13,10 +11,14 @@ import TabGroup, { Tab } from '@/components/common/TabGroup'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
 import { WikiIdBus } from '@/lib/eventBus/WikiIdBus'
+import { getHelpTitleIndex } from '@/lib/help'
 import { fetchPosts } from '@/lib/posts'
-import { postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
+import { helpKeys, postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
 import { fetchTagByName } from '@/lib/tags'
 import { fetchWikiPage, fetchWikiPageByTitle } from '@/lib/wiki'
+import NotFound from '@/pages/NotFound'
+
+import type { FC } from 'react'
 
 import type { Tag } from '@/types'
 
@@ -33,15 +35,33 @@ const WikiDetailPage: FC = () => {
   const query = new URLSearchParams (location.search)
   const version = query.get ('version') || undefined
 
-  const { data: wikiPage, isLoading: loading } = useQuery ({
+  const { data: wikiPage, isLoading: loading, isSuccess, isFetching, error } = useQuery ({
       enabled:  Boolean (title) && !(/^\d+$/.test (title)),
       queryKey: wikiKeys.show (title, { version }),
       queryFn:  () => fetchWikiPageByTitle (title, { version }) })
 
+  const missingWiki = isSuccess && !(isFetching) && wikiPage == null
+  const { data: titleIndex, isPending: lookupPending,
+	  isFetching: lookupFetching, error: lookupError } = useQuery ({
+      enabled: missingWiki,
+      queryKey: helpKeys.titles ('ja'),
+      queryFn: () => getHelpTitleIndex ('ja'),
+      staleTime: Infinity })
+  const lookupTitle = title.trim ().normalize ('NFKC').toLowerCase ().replace (/^ヘルプ:/, '')
+  const identifiers = useMemo (() => (
+      (titleIndex != null && Object.hasOwn (titleIndex, lookupTitle))
+      ? titleIndex[lookupTitle] : []), [titleIndex, lookupTitle])
+
+  useEffect (() => {
+    if (missingWiki && !(lookupFetching) && lookupError == null && identifiers.length === 1)
+      navigate (`/help/${ encodeURIComponent (identifiers[0]) }`, { replace: true })
+  }, [missingWiki, lookupFetching, lookupError, identifiers, navigate])
+
   const effectiveTitle = wikiPage?.title ?? title
   const deprecated = wikiPage?.deprecatedAt != null
 
-  const { data: tag } = useQuery ({
+  const { data: tag, isPending: tagPending,
+	  isFetching: tagFetching, error: tagError } = useQuery ({
       enabled:  Boolean (effectiveTitle),
       queryKey: tagsKeys.show (effectiveTitle),
       queryFn:  () => fetchTagByName (effectiveTitle) })
@@ -73,19 +93,36 @@ const WikiDetailPage: FC = () => {
     if (!(/^\d+$/.test (title)))
       return
 
+    let active = true
     void (async () => {
       try
       {
 	const data = await fetchWikiPage (title, { })
-	navigate (`/wiki/${ encodeURIComponent(data.title) }`, { replace: true })
+	if (active)
+	  navigate (`/wiki/${ encodeURIComponent (data.title) }`, { replace: true })
       }
       catch
       {
 	;
       }
     }) ()
+
+    return () => {
+      active = false
+    }
   }, [title, navigate])
 
+  const displayError = error ?? (missingWiki ? lookupError ?? tagError : null)
+  if (displayError != null)
+    return <MainArea><p role="alert">{displayError.message}</p></MainArea>
+
+  const waiting = loading || (isFetching && wikiPage == null)
+      || (missingWiki && (lookupPending || lookupFetching || tagPending
+			  || (tagFetching && tag == null) || identifiers.length === 1))
+
+  if (missingWiki && !(waiting) && (tag == null || version != null))
+    return <NotFound/>
+
   return (
       <MainArea>
 	<Helmet>
@@ -119,7 +156,7 @@ const WikiDetailPage: FC = () => {
 		     {...(version && { to: `/wiki/${ encodeURIComponent (title) }` })}/>
 	    {deprecated && <span>（廃止）</span>}
 	  </h1>
-	  {loading ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
+	  {waiting ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
 
