#425

backend/app/controllers/tag_groups_controller.rb

@@ -0,0 +1,39 @@
+class TagGroupsController < ApplicationController
+  def index
+    groups = TagGroup.includes(:created_by_user, :updated_by_user).order(:id)
+    render json: TagGroupRepr.many(groups.to_a)
+  end
+
+  def show
+    group = TagGroup.includes(:created_by_user, :updated_by_user).find_by(id: params[:id])
+    return head :not_found unless group
+
+    render json: TagGroupRepr.one(group)
+  end
+
+  def create
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    group = TagGroupOperation.create!(**write_attributes, actor: current_user)
+    render json: TagGroupRepr.one(group), status: :created
+  end
+
+  def update
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    group = TagGroup.find_by(id: params[:id])
+    return head :not_found unless group
+
+    TagGroupOperation.update!(group:, **write_attributes, actor: current_user)
+    render json: TagGroupRepr.one(group.reload)
+  end
+
+  private
+
+  def write_attributes
+    { name: params[:name], description: params[:description],
+      members: params[:members], placements: params[:placements] }
+  end
+end

backend/app/controllers/wiki_pages_controller.rb

@@ -2,24 +2,25 @@ 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
-    descriptions = TagDescription.where(language_code: 'ja')
+    descriptions =
+        TagDescription.where(language_code: 'ja')
         .includes(tag: :tag_names)
     pages = unmigrated_wiki_pages.includes(tag_name: :tag)
 
+    tag_groups = TagGroup.all
     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)
+      tag_groups = tag_groups.where(
+          'CONCAT(?, name) LIKE ?', TagGroupRepr::PREFIX, pattern).limit(20)
       pages = pages.where('tag_names.name LIKE ?', pattern).limit(20)
     end
 
     json = descriptions.map { |description| WikiPageRepr.tag_description(description) }
+    json.concat(tag_groups.map { WikiPageRepr.tag_group(_1) })
     json.concat(WikiPageRepr.base(pages))
     json = json.first(20) if title.present?
     render json:
@@ -30,6 +31,9 @@ class WikiPagesController < ApplicationController
 
     return render_wiki_page_by_tag_description tag_description if tag_description
 
+    tag_group = TagGroup.find_by(id: params[:id])
+    return render_tag_group tag_group if tag_group
+
     page = WikiPage.joins(:tag_name)
                    .includes(tag_name: :tag)
                    .find_by(id: params[:id])
@@ -40,6 +44,13 @@ class WikiPagesController < ApplicationController
   def show_by_title
     title = params[:title].to_s.strip
 
+    if title.start_with?(TagGroupRepr::PREFIX)
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      tag_group = TagGroup.find_by(name:)
+      return render_tag_group tag_group if tag_group
+      return head :not_found
+    end
+
     tag_description = tag_description_by_title(title)
 
     return render_wiki_page_by_tag_description tag_description if tag_description
@@ -53,12 +64,17 @@ class WikiPagesController < ApplicationController
 
   def exists
     return head :no_content if TagDescription.exists?(id: params[:id])
+    return head :no_content if TagGroup.exists?(id: params[:id])
 
     head WikiPage.exists?(id: params[:id]) ? :no_content : :not_found
   end
 
   def exists_by_title
     title = params[:title].to_s.strip
+    if title.start_with?(TagGroupRepr::PREFIX)
+      exists = TagGroup.exists?(name: title.delete_prefix(TagGroupRepr::PREFIX))
+      return head exists ? :no_content : :not_found
+    end
     return head :no_content if tag_description_by_title(title)
 
     exists = WikiPage.joins(:tag_name).exists?(tag_names: { name: title })
@@ -78,6 +94,18 @@ class WikiPagesController < ApplicationController
       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
+      tag_group = TagGroup.find_by(id:)
+      if tag_group
+        from_rev = from && group_version(tag_group, from)
+        to_rev = to ? group_version(tag_group, to) : current_group_version(tag_group)
+        return head :not_found if (from && !from_rev) || !to_rev
+
+        from_body = from_rev && render_group_version(from_rev)
+        to_body = render_group_version(to_rev)
+        resource = { 'id' => tag_group.id,
+                     'title' => "#{ TagGroupRepr::PREFIX }#{ tag_group.name }",
+                     'deprecated_at' => nil }
       else
         page = WikiPage.joins(:tag_name).includes(tag_name: :tag).find(id)
         from_rev = from && page.wiki_revisions.find(from)
@@ -85,23 +113,15 @@ class WikiPagesController < ApplicationController
         if ((from_rev && !from_rev.content?) || !to_rev&.content?)
           return render_unprocessable_entity('差分を表示できない版です．')
         end
+        from_body = from_rev&.body
+        to_body = to_rev.body
         resource = WikiPageRepr.base(page)
       end
-
-    diffs = Diff::LCS.sdiff(from_rev&.body&.lines || [], to_rev.body.lines)
-    diff_json = diffs.map { |change|
-      case change.action
-      when ?=
-        { type: 'context', content: change.old_element }
-      when ?!
-        [{ type: 'removed', content: change.old_element },
-         { type: 'added', content: change.new_element }]
-      when ?+
-        { type: 'added', content: change.new_element }
-      when ?-
-        { type: 'removed', content: change.old_element }
     end
-    }.flatten.compact
+
+    from_body ||= from_rev&.body
+    to_body ||= to_rev.body
+    diff_json = wiki_diff(from_body, to_body)
 
     render json: { wiki_page_id:      resource.fetch('id'),
                    title:             resource.fetch('title'),
@@ -109,6 +129,8 @@ class WikiPagesController < ApplicationController
                    older_revision_id: from_rev&.id,
                    newer_revision_id: to_rev.id,
                    diff:              diff_json }
+  rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+    render_unprocessable_entity(error.message)
   end
 
   def create
@@ -122,6 +144,17 @@ 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?
 
+    if title.start_with?(TagGroupRepr::PREFIX)
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      parsed = TagGroupMarkdownParser.parse(body:, group: nil)
+      group = TagGroupOperation.create!(name:, **parsed, actor: current_user,
+                                         require_compatibility: true)
+      version = current_group_version(group)
+      return render_group_representation(TagGroupRepr.one(group), version,
+                                         body: parsed.fetch(:compatibility_body),
+                                         status: :created)
+    end
+
     page = if title.include?(':')
       ApplicationRecord.transaction do
         tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
@@ -146,6 +179,8 @@ class WikiPagesController < ApplicationController
     render_validation_error e.record
   rescue ActiveRecord::RecordNotUnique
     render_record_not_unique
+  rescue TagGroupMarkdownParser::InvalidDocument => error
+    render_unprocessable_entity(error.message)
   end
 
   def update
@@ -158,7 +193,26 @@ 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?
 
-    page = WikiPage.find(params[:id])
+    group = TagGroup.find_by(id: params[:id])
+    if title.start_with?(TagGroupRepr::PREFIX)
+      return head :not_found unless group
+
+      name = title.delete_prefix(TagGroupRepr::PREFIX)
+      parsed = TagGroupMarkdownParser.parse(body:, group:)
+      TagGroupOperation.update!(group:, name:, **parsed, actor: current_user,
+                                require_compatibility: true)
+      return head :ok
+    end
+
+    page = WikiPage.find_by(id: params[:id])
+    if legacy_group_page?(page)
+      return render_unprocessable_entity field: :title
+    end
+    if group && !legacy_update_identified?(page, title, group)
+      return render_unprocessable_entity field: :title
+    end
+    return head :not_found unless page
+
     base_revision_id = params[:base_revision_id].presence
 
     ApplicationRecord.transaction do
@@ -175,11 +229,17 @@ class WikiPagesController < ApplicationController
       page.tag_name.update!(name: title) if title != old_title
 
       message = params[:message].presence
-      Wiki::Commit.content!(page:,
+      description = TagDescription.find_by(id: page.id)
-                            body:,
+      description_page = description && (
-                            created_user: current_user,
+          tag&.id == description.tag_id ||
-                            message:,
+          (tag.nil? && !old_title.include?(':')))
-                            base_revision_id:)
+      if description && !description_page
+        Wiki::Commit.legacy_content!(page:, body:, created_user: current_user,
+                                     message:, base_revision_id:)
+      else
+        Wiki::Commit.content!(page:, body:, created_user: current_user,
+                              message:, base_revision_id:)
+      end
 
       if tag && title != old_title
         tag.reload
@@ -188,6 +248,12 @@ class WikiPagesController < ApplicationController
     end
 
     head :ok
+  rescue ActiveRecord::RecordInvalid => e
+    render_validation_error e.record
+  rescue ActiveRecord::RecordNotUnique
+    render_record_not_unique
+  rescue TagGroupMarkdownParser::InvalidDocument => error
+    render_unprocessable_entity(error.message)
   end
 
   def changes
@@ -197,6 +263,11 @@ class WikiPagesController < ApplicationController
       return render json: description_changes(TagDescription.where(id: description.id))
     end
 
+    tag_group = id && TagGroup.find_by(id:)
+    if tag_group
+      return render json: tag_group_changes(TagGroupVersion.where(tag_group_id: tag_group.id))
+    end
+
     pages = id ? WikiPage.where(id:) : unmigrated_wiki_pages
     revisions = WikiRevision.joins(wiki_page: :tag_name)
         .where(wiki_page_id: pages.select(:id))
@@ -215,14 +286,122 @@ class WikiPagesController < ApplicationController
         timestamp: rev.created_at }
     }
     unless id
+      json.concat(tag_group_changes(TagGroupVersion.all))
       json.concat(description_changes(TagDescription.where(language_code: 'ja')))
-      json.sort_by! { |row| -row[:revision_id] }
+      json = json.each_with_index.sort_by do |row, index|
+        [-row.fetch(:timestamp).to_f, index]
+      end.map(&:first)
     end
     render json: json.first(200)
   end
 
   private
 
+  def legacy_group_page? page
+    return false unless page
+    return true if page.title.start_with?(TagGroupRepr::PREFIX)
+
+    prefix = ApplicationRecord.sanitize_sql_like(TagGroupRepr::PREFIX)
+    page.wiki_versions.where('title LIKE ?', "#{ prefix }%").exists?
+  end
+
+  def legacy_update_identified? page, title, group
+    return false unless page
+    return true if page.title == title
+    return false if title == group.name
+
+    namespace = page.title.split(':', 2)
+    return true if namespace.size == 2 && title.start_with?("#{ namespace.first }:")
+
+    base = params[:base_revision_id].presence
+    base && page.wiki_revisions.exists?(id: base)
+  end
+
+  def render_tag_group group
+    version = if params[:version].present?
+      group_version(group, params[:version])
+    else
+      current_group_version(group)
+    end
+    return head :not_found unless version
+
+    representation = if params[:version].present?
+      TagGroupRepr.historical(version)
+    else
+      TagGroupRepr.one(group)
+    end
+    render_group_representation(representation, version)
+  end
+
+  def render_group_version version
+    representation = TagGroupRepr.historical(version)
+    TagGroupMarkdownRenderer.render(representation)
+  end
+
+  def render_group_representation representation, version, body: nil, status: :ok
+    body ||= TagGroupMarkdownRenderer.render(representation)
+    versions = TagGroupVersion.where(tag_group_id: version.tag_group_id)
+    pred = versions.find_by(version_no: version.version_no - 1)&.id
+    succ = versions.find_by(version_no: version.version_no + 1)&.id
+    updated_at = version.created_at
+    render json: {
+        'id' => version.tag_group_id,
+        'title' => "#{ TagGroupRepr::PREFIX }#{ representation.fetch('name') }",
+        'deprecated_at' => nil,
+        'body' => body,
+        'revision_id' => version.id,
+        'pred' => pred,
+        'succ' => succ,
+        'updated_at' => updated_at }, status:
+  rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+    render_unprocessable_entity(error.message)
+  end
+
+  def current_group_version group
+    TagGroupVersion.find_by(tag_group_id: group.id, version_no: group.version_no)
+  end
+
+  def group_version group, version_id
+    TagGroupVersion.find_by(tag_group_id: group.id, id: version_id)
+  end
+
+  def wiki_diff from_body, to_body
+    diffs = Diff::LCS.sdiff(from_body.to_s.lines, to_body.to_s.lines)
+    diffs.map { |change|
+      case change.action
+      when ?=
+        { type: 'context', content: change.old_element }
+      when ?!
+        [{ type: 'removed', content: change.old_element },
+         { type: 'added', content: change.new_element }]
+      when ?+
+        { type: 'added', content: change.new_element }
+      when ?-
+        { type: 'removed', content: change.old_element }
+      end
+    }.flatten.compact
+  end
+
+  def tag_group_changes versions
+    rows = versions.includes(:created_by_user).order(id: :desc).limit(200).to_a
+    groups = TagGroup.where(id: rows.map(&:tag_group_id).uniq).index_by(&:id)
+    predecessors = TagGroupVersion.where(tag_group_id: groups.keys,
+                                         version_no: rows.map { _1.version_no - 1 })
+        .pluck(:tag_group_id, :version_no, :id)
+        .to_h { |group_id, number, version_id| [[group_id, number], version_id] }
+    rows.map do |version|
+      group = groups.fetch(version.tag_group_id)
+      user = version.created_by_user
+      { revision_id: version.id,
+        pred: predecessors[[group.id, version.version_no - 1]],
+        succ: nil,
+        wiki_page: { id: group.id, title: "#{ TagGroupRepr::PREFIX }#{ version.name }",
+                     deprecated_at: nil },
+        user: user && { id: user.id, name: user.name },
+        kind: 'content', message: nil, timestamp: version.created_at }
+    end
+  end
+
   def render_wiki_page_or_404 page
     return head :not_found unless page
 
@@ -271,7 +450,11 @@ class WikiPagesController < ApplicationController
 
   def unmigrated_wiki_pages
     descriptions = TagDescription.where(language_code: 'ja')
-    WikiPage.joins(:tag_name).where.not(id: descriptions.select(:id))
+
+    WikiPage
+        .joins(:tag_name)
+        .where.not(id: descriptions.select(:id))
+        .where.not('tag_names.name LIKE ?', "#{ TagGroupRepr::PREFIX }%")
         .where('tag_names.tag_id IS NULL OR tag_names.tag_id NOT IN (?)',
                descriptions.select(:tag_id))
   end

backend/app/models/tag_group.rb

@@ -0,0 +1,16 @@
+class TagGroup < ApplicationRecord
+  belongs_to :created_by_user, class_name: 'User', optional: true
+  belongs_to :updated_by_user, class_name: 'User', optional: true
+
+  has_many :tag_group_tags, dependent: :delete_all
+  has_many :tags, through: :tag_group_tags
+  has_many :tag_group_groups, dependent: :delete_all
+  has_many :child_tag_groups, through: :tag_group_groups
+  has_many :placements, -> { order(:position) },
+           class_name: 'TagGroupPlacement', dependent: :delete_all
+  has_many :versions, -> { order(:version_no) },
+           class_name: 'TagGroupVersion', dependent: :delete_all
+
+  validates :name, presence: true, uniqueness: true, length: { maximum: 255 }
+  validates :version_no, numericality: { only_integer: true, greater_than: 0 }
+end

backend/app/models/tag_group_group.rb

@@ -0,0 +1,7 @@
+class TagGroupGroup < ApplicationRecord
+  self.primary_key = [:tag_group_id, :child_tag_group_id]
+
+  belongs_to :tag_group
+  belongs_to :child_tag_group, class_name: 'TagGroup'
+  belongs_to :created_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_placement.rb

@@ -0,0 +1,9 @@
+class TagGroupPlacement < ApplicationRecord
+  self.primary_key = [:tag_group_id, :position]
+
+  belongs_to :tag_group
+  belongs_to :tag, optional: true
+  belongs_to :child_tag_group, class_name: 'TagGroup', optional: true
+  belongs_to :created_by_user, class_name: 'User', optional: true
+  belongs_to :updated_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_tag.rb

