#399

backend/app/controllers/application_controller.rb

@@ -85,13 +85,4 @@ class ApplicationController < ActionController::API
                    base_errors: },
            status:
   end
-
-  def normalise_json value
-    return nil if value.nil?
-    return JSON.parse(value) if value.is_a?(String)
-
-    value
-  end
-
-  def resolve_locale! = Locale.find_by(code: params[:locale]) || Locale.nipponese
 end

backend/app/controllers/deerjikists_controller.rb

@@ -1,7 +1,5 @@
 class DeerjikistsController < ApplicationController
   def show
-    locale = resolve_locale!
-
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     return render_bad_request('platform は必須です．') if platform.blank?
@@ -9,10 +7,10 @@ class DeerjikistsController < ApplicationController
 
     deerjikist = Deerjikist
                  .joins(:tag)
-                 .includes(tag: :tag_names)
+                 .includes(tag: :tag_name)
                  .find_by(platform:, code:)
     if deerjikist
-      render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
+      render json: DeerjikistRepr.base(deerjikist)
     else
       head :not_found
     end
@@ -22,7 +20,6 @@ class DeerjikistsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
     platform = params[:platform].to_s.strip
     code = params[:code].to_s.strip
     tag_id = params[:tag_id].to_i
@@ -35,7 +32,7 @@ class DeerjikistsController < ApplicationController
       d.save!
     end
 
-    render json: DeerjikistRepr.base(deerjikist, language_code: locale.language_code)
+    render json: DeerjikistRepr.base(deerjikist)
   end
 
   def destroy

backend/app/controllers/gekanator_posts_controller.rb

@@ -2,7 +2,7 @@ class GekanatorPostsController < ApplicationController
   def index
     posts =
         Post
-        .preload(:post_similarities, tags: :tag_names)
+        .preload(:post_similarities, tags: :tag_name)
         .with_attached_thumbnail
         .order(Arel.sql(
             'COALESCE(posts.original_created_before - INTERVAL 1 MINUTE, ' \
@@ -56,7 +56,7 @@ class GekanatorPostsController < ApplicationController
   def tag_json tag
     {
       id: tag.id,
-      name: tag.name('ja'),
+      name: tag.name,
       category: tag.category
     }
   end

backend/app/controllers/gekanator_questions_controller.rb

@@ -126,9 +126,9 @@ class GekanatorQuestionsController < ApplicationController
     end
 
     Tag
-        .joins(:tag_names)
+        .joins(:tag_name)
         .where(category: categories.uniq)
-        .where(tag_names: { language_code: 'ja', primary_flg: true, name: names.uniq })
+        .where(tag_names: { name: names.uniq })
         .where.not(deprecated_at: nil)
         .pluck('tags.category', 'tag_names.name')
         .each_with_object({ }) do |(category, name), h|

backend/app/controllers/materials_controller.rb

@@ -7,8 +7,6 @@ class MaterialsController < ApplicationController
   rescue_from MaterialZipExporter::MissingFileError, with: :render_zip_missing_file
 
   def index
-    locale = resolve_locale!
-
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -22,7 +20,7 @@ class MaterialsController < ApplicationController
     q = Material.includes(:material_export_items,
                           thumbnail_attachment: :blob,
                           file_attachment: :blob,
-                          tag: :tag_names)
+                          tag: :tag_name)
     q = q.where(tag_id: nil) if filters[:tag_state] == 'untagged'
     q = q.where.not(tag_id: nil) if filters[:tag_state] == 'tagged'
     q = apply_material_tag_filter(q, filters, tag_graph)
@@ -44,10 +42,7 @@ class MaterialsController < ApplicationController
         .offset(offset)
         .to_a
 
-    response = { materials: MaterialRepr.list_many(
-                   materials,
-                   host: request.base_url,
-                   language_code: locale.language_code),
+    response = { materials: MaterialRepr.list_many(materials, host: request.base_url),
                  count: }
     if filters[:tag_id]
       response[:tag_scope] = material_index_tag_scope(filters, tag_graph)
@@ -60,8 +55,6 @@ class MaterialsController < ApplicationController
   end
 
   def show
-    locale = resolve_locale!
-
     material =
         Material
         .includes(:tag, :material_export_items)
@@ -70,17 +63,15 @@ class MaterialsController < ApplicationController
         .find_by(id: params[:id])
     return head :not_found unless material
 
-    wiki_page_body = material.tag&.tag_name('ja')&.wiki_page&.current_revision&.body
+    wiki_page_body = material.tag&.tag_name&.wiki_page&.current_revision&.body
 
-    render json: MaterialRepr.base(material, host: request.base_url,
-                                   language_code: locale.language_code).merge(wiki_page_body:)
+    render json: MaterialRepr.base(material, host: request.base_url).merge(wiki_page_body:)
   end
 
   def create
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
     tag_name_raw = params[:tag].to_s.strip
     file = params[:file]
     file_sha256 = MaterialFileSha256.from_upload(file)
@@ -98,14 +89,13 @@ class MaterialsController < ApplicationController
 
     begin
       Material.transaction do
-        tag = resolve_material_tag!(locale, tag_name_raw)
+        tag = resolve_material_tag!(tag_name_raw)
         material = Material.new(tag:, url:,
                                 created_by_user: current_user,
                                 updated_by_user: current_user)
         material.file.attach(uploaded_blob) if uploaded_blob
         material.save!
-        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user,
-                                           language_code: locale.language_code)
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :create,
                                         created_by_user: current_user)
@@ -117,8 +107,7 @@ class MaterialsController < ApplicationController
 
     if material
       log_thumbnail_generation(material, MaterialThumbnailGenerator.generate!(material))
-      render json: MaterialRepr.base(material, host: request.base_url,
-                                     language_code: locale.language_code), status: :created
+      render json: MaterialRepr.base(material, host: request.base_url), status: :created
     else
       render_validation_error material
     end
@@ -143,14 +132,12 @@ class MaterialsController < ApplicationController
     block = MaterialImportBlockMatcher.match_for_sha256(file_sha256)
     return render_material_import_block(block) if block
 
-    locale = resolve_locale!
-
     uploaded_blob = build_uploaded_material_blob!(file, file_sha256)
 
     begin
       Material.transaction do
         MaterialVersionRecorder.ensure_snapshot!(material, created_by_user: current_user)
-        tag = resolve_material_tag!(locale, tag_name_raw)
+        tag = resolve_material_tag!(tag_name_raw)
         material.assign_attributes(tag:, url:, updated_by_user: current_user)
         if uploaded_blob
           material.file.attach(uploaded_blob)
@@ -158,8 +145,7 @@ class MaterialsController < ApplicationController
           material.file.detach
         end
         material.save!
-        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user,
-                                           language_code: locale.language_code)
+        TagVersioning.record_tag_snapshot!(tag, created_by_user: current_user)
         upsert_export_paths!(material)
         MaterialVersionRecorder.record!(material:, event_type: :update,
                                         created_by_user: current_user)
@@ -171,8 +157,7 @@ class MaterialsController < ApplicationController
 
     log_thumbnail_generation(material, MaterialThumbnailGenerator.generate!(material))
 
-    render json: MaterialRepr.base(material, host: request.base_url,
-                                   language_code: locale.language_code)
+    render json: MaterialRepr.base(material, host: request.base_url)
   end
 
   def destroy
@@ -251,8 +236,10 @@ class MaterialsController < ApplicationController
     nil
   end
 
-  def resolve_material_tag! locale, tag_name_raw
-    Tag.find_or_create_by_tag_name!(locale, tag_name_raw, category: :material)
+  def resolve_material_tag! tag_name_raw
+    tag_name = TagName.find_undiscard_or_create_by!(name: tag_name_raw)
+    tag = tag_name.tag
+    tag || Tag.create!(tag_name:, category: :material)
   end
 
   def material_index_needs_tag_name? filters
@@ -266,12 +253,7 @@ class MaterialsController < ApplicationController
   end
 
   def material_index_join_tag_name q
-    q.left_joins(:tag).joins(<<~SQL.squish)
-      LEFT JOIN tag_names
-        ON tag_names.tag_id = tags.id
-       AND tag_names.language_code = 'ja'
-       AND tag_names.primary_flg = TRUE
-    SQL
+    q.left_joins(tag: :tag_name)
   end
 
   def material_index_join_file_blob q
@@ -287,11 +269,9 @@ class MaterialsController < ApplicationController
 
   def apply_material_query q, term
     like = "%#{ ActiveRecord::Base.sanitize_sql_like(term) }%"
-    q.where(<<~SQL.squish, q: like)
-      tag_names.name LIKE :q
-      OR materials.url LIKE :q
-      OR material_file_blobs.filename LIKE :q
-    SQL
+    q.where('tag_names.name LIKE :q OR materials.url LIKE :q OR ' \
+            'material_file_blobs.filename LIKE :q',
+            q: like)
   end
 
   def apply_material_media_kind q, media_kind
@@ -343,9 +323,8 @@ class MaterialsController < ApplicationController
         end
     tags_by_id =
         Tag
-        .joins(:tag_names)
-        .where(id: scope_tag_ids,
-               tag_names: { language_code: 'ja', primary_flg: true })
+        .joins(:tag_name)
+        .where(id: scope_tag_ids)
         .pluck('tags.id', 'tag_names.name', 'tags.category', 'tags.deprecated_at')
         .each_with_object({ }) do |(id, name, category, deprecated_at), hash|
           hash[id] = { id:, name:, category:, deprecated: deprecated_at.present? }

backend/app/controllers/nico_tags_controller.rb

@@ -1,7 +1,5 @@
 class NicoTagsController < ApplicationController
   def index
-    locale = resolve_locale!
-
     name = params[:name].presence
     linked_tag = params[:linked_tag].presence
     link_status = params[:link_status].presence
@@ -17,27 +15,21 @@ class NicoTagsController < ApplicationController
     limit = 1 if limit < 1
 
     post_tag_max_sql =
-        PostExternalTag
-        .select('external_tag_id, MAX(created_at) AS max_created_at')
-        .group('external_tag_id')
+        PostTag
+        .select('tag_id, MAX(created_at) AS max_created_at')
+        .group('tag_id')
         .to_sql
 
-    q =
-        ExternalTag
+    q = Tag.nico_tags
+           .joins(:tag_name)
            .joins("LEFT JOIN (#{ post_tag_max_sql }) post_tag_max " \
-               'ON post_tag_max.external_tag_id = external_tags.id')
-        .includes(linked_tags: { tag_names: :wiki_page })
-    if name
-      q = q.where(('external_tags.name LIKE ? ' +
-                   "OR CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?"),
-                  "%#{ name }%", "%#{ name }")
-    end
-
+                  'ON post_tag_max.tag_id = tags.id')
+           .includes(:tag_name, tag_name: :wiki_page, linked_tags: { tag_name: :wiki_page })
+    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
     if linked_tag
       linked_tag_ids =
         Tag
-          .joins(:tag_names)
-          .where(tag_names: { language_code: 'ja', primary_flg: true })
+        .joins(:tag_name)
         .where('tag_names.name LIKE ?', "%#{ linked_tag }%")
         .pluck(:id)
       linked_nico_tag_ids = NicoTagRelation.where(tag_id: linked_tag_ids).pluck(:nico_tag_id)
@@ -46,7 +38,7 @@ class NicoTagsController < ApplicationController
     if link_status.in?(['linked', 'unlinked'])
       exists_sql =
           'EXISTS (SELECT 1 FROM nico_tag_relations ' \
-          'WHERE nico_tag_relations.nico_tag_id = external_tags.id)'
+          'WHERE nico_tag_relations.nico_tag_id = tags.id)'
       q = link_status == 'linked' ? q.where(exists_sql) : q.where("NOT #{ exists_sql }")
     end
 
@@ -54,68 +46,54 @@ class NicoTagsController < ApplicationController
     sort_sql =
         case order[0]
         when 'name'
-          'external_tags.name'
+          'tag_names.name'
         when 'updated_at'
           'post_tag_max.max_created_at'
         else
-          "external_tags.#{ order[0] }"
+          "tags.#{ order[0] }"
         end
-    tags = q.reselect('external_tags.*',
+    tags = q.reselect('tags.*',
                       Arel.sql('post_tag_max.max_created_at AS recent_post_tag_created_at'))
-            .order(Arel.sql("#{ sort_sql } #{ order[1] }, external_tags.id #{ order[1] }"))
+            .order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
             .limit(limit)
             .offset((page - 1) * limit)
             .to_a
 
     render json: { tags: tags.map { |tag|
-      external_tag_json(tag).merge(
+      TagRepr.base(tag).merge(
           recent_post_tag_created_at: tag.recent_post_tag_created_at,
-          linked_tags: tag.linked_tags.map { |lt|
-            TagRepr.base(lt, language_code: locale.language_code)
-          })
+          linked_tags: tag.linked_tags.map { |lt| TagRepr.base(lt) })
     }, count: }
   end
 
-  def show
-    tag = ExternalTag.find(params[:id])
-
-    render json: external_tag_json(tag)
-  end
-
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
-
     id = params[:id].to_i
 
-    tag = ExternalTag.find(id)
+    tag = Tag.find(id)
+    return render_bad_request('ニコニコ・タグを指定してください．') unless tag.nico?
 
     linked_tag_names = params[:tags].to_s.split
     linked_tags = nil
 
     ApplicationRecord.transaction do
-      linked_tags = Tag.normalise_tags!(locale, linked_tag_names,
-                                        with_tagme: false,
+      linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
                                                           with_no_deerjikist: false)
+      if linked_tags.any? { |t| t.nico? }
+        raise Tag::NicoTagNormalisationError
+      end
 
-      TagVersioning.record_tag_snapshots!(
-          linked_tags,
-          created_by_user: current_user,
-          language_code: locale.language_code)
+      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
 
       tag.linked_tags = linked_tags
       tag.save!
 
-      NicoTagVersionRecorder.record!(external_tag: tag,
-                                     event_type: :update,
-                                     created_by_user: current_user)
+      NicoTagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
     end
 
-    render json: tag.linked_tags.map { |t|
-      TagRepr.base(t, language_code: locale.language_code)
-    }, status: :ok
+    render json: tag.linked_tags.map { |t| TagRepr.base(t) }, status: :ok
   rescue Tag::NicoTagNormalisationError
     render_validation_error fields: { tags: ['ニコニコ・タグ同士は連携できません．'] }
   rescue ActiveRecord::RecordInvalid => e
@@ -124,21 +102,6 @@ class NicoTagsController < ApplicationController
 
   private
 
-  def external_tag_json tag
-    { id: tag.id,
-      name: "#{ tag.platform }:#{ tag.name }",
-      category: 'nico',
-      post_count: tag.post_count,
-      created_at: tag.created_at,
-      updated_at: tag.created_at,
-      deprecated_at: nil,
-      aliases: [],
-      parents: [],
-      has_wiki: false,
-      material_id: nil,
-      has_deerjikists: false }
-  end
-
   def render_nico_tag_form_record_invalid record
     if record.is_a?(TagName) || record.is_a?(Tag)
       render_validation_error fields: { tags: record.errors.full_messages.map { |message|

backend/app/controllers/post_versions_controller.rb

@@ -1,10 +1,7 @@
 class PostVersionsController < ApplicationController
   def index
     post_id = params[:post].presence
-    tag_id = params[:tag].presence&.to_i
-    external_tag_id = params[:external_tag].presence&.to_i
-    return head :bad_request if tag_id && external_tag_id
-
+    tag_id = params[:tag].presence
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
 
@@ -13,6 +10,12 @@ class PostVersionsController < ApplicationController
 
     offset = (page - 1) * limit
 
+    tag_name =
+        if tag_id
+          TagName.joins(:tag).find_by(tag: { id: tag_id })
+        end
+    return render json: { versions: [], count: 0 } if tag_id && tag_name.blank?
+
     q = PostVersion.joins(<<~SQL.squish)
           LEFT JOIN
             post_versions prev
@@ -20,23 +23,17 @@ class PostVersionsController < ApplicationController
               prev.post_id = post_versions.post_id
               AND prev.version_no = post_versions.version_no - 1
         SQL
-        .select('post_versions.*',
-                'prev.title AS prev_title',
-                'prev.url AS prev_url',
-                'prev.thumbnail_base AS prev_thumbnail_base',
-                'prev.tags_json AS prev_tags_json',
+        .select('post_versions.*', 'prev.title AS prev_title', 'prev.url AS prev_url',
+                'prev.thumbnail_base AS prev_thumbnail_base', 'prev.tags AS prev_tags',
                 'prev.video_ms AS prev_video_ms',
                 'prev.original_created_from AS prev_original_created_from',
                 'prev.original_created_before AS prev_original_created_before')
     q = q.where('post_versions.post_id = ?', post_id) if post_id
-    if external_tag_id || (tag_id && !(Tag.exists?(id: tag_id)))
-      q = q.where('JSON_CONTAINS(post_versions.tags_json,' +
-                  "JSON_OBJECT('external_tag_id', #{ external_tag_id || tag_id })) " +
-                  'OR JSON_CONTAINS(prev.tags_json,' +
-                  "JSON_OBJECT('external_tag_id', #{ external_tag_id || tag_id }))")
-    elsif tag_id
-      q = q.where("JSON_CONTAINS(post_versions.tags_json, JSON_OBJECT('tag_id', #{ tag_id })) " +
-                  "OR JSON_CONTAINS(prev.tags_json, JSON_OBJECT('tag_id', #{ tag_id }))")
+    if tag_name
+      escaped = ActiveRecord::Base.sanitize_sql_like(tag_name.name)
+      q = q.where(("CONCAT(' ', post_versions.tags, ' ') LIKE :kw " +
+                   "OR CONCAT(' ', prev.tags, ' ') LIKE :kw"),
+                  kw: "% #{ escaped } %")
     end
 
     count = q.except(:select, :order, :limit, :offset).count
@@ -51,80 +48,59 @@ class PostVersionsController < ApplicationController
   private
 
   def serialise_versions rows
-    rows = rows.to_a
     user_ids = rows.map(&:created_by_user_id).compact.uniq
     users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
-    snapshots = rows.flat_map { |row|
-      [normalise_json(row.tags_json),
-       normalise_json(row.attributes['prev_tags_json']) || []]
-    }
-    external_tag_names = external_tag_names_for(snapshots)
 
     rows.map do |row|
-      cur_tags = snapshot_tag_literals(normalise_json(row.tags_json), external_tag_names)
-      prev_tags = snapshot_tag_literals(
-          normalise_json(row.attributes['prev_tags_json']) || [], external_tag_names)
+      cur_tags = split_tags(row.tags)
+      prev_tags = split_tags(row.attributes['prev_tags'])
 
-      { post_id: row.post_id,
+      {
+        post_id: row.post_id,
         version_no: row.version_no,
         event_type: row.event_type,
-        title: { current: row.title, prev: row.attributes['prev_title'] },
-        url: { current: row.url, prev: row.attributes['prev_url'] },
-        thumbnail: { current: nil, prev: nil },
-        thumbnail_base: { current: row.thumbnail_base,
-                          prev: row.attributes['prev_thumbnail_base'] },
-        video_ms: { current: row.video_ms, prev: row.attributes['prev_video_ms'] },
+        title: {
+          current: row.title,
+          prev: row.attributes['prev_title']
+        },
+        url: {
+          current: row.url,
+          prev: row.attributes['prev_url']
+        },
+        thumbnail: {
+          current: nil,
+          prev: nil
+        },
+        thumbnail_base: {
+          current: row.thumbnail_base,
+          prev: row.attributes['prev_thumbnail_base']
+        },
+        video_ms: {
+          current: row.video_ms,
+          prev: row.attributes['prev_video_ms']
+        },
         tags: build_version_tags(cur_tags, prev_tags),
         original_created_from: {
           current: row.original_created_from&.iso8601,
-            prev: row.attributes['prev_original_created_from']&.iso8601 },
+          prev: row.attributes['prev_original_created_from']&.iso8601
+        },
         original_created_before: {
           current: row.original_created_before&.iso8601,
-            prev: row.attributes['prev_original_created_before']&.iso8601 },
+          prev: row.attributes['prev_original_created_before']&.iso8601
+        },
         created_at: row.created_at.iso8601,
         created_by_user:
           if row.created_by_user_id
-              { id: row.created_by_user_id,
-                name: users_by_id[row.created_by_user_id] }
-            end }
-    end
-  end
-
-  def external_tag_names_for snapshots
-    ids = snapshots.flatten.filter_map { _1['external_tag_id'] }.uniq
-    names = ExternalTag.where(id: ids).pluck(:id, :platform, :name).to_h { |id, platform, name|
-      [id, "#{ platform }:#{ name }"]
+            {
+              id: row.created_by_user_id,
+              name: users_by_id[row.created_by_user_id]
             }
-    missing_ids = ids - names.keys
-
-    NicoTagVersion
-        .where(tag_id: missing_ids)
-        .order(:tag_id, version_no: :desc)
-        .pluck(:tag_id, :name)
-        .each { |id, name| names[id] ||= name }
-
-    names
-  end
-
-  def snapshot_tag_literals snapshots, external_tag_names
-    snapshots
-        .filter_map { |snapshot|
-          if snapshot.key?('tag_id')
-            [tag_category_order(snapshot['category']),
-             Post.tag_snapshot_literal(snapshot)]
-          elsif external_tag_names[snapshot['external_tag_id']]
-            [6, external_tag_names[snapshot['external_tag_id']]]
           end
       }
-        .sort_by { |order, name| [order, name.downcase] }
-        .map(&:second)
+    end
   end
 
-  def tag_category_order category
-    ['deerjikist', 'meme', 'character', 'general', 'material', 'meta'].index(category) || 6
-  end
-
-  def build_version_tags cur_tags, prev_tags
+  def build_version_tags(cur_tags, prev_tags)
     (cur_tags | prev_tags).map do |name|
       type =
         if cur_tags.include?(name) && prev_tags.include?(name)
@@ -135,7 +111,14 @@ class PostVersionsController < ApplicationController
           'removed'
         end
 
-      { name:, type: }
+      {
+        name:,
+        type:
+      }
     end
   end
+
+  def split_tags(tags)
+    tags.to_s.split(/\s+/).reject(&:blank?)
+  end
 end

backend/app/controllers/posts_controller.rb

@@ -7,8 +7,6 @@ class PostsController < ApplicationController
   end
 
   def index
-    locale = resolve_locale!
-
     url = params[:url].presence
     title = params[:title].presence
     original_created_from = params[:original_created_from].presence
@@ -38,8 +36,8 @@ class PostsController < ApplicationController
     offset = (page - 1) * limit
 
     pt_max_sql =
-        PostVersion
-        .select('post_id, MAX(created_at) AS max_updated_at')
+        PostTag
+        .select('post_id, MAX(updated_at) AS max_updated_at')
         .group('post_id')
         .to_sql
 
@@ -48,12 +46,13 @@ class PostsController < ApplicationController
         'COALESCE(pt_max.max_updated_at, posts.updated_at))'
 
     q =
-        filtered_posts(locale)
+        filtered_posts
         .joins("LEFT JOIN (#{ pt_max_sql }) pt_max ON pt_max.post_id = posts.id")
         .reselect('posts.*', Arel.sql("#{ updated_at_all_sql } AS updated_at_all"))
-        .preload(:external_tags, :uploaded_user, :parents, :children,
-                 post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_names: :wiki_page }] }])
+        .preload(:uploaded_user, :parents, :children,
+                 active_post_tags: [:sections,
+                                    { tag: [:deerjikists, :materials,
+                                            { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -92,8 +91,7 @@ class PostsController < ApplicationController
     q = q.except(:select, :order)
 
     render json: { posts: posts.map { |post|
-      PostRepr.base(post, language_code: locale.language_code)
-              .merge(updated_at: post.updated_at_all).tap do |json|
+      PostRepr.base(post).merge(updated_at: post.updated_at_all).tap do |json|
         json['thumbnail'] =
             if post.thumbnail.attached?
               rails_storage_proxy_url(post.thumbnail, only_path: false)
@@ -105,19 +103,16 @@ class PostsController < ApplicationController
   end
 
   def random
-    locale = resolve_locale!
-
-    post =
-        filtered_posts(locale)
-        .preload(:uploaded_user, :parents, :children,
-                 post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                { tag_names: :wiki_page }] }])
+    post = filtered_posts.preload(:uploaded_user, :parents, :children,
+                                  active_post_tags: [:sections,
+                                                     { tag: [:deerjikists, :materials,
+                                                             { tag_name: :wiki_page }] }])
                          .with_attached_thumbnail
                          .order('RAND()')
                          .first
     return head :not_found unless post
 
-    render json: PostRepr.base(post, current_user, language_code: locale.language_code)
+    render json: PostRepr.base(post, current_user)
   end
 
   def metadata
@@ -192,13 +187,12 @@ class PostsController < ApplicationController
   end
 
   def show
-    locale = resolve_locale!
-
     post =
         Post
         .includes(:uploaded_user, :parents, :children,
-                  post_tags: [:sections, { tag: [:deerjikists, :materials,
-                                                 { tag_names: :wiki_page }] }])
+                  active_post_tags: [:sections,
+                                     { tag: [:deerjikists, :materials,
+                                             { tag_name: :wiki_page }] }])
         .with_attached_thumbnail
         .find_by(id: params[:id])
     return head :not_found unless post
@@ -212,21 +206,18 @@ class PostsController < ApplicationController
                                  parent_posts:,
                                  child_posts:,
                                  sibling_posts:,
-                                 related:,
-                                 language_code: locale.language_code)
-                         .merge(tags: build_tag_tree_for(post, locale.language_code))
+                                 related:)
+                         .merge(tags: build_tag_tree_for(post))
   end
 
   def create
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
-
     preflight = PostCreatePreflight.new(
         attributes: post_create_attributes,
         thumbnail: params[:thumbnail],
-        host: request.base_url).run(locale)
+        host: request.base_url).run
     return render json: dry_run_json(preflight) if bool?(:dry)
     if preflight[:existing_post_id].present?
       post = Post.new(url: preflight[:url])
@@ -252,10 +243,10 @@ class PostsController < ApplicationController
                                    :post_tag_specs,
                                    :tag_sections,
                                    :normalised_parent_post_ids).symbolize_keys).merge(
-                               thumbnail: params[:thumbnail])).create!(locale)
+                               thumbnail: params[:thumbnail])).create!
 
     post.reload
-    render json: PostRepr.base(post, language_code: locale.language_code), status: :created
+    render json: PostRepr.base(post), status: :created
   rescue PostCreatePreflight::ValidationFailed => e
     render_validation_error fields: e.fields, base: e.base_errors
   rescue Tag::NicoTagNormalisationError
@@ -281,18 +272,13 @@ class PostsController < ApplicationController
     return head :forbidden unless current_user.gte_member?
     return head :unsupported_media_type unless request.content_mime_type == Mime[:multipart_form]
     return head :payload_too_large if request.content_length.to_i > MAX_BULK_REQUEST_BYTES
-
-    locale = resolve_locale!
-
     posts = parse_bulk_posts_manifest
     thumbnails = parse_bulk_thumbnails(posts.length)
-
     result = PostBulkCreator.new(
         actor: current_user,
         posts:,
         thumbnails:,
-        host: request.base_url).run(locale)
-
+        host: request.base_url).run
     render json: result
   rescue JSON::ParserError
     render_bad_request 'posts manifest の JSON が不正です．'
@@ -325,7 +311,6 @@ class PostsController < ApplicationController
     base_version_no = parse_base_version_no
     return render_bad_request('base_version_no は必須です．') if !(force) && !(base_version_no)
 
-    locale = Locale.find_by(code: params[:locale].presence) || Locale.nipponese
     title = params[:title].presence
     tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
@@ -345,10 +330,9 @@ class PostsController < ApplicationController
         base_version = post.post_versions.find_by!(version_no: base_version_no)
 
         base_snapshot = post_snapshot_from_version(base_version)
-        current_snapshot = post_snapshot_from_record(post, locale)
+        current_snapshot = post_snapshot_from_record(post)
       end
-      incoming_snapshot = post_incoming_snapshot(locale:,
-                                                 title:,
+      incoming_snapshot = post_incoming_snapshot(title:,
                                                  original_created_from:,
                                                  original_created_before:,
                                                  tag_names:,
@@ -377,14 +361,14 @@ class PostsController < ApplicationController
             end
           end
 
-      apply_post_snapshot!(locale, post, snapshot_to_apply)
+      apply_post_snapshot!(post, snapshot_to_apply)
     end
 
     return render json: conflict_json, status: :conflict if conflict_json
 
     post.reload
-    json = PostRepr.base(post, current_user, language_code: locale.language_code)
-    json['tags'] = build_tag_tree_for(post, locale.language_code)
+    json = PostRepr.base(post, current_user)
+    json['tags'] = build_tag_tree_for(post)
     render json:, status: :ok
   rescue Tag::NicoTagNormalisationError
     render_validation_error fields: { tags: ['ニコニコ・タグは直接指定できません．'] }
@@ -400,21 +384,65 @@ class PostsController < ApplicationController
     render_post_form_record_invalid e.record
   end
 
+  def changes
+    id = params[:id].presence
+    tag_id = params[:tag].presence
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
+
+    page = 1 if page < 1
+    limit = 1 if limit < 1
+
+    offset = (page - 1) * limit
+
+    pts = PostTag.with_discarded
+    pts = pts.where(post_id: id) if id.present?
+    pts = pts.where(tag_id:) if tag_id.present?
+    pts = pts.includes(:post, :created_user, :deleted_user,
+                       tag: [:deerjikists, :materials, { tag_name: :wiki_page }])
+
+    events = []
+    pts.each do |pt|
+      tag = TagRepr.base(pt.tag)
+      post = pt.post
+
+      events << Event.new(
+          post:,
+          tag:,
+          user: pt.created_user && { id: pt.created_user.id, name: pt.created_user.name },
+          change_type: 'add',
+          timestamp: pt.created_at)
+
+      if pt.discarded_at
+        events << Event.new(
+            post:,
+            tag:,
+            user: pt.deleted_user && { id: pt.deleted_user.id, name: pt.deleted_user.name },
+            change_type: 'remove',
+            timestamp: pt.discarded_at)
+      end
+    end
+    events.sort_by!(&:timestamp)
+    events.reverse!
+
+    render json: { changes: (events.slice(offset, limit) || []).as_json, count: events.size }
+  end
+
   private
 
-  def filtered_posts locale
+  def filtered_posts
     tag_names = params[:tags].to_s.split
     match_type = params[:match]
     if tag_names.present?
-      filter_posts_by_tags(locale, tag_names, match_type)
+      filter_posts_by_tags(tag_names, match_type)
     else
       Post.all
     end
   end
 
-  def filter_posts_by_tags locale, tag_names, match_type
+  def filter_posts_by_tags tag_names, match_type
     literals = tag_names.map do |raw_name|
-      { name: TagName.canonicalise(locale, raw_name.sub(/\Anot:/i, '')).first,
+      { name: TagName.canonicalise(raw_name.sub(/\Anot:/i, '')).first,
         negative: raw_name.downcase.start_with?('not:') }
     end
 
@@ -422,11 +450,11 @@ class PostsController < ApplicationController
 
     if match_type == 'any'
       literals.reduce(Post.none) do |posts, literal|
-        posts.or(tag_literal_relation(locale, literal[:name], negative: literal[:negative]))
+        posts.or(tag_literal_relation(literal[:name], negative: literal[:negative]))
       end
     else
       literals.reduce(Post.all) do |posts, literal|
-        ids = tagged_post_ids_for(locale, literal[:name])
+        ids = tagged_post_ids_for(literal[:name])
         if literal[:negative]
           posts.where.not(id: ids)
         else
@@ -436,8 +464,8 @@ class PostsController < ApplicationController
     end
   end
 
-  def tag_literal_relation locale, name, negative:
-    ids = tagged_post_ids_for(locale, name)
+  def tag_literal_relation name, negative:
+    ids = tagged_post_ids_for(name)
     if negative
       Post.where.not(id: ids)
     else
@@ -445,20 +473,8 @@ class PostsController < ApplicationController
     end
   end
 
-  def tagged_post_ids_for locale, name
-    posts_by_internal_tags =
-        Post
-        .joins(tags: :tag_names)
-        .where(tag_names: { language_code: locale.language_code, name: })
-        .select(:id)
-
-    posts_by_external_tags =
-        Post
-        .joins(:external_tags)
-        .where("CONCAT(external_tags.platform, ':', external_tags.name) = ?", name)
-
-    (posts_by_internal_tags + posts_by_external_tags).uniq(&:id)
-  end
+  def tagged_post_ids_for(name) =
+      Post.joins(tags: :tag_name).where(tag_names: { name: }).select(:id)
 
   def sync_post_tags! post, desired_tags, sections
     desired_tags.each do |t|
@@ -486,13 +502,13 @@ class PostsController < ApplicationController
       end
     end
 
-    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
-      pt.destroy!
+    PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+      pt.discard_by!(current_user)
     end
   end
 
-  def build_tag_tree_for post, language_code = 'ja'
-    post_tags = post.post_tags.reject { |post_tag| post_tag.tag.deprecated? }
+  def build_tag_tree_for post
+    post_tags = post.active_post_tags.reject { |post_tag| post_tag.tag.deprecated? }
     tags = post_tags.map(&:tag)
     tag_ids = tags.map(&:id)
 
@@ -521,7 +537,7 @@ class PostsController < ApplicationController
       sections = sections_by_tag_id.fetch(tag_id, [])
 
       if path.include?(tag_id)
-        return TagRepr.inline(tag, language_code:).merge(children: [], sections:)
+        return TagRepr.inline(tag).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -533,13 +549,10 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.inline(tag, language_code:).merge(children:, sections:)
+      memo[tag_id] = TagRepr.inline(tag).merge(children:, sections:)
     end
 
-    internal_tags = root_ids.filter_map { |id| build_node.call(id, []) }
-    external_tags =
-        post.external_tags.map { ExternalTagRepr.inline(_1).merge(children: [], sections: []) }
-    internal_tags + external_tags
+    root_ids.filter_map { |id| build_node.call(id, []) }
   end
 
   def sibling_posts_by_parent parent_post_ids
@@ -686,49 +699,43 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_version version
-    version.tags_json
-        .select { _1.key?('tag_id') }
-        .map { Post.tag_snapshot_literal(_1) }
-        .compact
-        .sort
+    version.tags.to_s.split.reject { |name| name.downcase.start_with?('nico:') }.sort
   end
 
-  def post_snapshot_from_record post, locale
+  def post_snapshot_from_record post
     { title: post.title,
       video_ms: post.video_ms,
       original_created_from: snapshot_time(post.original_created_from),
       original_created_before: snapshot_time(post.original_created_before),
-      tag_names: editable_tag_names_from_post(post, locale.language_code),
+      tag_names: editable_tag_names_from_post(post),
       parent_post_ids: post.parent_posts.order(:id).pluck(:id) }
   end
 
-  def editable_tag_names_from_post post, language_code
+  def editable_tag_names_from_post post
     post
         .post_tags
-        .joins(tag: :tag_names)
+        .kept
+        .joins(tag: :tag_name)
+        .merge(Tag.not_nico)
         .merge(Tag.where(deprecated_at: nil))
-        .where(tag_names: { language_code:, primary_flg: true })
-        .includes(:sections, tag: :tag_names)
+        .includes(:sections, tag: :tag_name)
         .order('tag_names.name')
         .map do |post_tag|
-      name = post_tag.tag.name(language_code)
+      name = post_tag.tag.tag_name.name
       sections = post_tag.sections.sort_by(&:begin_ms)
 
       next name if sections.empty?
 
       "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
-    end.compact.sort
+    end
   end
 
-  def post_incoming_snapshot locale:, title:, original_created_from:, original_created_before:,
+  def post_incoming_snapshot title:, original_created_from:, original_created_before:,
                              tag_names:, video_ms_param:, duration_param:, parent_post_ids:
     validate_original_created_values!(original_created_from, original_created_before)
-
-    Tag.normalise_tags!(locale, tag_names,
-                        with_tagme: false,
-                        with_no_deerjikist: false,
-                        deny_deprecated: true,
-                        with_sections: true) => { tags:, sections: }
+    Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
+                                        with_sections: true) =>
+        { tags:, sections: }
 
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
     video_ms = normalise_video_ms(tags, video_ms_param:, duration_param:)
@@ -739,7 +746,7 @@ class PostsController < ApplicationController
       original_created_from: snapshot_time(original_created_from),
       original_created_before: snapshot_time(original_created_before),
       tag_names: tags.uniq(&:id).map { |tag|
-        "#{ tag.name(locale.language_code) }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
+        "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
       }.sort,
       parent_post_ids: parent_post_ids.sort }
   end
@@ -863,7 +870,7 @@ class PostsController < ApplicationController
     (added_by_current & removed_by_me).present? || (removed_by_current & added_by_me).present?
   end
 
-  def apply_post_snapshot! locale, post, snapshot
+  def apply_post_snapshot! post, snapshot
     PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
 
     post.update!(title: snapshot[:title],
@@ -871,13 +878,15 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    Tag.normalise_tags!(locale, snapshot[:tag_names],
-                        with_tagme: false,
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
                                                deny_deprecated: true,
-                        with_sections: true) => { tags:, sections: }
-    TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user,
-                                        language_code: locale.language_code)
+                                               with_sections: true) =>
+        { tags: editable_tags, sections: }
+    TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
 
+    readonly_tags = post.tags.nico.to_a
+
+    tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
 
     post.video_ms = tags.any? { _1.id == Tag.video.id } ? snapshot[:video_ms] : nil

backend/app/controllers/tag_children_controller.rb

@@ -10,6 +10,7 @@ class TagChildrenController < ApplicationController
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
@@ -32,6 +33,7 @@ class TagChildrenController < ApplicationController
 
     parent = Tag.find(parent_id)
     child = Tag.find(child_id)
+    return render_bad_request('ニコニコ・タグの階層は変更できません．') if parent.nico? || child.nico?
 