 	  {(!(version) && posts.length > 0) && (
 	      <div className="not-prose">

frontend/src/pages/wiki/WikiHelpCompatibility.test.tsx

@@ -0,0 +1,144 @@
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
+import { Route, Routes, useLocation, useNavigate } from 'react-router-dom'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { apiGet } from '@/lib/api'
+import * as help from '@/lib/help'
+import HelpDetailPage from '@/pages/help/HelpDetailPage'
+import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
+import { buildWikiPage } from '@/test/factories'
+import { helpFixture } from '@/test/helpFixtures'
+import { renderWithProviders } from '@/test/render'
+
+vi.mock ('@/lib/api', () => ({ apiGet: vi.fn () }))
+vi.mock ('@/lib/help', async () => (await import ('@/test/helpFixtures')).helpFixture.api)
+vi.mock ('@/lib/tags', () => ({ fetchTagByName: async () => null }))
+vi.mock ('@/lib/posts', () => ({ fetchPosts: async () => ({ posts: [], count: 0 }) }))
+
+
+const Location = () => {
+  const location = useLocation ()
+  const navigate = useNavigate ()
+  return (
+      <>
+	<output data-testid="location">{location.pathname}{location.search}</output>
+	<button onClick={() => navigate (`/wiki/${ encodeURIComponent ('該当なし') }`)}>
+	  switch title
+	</button>
+      </>)
+}
+
+
+const renderWiki = (title: string) => {
+  const route = `/wiki/${encodeURIComponent (title)}`
+  const { queryClient } = renderWithProviders (
+      <>
+	<Location/>
+	<Routes>
+	  <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+	  <Route path="/help/:identifier" element={<HelpDetailPage/>}/>
+	  <Route path="/404" element={<div>unexpected redirect</div>}/>
+	</Routes>
+      </>, { route })
+  return { route, queryClient }
+}
+
+
+describe ('Legacy Wiki to Help compatibility', () => {
+  beforeEach (() => {
+    helpFixture.reset ()
+    vi.mocked (apiGet).mockReset ()
+    vi.mocked (apiGet).mockImplementation (async path => {
+      if (path === '/wiki')
+	return []
+      throw { isAxiosError: true, response: { status: 404 } }
+    })
+  })
+
+  it ('keeps a successful Wiki result even when Help has the same title', async () => {
+    vi.mocked (apiGet).mockResolvedValueOnce (buildWikiPage ({
+	title: 'ホーム', body: 'Wiki の現行本文' }))
+    const { route } = renderWiki ('ホーム')
+    await screen.findByText ('Wiki の現行本文')
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+    expect (screen.queryByText ('タグを検索する')).not.toBeInTheDocument ()
+    expect (helpFixture.loads.titles).not.toHaveBeenCalled ()
+  })
+
+  it.each (['ホーム', 'ヘルプ:ホーム', '旧ホーム', 'ヘルプ:旧ホーム', 'ホーム第十版']) (
+      'redirects a unique current or historical Japanese title: %s', async title => {
+	renderWiki (title)
+	await waitFor (() => {
+	  expect (screen.getByTestId ('location')).toHaveTextContent ('/help/guide')
+	})
+	expect (await screen.findByRole ('heading', { name: 'ホーム第十版' }))
+	    .toBeInTheDocument ()
+	Object.values (helpFixture.raw).forEach (load => expect (load).not.toHaveBeenCalled ())
+	expect (apiGet).toHaveBeenCalledWith (
+	    `/wiki/title/${encodeURIComponent (title)}`, expect.anything ())
+      })
+
+  it ('keeps the original URL and displays NotFound when no title matches', async () => {
+    const { route, queryClient } = renderWiki ('該当なし')
+    await screen.findByText ('404')
+    await waitFor (() => {
+      expect (helpFixture.loads.titles).toHaveBeenCalled ()
+      expect (queryClient.isFetching ()).toBe (0)
+    })
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+    expect (screen.queryByText ('unexpected redirect')).not.toBeInTheDocument ()
+  })
+
+  it ('does not choose between articles with the same title', async () => {
+    helpFixture.assets.titles.default.ja['ホーム'] = ['guide', '設定 手順']
+    const { route, queryClient } = renderWiki ('ホーム')
+    await screen.findByText ('404')
+    await waitFor (() => {
+      expect (helpFixture.loads.titles).toHaveBeenCalled ()
+      expect (queryClient.isFetching ()).toBe (0)
+    })
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+  })
+
+  it ('waits for title lookup and does not redirect a later Wiki URL using an old title',
+      async () => {
+	let finish!: (index: Record<string, string[]>) => void
+	const pending = new Promise<Record<string, string[]>> (resolve => {
+	  finish = resolve
+	})
+	const lookup = vi.spyOn (help, 'getHelpTitleIndex').mockReturnValueOnce (pending)
+	renderWiki ('ホーム')
+	await waitFor (() => expect (lookup).toHaveBeenCalled ())
+	expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+	fireEvent.click (screen.getByRole ('button', { name: 'switch title' }))
+	await waitFor (() => expect (apiGet).toHaveBeenCalledWith (
+	    `/wiki/title/${ encodeURIComponent ('該当なし') }`, expect.anything ()))
+	await act (async () => finish ({ 'ホーム': ['guide'] }))
+	await screen.findByText ('404')
+	expect (screen.getByTestId ('location'))
+	    .toHaveTextContent (`/wiki/${ encodeURIComponent ('該当なし') }`)
+      })
+
+  it ('does not treat a Wiki network failure as a missing Wiki', async () => {
+    vi.mocked (apiGet).mockRejectedValueOnce (new Error ('offline'))
+    const { route } = renderWiki ('ホーム')
+    expect (await screen.findByRole ('alert')).toHaveTextContent ('offline')
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+    expect (helpFixture.loads.titles).not.toHaveBeenCalled ()
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+  })
+
+  it.each ([403, 500]) ('does not redirect HTTP %s to Help', async status => {
+    vi.mocked (apiGet).mockRejectedValueOnce ({ isAxiosError: true, response: { status } })
+    const { route, queryClient } = renderWiki ('ホーム')
+    await waitFor (() => {
+      expect (apiGet).toHaveBeenCalled ()
+      expect (queryClient.isFetching ()).toBe (0)
+    })
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+    expect (screen.queryByText ('タグを検索する')).not.toBeInTheDocument ()
+    expect (helpFixture.loads.titles).not.toHaveBeenCalled ()
+  })
+})