@@ -0,0 +1,7 @@
+class TagGroupTag < ApplicationRecord
+  self.primary_key = [:tag_group_id, :tag_id]
+
+  belongs_to :tag_group
+  belongs_to :tag
+  belongs_to :created_by_user, class_name: 'User', optional: true
+end

backend/app/models/tag_group_version.rb

@@ -0,0 +1,7 @@
+class TagGroupVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag_group
+
+  scope :ordered, -> { order(:version_no) }
+end

backend/app/representations/tag_group_repr.rb

@@ -0,0 +1,194 @@
+module TagGroupRepr
+  PREFIX = 'タググループ:'
+
+  module_function
+
+  def many groups
+    ids = groups.map(&:id)
+    return [] if ids.empty?
+
+    tag_members = TagGroupTag.where(tag_group_id: ids)
+        .group_by(&:tag_group_id)
+    group_members = TagGroupGroup.where(tag_group_id: ids)
+        .group_by(&:tag_group_id)
+    placements = TagGroupPlacement.where(tag_group_id: ids).order(:position)
+        .group_by(&:tag_group_id)
+
+    target_ids = tag_members.values.flatten.map(&:tag_id) +
+        group_members.values.flatten.map(&:child_tag_group_id) +
+        placements.values.flatten.filter_map(&:tag_id)
+    child_ids = group_members.values.flatten.map(&:child_tag_group_id) +
+        placements.values.flatten.filter_map(&:child_tag_group_id)
+    tags = Tag.select(:id, :category).where(id: target_ids.uniq).index_by(&:id)
+    names = TagName.where(tag_id: target_ids.uniq, language_code: 'ja', primary_flg: true)
+        .pluck(:tag_id, :name).to_h
+    child_groups = TagGroup.where(id: child_ids.uniq).index_by(&:id)
+
+    groups.map do |group|
+      group_json(group,
+                 tag_members.fetch(group.id, []),
+                 group_members.fetch(group.id, []),
+                 placements.fetch(group.id, []), tags, names, child_groups)
+    end
+  end
+
+  def one group
+    many([group]).first
+  end
+
+  def tag_group wiki_page
+    { 'id' => wiki_page.id,
+      'title' => "#{ PREFIX }#{ wiki_page.name }",
+      'deprecated_at' => nil,
+      'created_at' => wiki_page.created_at,
+      'updated_at' => wiki_page.updated_at }
+  end
+
+  def current_version group
+    TagGroupVersion.find_by(tag_group_id: group.id, version_no: group.version_no)
+  end
+
+  def historical version
+    members = Array(version.members)
+    placements = Array(version.placements)
+    tag_references = members.filter_map { |member| member['tag_id'] } +
+        collect_ids(placements, 'tag_id')
+    group_references = members.filter_map { |member| member['tag_group_id'] } +
+        collect_ids(placements, 'tag_group_id')
+    tag_versions = historical_tag_versions(tag_references)
+    group_versions = historical_group_versions(group_references)
+    tag_version_numbers = members.filter_map do |member|
+      next unless member['tag_id']
+
+      [member.fetch('tag_id'), member.fetch('version_no')]
+    end.to_h
+    group_version_numbers = members.filter_map do |member|
+      next unless member['tag_group_id']
+
+      [member.fetch('tag_group_id'), member.fetch('version_no')]
+    end.to_h
+    historical_members = members.map do |member|
+      historical_member(member, tag_versions, group_versions)
+    end
+    historical_placements = placements.map do |node|
+      historical_placement(node, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    end
+    { 'id' => version.tag_group_id,
+      'name' => version.name,
+      'description' => version.description,
+      'version_no' => version.version_no,
+      'members' => historical_members,
+      'placements' => historical_placements,
+      'created_at' => version.created_at,
+      'updated_at' => version.created_at,
+      'created_by_user' => user_json(version.created_by_user),
+      'updated_by_user' => user_json(version.created_by_user) }
+  end
+
+  def group_json group, tag_members, group_members, rows, tags, names, child_groups
+    tree = placement_tree(rows, tags, names, child_groups)
+    members = tag_members.sort_by(&:tag_id).map do |member|
+      { 'tag' => tag_json(tags.fetch(member.tag_id), names.fetch(member.tag_id)) }
+    end
+    members.concat(group_members.sort_by(&:child_tag_group_id).map do |member|
+      { 'tag_group' => group_json_reference(child_groups.fetch(member.child_tag_group_id)) }
+    end)
+    { 'id' => group.id,
+      'name' => group.name,
+      'description' => group.description,
+      'version_no' => group.version_no,
+      'members' => members,
+      'placements' => tree,
+      'created_at' => group.created_at,
+      'updated_at' => group.updated_at,
+      'created_by_user' => user_json(group.created_by_user),
+      'updated_by_user' => user_json(group.updated_by_user) }
+  end
+
+  def user_json user
+    UserRepr.base(user) if user
+  end
+
+  def placement_tree rows, tags, names, child_groups
+    by_parent = rows.group_by(&:parent_position)
+    build = lambda do |parent|
+      by_parent.fetch(parent, []).sort_by(&:position).map do |row|
+        node = if row.tag_id
+          { 'tag' => tag_json(tags.fetch(row.tag_id), names.fetch(row.tag_id)) }
+        elsif row.child_tag_group_id
+          { 'tag_group' => group_json_reference(child_groups.fetch(row.child_tag_group_id)) }
+        else
+          { 'section_name' => row.section_name, 'description' => row.description }
+        end
+        node.merge('children' => build.call(row.position))
+      end
+    end
+    build.call(nil)
+  end
+
+  def tag_json tag, name
+    { 'id' => tag.id, 'name' => name, 'category' => tag.category }
+  end
+
+  def group_json_reference group
+    { 'id' => group.id, 'name' => group.name }
+  end
+
+  def collect_ids nodes, key
+    nodes.flat_map do |node|
+      [node[key], *collect_ids(Array(node['children']), key)].compact
+    end
+  end
+
+  def historical_tag_versions ids
+    TagVersion.where(tag_id: ids.uniq).to_a.index_by do |version|
+      [version.tag_id, version.version_no]
+    end
+  end
+
+  def historical_group_versions ids
+    TagGroupVersion.where(tag_group_id: ids.uniq).to_a.index_by do |version|
+      [version.tag_group_id, version.version_no]
+    end
+  end
+
+  def historical_member member, tag_versions, group_versions
+    if member['tag_id']
+      id = member.fetch('tag_id')
+      version = tag_versions.fetch([id, member.fetch('version_no')])
+      { 'tag' => { 'id' => id, 'name' => japanese_version_name(version),
+                   'category' => version.category } }
+    else
+      id = member.fetch('tag_group_id')
+      version = group_versions.fetch([id, member.fetch('version_no')])
+      { 'tag_group' => { 'id' => id, 'name' => version.name } }
+    end
+  end
+
+  def historical_placement(node, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    result = if node['tag_id']
+      id = node.fetch('tag_id')
+      version_no = tag_version_numbers.fetch(id)
+      version = tag_versions.fetch([id, version_no])
+      { 'tag' => { 'id' => id, 'name' => japanese_version_name(version),
+                   'category' => version.category } }
+    elsif node['tag_group_id']
+      id = node.fetch('tag_group_id')
+      version_no = group_version_numbers.fetch(id)
+      version = group_versions.fetch([id, version_no])
+      { 'tag_group' => { 'id' => id, 'name' => version.name } }
+    else
+      { 'section_name' => node.fetch('section_name'), 'description' => node['description'] }
+    end
+    result.merge('children' => Array(node['children']).map do |child|
+      historical_placement(child, tag_versions, group_versions,
+                           tag_version_numbers, group_version_numbers)
+    end)
+  end
+
+  def japanese_version_name version
+    version.names.fetch('ja').fetch('name')
+  end
+end

backend/app/representations/wiki_page_repr.rb

@@ -25,6 +25,10 @@ module WikiPageRepr
       'deprecated_at' => tag.deprecated_at }
   end
 
+  def tag_group tag_group
+    TagGroupRepr.tag_group(tag_group)
+  end
+
   def many wiki_pages
     wiki_pages.map { |p| base(p) }
   end

backend/app/services/tag_group_markdown_parser.rb

@@ -0,0 +1,177 @@
+require 'kramdown'
+
+class TagGroupMarkdownParser
+  PREFIX = TagGroupRepr::PREFIX
+
+  class InvalidDocument < StandardError
+    ;
+  end
+
+  def self.parse(body:, group: nil)
+    new(body:, group:).parse
+  end
+
+  def initialize(body:, group:)
+    @body = body.to_s.gsub(/\r\n?/, "\n")
+    @group = group
+  end
+
+  def parse
+    parse_body = @body.gsub(/([^\n])\n([\x23]{1,6}[ \t]+\S)/, "\\1\n\n\\2")
+    root = Kramdown::Document.new(parse_body, input: 'GFM', auto_ids: false).root
+    placements = []
+    description_parts = []
+    headings = []
+
+    root.children.each do |node|
+      case node.type
+      when :blank
+        next
+      when :header
+        level = node.options.fetch(:level)
+        name = inline_text(node).strip
+        invalid!('Section 名は必須です．') if name.blank?
+
+        headings.pop while headings.any? && headings.last.fetch(:level) >= level
+        parent = headings.last&.fetch(:node)
+        section = { 'section_name' => name, 'description' => nil,
+                    'children' => [] }
+        (parent ? parent.fetch('children') : placements) << section
+        headings << { level:, node: section }
+      when :p
+        text = inline_markdown(node).strip
+        next if text.empty?
+
+        if headings.any?
+          section = headings.last.fetch(:node)
+          section['description'] = [section['description'], text].compact.join("\n\n")
+        else
+          description_parts << text
+        end
+      when :ul
+        invalid!('未対応のリスト項目があります．') if node.attr.any?
+        target = headings.any? ? headings.last.fetch(:node).fetch('children') : placements
+        target.concat(node.children.map { parse_list_item(_1) })
+      else
+        invalid!("未対応の Markdown 構文 #{ node.type.inspect } です．")
+      end
+    end
+
+    description = description_parts.presence&.join("\n\n")
+    { description:, placements:, members: build_members(placements),
+      compatibility_body: @body.sub(/\n+\z/, '') }
+  rescue Kramdown::Error => error
+    invalid!("Markdown を解析できません：#{ error.message }")
+  end
+
+  private
+
+  def parse_list_item(item)
+    invalid!('リスト項目ではありません．') unless item.type == :li
+    invalid!('未対応のリスト項目があります．') if item.attr.any?
+
+    nested, own = item.children.partition { |child| child.type == :ul }
+    invalid!('順序付きリストは使用できません．') if own.any? { _1.type == :ol }
+    own.reject! { _1.type == :blank }
+    invalid!('未対応のリスト項目があります．') unless own.all? do |child|
+      [:p, :text].include?(child.type)
+    end
+    invalid!('リスト項目は一つの段落で指定してください．') if own.size != 1
+
+    label = own.map { inline_text(_1) }.join(' ').strip
+    invalid!('空のリスト項目は使用できません．') if label.blank?
+
+    node = if label.start_with?(PREFIX)
+      group_name = label.delete_prefix(PREFIX).strip
+      child_group = TagGroup.find_by(name: group_name)
+      invalid!("Tag Group #{ group_name.inspect } を解決できません．") unless child_group
+      invalid!('自分自身を含めることはできません．') if child_group.id == @group&.id
+      { 'tag_group_id' => child_group.id }
+    elsif label.end_with?(':', '：')
+      section_name = label.sub(/[:：]\z/, '').strip
+      invalid!('Section 名は必須です．') if section_name.blank?
+      { 'section_name' => section_name, 'description' => nil }
+    else
+      { 'tag_id' => resolve_tag(label) }
+    end
+
+    node['children'] = nested.flat_map do |list|
+      invalid!('未対応の入れ子リストです．') unless list.type == :ul
+      list.children.map { parse_list_item(_1) }
+    end
+    node
+  end
+
+  def resolve_tag(name)
+    names = TagName.where(language_code: 'ja', name:).to_a
+    tag_ids = names.filter_map(&:tag_id).uniq
+    invalid!("Tag #{ name.inspect } を解決できません．") if tag_ids.empty?
+    invalid!("Tag 名 #{ name.inspect } が曖昧です．") if tag_ids.many?
+
+    tag_ids.first
+  end
+
+  def build_members(nodes)
+    references = []
+    visit = lambda do |items|
+      items.each do |node|
+        references << node.slice('tag_id', 'tag_group_id') if
+            node.key?('tag_id') || node.key?('tag_group_id')
+        visit.call(node.fetch('children'))
+      end
+    end
+    visit.call(nodes)
+    references.uniq
+  end
+
+  def inline_text(node)
+    if node.attr.any?
+      invalid!("未対応のインライン構文 #{ node.type.inspect } です．")
+    end
+
+    case node.type
+    when :text
+      node.value.to_s
+    when :p, :header
+      node.children.map { inline_text(_1) }.join
+    else
+      invalid!("未対応のインライン構文 #{ node.type.inspect } です．")
+    end
+  end
+
+  def inline_markdown(node)
+    case node.type
+    when :text
+      node.value.to_s
+    when :codespan
+      text = node.value.to_s
+      longest = text.scan(/`+/).map(&:length).max || 0
+      delimiter = '`' * (longest + 1)
+      padded = text.start_with?('`', ' ') || text.end_with?('`', ' ')
+      content = padded ? " #{ text } " : text
+      "#{ delimiter }#{ content }#{ delimiter }"
+    when :softbreak
+      "\n"
+    when :br
+      "  \n"
+    when :p
+      node.children.map { inline_markdown(_1) }.join
+    when :a
+      href = node.attr.fetch('href')
+      label = node.children.map { inline_markdown(_1) }.join
+      title = node.attr['title']&.gsub('"', '\\"')
+      suffix = title ? " \"#{ title }\"" : ''
+      "[#{ label }](#{ href }#{ suffix })"
+    when :em
+      "*#{ node.children.map { inline_markdown(_1) }.join }*"
+    when :strong
+      "**#{ node.children.map { inline_markdown(_1) }.join }**"
+    else
+      invalid!("未対応の説明文構文 #{ node.type.inspect } です．")
+    end
+  end
+
+  def invalid! message
+    raise InvalidDocument, message
+  end
+end

