#425

Reviewed-on: #427

backend/app/controllers/tag_descriptions_controller.rb

@@ -0,0 +1,57 @@
+class TagDescriptionsController < ApplicationController
+  def show
+    description = TagDescription.find_by(tag_id: params[:id], language_code: 'ja')
+    return head :not_found unless description
+
+    render json: representation(description)
+  end
+
+  def show_by_title
+    tag_name = TagName.find_by(language_code: 'ja', name: params[:name].to_s.strip)
+    description = tag_name&.tag && TagDescription.find_by(tag: tag_name.tag, language_code: 'ja')
+    return head :not_found unless description
+
+    render json: representation(description)
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    body = params[:body].to_s
+    return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
+
+    tag = Tag.find_by(id: params[:id])
+    return head :not_found unless tag
+
+    description = TagDescription.find_by(tag:, language_code: 'ja')
+
+    if description
+      TagDescriptionOperation.update!(tag:, body:, updated_by_user: current_user)
+      description.reload
+      render json: representation(description)
+    else
+      TagDescriptionOperation.create!(tag:, body:, created_by_user: current_user)
+      description = TagDescription.find_by!(tag:, language_code: 'ja')
+      render json: representation(description), status: :created
+    end
+  rescue ActiveRecord::RecordInvalid => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
+  end
+
+  private
+
+  def representation description
+    description.as_json(only: [
+        :tag_id,
+        :language_code,
+        :body,
+        :version_no,
+        :created_by_user_id,
+        :updated_by_user_id,
+        :created_at,
+        :updated_at])
+  end
+end

backend/app/controllers/tags_controller.rb

@@ -464,7 +464,6 @@ class TagsController < ApplicationController
 
       old_name = tag.name(locale.language_code)
       name_changed = name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
       if tag.deprecated? == deprecated
         tag.update!(category:)
@@ -485,9 +484,7 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
-          name_changed:,
-          wiki_page:)
+          language_code: locale.language_code)
     end
 
     render json: TagRepr.base(tag.reload, language_code: locale.language_code)
@@ -518,7 +515,6 @@ class TagsController < ApplicationController
 
       old_name = tag.name(locale.language_code)
       name_changed = name.present? && name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
       rename_tag_name!(locale, tag, name) if name_changed
       tag.update!(category:) if category.present?
@@ -532,9 +528,7 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
-          name_changed:,
-          wiki_page:)
+          language_code: locale.language_code)
     end
 
     render json: TagRepr.base(tag.reload, language_code: locale.language_code)
@@ -722,19 +716,8 @@ class TagsController < ApplicationController
             language_code:))
   end
 
-  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja',
-                          name_changed: false, wiki_page: nil
+  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja'
     TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
-
-    return unless name_changed
-
-    wiki_page ||= tag.tag_name('ja')&.wiki_page
-    return unless wiki_page&.wiki_versions&.exists?
-
-    WikiVersionRecorder.record!(
-        page: wiki_page,
-        event_type: :update,
-        created_by_user:)
   end
 
   def validate_tag_rename locale, tag, name

backend/app/controllers/wiki_pages_controller.rb

@@ -2,47 +2,67 @@ class WikiPagesController < ApplicationController
   rescue_from Wiki::Commit::Conflict, with: :render_wiki_conflict
 
   def index
+    # 互換性のための化石リソース
+    # TODO: ヘルプおよびタグ・グループ追加後に，
+    # TODO: タグ説明とヘルプ、タグ・グループから取得する作りに変更する．
+    #
     title = params[:title].to_s.strip
-    if title.blank?
-      return render json: WikiPageRepr.base(
-          WikiPage.joins(:tag_name).includes(tag_name: :tag))
+    descriptions = TagDescription.where(language_code: 'ja')
+        .includes(tag: :tag_names)
+    pages = unmigrated_wiki_pages.includes(tag_name: :tag)
+
+    if title.present?
+      pattern = "%#{ ApplicationRecord.sanitize_sql_like(title) }%"
+      descriptions = descriptions.joins(tag: :tag_names)
+          .where(tag_names: { language_code: 'ja', primary_flg: true })
+          .where('tag_names.name LIKE ?', pattern).limit(20)
+      pages = pages.where('tag_names.name LIKE ?', pattern).limit(20)
     end
 
-    q = WikiPage.joins(:tag_name).includes(tag_name: :tag)
-        .where('tag_names.name LIKE ?', "%#{ WikiPage.sanitize_sql_like(title) }%")
-    render json: WikiPageRepr.base(q.limit(20))
+    json = descriptions.map { |description| WikiPageRepr.tag_description(description) }
+    json.concat(WikiPageRepr.base(pages))
+    json = json.first(20) if title.present?
+    render json:
   end
 
   def show
+    tag_description = TagDescription.find_by(id: params[:id])
+
+    return render_wiki_page_by_tag_description tag_description if tag_description
+
     page = WikiPage.joins(:tag_name)
                    .includes(tag_name: :tag)
                    .find_by(id: params[:id])
+
     render_wiki_page_or_404 page
   end
 
   def show_by_title
     title = params[:title].to_s.strip
+
+    tag_description = tag_description_by_title(title)
+
+    return render_wiki_page_by_tag_description tag_description if tag_description
+
     page = WikiPage.joins(:tag_name)
                    .includes(tag_name: :tag)
                    .find_by(tag_name: { name: title })
+
     render_wiki_page_or_404 page
   end
 
   def exists
-    if WikiPage.exists?(id: params[:id])
-      head :no_content
-    else
-      head :not_found
-    end
+    return head :no_content if TagDescription.exists?(id: params[:id])
+
+    head WikiPage.exists?(id: params[:id]) ? :no_content : :not_found
   end
 
   def exists_by_title
     title = params[:title].to_s.strip
-    if WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
-      head :no_content
-    else
-      head :not_found
-    end
+    return head :no_content if tag_description_by_title(title)
+
+    exists = WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
+    head exists ? :no_content : :not_found
   end
 
   def diff
@@ -52,12 +72,20 @@ class WikiPagesController < ApplicationController
     from = params[:from].presence
     to = params[:to].presence
 
-    page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
-
-    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．')
+    description = TagDescription.find_by(id:)
+    if description
+      versions = description_versions(description)
+      from_rev = from && versions.find(from)
+      to_rev = to ? versions.find(to) : versions.find_by!(version_no: description.version_no)
+      resource = WikiPageRepr.tag_description(description)
+    else
+      page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
+      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
+      resource = WikiPageRepr.base(page)
     end
 
     diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
@@ -75,9 +103,9 @@ class WikiPagesController < ApplicationController
       end
     }.flatten.compact
 
-    render json: { wiki_page_id:      page.id,
-                   title:             page.title,
-                   deprecated_at:     page.deprecated_at,
+    render json: { wiki_page_id:      resource.fetch('id'),
+                   title:             resource.fetch('title'),
+                   deprecated_at:     resource.fetch('deprecated_at'),
                    older_revision_id: from_rev&.id,
                    newer_revision_id: to_rev.id,
                    diff:              diff_json }
@@ -94,18 +122,24 @@ class WikiPagesController < ApplicationController
     return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
-    tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
-      name.script_code = 'Jpan'
-      name.primary_flg = true
-      name.auto_generated = false
-    end
+    page = if title.include?(':')
+      ApplicationRecord.transaction do
+        tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
+          name.script_code = 'Jpan'
+          name.primary_flg = true
+          name.auto_generated = false
+        end
 
-    page =
-        Wiki::Commit.create_content!(
-            tag_name:,
-            body:,
-            created_by_user: current_user,
-            message:)
+        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
+
+      TagDescriptionOperation.create!(
+          tag: tag_name.tag, body:, created_by_user: current_user, message:)
+    end
 
     render json: WikiPageRepr.base(page), status: :created
   rescue ActiveRecord::RecordInvalid => e
@@ -132,7 +166,7 @@ class WikiPagesController < ApplicationController
 
       old_title = page.title
 
-      tag = Tag.find_by(tag_name_id: page.tag_name_id)
+      tag = page.tag_name.tag
 
       if tag && title != old_title
         TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
@@ -156,29 +190,35 @@ class WikiPagesController < ApplicationController
     head :ok
   end
 
-  def search
-    index
-  end
-
   def changes
     id = params[:id].presence
-    q = WikiRevision.joins(wiki_page: :tag_name)
-                    .includes(:created_user, wiki_page: { tag_name: :tag })
-                    .order(id: :desc)
-    q = q.where(wiki_page_id: id) if id
+    description = id && TagDescription.find_by(id:)
+    if description
+      return render json: description_changes(TagDescription.where(id: description.id))
+    end
 
-    render json: q.limit(200).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 }
-    }.compact
+    pages = id ? WikiPage.where(id:) : unmigrated_wiki_pages
+    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(description_changes(TagDescription.where(language_code: 'ja')))
+      json.sort_by! { |row| -row[:revision_id] }
+    end
+    render json: json.first(200)
   end
 
   private
@@ -204,6 +244,67 @@ class WikiPagesController < ApplicationController
     render json: WikiPageRepr.base(page).merge(body:, revision_id:, pred:, succ:, updated_at:)
   end
 
+  def render_wiki_page_by_tag_description description
+    versions = description_versions(description)
+    historical = params[:version].present?
+    rev = historical ? versions.find_by(id: params[:version]) :
+        versions.find_by(version_no: description.version_no)
+    return head :not_found unless rev
+
+    pred = versions.find_by(version_no: rev.version_no - 1)&.id
+    succ = versions.find_by(version_no: rev.version_no + 1)&.id
+    body = historical ? rev.body : description.body
+    updated_at = historical ? rev.created_at : description.updated_at
+    render json: WikiPageRepr.tag_description(description).merge(
+        body:, revision_id: rev.id, pred:, succ:, updated_at:)
+  end
+
+  def description_versions description
+    TagDescriptionVersion.where(tag_id: description.tag_id,
+                                language_code: description.language_code)
+  end
+
+  def tag_description_by_title title
+    TagDescription.joins(tag: :tag_names)
+        .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(id: descriptions.select(:id))
+        .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))
+        .order(id: :desc).limit(200).to_a
+    return [] if versions.empty?
+
+    by_tag = descriptions.where(tag_id: versions.map(&:tag_id))
+        .includes(tag: :tag_names).index_by(&:tag_id)
+    users = User.where(id: versions.map(&:created_by_user_id)).index_by(&:id)
+    predecessors = TagDescriptionVersion.where(
+        language_code: 'ja', tag_id: by_tag.keys,
+        version_no: versions.map { |version| version.version_no - 1 })
+        .pluck(:tag_id, :version_no, :id)
+        .to_h { |tag_id, version_no, id| [[tag_id, version_no], id] }
+    versions.map do |version|
+      description = by_tag.fetch(version.tag_id)
+      user = users[version.created_by_user_id]
+      { revision_id: version.id,
+        pred: predecessors[[version.tag_id, version.version_no - 1]],
+        succ: nil,
+        wiki_page: { id: description.id, title: description.tag.name('ja'),
+                     deprecated_at: description.tag.deprecated_at },
+        user: user && { id: user.id, name: user.name },
+        kind: 'content',
+        message: nil,
+        timestamp: version.created_at }
+    end
+  end
+
   def find_revision page
     if params[:version].present?
       page.wiki_revisions.find_by(id: params[:version])

backend/app/models/tag_description.rb

@@ -0,0 +1,3 @@
+class TagDescription < ApplicationRecord
+  belongs_to :tag
+end

backend/app/models/tag_description_version.rb

@@ -0,0 +1,3 @@
+class TagDescriptionVersion < ApplicationRecord
+  ;
+end

backend/app/models/wiki_page.rb

@@ -48,8 +48,11 @@ class WikiPage < ApplicationRecord
     page
   end
 
-  def pred_revision_id(revision_id) =
-      wiki_revisions.where('id < ?', revision_id).order(id: :desc).limit(1).pick(:id)
-  def succ_revision_id(revision_id) =
-      wiki_revisions.where('id > ?', revision_id).order(id: :asc).limit(1).pick(:id)
+  def pred_revision_id revision_id
+    wiki_revisions.where('id < ?', revision_id).order(id: :desc).limit(1).pick(:id)
+  end
+
+  def succ_revision_id revision_id
+    wiki_revisions.where('id > ?', revision_id).order(id: :asc).limit(1).pick(:id)
+  end
 end

backend/app/representations/wiki_page_repr.rb

@@ -10,6 +10,21 @@ module WikiPageRepr
     wiki_page.as_json(BASE)
   end
 
+  def tag_description description
+    tag = description.tag
+    { 'id' => description.id,
+      'tag_name_id' => tag.tag_name('ja')&.id,
+      'body' => description.body,
+      'created_user_id' => description.created_by_user_id,
+      'updated_user_id' => description.updated_by_user_id,
+      'created_at' => description.created_at,
+      'updated_at' => description.updated_at,
+      'discarded_at' => nil,
+      'version_no' => description.version_no,
+      'title' => tag.name('ja'),
+      'deprecated_at' => tag.deprecated_at }
+  end
+
   def many wiki_pages
     wiki_pages.map { |p| base(p) }
   end