frontend/src/pages/wiki/WikiNewPage.tsx

@@ -1,10 +1,10 @@
-import type { FC } from 'react'
+import { useQueryClient } from '@tanstack/react-query'
-
 import MarkdownIt from 'markdown-it'
 import { useState } from 'react'
 import { Helmet } from 'react-helmet-async'
 import MdEditor from 'react-markdown-editor-lite'
 import { useLocation, useNavigate } from 'react-router-dom'
+import 'react-markdown-editor-lite/lib/index.css'
 
 import FieldError from '@/components/common/FieldError'
 import FormField from '@/components/common/FormField'
@@ -12,12 +12,13 @@ import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
 import { apiPost } from '@/lib/api'
+import { tagsKeys, wikiKeys } from '@/lib/queryKeys'
 import { canEditContent } from '@/lib/users'
 import { inputClass } from '@/lib/utils'
 import { useValidationErrors } from '@/lib/useValidationErrors'
 import Forbidden from '@/pages/Forbidden'
 
-import 'react-markdown-editor-lite/lib/index.css'
+import type { FC } from 'react'
 
 import type { User, WikiPage } from '@/types'
 
@@ -38,6 +39,7 @@ const WikiNewPage: FC<Props> = ({ user }) => {
 
   const location = useLocation ()
   const navigate = useNavigate ()
+  const qc = useQueryClient ()
 
   const query = new URLSearchParams (location.search)
   const titleQuery = query.get ('title') ?? ''
@@ -58,8 +60,13 @@ const WikiNewPage: FC<Props> = ({ user }) => {
     {
       const data = await apiPost<WikiPage> ('/wiki', formData,
 				  { headers: { 'Content-Type': 'multipart/form-data' } })
+      await qc.cancelQueries ({ queryKey: wikiKeys.root })
+      qc.setQueryData (wikiKeys.show (data.title, { }), data)
+      await Promise.all ([
+	  qc.invalidateQueries ({ queryKey: wikiKeys.root }),
+	  qc.invalidateQueries ({ queryKey: tagsKeys.root })])
       toast ({ title: '投稿成功!' })
-      navigate (`/wiki/${ data.title }`)
+      navigate (`/wiki/${ encodeURIComponent (data.title) }`)
     }
     catch (e)
     {

frontend/src/pages/wiki/WikiSearchPage.test.tsx

@@ -1,62 +1,58 @@
 import { fireEvent, screen, waitFor } from '@testing-library/react'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
+import { apiGet } from '@/lib/api'
 import WikiSearchPage from '@/pages/wiki/WikiSearchPage'
 import { buildWikiPage } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
-const api = vi.hoisted (() => ({
+vi.mock ('@/lib/api', () => ({ apiGet: vi.fn () }))
-  apiGet: vi.fn (),
-}))
 