backend/app/services/tag_group_markdown_renderer.rb

@@ -0,0 +1,114 @@
+class TagGroupMarkdownRenderer
+  class UnsupportedStructure < StandardError
+    ;
+  end
+
+  def self.render group
+    new(group).render
+  end
+
+  def initialize group
+    @group = group
+  end
+
+  def render
+    placements = @group.fetch('placements')
+    validate_membership!(placements)
+    blocks = []
+    blocks << clean_text(@group['description']) if @group['description'].present?
+
+    sections = placements.select { _1.key?('section_name') }
+    if sections.any? && sections.size != placements.size
+      raise UnsupportedStructure,
+          '最上位の見出し Section と Placement の混在は Markdown にできません．'
+    end
+
+    if placements.all? { _1.key?('section_name') }
+      blocks.concat(placements.map { render_heading(_1, 1) })
+    else
+      blocks << render_list(placements, 0)
+    end
+
+    blocks.compact.reject(&:empty?).join("\n").sub(/\n+\z/, '')
+  end
+
+  private
+
+  def validate_membership! placements
+    placed = placement_members(placements).uniq.sort
+    members = @group.fetch('members').map do |member|
+      if member['tag']
+        ['tag', member.fetch('tag').fetch('id')]
+      else
+        ['tag_group', member.fetch('tag_group').fetch('id')]
+      end
+    end.uniq.sort
+    missing = members - placed
+    raise UnsupportedStructure, '掲載位置のない membership は Markdown にできません．' if missing.any?
+  end
+
+  def placement_members nodes
+    nodes.flat_map do |node|
+      own = if node['tag']
+        [['tag', node.fetch('tag').fetch('id')]]
+      elsif node['tag_group']
+        [['tag_group', node.fetch('tag_group').fetch('id')]]
+      else
+        []
+      end
+      own + placement_members(node.fetch('children'))
+    end
+  end
+
+  def render_heading section, level
+    header = "#{ '#' * level } #{ clean_text(section.fetch('section_name')) }"
+    blocks = [header]
+    blocks << clean_text(section['description']) if section['description'].present?
+    children = section.fetch('children')
+    section_indexes = children.each_index.select { |index| children[index].key?('section_name') }
+    if section_indexes.any?
+      first_section = section_indexes.first
+      if children[first_section..].any? { !_1.key?('section_name') }
+        raise UnsupportedStructure,
+            '見出し Section と兄弟 Placement の交互配置は Markdown にできません．'
+      end
+      list_nodes = children[0...first_section]
+      blocks << render_list(list_nodes, 0) if list_nodes.any?
+      blocks.concat(children[first_section..].map { render_heading(_1, level + 1) })
+    elsif children.any?
+      blocks << render_list(children, 0)
+    end
+    blocks.join("\n")
+  end
+
+  def render_list nodes, depth
+    nodes.map do |node|
+      indent = '  ' * depth
+      if node.key?('section_name')
+        raise UnsupportedStructure,
+            'リスト内 Section の説明文は Markdown にできません．' if node['description'].present?
+
+        children = node.fetch('children')
+        head = "#{ indent }- #{ clean_text(node.fetch('section_name')) }:"
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      else
+        label = if node['tag']
+          node.fetch('tag').fetch('name')
+        else
+          "#{ TagGroupRepr::PREFIX }#{ node.fetch('tag_group').fetch('name') }"
+        end
+        raise UnsupportedStructure, '名称のない Placement は Markdown にできません．' if label.blank?
+
+        head = "#{ indent }- #{ clean_text(label) }"
+        children = node.fetch('children')
+        tail = render_list(children, depth + 1) if children.any?
+        [head, tail].compact.join("\n")
+      end
+    end.join("\n")
+  end
+
+  def clean_text value
+    value.to_s.gsub(/\r\n?/, "\n").lines.map(&:rstrip).join("\n").strip
+  end
+end

backend/app/services/tag_group_operation.rb

@@ -0,0 +1,365 @@
+class TagGroupOperation
+  MAX_PLACEMENT_DEPTH = 5
+  PREFIX = TagGroupRepr::PREFIX
+
+  def self.create!(name:, description:, members:, placements:, actor:,
+                   require_compatibility: false, compatibility_body: nil)
+    group, sync_issue = ApplicationRecord.transaction do
+      group = TagGroup.new(version_no: 1, created_by_user: actor,
+                           updated_by_user: actor)
+      attributes = prepare!(group:, name:, description:, members:, placements:)
+      group.assign_attributes(name: attributes.fetch(:name),
+                              description: attributes.fetch(:description))
+      group.save!
+      persist_structure!(group:, attributes:, actor:)
+      persist_version!(group:, attributes:, actor:, event_type: 'create')
+      issue = sync_compatibility!(group:, actor:, old_name: nil,
+                                  require_compatibility:, compatibility_body:)
+      [group, issue]
+    end
+    report_sync_issue(group, actor, sync_issue)
+    group
+  end
+
+  def self.update!(group:, name:, description:, members:, placements:, actor:,
+                   require_compatibility: false, compatibility_body: nil)
+    group, sync_issue = ApplicationRecord.transaction do
+      group.lock!
+      old_name = group.name
+      attributes = prepare!(group:, name:, description:, members:, placements:)
+      group.update!(name: attributes.fetch(:name),
+                    description: attributes.fetch(:description),
+                    version_no: group.version_no + 1,
+                    updated_by_user: actor)
+      persist_structure!(group:, attributes:, actor:)
+      persist_version!(group:, attributes:, actor:, event_type: 'update')
+      issue = sync_compatibility!(group:, actor:, old_name:,
+                                  require_compatibility:, compatibility_body:)
+      [group, issue]
+    end
+    report_sync_issue(group, actor, sync_issue)
+    group
+  end
+
+  def self.prepare!(group:, name:, description:, members:, placements:)
+    record = group
+    normalized_name = name.to_s.strip
+    invalid!(record, :name, 'グループ名は必須です．') if normalized_name.blank?
+    if normalized_name.length > 255
+      invalid!(record, :name, 'グループ名は 255 文字以内で入力してください．')
+    end
+    invalid!(record, :description, '説明文は文字列で入力してください．') unless
+        description.nil? || description.is_a?(String)
+
+    record.name = normalized_name
+    record.description = description
+    unless record.valid?
+      raise ActiveRecord::RecordInvalid, record
+    end
+
+    member_rows = normalize_members(record, members)
+    placement_tree = normalize_placements(record, placements)
+    validate_references!(record, member_rows, placement_tree)
+    validate_containment!(record, member_rows)
+    { name: normalized_name, description:, members: member_rows,
+      placements: placement_tree }
+  end
+  private_class_method :prepare!
+
+  def self.normalize_members(record, members)
+    invalid!(record, :members, 'members は配列で指定してください．') unless members.is_a?(Array)
+
+    result = members.map do |member|
+      member = stringify_keys(member)
+      unless member.is_a?(Hash) && member.keys.one? &&
+             (member.key?('tag_id') || member.key?('tag_group_id'))
+        invalid!(record, :members, '各 member は tag_id または tag_group_id を一つ指定してください．')
+      end
+      key = member.keys.first
+      id = integer_id(record, member.fetch(key), :members)
+      { key => id }
+    end
+    invalid!(record, :members, 'membership に重複があります．') unless result.uniq == result
+    result
+  end
+  private_class_method :normalize_members
+
+  def self.normalize_placements(record, placements)
+    invalid!(record, :placements, 'placements は配列で指定してください．') unless
+        placements.is_a?(Array)
+
+    normalize_placement_nodes(record, placements, 1)
+  end
+  private_class_method :normalize_placements
+
+  def self.normalize_placement_nodes(record, nodes, depth)
+    if depth > MAX_PLACEMENT_DEPTH && nodes.any?
+      invalid!(record, :placements, '配置の深さは 5 階層までです．')
+    end
+
+    nodes.map do |raw_node|
+      node = stringify_keys(raw_node)
+      unless node.is_a?(Hash) && node.key?('children')
+        invalid!(record, :placements, '各 Placement に children 配列が必要です．')
+      end
+      children = node.delete('children')
+      unless children.is_a?(Array)
+        invalid!(record, :placements, 'children は配列で指定してください．')
+      end
+
+      kinds = ['tag_id', 'tag_group_id', 'section_name'].select { node.key?(_1) }
+      invalid!(record, :placements, 'Placement の種類を一つ指定してください．') unless
+          kinds.one?
+      kind = kinds.first
+      allowed = [kind, 'description']
+      invalid!(record, :placements, '不明な Placement 項目があります．') unless
+          (node.keys - allowed).empty?
+
+      case kind
+      when 'tag_id', 'tag_group_id'
+        node[kind] = integer_id(record, node.fetch(kind), :placements)
+        if node['description'].present?
+          invalid!(record, :placements, 'Tag / Tag Group Placement に説明文は指定できません．')
+        end
+        node.delete('description')
+      when 'section_name'
+        section_name = node.fetch(kind)
+        unless section_name.is_a?(String) && section_name.strip.present? &&
+               section_name.length <= 255
+          invalid!(record, :placements, 'Section 名は 1〜255 文字で入力してください．')
+        end
+        node[kind] = section_name.strip
+        unless node['description'].nil? || node['description'].is_a?(String)
+          invalid!(record, :placements, 'Section の説明文は文字列で入力してください．')
+        end
+      end
+
+      node['children'] = normalize_placement_nodes(record, children, depth + 1)
+      node
+    end
+  end
+  private_class_method :normalize_placement_nodes
+
+  def self.validate_references!(record, members, placements)
+    membership = members.to_set
+    placed = placement_references(placements).uniq
+    missing = placed - membership.to_a
+    invalid!(record, :placements, 'Placement の対象は membership に含めてください．') if
+        missing.any?
+
+    tag_ids = members.filter_map { _1['tag_id'] }
+    group_ids = members.filter_map { _1['tag_group_id'] }
+    tags = Tag.where(id: tag_ids).index_by(&:id)
+    groups = TagGroup.where(id: group_ids).index_by(&:id)
+    invalid!(record, :members, '存在しない Tag が含まれています．') if
+        tags.size != tag_ids.uniq.size
+    invalid!(record, :members, '存在しない Tag Group が含まれています．') if
+        groups.size != group_ids.uniq.size
+
+    tag_versions = TagVersion.where(tag_id: tag_ids).pluck(:tag_id, :version_no).to_set
+    group_versions = TagGroupVersion.where(tag_group_id: group_ids)
+        .pluck(:tag_group_id, :version_no).to_set
+    tag_names = TagName.where(tag_id: tag_ids, language_code: 'ja', primary_flg: true)
+        .pluck(:tag_id).uniq
+
+    members.each do |member|
+      if member.key?('tag_id')
+        id = member.fetch('tag_id')
+        invalid!(record, :members, "Tag ##{ id } に日本語の正規名がありません．") unless
+            tag_names.include?(id)
+        version_no = tags.fetch(id).version_no
+        unless tag_versions.include?([id, version_no])
+          invalid!(record, :members, "Tag ##{ id } の Version がありません．")
+        end
+        member['version_no'] = version_no
+      else
+        id = member.fetch('tag_group_id')
+        version_no = groups.fetch(id).version_no
+        unless group_versions.include?([id, version_no])
+          invalid!(record, :members, "Tag Group ##{ id } の Version がありません．")
+        end
+        member['version_no'] = version_no
+      end
+    end
+  end
+  private_class_method :validate_references!
+
+  def self.validate_containment!(record, members)
+    target_id = record.id
+    return unless target_id
+
+    children = members.filter_map { _1['tag_group_id'] }
+    edges = TagGroupGroup.pluck(:tag_group_id, :child_tag_group_id)
+        .group_by(&:first).transform_values { _1.map(&:last) }
+    edges[target_id] = children
+    visiting = Set.new
+    visited = Set.new
+    visit = lambda do |group_id|
+      invalid!(record, :members, 'Tag Group の循環包含はできません．') if
+          group_id == target_id && visiting.include?(group_id)
+      return if visited.include?(group_id)
+
+      visiting.add(group_id)
+      edges.fetch(group_id, []).each do |child_id|
+        invalid!(record, :members, 'Tag Group の循環包含はできません．') if
+            child_id == target_id
+        visit.call(child_id)
+      end
+      visiting.delete(group_id)
+      visited.add(group_id)
+    end
+    children.each { visit.call(_1) }
+  end
+  private_class_method :validate_containment!
+
+  def self.persist_structure!(group:, attributes:, actor:)
+    tag_members = TagGroupTag.where(tag_group_id: group.id).index_by(&:tag_id)
+    group_members = TagGroupGroup.where(tag_group_id: group.id).index_by(&:child_tag_group_id)
+    attributes.fetch(:members).each do |member|
+      if member.key?('tag_id')
+        next if tag_members.delete(member.fetch('tag_id'))
+
+        TagGroupTag.create!(tag_group_id: group.id, tag_id: member.fetch('tag_id'),
+                            created_by_user: actor)
+      else
+        next if group_members.delete(member.fetch('tag_group_id'))
+
+        TagGroupGroup.create!(tag_group_id: group.id,
+                              child_tag_group_id: member.fetch('tag_group_id'),
+                              created_by_user: actor)
+      end
+    end
+    existing = TagGroupPlacement.where(tag_group_id: group.id).index_by(&:position)
+    persist_placements!(group:, nodes: attributes.fetch(:placements), actor:, existing:)
+    existing.values.sort_by(&:position).reverse_each(&:delete)
+    tag_members.each_value(&:delete)
+    group_members.each_value(&:delete)
+  end
+  private_class_method :persist_structure!
+
+  def self.persist_placements!(group:, nodes:, actor:, existing:, parent_position: nil,
+                               next_position: [0])
+    nodes.each do |node|
+      next_position[0] += 1
+      position = next_position[0]
+      row = existing.delete(position) || TagGroupPlacement.new(
+          tag_group_id: group.id, position:, created_by_user: actor)
+      row.assign_attributes(
+          parent_position:,
+          section_name: node['section_name'], description: node['description'],
+          tag_id: node['tag_id'], child_tag_group_id: node['tag_group_id'])
+      if row.new_record? || row.changed?
+        row.updated_by_user = actor
+        row.save!
+      end
+      persist_placements!(group:, nodes: node.fetch('children'), actor:, existing:,
+                          parent_position: position, next_position:)
+    end
+  end
+  private_class_method :persist_placements!
+
+  def self.persist_version!(group:, attributes:, actor:, event_type:)
+    TagGroupVersion.create!(tag_group: group, version_no: group.version_no,
+                            event_type:, name: group.name,
+                            description: group.description,
+                            members: attributes.fetch(:members),
+                            placements: attributes.fetch(:placements),
+                            created_by_user: actor)
+  end
+  private_class_method :persist_version!
+
+  def self.sync_compatibility!(group:, actor:, old_name:,
+                               require_compatibility:, compatibility_body:)
+    representation = TagGroupRepr.one(group)
+    body = begin
+      TagGroupMarkdownRenderer.render(representation)
+    rescue TagGroupMarkdownRenderer::UnsupportedStructure => error
+      if compatibility_body.present?
+        compatibility_body
+      elsif require_compatibility
+        invalid!(group, :base, error.message)
+      else
+        return error.message
+      end
+    end
+    invalid!(group, :base, '本文は必須です．') if body.blank?
+
+    title = "#{ PREFIX }#{ group.name }"
+    old_title = old_name && "#{ PREFIX }#{ old_name }"
+    page = if old_title
+      WikiPage.joins(:tag_name).find_by(tag_names: { name: old_title })
+    else
+      nil
+    end
+    page ||= WikiPage.joins(:tag_name).find_by(tag_names: { name: title })
+
+    if page
+      tag_name = page.tag_name
+      tag_name.update!(name: title) if tag_name.name != title
+      Wiki::Commit.legacy_content!(page:, body:, created_user: actor, message: nil,
+                                   base_revision_id: nil)
+    else
+      tag_name = TagName.find_or_initialize_by(language_code: 'ja', name: title)
+      tag_name.script_code = 'Jpan'
+      tag_name.primary_flg = true
+      tag_name.auto_generated = false
+      tag_name.save!
+      Wiki::Commit.create_legacy_content!(tag_name:, body:, created_by_user: actor)
+    end
+    nil
+  end
+  private_class_method :sync_compatibility!
+
+  def self.report_sync_issue(group, actor, reason)
+    return unless reason
+
+    payload = { status: 'unsupported_structure', tag_group_id: group.id,
+                version_no: group.version_no, user_id: actor&.id, reason: }
+    Rails.logger.warn("tag_group_wiki_sync_skipped #{ payload.to_json }")
+  end
+  private_class_method :report_sync_issue
+
+  def self.placement_references(nodes)
+    nodes.flat_map do |node|
+      own = if node.key?('tag_id')
+        [{ 'tag_id' => node.fetch('tag_id') }]
+      elsif node.key?('tag_group_id')
+        [{ 'tag_group_id' => node.fetch('tag_group_id') }]
+      else
+        []
+      end
+      own + placement_references(node.fetch('children'))
+    end
+  end
+  private_class_method :placement_references
+
+  def self.stringify_keys(value)
+    case value
+    when ActionController::Parameters
+      value.to_unsafe_h.deep_stringify_keys
+    when Hash
+      value.deep_stringify_keys
+    else
+      value
+    end
+  end
+  private_class_method :stringify_keys
+
+  def self.integer_id(record, value, attribute)
+    integer = if value.is_a?(Integer)
+      value
+    elsif value.is_a?(String) && value.match?(/\A[0-9]+\z/)
+      value.to_i
+    end
+    invalid!(record, attribute, 'ID は正の整数で指定してください．') unless integer
+    invalid!(record, attribute, 'ID は正の整数で指定してください．') unless integer.positive?
+    integer
+  end
+  private_class_method :integer_id
+
+  def self.invalid!(record, attribute, message)
+    record.errors.add(attribute, message)
+    raise ActiveRecord::RecordInvalid, record
+  end
+  private_class_method :invalid!
+end

backend/config/routes.rb

@@ -1,4 +1,6 @@
 Rails.application.routes.draw do
+  resources :tag_groups, only: [:index, :show, :create, :update]
+
   resources :nico_tags, path: 'tags/nico', only: [:index, :show, :update]
 
   scope 'tags/:parent_id/children', controller: :tag_children do

backend/db/migrate/20261008000000_create_tag_groups.rb

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

backend/db/migrate/20261008010000_migrate_tag_groups_from_wiki_pages.rb

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

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_10_05_000000) do
+ActiveRecord::Schema[8.0].define(version: 2026_10_08_010000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -483,6 +483,80 @@ ActiveRecord::Schema[8.0].define(version: 2026_10_05_000000) do
     t.check_constraint "`version_no` > 0", name: "chk_tag_descriptions_version_no_positive"
   end
 