backend/app/services/tag_description_operation.rb

@@ -0,0 +1,54 @@
+class TagDescriptionOperation
+  LANGUAGE_CODE = 'ja'
+
+  def self.create!(tag:, body:, created_by_user:, message: nil)
+    ApplicationRecord.transaction do
+      tag.lock!
+      raise ActiveRecord::RecordNotUnique if TagDescription.exists?(
+          tag_id: tag.id, language_code: LANGUAGE_CODE)
+
+      page = Wiki::CompatibilityWriter.create!(
+          tag_name: tag.tag_name(LANGUAGE_CODE), body:, created_by_user:, message:)
+      revision = page.wiki_revisions.order(id: :desc).first
+      record_version!(tag:, revision:, body:, user: created_by_user,
+                      description: nil)
+      page
+    end
+  end
+
+  def self.update!(tag:, body:, updated_by_user:, message: nil,
+                   base_revision_id: nil)
+    ApplicationRecord.transaction do
+      tag.lock!
+      description = TagDescription.lock.find_by!(
+          tag_id: tag.id, language_code: LANGUAGE_CODE)
+      page = WikiPage.lock.find(description.id)
+      revision = Wiki::CompatibilityWriter.update!(
+          page:, body:, updated_by_user:, message:,
+          base_revision_id:)
+      next unless revision
+
+      record_version!(tag:, revision:, body: revision.body,
+                      user: updated_by_user, description:)
+      revision
+    end
+  end
+
+  def self.record_version! tag:, revision:, body:, user:, description:
+    version_no = description ? description.version_no + 1 : 1
+    TagDescriptionVersion.create!(
+        id: revision.id, tag_id: tag.id, language_code: LANGUAGE_CODE,
+        version_no:, event_type: description ? 'update' : 'create', body:,
+        created_by_user_id: user.id, created_at: revision.created_at)
+    if description
+      description.update!(body:, version_no:, updated_by_user_id: user.id)
+    else
+      TagDescription.create!(
+          id: revision.wiki_page_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
+  end
+
+  private_class_method :record_version!
+end

backend/app/services/wiki/commit.rb

@@ -8,6 +8,15 @@ module Wiki
     end
 
     def self.create_content! tag_name:, body:, created_by_user:, message: nil
+      if tag_name.tag && tag_name.language_code == 'ja'
+        return TagDescriptionOperation.create!(
+            tag: tag_name.tag, body:, created_by_user:, message:)
+      end
+
+      create_legacy_content!(tag_name:, body:, created_by_user:, message:)
+    end
+
+    def self.create_legacy_content! tag_name:, body:, created_by_user:, message: nil
       normalised = normalise_body(body)
 
       page = WikiPage.new(tag_name:,
@@ -33,6 +42,18 @@ module Wiki
     end
 
     def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
+      description = TagDescription.find_by(id: page.id)
+      if description
+        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:)
+    end
+
+    def self.legacy_content! page:, body:, created_user:, message: nil,
+                             base_revision_id: nil
       new(page:, created_user:).content!(body:, message:, base_revision_id:)
     end
 
@@ -57,9 +78,6 @@ module Wiki
       line_shas = lines.map { |line| Digest::SHA256.hexdigest(line) }
       tree_sha = Digest::SHA256.hexdigest(line_shas.join(','))
 
-      line_id_by_sha = upsert_lines!(lines, line_shas)
-      line_ids = line_shas.map { |sha| line_id_by_sha.fetch(sha) }
-
       ActiveRecord::Base.transaction do
         @page.lock!
 
@@ -72,6 +90,8 @@ module Wiki
           end
         end
 
+        line_id_by_sha = upsert_lines!(lines, line_shas)
+        line_ids = line_shas.map { |sha| line_id_by_sha.fetch(sha) }
         @page.update!(body: normalised)
 
         WikiVersionRecorder.record!(
@@ -94,7 +114,6 @@ module Wiki
           { wiki_revision_id: rev.id, wiki_line_id: line_id, position: pos }
         end
         WikiRevisionLine.insert_all!(rows) if rows.any?
-
         rev
       end
     end

backend/app/services/wiki/compatibility_writer.rb

@@ -0,0 +1,33 @@
+module Wiki
+  class CompatibilityWriter
+    def self.create! tag_name:, body:, created_by_user:, message: nil
+      Commit.create_legacy_content!(
+          tag_name:, body:, created_by_user:, message:)
+    end
+
+    def self.update! page:, body:, updated_by_user:, message: nil,
+                     base_revision_id: nil
+      normalised = Commit.normalise_body(body)
+      if normalised.blank?
+        return Commit.legacy_content!(
+            page:, body: normalised, created_user: updated_by_user, message:,
+            base_revision_id:)
+      end
+
+      if base_revision_id.present?
+        current_id = page.wiki_revisions.maximum(:id)
+        if current_id && current_id != base_revision_id.to_i
+          raise Commit::Conflict,
+              "競合が発生してゐます" +
+              "（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
+        end
+      end
+
+      return if Commit.normalise_body(page.body) == normalised
+
+      Commit.legacy_content!(
+          page:, body: normalised, created_user: updated_by_user, message:,
+          base_revision_id:)
+    end
+  end
+end

backend/config/routes.rb

@@ -14,6 +14,7 @@ Rails.application.routes.draw do
 
       scope :name do
         get ':name/deerjikists', action: :deerjikists_by_name
+        get ':name/description', to: 'tag_descriptions#show_by_title'
         get ':name/materials', action: :materials_by_name
         get ':name', action: :show_by_name
       end
@@ -25,6 +26,9 @@ Rails.application.routes.draw do
 
       get :deerjikists
       put :deerjikists, action: :update_deerjikists
+
+      get :description, to: 'tag_descriptions#show'
+      put :description, to: 'tag_descriptions#update'
     end
   end
 
@@ -35,7 +39,7 @@ Rails.application.routes.draw do
 
   resources :wiki_pages, path: 'wiki', only: [:index, :show, :create, :update] do
     collection do
-      get :search
+      get :search, action: :index
       get :changes
 
       scope :title do

backend/db/migrate/20261003000000_create_tag_descriptions.rb

@@ -0,0 +1,63 @@
+class CreateTagDescriptions < ActiveRecord::Migration[8.0]
+  def change
+    create_table :tag_description_versions do |t|
+      t.references :tag, null: false, foreign_key: false
+      t.string :language_code, limit: 16, null: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.text :body, null: false
+      t.string :source_language_code, limit: 16
+      t.integer :source_version_no
+      t.references :created_by_user
+      t.datetime :created_at, null: false
+
+      t.index [:tag_id, :language_code, :version_no], unique: true
+      t.foreign_key :tag_description_versions,
+                    column: [:tag_id, :source_language_code, :source_version_no],
+                    primary_key: [:tag_id, :language_code, :version_no]
+
+      t.check_constraint 'version_no > 0',
+                         name: 'chk_tag_description_versions_version_no_positive'
+
+      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')",
+                         name: 'tag_description_versions_event_type_valid'
+
+      t.check_constraint ('(source_language_code IS NULL AND source_version_no IS NULL) OR ' +
+                          '(source_language_code IS NOT NULL AND source_version_no IS NOT NULL)'),
+                         name: 'chk_tag_description_versions_source_pair'
+
+      t.check_constraint 'source_language_code IS NULL OR source_language_code <> language_code',
+                         name: 'chk_tag_description_versions_source_language_code_different'
+    end
+
+    create_table :tag_descriptions do |t|
+      t.references :tag, null: false, foreign_key: true
+      t.string :language_code, limit: 16, null: false, index: true
+      t.integer :version_no, null: false
+      t.text :body, null: false
+      t.string :source_language_code, limit: 16
+      t.integer :source_version_no
+      t.references :created_by_user, foreign_key: { to_table: :users }
+      t.references :updated_by_user, foreign_key: { to_table: :users }
+      t.timestamps
+
+      t.foreign_key :languages, column: :language_code, primary_key: :code
+      t.foreign_key :tag_description_versions,
+                    column: [:tag_id, :source_language_code, :source_version_no],
+                    primary_key: [:tag_id, :language_code, :version_no]
+
+      t.index [:tag_id, :language_code], unique: true
+      t.index [:source_language_code, :source_version_no]
+
+      t.check_constraint 'version_no > 0',
+                         name: 'chk_tag_descriptions_version_no_positive'
+
+      t.check_constraint ('(source_language_code IS NULL AND source_version_no IS NULL) OR ' +
+                          '(source_language_code IS NOT NULL AND source_version_no IS NOT NULL)'),
+                         name: 'chk_tag_descriptions_source_pair'
+
+      t.check_constraint 'source_language_code IS NULL OR source_language_code <> language_code',
+                         name: 'chk_tag_descriptions_source_language_code_different'
+    end
+  end
+end

backend/db/migrate/20261003010000_migrate_tag_descriptions_from_wiki_pages.rb

@@ -0,0 +1,104 @@
+class MigrateTagDescriptionsFromWikiPages < ActiveRecord::Migration[8.0]
+  class WikiPage < ActiveRecord::Base
+    self.table_name = 'wiki_pages'
+  end
+
+  class WikiRevision < ActiveRecord::Base
+    self.table_name = 'wiki_revisions'
+  end
+
+  class WikiRevisionLine < ActiveRecord::Base
+    self.table_name = 'wiki_revision_lines'
+  end
+
+  class TagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  class TagDescription < ActiveRecord::Base
+    self.table_name = 'tag_descriptions'
+  end
+
+  class TagDescriptionVersion < ActiveRecord::Base
+    self.table_name = 'tag_description_versions'
+  end
+
+  def up
+    WikiPage.find_each do |page|
+      tag_name = TagName.find_by(id: page.tag_name_id, language_code: 'ja')
+      next unless tag_name&.tag_id
+
+      revisions = WikiRevision.where(wiki_page_id: page.id).order(:id).to_a
+
+      revisions.each_with_index do |revision, index|
+        version_no = index + 1
+
+        tag_id = tag_name[:tag_id]
+
+        unless tag_id
+          raise (
+              'tag_id is nil: ' +
+              "wiki_page_id=#{ page.id }, " +
+              "tag_name_id=#{ tag_name.id }, " +
+              "tag_name=#{ tag_name.attributes.inspect}")
+        end
+
+        revision_id = revision.id
+
+        say (
+            "wiki_page_id=#{ page.id }, " +
+            "tag_name_id=#{ tag_name.id }, " +
+            "tag_id=#{ tag_id }, " +
+            "revision_id=#{ revision_id }")
+
+        version = TagDescriptionVersion.new(
+            id: revision_id,
+            tag_id:,
+            language_code: 'ja',
+            version_no:,
+            event_type: version_no == 1 ? 'create' : 'update',
+            body: revision_body(revision_id),
+            source_language_code: nil,
+            source_version_no: nil,
+            created_by_user_id: revision.created_user_id,
+            created_at: revision.created_at)
+
+        say version.attributes.inspect
+
+        version.save!
+      end
+
+      next if page.discarded_at.present?
+      next if revisions.empty?
+
+      TagDescription.create!(
+          id: page.id,
+          tag_id: tag_name.tag_id,
+          language_code: 'ja',
+          version_no: revisions.length,
+          body: page.body,
+          source_language_code: nil,
+          source_version_no: nil,
+          created_by_user_id: page.created_user_id,
+          updated_by_user_id: page.updated_user_id,
+          created_at: page.created_at,
+          updated_at: page.updated_at)
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+
+  private
+
+  def revision_body revision_id
+    WikiRevisionLine
+        .joins('INNER JOIN wiki_lines ' +
+               'ON wiki_lines.id = wiki_revision_lines.wiki_line_id')
+        .where(wiki_revision_id: revision_id)
+        .order(:position)
+        .pluck('wiki_lines.body')
+        .join("\n")
+  end
+end

backend/db/migrate/20261005000000_repair_wiki_updated_at.rb

@@ -0,0 +1,53 @@
+class RepairWikiUpdatedAt < ActiveRecord::Migration[8.0]
+  class WikiPage < ActiveRecord::Base
+    self.table_name = 'wiki_pages'
+  end
+
+  class WikiVersion < ActiveRecord::Base
+    self.table_name = 'wiki_versions'
+  end
+
+  class TagDescription < ActiveRecord::Base
+    self.table_name = 'tag_descriptions'
+  end
+
+  class TagDescriptionVersion < ActiveRecord::Base
+    self.table_name = 'tag_description_versions'
+  end
+
+  def up
+    say_with_time 'Repairing wiki_pages.updated_at from wiki_versions' do
+      WikiPage.find_each do |page|
+        version =
+            WikiVersion
+            .where(wiki_page_id: page.id)
+            .order(version_no: :desc)
+            .first
+
+        next unless version
+
+        page.update_columns(updated_at: version.created_at)
+      end
+    end
+
+    say_with_time 'Repairing tag_descriptions.updated_at from tag_description_versions' do
+      TagDescription.find_each do |description|
+        version =
+            TagDescriptionVersion
+            .where(
+                tag_id: description.tag_id,
+                language_code: description.language_code)
+            .order(version_no: :desc)
+            .first
+
+        next unless version
+
+        description.update_columns(updated_at: version.created_at)
+      end
+    end
+  end
+
+  def down
+    ;
+  end
+end