     ApplicationRecord.transaction do
       TagVersioning.ensure_snapshot!(child, created_by_user: current_user)

backend/app/controllers/tag_versions_controller.rb

@@ -1,6 +1,5 @@
 class TagVersionsController < ApplicationController
   def index
-    locale = resolve_locale!
     tag_id = params[:id].presence
     page = (params[:page].presence || 1).to_i
     limit = (params[:limit].presence || 20).to_i
@@ -19,8 +18,7 @@ class TagVersionsController < ApplicationController
         SQL
       .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
               'prev.deprecated_at AS prev_deprecated_at',
-              'prev.aliases AS prev_aliases', 'prev.names AS prev_names',
-              'prev.parent_tag_ids AS prev_parent_tag_ids')
+              'prev.aliases AS prev_aliases', 'prev.parent_tag_ids AS prev_parent_tag_ids')
     q = q.where('tag_versions.tag_id = ?', tag_id) if tag_id
 
     count = q.except(:select, :order, :limit, :offset).count
@@ -29,20 +27,18 @@ class TagVersionsController < ApplicationController
                 .limit(limit)
                 .offset(offset)
 
-    render json: { versions: serialise_versions(versions, locale.language_code), count: }
+    render json: { versions: serialise_versions(versions), count: }
   end
 
   private
 
-  def serialise_versions rows, language_code
+  def serialise_versions rows
     user_ids = rows.map(&:created_by_user_id).compact.uniq
     users_by_id = User.where(id: user_ids).pluck(:id, :name).to_h
 
     rows.map do |row|
-      current_names = names_for_locale(row.names, language_code)
-      previous_names = names_for_locale(row.attributes['prev_names'], language_code)
-      cur_aliases = current_names.reject { _1['primary_flg'] }.map { _1['name'] }
-      prev_aliases = previous_names.reject { _1['primary_flg'] }.map { _1['name'] }
+      cur_aliases = split_values(row.aliases)
+      prev_aliases = split_values(row.attributes['prev_aliases'])
 
       cur_parent_tag_ids = split_parent_tag_ids(row.parent_tag_ids)
       prev_parent_tag_ids = split_parent_tag_ids(row.attributes['prev_parent_tag_ids'])
@@ -51,23 +47,21 @@ class TagVersionsController < ApplicationController
 
       tags_by_id =
           Tag
-          .includes(:tag_names, :materials, tag_names: :wiki_page)
+          .includes(:tag_name, :materials, { tag_name: :wiki_page })
           .where(id: all_parent_tag_ids)
           .index_by(&:id)
 
       parent_tags =
           build_version_values(cur_parent_tag_ids, prev_parent_tag_ids, key: :tag_id)
           .map do |h|
-            { tag: TagRepr.base(tags_by_id[h[:tag_id]], language_code:),
+            { tag: TagRepr.base(tags_by_id[h[:tag_id]]),
               type: h[:type] }
           end
 
       { tag_id: row.tag_id,
         version_no: row.version_no,
         event_type: row.event_type,
-        names: row.names,
-        name: { current: current_names.find { _1['primary_flg'] }&.fetch('name'),
-                prev: previous_names.find { _1['primary_flg'] }&.fetch('name') },
+        name: { current: row.name, prev: row.attributes['prev_name'] },
         category: { current: row.category, prev: row.attributes['prev_category'] },
         deprecated_at: { current: row.deprecated_at&.iso8601,
                          prev: row.attributes['prev_deprecated_at']&.iso8601 },
@@ -97,12 +91,5 @@ class TagVersionsController < ApplicationController
 
   def split_values(values) = values.to_s.split(/\s+/).reject(&:blank?)
 
-  def names_for_locale names, language_code
-    values = names.is_a?(String) ? JSON.parse(names) : Array(names)
-    values.select { _1['language_code'] == language_code }
-  rescue JSON::ParserError
-    []
-  end
-
   def split_parent_tag_ids(values) = split_values(values).map(&:to_i)
 end

backend/app/controllers/tags_controller.rb

@@ -5,8 +5,6 @@ require 'set'
 
 class TagsController < ApplicationController
   def index
-    locale = resolve_locale!
-
     post_id = params[:post]
 
     name = params[:name].presence
@@ -36,161 +34,49 @@ class TagsController < ApplicationController
 
     offset = (page - 1) * limit
 
-    tags =
+    q =
         if post_id.present?
-          Tag
-              .joins(:posts, :tag_names)
-              .where(tag_names: { language_code: locale.language_code, primary_flg: true },
-                     posts: { id: post_id })
+          Tag.joins(:posts, :tag_name)
         else
-          Tag
-              .joins(:tag_names)
-              .where(tag_names: { language_code: locale.language_code, primary_flg: true })
-        end
-
-    external_tags =
-        if post_id.present?
-          ExternalTag.joins(:posts).where(posts: { id: post_id })
-        else
-          ExternalTag.all
-        end
-
-    if name
-      tags = tags.where('tag_names.name LIKE ?', "%#{ name }%")
-      external_tags =
-          external_tags.where("CONCAT(external_tags.platform, ':', external_tags.name) LIKE ?",
-                              "%#{ name }%")
-    end
-
-    if category == 'nico'
-      tags = tags.none
-    elsif category
-      tags = tags.where(category:)
-      external_tags = external_tags.none
-    end
-
-    if post_count_between[0]
-      tags = tags.where('tags.post_count >= ?', post_count_between[0])
-      external_tags = external_tags.where('external_tags.post_count >= ?', post_count_between[0])
-    end
-
-    if post_count_between[1]
-      tags = tags.where('tags.post_count <= ?', post_count_between[1])
-      external_tags = external_tags.where('external_tags.post_count <= ?', post_count_between[1])
-    end
-
-    if created_between[0]
-      tags = tags.where('tags.created_at >= ?', created_between[0])
-      external_tags = external_tags.where('external_tags.created_at >= ?', created_between[0])
-    end
-
-    if created_between[1]
-      tags = tags.where('tags.created_at <= ?', created_between[1])
-      external_tags = external_tags.where('external_tags.created_at <= ?', created_between[1])
-    end
-
-    if updated_between[0]
-      tags = tags.where('tags.updated_at >= ?', updated_between[0])
-      external_tags = external_tags.where('external_tags.created_at >= ?', updated_between[0])
-    end
-
-    if updated_between[1]
-      tags = tags.where('tags.updated_at <= ?', updated_between[1])
-      external_tags = external_tags.where('external_tags.created_at <= ?', updated_between[1])
+          Tag.joins(:tag_name)
         end
+        .includes(:tag_name, :materials, tag_name: :wiki_page)
+    q = q.where(posts: { id: post_id }) if post_id.present?
 
+    q = q.where('tag_names.name LIKE ?', "%#{ name }%") if name
+    q = q.where(category:) if category
+    q = q.where('tags.post_count >= ?', post_count_between[0]) if post_count_between[0]
+    q = q.where('tags.post_count <= ?', post_count_between[1]) if post_count_between[1]
+    q = q.where('tags.created_at >= ?', created_between[0]) if created_between[0]
+    q = q.where('tags.created_at <= ?', created_between[1]) if created_between[1]
+    q = q.where('tags.updated_at >= ?', updated_between[0]) if updated_between[0]
+    q = q.where('tags.updated_at <= ?', updated_between[1]) if updated_between[1]
     if deprecated_given
-      if deprecated
-        tags = tags.where.not(deprecated_at: nil)
-        external_tags = external_tags.none
-      else
-        tags = tags.where(deprecated_at: nil)
+      q = deprecated ? q.where.not(deprecated_at: nil) : q.where(deprecated_at: nil)
     end
-    end
-
-    tag_sql = tags.select("'tag' AS source",
-                          'tags.id',
-                          'tag_names.name',
-                          'tags.category',
-                          'tags.post_count',
-                          'tags.created_at',
-                          'tags.updated_at',
-                          'tags.deprecated_at').to_sql
-
-    external_tag_sql = external_tags.select(
-        "'external_tag' AS source",
-        'external_tags.id',
-        "CONCAT(external_tags.platform, ':', external_tags.name) AS name",
-        "'nico' AS category",
-        'external_tags.post_count',
-        'external_tags.created_at',
-        'external_tags.created_at AS updated_at',
-        'NULL AS deprecated_at').to_sql
-
-    union_sql = "#{ tag_sql } UNION ALL #{ external_tag_sql }"
 
     sort_sql =
-        if order[0] == 'category'
-          'CASE category ' +
+        case order[0]
+        when 'name'
+          'tag_names.name'
+        when 'category'
+          'CASE tags.category ' +
           "WHEN 'deerjikist' THEN 0 " +
           "WHEN 'meme' THEN 1 " +
           "WHEN 'character' THEN 2 " +
           "WHEN 'general' THEN 3 " +
           "WHEN 'material' THEN 4 " +
           "WHEN 'meta' THEN 5 " +
-          "WHEN 'nico' THEN 6 " +
-          'END'
+          "WHEN 'nico' THEN 6 END"
         else
-          order[0]
+          "tags.#{ order[0] }"
         end
+    tags = q.order(Arel.sql("#{ sort_sql } #{ order[1] }, tags.id #{ order[1] }"))
+            .limit(limit)
+            .offset(offset)
+            .to_a
 
-    connection = ApplicationRecord.connection
-
-    count = connection.select_value(<<~SQL)
-      SELECT
-        COUNT(0)
-      FROM
-        (#{ union_sql }) legacy_tags
-    SQL
-
-    rows = connection.select_all(<<~SQL).to_a
-      SELECT
-        source
-      , id
-      FROM
-        (#{ union_sql }) legacy_tags
-      ORDER BY
-        #{ sort_sql } #{ order[1] }
-      , id #{ order[1] }
-      , source #{ order[1] }
-      LIMIT
-        #{ limit }
-      OFFSET
-        #{ offset }
-    SQL
-
-    tag_ids = rows.filter { _1['source'] == 'tag' }.map { _1['id'] }
-    external_tag_ids = rows.filter { _1['source'] == 'external_tag' }.map { _1['id'] }
-
-    tags_by_id =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
-        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
-               id: tag_ids)
-        .index_by(&:id)
-    external_tags_by_id =
-        ExternalTag
-        .where(id: external_tag_ids)
-        .index_by(&:id)
-
-    render json: { tags: rows.map { |row|
-      if row['source'] == 'tag'
-        TagRepr.base(tags_by_id.fetch(row['id']), language_code: locale.language_code)
-      else
-        external_tag_json(external_tags_by_id.fetch(row['id']))
-      end
-    }, count: }
+    render json: { tags: TagRepr.many(tags), count: q.size }
   end
 
   def with_depth
@@ -198,8 +84,7 @@ class TagsController < ApplicationController
     parent_tag_id = nil if parent_tag_id <= 0
     material_filter = material_filter_param(default: 'any')
 
-    locale = resolve_locale!
-    graph = build_with_depth_graph(material_filter, locale.language_code)
+    graph = build_with_depth_graph(material_filter)
 
     tag_ids =
         if parent_tag_id
@@ -214,223 +99,137 @@ class TagsController < ApplicationController
   end
 
   def autocomplete
-    locale = resolve_locale!
-
     q = params[:q].to_s.strip.sub(/\Anot:/i, '')
-    prefix = "#{ ActiveRecord::Base.sanitize_sql_like(q) }%"
 
     with_nico = bool?(:nico, default: true)
     present_only = bool?(:present, default: true)
 
     alias_rows =
         TagName
-        .where(language_code: locale.language_code, primary_flg: false)
-        .where('name LIKE ?', prefix)
-        .pluck(:tag_id, :name)
+        .where('name LIKE ?', "#{ q }%")
+        .where.not(canonical_id: nil)
+        .pluck(:canonical_id, :name)
 
-    matched_alias_by_tag_id = { }
-    tag_ids = []
-    alias_rows.each do |tag_id, alias_name|
-      tag_ids << tag_id
-      matched_alias_by_tag_id[tag_id] ||= alias_name
+    matched_alias_by_tag_name_id = { }
+    canonical_ids = []
+
+    alias_rows.each do |canonical_id, alias_name|
+      canonical_ids << canonical_id
+      matched_alias_by_tag_name_id[canonical_id] ||= alias_name
     end
 
-    base =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
-        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
-               deprecated_at: nil)
+    base = Tag.joins(:tag_name)
+              .includes(:tag_name, :materials, tag_name: :wiki_page)
+              .where(deprecated_at: nil)
     base = base.where('tags.post_count > 0') if present_only
 
-    canonical_hit = base.where('tag_names.name LIKE ?', prefix)
+    canonical_hit =
+        base
+        .where(((with_nico ? '(tags.category = ? AND tag_names.name LIKE ?) OR ' : '') +
+                'tag_names.name LIKE ?'),
+               *(with_nico ? ['nico', "nico:#{ q }%"] : []), "#{ q }%")
 
-    internal_tags = canonical_hit.or(base.where(id: tag_ids.uniq))
+    tags =
+        if canonical_ids.present?
+          canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
+        else
+          canonical_hit
+        end
 
-    internal_rows =
-        internal_tags
-        .order(Arel.sql('tags.post_count DESC, tag_names.name'))
-        .limit(20)
-        .map { |tag|
-          TagRepr.base(tag, language_code: locale.language_code)
-                 .merge(matched_alias: matched_alias_by_tag_id[tag.id])
+    tags = tags.order(Arel.sql('post_count DESC, tag_names.name')).limit(20).to_a
+
+    render json: tags.map { |tag|
+      TagRepr.base(tag).merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
     }
-
-    return render json: internal_rows unless with_nico
-
-    external_base = ExternalTag.all
-    external_base = external_base.where('post_count > 0') if present_only
-
-    external_rows =
-        external_base
-        .where("CONCAT(platform, ':', name) LIKE ? OR name LIKE ?", prefix, prefix)
-        .order(post_count: :desc, name: :asc)
-        .limit(20)
-        .map { external_tag_json(_1) }
-
-    rows =
-    (internal_rows + external_rows)
-        .sort_by { |row| [-row['post_count'], row['name'] || row[:name]] }
-        .first(20)
-
-    render json: rows
   end
 
   def show
-    locale = resolve_locale!
-
-    tag =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
-        .find_by(id: params[:id],
-                 tag_names: { language_code: locale.language_code, primary_flg: true })
-    return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
-
-    external_tag = ExternalTag.find_by(id: params[:id])
-    return render json: ExternalTagRepr.base(external_tag) if external_tag
-
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    if tag
+      render json: TagRepr.base(tag)
+    else
       head :not_found
     end
+  end
 
   def show_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
 
-    locale = resolve_locale!
-
-    tag =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
-        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
-    return render json: TagRepr.base(tag, language_code: locale.language_code) if tag
-
-    platform, external_name = name.split(':', 2)
-    return head :not_found unless external_name
-
-    external_tag = ExternalTag.find_by(platform:, name: external_name)
-    return head :not_found unless external_tag
-
-    render json: ExternalTagRepr.base(external_tag)
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
+    if tag
+      render json: TagRepr.base(tag)
+    else
+      head :not_found
+    end
   end
 
   def deerjikists
-    locale = resolve_locale!
-
-    tag = 
-        Tag.joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
-        .find_by(id: params[:id],
-                 tag_names: { language_code: locale.language_code, primary_flg: true })
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
     return head :not_found unless tag
 
-    render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
-                   deerjikists: DeerjikistRepr.many(
-                       tag.deerjikists,
-                       language_code: locale.language_code) }
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
   end
 
   def deerjikists_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
 
-    locale = resolve_locale!
-
-    tag =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
-        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
     return head :not_found unless tag
 
-    render json: { tag: TagRepr.base(tag, language_code: locale.language_code),
-                   deerjikists: DeerjikistRepr.many(
-                       tag.deerjikists,
-                       language_code: locale.language_code) }
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
   end
 
   def update_deerjikists
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
-
-    tag =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, tag_names: :wiki_page)
-        .find_by(id: params[:id],
-                 tag_names: { language_code: locale.language_code, primary_flg: true })
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
     return head :not_found unless tag
 
-    rows = normalise_deerjikist_rows(tag)
-    return if performed?
-
     ApplicationRecord.transaction do
-      tag.lock!
-
-      requested_keys = rows.map { |row| [row[:platform], row[:code]] }.uniq
-      row_indexes_by_key = rows_by_key(rows)
-      locked_deerjikists = lock_deerjikists_for_tag_update(tag.id, requested_keys)
-      current_deerjikists = locked_deerjikists.filter { |deerjikist|
-        deerjikist.tag_id == tag.id
-      }
-      requested_deerjikists = locked_deerjikists.filter { |deerjikist|
-        row_indexes_by_key.key?([deerjikist.platform, deerjikist.code])
-      }
-
-      render_deerjikist_conflicts(locale, requested_deerjikists, row_indexes_by_key, tag)
-      raise ActiveRecord::Rollback if performed?
-
-      requested_keys_set = requested_keys.to_set
-      current_deerjikists.each do |deerjikist|
-        key = [deerjikist.platform, deerjikist.code]
-        deerjikist.destroy! unless requested_keys_set.include?(key)
-      end
-
-      existing_keys = requested_deerjikists.to_h { |deerjikist|
-        [[deerjikist.platform, deerjikist.code], true]
-      }
-      requested_keys.each do |platform, code|
-        next if existing_keys[[platform, code]]
-
-        deerjikist = Deerjikist.new(platform:, code:, tag:)
-        row_index = row_indexes_by_key[[platform, code]].first
-        begin
-          render_deerjikist_form_record_invalid(deerjikist, row_index) unless deerjikist.save
-        rescue ActiveRecord::RecordNotUnique
-          conflicts = lock_deerjikists_for_tag_update(tag.id, [[platform, code]])
-          render_deerjikist_conflicts(locale, conflicts, row_indexes_by_key, tag)
-        end
+      tag.deerjikists = []
+      params[:_json].each.with_index do |item, i|
+        platform = item[:platform]
+        code = normalise_deerjikist_code(platform, item[:code])
+        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
+        deerjikist.tag = tag
+        render_deerjikist_form_record_invalid(deerjikist, i) unless deerjikist.save
         raise ActiveRecord::Rollback if performed?
       end
     end
 
     return if performed?
 
-    render json: DeerjikistRepr.many(tag.reload.deerjikists,
-                                     language_code: locale.language_code)
+    render json: DeerjikistRepr.many(tag.reload.deerjikists)
   end
 
   def materials_by_name
     name = params[:name].to_s.strip
     return render_bad_request('name は必須です．') if name.blank?
-
-    locale = resolve_locale!
-
     material_filter = material_filter_param(default: 'any')
 
-    tag =
-        Tag
-        .joins(:tag_names)
-        .includes(:tag_names, :materials, tag_names: :wiki_page)
-        .find_by(tag_names: { name:, language_code: locale.language_code, primary_flg: true })
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, :materials, tag_name: :wiki_page)
+             .find_by(tag_names: { name: })
     return head :not_found unless tag
 
-    graph = build_with_depth_graph(material_filter, locale.language_code)
+    graph = build_with_depth_graph(material_filter)
 
-    render json: build_tag_children(tag, graph:, language_code: locale.language_code)
+    render json: build_tag_children(tag, graph:)
   end
 
   def update_all
@@ -446,38 +245,39 @@ class TagsController < ApplicationController
     return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
     return render_unprocessable_entity '廃止状態は必須です．', field: :deprecated unless params.key?(:deprecated)
 
-    locale = resolve_locale!
-
-    return unless validate_tag_rename(locale, tag, name)
+    return unless validate_tag_rename(tag, name)
 
     alias_names = params[:aliases].to_s.split.uniq
     parent_names = params[:parent_tags].to_s.split.uniq
     deprecated = bool?(:deprecated)
 
-    if category == 'nico'
+    if tag.nico? && deprecated
+      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
+    end
+
+    if tag.nico? || category == 'nico'
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
 
     ApplicationRecord.transaction do
-      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user,
-                                     language_code: locale.language_code)
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
 
-      old_name = tag.name(locale.language_code)
+      old_name = tag.name
       name_changed = name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
+      wiki_page = tag.tag_name.wiki_page if name_changed
 
       if tag.deprecated? == deprecated
         tag.update!(category:)
       else
         tag.update!(category:, deprecated_at: deprecated ? Time.current : nil)
       end
-      rename_tag_name!(locale, tag, name) if name_changed
+      rename_tag_name!(tag, name) if name_changed
 
-      alias_names << old_name if name_changed && old_name.present?
+      alias_names << old_name if name_changed
       alias_names.delete(name)
 
-      update_aliases!(locale, tag, alias_names)
-      update_parent_tags!(locale, tag, parent_names)
+      update_aliases!(tag, alias_names)
+      update_parent_tags!(tag, parent_names)
 
       tag.reload
 
@@ -485,20 +285,17 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
           name_changed:,
           wiki_page:)
     end
 
-    render json: TagRepr.base(tag.reload, language_code: locale.language_code)
+    render json: TagRepr.base(tag.reload)
   end
 
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    locale = resolve_locale!
-
     name = params[:name].presence
     category = params[:category].presence
     deprecated_given = params.key?(:deprecated)
@@ -506,21 +303,24 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    return unless validate_tag_rename(locale, tag, name)
+    if tag.nico? && deprecated_given && deprecated
+      return render_unprocessable_entity 'ニコタグは廃止できません．', field: :deprecated
+    end
 
-    if category.present? && category == 'nico'
+    return unless validate_tag_rename(tag, name)
+
+    if tag.nico? || (category.present? && category == 'nico')
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
     end
 
     ApplicationRecord.transaction do
-      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user,
-                                     language_code: locale.language_code)
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
 
-      old_name = tag.name(locale.language_code)
+      old_name = tag.name
       name_changed = name.present? && name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
+      wiki_page = tag.tag_name.wiki_page if name_changed
 
-      rename_tag_name!(locale, tag, name) if name_changed
+      rename_tag_name!(tag, name) if name_changed
       tag.update!(category:) if category.present?
       if deprecated_given && tag.deprecated? != deprecated
         tag.update!(deprecated_at: deprecated ? Time.current : nil)
@@ -532,12 +332,11 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
           name_changed:,
           wiki_page:)
     end
 
-    render json: TagRepr.base(tag.reload, language_code: locale.language_code)
+    render json: TagRepr.base(tag.reload)
   end
 
   private
@@ -549,7 +348,7 @@ class TagsController < ApplicationController
     value
   end
 
-  def build_with_depth_graph material_filter, language_code
+  def build_with_depth_graph material_filter
     children_by_parent_id = Hash.new { |h, k| h[k] = [] }
     parent_ids_by_child_id = Hash.new { |h, k| h[k] = [] }
 
@@ -564,11 +363,8 @@ class TagsController < ApplicationController
 
     material_tag_ids = Material.unscoped.kept.where.not(tag_id: nil).distinct.pluck(:tag_id).to_set
 
-    tags_by_id =
-        Tag
-        .joins(:tag_names)
-        .where(id: tag_ids,
-               tag_names: { language_code:, primary_flg: true })
+    tags_by_id = Tag.joins(:tag_name)
+                    .where(id: tag_ids)
                     .pluck('tags.id', 'tag_names.name', 'tags.category', 'tags.deprecated_at')
                     .each_with_object({ }) do |(id, name, category, deprecated_at), h|
       h[id] = { name:, category:, deprecated: deprecated_at.present?,
@@ -702,33 +498,34 @@ class TagsController < ApplicationController
       children: [] }
   end
 
-  def build_tag_children tag, graph: nil, language_code: 'ja'
+  def build_tag_children tag, graph: nil
     material = tag.materials.first
     tag_graph = graph && graph[:tags_by_id][tag.id]
     material =
         nil if tag_graph && !with_depth_visible_tag?(tag_graph, graph[:material_filter])
 
-    children = tag.children.sort_by { _1.name(language_code) }
+    children = tag.children.sort_by(&:name)
     if graph
       children = children.filter { |child_tag| visible_subtree?(child_tag.id, graph) }
     end
 
-    TagRepr.base(tag, language_code:).merge(
-        children: children.map { build_tag_children(_1, graph:, language_code:) },
+    TagRepr.base(tag).merge(
+        children: children.map { build_tag_children(_1, graph:) },
         has_material: tag_graph ? tag_graph[:has_material] : material.present?,
-        material: material && MaterialRepr.base(
-            material,
-            host: request.base_url,
-            language_code:))
+        material: material && MaterialRepr.base(material, host: request.base_url))
   end
 
-  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja',
-                          name_changed: false, wiki_page: nil
-    TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
+  def record_tag_version! tag, event_type:, created_by_user:, name_changed: false, wiki_page: nil
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+      return
+    end
+
+    TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
 
     return unless name_changed
 
-    wiki_page ||= tag.tag_name('ja')&.wiki_page
+    wiki_page ||= tag.tag_name.wiki_page
     return unless wiki_page&.wiki_versions&.exists?
 
     WikiVersionRecorder.record!(
@@ -737,134 +534,109 @@ class TagsController < ApplicationController
         created_by_user:)
   end
 
-  def validate_tag_rename locale, tag, name
-    return true if name.blank? || name == tag.name(locale.language_code)
+  def validate_tag_rename tag, name
+    return true if name.blank? || name == tag.name
 
-    system_tag_names = ['タグ希望', 'bot操作', 'ニジラー情報不詳', '動画', 'ニコニコ']
-    if TagName.exists?(tag_id: tag.id,
-                       language_code: 'ja',
-                       primary_flg: true,
-                       name: system_tag_names)
+    if tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
       render_unprocessable_entity 'システム・タグの名称は変更できません．', field: :name
       return false
     end
 
-    target_tag_name = TagName.find_by(language_code: locale.language_code, name:)
-    return true unless target_tag_name&.primary_flg
+    target_tag_name = TagName.with_discarded.find_by(name:)
+    return true if target_tag_name.nil?
+    return true if target_tag_name.canonical_id?
 
     render_unprocessable_entity 'その名前は既に使はれてゐます．', field: :name
     false
   end
 
-  def rename_tag_name! locale, tag, name
-    return if name == tag.name(locale.language_code)
+  def rename_tag_name! tag, name
+    return if name == tag.name
 
-    current_tag_name = tag.tag_name(locale.language_code)
-    target_tag_name = TagName.find_by(language_code: locale.language_code, name:)
+    current_tag_name = tag.tag_name
+    target_tag_name = TagName.with_discarded.find_by(name:)
 
-    unless target_tag_name
-      if current_tag_name
+    if target_tag_name.nil?
       current_tag_name.update!(name:)
-      else
-        current_tag_name = TagName.create!(
-            tag:,
-            language_code: locale.language_code,
-            script_code: locale.script_code,
-            name:,
-            primary_flg: true)
-        tag.association(:tag_names).reset
-      end
       return
     end
 
-    promote_tag_alias!(tag, current_tag_name:, promoted_tag_name: target_tag_name)
+    promote_tag_alias!(
+        tag,
+        current_tag_name:,
+        promoted_tag_name: target_tag_name)
   end
 
   def promote_tag_alias! tag, current_tag_name:, promoted_tag_name:
-    old_owner_tag = promoted_tag_name.tag
+    old_owner_tag = promoted_tag_name.canonical&.tag
 
     if old_owner_tag && old_owner_tag != tag
       TagVersioning.ensure_snapshot!(old_owner_tag, created_by_user: current_user)
     end
 
-    current_tag_name.wiki_page&.update!(tag_name_id: promoted_tag_name.id)
-    current_tag_name.association(:wiki_page).reset
+    promoted_tag_name.undiscard! if promoted_tag_name.discarded?
+    promoted_tag_name.update!(canonical: nil)
 
-    current_tag_name.update!(canonical_id: promoted_tag_name.id, primary_flg: false)
-    promoted_tag_name.update!(tag:, canonical_id: nil, primary_flg: true)
-
-    TagName.where(tag:,
-                  language_code: current_tag_name.language_code,
-                  primary_flg: false)
+    TagName.with_discarded
+           .where(canonical_id: current_tag_name.id)
            .where.not(id: promoted_tag_name.id)
            .find_each do |alias_tag_name|
-      alias_tag_name.update!(canonical_id: promoted_tag_name.id, primary_flg: false)
+      alias_tag_name.update!(canonical: promoted_tag_name)
     end
 
-    tag.update!(tag_name_id: promoted_tag_name.id)
+    current_tag_name.wiki_page&.update!(tag_name: promoted_tag_name)
+    tag.update!(tag_name: promoted_tag_name)
     current_tag_name.association(:wiki_page).reset
     current_tag_name.association(:tag).reset
-    current_tag_name.reload.update!(canonical_id: promoted_tag_name.id, primary_flg: false)
+    current_tag_name.reload.update!(canonical: promoted_tag_name)
 
     return unless old_owner_tag && old_owner_tag != tag
 
-    record_tag_version!(old_owner_tag.reload, event_type: :update,
-                        created_by_user: current_user,
-                        language_code: current_tag_name.language_code)
+    record_tag_version!(old_owner_tag.reload, event_type: :update, created_by_user: current_user)
   end
 
-  def update_aliases! locale, tag, alias_names
+  def update_aliases! tag, alias_names
     alias_names = alias_names.uniq
 
     affected_tags = [tag]
 
-    primary_tag_name = TagName.find_by!(tag:,
-                                        language_code: locale.language_code,
-                                        primary_flg: true)
-    current_aliases = tag.tag_names.where(language_code: locale.language_code,
-                                          primary_flg: false).to_a
+    current_aliases = tag.tag_name.aliases.to_a
 
     current_aliases.each do |alias_tag_name|
       next if alias_names.include?(alias_tag_name.name)
 
-      affected_tags << alias_tag_name.tag
+      affected_tags << alias_tag_name.canonical&.tag
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_by(language_code: locale.language_code, name: alias_name)
-      affected_tags << alias_tag_name&.tag
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      affected_tags << alias_tag_name.canonical&.tag
     end
 
     affected_tags.compact.uniq.each do |affected_tag|
-      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user,
-                                     language_code: locale.language_code)
+      TagVersioning.ensure_snapshot!(affected_tag, created_by_user: current_user)
     end
 
     current_aliases.each do |alias_tag_name|
       next if alias_names.include?(alias_tag_name.name)
 
-      alias_tag_name.update!(canonical_id: nil, tag_id: nil)
+      alias_tag_name.update!(canonical: nil)
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_or_initialize_by(
-          language_code: locale.language_code,
-          name: alias_name)
-      alias_tag_name.script_code = locale.script_code
-      alias_tag_name.update!(tag:, primary_flg: false, canonical_id: primary_tag_name.id)
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
+      alias_tag_name.update!(canonical: tag.tag_name)
     end
 
     affected_tags.compact.uniq.each do |affected_tag|
-      record_tag_version!(affected_tag, event_type: :update,
-                          created_by_user: current_user,
-                          language_code: locale.language_code)
+      record_tag_version!(affected_tag, event_type: :update, created_by_user: current_user)
     end
   end
 
-  def update_parent_tags! locale, tag, parent_names
-    parent_tags = Tag.normalise_tags!(locale, parent_names,
-                                      with_tagme: false,
-                                      with_no_deerjikist: false)
+  def update_parent_tags! tag, parent_names
+    parent_tags = Tag.normalise_tags!(parent_names, with_tagme: false,
+                                                    with_no_deerjikist: false,
+                                                    deny_nico: true)
 
     old_parent_tags = tag.parents.to_a
 
@@ -881,7 +653,6 @@ class TagsController < ApplicationController
   end
 
   def normalise_deerjikist_code platform, code
-    code = code.to_s
     return code if platform != 'youtube' || code[0] != '@'
 
     url = "https://www.youtube.com/#{ code }"
@@ -898,84 +669,6 @@ class TagsController < ApplicationController
     nil
   end
 
-  def normalise_deerjikist_rows tag
-    rows = []
-
-    params[:_json].each.with_index do |item, index|
-      platform = item[:platform]
-      unless Deerjikist.platforms.key?(platform)
-        render_deerjikist_platform_invalid(index)
-        return rows
-      end
-
-      code = normalise_deerjikist_code(platform, item[:code])
-      deerjikist = Deerjikist.new(platform:, code:, tag:)
-      unless deerjikist.valid?
-        render_deerjikist_form_record_invalid(deerjikist, index)
-        return rows
-      end
-
-      rows << { index:, platform:, code: }
-    end
-
-    rows
-  end
-
-  def lock_deerjikists_for_tag_update tag_id, keys
-    clauses = ['tag_id = ?']
-    values = [tag_id]
-
-    keys.each do |platform, code|
-      clauses << '(platform = ? AND code = ?)'
-      values << platform << code
-    end
-
-    Deerjikist
-      .where(clauses.join(' OR '), *values)
-      .order(:platform, :code)
-      .lock
-      .to_a
-  end
-
-  def render_deerjikist_conflicts locale, deerjikists, row_indexes_by_key, tag
-    conflicts = deerjikists.filter { |deerjikist| deerjikist.tag_id != tag.id }
-    return if conflicts.empty?
-
-    tag_names_by_id =
-        Tag
-        .joins(:tag_names)
-        .where(tag_names: { language_code: locale.language_code, primary_flg: true },
-               id: conflicts.map(&:tag_id).uniq)
-        .pluck('tags.id', 'tag_names.name')
-        .to_h
-    fields = { }
-
-    conflicts.each do |deerjikist|
-      message = "この情報は既に「#{ tag_names_by_id[deerjikist.tag_id] }」に紐づいてゐます．"
-      row_indexes_by_key[[deerjikist.platform, deerjikist.code]].each do |index|
-        field = :"deerjikists.#{ index }.code"
-        fields[field] ||= []
-        fields[field] << message
-      end
-    end
-
-    render_validation_error fields:
-  end
-
-  def render_deerjikist_platform_invalid index
-    render_validation_error fields: {
-      :"deerjikists.#{ index }.platform" => ['値が不正です．'],
-    }
-  end
-
-  def rows_by_key rows
-    rows.each_with_object({ }) do |row, result|
-      key = [row[:platform], row[:code]]
-      result[key] ||= []
-      result[key] << row[:index]
-    end
-  end
-
   def render_deerjikist_form_record_invalid deerjikist, index
     fields = { }
 
@@ -994,20 +687,4 @@ class TagsController < ApplicationController
 
     render_validation_error fields:
   end
-
-  def external_tag_json tag
-    { 'id' => tag.id,
-      'name' => "#{ tag.platform }:#{ tag.name }",
-      'category' => 'nico',
-      'deprecated_at' => nil,
-      'created_at' => tag.created_at,
-      'updated_at' => tag.created_at,
-      'post_count' => tag.post_count,
-      'matched_alias' => nil,
-      'aliases' => [],
-      'parents' => [],
-      'has_wiki' => false,
-      'material_id' => nil,
-      'has_deerjikists' => false }
-  end
 end

backend/app/controllers/theatre_skip_events_controller.rb

@@ -6,7 +6,7 @@ class TheatreSkipEventsController < ApplicationController
     events =
         TheatreSkipEvent
         .where(theatre_id: params[:theatre_id])
-        .includes(:post, tags: :tag_names)
+        .includes(:post, tags: :tag_name)
         .order(created_at: :desc)
         .limit(limit)
 
@@ -14,7 +14,7 @@ class TheatreSkipEventsController < ApplicationController
       { id: event.id,
         theatre_id: event.theatre_id,
         post: { id: event.post.id, title: event.post.title, url: event.post.url },
-        tags: event.tags.map { |tag| { id: tag.id, name: tag.name('ja') } },
+        tags: event.tags.map { |tag| { id: tag.id, name: tag.name } },
         programme_position: event.programme_position,
         created_at: event.created_at }
     }

backend/app/controllers/wiki_pages_controller.rb

@@ -94,11 +94,7 @@ class WikiPagesController < ApplicationController
     return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
-    tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
-      name.script_code = 'Jpan'
-      name.primary_flg = true
-      name.auto_generated = false
-    end
+    tag_name = TagName.find_undiscard_or_create_by!(name: title)
 
     page =
         Wiki::Commit.create_content!(

backend/app/models/external_tag.rb

@@ -1,24 +0,0 @@
-class ExternalTag < ApplicationRecord
-  enum :platform, nico: 'nico'
-  validates :platform, presence: true, inclusion: { in: ExternalTag.platforms.keys }
-
-  has_many :post_external_tags, dependent: :delete_all
-  has_many :posts, through: :post_external_tags
-
-  has_many :nico_tag_versions, foreign_key: :tag_id, inverse_of: :external_tag
-
-  has_many :nico_tag_relations,
-           foreign_key: :nico_tag_id,
-           inverse_of: :nico_tag,
-           dependent: :destroy
-
-  has_many :linked_tags, through: :nico_tag_relations, source: :tag
-
-  def snapshot_linked_tag_names language_code = 'ja'
-    linked_tags
-        .joins(:tag_names)
-        .where(tag_names: { language_code:, primary_flg: true })
-        .order('tag_names.name')
-        .pluck('tag_names.name')
-  end
-end

backend/app/models/language.rb

@@ -1,3 +0,0 @@
-class Language < ApplicationRecord
-  has_many :locales, foreign_key: :language_code, primary_key: :code
-end

backend/app/models/locale.rb

@@ -1,24 +0,0 @@
-class Locale < ApplicationRecord
-  after_create_commit :generate_tag_names!
-
-  belongs_to :language, foreign_key: :language_code, primary_key: :code
-  belongs_to :script, foreign_key: :script_code, primary_key: :code
-
-  def self.nipponese = Locale.find('ja')
-
-  private
-
-  def generate_tag_names!
-    tag_ids = TagName.where(language_code:, primary_flg: true).pluck(:tag_id)
-    Tag.where.not(id: tag_ids).find_each do
-      TagName.create!(tag_id: _1.id,
-                      language_code:,
-                      name: TagName.generate_name(self, _1, _1.name('ja')),
-                      script_code:,
-                      primary_flg: true,
-                      # TODO: 公証実装したら書く．
-                      # auto_generated: true,
-                      canonical_id: nil)
-    end
-  end
-end

backend/app/models/nico_tag_relation.rb

@@ -1,10 +1,24 @@
 class NicoTagRelation < ApplicationRecord
-  belongs_to :nico_tag,
-             class_name: 'ExternalTag',
-             foreign_key: :nico_tag_id,
-             inverse_of: :nico_tag_relations
-  belongs_to :tag, class_name: 'Tag', foreign_key: :tag_id
+  belongs_to :nico_tag, class_name: 'Tag'
+  belongs_to :tag, class_name: 'Tag'
 
   validates :nico_tag_id, presence: true
   validates :tag_id, presence: true
+
+  validate :nico_tag_must_be_nico
+  validate :tag_mustnt_be_nico
+
+  private
+
+  def nico_tag_must_be_nico
+    if nico_tag && nico_tag.category != 'nico'
+      errors.add :nico_tag_id, 'タグのカテゴリがニコニコである必要があります．'
+    end
+  end
+
+  def tag_mustnt_be_nico
+    if tag && tag.category == 'nico'
+      errors.add :tag_id, '連携先タグのカテゴリはニコニコであってはなりません．'
+    end
+  end
 end

backend/app/models/nico_tag_version.rb

@@ -1,7 +1,7 @@
 class NicoTagVersion < ApplicationRecord
   include VersionRecord
 