+  create_table "tag_group_groups", primary_key: ["tag_group_id", "child_tag_group_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.bigint "child_tag_group_id", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["child_tag_group_id"], name: "index_tag_group_groups_on_child_tag_group_id"
+    t.index ["created_by_user_id"], name: "index_tag_group_groups_on_created_by_user_id"
+    t.check_constraint "`tag_group_id` <> `child_tag_group_id`", name: "chk_tag_group_groups_tag_group_id_not_child_tag_group_id"
+  end
+
+  create_table "tag_group_placements", primary_key: ["tag_group_id", "position"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.integer "position", null: false
+    t.integer "parent_position"
+    t.string "section_name"
+    t.text "description"
+    t.bigint "tag_id"
+    t.bigint "child_tag_group_id"
+    t.bigint "created_by_user_id"
+    t.bigint "updated_by_user_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["child_tag_group_id"], name: "index_tag_group_placements_on_child_tag_group_id"
+    t.index ["created_by_user_id"], name: "index_tag_group_placements_on_created_by_user_id"
+    t.index ["tag_group_id", "child_tag_group_id"], name: "fk_rails_7342b54ced"
+    t.index ["tag_group_id", "parent_position"], name: "fk_rails_3af6ee71ca"
+    t.index ["tag_group_id", "tag_id"], name: "fk_rails_365dc60759"
+    t.index ["tag_id"], name: "index_tag_group_placements_on_tag_id"
+    t.index ["updated_by_user_id"], name: "index_tag_group_placements_on_updated_by_user_id"
+    t.check_constraint "(((`section_name` is not null) and (`tag_id` is null) and (`child_tag_group_id` is null)) or ((`section_name` is null) and (`tag_id` is not null) and (`child_tag_group_id` is null)) or ((`section_name` is null) and (`tag_id` is null) and (`child_tag_group_id` is not null))) and ((`section_name` is not null) or (`description` is null))", name: "chk_tag_group_placements_references_exclusive"
+    t.check_constraint "`position` > `parent_position`", name: "chk_tag_group_placements_position_gt_parent_position"
+  end
+
+  create_table "tag_group_tags", primary_key: ["tag_group_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.bigint "tag_id", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_group_tags_on_created_by_user_id"
+    t.index ["tag_id"], name: "index_tag_group_tags_on_tag_id"
+  end
+
+  create_table "tag_group_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_group_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.text "description"
+    t.json "members", null: false
+    t.json "placements", null: false
+    t.bigint "created_by_user_id"
+    t.datetime "created_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_group_versions_on_created_by_user_id"
+    t.index ["tag_group_id", "version_no"], name: "index_tag_group_versions_on_tag_group_id_and_version_no", unique: true
+    t.index ["tag_group_id"], name: "index_tag_group_versions_on_tag_group_id"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_group_versions_version_no_positive"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"required\":[\"children\"],\"properties\":{\"section_name\":{\"type\":\"string\"},\"description\":{\"type\":[\"string\",\"null\"]},\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"children\":{\"type\":\"array\",\"maxItems\":0}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}},\"oneOf\":[{\"required\":[\"section_name\"]},{\"required\":[\"tag_id\"]},{\"required\":[\"tag_group_id\"]}],\"dependencies\":{\"description\":[\"section_name\"]},\"additionalProperties\":false}}',`placements`)", name: "chk_tag_group_versions_placements_schema"
+    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"uniqueItems\":true,\"items\":{\"oneOf\":[{\"type\":\"object\",\"required\":[\"tag_id\",\"version_no\"],\"properties\":{\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1}},\"additionalProperties\":false},{\"type\":\"object\",\"required\":[\"tag_group_id\",\"version_no\"],\"properties\":{\"tag_group_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1}},\"additionalProperties\":false}]}}',`members`)", name: "chk_tag_group_versions_members_schema"
+  end
+
+  create_table "tag_groups", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.integer "version_no", null: false
+    t.string "name", null: false
+    t.text "description"
+    t.bigint "created_by_user_id"
+    t.bigint "updated_by_user_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_tag_groups_on_created_by_user_id"
+    t.index ["name"], name: "index_tag_groups_on_name", unique: true
+    t.index ["updated_by_user_id"], name: "index_tag_groups_on_updated_by_user_id"
+    t.check_constraint "`version_no` > 0", name: "chk_tag_groups_version_no_positive"
+  end
+
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
@@ -823,6 +897,20 @@ ActiveRecord::Schema[8.0].define(version: 2026_10_05_000000) do
   add_foreign_key "tag_descriptions", "tags"
   add_foreign_key "tag_descriptions", "users", column: "created_by_user_id"
   add_foreign_key "tag_descriptions", "users", column: "updated_by_user_id"
+  add_foreign_key "tag_group_groups", "tag_groups"
+  add_foreign_key "tag_group_groups", "tag_groups", column: "child_tag_group_id"
+  add_foreign_key "tag_group_groups", "users", column: "created_by_user_id"
+  add_foreign_key "tag_group_placements", "tag_group_groups", column: ["tag_group_id", "child_tag_group_id"], primary_key: ["tag_group_id", "child_tag_group_id"]
+  add_foreign_key "tag_group_placements", "tag_group_placements", column: ["tag_group_id", "parent_position"], primary_key: ["tag_group_id", "position"]
+  add_foreign_key "tag_group_placements", "tag_group_tags", column: ["tag_group_id", "tag_id"], primary_key: ["tag_group_id", "tag_id"]
+  add_foreign_key "tag_group_placements", "tag_groups"
+  add_foreign_key "tag_group_placements", "users", column: "created_by_user_id"
+  add_foreign_key "tag_group_placements", "users", column: "updated_by_user_id"
+  add_foreign_key "tag_group_tags", "tag_groups"
+  add_foreign_key "tag_group_tags", "tags"
+  add_foreign_key "tag_group_tags", "users", column: "created_by_user_id"
+  add_foreign_key "tag_groups", "users", column: "created_by_user_id"
+  add_foreign_key "tag_groups", "users", column: "updated_by_user_id"
   add_foreign_key "tag_implications", "tags"
   add_foreign_key "tag_implications", "tags", column: "parent_tag_id"
   add_foreign_key "tag_names", "languages", column: "language_code", primary_key: "code"

backend/spec/db/tag_group_constraints_spec.rb

@@ -0,0 +1,110 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group persistence constraints' do
+  include TagGroupRecords
+
+  let!(:user) { create_member_user! }
+  let!(:tag) { group_tag('制約確認') }
+  let!(:group_id) do
+    seed_group(
+        name: '制約確認',
+        members: [{ 'tag_id' => tag.id, 'version_no' => tag.version_no }])
+  end
+
+  def placement attributes
+    insert_group_row('tag_group_placements', {
+        tag_group_id: group_id, position: 1,
+        created_at: Time.current, updated_at: Time.current }.merge(attributes))
+  end
+
+  def reject_statement
+    before_state = group_state
+    expect { yield }.to raise_error(ActiveRecord::StatementInvalid)
+    expect(group_state).to eq(before_state)
+  end
+
+  it 'allows membership without placement' do
+    expect(group_rows('tag_group_tags', tag_group_id: group_id).size).to eq(1)
+    expect(group_rows('tag_group_placements', tag_group_id: group_id)).to be_empty
+  end
+
+  it 'allows repeated Tag placements with unique membership' do
+    placement(tag_id: tag.id)
+    placement(tag_id: tag.id, position: 2)
+    expect(group_rows('tag_group_tags', tag_group_id: group_id).size).to eq(1)
+    expect(group_rows('tag_group_placements', tag_group_id: group_id).size).to eq(2)
+  end
+
+  it 'rejects duplicate Tag membership' do
+    reject_statement do
+      insert_group_row('tag_group_tags', {
+          tag_group_id: group_id, tag_id: tag.id, created_at: Time.current })
+    end
+  end
+
+  it 'rejects duplicate child membership' do
+    child_id = seed_group(name: '子')
+    attributes = { tag_group_id: group_id, child_tag_group_id: child_id,
+                   created_at: Time.current }
+    insert_group_row('tag_group_groups', attributes)
+    reject_statement { insert_group_row('tag_group_groups', attributes) }
+  end
+
+  it 'rejects direct self membership' do
+    reject_statement do
+      insert_group_row('tag_group_groups', {
+          tag_group_id: group_id, child_tag_group_id: group_id, created_at: Time.current })
+    end
+  end
+
+  it 'rejects a placement without a kind' do
+    reject_statement { placement({ }) }
+  end
+
+  it 'rejects simultaneous Section and Tag kinds' do
+    reject_statement { placement(section_name: '区分', tag_id: tag.id) }
+  end
+
+  it 'rejects a description attached to a Tag placement' do
+    reject_statement { placement(tag_id: tag.id, description: '不正') }
+  end
+
+  it 'allows an optional description on a Section' do
+    placement(section_name: '区分', description: '説明')
+    expect(group_rows('tag_group_placements', tag_group_id: group_id).sole)
+        .to include('section_name' => '区分', 'description' => '説明')
+  end
+
+  it 'rejects a Tag placement absent from membership' do
+    other = group_tag('非メンバー')
+    reject_statement { placement(tag_id: other.id) }
+  end
+
+  it 'rejects a missing parent placement' do
+    reject_statement { placement(section_name: '子', parent_position: 9) }
+  end
+
+  it 'rejects a child ordered before its parent' do
+    placement(section_name: '親', position: 2)
+    reject_statement { placement(section_name: '子', position: 1, parent_position: 2) }
+  end
+
+  it 'rejects duplicate group names' do
+    reject_statement { seed_group(name: '制約確認') }
+  end
+
+  it 'rejects a missing mandatory group name' do
+    reject_statement { seed_group(name: nil) }
+  end
+
+  it 'rejects a six-level snapshot' do
+    nodes = []
+    6.times { nodes = [{ 'tag_id' => tag.id, 'children' => nodes }] }
+    reject_statement do
+      insert_group_row('tag_group_versions', {
+          tag_group_id: group_id, version_no: 2, event_type: 'update', name: '制約確認',
+          members: [{ 'tag_id' => tag.id, 'version_no' => tag.version_no }].to_json,
+          placements: nodes.to_json, created_at: Time.current })
+    end
+  end
+end

backend/spec/db/tag_group_migration_spec.rb

@@ -0,0 +1,119 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group migration identity and structure' do
+  include TagGroupRecords
+
+  let!(:user) { create_member_user! }
+
+  before { I18n.locale = :ja }
+
+  it 'preserves page and revision IDs, timestamps and repeated historical structures' do
+    tag = group_tag('洗澡鹿')
+    body = "説明文\n\n- 洗澡鹿\n- 洗澡鹿"
+    page = legacy_group('伊地知ニジカ亜種', body)
+    revisions = [page.current_revision]
+    [body, '# 空の区分', body].each do |text|
+      revisions << Wiki::Commit.legacy_content!(page:, body: text, created_user: user)
+    end
+    before_state = group_state.except(*TagGroupRecords::GROUP_TABLES)
+
+    migrate_groups
+
+    versions = group_rows('tag_group_versions', tag_group_id: page.id)
+        .sort_by { _1.fetch('version_no') }
+    expect(versions.map { _1.fetch('id') }).to eq(revisions.map(&:id))
+    expect(versions.map { _1.fetch('version_no') }).to eq([1, 2, 3, 4])
+    expect(versions.map { _1.fetch('created_at') }).to eq(revisions.map(&:created_at))
+    expect(versions.map { _1.fetch('created_by_user_id') }).to eq([user.id] * 4)
+    expect(versions.map { _1.fetch('event_type') }).to eq(['create', 'update', 'update', 'update'])
+    expect(group_version(page.id, 1).fetch('placements')).to eq(
+        group_version(page.id, 2).fetch('placements'))
+    expect(group_version(page.id, 3).fetch('placements')).to eq([
+        { 'section_name' => '空の区分', 'description' => nil, 'children' => [] }])
+    expect_group_snapshot(
+        page.id, number: 4, description: '説明文',
+        members: [{ 'tag_id' => tag.id, 'version_no' => tag.version_no }],
+        placements: [{ 'tag_id' => tag.id, 'children' => [] }] * 2)
+    expect(group_rows('tag_groups', id: page.id).sole).to include(
+        'created_at' => page.created_at, 'updated_at' => page.reload.updated_at)
+    expect(group_state.except(*TagGroupRecords::GROUP_TABLES)).to eq(before_state)
+  end
+
+  it 'migrates nested list Sections and child groups as different placement kinds' do
+    series = group_tag('ぼざろクリーチャーシリーズ')
+    deer = group_tag('洗澡鹿')
+    nijika = group_tag('伊地知ニジカ')
+    child = legacy_group('伊地知ニジカ亜種', <<~MARKDOWN)
+      - ぼざろクリーチャーシリーズ
+        - 伊地知ニジカ亜種:
+          - 洗澡鹿
+    MARKDOWN
+    parent = legacy_group('ぼざろクリーチャーシリーズのキャラクター', <<~MARKDOWN)
+      - ぼざろクリーチャーシリーズ
+        - 伊地知ニジカ
+          - タググループ:伊地知ニジカ亜種
+    MARKDOWN
+
+    migrate_groups
+
+    expect_group_snapshot(
+        child.id, number: 1,
+        members: [series, deer].map { { 'tag_id' => _1.id, 'version_no' => _1.version_no } },
+        placements: [{ 'tag_id' => series.id, 'children' => [
+            { 'section_name' => '伊地知ニジカ亜種', 'description' => nil,
+              'children' => [{ 'tag_id' => deer.id, 'children' => [] }] }] }])
+    expect_group_snapshot(
+        parent.id, number: 1,
+        members: [
+            { 'tag_id' => series.id, 'version_no' => series.version_no },
+            { 'tag_id' => nijika.id, 'version_no' => nijika.version_no },
+            { 'tag_group_id' => child.id, 'version_no' => 1 }],
+        placements: [{ 'tag_id' => series.id, 'children' => [
+            { 'tag_id' => nijika.id, 'children' => [
+                { 'tag_group_id' => child.id, 'children' => [] }] }] }])
+  end
+
+  it 'preserves heading order, group paragraphs and Section descriptions' do
+    names = ['タグ希望', 'キャラクター名希望', '楽曲情報希望', 'bot操作', 'ニジラー情報不詳']
+    tags = names.map { group_tag(_1) }
+    markdown = <<~MARKDOWN
+      全体の説明
+
+      # 要求
+      要求の説明
+
+      - タグ希望
+        - キャラクター名希望
+        - 楽曲情報希望
+
+      # 情報
+      - bot操作
+      - ニジラー情報不詳
+    MARKDOWN
+    page = legacy_group('メタタグ', markdown)
+    expect(page.current_revision.body).to eq(markdown.chomp)
+
+    migrate_groups
+
+    leaves = tags.map { { 'tag_id' => _1.id, 'children' => [] } }
+    leaves.first['children'] = leaves[1..2]
+    expect_group_snapshot(
+        page.id, number: 1, description: '全体の説明',
+        members: tags.map { { 'tag_id' => _1.id, 'version_no' => _1.version_no } },
+        placements: [
+            { 'section_name' => '要求', 'description' => '要求の説明',
+              'children' => [leaves.first] },
+            { 'section_name' => '情報', 'description' => nil,
+              'children' => leaves[3..4] }])
+  end
+
+  it 'leaves Help in the legacy domain' do
+    page = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:移行対象外'),
+        body: 'Help 本文', created_by_user: user)
+    before_state = group_state
+    migrate_groups
+    expect(group_state).to eq(before_state)
+    expect(page.reload.body).to eq('Help 本文')
+  end
+end