backend/db/migrate/20261008000000_create_tag_groups.rb

@@ -0,0 +1,149 @@
+class CreateTagGroups < ActiveRecord::Migration[8.0]
+  def change
+    # 翻訳系は上流の Translation リソースが未完のため保留
+
+    create_table :tag_groups do |t|
+      t.integer :version_no, null: false
+      t.string :name, limit: 255, null: false
+      t.text :description
+      t.references :created_by_user, foreign_key: { to_table: :users }
+      t.references :updated_by_user, foreign_key: { to_table: :users }
+      t.timestamps
+
+      t.check_constraint 'version_no > 0', name: 'chk_tag_groups_version_no_positive'
+      t.index :name, unique: true
+    end
+
+    create_table :tag_group_tags, primary_key: [:tag_group_id, :tag_id] do |t|
+      t.references :tag_group, null: false, foreign_key: true, index: false
+      t.references :tag, null: false, foreign_key: true
+      t.references :created_by_user, foreign_key: { to_table: :users }
+      t.datetime :created_at, null: false
+    end
+
+    create_table :tag_group_groups, primary_key: [:tag_group_id, :child_tag_group_id] do |t|
+      t.references :tag_group, null: false, foreign_key: true, index: false
+      t.references :child_tag_group,
+                   null: false, foreign_key: { to_table: :tag_groups }
+      t.references :created_by_user, foreign_key: { to_table: :users }
+      t.datetime :created_at, null: false
+
+      t.check_constraint 'tag_group_id <> child_tag_group_id',
+                         name: 'chk_tag_group_groups_tag_group_id_not_child_tag_group_id'
+    end
+
+    create_table :tag_group_placements, primary_key: [:tag_group_id, :position] do |t|
+      t.references :tag_group, null: false, foreign_key: true, index: false
+      t.integer :position, null: false
+      t.integer :parent_position
+      t.string :section_name, limit: 255
+      t.text :description
+      t.references :tag
+      t.references :child_tag_group
+      t.references :created_by_user, foreign_key: { to_table: :users }
+      t.references :updated_by_user, foreign_key: { to_table: :users }
+      t.timestamps
+
+      t.foreign_key :tag_group_placements,
+                    column: [:tag_group_id, :parent_position],
+                    primary_key: [:tag_group_id, :position]
+
+      t.foreign_key :tag_group_tags,
+                    column: [:tag_group_id, :tag_id],
+                    primary_key: [:tag_group_id, :tag_id]
+
+      t.foreign_key :tag_group_groups,
+                    column: [:tag_group_id, :child_tag_group_id],
+                    primary_key: [:tag_group_id, :child_tag_group_id]
+
+      t.check_constraint 'position > parent_position',
+                         name: 'chk_tag_group_placements_position_gt_parent_position'
+
+      t.check_constraint ('((section_name IS NOT NULL AND tag_id IS NULL AND child_tag_group_id IS NULL) OR ' +
+                          '(section_name IS NULL AND tag_id IS NOT NULL AND child_tag_group_id IS NULL) OR ' +
+                          '(section_name IS NULL AND tag_id IS NULL AND child_tag_group_id IS NOT NULL)) AND ' +
+                          '(section_name IS NOT NULL OR description IS NULL)'),
+                         name: 'chk_tag_group_placements_references_exclusive'
+    end
+
+    create_table :tag_group_versions do |t|
+      t.references :tag_group, null: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :name, limit: 255, null: false
+      t.text :description
+      t.json :members, null: false
+      t.json :placements, null: false
+      t.references :created_by_user
+      t.datetime :created_at, null: false
+
+      t.check_constraint 'version_no > 0',
+                         name: 'chk_tag_group_versions_version_no_positive'
+      t.index [:tag_group_id, :version_no], unique: true
+
+      add_members_constraint!(t)
+      add_placements_constraint!(t)
+    end
+  end
+
+  private
+
+  def add_members_constraint! t
+    schema = { type: 'array',
+               uniqueItems: true,
+               items: member_schema }
+
+    quoted_schema = connection.quote(JSON.generate(schema))
+
+    t.check_constraint "JSON_SCHEMA_VALID(#{ quoted_schema }, members)", 
+                       name: 'chk_tag_group_versions_members_schema'
+  end
+
+  def member_schema
+    { oneOf: [tag_member_schema, group_member_schema] }
+  end
+
+  def tag_member_schema
+    { type: 'object',
+      required: ['tag_id', 'version_no'],
+      properties: { tag_id: { type: 'integer', minimum: 1 },
+                    version_no: { type: 'integer', minimum: 1 } },
+      additionalProperties: false }
+  end
+
+  def group_member_schema
+    { type: 'object',
+      required: ['tag_group_id', 'version_no'],
+      properties: { tag_group_id: { type: 'integer', minimum: 1 },
+                    version_no: { type: 'integer', minimum: 1 } },
+      additionalProperties: false }
+  end
+
+  def add_placements_constraint! t
+    schema = { type: 'array', items: placement_schema(5) }
+
+    quoted_schema = connection.quote(JSON.generate(schema))
+
+    t.check_constraint "JSON_SCHEMA_VALID(#{ quoted_schema }, placements)",
+                       name: 'chk_tag_group_versions_placements_schema'
+  end
+
+  def placement_schema rest
+    { type: 'object',
+      required: ['children'],
+      properties: { section_name: { type: 'string' },
+                    description: { type: ['string', 'null'] },
+                    tag_id: { type: 'integer', minimum: 1 },
+                    tag_group_id: { type: 'integer', minimum: 1 },
+                    children: if rest > 1
+                                { type: 'array', items: placement_schema(rest - 1) }
+                              else
+                                { type: 'array', maxItems: 0 }
+                              end },
+      oneOf: [{ required: ['section_name'] },
+              { required: ['tag_id'] },
+              { required: ['tag_group_id'] }],
+      dependencies: { description: ['section_name'] },
+      additionalProperties: false }
+  end
+end