-vi.mock ('@/lib/api', () => api)
 
-describe ('WikiSearchPage', () => {
+describe ('Wiki resource identity', () => {
+  beforeEach (() => vi.mocked (apiGet).mockReset ())
+
   it ('loads initial wiki pages and renders links', async () => {
-    api.apiGet.mockResolvedValueOnce ([buildWikiPage ({ title: '虹夏' })])
+    vi.mocked (apiGet).mockResolvedValueOnce ([buildWikiPage ({ title: '虹夏' })])
-
     renderWithProviders (<WikiSearchPage/>)
-
+    expect (await screen.findByRole ('link', { name: '虹夏' }))
-    expect (await screen.findByRole ('link', { name: '虹夏' })).toHaveAttribute (
+	.toHaveAttribute ('href', '/wiki/%E8%99%B9%E5%A4%8F')
-        'href',
+    expect (apiGet).toHaveBeenCalledWith ('/wiki', { params: { title: '' } })
-        '/wiki/%E8%99%B9%E5%A4%8F',
-    )
-    expect (api.apiGet).toHaveBeenCalledWith ('/wiki', { params: { title: '' } })
   })
 
   it ('searches by title on submit', async () => {
-    api.apiGet
+    vi.mocked (apiGet).mockResolvedValueOnce ([])
-      .mockResolvedValueOnce ([])
 	.mockResolvedValueOnce ([buildWikiPage ({ title: '検索結果' })])
-
     renderWithProviders (<WikiSearchPage/>)
-
+    await waitFor (() => expect (apiGet).toHaveBeenCalledTimes (1))
     fireEvent.change (screen.getAllByRole ('textbox')[0], { target: { value: '検索' } })
     fireEvent.click (screen.getByRole ('button', { name: '検索' }))
-
+    await waitFor (() => expect (apiGet).toHaveBeenLastCalledWith (
-    await waitFor (() => {
+	'/wiki', { params: { title: '検索' } }))
-      expect (api.apiGet).toHaveBeenLastCalledWith (
-          '/wiki',
-          { params: { title: '検索' } },
-      )
-    })
     expect (await screen.findByRole ('link', { name: '検索結果' })).toBeInTheDocument ()
   })
 
   it ('marks deprecated wiki tags in the result title', async () => {
-    api.apiGet.mockResolvedValueOnce ([
+    vi.mocked (apiGet).mockResolvedValueOnce ([buildWikiPage ({
-        buildWikiPage ({
+	title: '旧タグ', deprecatedAt: '2026-06-01T00:00:00.000Z' })])
-            title:        '旧タグ',
+    renderWithProviders (<WikiSearchPage/>)
-            deprecatedAt: '2026-06-01T00:00:00.000Z',
+    expect (await screen.findByRole ('link', { name: '旧タグ' })).toBeInTheDocument ()
-        }),
+    expect (screen.getByText ('（廃止）').closest ('a')).toBeNull ()
-    ])
+  })
 
+  it ('renders colliding description and group IDs with stable distinct keys', async () => {
+    const errors = vi.spyOn (console, 'error').mockImplementation (() => {})
+    const description = buildWikiPage ({ id: 51, title: '説明', resourceType: 'tag_description' })
+    const group = buildWikiPage ({ id: 51, title: 'タググループ:一覧', resourceType: 'tag_group' })
+    vi.mocked (apiGet).mockResolvedValue ([description, group])
     renderWithProviders (<WikiSearchPage/>)
 