backend/spec/requests/tag_group_markdown_spec.rb

@@ -0,0 +1,139 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group Markdown round trips through the Wiki facade', type: :request do
+  include TagGroupRecords
+
+  let!(:user) { create_member_user! }
+  let!(:series) { group_tag('ぼざろクリーチャーシリーズ') }
+  let!(:deer) { group_tag('洗澡鹿') }
+  let!(:nijika) { group_tag('伊地知ニジカ') }
+  let!(:wanted) { group_tag('タグ希望') }
+  let!(:character) { group_tag('キャラクター名希望') }
+  let!(:music) { group_tag('楽曲情報希望') }
+  let!(:bot) { group_tag('bot操作') }
+  let!(:unknown) { group_tag('ニジラー情報不詳') }
+  let!(:child_id) { seed_group(name: '伊地知ニジカ亜種', description: '子の説明') }
+
+  before { I18n.locale = :ja }
+
+  def tag_node tag, children = []
+    { 'tag_id' => tag.id, 'children' => children }
+  end
+
+  def tag_member tag
+    { 'tag_id' => tag.id, 'version_no' => tag.version_no }
+  end
+
+  def check_round_trip placements:, members:, markdown:, description: nil
+    id = seed_group(name: '変換元', placements:, members:, description:)
+    without_group_legacy_reads { get group_title_path('変換元') }
+    expect(response).to have_http_status(:ok)
+    expect(json).to include('id' => id)
+    body = json.fetch('body')
+    expect(body).not_to include("\r")
+    expect(body.lines.map(&:chomp)).to all(satisfy { |line| line == line.rstrip })
+    # A trailing LF or a blank line between blocks is semantically irrelevant.
+    expect(body.lines.map(&:chomp).reject(&:empty?)).to eq(
+        markdown.lines.map(&:chomp).reject(&:empty?))
+
+    post '/wiki', params: { title: 'タググループ:再解析', body: },
+         headers: { 'X-Transfer-Code' => user.inheritance_code }
+    expect(response).to have_http_status(:created)
+    parsed = group_rows('tag_groups', name: '再解析').sole
+    expect_group_snapshot(parsed.fetch('id'), number: 1, placements:, members:, description:)
+  end
+
+  it 'renders a list Section under a Tag with two-space indentation' do
+    check_round_trip(
+        members: [series, deer].map { tag_member(_1) },
+        placements: [tag_node(series, [
+            { 'section_name' => '伊地知ニジカ亜種', 'description' => nil,
+              'children' => [tag_node(deer)] }])],
+        markdown: <<~MARKDOWN)
+          - ぼざろクリーチャーシリーズ
+            - 伊地知ニジカ亜種:
+              - 洗澡鹿
+        MARKDOWN
+  end
+
+  it 'renders a child Tag Group distinctly from its parent Tags' do
+    check_round_trip(
+        members: [tag_member(series), tag_member(nijika),
+                  { 'tag_group_id' => child_id, 'version_no' => 1 }],
+        placements: [tag_node(series, [tag_node(nijika, [
+            { 'tag_group_id' => child_id, 'children' => [] }])])],
+        markdown: <<~MARKDOWN)
+          - ぼざろクリーチャーシリーズ
+            - 伊地知ニジカ
+              - タググループ:伊地知ニジカ亜種
+        MARKDOWN
+  end
+
+  it 'renders top-level heading Sections, descriptions and ordered nested Tags' do
+    check_round_trip(
+        description: '全体の説明',
+        members: [wanted, character, music, bot, unknown].map { tag_member(_1) },
+        placements: [
+            { 'section_name' => '要求', 'description' => '要求の説明',
+              'children' => [tag_node(wanted, [tag_node(character), tag_node(music)])] },
+            { 'section_name' => '情報', 'description' => nil,
+              'children' => [tag_node(bot), tag_node(unknown)] }],
+        markdown: <<~MARKDOWN)
+          全体の説明
+
+          # 要求
+          要求の説明
+
+          - タグ希望
+            - キャラクター名希望
+            - 楽曲情報希望
+
+          # 情報
+          - bot操作
+          - ニジラー情報不詳
+        MARKDOWN
+  end
+
+  it 'renders nested heading Sections and all repeated Tag placements' do
+    check_round_trip(
+        members: [tag_member(deer)],
+        placements: [
+            { 'section_name' => '親', 'description' => '親の説明', 'children' => [
+                tag_node(deer),
+                { 'section_name' => '子', 'description' => '子の説明',
+                  'children' => [tag_node(deer)] }] }],
+        markdown: <<~MARKDOWN)
+          # 親
+          親の説明
+
+          - 洗澡鹿
+
+          ## 子
+          子の説明
+
+          - 洗澡鹿
+        MARKDOWN
+  end
+
+  it 'rejects mixed top-level heading Sections and Tags without losing structure' do
+    id = seed_group(
+        name: '混在構造', members: [tag_member(series)],
+        placements: [
+            { 'section_name' => '区分', 'description' => nil, 'children' => [] },
+            tag_node(series)])
+
+    get group_title_path('混在構造')
+
+    expect(response).to have_http_status(:unprocessable_entity)
+    expect(group_rows('tag_groups', id:).sole.fetch('id')).to eq(id)
+  end
+
+  it 'rejects membership without a placement instead of omitting it' do
+    id = seed_group(name: '未配置構造', members: [tag_member(series)])
+
+    get group_title_path('未配置構造')
+
+    expect(response).to have_http_status(:unprocessable_entity)
+    expect(group_rows('tag_groups', id:).sole.fetch('id')).to eq(id)
+  end
+end

backend/spec/requests/tag_group_wiki_spec.rb

@@ -0,0 +1,231 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group Wiki facade reads', type: :request do
+  include TagGroupRecords
+
+  let!(:user) { create_member_user! }
+  let!(:old_tag) { group_tag('旧タグ') }
+  let!(:new_tag) { group_tag('新タグ') }
+  let!(:page) { legacy_group('読取り契約', '- 旧タグ') }
+  let!(:first_revision) { page.current_revision }
+  let!(:last_revision) do
+    Wiki::Commit.legacy_content!(page:, body: '- 新タグ', created_user: user)
+  end
+
+  before do
+    I18n.locale = :ja
+    migrate_groups
+    page.update_columns(body: 'legacy stale current')
+    page.wiki_revisions.each do |revision|
+      revision.wiki_lines.update_all(body: 'legacy stale revision')
+    end
+    page.wiki_versions.update_all(body: 'legacy stale version')
+  end
+
+  [:id, :title].each do |lookup|
+    context "with #{ lookup } lookup" do
+      let(:path) { lookup == :id ? "/wiki/#{ page.id }" : group_title_path('読取り契約') }
+
+      it 'reads current structure without consulting migrated Wiki tables' do
+        without_group_legacy_reads { get path }
+        expect(response).to have_http_status(:ok)
+        expect(json).to include(
+            'id' => page.id, 'title' => 'タググループ:読取り契約',
+            'revision_id' => last_revision.id, 'pred' => first_revision.id, 'succ' => nil)
+        expect(json.fetch('body').strip).to eq('- 新タグ')
+      end
+
+      it 'reads the old snapshot rather than current membership or placement' do
+        without_group_legacy_reads { get path, params: { version: first_revision.id } }
+        expect(response).to have_http_status(:ok)
+        expect(json.fetch('body').strip).to eq('- 旧タグ')
+        expect(json).to include(
+            'revision_id' => first_revision.id, 'pred' => nil, 'succ' => last_revision.id,
+            'updated_at' => first_revision.created_at.iso8601(3))
+      end
+
+      it 'checks existence without consulting migrated Wiki tables' do
+        without_group_legacy_reads { get "#{ path }/exists" }
+        expect(response).to have_http_status(:no_content)
+      end
+
+      it 'does not fall back to legacy history when a group version is missing' do
+        group_connection.execute(
+            "DELETE FROM tag_group_versions WHERE id = #{ first_revision.id }")
+        without_group_legacy_reads { get path, params: { version: first_revision.id } }
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  ['/wiki', '/wiki/search'].each do |path|
+    it "lists migrated groups once with current titles at #{ path }" do
+      get path, params: { title: 'タググループ:読取り' }
+      expect(response).to have_http_status(:ok)
+      rows = json.select { _1.fetch('title') == 'タググループ:読取り契約' }
+      expect(rows.size).to eq(1)
+      expect(rows.sole).to include('id' => page.id)
+      expect(response.body).not_to include('legacy stale')
+    end
+  end
+
+  it 'combines Tag Groups, Help and Tag Descriptions in the unfiltered list' do
+    help = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:混在'), body: 'help', created_by_user: user)
+    TagDescriptionOperation.create!(tag: new_tag, body: 'tag description', created_by_user: user)
+    get '/wiki'
+    expect(response).to have_http_status(:ok)
+    expect(json.map { _1.fetch('title') }).to include(
+        'タググループ:読取り契約', help.title, '新タグ')
+  end
+
+  it 'keeps Help readable when its ID collides with a new group' do
+    help = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:ID重複'), body: 'help body',
+        created_by_user: user)
+    seed_group(name: '別 ID重複', id: help.id, description: 'group body')
+
+    get '/wiki'
+    expect(response).to have_http_status(:ok)
+    expect(json.map { _1.fetch('title') }).to include(help.title, 'タググループ:別 ID重複')
+
+    get "/wiki/title/#{ CGI.escapeURIComponent(help.title) }"
+    expect(response).to have_http_status(:ok)
+    expect(json.fetch('body')).to eq('help body')
+
+    get '/wiki/changes'
+    expect(response).to have_http_status(:ok)
+    expect(json.map { _1.dig('wiki_page', 'title') }).to include(
+        help.title, 'タググループ:別 ID重複')
+  end
+
+  it 'finds groups by a partial prefix of their displayed title' do
+    get '/wiki', params: { title: 'タググル' }
+
+    expect(response).to have_http_status(:ok)
+    expect(json.map { _1.fetch('title') }).to include('タググループ:読取り契約')
+    expect(json.find { _1.fetch('title') == 'タググループ:読取り契約' })
+        .to include('updated_at' => be_present)
+  end
+
+  it 'does not restore a stale namespaced Wiki page after a group rename' do
+    old_page = legacy_group('旧名称', '- 旧本文')
+    seed_group(name: '新名称', id: old_page.id, description: '正本')
+
+    get group_title_path('旧名称')
+    expect(response).to have_http_status(:not_found)
+    get "#{ group_title_path('旧名称') }/exists"
+    expect(response).to have_http_status(:not_found)
+    get group_title_path('新名称')
+    expect(response).to have_http_status(:ok)
+    expect(json.fetch('body').strip).to eq('正本')
+  end
+
+  it 'orders mixed resource history by timestamp rather than independent IDs' do
+    help = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:時系列'), body: 'help',
+        created_by_user: user)
+    TagDescriptionOperation.create!(tag: new_tag, body: 'description', created_by_user: user)
+    TagGroupVersion.update_all(created_at: 3.days.ago)
+    WikiRevision.where(wiki_page_id: help.id).update_all(created_at: 2.days.ago)
+    TagDescriptionVersion.update_all(created_at: 1.day.ago)
+
+    get '/wiki/changes'
+
+    expect(response).to have_http_status(:ok)
+    timestamps = json.map { Time.iso8601(_1.fetch('timestamp')) }
+    expect(timestamps).to eq(timestamps.sort.reverse)
+    titles = json.map { _1.dig('wiki_page', 'title') }
+    expect(titles.index('新タグ')).to be < titles.index(help.title)
+    expect(titles.index(help.title)).to be < titles.index('タググループ:読取り契約')
+  end
+
+  it 'renders nullable group editors without raising' do
+    group_connection.execute(
+        "UPDATE tag_groups SET created_by_user_id = NULL, updated_by_user_id = NULL " +
+        "WHERE id = #{ page.id }")
+    group_connection.execute(
+        "UPDATE tag_group_versions SET created_by_user_id = NULL " +
+        "WHERE tag_group_id = #{ page.id }")
+
+    get "/tag_groups/#{ page.id }"
+    expect(response).to have_http_status(:ok)
+    expect(json).to include('created_by_user' => nil, 'updated_by_user' => nil)
+    get "/wiki/title/#{ CGI.escapeURIComponent('タググループ:読取り契約') }"
+    expect(response).to have_http_status(:ok)
+  end
+
+  it 'reads group version IDs, editor and timestamps in scoped changes' do
+    without_group_legacy_reads { get '/wiki/changes', params: { id: page.id } }
+    expect(response).to have_http_status(:ok)
+    expect(json.map { _1.fetch('revision_id') }).to eq([last_revision.id, first_revision.id])
+    expect(json.first).to include(
+        'pred' => first_revision.id, 'succ' => nil, 'kind' => 'content',
+        'timestamp' => last_revision.created_at.iso8601(3),
+        'user' => { 'id' => user.id, 'name' => user.name },
+        'wiki_page' => include('id' => page.id, 'title' => 'タググループ:読取り契約'))
+  end
+
+  it 'includes Help and group history but excludes legacy-only migrated revisions' do
+    extra = Wiki::Commit.legacy_content!(page:, body: 'legacy only', created_user: user)
+    help = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:変更一覧'), body: 'help', created_by_user: user)
+    get '/wiki/changes'
+    expect(response).to have_http_status(:ok)
+    rows = json.select { _1.fetch('wiki_page').fetch('title') == 'タググループ:読取り契約' }
+    expect(rows.map { _1.fetch('revision_id') }).to eq([last_revision.id, first_revision.id])
+    expect(rows.map { _1.fetch('revision_id') }).not_to include(extra.id)
+    expect(json).to include(include(
+        'revision_id' => help.current_revision.id,
+        'wiki_page' => include('title' => help.title)))
+  end
+
+  [false, true].each do |explicit|
+    it "diffs structured snapshots with #{ explicit ? 'explicit' : 'current' } target" do
+      params = { from: first_revision.id }
+      params[:to] = last_revision.id if explicit
+      without_group_legacy_reads { get "/wiki/#{ page.id }/diff", params: }
+      expect(response).to have_http_status(:ok)
+      expect(json).to include(
+          'wiki_page_id' => page.id, 'older_revision_id' => first_revision.id,
+          'newer_revision_id' => last_revision.id)
+      differences = json.fetch('diff').map { [_1.fetch('type'), _1.fetch('content').strip] }
+      expect(differences).to include(['removed', '- 旧タグ'], ['added', '- 新タグ'])
+    end
+  end
+
+  it 'does not use a version belonging to another group' do
+    other_id = seed_group(name: '別グループ', description: '別本文')
+    other_version = group_version(other_id, 1)
+    get group_title_path('読取り契約'), params: { version: other_version.fetch('id') }
+    expect(response).to have_http_status(:not_found)
+    get "/wiki/#{ page.id }/diff",
+        params: { from: other_version.fetch('id'), to: last_revision.id }
+    expect(response).to have_http_status(:not_found)
+  end
+
+  it 'resolves a group without any compatibility Wiki page' do
+    id = seed_group(name: '独立グループ', description: '独立した説明')
+    without_group_legacy_reads { get group_title_path('独立グループ') }
+    expect(response).to have_http_status(:ok)
+    expect(json).to include('id' => id, 'title' => 'タググループ:独立グループ')
+    expect(json.fetch('body').strip).to eq('独立した説明')
+  end
+
+  it 'resolves colliding group, Help and description IDs by title' do
+    help = Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:ID衝突'), body: 'help', created_by_user: user)
+    seed_group(name: 'ID衝突', id: help.id, description: 'group')
+    TagDescription.create!(
+        id: help.id, tag: new_tag, language_code: 'ja', body: 'description', version_no: 1)
+    TagDescriptionVersion.create!(
+        tag_id: new_tag.id, language_code: 'ja', version_no: 1,
+        event_type: 'create', body: 'description', created_at: Time.current)
+    { 'タググループ:ID衝突' => 'group', 'Help:ID衝突' => 'help', '新タグ' => 'description' }
+        .each do |title, body|
+      get "/wiki/title/#{ CGI.escapeURIComponent(title) }"
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('body').strip).to eq(body)
+    end
+  end
+end