backend/db/migrate/20261008010000_migrate_tag_groups_from_wiki_pages.rb

@@ -0,0 +1,518 @@
+class MigrateTagGroupsFromWikiPages < ActiveRecord::Migration[8.0]
+  PREFIX = 'タググループ:'
+
+  def up
+    require 'json'
+    require 'time'
+    require 'kramdown'
+    require 'kramdown-parser-gfm'
+
+    assert_empty_destination!
+
+    pages = connection.select_all(<<~SQL).to_a
+      SELECT
+        wp.id
+      , wp.created_user_id
+      , wp.updated_user_id
+      , wp.created_at
+      , wp.updated_at
+      , wp.discarded_at
+      , tn.name
+      FROM
+        wiki_pages wp
+        INNER JOIN
+          tag_names tn
+          ON
+            tn.id = wp.tag_name_id
+      WHERE
+        tn.language_code = 'ja'
+        AND tn.name LIKE #{ quote("#{ PREFIX }%") }
+      ORDER BY
+        wp.id
+    SQL
+
+    return if pages.empty?
+
+    pages.each do |page|
+      if page['discarded_at']
+        say "Wiki ##{ page.fetch('id') }: 破棄済みですが，Revision の移行を継続します．"
+      end
+    end
+
+    tag_ids = load_tag_ids
+    page_ids = pages.map { |page| page.fetch('id').to_i }
+
+    revisions = connection.select_all(<<~SQL).to_a
+      SELECT
+        wr.id
+      , wr.wiki_page_id
+      , wr.kind
+      , wr.redirect_page_id
+      , wr.created_user_id
+      , wr.created_at
+      FROM
+        wiki_revisions wr
+      WHERE
+        wr.wiki_page_id IN (#{ page_ids.join(', ') })
+      ORDER BY
+        wr.wiki_page_id
+      , wr.id
+    SQL
+
+    revisions_by_page = revisions.group_by { |row| row.fetch('wiki_page_id').to_i }
+
+    pages = pages.select do |page|
+      page_id = page.fetch('id').to_i
+      if revisions_by_page.fetch(page_id, []).empty?
+        # tag_groups.version_no > 0 のため，Revision 0 件の Wiki は作成しない．
+        say "Wiki ##{ page_id }: Revision が 0 件のため移行対象から除外します．"
+        false
+      else
+        true
+      end
+    end
+
+    return if pages.empty?
+
+    group_ids = pages.to_h { |page| [page.fetch('name'), page.fetch('id').to_i] }
+    revision_history = pages.to_h do |page|
+      page_id = page.fetch('id').to_i
+      history = revisions_by_page.fetch(page_id).each_with_index.map do |revision, index|
+        { 'id' => revision.fetch('id').to_i,
+          'version_no' => index + 1,
+          'created_at' => revision.fetch('created_at') }
+      end
+      [page_id, history]
+    end
+
+    tag_history = connection.select_all(<<~SQL).to_a.group_by { |row| row.fetch('tag_id').to_i }
+      SELECT
+        tag_id
+      , version_no
+      , created_at
+      FROM
+        tag_versions
+      ORDER BY
+        tag_id
+      , created_at
+      , version_no
+    SQL
+
+    prepared = { }
+    pages.each do |page|
+      page_id = page.fetch('id').to_i
+      history = revisions_by_page.fetch(page_id)
+
+      prepared[page_id] = history.each_with_index.map do |revision, index|
+        context = "Wiki ##{ page_id } / Revision ##{ revision.fetch('id') }"
+        body = revision_body(revision.fetch('id').to_i)
+
+        if revision.fetch('kind').to_i == 1
+          destination = revision['redirect_page_id']
+          description = "旧 Wiki のリダイレクト先: Wiki ##{ destination }"
+          placements = []
+          members = []
+          say "#{ context }: リダイレクトを説明文として移行します．"
+        else
+          begin
+            description, placements = parse_wiki(body, tag_ids, group_ids, context)
+            validate_tree!(placements, context)
+            members = build_members(placements, revision.fetch('created_at'),
+                                    tag_history, revision_history, context)
+          rescue StandardError => error
+            # 解析できない版も捨てず，当時の Markdown を説明文として保存する．
+            say "#{ context }: 構造化を保留し，本文を保存します (#{ error.message })．"
+            description = body
+            placements = []
+            members = []
+          end
+        end
+
+        { revision:, version_no: index + 1, description:, members:, placements:, body: }
+      end
+    end
+
+    # 自己包含は禁止されてゐるため，当該版は原文の保存を優先する．
+    prepared.each do |group_id, versions|
+      current = versions.last
+      next unless current.fetch(:members).any? { |member| member['tag_group_id'] == group_id }
+
+      say "Tag Group ##{ group_id }: 直接の自己参照を検出したため，現行構造化を保留します．"
+      current[:description] = current.fetch(:body)
+      current[:members] = []
+      current[:placements] = []
+    end
+
+    begin
+      validate_current_groups!(prepared)
+    rescue StandardError => error
+      say "Tag Group の包含関係に問題がありますが，移行を継続します (#{ error.message })．"
+    end
+
+    # 移行先の書込みはすべて検証の後．DDL は含めない．
+    connection.transaction do
+      pages.each do |page|
+        page_id = page.fetch('id').to_i
+        current = prepared.fetch(page_id).last
+
+        insert_row('tag_groups', {
+            id: page_id,
+            # page.version_no ではなく，この Wiki に紐付く Revision の総数．
+            version_no: revisions_by_page.fetch(page_id).size,
+            name: page.fetch('name').delete_prefix(PREFIX),
+            description: current.fetch(:description),
+            created_by_user_id: page.fetch('created_user_id'),
+            updated_by_user_id: page.fetch('updated_user_id'),
+            created_at: page.fetch('created_at'),
+            updated_at: page.fetch('updated_at') })
+      end
+
+      pages.each do |page|
+        page_id = page.fetch('id').to_i
+        name = page.fetch('name').delete_prefix(PREFIX)
+
+        prepared.fetch(page_id).each do |item|
+          revision = item.fetch(:revision)
+
+          insert_row('tag_group_versions', {
+              id: revision.fetch('id'),
+              tag_group_id: page_id,
+              version_no: item.fetch(:version_no),
+              event_type: item.fetch(:version_no) == 1 ? 'create' : 'update',
+              name:,
+              description: item.fetch(:description),
+              members: JSON.generate(item.fetch(:members)),
+              placements: JSON.generate(item.fetch(:placements)),
+              created_by_user_id: revision.fetch('created_user_id'),
+              created_at: revision.fetch('created_at') })
+        end
+      end
+
+      pages.each do |page|
+        page_id = page.fetch('id').to_i
+        current = prepared.fetch(page_id).last
+        revision = current.fetch(:revision)
+
+        current.fetch(:members).each do |member|
+          if member.key?('tag_id')
+            insert_row('tag_group_tags', {
+                tag_group_id: page_id,
+                tag_id: member.fetch('tag_id'),
+                created_by_user_id: revision.fetch('created_user_id'),
+                created_at: revision.fetch('created_at') })
+          else
+            insert_row('tag_group_groups', {
+                tag_group_id: page_id,
+                child_tag_group_id: member.fetch('tag_group_id'),
+                created_by_user_id: revision.fetch('created_user_id'),
+                created_at: revision.fetch('created_at') })
+          end
+        end
+      end
+
+      pages.each do |page|
+        page_id = page.fetch('id').to_i
+        current = prepared.fetch(page_id).last
+        revision = current.fetch(:revision)
+        position = 0
+
+        append = -> nodes, parent_position do
+          nodes.each do |node|
+            position += 1
+            own_position = position
+
+            insert_row('tag_group_placements', {
+                tag_group_id: page_id,
+                position: own_position,
+                parent_position:,
+                section_name: node['section_name'],
+                description: node['description'],
+                tag_id: node['tag_id'],
+                child_tag_group_id: node['tag_group_id'],
+                created_by_user_id: revision.fetch('created_user_id'),
+                updated_by_user_id: revision.fetch('created_user_id'),
+                created_at: revision.fetch('created_at'),
+                updated_at: revision.fetch('created_at') })
+
+            append.(node.fetch('children'), own_position)
+          end
+        end
+
+        append.(current.fetch(:placements), nil)
+      end
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration, '戻せません．'
+  end
+
+  private
+
+  def assert_empty_destination!
+    ['tag_groups', 'tag_group_versions', 'tag_group_tags',
+     'tag_group_groups', 'tag_group_placements'].each do |table|
+      count = connection.select_value("SELECT COUNT(*) FROM #{ table }").to_i
+      raise "#{ table } が空ではありません．" if count.positive?
+    end
+  end
+
+  # 解決は tag_names.name -> tag_names.tag_id のみ．
+  # tags.tag_name_id は読まない．
+  def load_tag_ids
+    rows = connection.select_all(<<~SQL).to_a
+      SELECT
+        name
+      , tag_id
+      FROM
+        tag_names
+      WHERE
+        language_code = 'ja'
+        AND tag_id IS NOT NULL
+    SQL
+
+    rows.each_with_object({ }) do |row, by_name|
+      name = row.fetch('name')
+      id = row.fetch('tag_id').to_i
+      by_name[name] ||= []
+      by_name[name] << id unless by_name[name].include?(id)
+    end
+  end
+
+  def revision_body revision_id
+    connection.select_rows(<<~SQL).flatten.join("\n")
+      SELECT
+        wl.body
+      FROM
+        wiki_revision_lines wrl
+        INNER JOIN wiki_lines wl ON wl.id = wrl.wiki_line_id
+      WHERE
+        wrl.wiki_revision_id = #{ Integer(revision_id) }
+      ORDER BY
+        wrl.position
+    SQL
+  end
+
+  def parse_wiki markdown, tag_ids, group_ids, context
+    root = Kramdown::Document.new(markdown, input: 'GFM').root
+    placements = []
+    description_parts = []
+    headings = []
+
+    root.children.each_with_index do |node, index|
+      case node.type
+      when :blank
+        next
+      when :header
+        level = node.options.fetch(:level)
+        name = inline_text(node).strip
+        raise "#{ context }: 名前のない見出しがあります．" if name.empty?
+
+        headings.pop while headings.any? && headings.last.first >= level
+        parent = headings.last&.last
+        section = { 'section_name' => name, 'description' => nil, 'children' => [] }
+        (parent ? parent.fetch('children') : placements) << section
+        headings << [level, section]
+      when :p
+        text = inline_markdown(node).strip
+        next if text.empty?
+
+        if headings.any?
+          heading = headings.last.last
+          heading['description'] = [heading['description'], text].compact.join("\n\n")
+        else
+          description_parts << text
+        end
+      when :ul, :ol
+        if headings.any? && see_also_heading?(headings.last.last.fetch('section_name'))
+          heading = headings.last.last
+          raw = original_block(markdown, root.children, index)
+          heading['description'] = [heading['description'], raw].compact.join("\n\n")
+        else
+          target = headings.any? ? headings.last.last.fetch('children') : placements
+          target.concat(node.children.map { |item| parse_list_item(item, tag_ids, group_ids, context) })
+        end
+      else
+        raise "#{ context }: 未対応の Markdown 構文 #{ node.type.inspect }"
+      end
+    end
+
+    [description_parts.empty? ? nil : description_parts.join("\n\n"), placements]
+  end
+
+  def see_also_heading? name
+    ['see also', '関連項目'].include?(name.strip.downcase.sub(/[:：]\z/, ''))
+  end
+
+  def original_block markdown, siblings, index
+    current = siblings.fetch(index)
+    start_line = current.options[:location]
+    raise 'Markdown block の位置が不明です．' unless start_line
+
+    following = siblings[(index + 1)..].find do |node|
+      node.options[:location] && node.options[:location] > start_line
+    end
+    end_line = following ? following.options.fetch(:location) - 1 : markdown.lines.length
+    markdown.lines[(start_line - 1)...end_line].join.strip
+  end
+
+  def parse_list_item item, tag_ids, group_ids, context
+    raise "#{ context }: リスト項目ではありません．" if item.type != :li
+
+    nested, own = item.children.partition { |child| [:ul, :ol].include?(child.type) }
+    own.reject! { |child| child.type == :blank }
+    unless own.all? { |child| [:p, :text, :a, :codespan].include?(child.type) }
+      raise "#{ context }: 未対応のリスト項目があります．"
+    end
+
+    label = own.map { |child| inline_text(child) }.join(' ').strip
+    raise "#{ context }: 空のリスト項目があります．" if label.empty?
+
+    node =
+        if group_ids.key?(label)
+          { 'tag_group_id' => group_ids.fetch(label) }
+        elsif tag_ids.key?(label)
+          ids = tag_ids.fetch(label)
+          unless ids.one?
+            raise "#{ context }: タグ名 #{ label.inspect } が複数の ID を指します：#{ ids.inspect }"
+          end
+          { 'tag_id' => ids.first }
+        elsif label.end_with?(':', '：')
+          name = label.sub(/[:：]\z/, '')
+          raise "#{ context }: 空の区分名があります．" if name.empty?
+          if see_also_heading?(name) && nested.any?
+            raise "#{ context }: リスト内の See also は説明文への保管処理が未実装です．"
+          end
+          { 'section_name' => name, 'description' => nil }
+        else
+          raise "#{ context }: 解決不能なリスト項目 #{ label.inspect }"
+        end
+
+    node['children'] = nested.flat_map do |list|
+      list.children.map { |child| parse_list_item(child, tag_ids, group_ids, context) }
+    end
+
+    node
+  end
+
+  def inline_text node
+    case node.type
+    when :text, :codespan
+      node.value.to_s
+    when :softbreak, :br
+      ' '
+    when :a, :p, :header, :em, :strong, :span, :li
+      node.children.map { |child| inline_text(child) }.join
+    else
+      raise "未対応のインライン構文 #{ node.type.inspect }"
+    end
+  end
+
+  def inline_markdown node
+    case node.type
+    when :text
+      node.value.to_s
+    when :codespan
+      "`#{ node.value }`"
+    when :softbreak
+      "\n"
+    when :br
+      "  \n"
+    when :p
+      node.children.map { |child| inline_markdown(child) }.join
+    when :a
+      href = node.attr.fetch('href')
+      "[#{ node.children.map { |child| inline_markdown(child) }.join }](#{ href })"
+    when :em
+      "*#{ node.children.map { |child| inline_markdown(child) }.join }*"
+    when :strong
+      "**#{ node.children.map { |child| inline_markdown(child) }.join }**"
+    else
+      raise "未対応のインライン構文 #{ node.type.inspect }"
+    end
+  end
+
+  def validate_tree! nodes, context, depth = 1
+    raise "#{ context }: 配置の深さが 5 を超えてゐます．" if depth > 5 && nodes.any?
+
+    nodes.each do |node|
+      name = node['section_name']
+      if name && name.length > 255
+        raise "#{ context }: 区分名が 255 文字を超えてゐます．"
+      end
+      validate_tree!(node.fetch('children'), context, depth + 1)
+    end
+  end
+
+  def build_members nodes, date, tag_history, group_history, context
+    ids_of_tags = []
+    ids_of_groups = []
+
+    visit = -> items do
+      items.each do |node|
+        ids_of_tags << node['tag_id'] if node.key?('tag_id')
+        ids_of_groups << node['tag_group_id'] if node.key?('tag_group_id')
+        visit.(node.fetch('children'))
+      end
+    end
+    visit.(nodes)
+
+    tags = ids_of_tags.uniq.map do |id|
+      { 'tag_id' => id,
+        'version_no' => version_at(tag_history[id], date, context, "Tag ##{ id }") }
+    end
+
+    groups = ids_of_groups.uniq.map do |id|
+      { 'tag_group_id' => id,
+        'version_no' => version_at(group_history[id], date, context, "TagGroup ##{ id }") }
+    end
+
+    tags + groups
+  end
+
+  def version_at history, date, context, target
+    raise "#{ context }: #{ target } の履歴が存在しません．" unless history&.any?
+
+    timestamp = Time.parse(date.to_s)
+    candidates = history.select do |row|
+      Time.parse(row.fetch('created_at').to_s) <= timestamp
+    end
+    if candidates.empty?
+      raise "#{ context }: #{ target } は #{ date } 時点で存在しません．"
+    end
+
+    candidates.max_by { |row|
+      [Time.parse(row.fetch('created_at').to_s), row.fetch('version_no').to_i]
+    }.fetch('version_no').to_i
+  end
+
+  def validate_current_groups! prepared
+    edges = { }
+    prepared.each do |group_id, versions|
+      edges[group_id] = versions.last.fetch(:members)
+                              .filter_map { |member| member['tag_group_id'] }
+    end
+
+    visiting = { }
+    visited = { }
+    visit = -> group_id do
+      raise "Tag Group の循環参照を検出しました：#{ group_id }" if visiting[group_id]
+      return if visited[group_id]
+
+      visiting[group_id] = true
+      edges.fetch(group_id, []).each { |child_id| visit.(child_id) }
+      visiting.delete(group_id)
+      visited[group_id] = true
+    end
+
+    edges.keys.each { |group_id| visit.(group_id) }
+  end
+
+  def quote(value) = connection.quote(value)
+
+  def insert_row table, values
+    columns = values.keys.join(', ')
+    payload = values.values.map { |value| quote(value) }.join(', ')
+    execute "INSERT INTO #{ table } (#{ columns }) VALUES (#{ payload })"
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
+ActiveRecord::Schema[8.0].define(version: 2026_10_08_010000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -440,6 +440,123 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
     t.index ["user_id"], name: "index_settings_on_user_id", unique: true
   end
 