-    const link = await screen.findByRole ('link', { name: '旧タグ' })
+    await screen.findByRole ('link', { name: '説明' })
-    const marker = screen.getByText ('（廃止）')
+    expect (screen.getByRole ('link', { name: 'タググループ:一覧' }))
-
+	.toHaveAttribute ('href', `/wiki/${ encodeURIComponent (group.title) }`)
-    expect (link).toBeInTheDocument ()
+    await waitFor (() => {
-    expect (marker.closest ('a')).toBeNull ()
+      expect (errors.mock.calls.some (args => args.some (value =>
+	  String (value).includes ('same key')))).toBe (false)
+    })
   })
 })

frontend/src/pages/wiki/WikiSearchPage.tsx

@@ -81,7 +81,8 @@ const WikiSearchPage: FC = () => {
 	    </thead>
 	    <tbody>
 	      {results.map (page => (
-		  <tr key={page.id} className="even:bg-gray-100 dark:even:bg-gray-700">
+		  <tr key={`${ page.resourceType }:${ page.id }`}
+		      className="even:bg-gray-100 dark:even:bg-gray-700">
 		    <td className="p-2">
 		      <PrefetchLink to={`/wiki/${ encodeURIComponent (page.title) }`}>
 			{page.title}

frontend/src/test/compileMdx.ts

@@ -0,0 +1,37 @@
+import * as jsxRuntime from 'react/jsx-runtime'
+import { ModuleKind, ScriptTarget, transpileModule } from 'typescript'
+
+import { useMDXComponents } from '@/mdx-components'
+import viteConfig from '../../vite.config'
+
+import type { ComponentType } from 'react'
+
+type Transform = (source: string, id: string) => Promise<{ code: string } | null>
+
+
+export const transformMdx = async (source: string, suffix = '.mdx') => {
+  const plugins = viteConfig.plugins?.flat () as { name: string; transform: Transform }[]
+  const plugin = plugins.find (entry => entry.name === '@mdx-js/rollup')
+  if (plugin == null)
+    throw new Error ('The application MDX compiler is not registered')
+  return plugin.transform.call (plugin, source, `/test/help-table${suffix}`)
+}
+
+
+export const compileMdx = async (source: string): Promise<ComponentType> => {
+  const result = await transformMdx (source)
+  if (result == null)
+    throw new Error ('MDX was not compiled')
+  const code = transpileModule (result.code, {
+      compilerOptions: { module: ModuleKind.CommonJS, target: ScriptTarget.ES2022 } }).outputText
+  const exports = { } as { default: ComponentType }
+  const requireFixture = (name: string) => {
+    if (name === 'react/jsx-runtime')
+      return jsxRuntime
+    if (name === '@/mdx-components')
+      return { useMDXComponents }
+    throw new Error (`Unexpected MDX dependency: ${name}`)
+  }
+  new Function ('require', 'exports', code) (requireFixture, exports)
+  return exports.default
+}

frontend/src/test/factories.ts

@@ -59,6 +59,7 @@ export const buildUser = (overrides: Partial<User> = {}): User => ({
 })
 
 export const buildWikiPage = (overrides: Partial<WikiPage> = {}): WikiPage => ({
+  resourceType: 'tag_description',
   id:            1,
   title:         'テストWiki',
   deprecatedAt:  null,