-  belongs_to :external_tag, foreign_key: :tag_id, inverse_of: :nico_tag_versions
+  belongs_to :tag
 
   validates :name, presence: true
 end

backend/app/models/post.rb

@@ -55,27 +55,25 @@ class Post < ApplicationRecord
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
-  has_many :tags, through: :post_tags
+  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
+  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
+  has_many :tags, through: :active_post_tags
   has_many :active_tags, -> { where(tags: { deprecated_at: nil }) },
-           through: :post_tags,
-           source: :tag
+           through: :active_post_tags, source: :tag
 
   has_many :user_post_views, dependent: :delete_all
   has_many :post_similarities, dependent: :delete_all
   has_many :post_versions
-
   has_many :gekanator_guessed_games,
            class_name: 'GekanatorGame',
            foreign_key: :guessed_post_id,
            dependent: :delete_all,
            inverse_of: :guessed_post
-
   has_many :gekanator_correct_games,
            class_name: 'GekanatorGame',
            foreign_key: :correct_post_id,
            dependent: :delete_all,
            inverse_of: :correct_post
-
   has_many :gekanator_question_examples, dependent: :delete_all
 
   has_many :parent_post_implications,
@@ -92,9 +90,6 @@ class Post < ApplicationRecord
            inverse_of: :parent_post
   has_many :children, through: :child_post_implications, source: :post
 
-  has_many :post_external_tags, dependent: :destroy
-  has_many :external_tags, through: :post_external_tags
-
   has_one_attached :thumbnail
 
   attribute :version_no, :integer, default: 1
@@ -126,14 +121,14 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def snapshot_tag_names language_code = 'ja'
+  def snapshot_tag_names
     post_tags
-        .joins(tag: :tag_names)
-        .where(tag_names: { language_code:, primary_flg: true })
-        .includes(:sections, tag: :tag_names)
+        .kept
+        .joins(tag: :tag_name)
+        .includes(:sections, tag: :tag_name)
         .order('tag_names.name')
         .map do |post_tag|
-      name = post_tag.tag.name(language_code)
+      name = post_tag.tag.tag_name.name
       sections = post_tag.sections.sort_by(&:begin_ms)
 
       next name if sections.empty?
@@ -142,42 +137,6 @@ class Post < ApplicationRecord
     end
   end
 
-  def self.tag_snapshot_literal tag
-    sections = tag.fetch('sections', []).map do |sec|
-      begin_ms = sec.fetch('begin_ms')
-      end_ms = sec['end_ms']
-
-      "[#{ Post.ms_to_time(begin_ms) }-#{ end_ms ? Post.ms_to_time(end_ms) : '' }]"
-    end
-
-    "#{ tag.fetch('name') }#{ sections.join }"
-  end
-
-  def snapshot_tags_json language_code = 'ja'
-    tag_snapshots =
-        post_tags
-            .joins(tag: :tag_names)
-            .where(tag_names: { language_code:, primary_flg: true })
-            .includes(:sections, tag: :tag_names)
-            .order('tags.id')
-            .map { |pt|
-          { 'tag_id' => pt.tag.id,
-            'version_no' => pt.tag.version_no,
-            'name' => pt.tag.name(language_code),
-            'category' => pt.tag.category,
-            'sections' => pt.sections.sort_by(&:begin_ms).map {
-                            { 'begin_ms' => _1.begin_ms, 'end_ms' => _1.end_ms }
-                          } }
-        }
-
-    external_tag_snapshots =
-        post_external_tags.order(:external_tag_id).map {
-          { 'external_tag_id' => _1.external_tag_id }
-        }
-
-    tag_snapshots + external_tag_snapshots
-  end
-
   def self.section_literal section
     end_ms =
         section.end_ms ? Post.ms_to_time(section.end_ms) : ''

backend/app/models/post_external_tag.rb

@@ -1,4 +0,0 @@
-class PostExternalTag < ApplicationRecord
-  belongs_to :post
-  belongs_to :external_tag, counter_cache: :post_count
-end

backend/app/models/post_tag.rb

@@ -1,7 +1,14 @@
 class PostTag < ApplicationRecord
+  include Discard::Model
+
+  before_destroy do
+    raise ActiveRecord::ReadOnlyRecord, '消さないでください．'
+  end
+
   belongs_to :post
   belongs_to :tag, counter_cache: :post_count
   belongs_to :created_user, class_name: 'User', optional: true
+  belongs_to :deleted_user, class_name: 'User', optional: true
 
   has_many :sections, -> { order(:begin_ms) }, class_name: 'PostTagSection',
                                                foreign_key: [:post_id, :tag_id],
@@ -11,5 +18,18 @@ class PostTag < ApplicationRecord
 
   validates :post_id, presence: true
   validates :tag_id, presence: true
-  validates :post_id, uniqueness: { scope: :tag_id }
+  validates :post_id, uniqueness: {
+      scope: :tag_id,
+      conditions: -> { where(discarded_at: nil) } }
+
+  def discard_by! deleted_user
+    return self if discarded?
+
+    transaction do
+      update!(discarded_at: Time.current, deleted_user:)
+      Tag.where(id: tag_id).update_all('post_count = GREATEST(post_count - 1, 0)')
+    end
+
+    self
+  end
 end

backend/app/models/post_tag_section.rb

@@ -4,7 +4,7 @@ class PostTagSection < ApplicationRecord
   belongs_to :post
   belongs_to :tag
 
-  belongs_to :post_tag, foreign_key: [:post_id, :tag_id],
+  belongs_to :post_tag, -> { kept }, foreign_key: [:post_id, :tag_id],
                                      primary_key: [:post_id, :tag_id],
                                      inverse_of: :sections,
                                      optional: true

backend/app/models/script.rb

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

backend/app/models/tag.rb

@@ -2,6 +2,8 @@ require 'set'
 
 
 class Tag < ApplicationRecord
+  include MyDiscard
+
   class NicoTagNormalisationError < ArgumentError
     ;
   end
@@ -26,12 +28,15 @@ class Tag < ApplicationRecord
   end
 
   has_many :post_tags, inverse_of: :tag
-  has_many :posts, through: :post_tags
+  has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
+  has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
+  has_many :posts, through: :active_post_tags
+
+  has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
+  has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
   has_many :reversed_nico_tag_relations,
-           class_name: 'NicoTagRelation',
-           foreign_key: :tag_id,
-           dependent: :destroy
+           class_name: 'NicoTagRelation', foreign_key: :tag_id, dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
   has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
@@ -49,22 +54,32 @@ class Tag < ApplicationRecord
   has_many :materials
 
   has_many :tag_versions
+  has_many :nico_tag_versions
 
-  has_many :tag_names
+  belongs_to :tag_name
+  delegate :wiki_page, to: :tag_name
 
   attribute :version_no, :integer, default: 1
 
+  delegate :name, to: :tag_name, allow_nil: true
+  validates :tag_name, presence: true
+
   enum :category, deerjikist:  'deerjikist',
                   meme:        'meme',
                   character:   'character',
                   general:     'general',
                   material:    'material',
+                  nico:        'nico',
                   meta:        'meta'
 
   validates :category, presence: true, inclusion: { in: Tag.categories.keys }
 
+  validate :nico_tag_name_must_start_with_nico
+  validate :tag_name_must_be_canonical
   validate :category_must_be_deerjikist_with_deerjikists
-  validate :tag_names_must_be_valid
+  validate :nico_tags_cannot_be_deprecated
+
+  scope :nico_tags, -> { nico }
 
   CATEGORY_PREFIXES = {
       'general:'    => :general,
@@ -78,20 +93,8 @@ class Tag < ApplicationRecord
       'mtr:'        => :material,
       'meta:'       => :meta }.freeze
 
-  SYSTEM_TAG_NAMES = ['タグ希望', 'bot操作', 'ニジラー情報不詳', '動画', 'ニコニコ', 'YouTube'].freeze
-
-  def tag_name language_code
-    if tag_names.loaded?
-      tag_names.find { _1.language_code == language_code && _1.primary_flg }
-    else
-      tag_names.find_by(language_code:, primary_flg: true)
-    end
-  end
-  def name(language_code) = tag_name(language_code)&.name
-  def wiki_page = tag_name('ja')&.wiki_page
-
-  def system?
-    tag_name('ja')&.name.in?(SYSTEM_TAG_NAMES)
+  def name= val
+    (self.tag_name ||= build_tag_name).name = val
   end
 
   def deprecated? = deprecated_at?
@@ -102,20 +105,19 @@ class Tag < ApplicationRecord
 
   def has_deerjikists = deerjikists.loaded? ? deerjikists.any? : deerjikists.exists?
 
-  def self.tagme = find_or_create_by_tag_name!(Locale.nipponese, 'タグ希望', category: :meta)
-  def self.bot = find_or_create_by_tag_name!(Locale.nipponese, 'bot操作', category: :meta)
-  def self.no_deerjikist =
-      find_or_create_by_tag_name!(Locale.nipponese, 'ニジラー情報不詳', category: :meta)
-  def self.video = find_or_create_by_tag_name!(Locale.nipponese, '動画', category: :meta)
-  def self.niconico = find_or_create_by_tag_name!(Locale.nipponese, 'ニコニコ', category: :meta)
-  def self.youtube = find_or_create_by_tag_name!(Locale.nipponese, 'YouTube', category: :meta)
+  def self.tagme = find_or_create_by_tag_name!('タグ希望', category: :meta)
+  def self.bot = find_or_create_by_tag_name!('bot操作', category: :meta)
+  def self.no_deerjikist = find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
+  def self.video = find_or_create_by_tag_name!('動画', category: :meta)
+  def self.niconico = find_or_create_by_tag_name!('ニコニコ', category: :meta)
+  def self.youtube = find_or_create_by_tag_name!('YouTube', category: :meta)
 
-  def self.normalise_tags! locale, tag_names,
-                           with_tagme: true,
+  def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
+                                      deny_nico: true,
                                       deny_deprecated: false,
                                       with_sections: false
-    if tag_names.any? { |n| n.downcase.start_with?('nico:') }
+    if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
     end
 
@@ -141,11 +143,11 @@ class Tag < ApplicationRecord
         raise SectionLiteralParseError.new(raw_name, raw_name)
       end
 
-      name = TagName.canonicalise(locale, name).first
+      name = TagName.canonicalise(name).first
 
-      find_or_create_by_tag_name!(locale, name, category: (cat || :general)).tap do |tag|
+      find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         if deny_deprecated && tag.deprecated?
-          raise DeprecatedTagNormalisationError, [tag.name(locale.language_code)]
+          raise DeprecatedTagNormalisationError, [tag.name]
         end
 
         tag.update!(category: cat) if cat && tag.category != cat
@@ -231,23 +233,13 @@ class Tag < ApplicationRecord
     [left_end_ms, right_end_ms].max
   end
 
-  def self.find_or_create_by_tag_name! locale, name, category:
-    language_code = locale.language_code
-    name = name.to_s.strip
+  def self.find_or_create_by_tag_name! name, category:
+    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
+    tn = tn.canonical if tn.canonical_id?
 
-    tn = TagName.find_or_create_by!(language_code:, name:) do
-      _1.script_code = locale.script_code
-      _1.primary_flg = true
+    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) do |t|
+      t.category = category
     end
-
-    tag = tn.tag
-    return tag if tag
-
-    tag = Tag.create!(tag_name_id: tn.id, category:)
-    tn.update!(tag:)
-    tag.association(:tag_names).reset
-
-    tag
   rescue ActiveRecord::RecordNotUnique
     retry
   end
@@ -267,28 +259,30 @@ class Tag < ApplicationRecord
 
         TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
 
-        source_tag.post_tags.find_each do |source_pt|
+        source_tag.post_tags.kept.find_each do |source_pt|
           post_id = source_pt.post_id
           affected_post_ids << post_id
-          source_pt.destroy!
-          unless PostTag.exists?(post_id:, tag: target_tag)
+          source_pt.discard_by!(created_by_user)
+          unless PostTag.kept.exists?(post_id:, tag: target_tag)
             PostTag.create!(post_id:, tag: target_tag)
           end
         end
 
-        source_tag_name = source_tag.tag_name('ja')
+        source_tag_name = source_tag.tag_name
 
         if source_tag_name.wiki_page.present?
           raise ActiveRecord::RecordInvalid.new(source_tag_name)
         end
 
         TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
-        source_tag.tag_names.update_all(tag_id: target_tag.id, primary_flg: false,
-                                        updated_at: Time.current)
-        source_tag.destroy!
+        source_tag.discard!
 
+        if source_tag.nico?
+          source_tag_name.discard!
+        else
           source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
                                          updated_at: Time.current)
+        end
 
         TagVersioning.record!(target_tag, event_type: :update, created_by_user:)
       end
@@ -299,33 +293,33 @@ class Tag < ApplicationRecord
       end
 
       # 投稿件数を再集計
-      target_tag.update_columns(post_count: PostTag.where(tag: target_tag).count)
+      target_tag.update_columns(post_count: PostTag.kept.where(tag: target_tag).count)
     end
 
     target_tag.reload
   end
 
-  def snapshot_aliases(language_code)
-    tag_names.where(language_code:, primary_flg: false).order(:name).pluck(:name)
-  end
+  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
 
   def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
 
-  def snapshot_linked_tag_names language_code
-    linked_tags
-        .joins(:tag_names)
-        .where(tag_names: { language_code:, primary_flg: true })
-        .order('tag_names.name')
-        .pluck('tag_names.name')
+  def snapshot_linked_tag_names
+    linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
   end
 
   private
 
-  def tag_names_must_be_valid
-    tag_names.each do |tag_name|
-      next if tag_name.valid?
+  def nico_tag_name_must_start_with_nico
+    n = name.to_s
+    if ((nico? && !(n.downcase.start_with?('nico:'))) || 
+        (!(nico?) && n.downcase.start_with?('nico:')))
+      errors.add :name, 'ニコニコ・タグの命名規則に反してゐます．'
+    end
+  end
 
-      tag_name.errors[:name].each { errors.add :name, _1 }
+  def tag_name_must_be_canonical
+    if tag_name&.canonical_id?
+      errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
     end
   end
 
@@ -360,4 +354,10 @@ class Tag < ApplicationRecord
 
     total_s * 1_000 + match[:ms].to_s.ljust(3, '0')[0, 3].to_i
   end
+
+  def nico_tags_cannot_be_deprecated
+    if nico? && deprecated_at.present?
+      errors.add :deprecated_at, 'ニコタグは廃止できません．'
+    end
+  end
 end

backend/app/models/tag_name.rb

@@ -1,54 +1,45 @@
 class TagName < ApplicationRecord
-  belongs_to :language, foreign_key: :language_code, primary_key: :code
-  belongs_to :tag, optional: true
+  include MyDiscard
+
+  has_one :tag
   has_one :wiki_page
 
-  validates :name, presence: true,
-                   length: { maximum: 255 },
-                   uniqueness: { scope: :language_code }
+  belongs_to :canonical, class_name: 'TagName', optional: true
+  has_many :aliases, class_name: 'TagName', foreign_key: :canonical_id
 
+  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
+
+  validate :canonical_must_be_canonical
   validate :alias_name_must_not_have_prefix
-  validate :alias_must_not_have_wiki_page
+  validate :canonical_must_not_be_present_with_tag_or_wiki_page
   validate :name_must_be_sanitised
-  validate :name_mustnt_start_with_nico
 
-  def primary? = primary_flg
-
-  def self.canonicalise locale, names
+  def self.canonicalise names
     names = Array(names).map { |n| n.to_s.strip }.reject(&:blank?)
     return [] if names.blank?
 
-    tns = TagName.where(language_code: locale.language_code, name: names).index_by(&:name)
+    tns = TagName.includes(:canonical).where(name: names).index_by(&:name)
 
-    names.map { |name|
-      tag_name = tns[name]
-      if !tag_name || tag_name.primary?
-        name
-      else
-        TagName.find_by(language_code: locale.language_code,
-                        tag_id: tag_name.tag_id,
-                        primary_flg: true)&.name || name
-      end
-    }.uniq
-  end
-
-  def self.generate_name locale, tag, name
-    # TODO: 言語ごとの自動命名ロジック完成したら書く．
-
-    "Tag_##{ tag.id }"
+    names.map { |name| tns[name]&.canonical&.name || name }.uniq
   end
 
   private
 
+  def canonical_must_be_canonical
+    if canonical&.canonical_id?
+      errors.add :canonical, 'canonical は実体を示す必要があります．'
+    end
+  end
+
   def alias_name_must_not_have_prefix
-    if !(primary?) && name.to_s.include?(':')
+    if canonical_id? && name.to_s.include?(':')
       errors.add :name, 'エーリアス名にプレフィクスを含むことはできません．'
     end
   end
 
-  def alias_must_not_have_wiki_page
-    if !(primary?) && wiki_page
-      errors.add :primary_flg, 'Wiki 参照がある名前はエーリアスになれません．'
+  def canonical_must_not_be_present_with_tag_or_wiki_page
+    if canonical_id? && (tag || wiki_page)
+      errors.add :canonical, 'タグもしくは Wiki の参照がある名前はエーリアスになれません．'
     end
   end
 
@@ -57,10 +48,4 @@ class TagName < ApplicationRecord
       errors.add :name, '名前に使用できない文字が含まれてゐます．'
     end
   end
-
-  def name_mustnt_start_with_nico
-    if name.to_s.downcase.start_with?('nico:')
-      errors.add :name, 'タグの命名規則に反してゐます．'
-    end
-  end
 end

backend/app/models/tag_name_sanitisation_rule.rb

@@ -10,37 +10,29 @@ class TagNameSanitisationRule < ApplicationRecord
   validate :source_pattern_must_be_regexp
 
   class << self
-    def sanitise(name)
+    def sanitise(name) =
         rules.reduce(name.dup) { |name, (pattern, replacement)| name.gsub(pattern, replacement) }
-    end
 
     def apply!
-      Language.find_each do |language|
-        TagName.where(language:).find_each do |tn|
+      TagName.find_each do |tn|
         name = sanitise(tn.name)
         next if name == tn.name
 
         TagName.transaction do
-            existing_tn = TagName.find_by(language:, name:)
+          existing_tn = TagName.find_by(name:)
           if existing_tn
-              unless existing_tn.primary_flg
-                existing_tn = TagName.find_by!(language:,
-                                               tag_id: existing_tn.tag_id,
-                                               primary_flg: true)
-              end
+            existing_tn = existing_tn.canonical || existing_tn
             next if existing_tn.id == tn.id
 
-              existing_tag = existing_tn.tag
-              source_tag = tn.tag
+            existing_tag = Tag.find_by(tag_name_id: existing_tn.id)
+            source_tag = Tag.find_by(tag_name_id: tn.id)
 
             if existing_tag
               Tag.merge_tags!(existing_tag, source_tag) if tn.tag
             elsif source_tag
-                tn.update_columns(tag_id: nil, updated_at: Time.current)
               source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
-                existing_tn.update_columns(tag_id: source_tag.id, updated_at: Time.current)
             end
-              tn.destroy!
+            tn.discard!
 
             next
           end
@@ -50,7 +42,6 @@ class TagNameSanitisationRule < ApplicationRecord
         end
       end
     end
-    end
 
     private
 

backend/app/models/tag_version.rb

@@ -11,6 +11,5 @@ class TagVersion < ApplicationRecord
                     meta: 'meta' }, validate: true
 
   validates :name, presence: true
-  validates :names, presence: true
   validates :category, presence: true
 end

backend/app/representations/deerjikist_repr.rb

@@ -6,12 +6,11 @@ module DeerjikistRepr
 
   module_function
 
-  def base deerjikist, language_code: 'ja'
-    deerjikist.as_json(BASE).merge(
-        tag: deerjikist.tag && TagRepr.base(deerjikist.tag, language_code:))
+  def base deerjikist
+    deerjikist.as_json(BASE)
   end
 
-  def many deerjikists, language_code: 'ja'
-    deerjikists.map { |d| base(d, language_code:) }
+  def many deerjikists
+    deerjikists.map { |d| base(d) }
   end
 end

backend/app/representations/external_tag_repr.rb

@@ -1,20 +0,0 @@
-module ExternalTagRepr
-  module_function
-
-  def base tag
-    { 'id' => tag.id,
-      'name' => "#{ tag.platform }:#{ tag.name }",
-      'category' => 'nico',
-      'post_count' => tag.post_count,
-      'created_at' => tag.created_at,
-      'updated_at' => tag.created_at,
-      'deprecated_at' => nil,
-      'aliases' => [],
-      'parents' => [],
-      'has_wiki' => false,
-      'material_id' => nil,
-      'has_deerjikists' => false }
-  end
-
-  def inline(tag) = base(tag)
-end

backend/app/representations/material_repr.rb

@@ -12,15 +12,14 @@ module MaterialRepr
 
   module_function
 
-  def base material, host:, language_code: 'ja'
+  def base material, host:
     material.as_json(BASE).merge(
-        tag: material.tag && TagRepr.base(material.tag, language_code:),
         file: if material.file.attached?
                 Rails.application.routes.url_helpers.rails_storage_proxy_url(
                     material.file, host:)
               end,
         thumbnail: thumbnail_url(material, host:),
-        thumbnail_fallback_text: thumbnail_fallback_text(material, language_code:),
+        thumbnail_fallback_text: thumbnail_fallback_text(material),
         thumbnail_fallback_kind: thumbnail_fallback_kind(material),
         media_kind: media_kind(material),
         file_byte_size: material.file_byte_size,
@@ -28,11 +27,11 @@ module MaterialRepr
         export_items: export_items(material))
   end
 
-  def many materials, host:, language_code: 'ja'
-    materials.map { |m| base(m, host:, language_code:) }
+  def many materials, host:
+    materials.map { |m| base(m, host:) }
   end
 
-  def list material, host:, language_code: 'ja'
+  def list material, host:
     { id: material.id,
       version_no: material.version_no,
       url: material.url,
@@ -41,9 +40,9 @@ module MaterialRepr
       source_path: material.source_path,
       source_file_id: material.source_file_id,
       normalized_source_key: material.normalized_source_key,
-      tag: compact_tag(material.tag, language_code:),
+      tag: compact_tag(material.tag),
       thumbnail: thumbnail_url(material, host:),
-      thumbnail_fallback_text: thumbnail_fallback_text(material, language_code:),
+      thumbnail_fallback_text: thumbnail_fallback_text(material),
       thumbnail_fallback_kind: thumbnail_fallback_kind(material),
       media_kind: media_kind(material),
       content_type: material.content_type,
@@ -54,8 +53,8 @@ module MaterialRepr
       export_items: export_items(material) }
   end
 
-  def list_many materials, host:, language_code: 'ja'
-    materials.map { |m| list(m, host:, language_code:) }
+  def list_many materials, host:
+    materials.map { |m| list(m, host:) }
   end
 
   def export_paths material
@@ -80,8 +79,8 @@ module MaterialRepr
         material.thumbnail, host:)
   end
 
-  def thumbnail_fallback_text material, language_code:
-    material.tag&.name(language_code) || material.created_at&.strftime('%Y-%m-%d')
+  def thumbnail_fallback_text material
+    material.tag&.name || material.created_at&.strftime('%Y-%m-%d')
   end
 
   def thumbnail_fallback_kind material
@@ -99,11 +98,11 @@ module MaterialRepr
     'file_other'
   end
 
-  def compact_tag tag, language_code:
+  def compact_tag tag
     return nil unless tag
 
     { id: tag.id,
-      name: tag.name(language_code),
+      name: tag.name,
       category: tag.category,
       deprecated_at: tag.deprecated_at }
   end

backend/app/representations/post_repr.rb

@@ -17,23 +17,23 @@ module PostRepr
 
   module_function
 
-  def base post, current_user = nil, host: nil, language_code: 'ja'
+  def base post, current_user = nil, host: nil
     json =
         if host.present?
           common(post, host:)
         else
           common(post)
         end
-    json['tags'] = tag_json(post, language_code:)
+    json['tags'] = tag_json(post)
     json['uploaded_user'] = post.uploaded_user && UserRepr.base(post.uploaded_user)
     json['viewed'] = current_user ? current_user.viewed?(post) : false
     json
   end
 
   def detail post, current_user = nil, parent_posts: [], child_posts: [],
-             sibling_posts: { }, related: [], host: nil, language_code: 'ja'
+             sibling_posts: { }, related: [], host: nil
     if host.present?
-      base(post, current_user, host:, language_code:).merge(
+      base(post, current_user, host:).merge(
           'parent_posts' => cards(parent_posts, host:),
           'child_posts' => cards(child_posts, host:),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -41,7 +41,7 @@ module PostRepr
           },
           'related' => cards(related, host:))
     else
-      base(post, current_user, language_code:).merge(
+      base(post, current_user).merge(
           'parent_posts' => cards(parent_posts),
           'child_posts' => cards(child_posts),
           'sibling_posts' => sibling_posts.transform_keys(&:to_s).transform_values { |posts|
@@ -86,25 +86,16 @@ module PostRepr
                        end)
   end
 
-  def tag_json post, language_code:
-    internal_tags =
+  def tag_json post
     post
-        .post_tags
+        .active_post_tags
         .reject { _1.tag.deprecated? }
-        .sort_by { TagRepr.name_for(_1.tag, language_code) }
+        .sort_by { _1.tag.name }
         .map { |post_tag|
-          TagRepr.inline(post_tag.tag, language_code:).merge(
+      TagRepr.inline(post_tag.tag).merge(
           'children' => [],
           'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
     }
-
-    external_tags =
-        post
-        .external_tags
-        .sort_by { _1.name }
-        .map { ExternalTagRepr.base(_1).merge('children' => [], 'sections' => []) }
-
-    internal_tags + external_tags
   end
 
   def thumbnail_url post, host: nil

backend/app/representations/tag_repr.rb

@@ -3,23 +3,18 @@
 
 module TagRepr
   BASE = { only: [:id, :category, :post_count, :created_at, :updated_at, :deprecated_at],
-           methods: [:has_wiki, :material_id, :has_deerjikists] }.freeze
+           methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
 
   module_function
 
-  def base tag, language_code: 'ja'
-    tag.as_json(BASE).merge(name: name_for(tag, language_code),
-                            aliases: tag.snapshot_aliases(language_code),
-                            parents: tag.parents.map { inline(_1, language_code:) })
+  def base tag
+    tag.as_json(BASE).merge(aliases: tag.snapshot_aliases,
+                            parents: tag.parents.map { _1.as_json(BASE) })
   end
 
-  def inline tag, language_code: 'ja'
-    tag.as_json(BASE).merge(name: name_for(tag, language_code), aliases: [], parents: [])
+  def inline tag
+    tag.as_json(BASE).merge(aliases: [], parents: [])
   end
 
-  def many(tags, language_code: 'ja') = tags.map { |tag| base(tag, language_code:) }
-
-  def name_for tag, language_code
-    tag.name(language_code) || (tag.system? ? tag.name('ja') : nil)
-  end
+  def many(tags) = tags.map { |t| base(t) }
 end

backend/app/services/material_version_recorder.rb

@@ -31,7 +31,7 @@ class MaterialVersionRecorder < VersionRecorder
     { url: @record.url,
       parent: @record.parent,
       tag: @record.tag,
-      tag_name: @record.tag&.name('ja'),
+      tag_name: @record.tag&.name,
       tag_category: @record.tag&.category,
       source_kind: @record.source_kind,
       source_uri: @record.source_uri,

backend/app/services/nico_tag_version_recorder.rb

@@ -1,22 +1,19 @@
 class NicoTagVersionRecorder < VersionRecorder
-  def self.record! external_tag:, event_type:, created_by_user:
-    new(external_tag:, event_type:, created_by_user:).record!
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
   end
 
-  def initialize external_tag:, event_type:, created_by_user:
-    super(record: external_tag, event_type:, created_by_user:)
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
   end
 
   private
 
   def version_class = NicoTagVersion
   def version_association = :nico_tag_versions
-  def record_key = :external_tag
+  def record_key = :tag
 
   def snapshot_attributes
-    { name: "#{ @record.platform }:#{ @record.name }",
-      linked_tags: @record.snapshot_linked_tag_names.join(' ') }
+    { name: @record.name, linked_tags: @record.snapshot_linked_tag_names.join(' ') }
   end
-
-  def tracks_version_no_on_record? = false
 end

backend/app/services/post_bulk_creator.rb

@@ -6,7 +6,7 @@ class PostBulkCreator
     @host = host
   end
 
-  def run locale
+  def run
     results = Array.new(@posts.length)
     mutex = Mutex.new
     next_index = 0
@@ -27,7 +27,7 @@ class PostBulkCreator
                 break if index >= @posts.length
 
                 attributes = @posts[index]
-                results[index] = create_row(locale, actor, attributes, index)
+                results[index] = create_row(actor, attributes, index)
               rescue StandardError => e
                 Rails.logger.error(
                     "post_bulk_creator_worker_failure #{ { error: e.class.name,
@@ -61,12 +61,12 @@ class PostBulkCreator
 
   private
 
-  def create_row locale, actor, attributes, index
+  def create_row actor, attributes, index
     preflight =
         PostCreatePreflight.new(
             attributes: attributes,
             thumbnail: thumbnail_for(index, attributes),
-            host: @host).run(locale)
+            host: @host).run
     if preflight[:existing_post_id].present?
       return {
           status: 'skipped',
@@ -76,7 +76,7 @@ class PostBulkCreator
 
     post = PostCreator.new(
         actor: actor,
-        attributes: normalised_attributes(attributes, preflight, index)).create!(locale)
+        attributes: normalised_attributes(attributes, preflight, index)).create!
     result = {
         status: 'created',
         post: { id: post.id } }

backend/app/services/post_create_plan.rb

@@ -8,19 +8,20 @@ class PostCreatePlan
     @existing_tags_by_name = nil
   end
 
-  def build! locale
-    direct_tag_specs, tag_sections = parse_direct_tag_specs(locale)
-    default_tag_specs = build_default_tag_specs(locale, direct_tag_specs)
+  def build!
+    direct_tag_specs, tag_sections = parse_direct_tag_specs
+    default_tag_specs = build_default_tag_specs(direct_tag_specs)
     snapshot_tag_specs = merge_tag_specs(direct_tag_specs + default_tag_specs)
-    preload_existing_tags_by_name!(locale, snapshot_tag_specs.map { _1[:name] })
-    validate_new_tag_specs!(locale, snapshot_tag_specs)
-    post_tag_specs = expand_parent_tag_specs(locale, snapshot_tag_specs)
+    preload_existing_tags_by_name!(snapshot_tag_specs.map { _1[:name] })
+    validate_new_tag_specs!(snapshot_tag_specs)
+    post_tag_specs = expand_parent_tag_specs(snapshot_tag_specs)
     video_ms = normalise_video_ms(snapshot_tag_specs)
     validate_video_sections!(video_ms, tag_sections)
     parent_post_ids = normalise_parent_post_ids
     validate_parent_post_ids!(parent_post_ids)
 
-    { url: @attributes[:url],
+    {
+        url: @attributes[:url],
         title: @attributes[:title].to_s,
         thumbnail_base: @attributes[:thumbnail_base].presence,
         original_created_from: @attributes[:original_created_from].presence,
@@ -42,16 +43,15 @@ class PostCreatePlan
 
   def tag_names = @attributes[:tags].to_s.split
 
-  def parse_direct_tag_specs locale
+  def parse_direct_tag_specs
     tag_sections = { }
     direct_tag_specs = []
 
     tag_names.each do |raw_name|
-      tag_name, category, sections = parse_raw_tag_name(locale, raw_name)
-      existing_tag = existing_tags_by_name(locale)[tag_name]
-      if existing_tag&.deprecated?
-        raise Tag::DeprecatedTagNormalisationError, [existing_tag.name(locale.language_code)]
-      end
+      tag_name, category, sections = parse_raw_tag_name(raw_name)
+      existing_tag = existing_tags_by_name[tag_name]
+      raise Tag::NicoTagNormalisationError if existing_tag&.nico?
+      raise Tag::DeprecatedTagNormalisationError, [existing_tag.name] if existing_tag&.deprecated?
 
       direct_tag_specs << {
           name: tag_name,
@@ -67,7 +67,7 @@ class PostCreatePlan
     [merge_tag_specs(direct_tag_specs), tag_sections]
   end
 
-  def parse_raw_tag_name locale, raw_name
+  def parse_raw_tag_name raw_name
     name = raw_name.to_s
     prefix, category =
         Tag::CATEGORY_PREFIXES.find {
@@ -76,7 +76,7 @@ class PostCreatePlan
     name = name.sub(/\A#{ prefix }/i, '')
 
     sections = []
-    while match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/)
+    while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
       name = "#{ match[1] }#{ match[4] }"
       next if match[2].empty? && match[3].empty?
 
@@ -89,17 +89,17 @@ class PostCreatePlan
       raise Tag::SectionLiteralParseError.new(raw_name, raw_name)
     end
 
-    [resolved_tag_name(locale, name), category&.to_sym, sections]
+    [resolved_tag_name(name), category&.to_sym, sections]
   end
 
-  def build_default_tag_specs locale, direct_tag_specs
+  def build_default_tag_specs direct_tag_specs
     default_tag_specs = []
     if direct_tag_specs.length < 10 && direct_tag_specs.none? { _1[:name] == TAGME_TAG_NAME }
       default_tag_specs << {
           name: TAGME_TAG_NAME,
           category: :meta }
     end
-    if direct_tag_specs.none? { deerjikist_tag_spec?(locale, _1) }
+    if direct_tag_specs.none? { deerjikist_tag_spec?(_1) }
       default_tag_specs << {
           name: NO_DEERJIKIST_TAG_NAME,
           category: :meta }
@@ -108,18 +108,17 @@ class PostCreatePlan
     default_tag_specs
   end
 
-  def validate_new_tag_specs! locale, specs
+  def validate_new_tag_specs! specs
     Array(specs).each do |spec|
-      next if existing_tags_by_name(locale).key?(spec[:name])
+      next if existing_tags_by_name.key?(spec[:name])
 
-      validate_new_tag_spec!(locale, spec)
+      validate_new_tag_spec!(spec)
     end
   end
 
-  def validate_new_tag_spec! locale, spec
-    tag_name = TagName.new(name: spec[:name], language_code: locale.language_code,
-                           script_code: locale.script_code, primary_flg: true)
-    tag = Tag.new(category: spec[:category])
+  def validate_new_tag_spec! spec
+    tag_name = TagName.new(name: spec[:name])
+    tag = Tag.new(category: spec[:category], tag_name:)
     return if tag_name.valid? && tag.valid?
 
     post = Post.new
@@ -134,22 +133,20 @@ class PostCreatePlan
     raise ActiveRecord::RecordInvalid, post
   end
 
-  def expand_parent_tag_specs locale, snapshot_tag_specs
-    existing_snapshot_tags = snapshot_tag_specs.filter_map do
-      existing_tags_by_name(locale)[_1[:name]]
-    end
+  def expand_parent_tag_specs snapshot_tag_specs
+    existing_snapshot_tags = snapshot_tag_specs.filter_map { existing_tags_by_name[_1[:name]] }
     expanded_parent_specs =
         Tag.expand_parent_tags(existing_snapshot_tags)
            .reject(&:deprecated?)
            .map { |tag|
-             { name: tag.name(locale.language_code),
-               category: tag.category.to_sym }
-        }
+             {
+                 name: tag.name,
+                 category: tag.category.to_sym } }
     merge_tag_specs(snapshot_tag_specs + expanded_parent_specs)
   end
 
   def merge_tag_specs specs
-    specs.each_with_object({ }) { |spec, merged|
+    specs.each_with_object({ }) do |spec, merged|
       merged[spec[:name]] =
           if merged.key?(spec[:name]) && merged[spec[:name]][:category] != :general
             merged[spec[:name]]
@@ -158,40 +155,36 @@ class PostCreatePlan
                 name: spec[:name],
                 category: spec[:category] }
           end
-    }.values.sort_by { _1[:name] }
+    end.values.sort_by { _1[:name] }
   end
 
-  def existing_tags_by_name locale
+  def existing_tags_by_name
     @existing_tags_by_name ||= begin
-      names = tag_names.map { canonical_tag_name_without_sections(locale, _1) }.uniq
-      TagName.where(language_code: locale.language_code, primary_flg: true, name: names)
-             .includes(:tag)
-             .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag }
+      names = tag_names.map { canonical_tag_name_without_sections(_1) }.uniq
+      Tag.joins(:tag_name).where(tag_names: { name: names }).index_by(&:name)
     end
   end
 
-  def preload_existing_tags_by_name! locale, names
+  def preload_existing_tags_by_name! names
     wanted_names = Array(names).map { _1.to_s }.reject(&:blank?).uniq
-    missing_names = wanted_names - existing_tags_by_name(locale).keys
+    missing_names = wanted_names - existing_tags_by_name.keys
     return if missing_names.empty?
 
-    existing_tags_by_name(locale).merge!(
-        TagName.where(language_code: locale.language_code,
-                      primary_flg: true,
-                      name: missing_names)
-               .includes(:tag)
-               .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag })
+    existing_tags_by_name.merge!(
+        Tag.joins(:tag_name)
+           .where(tag_names: { name: missing_names })
+           .index_by(&:name))
   end
 
-  def canonical_tag_name_without_sections locale, raw_name
-    name, = parse_raw_tag_name(locale, raw_name)
+  def canonical_tag_name_without_sections raw_name
+    name, = parse_raw_tag_name(raw_name)
     name
   end
 
-  def deerjikist_tag_spec? locale, spec
+  def deerjikist_tag_spec? spec
     return true if spec[:category] == :deerjikist
 
-    existing_tags_by_name(locale)[spec[:name]]&.deerjikist?
+    existing_tags_by_name[spec[:name]]&.deerjikist?
   end
 
   def normalise_parent_post_ids
@@ -269,12 +262,10 @@ class PostCreatePlan
     end
   end
 
-  def resolved_tag_name locale, name
-    tag_name = TagName.find_by(language_code: locale.language_code, name:)
-    return name if !(tag_name) || tag_name.primary?
+  def resolved_tag_name name
+    tag_name = TagName.includes(:canonical).find_by(name:)
+    return name if tag_name.nil?
 