+  create_table "tag_description_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.string "language_code", limit: 16, null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.text "body", null: false
+    t.string "source_language_code", limit: 16
+    t.integer "source_version_no"
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_description_versions_on_created_by_user_id"
+    t.index ["tag_id", "language_code", "version_no"], name: "idx_on_tag_id_language_code_version_no_ced77e57e6", unique: true
+    t.index ["tag_id", "source_language_code", "source_version_no"], name: "fk_rails_4f13094dbc"
+    t.index ["tag_id"], name: "index_tag_description_versions_on_tag_id"
+    t.check_constraint "((`source_language_code` is null) and (`source_version_no` is null)) or ((`source_language_code` is not null) and (`source_version_no` is not null))", name: "chk_tag_description_versions_source_pair"
+    t.check_constraint "(`source_language_code` is null) or (`source_language_code` <> `language_code`)", name: "chk_tag_description_versions_source_language_code_different"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "tag_description_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_description_versions_version_no_positive"
+  end
+
+  create_table "tag_descriptions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.string "language_code", limit: 16, null: false
+    t.integer "version_no", null: false
+    t.text "body", null: false
+    t.string "source_language_code", limit: 16
+    t.integer "source_version_no"
+    t.bigint "created_by_user_id"
+    t.bigint "updated_by_user_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_descriptions_on_created_by_user_id"
+    t.index ["language_code"], name: "index_tag_descriptions_on_language_code"
+    t.index ["source_language_code", "source_version_no"], name: "idx_on_source_language_code_source_version_no_00117fe02a"
+    t.index ["tag_id", "language_code"], name: "index_tag_descriptions_on_tag_id_and_language_code", unique: true
+    t.index ["tag_id", "source_language_code", "source_version_no"], name: "fk_rails_d1be0a7696"
+    t.index ["tag_id"], name: "index_tag_descriptions_on_tag_id"
+    t.index ["updated_by_user_id"], name: "index_tag_descriptions_on_updated_by_user_id"
+    t.check_constraint "((`source_language_code` is null) and (`source_version_no` is null)) or ((`source_language_code` is not null) and (`source_version_no` is not null))", name: "chk_tag_descriptions_source_pair"
+    t.check_constraint "(`source_language_code` is null) or (`source_language_code` <> `language_code`)", name: "chk_tag_descriptions_source_language_code_different"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_descriptions_version_no_positive"
+  end
+
+  create_table "tag_group_groups", primary_key: ["tag_group_id", "child_tag_group_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.bigint "child_tag_group_id", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["child_tag_group_id"], name: "index_tag_group_groups_on_child_tag_group_id"
+    t.index ["created_by_user_id"], name: "index_tag_group_groups_on_created_by_user_id"
+    t.check_constraint "`tag_group_id` <> `child_tag_group_id`", name: "chk_tag_group_groups_tag_group_id_not_child_tag_group_id"
+  end
+
+  create_table "tag_group_placements", primary_key: ["tag_group_id", "position"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.integer "position", null: false
+    t.integer "parent_position"
+    t.string "section_name"
+    t.text "description"
+    t.bigint "tag_id"
+    t.bigint "child_tag_group_id"
+    t.bigint "created_by_user_id"
+    t.bigint "updated_by_user_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["child_tag_group_id"], name: "index_tag_group_placements_on_child_tag_group_id"
+    t.index ["created_by_user_id"], name: "index_tag_group_placements_on_created_by_user_id"
+    t.index ["tag_group_id", "child_tag_group_id"], name: "fk_rails_7342b54ced"
+    t.index ["tag_group_id", "parent_position"], name: "fk_rails_3af6ee71ca"
+    t.index ["tag_group_id", "tag_id"], name: "fk_rails_365dc60759"
+    t.index ["tag_id"], name: "index_tag_group_placements_on_tag_id"
+    t.index ["updated_by_user_id"], name: "index_tag_group_placements_on_updated_by_user_id"
+    t.check_constraint "(((`section_name` is not null) and (`tag_id` is null) and (`child_tag_group_id` is null)) or ((`section_name` is null) and (`tag_id` is not null) and (`child_tag_group_id` is null)) or ((`section_name` is null) and (`tag_id` is null) and (`child_tag_group_id` is not null))) and ((`section_name` is not null) or (`description` is null))", name: "chk_tag_group_placements_references_exclusive"
+    t.check_constraint "`position` > `parent_position`", name: "chk_tag_group_placements_position_gt_parent_position"
+  end
+
+  create_table "tag_group_tags", primary_key: ["tag_group_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.bigint "tag_id", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_group_tags_on_created_by_user_id"
+    t.index ["tag_id"], name: "index_tag_group_tags_on_tag_id"
+  end
+
+  create_table "tag_group_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.text "description"
+    t.json "members", null: false
+    t.json "placements", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_group_versions_on_created_by_user_id"
+    t.index ["tag_group_id", "version_no"], name: "index_tag_group_versions_on_tag_group_id_and_version_no", unique: true
+    t.index ["tag_group_id"], name: "index_tag_group_versions_on_tag_group_id"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_group_versions_version_no_positive"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"maxItems\":0}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}',`placements`)", name: "chk_tag_group_versions_placements_schema"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"uniqueItems\":true,\"items\":{\"oneOf\":[{\"type\":\"object\",\"required\":[\"tag_id\",\"version_no\"],\"properties\":{\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1}},\"additionalProperties\":false},{\"type\":\"object\",\"required\":[\"tag_group_id\",\"version_no\"],\"properties\":{\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1}},\"additionalProperties\":false}]}}',`members`)", name: "chk_tag_group_versions_members_schema"
+  end
+
+  create_table "tag_groups", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.integer "version_no", null: false
+    t.string "name", null: false
+    t.text "description"
+    t.bigint "created_by_user_id"
+    t.bigint "updated_by_user_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_groups_on_created_by_user_id"
+    t.index ["name"], name: "index_tag_groups_on_name", unique: true
+    t.index ["updated_by_user_id"], name: "index_tag_groups_on_updated_by_user_id"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_groups_version_no_positive"
+  end
+
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
@@ -656,19 +773,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
     t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
-  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "wiki_page_id", null: false
-    t.integer "no", null: false
-    t.string "alt_text"
-    t.binary "sha256", limit: 32, null: false
-    t.bigint "created_by_user_id", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
-    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
-    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
-  end
-
   create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "sha256", limit: 64, null: false
     t.text "body", null: false
@@ -685,7 +789,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "discarded_at"
-    t.integer "next_asset_no", default: 1, null: false
     t.integer "version_no", null: false
     t.index ["created_user_id"], name: "index_wiki_pages_on_created_user_id"
     t.index ["discarded_at"], name: "index_wiki_pages_on_discarded_at"
@@ -788,6 +891,26 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
+  add_foreign_key "tag_description_versions", "tag_description_versions", column: ["tag_id", "source_language_code", "source_version_no"], primary_key: ["tag_id", "language_code", "version_no"]
+  add_foreign_key "tag_descriptions", "languages", column: "language_code", primary_key: "code"
+  add_foreign_key "tag_descriptions", "tag_description_versions", column: ["tag_id", "source_language_code", "source_version_no"], primary_key: ["tag_id", "language_code", "version_no"]
+  add_foreign_key "tag_descriptions", "tags"
+  add_foreign_key "tag_descriptions", "users", column: "created_by_user_id"
+  add_foreign_key "tag_descriptions", "users", column: "updated_by_user_id"
+  add_foreign_key "tag_group_groups", "tag_groups"
+  add_foreign_key "tag_group_groups", "tag_groups", column: "child_tag_group_id"
+  add_foreign_key "tag_group_groups", "users", column: "created_by_user_id"
+  add_foreign_key "tag_group_placements", "tag_group_groups", column: ["tag_group_id", "child_tag_group_id"], primary_key: ["tag_group_id", "child_tag_group_id"]
+  add_foreign_key "tag_group_placements", "tag_group_placements", column: ["tag_group_id", "parent_position"], primary_key: ["tag_group_id", "position"]
+  add_foreign_key "tag_group_placements", "tag_group_tags", column: ["tag_group_id", "tag_id"], primary_key: ["tag_group_id", "tag_id"]
+  add_foreign_key "tag_group_placements", "tag_groups"
+  add_foreign_key "tag_group_placements", "users", column: "created_by_user_id"
+  add_foreign_key "tag_group_placements", "users", column: "updated_by_user_id"
+  add_foreign_key "tag_group_tags", "tag_groups"
+  add_foreign_key "tag_group_tags", "tags"
+  add_foreign_key "tag_group_tags", "users", column: "created_by_user_id"
+  add_foreign_key "tag_groups", "users", column: "created_by_user_id"
+  add_foreign_key "tag_groups", "users", column: "updated_by_user_id"
   add_foreign_key "tag_implications", "tags"
   add_foreign_key "tag_implications", "tags", column: "parent_tag_id"
   add_foreign_key "tag_names", "languages", column: "language_code", primary_key: "code"
@@ -822,8 +945,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_040000) do
   add_foreign_key "user_post_views", "posts"
   add_foreign_key "user_post_views", "users"
   add_foreign_key "user_theme_slots", "users"
-  add_foreign_key "wiki_assets", "users", column: "created_by_user_id"
-  add_foreign_key "wiki_assets", "wiki_pages"
   add_foreign_key "wiki_pages", "tag_names"
   add_foreign_key "wiki_pages", "users", column: "created_user_id"
   add_foreign_key "wiki_pages", "users", column: "updated_user_id"

backend/lib/tasks/export_nico.rake

@@ -3,8 +3,8 @@ namespace :nico do
   task export: :environment do
     require 'open3'
 
-    mysql_user = ENV.fetch('MYSQL_USER')
-    mysql_pass = ENV.fetch('MYSQL_PASS')
+    mysql_user = ENV.fetch('NIZIKA_NICO_MYSQL_USER')
+    mysql_pass = ENV.fetch('NIZIKA_NICO_MYSQL_PASS')
     nizika_nico_path = ENV.fetch('NIZIKA_NICO_PATH')
 
     videos = Post.where('url LIKE ?', '%nicovideo.jp/watch/%').pluck(:url).filter_map {
@@ -14,7 +14,7 @@ namespace :nico do
     next if videos.empty?
 
     _, stderr, status = Open3.capture3(
-        { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
+        { 'NIZIKA_NICO_MYSQL_USER' => mysql_user, 'NIZIKA_NICO_MYSQL_PASS' => mysql_pass },
         'python3', '-m', 'tracked_videos.put_bulk_upsert', *videos,
         chdir: nizika_nico_path)
 

backend/lib/tasks/sync_nico.rake

@@ -54,11 +54,11 @@ namespace :nico do
           .find_each(&:destroy!)
     end
 
-    mysql_user = ENV['MYSQL_USER']
-    mysql_pass = ENV['MYSQL_PASS']
+    mysql_user = ENV['NIZIKA_NICO_MYSQL_USER']
+    mysql_pass = ENV['NIZIKA_NICO_MYSQL_PASS']
     nizika_nico_path = ENV['NIZIKA_NICO_PATH']
     stdout, stderr, status = Open3.capture3(
-        { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
+        { 'NIZIKA_NICO_MYSQL_USER' => mysql_user, 'NIZIKA_NICO_MYSQL_PASS' => mysql_pass },
         'python3', "#{ nizika_nico_path }/get_videos.py")
 
     unless status.success?

backend/spec/db/tag_description_migration_spec.rb

@@ -0,0 +1,34 @@
+require 'rails_helper'
+require_relative '../../db/migrate/20261003010000_migrate_tag_descriptions_from_wiki_pages'
+
+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!(
+        tag_name:, body: 'A', created_by_user: user)
+    revisions = [page.current_revision]
+    ['A', 'B', 'B', 'A'].each do |body|
+      revisions << Wiki::Commit.content!(
+          page:, body:, created_user: user, base_revision_id: revisions.last.id)
+    end
+    tag = create(:tag, primary_tag_name: tag_name)
+    legacy_state = [page.reload.attributes, revisions.map(&:attributes)]
+    expect(page.wiki_versions.count).to eq(3)
+
+    migration = MigrateTagDescriptionsFromWikiPages.new
+    migration.suppress_messages { migration.up }
+
+    versions = TagDescriptionVersion.where(tag_id: tag.id, language_code: 'ja')
+        .order(:version_no)
+    expect(versions.pluck(:id)).to eq(revisions.map(&:id))
+    expect(versions.pluck(:version_no)).to eq([1, 2, 3, 4, 5])
+    expect(versions.pluck(:body)).to eq(['A', 'A', 'B', 'B', 'A'])
+    expect(versions.pluck(:created_by_user_id)).to eq([user.id] * 5)
+    expect(versions.pluck(:created_at)).to eq(revisions.map(&:created_at))
+    expect(TagDescription.find(page.id)).to have_attributes(
+        tag_id: tag.id, language_code: 'ja', version_no: 5, body: 'A')
+    expect([page.reload.attributes, revisions.map { |revision| revision.reload.attributes }])
+        .to eq(legacy_state)
+  end
+end

