タグ説明移行 (#422) (#423)

Reviewed-on: #423 Co-authored-by: miteruzo <miteruzo@naver.com>
2026-10-05 01:22:54 +09:00
@@ -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
@@ -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
@@ -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])
@@ -0,0 +1,3 @@
+class TagDescription < ApplicationRecord
+  belongs_to :tag
+end
@@ -0,0 +1,3 @@
+class TagDescriptionVersion < ApplicationRecord
+  ;
+end
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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_05_000000) do
  create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
    t.string "name", null: false
    t.string "record_type", null: false
@@ -440,6 +440,49 @@ 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_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 +699,6 @@ 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 +715,6 @@ 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 +817,12 @@ 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_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 +857,6 @@ 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"
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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
@@ -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

@@ -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,
@@ -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',
           },
@@ -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