-    TagName.find_by(language_code: locale.language_code,
-                    tag_id: tag_name.tag_id,
-                    primary_flg: true)&.name || name
+    (tag_name.canonical || tag_name).name
   end
 end

backend/app/services/post_create_preflight.rb

@@ -15,10 +15,9 @@ class PostCreatePreflight
     @host = host
   end
 
-  def run locale
+  def run
     preview = PostImportPreviewer.new.preview_rows(
         rows: [preview_row],
-        locale:,
         fetch_metadata: false).first
     if preview[:existing_post_id].present?
       return {
@@ -54,7 +53,7 @@ class PostCreatePreflight
             original_created_from: preview[:attributes]['original_created_from'],
             original_created_before: preview[:attributes]['original_created_before'],
             duration: preview[:attributes]['duration'],
-            video_ms: preview[:attributes]['video_ms'] }).build!(locale)
+            video_ms: preview[:attributes]['video_ms'] }).build!
 
     {
         url: plan[:url],

backend/app/services/post_creator.rb

@@ -9,7 +9,7 @@ class PostCreator
     @field_warnings = { }
   end
 
-  def create! locale
+  def create!
     thumbnail_attachment = prepare_thumbnail_attachment
     post = Post.new(title: @attributes[:title].presence,
                     url: @attributes[:url],
@@ -21,17 +21,14 @@ class PostCreator
     ApplicationRecord.transaction do
       post.save!
       post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
-      snapshot_tags = planned_snapshot_tags(locale)
-      post_tags = planned_post_tags(locale)
-      sections = planned_sections(locale)
-      TagVersioning.record_tag_snapshots!(
-          snapshot_tags,
-          created_by_user: @actor,
-          language_code: locale.language_code)
-      post.video_ms = planned_video_ms(locale)
+      snapshot_tags = planned_snapshot_tags
+      post_tags = planned_post_tags
+      sections = planned_sections
+      TagVersioning.record_tag_snapshots!(snapshot_tags, created_by_user: @actor)
+      post.video_ms = planned_video_ms
       post.save!
       sync_post_tags!(post, post_tags, sections)
-      sync_parent_posts!(post, planned_parent_post_ids(locale))
+      sync_parent_posts!(post, planned_parent_post_ids)
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
     end
     post
@@ -48,73 +45,69 @@ class PostCreator
         thumbnail_base: @attributes[:thumbnail_base].presence)
   end
 
-  def planned_snapshot_tags(locale) = planned_create_attributes(locale)[:snapshot_tags]
+  def planned_snapshot_tags = planned_create_attributes[:snapshot_tags]
 
-  def planned_post_tags(locale) = planned_create_attributes(locale)[:post_tags]
+  def planned_post_tags = planned_create_attributes[:post_tags]
 
-  def planned_sections(locale) = planned_create_attributes(locale)[:tag_sections]
+  def planned_sections = planned_create_attributes[:tag_sections]
 
-  def planned_parent_post_ids locale
-    planned_create_attributes(locale)[:normalised_parent_post_ids]
+  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
+
+  def planned_video_ms
+    planned_create_attributes[:video_ms]
   end
 
-  def planned_video_ms locale
-    planned_create_attributes(locale)[:video_ms]
-  end
-
-  def planned_create_attributes locale
+  def planned_create_attributes
     @planned_create_attributes ||= begin
       if @attributes.key?(:snapshot_tag_specs)
-        snapshot_tags = materialise_tags(locale, @attributes[:snapshot_tag_specs] || [])
-        post_tags = materialise_tags(locale, @attributes[:post_tag_specs] || [])
+        snapshot_tags = materialise_tags(@attributes[:snapshot_tag_specs] || [])
+        post_tags = materialise_tags(@attributes[:post_tag_specs] || [])
         {
             snapshot_tags: snapshot_tags,
             post_tags: post_tags,
             tag_sections: materialise_sections(
                 @attributes[:tag_sections] || { },
                 snapshot_tags,
-                post_tags,
-                locale),
+                post_tags),
             normalised_parent_post_ids: @attributes[:normalised_parent_post_ids] || [],
             video_ms: @attributes[:video_ms] }
       else
-        build_materialised_plan(locale)
+        build_materialised_plan
       end
     end
   end
 
-  def build_materialised_plan locale
-    plan = PostCreatePlan.new(attributes: @attributes).build!(locale)
-    snapshot_tags = materialise_tags(locale, plan[:snapshot_tag_specs] || [])
-    post_tags = materialise_tags(locale, plan[:post_tag_specs] || [])
+  def build_materialised_plan
+    plan = PostCreatePlan.new(attributes: @attributes).build!
+    snapshot_tags = materialise_tags(plan[:snapshot_tag_specs] || [])
+    post_tags = materialise_tags(plan[:post_tag_specs] || [])
     {
         snapshot_tags: snapshot_tags,
         post_tags: post_tags,
         tag_sections: materialise_sections(
             plan[:tag_sections] || { },
             snapshot_tags,
-            post_tags,
-            locale),
+            post_tags),
         normalised_parent_post_ids: plan[:normalised_parent_post_ids] || [],
         video_ms: plan[:video_ms] }
   end
 
-  def materialise_tags locale, specs
+  def materialise_tags specs
     Array(specs).each_with_object({ }) do |spec, tags|
       name = spec[:name] || spec['name']
       category = spec[:category] || spec['category']
       next if name.blank? || category.blank?
 
-      tag = Tag.find_or_create_by_tag_name!(locale, name, category:)
+      tag = Tag.find_or_create_by_tag_name!(name, category:)
       tag.update!(category:) if tag.category.to_sym != category.to_sym
       tags[name] ||= tag
     end.values
   end
 
-  def materialise_sections sections_by_name, snapshot_tags, post_tags, locale = Locale.nipponese
-    tags_by_name = post_tags.index_by { _1.name(locale.language_code) }
+  def materialise_sections sections_by_name, snapshot_tags, post_tags
+    tags_by_name = post_tags.index_by(&:name)
     snapshot_tags.each do |tag|
-      tags_by_name[tag.name(locale.language_code)] ||= tag
+      tags_by_name[tag.name] ||= tag
     end
 
     sections_by_name.each_with_object({ }) do |(tag_name, ranges), sections|
@@ -128,11 +121,9 @@ class PostCreator
   def sync_post_tags! post, desired_tags, sections
     desired_ids = desired_tags.map(&:id).to_set
     current_ids = post.tags.pluck(:id).to_set
-
     Tag.where(id: desired_ids - current_ids).find_each do |tag|
       PostTag.create_or_find_by!(post:, tag:, created_user: @actor)
     end
-
     PostTagSection.where(post_id: post.id).destroy_all
     sections.each do |tag_id, ranges|
       ranges.each do |begin_ms, end_ms|
@@ -142,9 +133,10 @@ class PostCreator
                                end_ms:)
       end
     end
-
     PostTag.where(post_id: post.id,
-                  tag_id: (current_ids - desired_ids).to_a).destroy_all
+                  tag_id: (current_ids - desired_ids).to_a).kept.find_each do |post_tag|
+      post_tag.discard_by!(@actor)
+    end
   end
 
   def sync_parent_posts! post, ids

backend/app/services/post_import_previewer.rb

@@ -16,7 +16,7 @@ class PostImportPreviewer
   THUMBNAIL_FETCH_WARNING = 'サムネールを取得できませんでした．'.freeze
   METADATA_FETCH_WARNING = '自動取得に失敗しました．'.freeze
 
-  def preview_rows rows:, locale: Locale.nipponese, fetch_metadata: true, metadata_cache: { }
+  def preview_rows rows:, fetch_metadata: true, metadata_cache: { }
     prepared_rows = rows.map { prepare_row(_1) }
     url_counts = prepared_rows.filter_map { _1[:normal_url] }.tally
     existing_posts =
@@ -30,14 +30,13 @@ class PostImportPreviewer
         url_counts)
     known_tags =
         preload_known_tags(
-            locale,
             prepared_rows,
             fetch_metadata,
             metadata_cache,
             existing_posts,
             url_counts)
     prepared_rows.map { |row|
-      preview_row(locale, row,
+      preview_row(row,
                   fetch_metadata:,
                   metadata_cache:,
                   existing_posts:,
@@ -60,7 +59,7 @@ class PostImportPreviewer
     source.merge(url_text: url, normal_url:, url_error: validate_url_safety(normal_url))
   end
 
-  def preview_row locale, row,
+  def preview_row row,
                   fetch_metadata:,
                   metadata_cache:,
                   existing_posts:,
@@ -125,8 +124,7 @@ class PostImportPreviewer
 
     attributes['url'] = url
     validate_basic_data(attributes, validation_errors)
-    validate_preview_tags(locale,
-                          merged_tags(tag_sources, provenance['tags']),
+    validate_preview_tags(merged_tags(tag_sources, provenance['tags']),
                           validation_errors,
                           known_tags)
     validate_parents(attributes['parent_post_ids'], validation_errors, existing_parent_ids)
@@ -348,7 +346,7 @@ class PostImportPreviewer
     { data: { }, warnings: { 'url' => [METADATA_FETCH_WARNING] }, validation_errors: { } }
   end
 
-  def preload_known_tags locale, prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
+  def preload_known_tags prepared_rows, fetch_metadata, metadata_cache, existing_posts, url_counts
     names = prepared_rows.flat_map { |row|
       attributes = initial_attributes(row)
       provenance = initial_provenance(row)
@@ -360,13 +358,15 @@ class PostImportPreviewer
         metadata = metadata_for(row[:normal_url], metadata_cache)
         apply_metadata!(attributes, provenance, tag_sources, metadata[:data])
       end
-      preview_tag_names(locale, merged_tags(tag_sources, provenance['tags']))
+      preview_tag_names(merged_tags(tag_sources, provenance['tags']))
     }.compact.uniq
     return { } if names.empty?
 
-    TagName.where(language_code: locale.language_code, primary_flg: true, name: names)
-           .includes(:tag)
-           .each_with_object({ }) { |tag_name, tags| tags[tag_name.name] = tag_name.tag }
+    Tag.joins(:tag_name)
+      .where(tag_names: { name: names })
+      .includes(:tag_name)
+      .to_a
+      .index_by(&:name)
   end
 
   def preload_parent_ids prepared_rows
@@ -437,21 +437,19 @@ class PostImportPreviewer
     sources['automatic'].to_s
   end
 
-  def preview_tag_names locale, raw
+  def preview_tag_names raw
     names = raw.to_s.split
     return [] if names.empty?
     if names.any? { _1.downcase.start_with?('nico:') }
       return []
     end
 
-    names.map { |name|
-      TagName.canonicalise(locale, name.sub(/\[.*\]\z/, '')).first
-    }
+    names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
   rescue Tag::SectionLiteralParseError
     []
   end
 
-  def validate_preview_tags locale, raw, errors, known_tags
+  def validate_preview_tags raw, errors, known_tags
     names = raw.to_s.split
     return if names.empty?
     if names.any? { _1.downcase.start_with?('nico:') }
@@ -459,11 +457,9 @@ class PostImportPreviewer
       return
     end
 
-    parsed = names.map { |name|
-      TagName.canonicalise(locale, name.sub(/\[.*\]\z/, '')).first
-    }
+    parsed = names.map { |name| TagName.canonicalise(name.sub(/\[.*\]\z/, '')).first }
     existing = parsed.filter_map { known_tags[_1] }
-    deprecated = existing.select(&:deprecated?).map { _1.name(locale.language_code) }
+    deprecated = existing.select(&:deprecated?).map(&:name)
     errors[:tags] = ["廃止済みタグがあります: #{ deprecated.join(' ') }"] if deprecated.present?
   rescue Tag::SectionLiteralParseError
     errors[:tags] = ['タグ区間の記法が不正です．']

backend/app/services/post_metadata_fetcher.rb

@@ -47,9 +47,9 @@ class PostMetadataFetcher
 
     existing_tags =
         Tag
-        .joins(:tag_names)
-        .where(tag_names: { language_code: 'ja', primary_flg: true, name: names })
-        .index_by { _1.name('ja') }
+        .joins(:tag_name)
+        .where(tag_names: { name: names })
+        .index_by(&:name)
 
     names.map { |name|
       tag = existing_tags[name]

backend/app/services/post_version_recorder.rb

@@ -25,7 +25,6 @@ class PostVersionRecorder < VersionRecorder
       thumbnail_base: @record.thumbnail_base,
       video_ms: @record.video_ms,
       tags: @record.snapshot_tag_names.join(' '),
-      tags_json: @record.snapshot_tags_json,
       parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
       original_created_from: @record.original_created_from,
       original_created_before: @record.original_created_before }

backend/app/services/tag_version_recorder.rb

@@ -1,5 +1,5 @@
 class TagVersionRecorder < VersionRecorder
-  def self.record! tag:, event_type:, created_by_user:, **_options
+  def self.record! tag:, event_type:, created_by_user:
     new(tag:, event_type:, created_by_user:).record!
   end
 
@@ -14,25 +14,10 @@ class TagVersionRecorder < VersionRecorder
   def record_key = :tag
 
   def snapshot_attributes
-    names = snapshot_names
-    japanese_names = names.select { _1['language_code'] == 'ja' }
-    compatibility_names = japanese_names.presence || names
-
-    { name: compatibility_names.find { _1['primary_flg'] }['name'],
+    { name: @record.name,
       category: @record.category,
       deprecated_at: @record.deprecated_at,
-      aliases: compatibility_names.reject { _1['primary_flg'] }.map { _1['name'] }.join(' '),
-      names:,
+      aliases: @record.snapshot_aliases.join(' '),
       parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
   end
-
-  def snapshot_names
-    @record.tag_names.order(:language_code, primary_flg: :desc).order(:name).map { |tag_name|
-      { 'language_code' => tag_name.language_code,
-        'name' => tag_name.name,
-        'script_code' => tag_name.script_code,
-        'primary_flg' => tag_name.primary_flg,
-        'auto_generated' => tag_name.auto_generated }
-    }
-  end
 end

backend/app/services/tag_versioning.rb

@@ -1,22 +1,38 @@
 class TagVersioning
-  def self.record! tag, event_type:, created_by_user:, language_code: 'ja'
-    TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
+  def self.record! tag, event_type:, created_by_user:
+    if tag.nico?
+      NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    else
+      TagVersionRecorder.record!(tag:, event_type:, created_by_user:)
+    end
   end
 
-  def self.ensure_snapshot! tag, created_by_user:, language_code: 'ja'
+  def self.ensure_snapshot! tag, created_by_user:
+    if tag.nico?
+      return if tag.nico_tag_versions.exists?
+
+      NicoTagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    else
       return if tag.tag_versions.exists?
 
-    TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:, language_code:)
+      TagVersionRecorder.record!(tag:, event_type: :create, created_by_user:)
+    end
   end
 
-  def self.record_tag_snapshot! tag, created_by_user:, language_code: 'ja'
-    event_type = tag.tag_versions.exists? ? :update : :create
-    record!(tag, event_type:, created_by_user:, language_code:)
+  def self.record_tag_snapshot! tag, created_by_user:
+    event_type =
+        if tag.nico?
+          tag.nico_tag_versions.exists? ? :update : :create
+        else
+          tag.tag_versions.exists? ? :update : :create
         end
 
-  def self.record_tag_snapshots! tags, created_by_user:, language_code: 'ja'
+    record!(tag, event_type:, created_by_user:)
+  end
+
+  def self.record_tag_snapshots! tags, created_by_user:
     tags.each do |tag|
-      record_tag_snapshot!(tag, created_by_user:, language_code:)
+      record_tag_snapshot!(tag, created_by_user:)
     end
   end
 end

backend/app/services/theatre_post_selector.rb

@@ -41,7 +41,7 @@ class TheatrePostSelector
   def weighted_candidates
     @weighted_candidates ||= begin
       penalties = tag_penalties
-      posts = eligible_posts.includes(tags: :tag_names).to_a
+      posts = eligible_posts.includes(tags: :tag_name).to_a
 
       posts.map do |post|
         post_tags = post.tags.to_a
@@ -82,7 +82,7 @@ class TheatrePostSelector
   def tag_penalty_json
     return [] if tag_penalties.empty?
 
-    tags = Tag.where(id: tag_penalties.keys).includes(:tag_names).index_by(&:id)
+    tags = Tag.where(id: tag_penalties.keys).includes(:tag_name).index_by(&:id)
 
     tag_penalties
       .map { |tag_id, penalty|
@@ -113,7 +113,7 @@ class TheatrePostSelector
 
   def light_tag_json tag
     { id: tag.id,
-      name: tag.name('ja'),
+      name: tag.name,
       category: tag.category }
   end
 end

backend/app/services/version_recorder.rb

@@ -47,14 +47,10 @@ class VersionRecorder
   end
 
   def update_record_version_no! version_no
-    return unless tracks_version_no_on_record?
-
     @record.update_columns(version_no:)
     @record.version_no = version_no
   end
 
-  def tracks_version_no_on_record? = true
-
   def validate_version_sequence! latest
     if !(latest) && @event_type != 'create'
       raise "#{ version_class.name } first event must be create"
@@ -64,7 +60,7 @@ class VersionRecorder
       raise "#{ version_class.name } create event already exists"
     end
 
-    return if !(latest) || !(tracks_version_no_on_record?)
+    return unless latest
 
     if @record.version_no != latest.version_no
       raise ("#{ record_class.name }##{ @record.id } version_no is #{ @record.version_no }, " +

backend/app/services/youtube/sync.rb

@@ -103,7 +103,7 @@ module Youtube
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -117,8 +117,8 @@ module Youtube
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each do |pt|
-        pt.destroy!
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+        pt.discard_by!(nil)
       end
     end
 

backend/config/routes.rb

@@ -1,5 +1,5 @@
 Rails.application.routes.draw do
-  resources :nico_tags, path: 'tags/nico', only: [:index, :show, :update]
+  resources :nico_tags, path: 'tags/nico', only: [:index, :update]
 
   scope 'tags/:parent_id/children', controller: :tag_children do
     post ':child_id', action: :create
@@ -55,6 +55,7 @@ Rails.application.routes.draw do
       get :metadata
       post :bulk
       get :random
+      get :changes
       get :versions, to: 'post_versions#index'
     end
 

backend/db/migrate/20260727123600_add_tags_json_to_post_versions.rb

@@ -1,299 +0,0 @@
-class AddTagsJsonToPostVersions < ActiveRecord::Migration[8.0]
-  RESOLUTION_GRACE = 1.second
-  SECTION_LITERAL_PATTERN = /\[[^\[\]\s]*-[^\[\]\s]*\]\z/
-
-  class MigrationPostVersion < ActiveRecord::Base
-    self.table_name = 'post_versions'
-  end
-
-  class MigrationTag < ActiveRecord::Base
-    self.table_name = 'tags'
-  end
-
-  class MigrationTagName < ActiveRecord::Base
-    self.table_name = 'tag_names'
-  end
-
-  class MigrationTagVersion < ActiveRecord::Base
-    self.table_name = 'tag_versions'
-  end
-
-  class MigrationNicoTagVersion < ActiveRecord::Base
-    self.table_name = 'nico_tag_versions'
-  end
-
-  def up
-    add_column :post_versions, :tags_json, :json, after: :tags
-    MigrationPostVersion.reset_column_information
-
-    backfill_missing_initial_tag_versions!
-    intervals_by_name = build_intervals_by_name
-
-    say_with_time 'Backfilling post_versions.tags_json' do
-      MigrationPostVersion.where(tags_json: nil).find_each(batch_size: 500) do |version|
-        version.update_columns(tags_json: build_tags_json(version, intervals_by_name))
-      end
-    end
-
-    change_column_null :post_versions, :tags_json, false
-
-    schema = connection.quote(JSON.generate({
-        type: 'array',
-        items: { type: 'object',
-                 properties: { id: { type: 'integer', minimum: 1 },
-                               version_no: { type: 'integer', minimum: 1 },
-                               name: { type: 'string', minLength: 1 },
-                               category: { type: 'string', enum: ['deerjikist',
-                                                                  'meme',
-                                                                  'character',
-                                                                  'general',
-                                                                  'material',
-                                                                  'meta',
-                                                                  'nico'] },
-                               sections: { type: 'array',
-                                           items: { type: 'object',
-                                                    properties: { begin_ms: { type: 'integer',
-                                                                              minimum: 0 },
-                                                                  end_ms: { type: ['integer',
-                                                                                   'null'],
-                                                                            minimum: 0 } },
-                                                    required: ['begin_ms', 'end_ms'],
-                                                    additionalProperties: false } } },
-                 required: ['id', 'version_no', 'name', 'category', 'sections'],
-                 additionalProperties: false } }))
-
-    add_check_constraint :post_versions,
-                         "JSON_SCHEMA_VALID(#{ schema }, tags_json)",
-                         name: 'chk_post_versions_tags_json_schema'
-  end
-
-  def down
-    remove_check_constraint :post_versions, name: 'chk_post_versions_tags_json_schema'
-
-    remove_column :post_versions, :tags_json
-  end
-
-  private
-
-  def backfill_missing_initial_tag_versions!
-    say_with_time 'Backfilling missing initial tag versions' do
-      tag_rows = missing_initial_version_rows(MigrationTagVersion, nico: false)
-      nico_rows = missing_initial_version_rows(MigrationNicoTagVersion, nico: true)
-
-      MigrationTagVersion.insert_all!(tag_rows) if tag_rows.any?
-      MigrationNicoTagVersion.insert_all!(nico_rows) if nico_rows.any?
-
-      tag_rows.length + nico_rows.length
-    end
-  end
-
-  def missing_initial_version_rows version_class, nico:
-    first_versions =
-        version_class
-        .order(:tag_id, :version_no)
-        .to_a
-        .group_by(&:tag_id)
-        .transform_values(&:first)
-    rows = []
-
-    MigrationTag.find_each do |tag|
-      next if (tag.category == 'nico') != nico
-
-      first_version = first_versions[tag.id]
-      next unless first_version
-      next if valid_initial_version?(first_version)
-
-      assert_inferable_initial_version!(tag, first_version)
-      rows << initial_version_row(tag, first_version, nico:)
-    end
-
-    rows
-  end
-
-  def valid_initial_version? version
-    version.version_no == 1 && version.event_type == 'create'
-  end
-
-  def assert_inferable_initial_version! tag, version
-    inferable =
-        version.version_no == 2 &&
-        version.event_type == 'discard' &&
-        tag.created_at < version.created_at
-    return if inferable
-
-    details = [
-        "tag_id=#{ tag.id }",
-        "version_no=#{ version.version_no }",
-        "event_type=#{ version.event_type.inspect }",
-        "tag_created_at=#{ tag.created_at.iso8601(6) }",
-        "version_created_at=#{ version.created_at.iso8601(6) }"]
-
-    raise "Cannot infer initial tag version: #{ details.join(', ') }"
-  end
-
-  def initial_version_row tag, discard_version, nico:
-    row = {
-        tag_id: tag.id,
-        version_no: 1,
-        event_type: 'create',
-        name: discard_version.name,
-        created_at: tag.created_at,
-        created_by_user_id: nil }
-
-    if nico
-      return row.merge(linked_tags: discard_version.linked_tags)
-    end
-
-    row.merge(
-        category: discard_version.category,
-        aliases: discard_version.aliases,
-        parent_tag_ids: discard_version.parent_tag_ids,
-        deprecated_at: discard_version.deprecated_at)
-  end
-
-  def build_intervals_by_name
-    intervals_by_name = Hash.new { |hash, name| hash[name] = [] }
-    versions_by_kind = {
-        tag: versions_by_tag_id(MigrationTagVersion),
-        nico: versions_by_tag_id(MigrationNicoTagVersion) }
-    current_names = current_names_by_tag_id
-
-    MigrationTag.find_each do |tag|
-      nico = tag.category == 'nico'
-      kind = nico ? :nico : :tag
-      versions = versions_by_kind.fetch(kind).fetch(tag.id, [])
-
-      intervals_for(
-          tag,
-          versions,
-          current_name: current_names.fetch(tag.id),
-          nico:).each do |interval|
-        name = interval.delete(:name)
-        intervals_by_name[name] << interval
-      end
-    end
-
-    intervals_by_name
-  end
-
-  def versions_by_tag_id version_class
-    version_class
-        .order(:tag_id, :version_no)
-        .to_a
-        .group_by(&:tag_id)
-  end
-
-  def current_names_by_tag_id
-    MigrationTagName
-        .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
-        .pluck('tags.id', 'tag_names.name')
-        .to_h
-  end
-
-  def intervals_for tag, versions, current_name:, nico:
-    if versions.empty?
-      return [{
-          name: current_name,
-          tag_id: tag.id,
-          version_no: tag.version_no,
-          category: nico ? 'nico' : tag.category,
-          from: tag.created_at,
-          to: tag.discarded_at }]
-    end
-
-    versions.each_with_index.filter_map do |version, index|
-      next if version.event_type == 'discard'
-
-      {
-          name: version.name,
-          tag_id: tag.id,
-          version_no: version.version_no,
-          category: nico ? 'nico' : version.category,
-          from: version.created_at,
-          to: versions[index + 1]&.created_at || tag.discarded_at }
-    end
-  end
-
-  def build_tags_json version, intervals_by_name
-    entries = version.tags.to_s.split.map do |literal|
-      name = tag_name_from_literal(literal)
-      interval = resolve_tag!(intervals_by_name.fetch(name, []), name:, version:)
-
-      { 'id' => interval.fetch(:tag_id),
-        'version_no' => interval.fetch(:version_no),
-        'name' => name,
-        'category' => interval.fetch(:category),
-        'sections' => [] }
-    end
-
-    assert_unique_tag_ids!(version, entries)
-
-    entries.sort_by { |entry| entry.fetch('id') }
-  end
-
-  def tag_name_from_literal literal
-    name = literal.dup
-    name.sub!(SECTION_LITERAL_PATTERN, '') while name.match?(
-        SECTION_LITERAL_PATTERN)
-
-    if name.empty? || name.include?('[') || name.include?(']')
-      raise "Invalid legacy tag literal: #{ literal.inspect }"
-    end
-
-    name
-  end
-
-  def resolve_tag! intervals, name:, version:
-    time = version.created_at
-    candidates = intervals.select do |interval|
-      interval.fetch(:from) <= time &&
-        (interval[:to].nil? || time < interval.fetch(:to))
-    end
-
-    candidates = future_candidates(intervals, time) if candidates.empty?
-
-    return candidates.first if candidates.one?
-
-    candidate_versions = candidates.map do |candidate|
-      [candidate.fetch(:tag_id), candidate.fetch(:version_no)]
-    end
-    details = [
-        "post_version_id=#{ version.id }",
-        "post_id=#{ version.post_id }",
-        "name=#{ name.inspect }",
-        "created_at=#{ time.iso8601(6) }",
-        "candidates=#{ candidate_versions.inspect }"].join(', ')
-
-    raise "Could not resolve tag snapshot: #{ details }"
-  end
-
-  def future_candidates intervals, time
-    candidates = intervals.select do |interval|
-      interval.fetch(:from) > time &&
-        interval.fetch(:from) <= time + RESOLUTION_GRACE
-    end
-    return [] if candidates.empty?
-
-    nearest_from = candidates.map { |interval| interval.fetch(:from) }.min
-
-    candidates.select do |interval|
-      interval.fetch(:from) == nearest_from
-    end
-  end
-
-  def assert_unique_tag_ids! version, entries
-    duplicate_tag_ids =
-        entries
-        .map { |entry| entry.fetch('id') }
-        .tally
-        .select { |_tag_id, count| count > 1 }
-        .keys
-    return if duplicate_tag_ids.empty?
-
-    details = [
-        "post_version_id=#{ version.id }",
-        "duplicate_tag_ids=#{ duplicate_tag_ids.inspect }"].join(', ')
-
-    raise "Duplicate tag IDs: #{ details }"
-  end
-end

backend/db/migrate/20260921000000_delete_inactive_records_from_post_tags.rb

@@ -1,53 +0,0 @@
-class DeleteInactiveRecordsFromPostTags < ActiveRecord::Migration[8.0]
-  def up
-    execute <<~SQL
-      DELETE
-      FROM
-        post_tags
-      WHERE
-        discarded_at IS NOT NULL
-    SQL
-
-    remove_index :post_tags, [:tag_id, :discarded_at]
-    remove_index :post_tags, [:post_id, :discarded_at]
-    remove_index :post_tags, name: 'idx_post_tags_active_unique'
-    remove_index :post_tags, :discarded_at
-
-    remove_foreign_key :post_tags, column: :deleted_user_id
-    remove_index :post_tags, :deleted_user_id
-
-    remove_column :post_tags, :active_unique_key
-    remove_column :post_tags, :is_active
-    remove_column :post_tags, :discarded_at
-    remove_column :post_tags, :deleted_user_id
-    remove_column :post_tags, :updated_at
-
-    execute <<~SQL
-      ALTER TABLE
-        post_tags
-      MODIFY COLUMN
-        id BIGINT NOT NULL
-    SQL
-
-    execute <<~SQL
-      ALTER TABLE
-        post_tags
-      DROP PRIMARY KEY
-    SQL
-
-    remove_column :post_tags, :id
-
-    execute <<~SQL
-      ALTER TABLE
-        post_tags
-      ADD PRIMARY KEY
-        (post_id, tag_id)
-    SQL
-
-    remove_index :post_tags, :post_id
-  end
-
-  def down
-    raise ActiveRecord::IrreversibleMigration, '戻せません．'
-  end
-end

backend/db/migrate/20260921010000_add_foreign_key_on_post_id_and_tag_id_in_post_tag_sections.rb

@@ -1,11 +0,0 @@
-class AddForeignKeyOnPostIdAndTagIdInPostTagSections < ActiveRecord::Migration[8.0]
-  def change
-    remove_foreign_key :post_tag_sections, :posts, column: :post_id
-    remove_foreign_key :post_tag_sections, :tags, column: :tag_id
-
-    add_foreign_key :post_tag_sections, :post_tags,
-                    column: [:post_id, :tag_id],
-                    primary_key: [:post_id, :tag_id],
-                    on_delete: :cascade
-  end
-end

backend/db/migrate/20260921020000_delete_discarded_records_from_tags.rb

@@ -1,46 +0,0 @@
-class DeleteDiscardedRecordsFromTags < ActiveRecord::Migration[8.0]
-  def up
-    remove_foreign_key :tag_versions, :tags, column: :tag_id
-    remove_foreign_key :nico_tag_versions, :tags, column: :tag_id
-    remove_foreign_key :material_versions, :tags, column: :tag_id
-
-    execute <<~SQL
-      DELETE
-        ntr
-      FROM
-        nico_tag_relations ntr
-        INNER JOIN
-          tags t
-          ON
-            t.discarded_at IS NOT NULL
-            AND t.id IN (ntr.tag_id, ntr.nico_tag_id)
-    SQL
-
-    execute <<~SQL
-      DELETE
-        ti
-      FROM
-        tag_implications ti
-        INNER JOIN
-          tags t
-          ON
-            t.discarded_at IS NOT NULL
-            AND t.id IN (ti.tag_id, ti.parent_tag_id)
-    SQL
-
-    execute <<~SQL
-      DELETE
-      FROM
-        tags
-      WHERE
-        discarded_at IS NOT NULL
-    SQL
-
-    remove_index :tags, :discarded_at
-    remove_column :tags, :discarded_at
-  end
-
-  def down
-    raise ActiveRecord::IrreversibleMigration, '戻せません．'
-  end
-end

backend/db/migrate/20260921030000_delete_discarded_records_from_tag_names.rb

@@ -1,18 +0,0 @@
-class DeleteDiscardedRecordsFromTagNames < ActiveRecord::Migration[8.0]
-  def up
-    execute <<~SQL
-      DELETE
-      FROM
-        tag_names
-      WHERE
-        discarded_at IS NOT NULL
-    SQL
-
-    remove_index :tag_names, :discarded_at
-    remove_column :tag_names, :discarded_at
-  end
-
-  def down
-    raise ActiveRecord::IrreversibleMigration, '戻せません．'
-  end
-end

backend/db/migrate/20260921040000_create_external_tags.rb

@@ -1,54 +0,0 @@
-class CreateExternalTags < ActiveRecord::Migration[8.0]
-  def up
-    create_table :external_tags do |t|
-      t.string :platform, limit: 16, null: false
-      t.string :name, limit: 255, null: false
-      t.integer :post_count, null: false, default: 0
-      t.datetime :created_at, null: false
-
-      t.index [:platform, :name], unique: true
-    end
-
-    execute <<~SQL
-      INSERT INTO
-        external_tags(id, platform, name, post_count, created_at)
-      SELECT
-        t.id
-      , 'nico' AS platform
-      , SUBSTR(tn.name, 6) AS name
-      , t.post_count
-      , t.created_at
-      FROM
-        tags t
-        INNER JOIN
-          tag_names tn
-          ON
-            tn.id = t.tag_name_id
-            AND t.category = 'nico'
-    SQL
-
-    execute <<~SQL
-      INSERT INTO
-        external_tags(id, platform, name, post_count, created_at)
-      SELECT
-        ntv.tag_id
-      , 'nico' AS platform
-      , SUBSTR(ntv.name, 6) AS name
-      , 0 AS post_count
-      , ntv.created_at
-      FROM
-        nico_tag_versions ntv
-        LEFT JOIN
-          external_tags et
-          ON
-            et.id = ntv.tag_id
-      WHERE
-        ntv.version_no = 1
-        AND et.id IS NULL
-    SQL
-  end
-
-  def down
-    drop_table :external_tags
-  end
-end

backend/db/migrate/20260921050000_create_post_external_tags.rb

@@ -1,29 +0,0 @@
-class CreatePostExternalTags < ActiveRecord::Migration[8.0]
-  def up
-    create_table :post_external_tags, primary_key: [:post_id, :external_tag_id] do |t|
-      t.references :post, null: false, index: false, foreign_key: true
-      t.references :external_tag, null: false, foreign_key: true
-      t.datetime :created_at, null: false
-    end
-
-    execute <<~SQL
-      INSERT INTO
-        post_external_tags(post_id, external_tag_id, created_at)
-      SELECT
-        pt.post_id
-      , pt.tag_id AS external_tag_id
-      , pt.created_at
-      FROM
-        post_tags pt
-        INNER JOIN
-          tags t
-          ON
-            pt.tag_id = t.id
-            AND t.category = 'nico'
-    SQL
-  end
-
-  def down
-    drop_table :post_external_tags
-  end
-end

backend/db/migrate/20260921060000_change_foreign_key_on_nico_tag_relations.rb

@@ -1,6 +0,0 @@
-class ChangeForeignKeyOnNicoTagRelations < ActiveRecord::Migration[8.0]
-  def change
-    remove_foreign_key :nico_tag_relations, :tags, column: :nico_tag_id
-    add_foreign_key :nico_tag_relations, :external_tags, column: :nico_tag_id
-  end
-end

backend/db/migrate/20260921230000_migrate_external_tags.rb

@@ -1,199 +0,0 @@
-class MigrateExternalTags < ActiveRecord::Migration[8.0]
-  class MigrationPostVersion < ActiveRecord::Base
-    self.table_name = 'post_versions'
-  end
-
-  def up
-    x = connection.select_value(<<~SQL)
-      SELECT
-        COUNT(0)
-      FROM
-        post_tag_sections pts
-      INNER JOIN
-        tags t
-        ON
-          t.id = pts.tag_id
-      WHERE
-        t.category = 'nico'
-    SQL
-    if x > 0
-      raise "post_tag_sections に #{ x } 件のチンカスがあります!"
-    end
-
-    x = connection.select_value(<<~SQL)
-      SELECT
-        COUNT(0)
-      FROM
-        materials m
-        INNER JOIN
-          tags t
-          ON
-            t.id = m.tag_id
-      WHERE
-        t.category = 'nico'
-    SQL
-    if x > 0
-      raise "materials に #{ x } 件のチンカスがあります!"
-    end
-
-    x = connection.select_value(<<~SQL)
-      SELECT
-        COUNT(0)
-      FROM
-        tag_implications ti
-        INNER JOIN
-          tags t
-          ON
-            t.id = ti.tag_id
-            OR t.id = ti.parent_tag_id
-      WHERE
-        t.category = 'nico'
-    SQL
-    if x > 0
-      raise "tag_implications に #{ x } 件のチンカスがあります!"
-    end
-
-    execute <<~SQL
-      DELETE
-        ts
-      FROM
-        tag_similarities ts
-        INNER JOIN
-          tags t
-          ON
-            t.category = 'nico'
-            AND (t.id = ts.tag_id
-                 OR t.id = ts.target_tag_id)
-    SQL
-
-    execute <<~SQL
-      DELETE
-        tset
-      FROM
-        theatre_skip_event_tags tset
-        INNER JOIN
-          tags t
-          ON
-            t.category = 'nico'
-            AND t.id = tset.tag_id
-    SQL
-
-    remove_check_constraint :post_versions, name: 'chk_post_versions_tags_json_schema'
-
-    say_with_time 'Migrate post_versions.tags_json' do
-      count = 0
-
-      MigrationPostVersion.find_each(batch_size: 500) do |version|
-        tags = version.tags_json.map do |tag|
-          if tag.fetch('category') == 'nico'
-            { 'external_tag_id' => tag.fetch('id') }
-          else
-            { 'tag_id' => tag.fetch('id'),
-              'version_no' => tag.fetch('version_no'),
-              'name' => tag.fetch('name'),
-              'category' => tag.fetch('category'),
-              'sections' => tag.fetch('sections') }
-          end
-        end
-
-        version.update_columns(tags_json: tags)
-        count += 1
-      end
-
-      count
-    end
-
-    add_tags_json_constraint!
-
-    tag_name_ids = connection.select_values(<<~SQL)
-      SELECT
-        tag_name_id
-      FROM
-        tags
-      WHERE
-        category = 'nico'
-    SQL
-
-    connection.transaction do
-      execute <<~SQL
-        DELETE
-          pt
-        FROM
-          post_tags pt
-          INNER JOIN
-            tags t
-            ON
-              t.category = 'nico'
-              AND t.id = pt.tag_id
-      SQL
-
-      execute <<~SQL
-        DELETE
-        FROM
-          tags
-        WHERE
-          category = 'nico'
-      SQL
-
-      unless tag_name_ids.empty?
-        execute <<~SQL
-          DELETE
-          FROM
-            tag_names
-          WHERE
-            id IN (#{ tag_name_ids.join(', ') })
-        SQL
-      end
-    end
-  end
-
-  def down
-    raise ActiveRecord::IrreversibleMigration, '戻せません．'
-  end
-
-  private
-
-  def add_tags_json_constraint!
-    schema = { type: 'array',
-               items: { oneOf: [internal_tag_schema, external_tag_schema] } }
-
-    quoted_schema = connection.quote(JSON.generate(schema))
-
-    add_check_constraint :post_versions,
-                         "JSON_SCHEMA_VALID(#{ quoted_schema }, tags_json)",
-                         name: 'chk_post_versions_tags_json_schema'
-  end
-
-  def internal_tag_schema
-    { type: 'object',
-      properties: { tag_id: { type: 'integer', minimum: 1 },
-                    version_no: { type: 'integer', minimum: 1 },
-                    name: { type: 'string', minLength: 1 },
-                    category: { type: 'string',
-                                enum: ['deerjikist',
-                                       'meme',
-                                       'character',
-                                       'general',
-                                       'material',
-                                       'meta'] },
-                    sections: sections_schema },
-      required: ['tag_id', 'version_no', 'sections'],
-      additionalProperties: false }
-  end
-
-  def external_tag_schema
-    { type: 'object',
-      properties: { external_tag_id: { type: 'integer', minimum: 1 } },
-      required: ['external_tag_id'],
-      additionalProperties: false }
-  end
-
-  def sections_schema
-    { type: 'array',
-      items: { type: 'object',
-               properties: { begin_ms: { type: 'integer', minimum: 0 },
-                             end_ms: { type: ['integer', 'null'], minimum: 0 } },
-               required: ['begin_ms', 'end_ms'],
-               additionalProperties: false } }
-  end
-end