backend/spec/requests/tag_description_wiki_spec.rb

@@ -0,0 +1,276 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag description Wiki compatibility', type: :request do
+  let!(:user) { create_member_user! }
+  let!(:tag_name) { create(:tag_name, name: 'description_contract') }
+  let!(:page) do
+    Wiki::Commit.create_content!(
+        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)
+    third = Wiki::Commit.content!(page:, body: 'old-third', created_user: user)
+    [first, second, third]
+  end
+  let!(:tag) { create(:tag, primary_tag_name: tag_name) }
+  let!(:versions) do
+    revisions.each_with_index.map do |revision, index|
+      TagDescriptionVersion.create!(
+          id: revision.id, tag_id: tag.id, language_code: 'ja',
+          version_no: index + 1, event_type: index.zero? ? 'create' : 'update',
+          body: index == 2 ? 'new-version' : 'A',
+          created_by_user_id: user.id, created_at: revision.created_at)
+    end
+  end
+  let!(:description) do
+    TagDescription.create!(
+        id: page.id, tag:, language_code: 'ja', version_no: 3, body: 'new',
+        created_by_user_id: user.id, updated_by_user_id: user.id)
+  end
+
+  before { page.update_columns(body: 'old') }
+
+  # Observe real SELECTs, including cached queries, only during the request.
+  def 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') { yield }
+    expect(queries).to be_empty
+  end
+
+  describe 'show' do
+    it 'uses current content and revision identity without legacy reads' do
+      without_legacy_reads { get "/wiki/#{ description.id }" }
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('body' => 'new', 'revision_id' => versions.last.id,
+                             'pred' => versions.second.id, 'succ' => nil)
+    end
+
+    [0, 1, 2].each do |index|
+      it "navigates displayed version #{ index + 1 }, preserving repeated bodies" do
+        without_legacy_reads do
+          get "/wiki/#{ description.id }", params: { version: versions[index].id }
+        end
+        expect(response).to have_http_status(:ok)
+        expect(json).to include(
+            'body' => versions[index].body,
+            'revision_id' => versions[index].id,
+            'pred' => index.zero? ? nil : versions[index - 1].id,
+            'succ' => index == 2 ? nil : versions[index + 1].id)
+      end
+    end
+
+    it 'does not fall back to a revision absent from new history' do
+      versions.first.destroy!
+      without_legacy_reads do
+        get "/wiki/#{ description.id }", params: { version: revisions.first.id }
+      end
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'does not fall back when the new current revision is missing' do
+      versions.last.destroy!
+      without_legacy_reads { get "/wiki/#{ description.id }" }
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'revision resource scope' do
+    let!(:other_tag) { create(:tag, primary_name: 'other_description_contract') }
+    let!(:other_version) do
+      TagDescriptionVersion.create!(
+          tag_id: other_tag.id, language_code: 'ja', version_no: 1,
+          event_type: 'create', body: 'other tag history',
+          created_by_user_id: user.id, created_at: Time.current)
+    end
+    let!(:other_description) do
+      TagDescription.create!(
+          tag: other_tag, language_code: 'ja', version_no: 1, body: 'other tag history',
+          created_by_user_id: user.id, updated_by_user_id: user.id)
+    end
+
+    it 'returns 404 when show specifies another tag description version' do
+      get "/wiki/#{ description.id }", params: { version: other_version.id }
+      expect(response).to have_http_status(:not_found)
+      expect(response.body).not_to include(other_version.body)
+    end
+
+    it 'returns 404 when diff from belongs to another tag description' do
+      get "/wiki/#{ description.id }/diff",
+          params: { from: other_version.id, to: versions.last.id }
+      expect(response).to have_http_status(:not_found)
+      expect(response.body).not_to include(other_version.body)
+    end
+
+    it 'returns 404 when diff to belongs to another tag description' do
+      get "/wiki/#{ description.id }/diff",
+          params: { from: versions.first.id, to: other_version.id }
+      expect(response).to have_http_status(:not_found)
+      expect(response.body).not_to include(other_version.body)
+    end
+  end
+
+  describe 'show_by_title' do
+    it 'resolves TagName and reads current content from new tables' do
+      without_legacy_reads { get "/wiki/title/#{ tag_name.name }" }
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('id' => description.id, 'body' => 'new',
+                             'revision_id' => versions.last.id)
+    end
+
+    it 'uses historical content and navigation from the new history' do
+      get "/wiki/title/#{ tag_name.name }", params: { version: versions.second.id }
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('body' => 'A', 'revision_id' => versions.second.id,
+                             'pred' => versions.first.id, 'succ' => versions.last.id)
+    end
+
+    it 'ignores changes to same-title legacy content and revision metadata' do
+      get "/wiki/title/#{ tag_name.name }"
+      original = json
+      page.update_columns(body: 'changed legacy body')
+      revisions.last.update_columns(message: 'legacy message', created_at: 1.day.ago)
+      revisions.last.wiki_lines.update_all(body: 'changed legacy revision')
+      get "/wiki/title/#{ tag_name.name }"
+      expect(json).to eq(original)
+      expect(json.fetch('body')).to eq('new')
+    end
+  end
+
+  describe 'exists' do
+    it 'recognises an ID without reading legacy tables' do
+      without_legacy_reads { get "/wiki/#{ description.id }/exists" }
+      expect(response).to have_http_status(:no_content)
+    end
+
+    it 'recognises a title without reading legacy tables' do
+      without_legacy_reads { get "/wiki/title/#{ tag_name.name }/exists" }
+      expect(response).to have_http_status(:no_content)
+    end
+
+    context 'without a legacy page' do
+      before do
+        WikiVersion.where(wiki_page_id: page.id).delete_all
+        page.destroy!
+      end
+
+      it 'recognises the description ID alone' do
+        get "/wiki/#{ description.id }/exists"
+        expect(response).to have_http_status(:no_content)
+      end
+
+      it 'recognises the TagName alone' do
+        get "/wiki/title/#{ tag_name.name }/exists"
+        expect(response).to have_http_status(:no_content)
+      end
+
+      it 'shows the description by title' do
+        get "/wiki/title/#{ tag_name.name }"
+        expect(response).to have_http_status(:ok)
+        expect(json).to include('body' => 'new', 'revision_id' => versions.last.id)
+      end
+    end
+  end
+
+  describe 'diff' do
+    [false, true].each do |current|
+      it "uses new bodies with #{ current ? 'implicit current' : 'explicit to' }" do
+        params = { from: versions.first.id }
+        params[:to] = versions.last.id unless current
+        get "/wiki/#{ description.id }/diff", params: params
+        expect(response).to have_http_status(:ok)
+        expect(json).to include(
+            'wiki_page_id' => description.id,
+            'older_revision_id' => versions.first.id,
+            'newer_revision_id' => versions.last.id,
+            'diff' => [{ 'type' => 'removed', 'content' => 'A' },
+                       { 'type' => 'added', 'content' => 'new-version' }])
+      end
+    end
+
+    it 'does not query legacy tables for diff' do
+      without_legacy_reads do
+        get "/wiki/#{ description.id }/diff",
+            params: { from: versions.first.id, to: versions.last.id }
+      end
+      expect(response).to have_http_status(:ok)
+    end
+
+    it 'keeps distinct revision IDs for identical consecutive bodies' do
+      get "/wiki/#{ description.id }/diff",
+          params: { from: versions.first.id, to: versions.second.id }
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'older_revision_id' => versions.first.id,
+          'newer_revision_id' => versions.second.id,
+          'diff' => [{ 'type' => 'context', 'content' => 'A' }])
+    end
+  end
+
+  describe 'changes' do
+    it 'lists every new version including consecutive identical bodies' do
+      without_legacy_reads { get '/wiki/changes', params: { id: description.id } }
+      expect(response).to have_http_status(:ok)
+      expect(json.map { |row| row.fetch('revision_id') }).to eq(versions.reverse.map(&:id))
+      expect(json.first.keys).to match_array(
+          ['revision_id', 'pred', 'succ', 'wiki_page', 'user', 'kind', 'message', 'timestamp'])
+      expect(json.first).to include(
+          'pred' => versions.second.id, 'succ' => nil, 'kind' => 'content',
+          'timestamp' => versions.last.created_at.iso8601(3),
+          'user' => { 'id' => user.id, 'name' => user.name })
+      expect(json.first.fetch('wiki_page')).to include('id' => description.id,
+                                                      'title' => tag_name.name)
+    end
+
+    it 'ignores legacy-only revisions and metadata changes' do
+      get '/wiki/changes', params: { id: description.id }
+      original = json
+      revisions.first.update_columns(message: 'legacy changed', created_at: 1.day.ago)
+      WikiRevision.create!(
+          wiki_page: page, created_user: user, kind: :content,
+          tree_sha256: Digest::SHA256.hexdigest('legacy only'), lines_count: 0)
+      get '/wiki/changes', params: { id: description.id }
+      expect(json).to eq(original)
+      expect(json.map { |row| row.fetch('revision_id') }).to eq(versions.reverse.map(&:id))
+    end
+  end
+
+  describe 'mixed changes' do
+    it 'includes unmigrated history and ignores migrated legacy-only revisions' do
+      legacy_page = Wiki::Commit.create_content!(
+          tag_name: create(:tag_name, name: 'Help_mixed'),
+          body: 'help', created_by_user: user)
+      legacy_revision = legacy_page.current_revision
+      extra = WikiRevision.create!(
+          wiki_page: page, created_user: user, kind: :content,
+          tree_sha256: Digest::SHA256.hexdigest('legacy only'), lines_count: 0)
+
+      get '/wiki/changes'
+      expect(response).to have_http_status(:ok)
+      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(
+          'revision_id' => legacy_revision.id,
+          'wiki_page' => include('id' => legacy_page.id, 'title' => 'Help_mixed')))
+    end
+  end
+
+  describe 'index' do
+    [nil, 'description_contract'].each do |title|
+      it "returns new content once in #{ title ? 'filtered' : 'unfiltered' } index" do
+        get '/wiki', params: { title: }
+        expect(response).to have_http_status(:ok)
+        rows = json.select { |row| row.fetch('id') == description.id }
+        expect(rows.size).to eq(1)
+        expect(rows.first).to include('body' => 'new', 'title' => tag_name.name)
+      end
+    end
+  end
+end

backend/spec/requests/tag_description_wiki_write_spec.rb

@@ -0,0 +1,274 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag description Wiki dual writes', type: :request do
+  let!(:user) { create_member_user! }
+  let!(:tag_name) { create(:tag_name, name: 'description_write') }
+  let(:tag) { create(:tag, primary_tag_name: tag_name) }
+  let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+
+  def stored_state
+    [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion,
+     TagName, TagVersion].map do |model|
+      model.order(:id).map(&:attributes)
+    end
+  end
+
+  # Fail after a real INSERT/UPDATE, exercising rollback rather than a mock write.
+  def fail_save model
+    failure = Class.new(StandardError)
+    callback = ->(_record) { raise failure, 'injected persistence failure' }
+    model.set_callback(:save, :after, callback)
+    expect { yield }.to raise_error(failure)
+  ensure
+    model.skip_callback(:save, :after, callback)
+  end
+
+  describe 'POST /wiki' do
+    before { tag }
+
+    def create_description
+      post '/wiki', params: { title: tag_name.name, body: 'initial', message: 'create' },
+           headers: headers
+    end
+
+    it 'creates both current records and histories with a shared revision ID' do
+      expect { create_description }
+          .to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+          .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(id: page.id, body: 'initial', version_no: 1)
+      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.wiki_versions.last.body).to eq(version.body)
+    end
+
+    ['missing_description', 'orphan_description'].each do |title|
+      it "rejects the bare title #{ title } without writing any resource" do
+        create(:tag_name, name: title) if title == 'orphan_description'
+        before_state = stored_state
+
+        post '/wiki', params: { title:, body: 'initial' }, headers: headers
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json).to include('type' => 'validation_error')
+        expect(stored_state).to eq(before_state)
+      end
+    end
+
+    it 'creates a namespaced legacy Wiki resource without a Tag' do
+      expect do
+        post '/wiki', params: { title: 'Help:description_write', 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(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.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
+        tag_name
+        before_state = stored_state
+        aggregate_failures do
+          fail_save(model) { create_description }
+          expect(stored_state).to eq(before_state)
+        end
+      end
+    end
+  end
+
+  describe 'PUT /wiki/:id' do
+    let!(:page) do
+      tag
+      Wiki::Commit.create_content!(
+          tag_name:, body: 'before', created_by_user: user)
+    end
+    let!(:first_revision) { page.current_revision }
+
+    let!(:description) do
+      TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
+    end
+
+    def update_description body: 'after', title: tag_name.name, base: first_revision.id
+      put "/wiki/#{ page.id }",
+          params: { title:, body:, message: 'edit', base_revision_id: base },
+          headers: headers
+    end
+
+    it 'increments the independent description sequence and shares revision identity' 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)
+          .and change(WikiVersion, :count).by(1)
+          .and change(TagDescriptionVersion, :count).by(1)
+      expect(response).to have_http_status(:ok)
+
+      revision = page.reload.current_revision
+      version = TagDescriptionVersion.find(revision.id)
+      expect(description.reload).to have_attributes(body: 'after', version_no: 2)
+      expect(version).to have_attributes(
+          body: 'after', version_no: 2, event_type: 'update', created_by_user_id: user.id)
+      expect(page).to have_attributes(body: 'after', version_no: 2)
+      expect(revision.body).to eq(version.body)
+      expect(page.wiki_versions.order(:version_no).last.body).to eq(version.body)
+    end
+
+    it 'uses description identity even when its Wiki TagName no longer owns the Tag' do
+      tag_name.update_columns(tag_id: nil)
+
+      expect { update_description }
+          .to change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+          .and change(TagDescriptionVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(description.reload).to have_attributes(body: 'after', version_no: 2)
+      expect(TagDescriptionVersion.find(page.reload.current_revision.id))
+          .to have_attributes(tag_id: tag.id, body: 'after', version_no: 2)
+    end
+
+    it 'does not add body history for a title-only update' do
+      revision_count = WikiRevision.count
+      wiki_version_count = WikiVersion.count
+      description_version_count = TagDescriptionVersion.count
+      wiki_version_no = page.reload.version_no
+      description_version_no = description.version_no
+      current_revision_id = page.current_revision.id
+      page_state = page.attributes
+      description_state = description.attributes
+
+      update_description(body: 'before', title: 'Help:description_renamed')
+
+      expect(response).to have_http_status(:ok)
+      expect(tag_name.reload.name).to eq('Help: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)
+      expect(page.reload).to have_attributes(body: 'before', version_no: wiki_version_no)
+      expect(page.current_revision.id).to eq(current_revision_id)
+      expect(page.reload.attributes).to eq(page_state)
+      expect(description.reload).to have_attributes(
+          body: 'before', version_no: description_version_no)
+      expect(description.reload.attributes).to eq(description_state)
+    end
+
+    it 'does not add body history for a TagName rename through tags' do
+      revision_count = WikiRevision.count
+      wiki_version_count = WikiVersion.count
+      description_version_count = TagDescriptionVersion.count
+      page_version_no = page.reload.version_no
+      current_revision_id = page.current_revision.id
+
+      patch "/tags/#{ tag.id }",
+            params: { name: 'description_tag_renamed' },
+            headers: headers
+
+      expect(response).to have_http_status(:ok)
+      expect(tag_name.reload.name).to eq('description_tag_renamed')
+      expect(WikiRevision.count).to eq(revision_count)
+      expect(WikiVersion.count).to eq(wiki_version_count)
+      expect(TagDescriptionVersion.count).to eq(description_version_count)
+      expect(page.reload.version_no).to eq(page_version_no)
+      expect(page.current_revision.id).to eq(current_revision_id)
+      expect(description.reload).to have_attributes(
+          body: 'before', version_no: 1)
+    end
+
+    it 'keeps both systems and the title unchanged on a stale revision conflict' do
+      update_description(body: 'current body', base: first_revision.id)
+      expect(response).to have_http_status(:ok)
+
+      stale_revision_id = first_revision.id
+      before_state = stored_state
+
+      update_description(
+          body: 'conflicting body',
+          title: 'conflicting_rename',
+          base: stale_revision_id)
+
+      expect(response).to have_http_status(:conflict)
+      expect(stored_state).to eq(before_state)
+      expect(tag_name.reload.name).not_to eq('conflicting_rename')
+    end
+
+    [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion].each do |model|
+      it "rolls back both systems when #{ model.name } persistence fails" do
+        before_state = stored_state
+        aggregate_failures do
+          fail_save(model) do
+            update_description(body: 'rollback body', title: 'rollback_rename')
+          end
+          expect(stored_state).to eq(before_state)
+        end
+      end
+    end
+
+    [['identical body', 'before'],
+     ['normalised-equivalent body', "before\n\n"]].each do |label, body|
+      it "does not write histories for #{ label }" do
+        before_state = stored_state
+        page_state = page.reload.attributes
+        description_state = description.reload.attributes
+        current_revision_id = page.current_revision.id
+        wiki_lines = WikiLine.order(:id).map(&:attributes)
+        revision_lines = WikiRevisionLine.order(:id).map(&:attributes)
+        page_version_no = page.version_no
+        description_version_no = description.version_no
+
+        update_description(body:)
+
+        expect(response).to have_http_status(:ok)
+        expect(WikiRevision.count).to eq(before_state[1].length)
+        expect(WikiVersion.count).to eq(before_state[2].length)
+        expect(TagDescriptionVersion.count).to eq(before_state[4].length)
+        expect(page.reload.version_no).to eq(page_version_no)
+        expect(description.reload.version_no).to eq(description_version_no)
+        expect(page.current_revision.id).to eq(current_revision_id)
+        expect(page.reload.attributes).to eq(page_state)
+        expect(description.reload.attributes).to eq(description_state)
+        expect(WikiLine.order(:id).map(&:attributes)).to eq(wiki_lines)
+        expect(WikiRevisionLine.order(:id).map(&:attributes)).to eq(revision_lines)
+      end
+    end
+  end
+end