frontend/src/test/helpFixtures.tsx

@@ -0,0 +1,126 @@
+import { createElement } from 'react'
+import { ModuleKind, ScriptTarget, transpileModule } from 'typescript'
+import { vi } from 'vitest'
+
+import source from '@/lib/help.ts?raw'
+
+import type { ComponentType } from 'react'
+
+import type * as Help from '@/lib/help'
+
+export const editionRows = [
+    ['guide', 'ja', '2026-10-01', '旧ホーム', '過去限定本文'],
+    ['guide', 'ja', '2026-10-02', 'ホーム', 'タグを検索する'],
+    ['guide', 'ja', '2026-10-02.2', 'ホーム第二版', '第二版本文'],
+    ['guide', 'ja', '2026-10-02.3', 'ホーム第三版', '第三版本文'],
+    ['guide', 'ja', '2026-10-02.10', 'ホーム第十版', 'タグを検索する 第十版本文'],
+    ['guide', 'ja', '2026-10-02.11', '未公開ホーム', '未公開限定本文'],
+    ['guide', 'en', '2026-10-02', 'Home', 'English body'],
+    ['設定 手順', 'ja', '2026-10-03', '設定', 'タグを設定する']] as const
+
+const compiled = transpileModule (source, {
+    compilerOptions: { module: ModuleKind.CommonJS, target: ScriptTarget.ES2022 } }).outputText
+
+
+// Supply generated virtual modules, executing the actual runtime Help module.
+export const createHelpFixture = () => {
+  const articles: Record<string, Help.ArticleMeta> = {
+      guide: { identifier: 'guide', canonicalLanguage: 'ja', languages: {
+	  ja: { currentEdition: '2026-10-02.10', publishedEditions: [
+	      '2026-10-01', '2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10'] },
+	  en: { currentEdition: '2026-10-02', publishedEditions: ['2026-10-02'] } } },
+      '設定 手順': { identifier: '設定 手順', canonicalLanguage: 'ja', languages: {
+	  ja: { currentEdition: '2026-10-03', publishedEditions: ['2026-10-03'] } } } }
+  const published = editionRows.filter (([id, language, edition]) =>
+      articles[id].languages[language].publishedEditions.includes (edition))
+  const raw = Object.fromEntries (editionRows.map (([id, language, edition, title, body]) => [
+      `../../help/${id}/editions/${language}/${edition}.mdx`,
+      vi.fn (async () => `# ${title}\n\n${body}`)]))
+  const moduleLoads = Object.fromEntries (published.map (([id, language, edition, title, body]) => [
+      `../../help/${id}/editions/${language}/${edition}.mdx`,
+      vi.fn (async (): Promise<{ default: ComponentType }> => ({
+	  default: () => createElement ('div', null,
+	      createElement ('h1', null, title), createElement ('p', null, body)) }))]))
+  // Dynamic imports reuse a module namespace even when called more than once.
+  const caches: Record<string, { promise?: Promise<{ default: ComponentType }> }> = { }
+  const modules = Object.fromEntries (Object.entries (moduleLoads).map (([path, load]) => {
+    caches[path] = { }
+    return [path, vi.fn (() => caches[path].promise ??= load ())]
+  }))
+  const texts = Object.fromEntries (published.map (([id, language, edition, title, body]) => [
+      `${ id }/${ language }/${ edition }`,
+      vi.fn (async () => ({ default: { title, body: `\n${ body }` } }))]))
+  const components = Object.fromEntries (published.map (([id, language, edition]) => [
+      `${ id }/${ language }/${ edition }`,
+      modules[`../../help/${ id }/editions/${ language }/${ edition }.mdx`]]))
+  const sources = Object.fromEntries (published.map (([id, language, edition]) => [
+      `${ id }/${ language }/${ edition }`,
+      async () => ({ default: await raw[
+	  `../../help/${ id }/editions/${ language }/${ edition }.mdx`] () })]))
+  const search: Record<string, Help.HelpSearchEntry[]> = { }
+  const changes: Record<string, Help.HelpChange[]> = { }
+  const titles: Record<string, Help.HelpTitleIndex> = { }
+  published.forEach (([id, language, edition, title, body]) => {
+    const editions = articles[id].languages[language].publishedEditions
+    const index = editions.indexOf (edition)
+    const searchRows = search[language] ??= []
+    if (articles[id].languages[language].currentEdition === edition)
+	searchRows.push ({ identifier: id, edition, title, body: `\n${ body }` })
+    const rows = changes[language] ??= []
+    rows.push ({ identifier: id, edition, title,
+	pred: editions[index - 1] ?? null,
+	change: index === 0 ? 'new' : 'update', date: edition.split ('.')[0] })
+    const lookup = (titles[language] ??= { })
+    const identifiers = lookup[title.trim ().normalize ('NFKC').toLowerCase ()] ??= []
+    if (!(identifiers.includes (id)))
+      identifiers.push (id)
+  })
+  Object.values (changes).forEach (rows => rows.sort ((a, b) => {
+    const [dateA, revisionA = '1'] = a.edition.split ('.')
+    const [dateB, revisionB = '1'] = b.edition.split ('.')
+    return dateB.localeCompare (dateA) || Number (revisionB) - Number (revisionA)
+	|| a.identifier.localeCompare (b.identifier)
+  }))
+  const assets = {
+      articles: { default: articles }, search: { default: search },
+      changes: { default: changes }, titles: { default: titles } }
+  const snapshot = JSON.stringify (assets)
+  const loaders = { components, sources, texts }
+  const loads = {
+      articles: vi.fn (() => assets.articles), search: vi.fn (() => assets.search),
+      changes: vi.fn (() => assets.changes), titles: vi.fn (() => assets.titles),
+      loaders: vi.fn (() => loaders) }
+  const api = { } as typeof Help
+  const requireFixture = (name: string) => {
+    const key = name.replace ('virtual:help/', '') as keyof typeof loads
+    if (Object.hasOwn (loads, key))
+      return loads[key] ()
+    throw new Error (`Unexpected Help dependency: ${name}`)
+  }
+  new Function ('require', 'exports', compiled) (requireFixture, api)
+  const reset = () => {
+    Object.assign (assets, JSON.parse (snapshot))
+    editionRows.forEach (([id, language, edition, title, body]) => {
+      const path = `../../help/${ id }/editions/${ language }/${ edition }.mdx`
+      raw[path].mockReset ().mockResolvedValue (`# ${ title }\n\n${ body }`)
+    })
+    published.forEach (([id, language, edition, title, body]) => {
+      const path = `../../help/${ id }/editions/${ language }/${ edition }.mdx`
+      caches[path].promise = undefined
+      moduleLoads[path].mockClear ()
+      modules[path].mockReset ().mockImplementation (() =>
+	  caches[path].promise ??= moduleLoads[path] ())
+      texts[`${ id }/${ language }/${ edition }`].mockReset ().mockResolvedValue ({
+	  default: { title, body: `\n${ body }` } })
+    })
+    loads.articles.mockReset ().mockImplementation (() => assets.articles)
+    loads.search.mockReset ().mockImplementation (() => assets.search)
+    loads.changes.mockReset ().mockImplementation (() => assets.changes)
+    loads.titles.mockReset ().mockImplementation (() => assets.titles)
+    loads.loaders.mockReset ().mockImplementation (() => loaders)
+  }
+  return { api, assets, loads, raw, modules, moduleLoads, texts, reset }
+}
+
+
+export const helpFixture = createHelpFixture ()