backend/db/migrate/20260922000000_create_languages.rb

@@ -1,20 +0,0 @@
-class CreateLanguages < ActiveRecord::Migration[8.0]
-  def up
-    create_table :languages, id: { type: :string, limit: 16 }, primary_key: :code do |t|
-      t.string :name, null: false
-      t.datetime :deprecated_at, index: true
-      t.datetime :created_at, null: false
-    end
-
-    execute <<~SQL
-      INSERT INTO
-        languages(code, name, created_at)
-      VALUES
-        ('ja', '日本語', #{ connection.quote Time.current })
-    SQL
-  end
-
-  def down
-    drop_table :languages
-  end
-end

backend/db/migrate/20260922010000_create_scripts.rb

@@ -1,20 +0,0 @@
-class CreateScripts < ActiveRecord::Migration[8.0]
-  def up
-    create_table :scripts, id: { type: 'CHAR(4)' }, primary_key: :code do |t|
-      t.string :name, null: false
-      t.datetime :deprecated_at, index: true
-      t.datetime :created_at, null: false
-    end
-
-    execute <<~SQL
-      INSERT INTO
-        scripts(code, name, created_at)
-      VALUES
-        ('Jpan', '漢字および仮名文字', #{ connection.quote Time.current })
-    SQL
-  end
-
-  def down
-    drop_table :scripts
-  end
-end

backend/db/migrate/20260922020000_create_locales.rb

@@ -1,25 +0,0 @@
-class CreateLocales < ActiveRecord::Migration[8.0]
-  def up
-    create_table :locales, id: { type: :string, limit: 32 }, primary_key: :code do |t|
-      t.string :language_code, limit: 16, null: false, index: true
-      t.column :script_code, 'CHAR(4)', null: false
-      t.string :name, null: false
-      t.datetime :deprecated_at, index: true
-      t.datetime :created_at, null: false
-
-      t.foreign_key :languages, column: :language_code, primary_key: :code
-      t.foreign_key :scripts, column: :script_code, primary_key: :code
-    end
-
-    execute <<~SQL
-      INSERT INTO
-        locales(code, language_code, script_code, name, created_at)
-      VALUES
-        ('ja', 'ja', 'Jpan', '日本語', #{ connection.quote Time.current })
-    SQL
-  end
-
-  def down
-    drop_table :locales
-  end
-end

backend/db/migrate/20260922030000_add_columns_to_tag_names.rb

@@ -1,59 +0,0 @@
-class AddColumnsToTagNames < ActiveRecord::Migration[8.0]
-  def up
-    add_reference :tag_names, :tag, after: :id, foreign_key: true
-    add_column :tag_names, :language_code, :string,
-               limit: 16, null: false, after: :tag_id, default: 'ja'
-    add_column :tag_names, :script_code, 'CHAR(4)',
-               null: false, after: :name, default: 'Jpan'
-    add_column :tag_names, :primary_flg, :boolean,
-               null: false, after: :script_code, default: true
-
-    add_foreign_key :tag_names, :languages, column: :language_code, primary_key: :code
-    add_foreign_key :tag_names, :scripts, column: :script_code, primary_key: :code
-
-    remove_index :tag_names, :name
-    add_index :tag_names, [:language_code, :name], unique: true
-
-    change_column_default :tag_names, :language_code, from: 'ja', to: nil
-    change_column_default :tag_names, :script_code, from: 'Jpan', to: nil
-
-    execute <<~SQL
-      UPDATE
-        tag_names tn
-        LEFT JOIN
-          tags AS t
-          ON
-            t.tag_name_id = COALESCE(tn.canonical_id, tn.id)
-      SET
-        tn.tag_id = t.id
-      , tn.primary_flg = CASE
-                         WHEN tn.canonical_id IS NULL THEN
-                           1
-                         ELSE
-                           0
-                         END
-    SQL
-
-    change_column_default :tag_names, :primary_flg, from: true, to: nil
-
-    add_column :tag_names, :primary_tag_id, :bigint,
-               as: 'CASE WHEN primary_flg THEN tag_id ELSE NULL END'
-    add_index :tag_names, [:primary_tag_id, :language_code], unique: true
-  end
-
-  def down
-    remove_index :tag_names, [:primary_tag_id, :language_code]
-    remove_column :tag_names, :primary_tag_id
-
-    remove_foreign_key :tag_names, column: :language_code
-    remove_foreign_key :tag_names, column: :script_code
-
-    remove_index :tag_names, [:language_code, :name]
-    add_index :tag_names, :name, unique: true
-
-    remove_column :tag_names, :primary_flg
-    remove_column :tag_names, :script_code
-    remove_column :tag_names, :language_code
-    remove_reference :tag_names, :tag, foreign_key: true
-  end
-end

backend/db/migrate/20260922040000_add_names_to_tag_versions.rb

@@ -1,38 +0,0 @@
-class AddNamesToTagVersions < ActiveRecord::Migration[8.0]
-  class TagVersion < ActiveRecord::Base
-    self.table_name = 'tag_versions'
-  end
-
-  def up
-    add_column :tag_versions, :names, :json
-    TagVersion.reset_column_information
-
-    say_with_time 'Backfilling multilingual tag version names' do
-      TagVersion.find_each do |version|
-        names = [{
-          language_code: 'ja',
-          name: version.name,
-          script_code: 'Jpan',
-          primary_flg: true,
-          auto_generated: false }]
-        names.concat(version.aliases.to_s.split.filter_map { |name|
-          next if name.blank?
-
-          {
-            language_code: 'ja',
-            name:,
-            script_code: 'Jpan',
-            primary_flg: false,
-            auto_generated: false }
-        })
-        version.update_columns(names: names)
-      end
-    end
-
-    change_column_null :tag_versions, :names, false
-  end
-
-  def down
-    remove_column :tag_versions, :names
-  end
-end

backend/db/migrate/20260922050000_add_auto_generated_to_tag_names.rb

@@ -1,19 +0,0 @@
-class AddAutoGeneratedToTagNames < ActiveRecord::Migration[8.0]
-  class TagVersion < ActiveRecord::Base
-    self.table_name = 'tag_versions'
-  end
-
-  def up
-    add_column :tag_names, :auto_generated, :boolean, null: false, default: false
-    TagVersion.reset_column_information
-
-    TagVersion.find_each do |version|
-      names = Array(version.names).map { |name| name.merge('auto_generated' => false) }
-      version.update_columns(names: names)
-    end
-  end
-
-  def down
-    remove_column :tag_names, :auto_generated
-  end
-end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
+ActiveRecord::Schema[8.0].define(version: 2026_07_13_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -48,14 +48,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.index ["tag_id"], name: "index_deerjikists_on_tag_id"
   end
 
-  create_table "external_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "platform", limit: 16, null: false
-    t.string "name", null: false
-    t.integer "post_count", default: 0, null: false
-    t.datetime "created_at", null: false
-    t.index ["platform", "name"], name: "index_external_tags_on_platform_and_name", unique: true
-  end
-
   create_table "gekanator_ai_runs", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "model", null: false
     t.integer "input_tokens", default: 0, null: false
@@ -138,24 +130,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
-  create_table "languages", primary_key: "code", id: { type: :string, limit: 16 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "name", null: false
-    t.datetime "deprecated_at"
-    t.datetime "created_at", null: false
-    t.index ["deprecated_at"], name: "index_languages_on_deprecated_at"
-  end
-
-  create_table "locales", primary_key: "code", id: { type: :string, limit: 32 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "language_code", limit: 16, null: false
-    t.string "script_code", limit: 4, null: false
-    t.string "name", null: false
-    t.datetime "deprecated_at"
-    t.datetime "created_at", null: false
-    t.index ["deprecated_at"], name: "index_locales_on_deprecated_at"
-    t.index ["language_code"], name: "index_locales_on_language_code"
-    t.index ["script_code"], name: "fk_rails_0b74ce96a8"
-  end
-
   create_table "material_export_items", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "material_id", null: false
     t.string "profile", default: "legacy_drive", null: false
@@ -307,13 +281,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.check_constraint "`version_no` > 0", name: "nico_tag_versions_version_no_positive"
   end
 
-  create_table "post_external_tags", primary_key: ["post_id", "external_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "post_id", null: false
-    t.bigint "external_tag_id", null: false
-    t.datetime "created_at", null: false
-    t.index ["external_tag_id"], name: "index_post_external_tags_on_external_tag_id"
-  end
-
   create_table "post_implications", primary_key: ["post_id", "parent_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "parent_post_id", null: false
@@ -344,12 +311,23 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
   end
 
-  create_table "post_tags", primary_key: ["post_id", "tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+  create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
     t.bigint "created_user_id"
+    t.bigint "deleted_user_id"
     t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.datetime "discarded_at"
+    t.virtual "is_active", type: :boolean, as: "(`discarded_at` is null)", stored: true
+    t.virtual "active_unique_key", type: :string, as: "(case when (`discarded_at` is null) then concat(`post_id`,_utf8mb4':',`tag_id`) else NULL end)", stored: true
+    t.index ["active_unique_key"], name: "idx_post_tags_active_unique", unique: true
     t.index ["created_user_id"], name: "index_post_tags_on_created_user_id"
+    t.index ["deleted_user_id"], name: "index_post_tags_on_deleted_user_id"
+    t.index ["discarded_at"], name: "index_post_tags_on_discarded_at"
+    t.index ["post_id", "discarded_at"], name: "index_post_tags_on_post_id_and_discarded_at"
+    t.index ["post_id"], name: "index_post_tags_on_post_id"
+    t.index ["tag_id", "discarded_at"], name: "index_post_tags_on_tag_id_and_discarded_at"
     t.index ["tag_id"], name: "index_post_tags_on_tag_id"
   end
 
@@ -371,7 +349,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
     t.text "tags", null: false
-    t.json "tags_json", null: false
     t.text "parent_post_ids", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
@@ -385,7 +362,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_post_versions_video_ms_positive"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
     t.check_constraint "`version_no` > 0", name: "post_versions_version_no_positive"
-    t.check_constraint "json_schema_valid(_utf8mb4'{\"type\":\"array\",\"items\":{\"oneOf\":[{\"type\":\"object\",\"properties\":{\"tag_id\":{\"type\":\"integer\",\"minimum\":1},\"version_no\":{\"type\":\"integer\",\"minimum\":1},\"name\":{\"type\":\"string\",\"minLength\":1},\"category\":{\"type\":\"string\",\"enum\":[\"deerjikist\",\"meme\",\"character\",\"general\",\"material\",\"meta\"]},\"sections\":{\"type\":\"array\",\"items\":{\"type\":\"object\",\"properties\":{\"begin_ms\":{\"type\":\"integer\",\"minimum\":0},\"end_ms\":{\"type\":[\"integer\",\"null\"],\"minimum\":0}},\"required\":[\"begin_ms\",\"end_ms\"],\"additionalProperties\":false}}},\"required\":[\"tag_id\",\"version_no\",\"sections\"],\"additionalProperties\":false},{\"type\":\"object\",\"properties\":{\"external_tag_id\":{\"type\":\"integer\",\"minimum\":1}},\"required\":[\"external_tag_id\"],\"additionalProperties\":false}]}}',`tags_json`)", name: "chk_post_versions_tags_json_schema"
   end
 
   create_table "posts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -406,13 +382,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
-  create_table "scripts", primary_key: "code", id: { type: :string, limit: 4 }, charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.string "name", null: false
-    t.datetime "deprecated_at"
-    t.datetime "created_at", null: false
-    t.index ["deprecated_at"], name: "index_scripts_on_deprecated_at"
-  end
-
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "user_id", null: false
     t.datetime "created_at", null: false
@@ -424,6 +393,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.index ["user_id"], name: "index_settings_on_user_id", unique: true
   end
 
+  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "no", null: false
+    t.string "alt_text"
+    t.binary "sha256", limit: 32, null: false
+    t.bigint "created_by_user_id", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
+    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
+    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
+  end
+
   create_table "tag_implications", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_id", null: false
     t.bigint "parent_tag_id", null: false
@@ -445,21 +427,14 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
   end
 
   create_table "tag_names", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "tag_id"
-    t.string "language_code", limit: 16, null: false
     t.string "name", null: false
-    t.string "script_code", limit: 4, null: false
-    t.boolean "primary_flg", null: false
     t.bigint "canonical_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.virtual "primary_tag_id", type: :bigint, as: "(case when `primary_flg` then `tag_id` else NULL end)"
-    t.boolean "auto_generated", default: false, null: false
+    t.datetime "discarded_at"
     t.index ["canonical_id"], name: "index_tag_names_on_canonical_id"
-    t.index ["language_code", "name"], name: "index_tag_names_on_language_code_and_name", unique: true
-    t.index ["primary_tag_id", "language_code"], name: "index_tag_names_on_primary_tag_id_and_language_code", unique: true
-    t.index ["script_code"], name: "fk_rails_dd783b3d1c"
-    t.index ["tag_id"], name: "index_tag_names_on_tag_id"
+    t.index ["discarded_at"], name: "index_tag_names_on_discarded_at"
+    t.index ["name"], name: "index_tag_names_on_name", unique: true
   end
 
   create_table "tag_similarities", primary_key: ["tag_id", "target_tag_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -481,7 +456,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.datetime "deprecated_at"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
-    t.json "names", null: false
     t.index ["created_at"], name: "index_tag_versions_on_created_at"
     t.index ["created_by_user_id", "created_at"], name: "index_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
@@ -496,8 +470,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.integer "post_count", default: 0, null: false
+    t.datetime "discarded_at"
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
+    t.index ["discarded_at"], name: "index_tags_on_discarded_at"
     t.index ["tag_name_id"], name: "index_tags_on_tag_name_id", unique: true
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
@@ -638,19 +614,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
     t.index ["banned_at"], name: "index_users_on_banned_at"
   end
 
-  create_table "wiki_assets", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
-    t.bigint "wiki_page_id", null: false
-    t.integer "no", null: false
-    t.string "alt_text"
-    t.binary "sha256", limit: 32, null: false
-    t.bigint "created_by_user_id", null: false
-    t.datetime "created_at", null: false
-    t.datetime "updated_at", null: false
-    t.index ["created_by_user_id"], name: "index_wiki_assets_on_created_by_user_id"
-    t.index ["wiki_page_id", "no"], name: "index_wiki_assets_on_wiki_page_id_and_no", unique: true
-    t.index ["wiki_page_id", "sha256"], name: "index_wiki_assets_on_wiki_page_id_and_sha256", unique: true
-  end
-
   create_table "wiki_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "sha256", limit: 64, null: false
     t.text "body", null: false
@@ -736,8 +699,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
   add_foreign_key "gekanator_question_suggestions", "users"
   add_foreign_key "gekanator_questions", "gekanator_question_suggestions"
   add_foreign_key "gekanator_questions", "users", column: "created_by_id"
-  add_foreign_key "locales", "languages", column: "language_code", primary_key: "code"
-  add_foreign_key "locales", "scripts", column: "script_code", primary_key: "code"
   add_foreign_key "material_export_items", "materials"
   add_foreign_key "material_export_items", "users", column: "created_by_user_id"
   add_foreign_key "material_import_blocks", "users", column: "created_by_user_id"
@@ -746,37 +707,37 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_22_050000) do
   add_foreign_key "material_sync_suppressions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "materials"
   add_foreign_key "material_versions", "materials", column: "parent_id"
+  add_foreign_key "material_versions", "tags"
   add_foreign_key "material_versions", "users", column: "created_by_user_id"
   add_foreign_key "material_versions", "users", column: "updated_by_user_id"
   add_foreign_key "materials", "materials", column: "parent_id"
   add_foreign_key "materials", "tags"
   add_foreign_key "materials", "users", column: "created_by_user_id"
   add_foreign_key "materials", "users", column: "updated_by_user_id"
-  add_foreign_key "nico_tag_relations", "external_tags", column: "nico_tag_id"
   add_foreign_key "nico_tag_relations", "tags"
+  add_foreign_key "nico_tag_relations", "tags", column: "nico_tag_id"
+  add_foreign_key "nico_tag_versions", "tags"
   add_foreign_key "nico_tag_versions", "users", column: "created_by_user_id"
-  add_foreign_key "post_external_tags", "external_tags"
-  add_foreign_key "post_external_tags", "posts"
   add_foreign_key "post_implications", "posts"
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
-  add_foreign_key "post_tag_sections", "post_tags", column: ["post_id", "tag_id"], primary_key: ["post_id", "tag_id"], on_delete: :cascade
+  add_foreign_key "post_tag_sections", "posts"
+  add_foreign_key "post_tag_sections", "tags"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
+  add_foreign_key "post_tags", "users", column: "deleted_user_id"
   add_foreign_key "post_versions", "posts"
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
   add_foreign_key "tag_implications", "tags"
   add_foreign_key "tag_implications", "tags", column: "parent_tag_id"
-  add_foreign_key "tag_names", "languages", column: "language_code", primary_key: "code"
-  add_foreign_key "tag_names", "scripts", column: "script_code", primary_key: "code"
   add_foreign_key "tag_names", "tag_names", column: "canonical_id"
-  add_foreign_key "tag_names", "tags"
   add_foreign_key "tag_similarities", "tags"
   add_foreign_key "tag_similarities", "tags", column: "target_tag_id"
+  add_foreign_key "tag_versions", "tags"
   add_foreign_key "tag_versions", "users", column: "created_by_user_id"
   add_foreign_key "tags", "tag_names"
   add_foreign_key "theatre_comments", "theatres"

backend/lib/tasks/sync_nico.rake

@@ -16,7 +16,7 @@ namespace :nico do
     end
 
     def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
-      current_tag_ids ||= PostTag.where(post_id: post.id).pluck(:tag_id).to_set
+      current_tag_ids ||= PostTag.kept.where(post_id: post.id).pluck(:tag_id).to_set
       desired_tag_ids = desired_tag_ids.compact.to_set
 
       to_add = desired_tag_ids - current_tag_ids
@@ -30,28 +30,9 @@ namespace :nico do
         end
       end
 
-      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).find_each(&:destroy!)
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+        pt.discard_by!(nil)
       end
-
-    def sync_post_external_tags! post, desired_external_tag_ids, current_external_tag_ids: nil
-      current_external_tag_ids ||=
-          PostExternalTag.where(post_id: post.id).pluck(:external_tag_id).to_set
-      desired_external_tag_ids = desired_external_tag_ids.compact.to_set
-
-      to_add = desired_external_tag_ids - current_external_tag_ids
-      to_remove = current_external_tag_ids - desired_external_tag_ids
-
-      ExternalTag.where(id: to_add.to_a).find_each do |external_tag|
-        begin
-          PostExternalTag.create!(post:, external_tag:)
-        rescue ActiveRecord::RecordNotUnique
-          ;
-        end
-      end
-
-      PostExternalTag
-          .where(post_id: post.id, external_tag_id: to_remove.to_a)
-          .find_each(&:destroy!)
     end
 
     mysql_user = ENV['MYSQL_USER']
@@ -130,64 +111,58 @@ namespace :nico do
         sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.niconico.id, Tag.video.id])
       end
 
+      tags = post.tags
       # 既存のタグ Id. 集合
-      kept_tag_ids = post.tags.pluck(:id).to_set
-
-      # 既存の外部タグ Id. 集合
-      kept_external_tag_ids = post.external_tags.nico.pluck(:id).to_set
-
-      # 記載すべき外部タグ Id. のリスト
-      desired_external_tag_ids = []
+      kept_tag_ids = tags.pluck(:id).to_set
+      # うち内部タグ Id. 集合
+      kept_non_nico_tag_ids = tags.not_nico.pluck(:id).to_set
 
+      # 記載すべき外部タグ Id. および連携される内部タグ Id. のリスト
+      desired_nico_tag_based_ids = []
       # 記載すべき内部タグ Id. のリスト
-      desired_tag_ids = kept_tag_ids.to_a
+      desired_non_nico_tag_ids = []
 
       datum['tags'].each do |raw|
-        name = TagNameSanitisationRule.sanitise("nico:#{ raw }").delete_prefix('nico:')
-        tag = ExternalTag.find_or_create_by!(platform: :nico, name:)
+        name = TagNameSanitisationRule.sanitise("nico:#{ raw }")
+        tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
 
-        unless tag.nico_tag_versions.exists?
-          NicoTagVersionRecorder.record!(external_tag: tag,
-                                         event_type: :create,
-                                         created_by_user: nil)
-        end
+        event_type = tag.nico_tag_versions.exists? ? :update : :create
+        NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user: nil)
 
-        desired_external_tag_ids << tag.id
+        desired_nico_tag_based_ids << tag.id
 
         # 新たに記載される外部タグと連携される内部タグを記載
-        # 連携タグは記載すれども消除せず．
-        unless tag.id.in?(kept_external_tag_ids)
-          desired_tag_ids.concat(tag.linked_tags.pluck(:id))
+        unless tag.id.in?(kept_tag_ids)
+          linked_ids = tag.linked_tags.pluck(:id)
+          desired_non_nico_tag_ids.concat(linked_ids)
+          desired_nico_tag_based_ids.concat(linked_ids)
         end
       end
 
       deerjikist = Deerjikist.find_by(platform: :nico, code: datum['user'])
       if deerjikist
-        desired_tag_ids << deerjikist.tag_id
-      elsif !(Tag.where(id: kept_tag_ids).where(category: :deerjikist).exists?)
-        desired_tag_ids << Tag.no_deerjikist.id
+        desired_non_nico_tag_ids << deerjikist.tag_id
+        desired_nico_tag_based_ids << deerjikist.tag_id
+      elsif !(Tag.where(id: kept_non_nico_tag_ids).where(category: :deerjikist).exists?)
+        desired_non_nico_tag_ids << Tag.no_deerjikist.id
+        desired_nico_tag_based_ids << Tag.no_deerjikist.id
       end
 
-      desired_external_tag_ids.uniq!
-      desired_tag_ids.uniq!
+      desired_nico_tag_based_ids.uniq!
 
-      # 外部タグの記載に際しては “bot 操作” タグを記載しなぃ．
-      if kept_tag_ids != desired_tag_ids.to_set
-        desired_tag_ids << Tag.bot.id
-        desired_tag_ids.uniq!
+      desired_all_tag_ids = kept_non_nico_tag_ids.to_a + desired_nico_tag_based_ids
+      desired_non_nico_tag_ids.concat(kept_non_nico_tag_ids.to_a)
+      desired_non_nico_tag_ids.uniq!
+      if kept_non_nico_tag_ids != desired_non_nico_tag_ids.to_set
+        desired_all_tag_ids << Tag.bot.id
       end
+      desired_all_tag_ids.uniq!
 
-      tags_changed =
-          kept_tag_ids != desired_tag_ids.to_set ||
-          kept_external_tag_ids != desired_external_tag_ids.to_set
-
-      sync_post_tags!(post, desired_tag_ids, current_tag_ids: kept_tag_ids)
-      sync_post_external_tags!(post, desired_external_tag_ids,
-                               current_external_tag_ids: kept_external_tag_ids)
+      sync_post_tags!(post, desired_all_tag_ids, current_tag_ids: kept_tag_ids)
 
       if post_created
         PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
-      elsif post_changed || tags_changed
+      elsif post_changed || kept_tag_ids != desired_all_tag_ids.to_set
         PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
         PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
       end

backend/spec/db/delete_discarded_tags_spec.rb

@@ -1,124 +0,0 @@
-require 'rails_helper'
-require_relative '../../db/migrate/20260921020000_delete_discarded_records_from_tags'
-require_relative '../../db/migrate/20260921030000_delete_discarded_records_from_tag_names'
-
-RSpec.describe 'discarded tag cleanup migrations' do
-  [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |migration_class|
-    it "rejects rollback of #{ migration_class.name }" do
-      expect { migration_class.new.down }
-          .to raise_error(ActiveRecord::IrreversibleMigration)
-    end
-  end
-
-  context 'with legacy records' do
-    # Reproduce the historical schema required by these pre-multilingual migrations.
-    self.use_transactional_tests = false
-
-    before do
-      record_class = Class.new(ActiveRecord::Base) do
-        self.abstract_class = true
-      end
-      stub_const('TagCleanupMigrationRecord', record_class)
-      config = ActiveRecord::Base.connection_db_config.configuration_hash
-      @database = "btrc_hub_test_tag_cleanup_#{ Process.pid }_#{ SecureRandom.hex(4) }"
-      record_class.establish_connection(config.merge(database: nil))
-      @connection = record_class.lease_connection
-      @connection.create_database(@database)
-      @database_created = true
-      @connection.execute("USE #{ @connection.quote_table_name(@database) }")
-    end
-
-    after do
-      @connection.drop_database(@database) if @database_created
-    ensure
-      TagCleanupMigrationRecord.remove_connection
-    end
-
-    before do
-      @connection.create_table(:tag_names) do |t|
-        t.string :name, null: false, index: { unique: true }
-        t.bigint :canonical_id
-        t.datetime :discarded_at, index: true
-      end
-      @connection.add_foreign_key(:tag_names, :tag_names, column: :canonical_id)
-      @connection.create_table(:tags) do |t|
-        t.references :tag_name, null: false, foreign_key: true, index: { unique: true }
-        t.datetime :discarded_at, index: true
-      end
-      @connection.create_table(:nico_tag_relations) do |t|
-        t.references :tag, null: false, foreign_key: true
-        t.references :nico_tag, null: false, foreign_key: { to_table: :tags }
-      end
-      @connection.create_table(:tag_implications) do |t|
-        t.references :tag, null: false, foreign_key: true
-        t.references :parent_tag, null: false, foreign_key: { to_table: :tags }
-      end
-      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
-        @connection.create_table(table) do |t|
-          t.references :tag, null: false, foreign_key: true
-        end
-      end
-
-      @connection.execute(<<~SQL)
-        INSERT INTO tag_names (id, name, canonical_id, discarded_at) VALUES
-          (1, 'kept', NULL, NULL),
-          (2, 'merged_alias', 1, NULL),
-          (3, 'nico:deleted', NULL, '2026-09-20'),
-          (4, 'nico:kept', NULL, NULL),
-          (5, 'deleted_name', NULL, '2026-09-20')
-      SQL
-      @connection.execute(<<~SQL)
-        INSERT INTO tags (id, tag_name_id, discarded_at) VALUES
-          (1, 1, NULL), (2, 2, '2026-09-20'),
-          (3, 3, '2026-09-20'), (4, 4, NULL)
-      SQL
-      @connection.execute(<<~SQL)
-        INSERT INTO nico_tag_relations (id, tag_id, nico_tag_id) VALUES
-          (1, 1, 4), (2, 2, 4), (3, 1, 3), (4, 2, 3)
-      SQL
-      @connection.execute(<<~SQL)
-        INSERT INTO tag_implications (id, tag_id, parent_tag_id) VALUES
-          (1, 1, 4), (2, 2, 1), (3, 1, 2), (4, 2, 3)
-      SQL
-      @connection.execute('INSERT INTO tag_versions (tag_id) VALUES (1), (2)')
-      @connection.execute('INSERT INTO nico_tag_versions (tag_id) VALUES (3), (4)')
-      @connection.execute('INSERT INTO material_versions (tag_id) VALUES (1), (2)')
-    end
-
-    it 'removes discarded records and their links while retaining aliases and history' do
-      [DeleteDiscardedRecordsFromTags, DeleteDiscardedRecordsFromTagNames].each do |klass|
-        migration = klass.new
-        allow(migration).to receive(:connection).and_return(@connection)
-        migration.suppress_messages { migration.up }
-      end
-
-      expect(@connection.select_values('SELECT id FROM tags ORDER BY id')).to eq([1, 4])
-      expect(@connection.select_rows('SELECT id, canonical_id FROM tag_names ORDER BY id'))
-          .to eq([[1, nil], [2, 1], [4, nil]])
-      expect(@connection.select_values('SELECT id FROM nico_tag_relations')).to eq([1])
-      expect(@connection.select_values('SELECT id FROM tag_implications')).to eq([1])
-      expect(@connection.select_values('SELECT tag_id FROM tag_versions ORDER BY tag_id'))
-          .to eq([1, 2])
-      expect(@connection.select_values('SELECT tag_id FROM nico_tag_versions ORDER BY tag_id'))
-          .to eq([3, 4])
-      expect(@connection.select_values('SELECT tag_id FROM material_versions ORDER BY tag_id'))
-          .to eq([1, 2])
-
-      [:tags, :tag_names].each do |table|
-        expect(@connection.column_exists?(table, :discarded_at)).to be(false)
-        expect(@connection.index_exists?(table, :discarded_at)).to be(false)
-      end
-      [:tag_versions, :nico_tag_versions, :material_versions].each do |table|
-        expect(@connection.foreign_key_exists?(table, :tags, column: :tag_id)).to be(false)
-      end
-      expect(@connection.foreign_key_exists?(:tags, :tag_names)).to be(true)
-      expect(@connection.foreign_key_exists?(:tag_names, :tag_names, column: :canonical_id))
-          .to be(true)
-      expect(@connection.index_exists?(:tag_names, :name, unique: true)).to be(true)
-      expect(@connection.index_exists?(:tags, :tag_name_id, unique: true)).to be(true)
-      [:nico_tag_relations, :tag_implications].each do |table|
-        expect(@connection.foreign_keys(table).map(&:to_table)).to eq(['tags', 'tags'])
-      end
-    end
-  end
-end

backend/spec/db/external_tags_spec.rb

@@ -1,191 +0,0 @@
-require 'rails_helper'
-require_relative '../../db/migrate/20260921040000_create_external_tags'
-require_relative '../../db/migrate/20260921050000_create_post_external_tags'
-require_relative '../../db/migrate/20260921060000_change_foreign_key_on_nico_tag_relations'
-require_relative '../../db/migrate/20260921230000_migrate_external_tags'
-
-RSpec.describe 'external tag migrations' do
-  self.use_transactional_tests = false
-
-  before do
-    record_class = Class.new(ActiveRecord::Base) do
-      self.abstract_class = true
-    end
-    stub_const('ExternalTagMigrationRecord', record_class)
-    config = ActiveRecord::Base.connection_db_config.configuration_hash
-    @database = "btrc_hub_test_external_tags_#{ Process.pid }_#{ SecureRandom.hex(4) }"
-    record_class.establish_connection(config.merge(database: nil))
-    @connection = record_class.lease_connection
-    @connection.create_database(@database)
-    @database_created = true
-    @connection.execute("USE #{ @connection.quote_table_name(@database) }")
-    version_class = Class.new(record_class) do
-      self.table_name = 'post_versions'
-    end
-    stub_const('MigrateExternalTags::MigrationPostVersion', version_class)
-    create_legacy_tables
-    seed_legacy_records
-  end
-
-  after do
-    @connection.drop_database(@database) if @database_created
-  ensure
-    ExternalTagMigrationRecord.remove_connection
-  end
-
-  def migrate klass
-    migration = klass.new
-    allow(migration).to receive(:connection).and_return(@connection)
-    migration.suppress_messages { migration.migrate(:up) }
-  end
-
-  def create_legacy_tables
-    @connection.create_table(:tag_names) { |t| t.string :name }
-    @connection.create_table(:tags) do |t|
-      t.references :tag_name, foreign_key: true
-      t.string :category
-      t.integer :post_count
-      t.datetime :created_at
-    end
-    @connection.create_table(:posts)
-    @connection.create_table(:post_tags) do |t|
-      t.references :post, foreign_key: true
-      t.references :tag, foreign_key: true
-      t.datetime :created_at
-    end
-    @connection.create_table(:nico_tag_versions) do |t|
-      t.bigint :tag_id
-      t.integer :version_no
-      t.string :name
-      t.datetime :created_at
-    end
-    @connection.create_table(:nico_tag_relations) do |t|
-      t.references :tag, foreign_key: true
-      t.references :nico_tag, foreign_key: { to_table: :tags }
-    end
-    [:post_tag_sections, :materials, :theatre_skip_event_tags].each do |table|
-      @connection.create_table(table) { |t| t.references :tag, foreign_key: true }
-    end
-    @connection.create_table(:tag_implications) do |t|
-      t.references :tag, foreign_key: true
-      t.references :parent_tag, foreign_key: { to_table: :tags }
-    end
-    @connection.create_table(:tag_similarities) do |t|
-      t.references :tag, foreign_key: true
-      t.references :target_tag, foreign_key: { to_table: :tags }
-    end
-    @connection.create_table(:post_versions) { |t| t.json :tags_json, null: false }
-    @connection.add_check_constraint(:post_versions, 'JSON_VALID(tags_json)',
-                                     name: 'chk_post_versions_tags_json_schema')
-  end
-
-  def seed_legacy_records
-    @connection.execute(<<~SQL)
-      INSERT INTO tag_names (id, name) VALUES (1, 'internal'), (2, 'nico:raw tag[]');
-    SQL
-    @connection.execute(<<~SQL)
-      INSERT INTO tags (id, tag_name_id, category, post_count, created_at) VALUES
-        (1, 1, 'general', 1, '2026-09-01'), (2, 2, 'nico', 1, '2026-09-02')
-    SQL
-    @connection.execute('INSERT INTO posts (id) VALUES (1)')
-    @connection.execute(<<~SQL)
-      INSERT INTO post_tags (post_id, tag_id, created_at) VALUES
-        (1, 1, '2026-09-03'), (1, 2, '2026-09-04')
-    SQL
-    @connection.execute(<<~SQL)
-      INSERT INTO nico_tag_versions (tag_id, version_no, name, created_at) VALUES
-        (2, 1, 'nico:raw tag[]', '2026-09-02'),
-        (3, 1, 'nico:deleted', '2026-09-01'),
-        (3, 2, 'nico:deleted_later', '2026-09-02')
-    SQL
-    @connection.execute('INSERT INTO nico_tag_relations (tag_id, nico_tag_id) VALUES (1, 2)')
-    @connection.execute(<<~SQL)
-      INSERT INTO tag_similarities (tag_id, target_tag_id) VALUES (1, 1), (1, 2), (2, 1)
-    SQL
-    @connection.execute('INSERT INTO theatre_skip_event_tags (tag_id) VALUES (1), (2)')
-    @legacy_internal = { 'id' => 1, 'version_no' => 2,
-                         'name' => 'internal', 'category' => 'general',
-                         'sections' => [{ 'begin_ms' => 1000, 'end_ms' => nil }] }
-    snapshots = [@legacy_internal,
-                 { 'id' => 2, 'category' => 'nico' },
-                 { 'id' => 3, 'category' => 'nico' }]
-    @connection.execute(<<~SQL)
-      INSERT INTO post_versions (tags_json) VALUES
-        (#{ @connection.quote(snapshots.to_json) }), ('[]')
-    SQL
-  end
-
-  def prepare_external_tables
-    migrate(CreateExternalTags)
-    migrate(CreatePostExternalTags)
-    migrate(ChangeForeignKeyOnNicoTagRelations)
-  end
-
-  it 'preserves ids, raw names, counts, timestamps, post links and historical-only tags' do
-    prepare_external_tables
-
-    rows = @connection.select_rows(<<~SQL)
-      SELECT id, platform, name, post_count, DATE_FORMAT(created_at, '%Y-%m-%d')
-      FROM external_tags ORDER BY id
-    SQL
-    expect(rows).to eq([
-        [2, 'nico', 'raw tag[]', 1, '2026-09-02'],
-        [3, 'nico', 'deleted', 0, '2026-09-01']])
-    expect(@connection.select_rows(<<~SQL)).to eq([[1, 2, '2026-09-04']])
-      SELECT post_id, external_tag_id, DATE_FORMAT(created_at, '%Y-%m-%d')
-      FROM post_external_tags
-    SQL
-    expect(@connection.foreign_key_exists?(:nico_tag_relations, :external_tags,
-                                           column: :nico_tag_id)).to be(true)
-    expect(@connection.foreign_key_exists?(:nico_tag_relations, :tags,
-                                           column: :tag_id)).to be(true)
-  end
-
-  it 'converts snapshots and removes only obsolete internal rows and derived links' do
-    prepare_external_tables
-    migrate(MigrateExternalTags)
-
-    expect(@connection.select_values('SELECT id FROM tags')).to eq([1])
-    expect(@connection.select_values('SELECT id FROM tag_names')).to eq([1])
-    expect(@connection.select_values('SELECT tag_id FROM post_tags')).to eq([1])
-    expect(@connection.select_rows('SELECT tag_id, nico_tag_id FROM nico_tag_relations'))
-        .to eq([[1, 2]])
-    expect(@connection.select_rows('SELECT tag_id, target_tag_id FROM tag_similarities'))
-        .to eq([[1, 1]])
-    expect(@connection.select_values('SELECT tag_id FROM theatre_skip_event_tags')).to eq([1])
-    expect(@connection.select_value('SELECT COUNT(*) FROM nico_tag_versions')).to eq(3)
-    versions = MigrateExternalTags::MigrationPostVersion.order(:id)
-    expect(versions.first.tags_json).to eq([
-        @legacy_internal.except('id').merge('tag_id' => 1),
-        { 'external_tag_id' => 2 }, { 'external_tag_id' => 3 }])
-    expect(versions.last.tags_json).to eq([])
-
-    invalid_snapshots = [@legacy_internal,
-                         { 'external_tag_id' => 0 },
-                         { 'external_tag_id' => 2, 'tag_id' => 1 },
-                         { 'external_tag_id' => 2, 'name' => 'extra' },
-                         { 'tag_id' => 1, 'version_no' => 1 }]
-    invalid_snapshots.each do |snapshot|
-      expect {
-        MigrateExternalTags::MigrationPostVersion.create!(tags_json: [snapshot])
-      }.to raise_error(ActiveRecord::StatementInvalid, /check constraint/i)
-    end
-    expect { MigrateExternalTags.new.down }
-        .to raise_error(ActiveRecord::IrreversibleMigration)
-  end
-
-  { post_tag_sections: '(tag_id) VALUES (2)',
-    materials: '(tag_id) VALUES (2)',
-    tag_implications: '(tag_id, parent_tag_id) VALUES (1, 2)' }.each do |table, values|
-    it "aborts before deleting data when #{ table } references a legacy nico tag" do
-      prepare_external_tables
-      @connection.execute("INSERT INTO #{ table } #{ values }")
-
-      expect { migrate(MigrateExternalTags) }.to raise_error(RuntimeError, /#{ table }/)
-
-      expect(@connection.select_values('SELECT id FROM tags ORDER BY id')).to eq([1, 2])
-      expect(MigrateExternalTags::MigrationPostVersion.first.tags_json.first)
-          .to eq(@legacy_internal)
-    end
-  end
-end

backend/spec/factories/external_tags.rb

@@ -1,6 +0,0 @@
-FactoryBot.define do
-  factory :external_tag do
-    platform { :nico }
-    sequence(:name) { |n| "external_tag_#{ n }" }
-  end
-end

backend/spec/factories/tag_names.rb

@@ -1,13 +1,5 @@
 FactoryBot.define do
   factory :tag_name do
-    language_code { 'ja' }
-    script_code { 'Jpan' }
-    primary_flg { true }
-    auto_generated { false }
-    sequence(:name) { |number| "tag-#{ SecureRandom.hex(4) }-#{ number }" }
-
-    trait :alias do
-      primary_flg { false }
-    end
+    name { "tag-#{SecureRandom.hex(4)}" }
   end
 end

backend/spec/factories/tags.rb

@@ -1,29 +1,22 @@
 FactoryBot.define do
   factory :tag do
     transient do
-      primary_name { nil }
-      primary_tag_name do
-        attributes = primary_name.nil? ? { } : { name: primary_name }
-        build(:tag_name, **attributes)
-      end
+      name { nil }
     end
 
     category { :general }
     post_count { 0 }
+    association :tag_name
 
     after(:build) do |tag, evaluator|
-      evaluator.primary_tag_name.primary_flg = true
-      tag.tag_names.target << evaluator.primary_tag_name
+      tag.name = evaluator.name if evaluator.name.present?
     end
 