backend/spec/requests/tag_descriptions_spec.rb

@@ -0,0 +1,359 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag description native API', type: :request do
+  let!(:author) { create_member_user! }
+  let(:editor) { create(:user, :member, name: 'description editor') }
+  let(:tag_name) { create(:tag_name, name: 'native_description') }
+  let(:tag) { create(:tag, primary_tag_name: tag_name) }
+  let(:headers) { { 'X-Transfer-Code' => editor.inheritance_code } }
+  let(:endpoint) { "/tags/#{ tag.id }/description" }
+
+  def stored_state
+    [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion,
+     WikiLine, WikiRevisionLine, TagName, TagVersion].map do |model|
+      model.order(:id).map(&:attributes)
+    end
+  end
+
+  def fail_save model
+    failure = Class.new(StandardError)
+    callback = ->(_record) { raise failure, 'injected persistence failure' }
+    model.set_callback(:save, :after, callback)
+    expect { yield }.to raise_error(failure)
+  ensure
+    model.skip_callback(:save, :after, callback)
+  end
+
+  def 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') { yield }
+    expect(queries).to be_empty
+  end
+
+  def native_get path, action: 'show'
+    get path
+    # A missing route must not make the resource-not-found examples pass.
+    expect(request.path_parameters).to include(controller: 'tag_descriptions', action:)
+  end
+
+  def native_write body:, request_headers: headers
+    put endpoint, params: { body: }, headers: request_headers
+    expect(request.path_parameters).to include(
+        controller: 'tag_descriptions', action: 'update')
+  end
+
+  def expect_current description
+    expect(json).to include(
+        'tag_id' => description.tag_id,
+        'language_code' => 'ja', 'body' => description.body,
+        'version_no' => description.version_no,
+        'created_by_user_id' => description.created_by_user_id,
+        'updated_by_user_id' => description.updated_by_user_id,
+        'created_at' => description.created_at.iso8601(3),
+        'updated_at' => description.updated_at.iso8601(3))
+    expect(json.keys).not_to include('title', 'name', 'wiki_page', 'tag_name_id')
+  end
+
+  describe 'routing', type: :routing do
+    it 'routes GET by Tag ID to show' do
+      expect(get: '/tags/123/description').to route_to(
+          controller: 'tag_descriptions', action: 'show', id: '123')
+    end
+
+    it 'routes GET by TagName to show_by_title' do
+      expect(get: '/tags/name/native_description/description').to route_to(
+          controller: 'tag_descriptions', action: 'show_by_title', name: 'native_description')
+    end
+
+    it 'does not route POST by Tag ID' do
+      expect(post: '/tags/123/description').not_to be_routable
+    end
+
+    it 'routes PUT by Tag ID to update' do
+      expect(put: '/tags/123/description').to route_to(
+          controller: 'tag_descriptions', action: 'update', id: '123')
+    end
+  end
+
+  describe 'native reads' do
+    let!(:description) do
+      TagDescription.create!(
+          id: tag.id + 1_000_000, tag:, language_code: 'ja', body: 'native current',
+          version_no: 1, created_by_user_id: author.id, updated_by_user_id: editor.id)
+    end
+    let!(:version) do
+      TagDescriptionVersion.create!(
+          tag_id: tag.id, language_code: 'ja', body: 'native version', version_no: 1,
+          event_type: 'create', created_by_user_id: author.id, created_at: Time.current)
+    end
+    let(:name_endpoint) { "/tags/name/#{ tag_name.name }/description" }
+
+    it 'reads the current resource by Tag ID without a WikiPage' do
+      expect(description.id).not_to eq(tag.id)
+      expect(WikiPage.exists?(id: description.id)).to be(false)
+      without_legacy_reads { native_get(endpoint) }
+      expect(response).to have_http_status(:ok)
+      expect_current(description)
+    end
+
+    it 'does not interpret a compatibility handle as a Tag ID' do
+      other_tag = create(:tag, id: description.id, primary_name: 'handle_collision')
+      other = TagDescription.create!(
+          tag: other_tag, language_code: 'ja', body: 'other current', version_no: 1,
+          created_by_user_id: author.id, updated_by_user_id: author.id)
+      without_legacy_reads { native_get("/tags/#{ other_tag.id }/description") }
+      expect(response).to have_http_status(:ok)
+      expect_current(other)
+    end
+
+    context 'with another language for the same Tag' do
+      before do
+        # Seed only the reference row; V1 does not enable an English locale.
+        Language.connection.execute(<<~SQL)
+          INSERT IGNORE INTO languages (code, name, created_at)
+          VALUES ('en', 'English', CURRENT_TIMESTAMP)
+        SQL
+      end
+
+      it 'selects the Japanese resource' do
+        TagDescription.create!(
+            tag:, language_code: 'en', body: 'English current', version_no: 4,
+            created_by_user_id: author.id, updated_by_user_id: author.id)
+        without_legacy_reads { native_get(endpoint) }
+        expect(response).to have_http_status(:ok)
+        expect_current(description)
+      end
+
+      it 'returns 404 if only the English description exists' do
+        description.update!(language_code: 'en')
+        without_legacy_reads { native_get(endpoint) }
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+
+    it 'resolves the primary Japanese TagName without a WikiPage' do
+      without_legacy_reads { native_get(name_endpoint, action: 'show_by_title') }
+      expect(response).to have_http_status(:ok)
+      expect_current(description)
+    end
+
+    it 'resolves an alias through the existing TagName canonicalisation semantics' do
+      alias_name = create(:tag_name, :alias, tag:, name: 'native_alias')
+      expect(TagName.canonicalise(Locale.nipponese, [alias_name.name])).to eq([tag_name.name])
+      without_legacy_reads do
+        native_get("/tags/name/#{ alias_name.name }/description", action: 'show_by_title')
+      end
+      expect(response).to have_http_status(:ok)
+      expect_current(description)
+    end
+
+    [:id, :name].each do |lookup|
+      it "ignores divergent legacy body and history for #{ lookup } lookup" do
+        page = WikiPage.create!(
+            id: description.id, tag_name:, body: 'old current',
+            created_user: author, updated_user: author)
+        revision = WikiRevision.create!(
+            wiki_page: page, created_user: author, kind: :content,
+            lines_count: 1, tree_sha256: Digest::SHA256.hexdigest('old revision'))
+        line = WikiLine.create!(body: 'old revision', sha256: revision.tree_sha256)
+        WikiRevisionLine.create!(wiki_revision: revision, wiki_line: line, position: 0)
+        WikiVersionRecorder.record!(page:, event_type: :create, created_by_user: author)
+        path = lookup == :id ? endpoint : name_endpoint
+        action = lookup == :id ? 'show' : 'show_by_title'
+
+        without_legacy_reads { native_get(path, action:) }
+        expect(response).to have_http_status(:ok)
+        expect_current(description)
+        original = json
+        page.update_columns(body: 'changed old current')
+        line.update_columns(body: 'changed old revision')
+        revision.update_columns(message: 'changed old history', created_at: 1.day.ago)
+        without_legacy_reads { native_get(path, action:) }
+        expect(response).to have_http_status(:ok)
+        expect(json).to eq(original)
+      end
+    end
+  end
+
+  describe 'missing native resources' do
+    it 'returns 404 for a Tag without a description' do
+      without_legacy_reads { native_get(endpoint) }
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'returns 404 for a primary name without a description' do
+      tag
+      without_legacy_reads do
+        native_get("/tags/name/#{ tag_name.name }/description", action: 'show_by_title')
+      end
+      expect(response).to have_http_status(:not_found)
+    end
+
+    it 'returns 404 for a missing Tag' do
+      missing_id = Tag.maximum(:id).to_i + 1
+      without_legacy_reads { native_get("/tags/#{ missing_id }/description") }
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+
+  describe 'PUT /tags/:id/description' do
+    context 'without an existing description' do
+      before { tag }
+
+      it 'creates both current resources and histories with matching compatibility IDs' do
+        expect { native_write(body: 'created natively') }
+            .to change(TagDescription, :count).by(1)
+            .and change(TagDescriptionVersion, :count).by(1)
+            .and change(WikiPage, :count).by(1)
+            .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, language_code: 'ja')
+        page = WikiPage.find(description.id)
+        revision = page.current_revision
+        version = TagDescriptionVersion.find(revision.id)
+        expect(description).to have_attributes(
+            body: 'created natively', version_no: 1,
+            created_by_user_id: editor.id, updated_by_user_id: editor.id)
+        expect(version).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', body: description.body,
+            version_no: 1, event_type: 'create', created_by_user_id: editor.id)
+        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)
+        expect_current(description)
+
+        get "/wiki/#{ description.id }"
+        expect(response).to have_http_status(:ok)
+        expect(json).to include('body' => description.body, 'revision_id' => version.id)
+      end
+
+      [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion].each do |model|
+        it "rolls back native create when #{ model.name } persistence fails" do
+          headers
+          before_state = stored_state
+          aggregate_failures do
+            fail_save(model) { native_write(body: 'rollback create') }
+            expect(stored_state).to eq(before_state)
+          end
+        end
+      end
+    end
+
+    context 'with an existing description' do
+      let!(:page) do
+        tag
+        Wiki::Commit.create_content!(tag_name:, body: 'before', created_by_user: author)
+      end
+      let!(:description) do
+        TagDescription.find_by!(tag_id: tag.id, language_code: 'ja')
+      end
+
+      it 'writes matching histories when the body changes' do
+        expect(page.reload.version_no).to eq(1)
+        expect(description.version_no).to eq(1)
+        expect { native_write(body: 'after') }
+            .to change(WikiRevision, :count).by(1)
+            .and change(WikiVersion, :count).by(1)
+            .and change(TagDescriptionVersion, :count).by(1)
+        expect(response).to have_http_status(:ok)
+        expect(description.reload).to have_attributes(
+            body: 'after', version_no: 2,
+            created_by_user_id: author.id, updated_by_user_id: editor.id)
+        expect(page.reload).to have_attributes(body: 'after', version_no: 2)
+
+        revision = page.current_revision
+        version = TagDescriptionVersion.find(revision.id)
+        expect(version).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', version_no: 2, event_type: 'update',
+            body: 'after', created_by_user_id: editor.id)
+        expect(revision.body).to eq(version.body)
+        expect(page.wiki_versions.order(:version_no).last.body).to eq(version.body)
+        get "/wiki/#{ description.id }"
+        expect(response).to have_http_status(:ok)
+        expect(json).to include('body' => 'after', 'revision_id' => version.id)
+      end
+
+      ['before', "before\n\n"].each do |body|
+        it 'does not write histories when the normalised body is unchanged' do
+          before_state = stored_state
+          page_state = page.reload.attributes
+          description_state = description.reload.attributes
+          current_revision_id = page.current_revision.id
+
+          native_write(body:)
+
+          expect(response).to have_http_status(:ok)
+          expect(stored_state).to eq(before_state)
+          expect(page.reload.attributes).to eq(page_state)
+          expect(description.reload.attributes).to eq(description_state)
+          expect(page.current_revision.id).to eq(current_revision_id)
+        end
+      end
+
+      [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion].each do |model|
+        it "rolls back native update when #{ model.name } persistence fails" do
+          headers
+          before_state = stored_state
+          aggregate_failures do
+            fail_save(model) { native_write(body: 'rollback update') }
+            expect(stored_state).to eq(before_state)
+          end
+        end
+      end
+    end
+  end
+
+  describe 'write access and validation' do
+    before { tag }
+
+    it 'requires authentication without changing either system' do
+      before_state = stored_state
+      native_write(body: 'unauthorised', request_headers: { })
+      expect(response).to have_http_status(:unauthorized)
+      expect(stored_state).to eq(before_state)
+    end
+
+    it 'rejects a guest without changing either system' do
+      guest = create(:user, :guest)
+      before_state = stored_state
+      native_write(body: 'forbidden',
+                   request_headers: { 'X-Transfer-Code' => guest.inheritance_code })
+      expect(response).to have_http_status(:forbidden)
+      expect(stored_state).to eq(before_state)
+    end
+
+    it 'rejects a banned member without changing either system' do
+      banned = create(:user, :member, :banned)
+      before_state = stored_state
+      native_write(body: 'forbidden',
+                   request_headers: { 'X-Transfer-Code' => banned.inheritance_code })
+      expect(response).to have_http_status(:forbidden)
+      expect(stored_state).to eq(before_state)
+    end
+
+    it 'rejects blank body using the existing validation error format' do
+      headers
+      before_state = stored_state
+      native_write(body: '')
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json).to include('type' => 'validation_error',
+                             'errors' => include('body' => a_kind_of(Array)))
+      expect(stored_state).to eq(before_state)
+    end
+
+    it 'returns 404 when PUT targets a missing Tag' do
+      missing_id = Tag.maximum(:id).to_i + 1
+      put "/tags/#{ missing_id }/description",
+          params: { body: 'missing' },
+          headers: headers
+      expect(response).to have_http_status(:not_found)
+    end
+  end
+end

backend/spec/requests/tag_wiki_history_integrity_spec.rb

@@ -25,9 +25,10 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   describe 'PATCH /tags/:id' do
-    it 'records wiki_version when tag name changes and tag has wiki' do
+    it 'renames the current Wiki resource without adding body history' do
       tag = create_tag!(name: 'patch_tag_wiki_before')
       wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+      wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
       expect {
         patch "/tags/#{ tag.id }", params: {
@@ -35,23 +36,17 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
         }
       }
           .to change(TagVersion, :count).by(2)
-          .and change(WikiVersion, :count).by(1)
+          .and change(WikiVersion, :count).by(0)
 
       expect(response).to have_http_status(:ok)
 
       tag.reload
       wiki_page.reload
-      version = wiki_page.wiki_versions.order(:version_no).last
 
       expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_wiki_after')
       expect(wiki_page.title).to eq('patch_tag_wiki_after')
 