backend/spec/requests/tag_group_wiki_write_spec.rb

@@ -0,0 +1,245 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group Wiki facade writes', type: :request do
+  include TagGroupRecords
+  include ActiveSupport::Testing::TimeHelpers
+
+  let!(:user) { create_member_user! }
+  let!(:tag) { group_tag('洗澡鹿') }
+  let!(:other_tag) { group_tag('伊地知ニジカ') }
+  let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+  let(:members) { [{ 'tag_id' => tag.id, 'version_no' => tag.version_no }] }
+  let(:placements) { [{ 'tag_id' => tag.id, 'children' => [] }] }
+
+  before { I18n.locale = :ja }
+
+  def create_group title: 'タググループ:新規', body: '- 洗澡鹿', request_headers: headers
+    post '/wiki', params: { title:, body: }, headers: request_headers
+  end
+
+  def expect_rejected_without_writes
+    before_state = group_state
+    yield
+    aggregate_failures do
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(group_state).to eq(before_state)
+      expect(response.media_type).to eq('application/json')
+      expect(response.body).not_to be_empty
+      next if response.body.empty?
+
+      expect(json).to include(
+          'type' => 'validation_error', 'errors' => a_kind_of(Hash),
+          'base_errors' => a_kind_of(Array))
+    end
+  end
+
+  it 'creates the group, first snapshot and compatibility Wiki history' do
+    create_group
+    expect(response).to have_http_status(:created)
+    group = group_rows('tag_groups', name: '新規').sole
+    expect(json).to include('id' => group.fetch('id'), 'title' => 'タググループ:新規')
+    expect_group_snapshot(group.fetch('id'), number: 1, members:, placements:)
+    version = group_version(group.fetch('id'), 1)
+    expect(version).to include('event_type' => 'create', 'created_by_user_id' => user.id)
+    expect(group).to include('created_by_user_id' => user.id, 'updated_by_user_id' => user.id)
+    page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:新規' })
+    expect(page.body.strip).to eq('- 洗澡鹿')
+    expect(page.current_revision.body).to eq(page.body)
+    expect(page.wiki_versions.sole.body).to eq(page.body)
+    # New IDs are independently allocated; no global identity assertion here.
+  end
+
+  it 'keeps repeated placements but only one membership and one snapshot member' do
+    create_group(body: "- 洗澡鹿\n# 再掲\n- 洗澡鹿")
+    expect(response).to have_http_status(:created)
+    id = group_rows('tag_groups', name: '新規').sole.fetch('id')
+    expect_group_snapshot(
+        id, number: 1, members:,
+        placements: placements + [
+            { 'section_name' => '再掲', 'description' => nil, 'children' => placements }])
+  end
+
+  it 'resolves a Japanese alias through tag_names.tag_id' do
+    create(:tag_name, :alias, tag:, name: '鹿の別名')
+    create_group(body: '- 鹿の別名')
+    expect(response).to have_http_status(:created)
+    id = group_rows('tag_groups', name: '新規').sole.fetch('id')
+    expect_group_snapshot(id, number: 1, members:, placements:)
+    get group_title_path('新規')
+    expect(response).to have_http_status(:ok)
+    expect(json.fetch('body').strip).to eq('- 洗澡鹿')
+  end
+
+  {
+      'unknown Tag' => '- 解決不能',
+      'unknown Tag Group' => '- タググループ:存在しない',
+      'empty Section' => '- :',
+      'unsupported placement syntax' => "```\n洗澡鹿\n```",
+      'six levels' => "- 洗澡鹿\n  - 洗澡鹿\n    - 洗澡鹿\n      - 洗澡鹿\n" +
+          "        - 洗澡鹿\n          - 洗澡鹿",
+      'blank body' => '',
+      'normalised blank body' => "\r\n\r\n" }.each do |label, body|
+    it "rejects #{ label } without fallback or partial create" do
+      expect_rejected_without_writes { create_group(body:) }
+    end
+  end
+
+  ['', 'タググループ:', "タググループ:#{ '長' * 256 }"].each do |title|
+    it "rejects an invalid required title of length #{ title.length }" do
+      expect_rejected_without_writes { create_group(title:) }
+    end
+  end
+
+  it 'rejects a duplicate group name even without a matching legacy Wiki' do
+    seed_group(name: '新規', description: '既存')
+    expect_rejected_without_writes { create_group }
+  end
+
+  it 'accepts the existing five-level placement depth boundary' do
+    body = (0...5).map { "#{ '  ' * _1 }- 洗澡鹿" }.join("\n")
+    create_group(body:)
+    expect(response).to have_http_status(:created)
+    id = group_rows('tag_groups', name: '新規').sole.fetch('id')
+    tree = []
+    5.times { tree = [{ 'tag_id' => tag.id, 'children' => tree }] }
+    expect_group_snapshot(id, number: 1, members:, placements: tree)
+  end
+
+  context 'updating a migrated group' do
+    let!(:page) { legacy_group('更新', '- 洗澡鹿') }
+    let!(:old_revision) { page.current_revision }
+
+    before { migrate_groups }
+
+    def update_group body: '- 伊地知ニジカ', title: 'タググループ:更新', request_headers: headers
+      put "/wiki/#{ page.id }", params: { title:, body: }, headers: request_headers
+    end
+
+    it 'replaces current membership and placement, retaining the old snapshot' do
+      old = group_version(page.id, 1)
+      update_group
+      expect(response).to have_http_status(:ok)
+      expect_group_snapshot(
+          page.id, number: 2,
+          members: [{ 'tag_id' => other_tag.id, 'version_no' => other_tag.version_no }],
+          placements: [{ 'tag_id' => other_tag.id, 'children' => [] }])
+      expect(group_version(page.id, 1)).to eq(old)
+      expect(group_version(page.id, 2)).to include(
+          'event_type' => 'update', 'created_by_user_id' => user.id)
+      expect(page.reload.body.strip).to eq('- 伊地知ニジカ')
+      expect(page.wiki_revisions.count).to eq(2)
+      expect(page.wiki_versions.count).to eq(2)
+      expect(page.current_revision.body).to eq(page.body)
+      expect(page.wiki_versions.order(:version_no).last.body).to eq(page.body)
+    end
+
+    it 'accepts the current base_revision_id used by the existing frontend' do
+      put "/wiki/#{ page.id }",
+          params: { title: page.title, body: '- 伊地知ニジカ',
+                    base_revision_id: old_revision.id }, headers: headers
+      expect(response).to have_http_status(:ok)
+      expect(group_rows('tag_groups', id: page.id).sole.fetch('version_no')).to eq(2)
+    end
+
+    it 'ignores a stale base_revision_id without rejecting the update' do
+      update_group
+      expect(response).to have_http_status(:ok)
+
+      put "/wiki/#{ page.id }",
+          params: { title: page.title, body: '- 洗澡鹿',
+                    base_revision_id: old_revision.id }, headers: headers
+
+      expect(response).to have_http_status(:ok)
+      expect(group_rows('tag_groups', id: page.id).sole.fetch('version_no')).to eq(3)
+      expect(page.reload.body.strip).to eq('- 洗澡鹿')
+    end
+
+    it 'records the editor and update time' do
+      editor = create(:user, :member, name: '編輯者')
+      travel_to(Time.current + 1.hour) do
+        update_group(request_headers: { 'X-Transfer-Code' => editor.inheritance_code })
+        expect(response).to have_http_status(:ok)
+        current = group_rows('tag_groups', id: page.id).sole
+        version = group_version(page.id, 2)
+        expect(current).to include('updated_by_user_id' => editor.id)
+        expect(version).to include('created_by_user_id' => editor.id)
+        expect(current.fetch('updated_at')).to be_within(1.second).of(Time.current)
+        expect(version.fetch('created_at')).to be_within(1.second).of(Time.current)
+      end
+    end
+
+    ['- 不明なタグ', '- タググループ:不明', '', '- :'].each do |body|
+      it "rejects invalid update #{ body.inspect } atomically" do
+        expect_rejected_without_writes { update_group(body:) }
+      end
+    end
+
+    it 'rejects direct self inclusion' do
+      expect_rejected_without_writes { update_group(body: '- タググループ:更新') }
+    end
+
+    it 'rejects indirect cyclic membership' do
+      seed_group(
+          name: '子', members: [{ 'tag_group_id' => page.id, 'version_no' => 1 }],
+          placements: [{ 'tag_group_id' => page.id, 'children' => [] }])
+      expect_rejected_without_writes { update_group(body: '- タググループ:子') }
+    end
+
+    it 'rejects duplicate rename without retaining a partial title or version' do
+      seed_group(name: '既存', description: '既存')
+      expect_rejected_without_writes { update_group(title: 'タググループ:既存') }
+    end
+  end
+
+  [:create, :update].each do |operation|
+    context "#{ operation } access and atomicity" do
+      let!(:page) do
+        next unless operation == :update
+
+        legacy = legacy_group('更新', '- 洗澡鹿')
+        seed_group(name: '更新', id: legacy.id, members:, placements:)
+        legacy
+      end
+      let!(:child_id) { seed_group(name: '子グループ', description: '子') }
+
+      def write_group operation, request_headers
+        body = "- 伊地知ニジカ\n- タググループ:子グループ"
+        if operation == :create
+          create_group(body:, request_headers:)
+        else
+          put "/wiki/#{ page.id }",
+              params: { title: 'タググループ:更新', body: }, headers: request_headers
+        end
+      end
+
+      [nil, :guest, :banned].each do |role|
+        it "rejects #{ role || 'anonymous' } without writes" do
+          actor = case role
+          when :guest then create(:user, :guest)
+          when :banned then create(:user, :member, :banned)
+          end
+          request_headers = actor ? { 'X-Transfer-Code' => actor.inheritance_code } : { }
+          before_state = group_state
+          write_group(operation, request_headers)
+          expect(response).to have_http_status(role ? :forbidden : :unauthorized)
+          expect(group_state).to eq(before_state)
+        end
+      end
+
+      it 'rejects a banned IP even for a member' do
+        IpAddress.create!(ip_address: IPAddr.new('127.0.0.1').hton, banned_at: Time.current)
+        before_state = group_state
+        write_group(operation, headers)
+        expect(response).to have_http_status(:forbidden)
+        expect(group_state).to eq(before_state)
+      end
+
+      (TagGroupRecords::GROUP_TABLES + ['wiki_pages', 'wiki_revisions', 'wiki_versions'])
+          .each do |table|
+        it "rolls back all writes after a real #{ table } write fails" do
+          expect_atomic_group_write(table) { write_group(operation, headers) }
+        end
+      end
+    end
+  end
+end