-    before(:create) do |tag, evaluator|
-      evaluator.primary_tag_name.save!
-      # Compatibility write only; ownership is established through tag_id below.
-      tag.tag_name_id = evaluator.primary_tag_name.id
+    trait :nico do
+      category { :nico }
+      transient do
+        name { "nico:#{ SecureRandom.hex(4) }" }
       end
-
-    after(:create) do |tag, evaluator|
-      evaluator.primary_tag_name.update!(tag:, primary_flg: true)
     end
   end
 end

backend/spec/models/external_tag_spec.rb

@@ -1,38 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe ExternalTag, type: :model do
-  it 'preserves names without internal tag sanitisation or TagName records' do
-    external = nil
-
-    expect {
-      external = described_class.create!(platform: :nico, name: 'raw tag[]')
-    }.not_to change(TagName, :count)
-
-    expect(external.reload.name).to eq('raw tag[]')
-  end
-
-  it 'deletes post associations without deleting posts or version history' do
-    external = create(:external_tag)
-    post = create(:post)
-    PostExternalTag.create!(post:, external_tag: external)
-    version = NicoTagVersionRecorder.record!(
-        external_tag: external, event_type: :create, created_by_user: nil)
-
-    external.destroy!
-
-    expect(PostExternalTag.where(external_tag_id: external.id)).to be_empty
-    expect(post.reload.external_tags).to be_empty
-    expect(version.reload.tag_id).to eq(external.id)
-  end
-
-  it 'deletes external links without deleting linked internal tags' do
-    external = create(:external_tag)
-    tag = create(:tag)
-    NicoTagRelation.create!(nico_tag: external, tag:)
-
-    external.destroy!
-
-    expect(NicoTagRelation.where(nico_tag_id: external.id)).to be_empty
-    expect(Tag.exists?(tag.id)).to be(true)
-  end
-end

backend/spec/models/locale_spec.rb

@@ -1,71 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe Locale, type: :model do
-  def prepare_french_reference!
-    Language.find_or_create_by!(code: 'fr') { _1.name = 'French' }
-    Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
-  end
-
-  def create_french_locale!
-    prepare_french_reference!
-    described_class.create!(code: 'fr', language_code: 'fr',
-                            script_code: 'Latn', name: 'French')
-  end
-
-  it 'generates a primary name for every existing tag using the name generator' do
-    first = create(:tag, primary_name: 'first_existing_tag')
-    second = create(:tag, primary_name: 'second_existing_tag')
-    allow(TagName).to receive(:generate_name).and_call_original
-    allow(TagName).to receive(:generate_name)
-        .with(kind_of(described_class), first, primary_tag_name_for(first, 'ja').name)
-        .and_return('name_from_generator')
-
-    locale = create_french_locale!
-
-    expect(TagName).to have_received(:generate_name)
-        .with(locale, first, primary_tag_name_for(first, 'ja').name)
-    expect(TagName).to have_received(:generate_name)
-        .with(locale, second, primary_tag_name_for(second, 'ja').name)
-    expect(first.tag_names.find_by!(language_code: 'fr', primary_flg: true))
-        .to have_attributes(name: 'name_from_generator', tag_id: first.id,
-                            language_code: 'fr', script_code: 'Latn',
-                            primary_flg: true)
-    expect(second.tag_names.find_by!(language_code: 'fr', primary_flg: true))
-        .to have_attributes(tag_id: second.id, language_code: 'fr',
-                            script_code: 'Latn', primary_flg: true)
-    expect(TagName.where(language_code: 'fr', primary_flg: true,
-                         tag_id: [first.id, second.id]).count).to eq(2)
-  end
-
-  it 'does not duplicate an existing primary name in the new language' do
-    prepare_french_reference!
-    tag = create(:tag, primary_name: 'already_named')
-    existing = create(:tag_name, name: 'nom_existant', tag:,
-                                 language_code: 'fr', script_code: 'Latn')
-
-    create_french_locale!
-
-    expect(TagName.where(tag_id: tag.id, language_code: 'fr', primary_flg: true))
-        .to contain_exactly(existing)
-    expect(existing.reload).to have_attributes(
-        tag_id: tag.id, language_code: 'fr', script_code: 'Latn', primary_flg: true)
-  end
-
-  it 'creates a primary name when the language has only an alias' do
-    prepare_french_reference!
-    tag = create(:tag, primary_name: 'alias_only_tag')
-    alias_name = create(:tag_name, :alias, name: 'alias_fr',
-                                          tag:,
-                                          language_code: 'fr', script_code: 'Latn')
-
-    create_french_locale!
-
-    expect(alias_name.reload).to have_attributes(
-        tag_id: tag.id,
-        language_code: 'fr', script_code: 'Latn', primary_flg: false)
-    generated = TagName.find_by!(tag_id: tag.id, language_code: 'fr', primary_flg: true)
-    expect(generated).to have_attributes(tag_id: tag.id, language_code: 'fr',
-                                         script_code: 'Latn', primary_flg: true)
-    expect(TagName.where(tag_id: tag.id, language_code: 'fr', primary_flg: true).count).to eq(1)
-  end
-end

backend/spec/models/material_export_item_spec.rb

@@ -2,7 +2,7 @@ require 'rails_helper'
 
 RSpec.describe MaterialExportItem, type: :model do
   let(:user) { create(:user, :member) }
-  let(:tag) { create(:tag, primary_name: 'export_item', category: :material) }
+  let(:tag) { Tag.create!(tag_name: TagName.create!(name: 'export_item'), category: :material) }
   let(:material) do
     Material.create!(tag:, url: 'https://example.com/material',
                      created_by_user: user, updated_by_user: user)

backend/spec/models/nico_tag_relation_spec.rb

@@ -1,27 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe NicoTagRelation, type: :model do
-  it 'does not constrain the ExternalTag association to the nico platform' do
-    external_tag = create(:external_tag)
-    tag = create(:tag)
-    allow(external_tag).to receive(:platform).and_return('registered_external')
-    allow(external_tag).to receive(:nico?).and_return(false)
-
-    expect {
-      described_class.create!(nico_tag: external_tag, tag:)
-    }.to change(described_class, :count).by(1)
-    expect(tag.linked_nico_tags).to contain_exactly(external_tag)
-  end
-
-  it 'rejects an internal Tag through the external association type' do
-    expect {
-      described_class.new(nico_tag: create(:tag), tag: create(:tag))
-    }.to raise_error(ActiveRecord::AssociationTypeMismatch)
-  end
-
-  it 'rejects an ExternalTag through the internal association type' do
-    expect {
-      described_class.new(nico_tag: create(:external_tag), tag: create(:external_tag))
-    }.to raise_error(ActiveRecord::AssociationTypeMismatch)
-  end
-end

backend/spec/models/post_external_tag_spec.rb

@@ -1,25 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe PostExternalTag, type: :model do
-  it 'exposes both sides and enforces a unique post and external tag pair' do
-    post = create(:post)
-    external_tag = create(:external_tag)
-    described_class.create!(post:, external_tag:)
-
-    expect(post.external_tags).to contain_exactly(external_tag)
-    expect(external_tag.posts).to contain_exactly(post)
-    expect { described_class.create!(post:, external_tag:) }
-        .to raise_error(ActiveRecord::RecordNotUnique)
-  end
-
-  it 'removes associations when the post is deleted while retaining the external tag' do
-    post = create(:post)
-    external_tag = create(:external_tag)
-    described_class.create!(post:, external_tag:)
-
-    post.destroy!
-
-    expect(described_class.where(post_id: post.id)).to be_empty
-    expect(external_tag.reload.posts).to be_empty
-  end
-end

backend/spec/models/post_spec.rb

@@ -6,25 +6,6 @@ RSpec.describe Post, type: :model do
     PostUrlSanitisationRule.unscoped.delete_all
   end
 
-  describe '#snapshot_tags_json' do
-    it 'keeps internal snapshots and external identifiers distinct, even with the same id' do
-      post = create(:post)
-      tag = create(:tag)
-      external = create(:external_tag, id: tag.id)
-      create(:post_tag, post:, tag:)
-      create(:post_tag_section, post:, tag:, begin_ms: 2000, end_ms: nil)
-      PostExternalTag.create!(post:, external_tag: external)
-
-      expect(post.snapshot_tags_json).to eq([
-          { 'tag_id' => tag.id,
-            'version_no' => tag.version_no,
-            'name' => primary_tag_name_for(tag, 'ja').name,
-            'category' => tag.category,
-            'sections' => [{ 'begin_ms' => 2000, 'end_ms' => nil }] },
-          { 'external_tag_id' => external.id }])
-    end
-  end
-
   describe 'URL normalisation' do
     it 'normalises the HTTP URL before applying sanitisation rules' do
       PostUrlSanitisationRule.create!(

backend/spec/models/post_tag_spec.rb

@@ -1,73 +1,5 @@
-require 'rails_helper'
-
 RSpec.describe PostTag, type: :model do
-  describe 'uniqueness' do
-    it 'rejects duplicate post and tag pairs but allows either to be reused' do
-      post_tag = create(:post_tag)
-      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
-
-      expect(duplicate).not_to be_valid
-      expect(duplicate.errors.of_kind?(:post_id, :taken)).to be(true)
-      expect(build(:post_tag, post: post_tag.post, tag: create(:tag))).to be_valid
-      expect(build(:post_tag, post: create(:post), tag: post_tag.tag)).to be_valid
-    end
-
-    it 'enforces uniqueness in the database when validation is bypassed' do
-      post_tag = create(:post_tag)
-      duplicate = build(:post_tag, post: post_tag.post, tag: post_tag.tag)
-
-      expect { duplicate.save!(validate: false) }
-          .to raise_error(ActiveRecord::RecordNotUnique)
-    end
-  end
-
-  describe '#destroy!' do
-    it 'deletes only the selected pair and its sections and updates the counter' do
-      post_tag = create(:post_tag)
-      same_post = create(:post_tag, post: post_tag.post)
-      same_tag = create(:post_tag, tag: post_tag.tag)
-      sections = [post_tag, same_post, same_tag].map do |link|
-        create(:post_tag_section, post: link.post, tag: link.tag,
-                                  begin_ms: 1000, end_ms: 2000)
-      end
-
-      expect { post_tag.destroy! }.to change(described_class, :count).by(-1)
-          .and change(PostTagSection, :count).by(-1)
-          .and change { post_tag.tag.reload.post_count }.from(2).to(1)
-
-      expect(described_class.exists?(post: post_tag.post, tag: post_tag.tag)).to be(false)
-      expect(same_post.reload).to be_persisted
-      expect(same_tag.reload).to be_persisted
-      expect(PostTagSection.all).to contain_exactly(*sections.drop(1))
-      expect(post_tag.post.reload.tags).to contain_exactly(same_post.tag)
-      expect(post_tag.tag.reload.posts).to contain_exactly(same_tag.post)
-    end
-
-    it 'allows a removed tag to be added again without restoring old sections' do
-      post_tag = create(:post_tag)
-      create(:post_tag_section, post: post_tag.post, tag: post_tag.tag,
-                                begin_ms: 1000, end_ms: 2000)
-      post_tag.destroy!
-
-      replacement = create(:post_tag, post: post_tag.post, tag: post_tag.tag)
-
-      expect(replacement.reload.sections).to be_empty
-      expect(replacement.tag.reload.post_count).to eq(1)
-    end
-  end
-
   describe '#sections' do
-    it 'loads the owning post_tag from a section using both keys' do
-      post_tag = create(:post_tag)
-      create(:post_tag, post: post_tag.post)
-      create(:post_tag, tag: post_tag.tag)
-      section = create(:post_tag_section, post: post_tag.post,
-                                         tag: post_tag.tag,
-                                         begin_ms: 1000, end_ms: 2000)
-
-      expect(section.reload.post_tag).to eq(post_tag)
-    end
-
     it 'loads sections by post_id and tag_id' do
       post_tag = create(:post_tag)
       section = create(:post_tag_section,
@@ -80,25 +12,18 @@ RSpec.describe PostTag, type: :model do
     end
 
     it 'does not load sections for another tag on the same post' do
-      post_tag = create(:post_tag)
-      post = post_tag.post
+      post = create(:post)
+      tag = create(:tag)
       other_tag = create(:tag)
 
-      own_section = create(:post_tag_section,
-                           post:,
-                           tag: post_tag.tag,
-                           begin_ms: 1000,
-                           end_ms: 2000)
-
-      create(:post_tag, post:, tag: other_tag)
-
+      post_tag = create(:post_tag, post:, tag:)
       create(:post_tag_section,
              post:,
              tag: other_tag,
              begin_ms: 1000,
              end_ms: 2000)
 
-      expect(post_tag.reload.sections).to contain_exactly(own_section)
+      expect(post_tag.sections).to be_empty
     end
 
     it 'allows open-ended sections' do

backend/spec/models/post_version_spec.rb

@@ -1,8 +1,8 @@
 require 'rails_helper'
 
 RSpec.describe PostVersion, type: :model do
-  let!(:tag_name) { create(:tag_name, name: 'post_version_spec_tag') }
-  let!(:tag) { create(:tag, primary_tag_name: tag_name, category: :general) }
+  let!(:tag_name) { TagName.create!(name: 'post_version_spec_tag') }
+  let!(:tag) { Tag.create!(tag_name: tag_name, category: :general) }
 
   let!(:post_record) do
     Post.create!(title: 'spec post', url: 'https://example.com/post-version-spec').tap do |post|
@@ -19,7 +19,6 @@ RSpec.describe PostVersion, type: :model do
       url: post_record.url,
       thumbnail_base: post_record.thumbnail_base,
       tags: post_record.snapshot_tag_names.join(' '),
-      tags_json: post_record.snapshot_tags_json,
       parent_post_ids: post_record.snapshot_parent_post_ids.join(' '),
       original_created_from: post_record.original_created_from,
       original_created_before: post_record.original_created_before,

backend/spec/models/tag_implication_spec.rb

@@ -2,8 +2,8 @@ require 'rails_helper'
 
 RSpec.describe TagImplication, type: :model do
   it 'rejects a parent tag that would create a cycle' do
-    child = create(:tag, primary_name: 'tag_implication_cycle_child')
-    parent = create(:tag, primary_name: 'tag_implication_cycle_parent')
+    child = create(:tag, name: 'tag_implication_cycle_child')
+    parent = create(:tag, name: 'tag_implication_cycle_parent')
 
     described_class.create!(tag: child, parent_tag: parent)
 
@@ -17,9 +17,9 @@ RSpec.describe TagImplication, type: :model do
   end
 
   it 'terminates even when existing data already contains a cycle' do
-    child = create(:tag, primary_name: 'tag_implication_existing_cycle_child')
-    parent = create(:tag, primary_name: 'tag_implication_existing_cycle_parent')
-    ancestor = create(:tag, primary_name: 'tag_implication_existing_cycle_ancestor')
+    child = create(:tag, name: 'tag_implication_existing_cycle_child')
+    parent = create(:tag, name: 'tag_implication_existing_cycle_parent')
+    ancestor = create(:tag, name: 'tag_implication_existing_cycle_ancestor')
 
     described_class.create!(tag: parent, parent_tag: ancestor)
     described_class.insert_all!(

backend/spec/models/tag_name_sanitisation_rule_spec.rb

@@ -34,41 +34,9 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       described_class.create!(priority: 10, source_pattern: '_', replacement: '')
     end
 
-    context 'when only another language has the sanitised name' do
-      include_context 'English locale'
-
-      it 'keeps both names when sanitisation produces a cross-language match' do
-        japanese = create(:tag_name, name: 'foobar')
-        english = create(:tag_name, name: 'temporary',
-                                   language_code: 'en', script_code: 'Latn')
-        english.update_columns(name: 'foo_bar')
-
-        expect { described_class.apply! }.not_to change(TagName, :count)
-
-        expect(english.reload).to have_attributes(name: 'foobar', language_code: 'en')
-        expect(japanese.reload).to have_attributes(name: 'foobar', language_code: 'ja')
-      end
-
-      it 'renames without merging tags or deleting either language identity' do
-        japanese = create(:tag, primary_name: 'foobar')
-        english_name = create(:tag_name, name: 'temporary',
-                                        language_code: 'en', script_code: 'Latn')
-        english = create(:tag, primary_tag_name: english_name)
-        english_name.update_columns(name: 'foo_bar')
-
-        described_class.apply!
-
-        expect(english_name.reload).to have_attributes(
-            name: 'foobar', language_code: 'en', tag_id: english.id)
-        expect(primary_tag_name_for(japanese.reload, 'ja')).to have_attributes(
-            name: 'foobar', language_code: 'ja', tag_id: japanese.id)
-        expect(primary_tag_name_for(english.reload, 'en')).to eq(english_name)
-      end
-    end
-
     context 'when no conflicting tag_name exists' do
       let!(:tag_name) do
-        create(:tag_name, name: 'tmp').tap do |tn|
+        TagName.create!(name: 'tmp').tap do |tn|
           tn.update_columns(name: 'foo_bar', updated_at: Time.current)
         end
       end
@@ -79,72 +47,44 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
     end
 
-    context 'when a conflicting primary tag name exists' do
-      let!(:existing) { create(:tag_name, name: 'foobar') }
+    context 'when a conflicting canonical tag_name exists' do
+      let!(:existing) { TagName.create!(name: 'foobar') }
       let!(:source) do
-        create(:tag_name, name: 'tmp').tap do |tn|
+        TagName.create!(name: 'tmp').tap do |tn|
           tn.update_columns(name: 'foo_bar', updated_at: Time.current)
         end
       end
 
       it 'deletes the source tag_name' do
         described_class.apply!
-        expect(TagName.unscoped.exists?(source.id)).to be(false)
+        expect(TagName.exists?(source.id)).to be(false)
         expect(existing.reload.name).to eq('foobar')
       end
     end
 
     context 'when the source tag_name has a tag and the existing one has no tag' do
-      let!(:existing) { create(:tag_name, name: 'foobar') }
-      let!(:source_tag) { create(:tag, primary_name: 'tmp', category: :general) }
-      let!(:source_tag_name_id) { primary_tag_name_for(source_tag, 'ja').id }
+      let!(:existing) { TagName.create!(name: 'foobar') }
+      let!(:source_tag) { create(:tag, name: 'tmp', category: :general) }
+      let!(:source_tag_name_id) { source_tag.tag_name_id }
 
       before do
-        primary_tag_name_for(source_tag, 'ja').update_columns(
-            name: 'foo_bar', updated_at: Time.current)
+        source_tag.tag_name.update_columns(name: 'foo_bar', updated_at: Time.current)
       end
 
       it 'moves the tag to the existing tag_name' do
         described_class.apply!
-        expect(existing.reload).to have_attributes(
-            tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
-        expect(primary_tag_name_for(source_tag, 'ja')).to eq(existing)
-        expect(primary_tag_name_for(source_tag.reload, 'ja')).to eq(existing)
-        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
-      end
-    end
-
-    context 'when the sanitised name is an alias of an existing tag' do
-      let!(:existing_tag) { create(:tag) }
-      let!(:existing_primary) { primary_tag_name_for(existing_tag, 'ja') }
-      let!(:alias_name) do
-        create(:tag_name, :alias, name: 'foobar', tag: existing_tag)
-      end
-      let!(:source) do
-        create(:tag_name, name: 'tmp').tap do |tn|
-          tn.update_columns(name: 'foo_bar', updated_at: Time.current)
-        end
-      end
-
-      it 'deletes only the source and preserves the alias and its owning tag' do
-        described_class.apply!
-
-        expect(TagName.unscoped.exists?(source.id)).to be(false)
-        expect(alias_name.reload).to have_attributes(
-            tag_id: existing_tag.id, language_code: 'ja', primary_flg: false)
-        expect(TagName.find_by!(tag_id: existing_tag.id,
-                                language_code: 'ja', primary_flg: true))
-            .to eq(existing_primary)
-        expect(Tag.find(existing_tag.id)).to eq(existing_tag)
+        expected_tag_name_id = existing.canonical_id || existing.id
+        expect(source_tag.reload.tag_name_id).to eq(expected_tag_name_id)
+        expect(TagName.exists?(source_tag_name_id)).to be(false)
       end
     end
 
     context 'when both source and existing tag_names have tags' do
-      let!(:existing_tn) { create(:tag_name, name: 'foobar') }
-      let!(:existing_tag) { create(:tag, primary_tag_name: existing_tn, category: :general) }
+      let!(:existing_tn) { TagName.create!(name: 'foobar') }
+      let!(:existing_tag) { Tag.create!(tag_name: existing_tn, category: :general) }
 
-      let!(:source_tn) { create(:tag_name, name: 'tmp') }
-      let!(:source_tag) { create(:tag, primary_tag_name: source_tn, category: :general) }
+      let!(:source_tn) { TagName.create!(name: 'tmp') }
+      let!(:source_tag) { Tag.create!(tag_name: source_tn, category: :general) }
       let!(:source_tag_name_id) { source_tn.id }
 
       before do
@@ -152,15 +92,13 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
 
       it 'merges the source tag into the existing tag and deletes the source tag_name' do
-        post = create(:post)
-        PostTag.create!(post:, tag: source_tag)
+        expect(TagName.find_by(name: 'foobar')&.tag&.id).to eq(existing_tag.id)
+        expect(TagName.find_by(name: 'foo_bar')&.tag&.id).to eq(source_tag.id)
 
         described_class.apply!
 
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
-        expect(post.reload.tags).to contain_exactly(existing_tag)
-        expect(primary_tag_name_for(existing_tag.reload, 'ja').name).to eq('foobar')
+        expect(Tag.exists?(source_tag.id)).to be(false)
+        expect(TagName.exists?(source_tag.tag_name_id)).to be(false)
       end
     end
   end

backend/spec/models/tag_name_spec.rb

@@ -1,127 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe TagName, type: :model do
-  include_context 'English locale'
-
-  it 'allows the same name in different languages' do
-    create(:tag_name, name: 'shared_name')
-    english = build(:tag_name, name: 'shared_name',
-                              language_code: 'en', script_code: 'Latn')
-
-    expect(english).to be_valid
-    expect { english.save! }.to change(described_class, :count).by(1)
-  end
-
-  it 'rejects a duplicate name within the same language' do
-    create(:tag_name, name: 'shared_name')
-    duplicate = build(:tag_name, name: 'shared_name')
-
-    expect(duplicate).to be_invalid
-    expect(duplicate.errors.of_kind?(:name, :taken)).to be(true)
-  end
-
-  it 'creates Japanese factory names without requiring a tag' do
-    name = create(:tag_name)
-
-    expect(name.reload).to have_attributes(
-        language_code: 'ja', script_code: 'Jpan', primary_flg: true, tag_id: nil)
-  end
-
-  it 'persists both sides of the representative tag factory association' do
-    name = create(:tag_name)
-    tag = create(:tag, primary_tag_name: name)
-
-    expect(name.reload).to have_attributes(
-        tag_id: tag.id, language_code: 'ja', script_code: 'Jpan', primary_flg: true)
-    expect(name.tag).to eq(tag)
-    expect(described_class.find_by!(tag_id: tag.id, language_code: 'ja', primary_flg: true))
-        .to eq(name)
-    expect(tag.reload.tag_name_id).to eq(name.id)
-  end
-
-  it 'builds a primary name without persisting the tag or its name' do
-    tag = nil
-
-    expect {
-      tag = build(:tag, primary_name: 'built_primary')
-    }.to change(Tag, :count).by(0).and change(described_class, :count).by(0)
-
-    expect(tag).to be_new_record
-    expect(tag.tag_names.target).to contain_exactly(have_attributes(
-        name: 'built_primary', language_code: 'ja', script_code: 'Jpan',
-        primary_flg: true))
-  end
-
-  it 'persists an alias owned by the same tag as its primary name' do
-    primary_name = create(:tag_name)
-    tag = create(:tag, primary_tag_name: primary_name)
-    alias_name = create(:tag_name, :alias, name: 'valid_alias', tag:)
-
-    expect(alias_name.reload).to have_attributes(
-        tag_id: tag.id,
-        primary_flg: false, language_code: 'ja')
-    primary = described_class.find_by!(tag_id: alias_name.tag_id,
-                                       language_code: alias_name.language_code,
-                                       primary_flg: true)
-    expect(primary).to eq(primary_name)
-  end
-
-  describe '.canonicalise' do
-    it 'leaves detached aliases unchanged' do
-      create(:tag_name, :alias, name: 'detached_alias')
-
-      expect(described_class.canonicalise(Locale.nipponese, ['detached_alias']))
-          .to eq(['detached_alias'])
-    end
-
-    it 'leaves an alias unchanged when its language has no primary' do
-      tag = create(:tag, primary_name: '日本語のみ')
-      create(:tag_name, :alias, tag:, name: 'orphan_english_alias',
-                                language_code: 'en', script_code: 'Latn')
-
-      expect(described_class.canonicalise(locale, ['orphan_english_alias']))
-          .to eq(['orphan_english_alias'])
-    end
-
-    it 'resolves the primary name of the alias language on the same tag' do
-      tag = create(:tag, primary_name: '日本語正本')
-      english_primary = create(:tag_name, tag:, name: 'english_primary',
-                                          language_code: 'en', script_code: 'Latn')
-      english_alias = create(:tag_name, :alias, tag:, name: 'english_alias',
-                                                 language_code: 'en', script_code: 'Latn')
-      representative_id = tag.tag_name_id
-
-      primary = described_class.find_by!(tag_id: english_alias.tag_id,
-                                         language_code: english_alias.language_code,
-                                         primary_flg: true)
-
-      expect(primary).to eq(english_primary)
-      expect(described_class.canonicalise(locale, [english_alias.name]))
-          .to eq([english_primary.name])
-      expect(tag.reload.tag_name_id).to eq(representative_id)
-    end
-
-    it 'resolves only aliases in the requested language' do
-      japanese = create(:tag, primary_name: 'japanese_canonical')
-      english_name = create(:tag_name, name: 'english_canonical',
-                                      language_code: 'en', script_code: 'Latn')
-      english = create(:tag, primary_tag_name: english_name)
-      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                 tag: japanese)
-      english_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                tag: english,
-                                                language_code: 'en', script_code: 'Latn')
-
-      expect(japanese_alias.reload).to have_attributes(
-          tag_id: japanese.id,
-          primary_flg: false, language_code: 'ja')
-      expect(english_alias.reload).to have_attributes(
-          tag_id: english.id,
-          primary_flg: false, language_code: 'en')
-      expect(described_class.canonicalise(locale, ['shared_alias']))
-          .to eq(['english_canonical'])
-      expect(described_class.canonicalise(Locale.nipponese, ['shared_alias']))
-          .to eq(['japanese_canonical'])
-    end
-  end
-end

backend/spec/models/tag_spec.rb

@@ -1,184 +1,129 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
-  describe 'external tag separation' do
-    ['nico:reserved', 'NiCo:reserved'].each do |name|
-      it "rejects the reserved prefix #{ name } for internal tags" do
-        tag = build(:tag, primary_name: name)
-
-        expect(tag).to be_invalid
-        expect(tag.errors[:name]).to be_present
-        expect {
-          described_class.normalise_tags!(Locale.nipponese, [name])
-        }.to raise_error(Tag::NicoTagNormalisationError)
-      end
-    end
-
-    it 'finds external links by the internal tag id even when ids differ' do
-      tag = create(:tag)
-      external = create(:external_tag, id: tag.id + 10_000)
-      # The migration retains existing links without running model validation.
-      NicoTagRelation.insert_all!([{ tag_id: tag.id, nico_tag_id: external.id }])
-
-      expect(tag.linked_nico_tags).to contain_exactly(external)
-    end
-  end
-
   describe '.normalise_tags!' do
-    it 'canonicalises aliases in the supplied language only' do
-      Language.find_or_create_by!(code: 'en') { _1.name = 'English' }
-      Script.find_or_create_by!(code: 'Latn') { _1.name = 'Latin' }
-      Locale.insert_all!([
-          { code: 'en', language_code: 'en', script_code: 'Latn',
-            name: 'English', created_at: Time.current }]) unless Locale.exists?(code: 'en')
-      english_locale = Locale.find('en')
-      japanese = create(:tag, primary_name: 'japanese_canonical')
-      english_name = create(:tag_name, name: 'english_canonical',
-                                      language_code: 'en', script_code: 'Latn')
-      english = create(:tag, primary_tag_name: english_name)
-      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                 tag: japanese)
-      english_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                tag: english,
-                                                language_code: 'en', script_code: 'Latn')
-
-      expect(japanese_alias.reload).to have_attributes(
-          tag_id: japanese.id,
-          primary_flg: false, language_code: 'ja')
-      expect(english_alias.reload).to have_attributes(
-          tag_id: english.id,
-          primary_flg: false, language_code: 'en')
-      expect(described_class.normalise_tags!(
-          english_locale, ['shared_alias'],
-          with_tagme: false, with_no_deerjikist: false)).to eq([english])
-      expect(described_class.normalise_tags!(
-          Locale.nipponese, ['shared_alias'],
-          with_tagme: false, with_no_deerjikist: false)).to eq([japanese])
-    end
-
     it 'rejects deprecated tags when deny_deprecated is enabled' do
-      tag_name = create(:tag_name, name: 'normalise deprecated tag')
-      deprecated_tag = create(:tag,
-          primary_tag_name: tag_name,
+      tag_name = TagName.create!(name: 'normalise deprecated tag')
+      deprecated_tag = Tag.create!(
+        tag_name:,
         category: :general,
-          deprecated_at: 1.day.from_now)
+        deprecated_at: 1.day.from_now
+      )
 
       expect {
-        described_class.normalise_tags!(Locale.nipponese,
-            [primary_tag_name_for(deprecated_tag, 'ja').name],
-            deny_deprecated: true)
+        described_class.normalise_tags!(
+          [deprecated_tag.name],
+          deny_deprecated: true
+        )
       }.to raise_error(Tag::DeprecatedTagNormalisationError) { |error|
-        expect(error.tag_names).to eq([primary_tag_name_for(deprecated_tag, 'ja').name])
+        expect(error.tag_names).to eq([deprecated_tag.name])
       }
     end
 
     it 'rejects invalid section literals instead of treating them as zero' do
       expect {
-        described_class.normalise_tags!(Locale.nipponese,
+        described_class.normalise_tags!(
           ['normalise_invalid_section[1:aa-2:00]'],
-            with_sections: true)
+          with_sections: true
+        )
       }.to raise_error(Tag::SectionLiteralParseError)
     end
 
     it 'parses open-ended section literals' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[1:00-]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
 
     it 'parses omitted begin as zero' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[-1:00]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[0, 60_000]])
     end
 
     it 'treats fully open section literals as plain tags' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[-]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections)[tag.id]).to be_nil
     end
 
     it 'treats [0:00-] as a plain tag' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[0:00-]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections)[tag.id]).to be_nil
     end
 
     it 'expands zero-width sections to one millisecond' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[1:00-1:00]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 60_001]])
     end
 
     it 'swaps reversed section boundaries' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[2:00-1:00]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, 120_000]])
     end
 
     it 'merges open-ended sections over later bounded sections' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[1:00-][2:00-3:00]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
 
     it 'merges adjacent bounded and open-ended sections' do
-      result = described_class.normalise_tags!(Locale.nipponese,
+      result = described_class.normalise_tags!(
         ['伊地知ニジカ[1:00-3:00][3:00-]'],
-          with_sections: true)
+        with_sections: true
+      )
 
-      tag = result.fetch(:tags).find do |candidate|
-        primary_tag_name_for(candidate, 'ja').name == '伊地知ニジカ'
-      end
+      tag = result.fetch(:tags).find { _1.name == '伊地知ニジカ' }
       expect(result.fetch(:sections).fetch(tag.id)).to eq([[60_000, nil]])
     end
   end
 
   describe '.expand_parent_tags' do
     it 'expands through multiple deprecated parents to an active ancestor' do
-      child = create(:tag, primary_name: 'expand_child')
-      deprecated_parent = create(:tag,
-          primary_name: 'expand_deprecated_parent',
-          deprecated_at: Time.current)
-      deprecated_grandparent = create(:tag,
-          primary_name: 'expand_deprecated_grandparent',
-          deprecated_at: Time.current)
-      active_ancestor = create(:tag, primary_name: 'expand_active_ancestor')
+      child = create(:tag, name: 'expand_child')
+      deprecated_parent = create(
+        :tag,
+        name: 'expand_deprecated_parent',
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = create(
+        :tag,
+        name: 'expand_deprecated_grandparent',
+        deprecated_at: Time.current
+      )
+      active_ancestor = create(:tag, name: 'expand_active_ancestor')
       TagImplication.create!(tag: child, parent_tag: deprecated_parent)
       TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
       TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
@@ -195,8 +140,8 @@ RSpec.describe Tag, type: :model do
     end
 
     it 'terminates when implications contain a cycle' do
-      first = create(:tag, primary_name: 'expand_cycle_first')
-      second = create(:tag, primary_name: 'expand_cycle_second')
+      first = create(:tag, name: 'expand_cycle_first')
+      second = create(:tag, name: 'expand_cycle_second')
       TagImplication.create!(tag: first, parent_tag: second)
       now = Time.current
       TagImplication.insert_all!(
@@ -214,170 +159,45 @@ RSpec.describe Tag, type: :model do
     end
   end
 
-  describe '.find_or_create_by_tag_name!' do
-    context 'with an explicit locale' do
-      include_context 'English locale'
+  describe 'deprecated validation' do
+    it 'rejects deprecated nico tags' do
+      tag = build(
+        :tag,
+        name: 'nico:deprecated_validation',
+        category: :nico,
+        deprecated_at: Time.current
+      )
 