-      expect(version).to have_attributes(
-        event_type: 'update',
-        title: 'patch_tag_wiki_after',
-        body: 'wiki body before',
-        created_by_user_id: member_user.id
-      )
+      expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
     end
 
     it 'does not record wiki_version when only category changes' do
@@ -79,9 +74,10 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   describe 'PUT /tags/:id' do
-    it 'records wiki_version when tag name changes and tag has wiki' do
+    it 'renames the current Wiki resource without adding body history' do
       tag = create_tag!(name: 'put_tag_wiki_before')
       wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+      wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
       expect {
         put "/tags/#{ tag.id }", params: {
@@ -93,23 +89,17 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
         }
       }
           .to change(TagVersion, :count).by(2)
-          .and change(WikiVersion, :count).by(1)
+          .and change(WikiVersion, :count).by(0)
 
       expect(response).to have_http_status(:ok)
 
       tag.reload
       wiki_page.reload
-      version = wiki_page.wiki_versions.order(:version_no).last
 
       expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_wiki_after')
       expect(wiki_page.title).to eq('put_tag_wiki_after')
 
-      expect(version).to have_attributes(
-        event_type: 'update',
-        title: 'put_tag_wiki_after',
-        body: 'wiki body before',
-        created_by_user_id: member_user.id
-      )
+      expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
     end
 
     it 'does not record wiki_version when only category changes' do

backend/spec/requests/tags_spec.rb

@@ -727,7 +727,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(tag.reload.category).to eq('general')
       end
 
-      it 'PATCH で tag の name を変更すると対応する wiki version を作成する' do
+      it 'PATCH の名称変更で Wiki の本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -735,24 +735,20 @@ RSpec.describe 'Tags API', type: :request do
                 created_by_user: member_user,
                 message: 'init')
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           patch "/tags/#{ tag.id }", params: {
             name: 'patch_wiki_renamed_tag',
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'patch_wiki_renamed_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('patch_wiki_renamed_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it 'tag の category だけを変更しても wiki version は作成しない' do
@@ -1380,7 +1376,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(system_tag.category).to eq(old_category)
       end
 
-      it 'wiki を持つ tag を更新すると wiki version も作成する' do
+      it 'Wiki を持つ Tag の名称変更で本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -1395,6 +1391,8 @@ RSpec.describe 'Tags API', type: :request do
           message: 'init'
         )
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           put "/tags/#{ tag.id }", params: {
             name: 'put_wiki_version_tag',
@@ -1405,18 +1403,12 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'put_wiki_version_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('put_wiki_version_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it 'wiki を持つ tag を旧 alias へ戻しても wiki を新しい正本名へ移す' do
@@ -1426,6 +1418,7 @@ RSpec.describe 'Tags API', type: :request do
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
         expect {
           put "/tags/#{ tag.id }", params: {
@@ -1445,7 +1438,7 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(3)
-            .and change(WikiVersion, :count).by(2)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
@@ -1457,10 +1450,8 @@ RSpec.describe 'Tags API', type: :request do
         expect(TagName.find_by!(language_code: 'ja', name: 'put_wiki_roundtrip_b'))
             .to have_attributes(tag_id: tag.id, primary_flg: false)
 
-        versions = wiki_page.wiki_versions.order(:version_no).last(2)
-
-        expect(versions.map(&:event_type)).to eq(['update', 'update'])
-        expect(versions.map(&:title)).to eq(['put_wiki_roundtrip_b', 'spec_tag'])
+        expect(wiki_page.title).to eq('spec_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it '別名を他 tag から奪った場合、奪はれた側の tag version も作成する' do
@@ -1570,7 +1561,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(TagImplication.where(tag:, parent_tag: child)).not_to exist
       end
 
-      it 'tag の name を変更すると対応する wiki version を作成する' do
+      it 'Tag の名称変更で Wiki の本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -1578,6 +1569,8 @@ RSpec.describe 'Tags API', type: :request do
                 created_by_user: member_user,
                 message: 'init')
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           put "/tags/#{ tag.id }", params: {
             name: 'put_wiki_renamed_tag',
@@ -1588,18 +1581,12 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'put_wiki_renamed_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('put_wiki_renamed_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
     end
   end

backend/spec/requests/wiki_history_integrity_spec.rb

@@ -21,7 +21,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_create_atomic',
+               title: 'Help:wiki_history_create_atomic',
                body: "a\nb\nc",
                message: 'initial commit',
              },
@@ -37,7 +37,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       revision = page.current_revision
       version = page.wiki_versions.order(:version_no).last
 
-      expect(page.title).to eq('wiki_history_create_atomic')
+      expect(page.title).to eq('Help:wiki_history_create_atomic')
       expect(page.body).to eq("a\nb\nc")
 
       expect(revision).to be_content
@@ -47,7 +47,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect(version).to have_attributes(
         version_no: 1,
         event_type: 'create',
-        title: 'wiki_history_create_atomic',
+        title: 'Help:wiki_history_create_atomic',
         body: "a\nb\nc",
         reason: 'initial commit',
         created_by_user_id: user.id
@@ -58,7 +58,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_blank_body',
+               title: 'Help:wiki_history_blank_body',
                body: "\r\n\r\n",
                message: 'blank',
              },
@@ -67,16 +67,17 @@ RSpec.describe 'Wiki history integrity', type: :request do
           .not_to change(WikiPage, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
-      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_blank_body' })).not_to exist
+      expect(WikiPage.joins(:tag_name)
+          .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
-      create_wiki_page(title: 'wiki_history_duplicate_title', body: 'first')
+      create_wiki_page(title: 'Help:wiki_history_duplicate_title', body: 'first')
 
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_duplicate_title',
+               title: 'Help:wiki_history_duplicate_title',
                body: 'second',
                message: 'duplicate',
              },
@@ -85,7 +86,8 @@ RSpec.describe 'Wiki history integrity', type: :request do
           .not_to change(WikiPage, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
-      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_duplicate_title' }).count).to eq(1)
+      expect(WikiPage.joins(:tag_name)
+          .where(tag_names: { name: 'Help:wiki_history_duplicate_title' }).count).to eq(1)
     end
   end
 

backend/spec/requests/wiki_spec.rb

@@ -11,6 +11,12 @@ RSpec.describe 'Wiki API', type: :request do
   let!(:user) { create_member_user! }
 
   let!(:tn) { create(:tag_name, name: 'spec_wiki_title') }
+  let!(:tag) do
+    create(:tag,
+        primary_tag_name: tn,
+        category: :general,
+        deprecated_at: Time.zone.local(2026, 6, 1))
+  end
   let!(:page) do
     Wiki::Commit.create_content!(
         tag_name: tn,
@@ -18,12 +24,6 @@ RSpec.describe 'Wiki API', type: :request do
         created_by_user: user,
         message: 'init')
   end
-  let!(:tag) do
-    create(:tag,
-        primary_tag_name: tn,
-        category: :general,
-        deprecated_at: Time.zone.local(2026, 6, 1))
-  end
 
   describe 'GET /wiki' do
     it 'returns wiki pages with title' do
@@ -111,7 +111,7 @@ RSpec.describe 'Wiki API', type: :request do
     context 'when success' do
       it 'creates wiki_page and first content revision' do
         expect do
-          post endpoint, params: { title: 'TestPage', body: "a\nb\nc", message: 'init' },
+          post endpoint, params: { title: 'Help:TestPage', body: "a\nb\nc", message: 'init' },
                          headers: auth_headers(member)
         end
             .to change(WikiPage, :count).by(1)
@@ -121,7 +121,7 @@ RSpec.describe 'Wiki API', type: :request do
         expect(response).to have_http_status(:created)
 
         page_id = json.fetch('id')
-        expect(json.fetch('title')).to eq('TestPage')
+        expect(json.fetch('title')).to eq('Help:TestPage')
 
         created_page = WikiPage.find(page_id)
         version = created_page.wiki_versions.order(:version_no).last
@@ -129,7 +129,7 @@ RSpec.describe 'Wiki API', type: :request do
         expect(version).to have_attributes(
           version_no: 1,
           event_type: 'create',
-          title: 'TestPage',
+          title: 'Help:TestPage',
           body: "a\nb\nc",
           created_by_user_id: member.id
         )
@@ -151,7 +151,7 @@ RSpec.describe 'Wiki API', type: :request do
         WikiLine.create!(sha256: Digest::SHA256.hexdigest('a'), body: 'a', created_at: Time.current, updated_at: Time.current)
 
         post endpoint,
-             params: { title: 'Reuse', body: "a\na" },
+             params: { title: 'Help:Reuse', body: "a\na" },
              headers: auth_headers(member)
 
         page = WikiPage.find(JSON.parse(response.body).fetch('id'))
@@ -166,7 +166,7 @@ RSpec.describe 'Wiki API', type: :request do
         duplicated = 'duplicated_line_for_wiki_line_upsert_spec'
 
         post endpoint,
-             params: { title: 'DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
+             params: { title: 'Help:DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
              headers: auth_headers(member)
 
         expect(response).to have_http_status(:created)
@@ -182,7 +182,8 @@ RSpec.describe 'Wiki API', type: :request do
 
       it 'normalises CRLF and strips trailing newlines' do
         post endpoint,
-             params: { title: 'NormalisedBody', body: "a\r\nb\r\n\r\n", message: 'normalise' },
+             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)
@@ -413,10 +414,10 @@ RSpec.describe 'Wiki API', type: :request do
       top = json.first
       expect(top).to include(
         'revision_id' => rev2.id,
-        'pred' => rev2.base_revision_id,
+        'pred' => rev1.id,
         'succ' => nil,
         'kind' => 'content',
-        'message' => 'r2'
+        'message' => nil
       )
       expect(top['wiki_page']).to include(
         'id' => page.id,

backend/spec/requests/wiki_title_collision_spec.rb

@@ -44,12 +44,12 @@ RSpec.describe 'Wiki title collision', type: :request do
   end
 
   it 'returns 422 when creating wiki with existing title' do
-    create_wiki_page(title: 'wiki_collision_create', body: 'already exists')
+    create_wiki_page(title: 'Help:wiki_collision_create', body: 'already exists')
 
     expect {
       post '/wiki',
            params: {
-             title: 'wiki_collision_create',
+             title: 'Help:wiki_collision_create',
              body: 'new body',
              message: 'duplicate create',
            },

backend/spec/requests/wiki_unmigrated_contract_spec.rb

@@ -0,0 +1,115 @@
+require 'rails_helper'
+
+RSpec.describe 'Unmigrated Wiki compatibility', type: :request do
+  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)
+  end
+  let!(:first_revision) { page.current_revision }
+  let!(:last_revision) do
+    Wiki::Commit.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
+    create(:tag, primary_tag_name: tag_name)
+
+    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)
+        .and change(WikiVersion, :count).by(1)
+        .and change(TagDescription, :count).by(0)
+        .and change(TagDescriptionVersion, :count).by(0)
+
+    expect(response).to have_http_status(:ok)
+    expect(page.reload).to have_attributes(body: 'changed legacy body')
+    expect(page.title).to eq('legacy_tag_renamed')
+    expect(page.current_revision).to have_attributes(message: 'legacy rename')
+  end
+
+  it 'shows legacy current and historical content by ID' do
+    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
+    get "/wiki/title/#{ tag_name.name }"
+    expect(response).to have_http_status(:ok)
+    expect(json).to include('body' => 'after', 'revision_id' => last_revision.id)
+    get "/wiki/title/#{ tag_name.name }", params: { version: first_revision.id }
+    expect(response).to have_http_status(:ok)
+    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
+    get '/wiki/changes', params: { id: page.id }
+    expect(response).to have_http_status(:ok)
+    expect(json.map { |row| row.fetch('revision_id') }).to eq(
+        [last_revision.id, first_revision.id])
+    expect(json.first).to include(
+        'pred' => first_revision.id, 'succ' => nil, 'kind' => 'content',
+        'message' => 'legacy edit', 'timestamp' => last_revision.created_at.iso8601(3),
+        'wiki_page' => { 'id' => page.id, 'title' => tag_name.name, 'deprecated_at' => nil },
+        'user' => { 'id' => user.id, 'name' => user.name })
+  end
+end