frontend/src/types.ts

@@ -452,6 +452,7 @@ export type ViewFlagBehavior = typeof ViewFlagBehavior[keyof typeof ViewFlagBeha
 
 export type WikiPage = {
     id:             number
+    resourceType:   'tag_description' | 'tag_group'
     title:          string
     deprecatedAt:   string | null
     createdUserId:  number

frontend/src/vite-env.d.ts

@@ -1 +1,29 @@
 /// <reference types="vite/client" />
+
+declare module 'virtual:help/articles' {
+  const articles: Record<string, import ('./lib/help').ArticleMeta>
+  export default articles
+}
+
+declare module 'virtual:help/search' {
+  const search: Record<string, import ('./lib/help').HelpSearchEntry[]>
+  export default search
+}
+
+declare module 'virtual:help/changes' {
+  const changes: Record<string, import ('./lib/help').HelpChange[]>
+  export default changes
+}
+
+declare module 'virtual:help/titles' {
+  const titles: Record<string, import ('./lib/help').HelpTitleIndex>
+  export default titles
+}
+
+declare module 'virtual:help/loaders' {
+  export const components: Record<string,
+      () => Promise<{ default: import ('react').ComponentType }>>
+  export const sources: Record<string, () => Promise<{ default: string }>>
+  export const texts: Record<string,
+      () => Promise<{ default: import ('./lib/help').HelpEditionText }>>
+}

frontend/vite.config.ts

@@ -1,12 +1,28 @@
 import mdx from '@mdx-js/rollup'
 import react from '@vitejs/plugin-react'
 import path from 'path'
+import remarkGFM from 'remark-gfm'
 import { defineConfig } from 'vite'
 
+import { helpAssets } from './scripts/help-assets'
+
+const mdxPlugin = mdx ({ providerImportSource: '@/mdx-components',
+			 remarkPlugins: [remarkGFM] })
+const originalTransform = mdxPlugin.transform
+
+if (typeof originalTransform === 'function')
+  {
+    mdxPlugin.transform =
+	function (code, id)
+	{
+	  return (/[?&](raw|url)(?:&|$)/.test (id)
+		  ? null
+		  : originalTransform.call (this, code, id))
+	}
+  }
 
-// https://vite.dev/config/
 export default defineConfig ({
-    plugins:  [mdx ({ providerImportSource: '@/mdx-components' }), react ()],
+    plugins:  [helpAssets (), mdxPlugin, react ()],
     resolve:  { alias: { '@': path.resolve (__dirname, './src') } },
     server:   { host:         true,
 		port:         5173,