-      it 'creates the representative name with locale attributes and ownership' do
-        tag = described_class.find_or_create_by_tag_name!(
-            locale, 'english_name', category: :character)
-
-        expect(primary_tag_name_for(tag, 'en')).to have_attributes(
-            language_code: 'en', script_code: 'Latn',
-            primary_flg: true, tag_id: tag.id)
-        expect(tag.category).to eq('character')
-      end
-
-      it 'creates separate tag identities for the same name in different languages' do
-        japanese = described_class.find_or_create_by_tag_name!(
-            Locale.nipponese, 'same_name', category: :general)
-        english = described_class.find_or_create_by_tag_name!(
-            locale, 'same_name', category: :character)
-
-        expect(english).not_to eq(japanese)
-        expect(primary_tag_name_for(english, 'en')).to have_attributes(
-            name: 'same_name', tag_id: english.id, language_code: 'en', primary_flg: true)
-        expect(primary_tag_name_for(japanese, 'ja')).to have_attributes(
-            name: 'same_name', tag_id: japanese.id, language_code: 'ja', primary_flg: true)
-        expect(described_class.find_or_create_by_tag_name!(
-            locale, 'same_name', category: :general)).to eq(english)
-        expect(described_class.find_or_create_by_tag_name!(
-            Locale.nipponese, 'same_name', category: :general)).to eq(japanese)
-      end
-
-      it 'preserves the V1 representative when looking up another primary language' do
-        tag = create(:tag, primary_name: '日本語代表名')
-        representative_id = tag.tag_name_id
-        english = create(:tag_name, name: 'english_primary', tag:,
-            language_code: 'en', script_code: 'Latn')
-
-        found = described_class.find_or_create_by_tag_name!(
-            locale, english.name, category: :general)
-
-        expect(found).to eq(tag)
-        expect(tag.reload.tag_name_id).to eq(representative_id)
-        expect(english.reload.tag_id).to eq(tag.id)
-      end
-
-      it 'normalises names using the supplied locale' do
-        tags = described_class.normalise_tags!(
-            locale, ['character:normalised_english'],
-            with_tagme: false, with_no_deerjikist: false)
-
-        expect(tags.length).to eq(1)
-        expect(primary_tag_name_for(tags.first, 'en')).to have_attributes(
-            name: 'normalised_english', language_code: 'en', script_code: 'Latn',
-            primary_flg: true, tag_id: tags.first.id)
-      end
-    end
-
-    it 'creates a tag and name with the requested category after stripping whitespace' do
-      tag = nil
-
-      expect {
-        tag = described_class.find_or_create_by_tag_name!(Locale.nipponese,
-            '  lookup_new  ', category: :character)
-      }.to change(Tag, :count).by(1).and change(TagName, :count).by(1)
-
-      expect(primary_tag_name_for(tag, 'ja').name).to eq('lookup_new')
-      expect(tag.category).to eq('character')
-    end
-
-    it 'reuses the owning tag for an alias without changing its category' do
-      tag = create(:tag, category: :character)
-      representative_id = tag.tag_name_id
-      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
-      expect(alias_name.reload).to have_attributes(
-          tag_id: tag.id,
-          primary_flg: false, language_code: 'ja')
-      found = nil
-
-      expect {
-        found = described_class.find_or_create_by_tag_name!(Locale.nipponese,
-            alias_name.name, category: :general)
-      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
-
-      expect(found).to eq(tag)
-      expect(found.category).to eq('character')
-      expect(tag.reload.tag_name_id).to eq(representative_id)
-    end
-
-    it 'reuses the owning tag through another alias' do
-      tag = create(:tag)
-      primary = primary_tag_name_for(tag, 'ja')
-      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
-      other_alias = create(:tag_name, :alias, name: 'lookup_other_alias', tag:)
-
-      expect([alias_name.reload, other_alias.reload]).to all(have_attributes(
-          tag_id: tag.id,
-          primary_flg: false, language_code: 'ja'))
-
-      expect {
-        found = described_class.find_or_create_by_tag_name!(Locale.nipponese,
-            alias_name.name, category: :general)
-        expect(found).to eq(tag)
-      }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
-
-      expect(primary_tag_name_for(tag.reload, 'ja')).to eq(primary)
+      expect(tag).not_to be_valid
+      expect(tag.errors[:deprecated_at]).to include('ニコタグは廃止できません．')
     end
   end
 
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
-    let!(:source_tag_name) { primary_tag_name_for(source_tag, 'ja') }
+    let!(:source_tag_name) { source_tag.tag_name }
 
     let!(:post_record) do
       Post.create!(url: 'https://example.com/posts/1', title: 'test post')
     end
 
-    context 'with names in multiple languages' do
-      include_context 'English locale'
-
-      it 'keeps the target primary and moves source names as aliases' do
-        english_primary = create(:tag_name, tag: target_tag,
-            name: 'target_english', language_code: 'en', script_code: 'Latn')
-        source_primary = create(:tag_name, tag: source_tag,
-            name: 'source_english', language_code: 'en', script_code: 'Latn')
-        source_alias = create(:tag_name, :alias, tag: source_tag,
-            name: 'source_english_alias', language_code: 'en', script_code: 'Latn')
-
-        described_class.merge_tags!(target_tag, [source_tag])
-
-        expect(primary_tag_name_for(target_tag.reload, 'en')).to eq(english_primary)
-        expect([source_primary.reload, source_alias.reload]).to all(have_attributes(
-            tag_id: target_tag.id, language_code: 'en', primary_flg: false))
-      end
-
-      it 'inherits a source primary when the target has no name in that language' do
-        source_primary = create(:tag_name, tag: source_tag,
-            name: 'inherited_english', language_code: 'en', script_code: 'Latn')
-        source_alias = create(:tag_name, :alias, tag: source_tag,
-            name: 'inherited_alias', language_code: 'en', script_code: 'Latn')
-
-        described_class.merge_tags!(target_tag, [source_tag])
-
-        expect(primary_tag_name_for(target_tag.reload, 'en')).to eq(source_primary)
-        expect(source_primary.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'en', primary_flg: true)
-        expect(source_alias.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'en', primary_flg: false)
-      end
-    end
-
     context 'when merging a simple source tag' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'deletes the source tag, moves its post link, and keeps its name as an alias' do
+      it 'discards the source post_tag, creates an active target post_tag, discards the source tag, and aliases the source tag_name' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        target_link = PostTag.find_by(post: post_record, tag: target_tag)
+        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
 
-        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(target_link).to be_present
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
+        expect(source_pt.discarded_at).to be_present
+        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(active_target).to be_present
+
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
+        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -386,111 +206,39 @@ RSpec.describe Tag, type: :model do
       let!(:target_post_tag) { PostTag.create!(post: post_record, tag: target_tag) }
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
-      it 'deletes the source link and preserves the existing target link' do
-        create(:post_tag_section, post: post_record, tag: source_tag,
-                                  begin_ms: 1000, end_ms: 2000)
-        target_section = create(:post_tag_section, post: post_record,
-                                                   tag: target_tag,
-                                                   begin_ms: 3000, end_ms: nil)
-
+      it 'discards the source post_tag, keeps one active target post_tag, discards the source tag, and aliases the source tag_name' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        target_links = PostTag.where(post: post_record, tag: target_tag)
+        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        active = PostTag.kept.where(post_id: post_record.id, tag_id: target_tag.id)
 
-        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(target_links).to contain_exactly(target_post_tag)
-        expect(PostTagSection.where(post: post_record, tag: source_tag)).to be_empty
-        expect(target_post_tag.reload.sections).to contain_exactly(target_section)
+        expect(source_pt.discarded_at).to be_present
+        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(active.count).to eq(1)
+        expect(active.first.id).to eq(target_post_tag.id)
 
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
+        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
 
-    it 'keeps source history and records the new target alias after deleting the source' do
-      user = create_member_user!
-      source_name = primary_tag_name_for(source_tag, 'ja').name
-      source_alias = create(:tag_name, :alias, name: 'merge_alias', tag: source_tag)
-      TagVersioning.ensure_snapshot!(source_tag, created_by_user: user)
-      original_version = source_tag.tag_versions.first
-
-      described_class.merge_tags!(target_tag, [source_tag], created_by_user: user)
-
-      versions = TagVersion.where(tag_id: source_tag.id).order(:version_no)
-      expect(versions.pluck(:version_no, :event_type))
-          .to eq([[1, 'create'], [2, 'discard']])
-      expect(versions.first).to eq(original_version)
-      expect(versions.last.created_by_user).to eq(user)
-      expect(versions.last.names).to include(
-          hash_including('language_code' => 'ja', 'name' => source_name,
-                         'primary_flg' => true, 'auto_generated' => false),
-          hash_including('language_code' => 'ja', 'name' => source_alias.name,
-                         'primary_flg' => false, 'auto_generated' => false))
-      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-
-      target_versions = target_tag.tag_versions.order(:version_no)
-      expect(target_versions.pluck(:event_type)).to eq(['create', 'update'])
-      target_aliases = target_versions.last.names.filter_map { |name|
-        name['name'] if name['language_code'] == 'ja' && !name['primary_flg']
-      }
-      expect(target_aliases).to contain_exactly('merge_alias', source_name)
-    end
-
-    it 'deletes source relationships while preserving unrelated relationships' do
-      parent = create(:tag)
-      child = create(:tag)
-      nico_tag = create(:external_tag)
-      TagImplication.create!(tag: source_tag, parent_tag: parent)
-      TagImplication.create!(tag: child, parent_tag: source_tag)
-      kept_implication = TagImplication.create!(tag: target_tag, parent_tag: parent)
-      NicoTagRelation.create!(tag: source_tag, nico_tag:)
-      kept_relation = NicoTagRelation.create!(tag: target_tag, nico_tag:)
-      TagSimilarity.create!(tag: source_tag, target_tag:, cos: 0.5)
-      TagSimilarity.create!(tag: target_tag, target_tag: source_tag, cos: 0.5)
-      kept_similarity = TagSimilarity.create!(tag: target_tag, target_tag: parent,
-                                               cos: 0.5)
-
-      described_class.merge_tags!(target_tag, [source_tag])
-
-      expect(TagImplication.all).to contain_exactly(kept_implication)
-      expect(NicoTagRelation.all).to contain_exactly(kept_relation)
-      expect(TagSimilarity.all).to contain_exactly(kept_similarity)
-      expect(TagVersion.where(tag_id: source_tag.id).order(:version_no).last.parent_tag_ids)
-          .to eq(parent.id.to_s)
-    end
-
-    it 'preserves material history referencing the deleted source tag' do
-      source_tag.update!(category: :material)
-      target_tag.update!(category: :material)
-      material = Material.create!(tag: source_tag, url: 'https://example.com/material')
-      version = MaterialVersionRecorder.record!(
-          material:, event_type: :create, created_by_user: nil)
-      material.update!(tag: target_tag)
-
-      described_class.merge_tags!(target_tag, [source_tag])
-
-      expect(version.reload).to have_attributes(
-          tag_id: source_tag.id, tag_name: source_tag_name.name, tag_category: 'material')
-      expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-      expect(material.reload.tag).to eq(target_tag)
-    end
-
     context 'when source_tags includes the target itself' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
       it 'ignores the target in source_tags while still merging the source tag' do
         described_class.merge_tags!(target_tag, [source_tag, target_tag])
 
-        target_link = PostTag.find_by(post: post_record, tag: target_tag)
+        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
 
         expect(Tag.find(target_tag.id)).to be_present
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(target_link).to be_present
-        expect(source_tag_name.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
+        expect(source_pt.discarded_at).to be_present
+        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(active_target).to be_present
+        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -512,17 +260,18 @@ RSpec.describe Tag, type: :model do
         )
       end
 
-      it 'still merges and keeps the source name as an alias without validating it' do
+      it 'still merges, but discards the source tag_name instead of aliasing it' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        target_link = PostTag.find_by(post: post_record, tag: target_tag)
+        source_pt = PostTag.with_discarded.find(source_post_tag.id)
+        active_target = PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)
+        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name.id)
 
-        expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
-        expect(target_link).to be_present
+        expect(source_pt.discarded_at).to be_present
+        expect(source_pt.tag_id).to eq(source_tag.id)
+        expect(active_target).to be_present
 
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload).to have_attributes(
-            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -539,30 +288,34 @@ RSpec.describe Tag, type: :model do
             message: 'init')
       end
 
-      it 'rolls back earlier deletions, links, and history when a later source has a wiki' do
-        earlier_source = create(:tag)
-        earlier_name = primary_tag_name_for(earlier_source, 'ja')
-        source_section = create(:post_tag_section, post: post_record,
-                                                   tag: source_tag,
-                                                   begin_ms: 1000, end_ms: 2000)
-
+      it 'rolls back the transaction' do
         expect {
-          described_class.merge_tags!(target_tag, [earlier_source, source_tag])
+          described_class.merge_tags!(target_tag, [source_tag])
         }.to raise_error(ActiveRecord::RecordInvalid)
 
-        expect(Tag.unscoped.exists?(earlier_source.id)).to be(true)
-        expect(earlier_name.reload).to have_attributes(
-            tag_id: earlier_source.id, language_code: 'ja', primary_flg: true)
-        expect(TagVersion.where(tag_id: [earlier_source.id, source_tag.id, target_tag.id]))
-            .to be_empty
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(true)
-        expect(TagName.unscoped.exists?(source_tag_name.id)).to be(true)
-        expect(source_post_tag.reload.tag_id).to eq(source_tag.id)
-        expect(source_post_tag.sections).to contain_exactly(source_section)
-        expect(PostTag.find_by(post: post_record, tag: target_tag)).to be_nil
-        expect(source_tag.reload.post_count).to eq(1)
-        expect(source_tag_name.reload).to have_attributes(
-            tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
+        expect(Tag.with_discarded.find(source_tag.id)).not_to be_discarded
+        expect(TagName.with_discarded.find(source_tag_name.id)).not_to be_discarded
+        expect(PostTag.kept.find(source_post_tag.id).tag_id).to eq(source_tag.id)
+        expect(PostTag.kept.find_by(post_id: post_record.id, tag_id: target_tag.id)).to be_nil
+        expect(source_tag_name.reload.canonical_id).to be_nil
+        expect(target_tag.reload.post_count).to eq(0)
+      end
+    end
+
+    context 'when merging a nico source tag' do
+      let!(:target_tag) { create(:tag, category: :nico, name: 'nico:foo') }
+      let!(:source_tag) { create(:tag, category: :nico, name: 'nico:bar') }
+      let!(:source_tag_name_id) { source_tag.tag_name_id }
+
+      it 'discards the source tag_name instead of aliasing it' do
+        described_class.merge_tags!(target_tag, [source_tag])
+
+        discarded_source_tag = Tag.with_discarded.find(source_tag.id)
+        discarded_source_tag_name = TagName.with_discarded.find(source_tag_name_id)
+
+        expect(discarded_source_tag).to be_discarded
+        expect(discarded_source_tag_name).to be_discarded
+        expect(discarded_source_tag_name.canonical_id).to be_nil
         expect(target_tag.reload.post_count).to eq(0)
       end
     end
@@ -580,7 +333,6 @@ RSpec.describe Tag, type: :model do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
-        tags_json: post.snapshot_tags_json,
         parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
@@ -612,15 +364,12 @@ RSpec.describe Tag, type: :model do
         expect(latest.event_type).to eq('update')
         expect(latest.created_by_user).to be_nil
         expect(latest.tags).to eq(snapshot_tags(post_record.reload))
-        expect(latest.tags_json.map { |item| item.fetch('tag_id') }).to eq([target_tag.id])
-        expect(affected_versions.first.tags_json.map { |item| item.fetch('tag_id') })
-            .to eq([source_tag.id])
 
         expect(unaffected_post.reload.post_versions.count).to eq(1)
       end
     end
 
-    context 'when the source tag has no post_tags' do
+    context 'when the source tag has no active post_tags' do
       let!(:another_post) do
         Post.create!(url: 'https://example.com/posts/3', title: 'another post')
       end

backend/spec/models/version_record_spec.rb

@@ -1,19 +1,17 @@
 require 'rails_helper'
 
 RSpec.describe VersionRecord, type: :model do
-  let!(:tag) { create(:tag, primary_name: 'version_record_tag') }
-  let!(:nico_tag) { create(:external_tag, name: 'version_record_tag') }
+  let!(:tag) { create(:tag, name: 'version_record_tag') }
+  let!(:nico_tag) { create(:tag, :nico, name: 'nico:version_record_tag') }
 
   it 'makes TagVersion read only after create' do
     version = TagVersion.create!(
       tag: tag,
       version_no: 1,
       event_type: 'create',
-      name: primary_tag_name_for(tag, 'ja').name,
+      name: tag.name,
       category: tag.category,
       aliases: '',
-      names: [{ language_code: 'ja', name: primary_tag_name_for(tag, 'ja').name,
-                script_code: 'Jpan', primary_flg: true }],
       parent_tag_ids: '',
       created_at: Time.current,
       created_by_user: nil
@@ -29,11 +27,9 @@ RSpec.describe VersionRecord, type: :model do
       tag: tag,
       version_no: 1,
       event_type: 'create',
-      name: primary_tag_name_for(tag, 'ja').name,
+      name: tag.name,
       category: tag.category,
       aliases: '',
-      names: [{ language_code: 'ja', name: primary_tag_name_for(tag, 'ja').name,
-                script_code: 'Jpan', primary_flg: true }],
       parent_tag_ids: '',
       created_at: Time.current,
       created_by_user: nil
@@ -46,10 +42,10 @@ RSpec.describe VersionRecord, type: :model do
 
   it 'makes NicoTagVersion read only after create' do
     version = NicoTagVersion.create!(
-      external_tag: nico_tag,
+      tag: nico_tag,
       version_no: 1,
       event_type: 'create',
-      name: "nico:#{ nico_tag.name }",
+      name: nico_tag.name,
       linked_tags: '',
       created_at: Time.current,
       created_by_user: nil
@@ -62,10 +58,10 @@ RSpec.describe VersionRecord, type: :model do
 
   it 'prevents NicoTagVersion destroy' do
     version = NicoTagVersion.create!(
-      external_tag: nico_tag,
+      tag: nico_tag,
       version_no: 1,
       event_type: 'create',
-      name: "nico:#{ nico_tag.name }",
+      name: nico_tag.name,
       linked_tags: '',
       created_at: Time.current,
       created_by_user: nil

backend/spec/requests/deerjikists_spec.rb

@@ -30,7 +30,7 @@ RSpec.describe 'Deerjikists API', type: :request do
 
         expect(json['tag']).to be_a(Hash)
         expect(json['tag']['id']).to eq(tag1.id)
-        expect(json['tag']['name']).to eq(primary_tag_name_for(tag1, 'ja').name)
+        expect(json['tag']['name']).to eq(tag1.name)
       end
     end
 

backend/spec/requests/error_responses_spec.rb

@@ -15,7 +15,7 @@ RSpec.describe 'error responses', type: :request do
 
     it 'returns a stable field-error payload for unprocessable requests' do
       member = create(:user, :member)
-      tag = create(:tag, category: :general, primary_name: 'error_response_tag')
+      tag = create(:tag, :general, name: 'error_response_tag')
       sign_in_as(member)
 
       patch "/tags/#{ tag.id }", params: { category: 'nico' }

backend/spec/requests/gekanator_learning_spec.rb

@@ -898,22 +898,23 @@ RSpec.describe 'Gekanator learning API', type: :request do
 
   describe 'GET /gekanator/questions' do
     it 'omits questions for deprecated tags' do
-      active_tag = create(:tag, primary_name: 'active_question_tag', category: :general)
-      deprecated_tag = create(:tag,
-          primary_name: 'deprecated_question_tag',
+      active_tag = Tag.create!(name: 'active_question_tag', category: :general)
+      deprecated_tag = Tag.create!(
+        name: 'deprecated_question_tag',
         category: :general,
-          deprecated_at: Time.current)
+        deprecated_at: Time.current
+      )
 
       [active_tag, deprecated_tag].each do |question_tag|
         GekanatorQuestion.create!(
-          text: "#{ primary_tag_name_for(question_tag, 'ja').name }?",
+          text: "#{ question_tag.name }?",
           kind: 'tag',
           source: 'admin_curated',
           status: 'accepted',
           priority_weight: 1.0,
           condition: {
             type: 'tag',
-            key: "#{ question_tag.category }:#{ primary_tag_name_for(question_tag, 'ja').name }"
+            key: "#{ question_tag.category }:#{ question_tag.name }"
           },
           created_by: admin
         )

backend/spec/requests/gekanator_posts_spec.rb

@@ -4,11 +4,12 @@ require 'rails_helper'
 RSpec.describe 'Gekanator posts API', type: :request do
   describe 'GET /gekanator/posts' do
     it 'omits deprecated tags and returns the stored similarity cosine' do
-      active_tag = create(:tag, primary_name: 'active tag', category: :general)
-      deprecated_tag = create(:tag,
-          primary_name: 'deprecated tag',
+      active_tag = Tag.create!(name: 'active tag', category: :general)
+      deprecated_tag = Tag.create!(
+        name: 'deprecated tag',
         category: :general,
-          deprecated_at: Time.current)
+        deprecated_at: Time.current
+      )
       post_record = Post.create!(title: 'source', url: 'https://example.com/source')
       target_post = Post.create!(title: 'target', url: 'https://example.com/target')
 

backend/spec/requests/locale_write_paths_spec.rb

@@ -1,237 +0,0 @@
-require 'rails_helper'
-
-RSpec.describe 'Locale propagation on write paths', type: :request do
-  include_context 'English locale'
-
-  let(:member) { create(:user, :member) }
-
-  before do
-    sign_in_as(member)
-  end
-
-  def expect_localised_tag(name, expected_locale)
-    tag_name = TagName.find_by!(name:, language_code: expected_locale.language_code)
-    expect(tag_name).to have_attributes(
-        script_code: expected_locale.script_code, primary_flg: true)
-    expect(tag_name.tag_id).to be_present
-    tag_name.tag
-  end
-
-  ['en', nil].each do |requested_locale|
-    context "with locale #{ requested_locale.inspect }" do
-      let(:locale_params) { requested_locale ? { locale: requested_locale } : { } }
-      let(:expected_locale) { requested_locale ? locale : Locale.nipponese }
-
-      it 'creates post tags in the requested language or Japanese fallback' do
-        post '/posts', params: locale_params.merge(
-            title: 'Locale post', url: 'https://example.com/locale-post',
-            tags: 'locale_post_tag', parent_post_ids: '')
-
-        expect(response).to have_http_status(:created), response.body
-        tag = expect_localised_tag('locale_post_tag', expected_locale)
-        expect(Post.find(json.fetch('id')).tags).to include(tag)
-      end
-
-      it 'updates post tags in the requested language or Japanese fallback' do
-        record = create(:post)
-        PostVersionRecorder.record!(post: record, event_type: :create, created_by_user: member)
-
-        put "/posts/#{ record.id }", params: locale_params.merge(
-            title: record.title, tags: 'locale_updated_tag', parent_post_ids: '',
-            base_version_no: record.reload.version_no)
-
-        expect(response).to have_http_status(:ok), response.body
-        tag = expect_localised_tag('locale_updated_tag', expected_locale)
-        expect(record.reload.tags).to include(tag)
-      end
-
-      it 'passes the resolved locale to bulk creation' do
-        # Worker propagation is exercised in post_bulk_creator_spec.
-        expect_any_instance_of(PostBulkCreator).to receive(:run)
-            .with(expected_locale).and_return(results: [])
-        manifest = [{ title: 'Bulk locale', url: 'https://example.com/bulk-locale',
-                      tags: 'bulk_locale_tag', parent_post_ids: '' }]
-
-        post '/posts/bulk', params: locale_params.merge(posts: JSON.generate(manifest)),
-                            headers: { 'CONTENT_TYPE' => 'multipart/form-data' }
-
-        expect(response).to have_http_status(:ok), response.body
-      end
-
-      it 'creates materials with tags in the resolved locale' do
-        post '/materials', params: locale_params.merge(
-            tag: 'locale_material', url: 'https://example.com/material')
-
-        expect(response).to have_http_status(:created), response.body
-        tag = expect_localised_tag('locale_material', expected_locale)
-        expect(Material.find(json.fetch('id')).tag).to eq(tag)
-      end
-
-      it 'updates materials with tags in the resolved locale' do
-        tag = create(:tag, category: :material)
-        material = Material.create!(tag:, url: 'https://example.com/material')
-
-        put "/materials/#{ material.id }", params: locale_params.merge(
-            tag: 'locale_material_updated', url: material.url)
-
-        expect(response).to have_http_status(:ok), response.body
-        resolved_tag = expect_localised_tag('locale_material_updated', expected_locale)
-        expect(material.reload.tag).to eq(resolved_tag)
-      end
-
-      it 'links Nico external tags to internal tags in the resolved locale' do
-        external = create(:external_tag)
-        NicoTagVersionRecorder.record!(
-            external_tag: external, event_type: :create, created_by_user: member)
-
-        put "/tags/nico/#{ external.id }", params: locale_params.merge(tags: 'locale_link')
-
-        expect(response).to have_http_status(:ok), response.body
-        tag = expect_localised_tag('locale_link', expected_locale)
-        expect(external.reload.linked_tags).to contain_exactly(tag)
-      end
-
-      it 'creates parent tags in the resolved locale' do
-        tag = create(:tag)
-
-        put "/tags/#{ tag.id }", params: locale_params.merge(
-            name: primary_tag_name_for(tag, 'ja').name, category: tag.category, deprecated: false,
-            aliases: '', parent_tags: 'locale_parent')
-
-        expect(response).to have_http_status(:ok), response.body
-        parent = expect_localised_tag('locale_parent', expected_locale)
-        expect(TagImplication.where(tag:).pluck(:parent_tag_id)).to eq([parent.id])
-      end
-    end
-  end
-
-  context 'with existing names in both languages' do
-    let!(:english_name) do
-      create(:tag_name, name: 'shared_name', language_code: 'en', script_code: 'Latn')
-    end
-    let!(:english_tag) { create(:tag, primary_tag_name: english_name, category: :material) }
-    let!(:japanese_tag) do
-      create(:tag, primary_name: 'temporary_japanese', category: :general).tap do |tag|
-        # Isolate lookup from the separately tested uniqueness validation.
-        primary_tag_name_for(tag, 'ja').update_columns(name: 'shared_name')
-      end
-    end
-
-    it 'plans and creates the post using the English identity and category' do
-      post '/posts', params: {
-          locale: 'en', title: 'English identity',
-          url: 'https://example.com/english-identity', tags: 'shared_name', parent_post_ids: '' }
-
-      expect(response).to have_http_status(:created), response.body
-      record = Post.find(json.fetch('id'))
-      expect(record.tags).to include(english_tag)
-      expect(record.tags).not_to include(japanese_tag)
-      expect(english_tag.reload.category).to eq('material')
-      expect(japanese_tag.reload.category).to eq('general')
-    end
-
-    it 'updates the post using the English identity' do
-      record = create(:post)
-      PostVersionRecorder.record!(post: record, event_type: :create, created_by_user: member)
-
-      put "/posts/#{ record.id }", params: {
-          locale: 'en', title: record.title, tags: 'shared_name', parent_post_ids: '',
-          base_version_no: record.reload.version_no }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(record.reload.tags).to include(english_tag)
-      expect(record.tags).not_to include(japanese_tag)
-    end
-
-    it 'resolves the English material tag' do
-      post '/materials', params: {
-          locale: 'en', tag: 'shared_name', url: 'https://example.com/english-material' }
-
-      expect(response).to have_http_status(:created), response.body
-      expect(Material.find(json.fetch('id')).tag).to eq(english_tag)
-      expect(Material.where(tag: japanese_tag)).to be_empty
-    end
-
-    it 'resolves the English parent tag' do
-      child = create(:tag)
-
-      put "/tags/#{ child.id }", params: {
-          locale: 'en', name: primary_tag_name_for(child, 'ja').name,
-          category: child.category, deprecated: false,
-          aliases: '', parent_tags: 'shared_name' }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(TagImplication.where(tag: child).pluck(:parent_tag_id)).to eq([english_tag.id])
-    end
-
-    it 'resolves the English internal tag for a Nico link' do
-      external = create(:external_tag)
-      NicoTagVersionRecorder.record!(
-          external_tag: external, event_type: :create, created_by_user: member)
-
-      put "/tags/nico/#{ external.id }", params: { locale: 'en', tags: 'shared_name' }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(external.reload.linked_tags).to contain_exactly(english_tag)
-    end
-  end
-
-  context 'when renaming or updating aliases in English' do
-    let!(:english_name) do
-      create(:tag_name, name: 'english_original', language_code: 'en', script_code: 'Latn')
-    end
-    let!(:tag) { create(:tag, primary_tag_name: english_name) }
-
-    it 'allows a rename to a name already used in Japanese' do
-      japanese = create(:tag, primary_name: 'rename_target')
-
-      patch "/tags/#{ tag.id }", params: { locale: 'en', name: 'rename_target' }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(primary_tag_name_for(tag.reload, 'en')).to have_attributes(
-          name: 'rename_target', language_code: 'en', tag_id: tag.id)
-      expect(primary_tag_name_for(japanese.reload, 'ja')).to have_attributes(
-          name: 'rename_target', language_code: 'ja', tag_id: japanese.id)
-    end
-
-    it 'creates aliases in the requested language' do
-      put "/tags/#{ tag.id }", params: {
-          locale: 'en', name: english_name.name,
-          category: tag.category, deprecated: false,
-          aliases: 'english_alias', parent_tags: '' }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(TagName.find_by!(language_code: 'en', name: 'english_alias'))
-          .to have_attributes(
-              script_code: 'Latn',
-              tag_id: tag.id, primary_flg: false, language_code: 'en')
-      primary = TagName.find_by!(tag_id: tag.id, language_code: 'en', primary_flg: true)
-      expect(primary).to have_attributes(name: 'english_original', script_code: 'Latn')
-    end
-
-    it 'does not take an alias from another language' do
-      japanese = create(:tag, primary_name: 'japanese_owner')
-      japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                tag: japanese)
-      expect(japanese_alias.reload).to have_attributes(
-          tag_id: japanese.id,
-          primary_flg: false, language_code: 'ja')
-
-      put "/tags/#{ tag.id }", params: {
-          locale: 'en', name: english_name.name,
-          category: tag.category, deprecated: false,
-          aliases: 'shared_alias', parent_tags: '' }
-
-      expect(response).to have_http_status(:ok), response.body
-      expect(japanese_alias.reload).to have_attributes(
-          tag_id: japanese.id,
-          primary_flg: false, language_code: 'ja')
-      expect(TagName.find_by!(language_code: 'en', name: 'shared_alias'))
-          .to have_attributes(
-              tag_id: tag.id, script_code: 'Latn',
-              primary_flg: false, language_code: 'en')
-      expect(TagName.where(name: 'shared_alias').pluck(:language_code, :tag_id))
-          .to contain_exactly(['ja', japanese.id], ['en', tag.id])
-    end
-  end
-end

backend/spec/requests/materials_spec.rb

@@ -26,10 +26,10 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials' do
     let!(:tag_a) do
-      create(:tag, primary_name: 'material_index_a', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_index_a'), category: :material)
     end
     let!(:tag_b) do
-      create(:tag, primary_name: 'material_index_b', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_index_b'), category: :material)
     end
 
     let!(:material_a) do
@@ -116,20 +116,20 @@ RSpec.describe 'Materials API', type: :request do
 
     it 'filters by descendant tags and returns stable parent tag groups' do
       root =
-          create(:tag, primary_name: 'material_scope_root',
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_root'),
                       category: :material)
       child_b =
-          create(:tag, primary_name: 'material_scope_b',
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_b'),
                       category: :material)
       child_a =
-          create(:tag, primary_name: 'material_scope_a',
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_a'),
                       category: :material)
       deprecated =
-          create(:tag, primary_name: 'material_scope_old',
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_old'),
                       category: :material,
                       deprecated_at: Time.current)
       grandchild =
-          create(:tag, primary_name: 'material_scope_grandchild',
+          Tag.create!(tag_name: TagName.create!(name: 'material_scope_grandchild'),
                       category: :material)
       root_material =
           build_material(tag: root, user: member_user,
@@ -179,7 +179,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials/:id' do
     let!(:tag) do
-      create(:tag, primary_name: 'material_show', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_show'), category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'show.png'))
@@ -269,7 +269,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:created)
 
         material = Material.order(:id).last
-        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_create_new')
+        expect(material.tag.name).to eq('material_create_new')
         expect(material.tag.category).to eq('material')
         expect(material.created_by_user).to eq(member_user)
         expect(material.updated_by_user).to eq(member_user)
@@ -297,8 +297,7 @@ RSpec.describe 'Materials API', type: :request do
 
         expect(response).to have_http_status(:created)
 
-        tag = TagName.find_by!(name: 'material_create_versioned_tag',
-                               language_code: 'ja', primary_flg: true).tag
+        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_create_versioned_tag' })
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('create')
@@ -324,8 +323,8 @@ RSpec.describe 'Materials API', type: :request do
       end
 
       it 'returns 422 when the existing tag is not material/character' do
-        general_tag_name = create(:tag_name, name: 'material_create_general_tag')
-        create(:tag, primary_tag_name: general_tag_name, category: :general)
+        general_tag_name = TagName.create!(name: 'material_create_general_tag')
+        Tag.create!(tag_name: general_tag_name, category: :general)
 
         post '/materials', params: {
           tag: 'material_create_general_tag',
@@ -346,7 +345,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:created)
 
         material = Material.order(:id).last
-        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_create_url_only')
+        expect(material.tag.name).to eq('material_create_url_only')
         expect(material.url).to eq('https://example.com/material-source')
         expect(material.file.attached?).to be(false)
       end
@@ -385,7 +384,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'PUT /materials/:id' do
     let!(:tag) do
-      create(:tag, primary_name: 'material_update_old', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_update_old'), category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'old.png'))
@@ -464,7 +463,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:ok)
 
         material.reload
-        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_update_new')
+        expect(material.tag.name).to eq('material_update_new')
         expect(material.tag.category).to eq('material')
         expect(material.url).to eq('https://example.com/updated-source')
         expect(material.updated_by_user).to eq(member_user)
@@ -498,8 +497,7 @@ RSpec.describe 'Materials API', type: :request do
 
         expect(response).to have_http_status(:ok)
 
-        tag = TagName.find_by!(name: 'material_update_versioned_tag',
-                               language_code: 'ja', primary_flg: true).tag
+        tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'material_update_versioned_tag' })
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('create')
@@ -510,7 +508,7 @@ RSpec.describe 'Materials API', type: :request do
 
       it 'backfills a create tag_version for an existing material tag without history' do
         existing_tag =
-            create(:tag, primary_name: 'material_update_existing_no_history',
+            Tag.create!(tag_name: TagName.create!(name: 'material_update_existing_no_history'),
                         category: :material)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -533,7 +531,7 @@ RSpec.describe 'Materials API', type: :request do
 
       it 'backfills a create tag_version for an existing character tag without history' do
         existing_tag =
-            create(:tag, primary_name: 'material_update_character_no_history',
+            Tag.create!(tag_name: TagName.create!(name: 'material_update_character_no_history'),
                         category: :character)
 
         expect(existing_tag.tag_versions).to be_empty
@@ -565,7 +563,7 @@ RSpec.describe 'Materials API', type: :request do
         expect(response).to have_http_status(:ok)
 
         material.reload
-        expect(primary_tag_name_for(material.tag, 'ja').name).to eq('material_update_remove_file')
+        expect(material.tag.name).to eq('material_update_remove_file')
         expect(material.url).to eq('https://example.com/updated-source')
         expect(material.updated_by_user).to eq(member_user)
         expect(material.file.attached?).to be(false)
@@ -653,8 +651,8 @@ RSpec.describe 'Materials API', type: :request do
   end
 
   describe 'GET /materials/download.zip' do
-    let!(:tag_a) { create(:tag, primary_name: 'zip_a', category: :material) }
-    let!(:tag_b) { create(:tag, primary_name: 'zip_b', category: :material) }
+    let!(:tag_a) { Tag.create!(tag_name: TagName.create!(name: 'zip_a'), category: :material) }
+    let!(:tag_b) { Tag.create!(tag_name: TagName.create!(name: 'zip_b'), category: :material) }
     let!(:material_a) do
       build_material(tag: tag_a, user: member_user,
                      file: dummy_upload(filename: 'a.png', body: 'zip-a'))
@@ -703,7 +701,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'GET /materials/versions' do
     let!(:tag) do
-      create(:tag, primary_name: 'material_history', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_history'), category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'history.png'))
@@ -778,7 +776,7 @@ RSpec.describe 'Materials API', type: :request do
 
   describe 'DELETE /materials/:id' do
     let!(:tag) do
-      create(:tag, primary_name: 'material_destroy', category: :material)
+      Tag.create!(tag_name: TagName.create!(name: 'material_destroy'), category: :material)
     end
     let!(:material) do
       build_material(tag:, user: member_user, file: dummy_upload(filename: 'destroy.png'))

backend/spec/requests/nico_tags_spec.rb

@@ -3,34 +3,10 @@ require 'rails_helper'
 
 RSpec.describe 'NicoTags', type: :request do
   describe 'GET /tags/nico' do
-    it 'returns the legacy Tag-compatible external fields' do
-      external = create(:external_tag, name: 'legacy_external', post_count: 3)
-
-      get '/tags/nico', params: { name: 'legacy_external' }
-
-      expect(response).to have_http_status(:ok)
-      expect(json.fetch('count')).to eq(1)
-      expect(json.fetch('tags')).to contain_exactly(
-          a_hash_including(
-              'id' => external.id,
-              'name' => 'nico:legacy_external',
-              'category' => 'nico',
-              'post_count' => 3,
-              'created_at' => external.created_at.as_json,
-              'updated_at' => external.created_at.as_json,
-              'deprecated_at' => nil,
-              'aliases' => [],
-              'parents' => [],
-              'has_wiki' => false,
-              'material_id' => nil,
-              'has_deerjikists' => false,
-              'linked_tags' => []))
-    end
-
     it 'returns paginated tags and total count' do
-      3.times { |i| create(:external_tag, name: "pagination_#{ i }") }
+      create_list(:tag, 3, :nico)
 
-      get '/tags/nico', params: { page: 2, limit: 2, name: 'pagination_' }
+      get '/tags/nico', params: { page: 2, limit: 2 }
 
       expect(response).to have_http_status(:ok)
       expect(json['tags'].size).to eq(1)
@@ -38,16 +14,16 @@ RSpec.describe 'NicoTags', type: :request do
     end
 
     it 'filters by nico tag name, linked tag name, and link status' do
-      linked = create(:external_tag)
-      linked.update!(name: 'search_linked')
-      unlinked = create(:external_tag)
-      unlinked.update!(name: 'search_unlinked')
-      other = create(:external_tag)
-      other.update!(name: 'other')
-      destination = create(:tag, category: :general)
-      primary_tag_name_for(destination, 'ja').update!(name: 'destination_search')
+      linked = create(:tag, :nico)
+      linked.tag_name.update!(name: 'nico:search_linked')
+      unlinked = create(:tag, :nico)
+      unlinked.tag_name.update!(name: 'nico:search_unlinked')
+      other = create(:tag, :nico)
+      other.tag_name.update!(name: 'nico:other')
+      destination = create(:tag, :general)
+      destination.tag_name.update!(name: 'destination_search')
       NicoTagRelation.create!(nico_tag: linked, tag: destination)
-      NicoTagRelation.create!(nico_tag: other, tag: create(:tag, category: :general))
+      NicoTagRelation.create!(nico_tag: other, tag: create(:tag, :general))
 
       get '/tags/nico', params: {
         name: 'search_',
@@ -65,77 +41,37 @@ RSpec.describe 'NicoTags', type: :request do
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([unlinked.id])
     end
 