backend/spec/requests/tag_group_write_integrity_spec.rb

@@ -0,0 +1,329 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group write integrity', type: :request do
+  include TagGroupRecords
+  include ActiveSupport::Testing::TimeHelpers
+
+  let!(:user) { create_member_user! }
+  let!(:tag) { group_tag('洗澡鹿') }
+  let!(:other_tag) { group_tag('伊地知ニジカ') }
+  let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+  let(:members) { [{ 'tag_id' => tag.id, 'version_no' => tag.version_no }] }
+  let(:placements) { [{ 'tag_id' => tag.id, 'children' => [] }] }
+
+  before { I18n.locale = :ja }
+
+  def native_payload name: '更新', nodes: placements, member_rows: members
+    { name:, description: nil, members: member_rows.map do |member|
+      member.except('version_no')
+    end, placements: nodes }
+  end
+
+  def put_wiki id, title:, body: '- 伊地知ニジカ', base: nil
+    put "/wiki/#{ id }", params: { title:, body:, base_revision_id: base }, headers: headers
+  end
+
+  def create_help body
+    Wiki::Commit.create_legacy_content!(
+        tag_name: create(:tag_name, name: 'Help:既存'), body:, created_by_user: user)
+  end
+
+  def expect_no_writes
+    before_state = group_state
+    yield
+    expect(response).to have_http_status(:unprocessable_entity)
+    expect(group_state).to eq(before_state)
+  end
+
+  context 'resource identity' do
+    it 'rejects removing the prefix from a migrated group atomically' do
+      page = legacy_group('更新', '- 洗澡鹿')
+      seed_group(name: '更新', id: page.id, members:, placements:)
+
+      expect_no_writes do
+        put_wiki(page.id, title: '更新', base: page.current_revision.id)
+      end
+    end
+
+    it 'rejects an unprefixed update to an independent group' do
+      id = seed_group(name: '独立', members:, placements:)
+      expect_no_writes { put_wiki(id, title: '独立') }
+    end
+
+    it 'does not revive legacy writes when the compatibility title is stale' do
+      page = legacy_group('更新', '- 洗澡鹿')
+      seed_group(name: '更新', id: page.id, members:, placements:)
+      page.tag_name.update!(name: '古い別名')
+
+      expect_no_writes { put_wiki(page.id, title: '古い別名') }
+    end
+
+    it 'renames the group and its compatibility page through the operation' do
+      page = legacy_group('更新', '- 洗澡鹿')
+      seed_group(name: '更新', id: page.id, members:, placements:)
+
+      put_wiki(page.id, title: 'タググループ:改名')
+
+      expect(response).to have_http_status(:ok)
+      expect(TagGroup.find(page.id)).to have_attributes(name: '改名', version_no: 2)
+      expect(page.reload.title).to eq('タググループ:改名')
+      expect(page.body).to eq('- 伊地知ニジカ')
+    end
+
+    it 'updates Help with a colliding group ID without altering the group' do
+      page = create_help('Help body')
+      id = seed_group(name: '別グループ', id: page.id, members:, placements:)
+      group_before = TagGroup.find(id).attributes
+      version_before = group_version(id, 1)
+
+      put_wiki(id, title: 'Help:改名', body: 'Help after')
+
+      expect(response).to have_http_status(:ok)
+      expect(page.reload.body).to eq('Help after')
+      expect(page.title).to eq('Help:改名')
+      expect(TagGroup.find(id).attributes).to eq(group_before)
+      expect(group_version(id, 1)).to eq(version_before)
+    end
+
+    it 'rejects an ambiguous unprefixed rename when Help and group IDs collide' do
+      page = create_help('Help body')
+      seed_group(name: '更新', id: page.id, members:, placements:)
+
+      expect_no_writes { put_wiki(page.id, title: '更新') }
+      expect_no_writes do
+        put_wiki(page.id, title: '更新', base: page.current_revision.id)
+      end
+    end
+
+    it 'keeps a description update separate from a colliding group' do
+      page = Wiki::Commit.create_content!(
+          tag_name: tag.tag_name('ja'), body: 'description before', created_by_user: user)
+      id = seed_group(name: '更新', id: page.id, members:, placements:)
+      group_before = TagGroup.find(id).attributes
+
+      put_wiki(id, title: '洗澡鹿', body: 'description after')
+
+      expect(response).to have_http_status(:ok)
+      expect(TagDescription.find(id).body).to eq('description after')
+      expect(page.reload.body).to eq('description after')
+      expect(TagGroup.find(id).attributes).to eq(group_before)
+    end
+
+    it 'does not route a colliding Help write into an unrelated description' do
+      page = create_help('Help before')
+      id = seed_group(name: '更新', id: page.id, members:, placements:)
+      description = TagDescription.create!(
+          id:, tag:, language_code: 'ja', version_no: 1, body: 'description')
+
+      put_wiki(id, title: 'Help:既存', body: 'Help after')
+
+      expect(response).to have_http_status(:ok)
+      expect(page.reload.body).to eq('Help after')
+      expect(description.reload.body).to eq('description')
+      expect(TagGroup.find(id).version_no).to eq(1)
+      expect_no_writes { put_wiki(id, title: '洗澡鹿', body: 'description after') }
+      put_wiki(id, title: 'タググループ:更新')
+      expect(response).to have_http_status(:ok)
+      expect(TagGroup.find(id).version_no).to eq(2)
+      expect(page.reload.body).to eq('Help after')
+      expect(description.reload.body).to eq('description')
+    end
+  end
+
+  context 'compatibility synchronisation' do
+    it 'synchronises a native rename without modifying an ID-colliding Help page' do
+      help = create_help('Help before')
+      id = seed_group(name: '更新', id: help.id, members:, placements:)
+      help_before = help.attributes
+
+      put "/tag_groups/#{ id }", params: native_payload(name: '改名'), headers:, as: :json
+
+      expect(response).to have_http_status(:ok)
+      page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:改名' })
+      expect(page.id).not_to eq(help.id)
+      expect(page.body).to eq('- 洗澡鹿')
+      expect(page.current_revision.body).to eq(page.body)
+      expect(page.wiki_versions.sole.body).to eq(page.body)
+      expect(help.reload.attributes).to eq(help_before)
+    end
+
+    ['wiki_lines', 'wiki_revision_lines'].each do |table|
+      it "rolls back native and compatibility state on #{ table } failure" do
+        expect_atomic_group_write(table) do
+          post '/tag_groups', params: native_payload, headers:, as: :json
+        end
+      end
+    end
+
+    it 'rolls back a renderer failure instead of treating it as unsupported structure' do
+      allow(TagGroupMarkdownRenderer).to receive(:render).and_raise('renderer failure')
+      before_state = group_state
+
+      expect do
+        post '/tag_groups', params: native_payload, headers:, as: :json
+      end.to raise_error(RuntimeError, 'renderer failure')
+
+      expect(group_state).to eq(before_state)
+    end
+
+    it 'preserves unplaced membership and reports the skipped sync with its version' do
+      page = legacy_group('更新', '- 洗澡鹿')
+      id = seed_group(name: '更新', id: page.id, members:, placements:)
+      wiki_before = group_state.slice(*TagGroupRecords::WRITE_TABLES.drop(5))
+      warnings = []
+      allow(Rails.logger).to receive(:warn) { warnings << _1 }
+
+      put "/tag_groups/#{ id }",
+          params: native_payload(member_rows: members + [{ 'tag_id' => other_tag.id }]),
+          headers:, as: :json
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('members').map { _1.fetch('tag').fetch('id') })
+          .to contain_exactly(tag.id, other_tag.id)
+      expect(group_version(id, 2).fetch('members')).to include(
+          { 'tag_id' => other_tag.id, 'version_no' => other_tag.version_no })
+      expect(group_state.slice(*TagGroupRecords::WRITE_TABLES.drop(5))).to eq(wiki_before)
+      payload = JSON.parse(warnings.grep(/tag_group_wiki_sync_skipped/).sole.split(' ', 2).last)
+      expect(payload).to include(
+          'status' => 'unsupported_structure', 'tag_group_id' => id,
+          'version_no' => 2, 'user_id' => user.id,
+          'reason' => '掲載位置のない membership は Markdown にできません．')
+    end
+
+    it 'preserves a list Section description and records why no Wiki was created' do
+      nodes = [{ 'tag_id' => tag.id, 'children' => [
+          { 'section_name' => '区分', 'description' => '構造化の説明', 'children' => [] }] }]
+      warnings = []
+      allow(Rails.logger).to receive(:warn) { warnings << _1 }
+      before_count = WikiPage.count
+
+      post '/tag_groups', params: native_payload(nodes:), headers:, as: :json
+
+      expect(response).to have_http_status(:created)
+      id = json.fetch('id')
+      expect(group_version(id, 1).fetch('placements')).to eq(nodes)
+      expect(json.fetch('placements').sole.fetch('children').sole)
+          .to include('description' => '構造化の説明')
+      expect(WikiPage.count).to eq(before_count)
+      expect(warnings.grep(/tag_group_wiki_sync_skipped/).sole)
+          .to include('リスト内 Section の説明文は Markdown にできません．')
+    end
+  end
+
+  context 'identifier Markdown' do
+    ['[洗澡鹿](https://example.com)', '*洗澡鹿*', '**洗澡鹿**', '`洗澡鹿`',
+     '![洗澡鹿](https://example.com/image.png)',
+     '[タググループ:子](https://example.com)', '*区分*:',
+     '[区分](https://example.com):'].each do |label|
+      [:create, :update].each do |operation|
+        it "rejects decorated #{ label } on #{ operation } without writes" do
+          seed_group(name: '子', description: '子')
+          id = seed_group(name: '更新', members:, placements:)
+          expect_no_writes do
+            if operation == :create
+              post '/wiki', params: { title: 'タググループ:新規', body: "- #{ label }" },
+                   headers: headers
+            else
+              put_wiki(id, title: 'タググループ:更新', body: "- #{ label }")
+            end
+          end
+        end
+      end
+    end
+
+    ['# [区分](https://example.com)', '# *区分*', '# `区分`', '# 区分 {#custom}',
+     '# ![区分](https://example.com/image.png)'].each do |heading|
+      it "rejects a decorated heading #{ heading } without writes" do
+        expect_no_writes do
+          post '/wiki', params: { title: 'タググループ:新規', body: "#{ heading }\n- 洗澡鹿" },
+               headers: headers
+        end
+      end
+    end
+
+    it 'preserves allowed markup in group and heading descriptions' do
+      description = '[参照](https://example.com "リンクの説明") と *強調* と ``a`b``'
+      body = "#{ description }\n\n# 区分\n#{ description }\n\n- 洗澡鹿"
+      post '/wiki', params: { title: 'タググループ:説明構文', body: }, headers: headers
+
+      expect(response).to have_http_status(:created)
+      id = json.fetch('id')
+      version = group_version(id, 1)
+      expect(version.fetch('description')).to eq(description)
+      expect(version.fetch('placements').sole.fetch('description')).to eq(description)
+    end
+  end
+
+  context 'structure audit information' do
+    let!(:child_id) { seed_group(name: '子', description: '子') }
+    let(:members) do
+      [{ 'tag_id' => tag.id, 'version_no' => tag.version_no },
+       { 'tag_group_id' => child_id, 'version_no' => 1 }]
+    end
+    let(:placements) do
+      [{ 'tag_id' => tag.id, 'children' => [
+          { 'tag_group_id' => child_id, 'children' => [] }] }]
+    end
+    let!(:id) { seed_group(name: '更新', members:, placements:) }
+    let!(:editor) { create(:user, :member) }
+    let(:headers) { { 'X-Transfer-Code' => editor.inheritance_code } }
+
+    it 'keeps all membership and placement audit fields on a name-only edit' do
+      before_rows = group_state.slice('tag_group_tags', 'tag_group_groups', 'tag_group_placements')
+      travel_to(1.hour.from_now) do
+        put "/tag_groups/#{ id }", params: native_payload(name: '改名'), headers:, as: :json
+      end
+
+      expect(response).to have_http_status(:ok)
+      expect(group_state.slice(*before_rows.keys)).to eq(before_rows)
+      expect(group_version(id, 2)).to include('name' => '改名', 'members' => members)
+    end
+
+    it 'keeps membership and placement audit fields on a description-only edit' do
+      before_rows = group_state.slice('tag_group_tags', 'tag_group_groups', 'tag_group_placements')
+      travel_to(1.hour.from_now) do
+        put "/tag_groups/#{ id }",
+            params: native_payload.merge(description: '説明を追加'), headers:, as: :json
+      end
+
+      expect(response).to have_http_status(:ok)
+      expect(group_state.slice(*before_rows.keys)).to eq(before_rows)
+      expect(group_version(id, 2)).to include('description' => '説明を追加', 'members' => members)
+    end
+
+    it 'rolls back membership removal and placement edits on a late sync failure' do
+      new_members = [{ 'tag_id' => tag.id }]
+      new_nodes = [{ 'tag_id' => tag.id, 'children' => [] }]
+      expect_atomic_group_write('wiki_versions') do
+        put "/tag_groups/#{ id }",
+            params: native_payload(nodes: new_nodes, member_rows: new_members), headers:, as: :json
+      end
+    end
+
+    it 'changes only added or removed membership and keeps placement creation audit' do
+      tag_row = TagGroupTag.find([id, tag.id]).attributes
+      placement_row = TagGroupPlacement.find([id, 1]).attributes
+      new_members = [{ 'tag_id' => tag.id }, { 'tag_id' => other_tag.id }]
+      new_nodes = [{ 'tag_id' => tag.id, 'children' => [
+          { 'tag_id' => other_tag.id, 'children' => [] }] }]
+      child_row = TagGroupPlacement.find([id, 2]).attributes
+      travel_to(1.hour.from_now) do
+        put "/tag_groups/#{ id }",
+            params: native_payload(nodes: new_nodes, member_rows: new_members), headers:, as: :json
+      end
+
+      expect(response).to have_http_status(:ok)
+      expect(TagGroupTag.find([id, tag.id]).attributes).to eq(tag_row)
+      expect(TagGroupGroup.exists?(tag_group_id: id, child_tag_group_id: child_id)).to be(false)
+      expect(TagGroupTag.find([id, other_tag.id]).created_by_user_id).to eq(editor.id)
+      expect(TagGroupPlacement.find([id, 1]).attributes).to eq(placement_row)
+      changed = TagGroupPlacement.find([id, 2])
+      expect(changed).to have_attributes(
+          tag_id: other_tag.id, child_tag_group_id: nil, updated_by_user_id: editor.id,
+          created_at: child_row.fetch('created_at'),
+          created_by_user_id: child_row.fetch('created_by_user_id'))
+      expect(changed.updated_at).to be > child_row.fetch('updated_at')
+      expect(group_version(id, 1).fetch('members')).to eq(members)
+    end
+  end
+end

backend/spec/requests/tag_groups_spec.rb

@@ -0,0 +1,308 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag group native API', type: :request do
+  include TagGroupRecords
+
+  let!(:user) { create_member_user! }
+  let!(:group_id) { seed_group(name: '専用API', description: '説明') }
+
+  before { I18n.locale = :ja }
+
+  def expect_native_group value
+    expect(value).to include(
+        'id' => group_id, 'name' => '専用API', 'description' => '説明',
+        'version_no' => 1, 'members' => [], 'placements' => [],
+        'created_by_user' => UserRepr.base(user), 'updated_by_user' => UserRepr.base(user))
+    current = group_rows('tag_groups', id: group_id).sole
+    expect(value).to include(
+        'created_at' => current.fetch('created_at').iso8601(3),
+        'updated_at' => current.fetch('updated_at').iso8601(3))
+  end
+
+  it 'serves the collection as JSON without reading Wiki tables' do
+    without_group_legacy_reads { get '/tag_groups' }
+    expect(response).to have_http_status(:ok)
+    expect(response.media_type).to eq('application/json')
+    expect(json).to be_a(Array)
+    expect_native_group(json.find { _1.fetch('id') == group_id })
+  end
+
+  it 'serves an independent group as JSON without reading Wiki tables' do
+    without_group_legacy_reads { get "/tag_groups/#{ group_id }" }
+    expect(response).to have_http_status(:ok)
+    expect(response.media_type).to eq('application/json')
+    expect_native_group(json)
+  end
+
+  it 'provides the confirmed PUT update route' do
+    route = Rails.application.routes.recognize_path("/tag_groups/#{ group_id }", method: :put)
+    expect(route).to include(action: 'update', id: group_id.to_s)
+  end
+
+  [:create, :update].each do |operation|
+    [nil, :guest, :banned].each do |role|
+      it "rejects #{ role || 'anonymous' } native #{ operation } without writes" do
+        actor = case role
+        when :guest then create(:user, :guest)
+        when :banned then create(:user, :member, :banned)
+        end
+        headers = actor ? { 'X-Transfer-Code' => actor.inheritance_code } : { }
+        before_state = group_state
+        if operation == :create
+          post '/tag_groups', params: { }, headers:, as: :json
+        else
+          put "/tag_groups/#{ group_id }", params: { }, headers:, as: :json
+        end
+        expect(response).to have_http_status(role ? :forbidden : :unauthorized)
+        expect(group_state).to eq(before_state)
+      end
+    end
+
+    it "rejects a banned IP for native #{ operation }" do
+      IpAddress.create!(ip_address: IPAddr.new('127.0.0.1').hton, banned_at: Time.current)
+      headers = { 'X-Transfer-Code' => user.inheritance_code }
+      before_state = group_state
+      if operation == :create
+        post '/tag_groups', params: { }, headers:, as: :json
+      else
+        put "/tag_groups/#{ group_id }", params: { }, headers:, as: :json
+      end
+      expect(response).to have_http_status(:forbidden)
+      expect(group_state).to eq(before_state)
+    end
+  end
+
+  context 'structured membership and placements' do
+    let!(:tag) { group_tag('掲載タグ') }
+    let!(:unplaced) { group_tag('未掲載タグ') }
+    let!(:child_id) { seed_group(name: '子', description: '子の説明') }
+    let(:headers) { { 'X-Transfer-Code' => user.inheritance_code } }
+    let(:members) do
+      [{ 'tag_id' => tag.id }, { 'tag_group_id' => child_id }, { 'tag_id' => unplaced.id }]
+    end
+    let(:snapshot_members) do
+      [{ 'tag_id' => tag.id, 'version_no' => tag.version_no },
+       { 'tag_group_id' => child_id, 'version_no' => 1 },
+       { 'tag_id' => unplaced.id, 'version_no' => unplaced.version_no }]
+    end
+    let(:placements) do
+      [{ 'section_name' => '区分', 'description' => '区分の説明', 'children' => [
+          { 'tag_id' => tag.id, 'children' => [
+              { 'tag_group_id' => child_id, 'children' => [] }] },
+          { 'tag_id' => tag.id, 'children' => [] }] }]
+    end
+    let(:payload) { { name: '構造化', description: '全体の説明', members:, placements: } }
+
+    def native_write operation, attributes = payload
+      if operation == :create
+        post '/tag_groups', params: attributes, headers:, as: :json
+      else
+        put "/tag_groups/#{ group_id }", params: attributes, headers:, as: :json
+      end
+    end
+
+    def expect_structured_response
+      tag_repr = { 'id' => tag.id, 'name' => '掲載タグ', 'category' => tag.category }
+      unplaced_repr = { 'id' => unplaced.id, 'name' => '未掲載タグ',
+                        'category' => unplaced.category }
+      expect(json.fetch('members')).to contain_exactly(
+          include('tag' => include(tag_repr)),
+          include('tag' => include(unplaced_repr)),
+          include('tag_group' => include('id' => child_id, 'name' => '子')))
+      expect(json.fetch('placements')).to match([
+          include('section_name' => '区分', 'description' => '区分の説明', 'children' => [
+              include('tag' => include(tag_repr), 'children' => [
+                  include('tag_group' => include('id' => child_id, 'name' => '子'),
+                          'children' => [])]),
+              include('tag' => include(tag_repr), 'children' => [])])])
+    end
+
+    [:create, :update].each do |operation|
+      it "#{ operation }s structured data and keeps unplaced membership" do
+        previous = group_version(group_id, 1)
+        native_write(operation)
+        expect(response).to have_http_status(operation == :create ? :created : :ok)
+        id = operation == :create ? json.fetch('id') : group_id
+        number = operation == :create ? 1 : 2
+        expect_group_snapshot(
+            id, number:, members: snapshot_members, placements:, description: '全体の説明')
+        expect(group_version(group_id, 1)).to eq(previous)
+        get "/tag_groups/#{ id }"
+        expect(response).to have_http_status(:ok)
+        expect(json).to include(
+            'id' => id, 'name' => '構造化', 'description' => '全体の説明', 'version_no' => number,
+            'created_by_user' => UserRepr.base(user), 'updated_by_user' => UserRepr.base(user))
+        expect_structured_response
+      end
+
+      {
+          'blank name' => { name: '' },
+          'missing name' => { name: nil },
+          'oversized name' => { name: '長' * 256 },
+          'duplicate name' => { name: '子' },
+          'placement without a kind' => { placements: [{ children: [] }] },
+          'empty Section name' => { placements: [{ section_name: '', children: [] }] } }
+          .each do |label, invalid|
+        it "rejects #{ label } on #{ operation } without partial writes" do
+          before_state = group_state
+          native_write(operation, payload.merge(invalid))
+          aggregate_failures do
+            expect(response).to have_http_status(:unprocessable_entity)
+            expect(group_state).to eq(before_state)
+          end
+        end
+      end
+
+      it "rejects multiple placement kinds on #{ operation }" do
+        before_state = group_state
+        invalid = [{ tag_id: tag.id, section_name: '不正', children: [] }]
+        native_write(operation, payload.merge(placements: invalid))
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(group_state).to eq(before_state)
+      end
+
+      it "rejects a missing referenced Tag on #{ operation }" do
+        missing = Tag.maximum(:id).to_i + 1
+        before_state = group_state
+        native_write(operation, payload.merge(
+            members: [{ tag_id: missing }], placements: [{ tag_id: missing, children: [] }]))
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(group_state).to eq(before_state)
+      end
+
+      it "rejects a missing referenced group on #{ operation }" do
+        missing = group_rows('tag_groups').map { _1.fetch('id') }.max + 1
+        before_state = group_state
+        native_write(operation, payload.merge(
+            members: [{ tag_group_id: missing }],
+            placements: [{ tag_group_id: missing, children: [] }]))
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(group_state).to eq(before_state)
+      end
+
+      it "rejects six descendant placement levels on #{ operation }" do
+        nodes = []
+        6.times { nodes = [{ tag_id: tag.id, children: nodes }] }
+        before_state = group_state
+        native_write(operation, payload.merge(placements: nodes))
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(group_state).to eq(before_state)
+      end
+    end
+
+    it 'preserves membership-only data in structured reads without inventing placements' do
+      id = seed_group(name: '未掲載のみ', members: [snapshot_members.last])
+      without_group_legacy_reads { get "/tag_groups/#{ id }" }
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('placements')).to eq([])
+      expect(json.fetch('members')).to match([
+          include('tag' => include('id' => unplaced.id, 'name' => '未掲載タグ'))])
+    end
+
+    it 'rejects indirect containment cycles' do
+      parent = seed_group(
+          name: '親', members: [{ 'tag_group_id' => group_id, 'version_no' => 1 }])
+      before_state = group_state
+      native_write(:update, payload.merge(
+          members: [{ tag_group_id: parent }], placements: []))
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(group_state).to eq(before_state)
+    end
+
+    it 'rejects direct containment even without a corresponding placement' do
+      before_state = group_state
+      native_write(:update, payload.merge(
+          members: [{ tag_group_id: group_id }], placements: []))
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(group_state).to eq(before_state)
+    end
+
+    it 'preserves list Section descriptions in native structured data' do
+      nodes = [{ tag_id: tag.id, children: [
+          { section_name: 'リスト内区分', description: '消してはいけない説明', children: [] }] }]
+      native_write(:update, payload.merge(placements: nodes))
+      expect(response).to have_http_status(:ok)
+      expect(group_version(group_id, 2).fetch('placements')).to eq(
+          JSON.parse(nodes.to_json))
+      get "/tag_groups/#{ group_id }"
+      expect(response).to have_http_status(:ok)
+      section = json.fetch('placements').sole.fetch('children').sole
+      expect(section).to include(
+          'section_name' => 'リスト内区分', 'description' => '消してはいけない説明')
+    end
+
+    context 'compatibility writes for representable structures' do
+      let(:group_id) do
+        page = legacy_group('専用API', '説明')
+        seed_group(name: '専用API', id: page.id, description: '説明')
+      end
+      let(:members) { [{ 'tag_id' => tag.id }, { 'tag_group_id' => child_id }] }
+      let(:snapshot_members) do
+        [{ 'tag_id' => tag.id, 'version_no' => tag.version_no },
+         { 'tag_group_id' => child_id, 'version_no' => 1 }]
+      end
+
+      [:create, :update].each do |operation|
+        it "synchronises Wiki current state and histories on native #{ operation }" do
+          native_write(operation)
+          expect(response).to have_http_status(operation == :create ? :created : :ok)
+          id = operation == :create ? json.fetch('id') : group_id
+          number = operation == :create ? 1 : 2
+          expect_group_snapshot(
+              id, number:, members: snapshot_members, placements:, description: '全体の説明')
+          page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'タググループ:構造化' })
+          expect(page.body).to include('全体の説明', '# 区分', '- 掲載タグ', '- タググループ:子')
+          expect(page.current_revision.body).to eq(page.body)
+          expect(page.wiki_versions.order(:version_no).last.body).to eq(page.body)
+          expect(page.wiki_revisions.count).to eq(number)
+          expect(page.wiki_versions.count).to eq(number)
+          get group_title_path('構造化')
+          expect(response).to have_http_status(:ok)
+          expect(json.fetch('body')).to eq(page.body)
+        end
+
+        (TagGroupRecords::GROUP_TABLES + ['wiki_pages', 'wiki_revisions', 'wiki_versions'])
+            .each do |table|
+          it "rolls back native #{ operation } after #{ table } writes" do
+            expect_atomic_group_write(table) { native_write(operation) }
+          end
+        end
+      end
+
+      it 'uses AUTO_INCREMENT for a new group instead of supplying a compatibility ID' do
+        inserts = []
+        subscriber = lambda do |*args|
+          sql = args.last.fetch(:sql)
+          inserts << sql if sql.match?(/\A\s*INSERT INTO `?tag_groups`?\s/i)
+        end
+        ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') do
+          native_write(:create)
+        end
+        expect(response).to have_http_status(:created)
+        expect(inserts.size).to eq(1)
+        columns = inserts.sole[/\((.*?)\)/, 1].split(',').map { _1.strip.delete('`') }
+        expect(columns).not_to include('id')
+      end
+
+      it 'updates a native group through Wiki and then reads structured current data' do
+        native_write(:create)
+        expect(response).to have_http_status(:created)
+        id = json.fetch('id')
+        previous = group_version(id, 1)
+        put "/wiki/#{ id }",
+            params: { title: 'タググループ:構造化', body: '- 未掲載タグ' }, headers: headers
+        expect(response).to have_http_status(:ok)
+        expect_group_snapshot(
+            id, number: 2,
+            members: [{ 'tag_id' => unplaced.id, 'version_no' => unplaced.version_no }],
+            placements: [{ 'tag_id' => unplaced.id, 'children' => [] }])
+        expect(group_version(id, 1)).to eq(previous)
+        get "/tag_groups/#{ id }"
+        expect(response).to have_http_status(:ok)
+        expect(json).to include('version_no' => 2)
+        expect(json.fetch('members')).to match([
+            include('tag' => include('id' => unplaced.id, 'name' => '未掲載タグ'))])
+      end
+    end
+  end
+end

backend/spec/support/tag_group_records.rb

@@ -0,0 +1,189 @@
+require 'cgi'
+
+# SQL fixtures use the migration contract without inventing application models.
+# Include explicitly; these helpers must not affect unrelated examples.
+module TagGroupRecords
+  GROUP_TABLES = [
+      'tag_groups', 'tag_group_tags', 'tag_group_groups',
+      'tag_group_placements', 'tag_group_versions'].freeze
+  WRITE_TABLES = GROUP_TABLES + [
+      'wiki_pages', 'wiki_revisions', 'wiki_versions', 'wiki_lines',
+      'wiki_revision_lines', 'tag_names', 'tag_description_versions',
+      'tag_descriptions']
+
+  def group_connection = ApplicationRecord.connection
+
+  def group_rows table, conditions = { }
+    clauses = conditions.map do |column, value|
+      "#{ group_connection.quote_column_name(column) } = #{ group_connection.quote(value) }"
+    end
+    sql = "SELECT * FROM #{ group_connection.quote_table_name(table) }"
+    sql += " WHERE #{ clauses.join(' AND ') }" if clauses.any?
+    group_connection.select_all(sql).to_a.sort_by { |row| row.values.map(&:to_s) }
+  end
+
+  def insert_group_row table, attributes
+    columns = attributes.keys.map { group_connection.quote_column_name(_1) }.join(', ')
+    values = attributes.values.map { group_connection.quote(_1) }.join(', ')
+    group_connection.insert(
+        "INSERT INTO #{ group_connection.quote_table_name(table) } (#{ columns }) " +
+        "VALUES (#{ values })")
+  end
+
+  def group_state
+    WRITE_TABLES.to_h { |table| [table, group_rows(table)] }
+  end
+
+  def expect_atomic_group_write table
+    before_state = group_state
+    failure = Class.new(StandardError)
+    injected = false
+    subscriber = lambda do |*args|
+      sql = args.last.fetch(:sql)
+      next unless sql.match?(/\A\s*(?:INSERT INTO|UPDATE)\s+`?#{ table }`?\s/i)
+
+      injected = true
+      raise failure, 'injected after SQL write'
+    end
+    begin
+      ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') { yield }
+    rescue failure
+      # Inspect the database after the operation's transaction unwinds.
+    end
+    aggregate_failures do
+      expect(injected).to be(true), "No INSERT/UPDATE reached #{ table }"
+      expect(group_state).to eq(before_state)
+    end
+  end
+
+  def group_version group_id, number
+    row = group_rows('tag_group_versions', tag_group_id: group_id, version_no: number).sole
+    row.merge('members' => JSON.parse(row.fetch('members')),
+              'placements' => JSON.parse(row.fetch('placements')))
+  end
+
+  def group_tag name
+    tag = create(:tag, primary_name: name)
+    TagVersioning.ensure_snapshot!(tag, created_by_user: user)
+    tag.reload
+  end
+
+  def legacy_group name, body
+    # Historical fixtures preserve blank lines independently of today's writer.
+    body = body.sub(/\n+\z/, '')
+    page = WikiPage.create!(
+        tag_name: create(:tag_name, name: "タググループ:#{ name }"),
+        body:, created_user: user, updated_user: user)
+    WikiVersionRecorder.record!(page:, event_type: :create, created_by_user: user)
+    lines = body.split("\n")
+    shas = lines.map { Digest::SHA256.hexdigest(_1) }
+    revision = WikiRevision.create!(
+        wiki_page: page, kind: :content, created_user: user, lines_count: lines.size,
+        tree_sha256: Digest::SHA256.hexdigest(shas.join(',')))
+    lines.each_with_index do |line, position|
+      sha = shas.fetch(position)
+      line_id = WikiLine.find_by(sha256: sha)&.id || insert_group_row('wiki_lines', {
+          body: line, sha256: sha, created_at: Time.current, updated_at: Time.current })
+      WikiRevisionLine.create!(wiki_revision: revision, wiki_line_id: line_id, position:)
+    end
+    page
+  end
+
+  def seed_group name:, placements: [], members: [], description: nil, id: nil
+    now = Time.current.change(usec: 0)
+    attributes = {
+        name:, description:, version_no: 1,
+        created_by_user_id: user.id, updated_by_user_id: user.id,
+        created_at: now, updated_at: now }
+    attributes[:id] = id if id
+    group_id = insert_group_row('tag_groups', attributes)
+    insert_group_row('tag_group_versions', {
+        tag_group_id: group_id, version_no: 1, event_type: 'create',
+        name:, description:, members: members.to_json, placements: placements.to_json,
+        created_by_user_id: user.id, created_at: now })
+    members.each do |member|
+      tag_member = member.key?('tag_id')
+      table = tag_member ? 'tag_group_tags' : 'tag_group_groups'
+      key = tag_member ? :tag_id : :child_tag_group_id
+      value = member.fetch(tag_member ? 'tag_id' : 'tag_group_id')
+      insert_group_row(table, {
+          tag_group_id: group_id, key => value,
+          created_by_user_id: user.id, created_at: now })
+    end
+    position = 0
+    append = lambda do |nodes, parent|
+      nodes.each do |node|
+        position += 1
+        own_position = position
+        insert_group_row('tag_group_placements', {
+            tag_group_id: group_id, position:, parent_position: parent,
+            section_name: node['section_name'], description: node['description'],
+            tag_id: node['tag_id'], child_tag_group_id: node['tag_group_id'],
+            created_by_user_id: user.id, updated_by_user_id: user.id,
+            created_at: now, updated_at: now })
+        append.call(node.fetch('children'), own_position)
+      end
+    end
+    append.call(placements, nil)
+    group_id
+  end
+
+  def without_group_legacy_reads
+    queries = []
+    subscriber = lambda do |*args|
+      sql = args.last.fetch(:sql)
+      if (sql.match?(/\bSELECT\b/i) &&
+          sql.match?(/\bwiki_(pages|revisions|versions|lines|revision_lines)\b/i))
+        queries << sql
+      end
+    end
+    ActiveSupport::Notifications.subscribed(subscriber, 'sql.active_record') { yield }
+    expect(queries).to be_empty
+  end
+
+  def group_title_path name
+    "/wiki/title/#{ CGI.escapeURIComponent("タググループ:#{ name }") }"
+  end
+
+  def migrate_groups
+    require_relative '../../db/migrate/20261008010000_migrate_tag_groups_from_wiki_pages'
+    migration = MigrateTagGroupsFromWikiPages.new
+    @group_migration_messages = []
+    allow(migration).to receive(:say) do |message, *_args|
+      @group_migration_messages << message if message.start_with?('Wiki #', 'Tag Group')
+    end
+    migration.suppress_messages { migration.up }
+  end
+
+  def expect_group_snapshot group_id, number:, placements:, members:, description: nil
+    current = group_rows('tag_groups', id: group_id).sole
+    version = group_version(group_id, number)
+    expect(current).to include('version_no' => number, 'description' => description),
+                       @group_migration_messages&.join("\n")
+    expect(version).to include(
+        'name' => current.fetch('name'), 'description' => description,
+        'version_no' => number, 'placements' => placements)
+    expect(version.fetch('members')).to match_array(members)
+    expect(group_rows('tag_group_tags', tag_group_id: group_id).map { _1.fetch('tag_id') })
+        .to match_array(members.filter_map { _1['tag_id'] })
+    children = group_rows('tag_group_groups', tag_group_id: group_id)
+    expect(children.map { _1.fetch('child_tag_group_id') })
+        .to match_array(members.filter_map { _1['tag_group_id'] })
+
+    rows = group_rows('tag_group_placements', tag_group_id: group_id)
+    tree = lambda do |parent|
+      rows.select { _1['parent_position'] == parent }.sort_by { _1.fetch('position') }
+          .map do |row|
+        node = if row['tag_id']
+          { 'tag_id' => row.fetch('tag_id') }
+        elsif row['child_tag_group_id']
+          { 'tag_group_id' => row.fetch('child_tag_group_id') }
+        else
+          { 'section_name' => row.fetch('section_name'), 'description' => row['description'] }
+        end
+        node.merge('children' => tree.call(row.fetch('position')))
+      end
+    end
+    expect(tree.call(nil)).to eq(placements)
+  end
+end