-    it 'filters by the qualified legacy name as well as the raw name' do
-      external = create(:external_tag, name: 'qualified_filter')
-      create(:external_tag, name: 'unrelated_filter')
-
-      ['qualified_filter', 'nico:qualified_filter'].each do |name|
-        get '/tags/nico', params: { name: }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(1)
-        expect(json.fetch('tags')).to contain_exactly(
-            a_hash_including('id' => external.id, 'name' => 'nico:qualified_filter'))
-      end
-    end
-
     it 'sorts by name and timestamps' do
-      older = create(:external_tag)
-      older.update!(name: 'ordered_a')
+      older = create(:tag, :nico)
+      older.tag_name.update!(name: 'nico:a')
       older.update_columns(created_at: 2.days.ago)
-      newer = create(:external_tag)
-      newer.update!(name: 'ordered_b')
+      newer = create(:tag, :nico)
+      newer.tag_name.update!(name: 'nico:b')
       newer.update_columns(created_at: 1.day.ago)
       older_post_tag =
-        PostExternalTag.create!(post: create(:post), external_tag: older)
+        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-older'), tag: older)
       older_post_tag.update_columns(created_at: 1.hour.ago)
       newer_post_tag =
-        PostExternalTag.create!(post: create(:post), external_tag: newer)
+        PostTag.create!(post: Post.create!(url: 'https://example.com/nico-newer'), tag: newer)
       newer_post_tag.update_columns(created_at: 2.hours.ago)
 
-      get '/tags/nico', params: { order: 'name:desc', name: 'ordered_' }
+      get '/tags/nico', params: { order: 'name:desc' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([newer.id, older.id])
 
-      get '/tags/nico', params: { order: 'created_at:asc', name: 'ordered_' }
+      get '/tags/nico', params: { order: 'created_at:asc' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
 
-      get '/tags/nico', params: { order: 'updated_at:desc', name: 'ordered_' }
+      get '/tags/nico', params: { order: 'updated_at:desc' }
       expect(json.fetch('tags').map { |tag| tag['id'] }).to eq([older.id, newer.id])
       expect(Time.zone.parse(json.fetch('tags').first.fetch('recent_post_tag_created_at')))
         .to be_within(1.second).of(older_post_tag.created_at)
     end
   end
 
-  describe 'GET /tags/nico/:id' do
-    it 'returns the external tag even when an internal tag has the same id' do
-      internal = create(:tag)
-      external = create(
-          :external_tag,
-          id: internal.id,
-          name: 'external_detail')
-
-      get "/tags/nico/#{ external.id }"
-
-      expect(response).to have_http_status(:ok)
-      expect(json).to include(
-          'id' => external.id,
-          'name' => 'nico:external_detail',
-          'category' => 'nico')
-    end
-
-    it 'returns 404 when the external tag does not exist' do
-      internal = create(:tag)
-
-      get "/tags/nico/#{ internal.id }"
-
-      expect(response).to have_http_status(:not_found)
-    end
-  end
-
   describe 'PATCH /tags/nico/:id' do
     let(:member) { create(:user, :member) }
     let(:admin) { create(:user, :admin) }
-    let(:nico_tag) { create(:external_tag) }
+    let(:nico_tag) { create(:tag, :nico) }
 
     it '401 when not logged in' do
       sign_out
@@ -149,31 +85,30 @@ RSpec.describe 'NicoTags', type: :request do
       expect(response).to have_http_status(:forbidden)
     end
 
-    it '404 when only an internal tag exists for the target id' do
+    it '400 when target is not nico category' do
       sign_in_as(member)
-      non_nico = create(:tag, category: :general)
-      expect(ExternalTag.exists?(non_nico.id)).to be(false)
+      non_nico = create(:tag, :general)
       patch "/tags/nico/#{non_nico.id}", params: { tags: 'a b' }
-      expect(response).to have_http_status(:not_found)
+      expect(response).to have_http_status(:bad_request)
     end
 
     it '200 and updates linked tags while recording tag versions' do
       sign_in_as(admin)
 
-      nico_tag = create(:external_tag, name: 'nico_tags_spec_source')
+      nico_tag_name = TagName.create!(name: 'nico:nico_tags_spec_source')
+      nico_tag = Tag.create!(tag_name: nico_tag_name, category: :nico)
 
-      linked_a_name = create(:tag_name, name: 'nico_linked_a')
-      linked_a = create(:tag, primary_tag_name: linked_a_name, category: :general)
+      linked_a_name = TagName.create!(name: 'nico_linked_a')
+      linked_a = Tag.create!(tag_name: linked_a_name, category: :general)
 
-      linked_b_name = create(:tag_name, name: 'nico_linked_b')
-      linked_b = create(:tag, primary_tag_name: linked_b_name, category: :general)
+      linked_b_name = TagName.create!(name: 'nico_linked_b')
+      linked_b = Tag.create!(tag_name: linked_b_name, category: :general)
 
-      NicoTagVersionRecorder.record!(external_tag: nico_tag,
-                                     event_type: :create, created_by_user: admin)
+      TagVersioning.ensure_snapshot!(nico_tag, created_by_user: admin)
 
       expect {
         patch "/tags/nico/#{nico_tag.id}", params: {
-          tags: "  #{ linked_a_name.name }\n#{ linked_b_name.name }  "
+          tags: "  #{linked_a.name}\n#{linked_b.name}  "
         }
       }.to change(TagVersion, :count).by(2)
        .and change(NicoTagVersion, :count).by(1)
@@ -191,26 +126,26 @@ RSpec.describe 'NicoTags', type: :request do
       expect(versions.map(&:event_type)).to eq(['create', 'update'])
       expect(versions.last.linked_tags.split).to match_array([
         'nico_linked_a',
-        'nico_linked_b'])
+        'nico_linked_b'
+      ])
       expect(versions.last.created_by_user_id).to eq(admin.id)
     end
 
-    it 'clears existing links and records the empty mapping for a member' do
+    it 'returns 422 when linked tag normalises to nico tag' do
       sign_in_as(member)
-      linked = create(:tag)
-      NicoTagRelation.insert_all!([{ nico_tag_id: nico_tag.id, tag_id: linked.id }])
-      NicoTagVersionRecorder.record!(external_tag: nico_tag,
-                                     event_type: :create, created_by_user: member)
+
+      other_nico = create(:tag, :nico, name: 'nico:linked_ng')
+      TagName.create!(name: 'linked_ng_alias', canonical: other_nico.tag_name)
+
+      TagVersioning.ensure_snapshot!(nico_tag, created_by_user: member)
 
       expect {
-        patch "/tags/nico/#{ nico_tag.id }", params: { tags: '' }
-      }.to change(NicoTagVersion, :count).by(1)
+        patch "/tags/nico/#{nico_tag.id}", params: { tags: 'linked_ng_alias' }
+      }.not_to change(NicoTagVersion, :count)
 
-      expect(response).to have_http_status(:ok)
-      expect(json).to eq([])
-      expect(nico_tag.reload.linked_tags).to be_empty
-      expect(nico_tag.nico_tag_versions.order(:version_no).last)
-          .to have_attributes(linked_tags: '', created_by_user: member)
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(json.fetch('errors')).to include(
+          'tags' => ['ニコニコ・タグ同士は連携できません．'])
     end
 
     it 'returns the tags field error when a nico tag is specified directly' do

backend/spec/requests/posts_spec.rb

@@ -17,7 +17,7 @@ RSpec.describe 'Posts API', type: :request do
   end
 
   def create_nico_tag!(name)
-    ExternalTag.find_or_create_by!(platform: :nico, name: name.delete_prefix('nico:'))
+    Tag.find_or_create_by_tag_name!(name, category: :nico)
   end
 
   def dummy_upload
@@ -55,7 +55,6 @@ RSpec.describe 'Posts API', type: :request do
             thumbnail_base: post.thumbnail_base,
             video_ms: post.video_ms,
             tags: post.snapshot_tag_names.join(' '),
-            tags_json: post.snapshot_tags_json,
             parent_post_ids: post.snapshot_parent_post_ids.join(' '),
             original_created_from: post.original_created_from,
             original_created_before: post.original_created_before,
@@ -93,28 +92,8 @@ RSpec.describe 'Posts API', type: :request do
     count
   end
 
-  def expect_external_tag_json tag_json, external_tag
-    external_tag.reload
-
-    expect(tag_json).to include(
-        'id' => external_tag.id,
-        'name' => "#{ external_tag.platform }:#{ external_tag.name }",
-        'category' => 'nico',
-        'created_at' => external_tag.created_at.as_json,
-        'updated_at' => external_tag.created_at.as_json,
-        'deprecated_at' => nil,
-        'aliases' => [],
-        'parents' => [],
-        'post_count' => external_tag.post_count,
-        'has_wiki' => false,
-        'material_id' => nil,
-        'has_deerjikists' => false,
-        'children' => [],
-        'sections' => [])
-  end
-
-  let!(:tag_name) { create(:tag_name, name: 'spec_tag') }
-  let!(:tag)      { create(:tag, primary_tag_name: tag_name, category: :general) }
+  let!(:tag_name) { TagName.create!(name: 'spec_tag') }
+  let!(:tag)      { Tag.create!(tag_name: tag_name, category: :general) }
 
   let!(:post_record) do
     Post.create!(title: 'spec post', url: 'https://example.com/spec').tap do |p|
@@ -125,11 +104,11 @@ RSpec.describe 'Posts API', type: :request do
   describe 'GET /posts' do
     let!(:user) { create_member_user! }
 
-    let!(:tag_name) { create(:tag_name, name: 'spec_tag') }
-    let!(:tag) { create(:tag, primary_tag_name: tag_name, category: :general) }
-    let!(:tag_name2) { create(:tag_name, name: 'unko') }
-    let!(:tag2) { create(:tag, primary_tag_name: tag_name2, category: :deerjikist) }
-    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
+    let!(:tag_name) { TagName.create!(name: 'spec_tag') }
+    let!(:tag) { Tag.create!(tag_name:, category: :general) }
+    let!(:tag_name2) { TagName.create!(name: 'unko') }
+    let!(:tag2) { Tag.create!(tag_name: tag_name2, category: :deerjikist) }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     let!(:hit_post) do
       Post.create!(uploaded_user: user, title: 'hello spec world',
@@ -168,15 +147,12 @@ RSpec.describe 'Posts API', type: :request do
 
     it 'keeps children and sections keys in non-detail tag responses' do
       PostTagSection.create!(post: hit_post, tag:, begin_ms: 1_000, end_ms: nil)
-      deprecated_tag = create(:tag, deprecated_at: Time.current)
-      create(:post_tag, post: hit_post, tag: deprecated_tag)
 
       get '/posts'
 
       expect(response).to have_http_status(:ok)
 
       hit_json = json.fetch('posts').find { |post| post['id'] == hit_post.id }
-      expect(hit_json.fetch('tags').map { |item| item.fetch('id') }).to eq([tag.id])
       tag_json = hit_json.fetch('tags').find { |item| item['name'] == 'spec_tag' }
 
       expect(tag_json.fetch('children')).to eq([])
@@ -185,26 +161,6 @@ RSpec.describe 'Posts API', type: :request do
       ])
     end
 
-    it 'preloads tag details and sections as the number of posts grows' do
-      5.times do
-        link = create(:post_tag, post: create(:post, uploaded_user: user))
-        create(:post_tag_section, post: link.post, tag: link.tag,
-                                  begin_ms: 1000, end_ms: 2000)
-      end
-      get '/posts', params: { limit: 1 }
-
-      one_post_queries = count_sql_queries do
-        get '/posts', params: { limit: 1 }
-      end
-      many_post_queries = count_sql_queries do
-        get '/posts', params: { limit: 20 }
-      end
-
-      expect(response).to have_http_status(:ok)
-      expect(json.fetch('posts').size).to eq(8)
-      expect(many_post_queries).to be <= one_post_queries
-    end
-
     context 'when q is provided' do
       it 'filters posts by q (hit case)' do
         get '/posts', params: { tags: 'spec_tag' }
@@ -253,110 +209,18 @@ RSpec.describe 'Posts API', type: :request do
       end
     end
 
-    context 'with legacy external tag name searches' do
-      let!(:external_tag) { create(:external_tag, id: tag.id, name: 'search_external') }
-      let!(:both_post) do
-        create(:post).tap do |post|
-          PostTag.create!(post:, tag:)
-          PostExternalTag.create!(post:, external_tag:)
-        end
-      end
-
-      before do
-        PostExternalTag.create!(post: miss_post, external_tag:)
-      end
-
-      it 'keeps internal name searches independent of colliding external ids' do
-        get '/posts', params: { tags: primary_tag_name_for(tag, 'ja').name }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(3)
-        expect(json.fetch('posts').map { _1.fetch('id') })
-            .to contain_exactly(post_record.id, hit_post.id, both_post.id)
-      end
-
-      it 'finds posts through PostExternalTag by the qualified legacy name' do
-        get '/posts', params: { tags: 'nico:search_external' }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(2)
-        expect(json.fetch('posts').map { _1.fetch('id') })
-            .to contain_exactly(miss_post.id, both_post.id)
-      end
-
-      [nil, 'all'].each do |match|
-        it "intersects internal and external matches with match=#{ match || 'omitted' }" do
-          params = { tags: "#{ primary_tag_name_for(tag, 'ja').name } nico:search_external" }
-          params[:match] = match if match
-
-          get '/posts', params: params
-
-          expect(response).to have_http_status(:ok)
-          expect(json.fetch('count')).to eq(1)
-          expect(json.fetch('posts').map { _1.fetch('id') }).to eq([both_post.id])
-        end
-      end
-
-      it 'unions internal alias and external matches without duplicate posts' do
-        get '/posts', params: { tags: 'manko nico:search_external', match: 'any' }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(4)
-        expect(json.fetch('posts').map { _1.fetch('id') })
-            .to contain_exactly(post_record.id, hit_post.id, miss_post.id, both_post.id)
-      end
-
-      it 'excludes external matches from an internal tag search' do
-        get '/posts', params: {
-            tags: "#{ primary_tag_name_for(tag, 'ja').name } not:nico:search_external" }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(2)
-        expect(json.fetch('posts').map { _1.fetch('id') })
-            .to contain_exactly(post_record.id, hit_post.id)
-      end
-
-      it 'unions an external match with a negated internal match' do
-        get '/posts', params: {
-            tags: "nico:search_external not:#{ primary_tag_name_for(tag, 'ja').name }",
-            match: 'any' }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(2)
-        expect(json.fetch('posts').map { _1.fetch('id') })
-            .to contain_exactly(miss_post.id, both_post.id)
-      end
-
-      it 'keeps a missing qualified external name empty' do
-        get '/posts', params: { tags: 'nico:missing_search_external' }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(0)
-        expect(json.fetch('posts')).to be_empty
-      end
-
-      it 'applies the same mixed name search to the existing random endpoint' do
-        get '/posts/random', params: {
-            tags: "#{ primary_tag_name_for(tag, 'ja').name } nico:search_external",
-            match: 'all' }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('id')).to eq(both_post.id)
-      end
-    end
-
     context 'when tags contain not:' do
-      let!(:foo_tag_name) { create(:tag_name, name: 'not_spec_foo') }
-      let!(:foo_tag) { create(:tag, primary_tag_name: foo_tag_name, category: :general) }
+      let!(:foo_tag_name) { TagName.create!(name: 'not_spec_foo') }
+      let!(:foo_tag) { Tag.create!(tag_name: foo_tag_name, category: :general) }
 
-      let!(:bar_tag_name) { create(:tag_name, name: 'not_spec_bar') }
-      let!(:bar_tag) { create(:tag, primary_tag_name: bar_tag_name, category: :general) }
+      let!(:bar_tag_name) { TagName.create!(name: 'not_spec_bar') }
+      let!(:bar_tag) { Tag.create!(tag_name: bar_tag_name, category: :general) }
 
-      let!(:baz_tag_name) { create(:tag_name, name: 'not_spec_baz') }
-      let!(:baz_tag) { create(:tag, primary_tag_name: baz_tag_name, category: :general) }
+      let!(:baz_tag_name) { TagName.create!(name: 'not_spec_baz') }
+      let!(:baz_tag) { Tag.create!(tag_name: baz_tag_name, category: :general) }
 
       let!(:foo_alias_tag_name) do
-        create(:tag_name, :alias, name: 'not_spec_foo_alias', tag: foo_tag)
+        TagName.create!(name: 'not_spec_foo_alias', canonical: foo_tag_name)
       end
 
       let!(:foo_only_post) do
@@ -595,71 +459,6 @@ RSpec.describe 'Posts API', type: :request do
       end
     end
 
-    context 'when update times include version history' do
-      let(:t0) { Time.zone.parse('2020-01-01 12:00:00') }
-      let(:t1) { t0 + 1.day }
-      let(:t2) { t0 + 2.days }
-      let(:t3) { t0 + 3.days }
-      let!(:history_post) do
-        create(:post, url: 'https://example.com/version-time/history',
-                      created_at: t0, updated_at: t0)
-      end
-      let!(:plain_post) do
-        create(:post, url: 'https://example.com/version-time/plain',
-                      created_at: t1, updated_at: t1)
-      end
-      let!(:newer_post) do
-        create(:post, url: 'https://example.com/version-time/newer',
-                      created_at: t0, updated_at: t3)
-      end
-
-      before do
-        link = create(:post_tag, post: history_post, tag:)
-        travel_to(t0) do
-          PostVersionRecorder.record!(post: history_post,
-                                      event_type: :create, created_by_user: nil)
-          PostVersionRecorder.record!(post: newer_post,
-                                      event_type: :create, created_by_user: nil)
-        end
-        travel_to(t2) do
-          link.destroy!
-          PostVersionRecorder.record!(post: history_post,
-                                      event_type: :update, created_by_user: nil)
-        end
-        create(:post_tag, post: plain_post, tag:, created_at: t3)
-      end
-
-      ['asc', 'desc'].each do |direction|
-        it "sorts by the later of post update and latest version time (#{ direction })" do
-          get '/posts', params: { url: '/version-time/', order: "updated_at:#{ direction }" }
-
-          expect(response).to have_http_status(:ok)
-          expected_ids = [plain_post.id, history_post.id, newer_post.id]
-          expected_ids.reverse! if direction == 'desc'
-          expect(json.fetch('posts').map { |item| item.fetch('id') }).to eq(expected_ids)
-          expect(json.fetch('count')).to eq(3)
-
-          times = json.fetch('posts').to_h do |item|
-            [item.fetch('id'), Time.zone.parse(item.fetch('updated_at'))]
-          end
-          expect(times).to eq({ plain_post.id => t1,
-                               history_post.id => t2,
-                               newer_post.id => t3 })
-          expect(history_post.reload.updated_at).to eq(t0)
-        end
-      end
-
-      it 'filters inclusively by the latest version time after a tag is deleted' do
-        get '/posts', params: { url: '/version-time/',
-                               updated_from: t2.iso8601,
-                               updated_to: t2.iso8601 }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('posts').map { |item| item.fetch('id') }).to eq([history_post.id])
-        expect(json.fetch('count')).to eq(1)
-      end
-    end
-
     context 'when original_created_from/original_created_to are provided' do
       # 注意: controller の現状ロジックに合わせてる
       # original_created_from は `original_created_before > ?`
@@ -724,32 +523,6 @@ RSpec.describe 'Posts API', type: :request do
         expect(json.fetch('count')).to eq(2)
       end
     end
-
-    it 'returns internal and external tags with colliding ids in the legacy tags array' do
-      external_tag = create(:external_tag, id: tag.id, name: 'post_index_external')
-      PostExternalTag.create!(post: hit_post, external_tag:)
-
-      get '/posts'
-
-      expect(response).to have_http_status(:ok)
-
-      post_json =
-          json
-          .fetch('posts')
-          .find { _1.fetch('id') == hit_post.id }
-
-      external_json =
-          post_json
-          .fetch('tags')
-          .find { _1['name'] == 'nico:post_index_external' }
-
-      expect(post_json.fetch('tags')).to include(
-          a_hash_including('id' => tag.id,
-                           'name' => primary_tag_name_for(tag, 'ja').name,
-                           'category' => 'general'))
-      expect(external_json).not_to be_nil
-      expect_external_tag_json(external_json, external_tag)
-    end
   end
 
   describe 'GET /posts/:id' do
@@ -779,10 +552,11 @@ RSpec.describe 'Posts API', type: :request do
       end
 
       it 'omits deprecated tags' do
-        deprecated_tag = create(:tag,
-            primary_name: 'deprecated_post_tag',
+        deprecated_tag = Tag.create!(
+          name: 'deprecated_post_tag',
           category: :general,
-            deprecated_at: Time.current)
+          deprecated_at: Time.current
+        )
         PostTag.create!(post: post_record, tag: deprecated_tag)
 
         request
@@ -859,9 +633,9 @@ RSpec.describe 'Posts API', type: :request do
 
         tags =
             15.times.map do |i|
-              tag_name = create(:tag_name, name: "show_query_tag_#{ i }")
-              tag = create(:tag, primary_tag_name: tag_name, category: :general)
-              create(:tag_name, :alias, name: "show_query_alias_#{ i }", tag:)
+              tag_name = TagName.create!(name: "show_query_tag_#{ i }")
+              tag = Tag.create!(tag_name:, category: :general)
+              TagName.create!(name: "show_query_alias_#{ i }", canonical: tag_name)
               PostTag.create!(post: post_record, tag:)
               tag
             end
@@ -906,27 +680,6 @@ RSpec.describe 'Posts API', type: :request do
         expect(response).to have_http_status(:ok)
         expect(query_count).to be <= 45
       end
-
-      it 'returns external tags as root nodes in the legacy tag tree' do
-        external_tag = create(:external_tag, id: tag.id, name: 'post_detail_external')
-        PostExternalTag.create!(post: post_record, external_tag:)
-
-        request
-
-        expect(response).to have_http_status(:ok)
-
-        expect(json.fetch('tags')).to include(
-            a_hash_including('id' => tag.id,
-                             'name' => primary_tag_name_for(tag, 'ja').name,
-                             'category' => 'general'))
-        external_json =
-            json
-            .fetch('tags')
-            .find { _1['name'] == 'nico:post_detail_external' }
-
-        expect(external_json).not_to be_nil
-        expect_external_tag_json(external_json, external_tag)
-      end
     end
 
     context 'when post does not exist' do
@@ -1008,7 +761,7 @@ RSpec.describe 'Posts API', type: :request do
 
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
-    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     it '401 when not logged in' do
       sign_out
@@ -1165,10 +918,11 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     it 'rejects a deprecated tag specified directly' do
-      create(:tag,
-          primary_name: 'deprecated_direct_tag',
+      Tag.create!(
+        name: 'deprecated_direct_tag',
         category: :general,
-          deprecated_at: Time.current)
+        deprecated_at: Time.current
+      )
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
@@ -1185,16 +939,18 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     it 'expands through multiple deprecated parent tags and saves active ancestors' do
-      child = create(:tag, primary_name: 'active_child', category: :general)
-      deprecated_parent = create(:tag,
-          primary_name: 'deprecated_parent',
+      child = Tag.create!(name: 'active_child', category: :general)
+      deprecated_parent = Tag.create!(
+        name: 'deprecated_parent',
         category: :general,
-          deprecated_at: Time.current)
-      deprecated_grandparent = create(:tag,
-          primary_name: 'deprecated_grandparent',
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = Tag.create!(
+        name: 'deprecated_grandparent',
         category: :general,
-          deprecated_at: Time.current)
-      active_grandparent = create(:tag, primary_name: 'active_grandparent', category: :general)
+        deprecated_at: Time.current
+      )
+      active_grandparent = Tag.create!(name: 'active_grandparent', category: :general)
       TagImplication.create!(tag: child, parent_tag: deprecated_parent)
       TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
       TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_grandparent)
@@ -1208,8 +964,7 @@ RSpec.describe 'Posts API', type: :request do
       )
 
       expect(response).to have_http_status(:created)
-      saved_names = TagName.where(tag_id: Post.find(json.fetch('id')).tags.select(:id),
-                                  language_code: 'ja', primary_flg: true).pluck(:name)
+      saved_names = Post.find(json.fetch('id')).tags.map(&:name)
       expect(saved_names).to include('active_child', 'active_grandparent')
       expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
     end
@@ -1312,8 +1067,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = TagName.find_by!(name: '伊地知ニジカ',
-                             language_code: 'ja', primary_flg: true).tag
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
       section = PostTagSection.find_by!(post: created_post, tag:)
 
       expect(section.begin_ms).to eq(60_000)
@@ -1333,8 +1087,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = TagName.find_by!(name: '伊地知ニジカ',
-                             language_code: 'ja', primary_flg: true).tag
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
       expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
     end
 
@@ -1351,8 +1104,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
 
       created_post = Post.find(json.fetch('id'))
-      tag = TagName.find_by!(name: '伊地知ニジカ',
-                             language_code: 'ja', primary_flg: true).tag
+      tag = Tag.joins(:tag_name).find_by!(tag_names: { name: '伊地知ニジカ' })
       expect(PostTagSection.find_by(post: created_post, tag:)).to be_nil
     end
 
@@ -1409,9 +1161,11 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
-    context 'when the external nico tag already exists' do
+    context 'when nico tag already exists in tags' do
       before do
-        create(:external_tag, name: 'nico_tag')
+        Tag.find_undiscard_or_create_by!(
+            tag_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
+            category: :nico)
       end
 
       it 'returns 422 with tag field errors' do
@@ -1631,7 +1385,6 @@ RSpec.describe 'Posts API', type: :request do
         expect(arguments[:thumbnails].keys).to eq([0])
         expect(arguments[:host]).to eq('http://www.example.com')
       end
-      expect(creator).to have_received(:run).with(Locale.nipponese)
     end
 
     it 'rejects malformed manifests as a request-level error' do
@@ -1665,11 +1418,9 @@ RSpec.describe 'Posts API', type: :request do
 
     it '200 and updates title + resync tags when member' do
       sign_in_as(member)
-      create(:post_tag_section, post: post_record, tag:,
-                                begin_ms: 1000, end_ms: 2000)
 
-      tn2 = create(:tag_name, name: 'spec_tag_2')
-      replacement_tag = create(:tag, primary_tag_name: tn2, category: :general)
+      tn2 = TagName.create!(name: 'spec_tag_2')
+      Tag.create!(tag_name: tn2, category: :general)
 
       put "/posts/#{post_record.id}", params: post_update_params(
           post_record,
@@ -1682,45 +1433,14 @@ RSpec.describe 'Posts API', type: :request do
 
       names = json['tags'].map { |n| n['name'] }
       expect(names).to include('spec_tag_2')
-      expect(names).not_to include('spec_tag')
-      expect(PostTag.exists?(post: post_record, tag:)).to be(false)
-      expect(PostTagSection.exists?(post: post_record, tag:)).to be(false)
-      expect(tag.reload.post_count).to eq(0)
-      expect(replacement_tag.reload.post_count).to eq(1)
-
-      versions = post_record.post_versions.order(:version_no)
-      expect(versions.first.tags_json).to include(
-          a_hash_including('tag_id' => tag.id,
-                           'sections' => [{ 'begin_ms' => 1000, 'end_ms' => 2000 }]))
-      expect(versions.last.tags_json.map { |item| item.fetch('tag_id') })
-          .not_to include(tag.id)
-    end
-
-    it 'can add a removed tag again and records both changes' do
-      sign_in_as(member)
-
-      put "/posts/#{ post_record.id }", params: post_update_params(post_record, tags: '')
-      expect(response).to have_http_status(:ok)
-      expect(PostTag.exists?(post: post_record, tag:)).to be(false)
-
-      put "/posts/#{ post_record.id }", params: post_update_params(
-          post_record, tags: 'spec_tag')
-
-      expect(response).to have_http_status(:ok)
-      expect(PostTag.where(post: post_record, tag:).count).to eq(1)
-      expect(PostTag.find_by!(post: post_record, tag:).created_user).to eq(member)
-      expect(tag.reload.post_count).to eq(1)
-      snapshots = post_record.post_versions.order(:version_no).map do |version|
-        version.tags_json.map { |item| item.fetch('tag_id') }
-      end
-      expect(snapshots.map { |ids| ids.include?(tag.id) }).to eq([true, false, true])
     end
 
     it 'rejects a deprecated tag specified directly' do
-      create(:tag,
-          primary_name: 'deprecated_update_tag',
+      Tag.create!(
+        name: 'deprecated_update_tag',
         category: :general,
-          deprecated_at: Time.current)
+        deprecated_at: Time.current
+      )
       sign_in_as(member)
 
       put "/posts/#{ post_record.id }", params: post_update_params(
@@ -1735,9 +1455,11 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
-    context 'when the external nico tag already exists' do
+    context 'when nico tag already exists in tags' do
       before do
-        create(:external_tag, name: 'nico_tag')
+        Tag.find_undiscard_or_create_by!(
+            tag_name: TagName.find_undiscard_or_create_by!(name: 'nico:nico_tag'),
+            category: :nico)
       end
 
       it 'returns 422 with tag field errors' do
@@ -1975,7 +1697,7 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: 'updated by me',
-            tags: "spec_tag #{primary_tag_name_for(Tag.no_deerjikist, 'ja').name}")
+            tags: "spec_tag #{Tag.no_deerjikist.name}")
 
         expect(response).to have_http_status(:conflict)
 
@@ -1995,8 +1717,7 @@ RSpec.describe 'Posts API', type: :request do
 
         base_version = create_post_version_for!(post_record.reload)
 
-        current_tag = Tag.find_or_create_by_tag_name!(
-            Locale.nipponese, 'current_added_tag', category: :general)
+        current_tag = Tag.find_or_create_by_tag_name!('current_added_tag', category: :general)
         PostTag.create!(post: post_record, tag: current_tag, created_user: member)
 
         PostVersionRecorder.record!(
@@ -2007,8 +1728,7 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: ['spec_tag', primary_tag_name_for(Tag.no_deerjikist, 'ja').name,
-                   'incoming_added_tag'].join(' '))
+            tags: "spec_tag #{Tag.no_deerjikist.name} incoming_added_tag")
 
         expect(response).to have_http_status(:conflict)
 
@@ -2026,8 +1746,7 @@ RSpec.describe 'Posts API', type: :request do
 
         base_version = create_post_version_for!(post_record.reload)
 
-        current_tag = Tag.find_or_create_by_tag_name!(
-            Locale.nipponese, 'current_merge_tag', category: :general)
+        current_tag = Tag.find_or_create_by_tag_name!('current_merge_tag', category: :general)
         PostTag.create!(post: post_record, tag: current_tag, created_user: member)
 
         PostVersionRecorder.record!(
@@ -2038,17 +1757,15 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: ['spec_tag', primary_tag_name_for(Tag.no_deerjikist, 'ja').name,
-                   'incoming_merge_tag'].join(' '),
+            tags: "spec_tag #{Tag.no_deerjikist.name} incoming_merge_tag",
             merge: '1')
 
         expect(response).to have_http_status(:ok)
 
-        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
-                              language_code: 'ja', primary_flg: true).pluck(:name)
+        names = post_record.reload.tags.map(&:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
+        expect(names).to include(Tag.no_deerjikist.name)
         expect(names).to include('current_merge_tag')
         expect(names).to include('incoming_merge_tag')
       end
@@ -2059,7 +1776,7 @@ RSpec.describe 'Posts API', type: :request do
         base_version = create_post_version_for!(post_record.reload)
 
         nico_tag = create_nico_tag!('nico:optimistic_lock_nico')
-        PostExternalTag.create!(post: post_record, external_tag: nico_tag)
+        PostTag.create!(post: post_record, tag: nico_tag, created_user: member)
 
         PostVersionRecorder.record!(
             post: post_record.reload,
@@ -2071,58 +1788,47 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
+            tags: "spec_tag #{ Tag.no_deerjikist.name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
-                              language_code: 'ja', primary_flg: true).pluck(:name)
+        names = post_record.reload.tags.map(&:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
-        expect(post_record.external_tags).to contain_exactly(nico_tag)
+        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).to include(nico_tag.name)
       end
 
       it 'keeps nico tags even when they are not included in PUT tags' do
         sign_in_as(member)
 
         nico_tag = create_nico_tag!('nico:readonly_update_nico')
-        PostExternalTag.create!(post: post_record, external_tag: nico_tag)
+        PostTag.create!(post: post_record, tag: nico_tag, created_user: member)
 
         base_version = create_post_version_for!(post_record.reload)
 
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: 'updated title',
-            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
+            tags: "spec_tag #{ Tag.no_deerjikist.name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
-                              language_code: 'ja', primary_flg: true).pluck(:name)
+        names = post_record.reload.tags.map(&:name)
 
         expect(names).to include('spec_tag')
-        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
-        expect(post_record.external_tags).to contain_exactly(nico_tag)
-
-        external_json =
-            json
-            .fetch('tags')
-            .find { _1['name'] == "nico:#{ nico_tag.name }" }
-
-        expect(external_json).not_to be_nil
-        expect_external_tag_json(external_json, nico_tag)
+        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).to include(nico_tag.name)
       end
 
       it 'allows non-nico tags linked from nico tags to be removed by normal post update' do
         sign_in_as(member)
 
         nico_tag = create_nico_tag!('nico:relation_source')
-        linked_tag = Tag.find_or_create_by_tag_name!(
-            Locale.nipponese, 'relation_linked_tag', category: :general)
+        linked_tag = Tag.find_or_create_by_tag_name!('relation_linked_tag', category: :general)
 
         NicoTagRelation.create!(nico_tag:, tag: linked_tag)
-        PostExternalTag.create!(post: post_record, external_tag: nico_tag)
+        PostTag.create!(post: post_record, tag: nico_tag, created_user: member)
         PostTag.create!(post: post_record, tag: linked_tag, created_user: member)
 
         base_version = create_post_version_for!(post_record.reload)
@@ -2130,17 +1836,16 @@ RSpec.describe 'Posts API', type: :request do
         put "/posts/#{post_record.id}", params: post_write_params(
             base_version_no: base_version.version_no,
             title: post_record.title,
-            tags: "spec_tag #{ primary_tag_name_for(Tag.no_deerjikist, 'ja').name }")
+            tags: "spec_tag #{ Tag.no_deerjikist.name }")
 
         expect(response).to have_http_status(:ok)
 
-        names = TagName.where(tag_id: post_record.reload.tags.select(:id),
-                              language_code: 'ja', primary_flg: true).pluck(:name)
+        names = post_record.reload.tags.map(&:name)
 
-        expect(post_record.external_tags).to contain_exactly(nico_tag)
+        expect(names).to include(nico_tag.name)
         expect(names).to include('spec_tag')
-        expect(names).to include(primary_tag_name_for(Tag.no_deerjikist, 'ja').name)
-        expect(names).not_to include(primary_tag_name_for(linked_tag, 'ja').name)
+        expect(names).to include(Tag.no_deerjikist.name)
+        expect(names).not_to include(linked_tag.name)
       end
 
       it 'force-updates stale posts without base_version_no' do
@@ -2156,7 +1861,7 @@ RSpec.describe 'Posts API', type: :request do
 
         put "/posts/#{post_record.id}", params: post_write_params(
             title: 'forced title',
-            tags: "spec_tag #{primary_tag_name_for(Tag.no_deerjikist, 'ja').name}",
+            tags: "spec_tag #{Tag.no_deerjikist.name}",
             force: '1')
 
         expect(response).to have_http_status(:ok)
@@ -2173,29 +1878,123 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:not_found)
     end
 
-    it 'returns viewed state and current tags with their sections' do
-      create(:post_tag_section, post: post_record, tag:,
-                                begin_ms: 1000, end_ms: nil)
-      deprecated_tag = create(:tag, deprecated_at: Time.current)
-      create(:post_tag, post: post_record, tag: deprecated_tag)
-
+    it '200 and returns viewed boolean' do
       get '/posts/random'
-
       expect(response).to have_http_status(:ok)
       expect(json).to have_key('viewed')
       expect([true, false]).to include(json['viewed'])
-      expect(json.fetch('tags')).to contain_exactly(
-          a_hash_including('id' => tag.id,
-                           'children' => [],
-                           'sections' => [{ 'begin_ms' => 1000, 'end_ms' => nil }]))
     end
   end
 
   describe 'GET /posts/changes' do
-    it 'returns 404 for the retired history endpoint' do
-      get '/posts/changes'
+    let(:member) { create(:user, :member) }
 
-      expect(response).to have_http_status(:not_found)
+    it 'returns add/remove events (history) for a post' do
+      # add
+      tn2 = TagName.create!(name: 'spec_tag2')
+      tag2 = Tag.create!(tag_name: tn2, category: :general)
+      pt = PostTag.create!(post: post_record, tag: tag2, created_user: member)
+
+      # remove (discard)
+      pt.discard_by!(member)
+
+      get '/posts/changes', params: { id: post_record.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('changes', 'count')
+      expect(json['changes']).to be_an(Array)
+      expect(json['count']).to be >= 2
+
+      types = json['changes'].map { |e| e['change_type'] }.uniq
+      expect(types).to include('add')
+      expect(types).to include('remove')
+    end
+
+    it 'filters history by tag' do
+      tn2 = TagName.create!(name: 'history_tag_hit')
+      tag2 = Tag.create!(tag_name: tn2, category: :general)
+
+      tn3 = TagName.create!(name: 'history_tag_miss')
+      tag3 = Tag.create!(tag_name: tn3, category: :general)
+
+      other_post = Post.create!(
+        title: 'other post',
+        url: 'https://example.com/history-other'
+      )
+
+      # hit: add
+      PostTag.create!(post: post_record, tag: tag2, created_user: member)
+
+      # hit: add + remove
+      pt2 = PostTag.create!(post: other_post, tag: tag2, created_user: member)
+      pt2.discard_by!(member)
+
+      # miss: add + remove
+      pt3 = PostTag.create!(post: post_record, tag: tag3, created_user: member)
+      pt3.discard_by!(member)
+
+      get '/posts/changes', params: { tag: tag2.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('changes', 'count')
+      expect(json['count']).to eq(3)
+
+      changes = json.fetch('changes')
+
+      expect(changes.map { |e| e.dig('tag', 'id') }.uniq).to eq([tag2.id])
+      expect(changes.map { |e| e['change_type'] }).to match_array(%w[add add remove])
+      expect(changes.map { |e| e.dig('post', 'id') }).to match_array([
+        post_record.id,
+        other_post.id,
+        other_post.id
+      ])
+    end
+
+    it 'filters history by post and tag together' do
+      tn2 = TagName.create!(name: 'history_tag_combo_hit')
+      tag2 = Tag.create!(tag_name: tn2, category: :general)
+
+      tn3 = TagName.create!(name: 'history_tag_combo_miss')
+      tag3 = Tag.create!(tag_name: tn3, category: :general)
+
+      other_post = Post.create!(
+        title: 'other combo post',
+        url: 'https://example.com/history-combo-other'
+      )
+
+      # hit
+      PostTag.create!(post: post_record, tag: tag2, created_user: member)
+
+      # miss by post
+      pt2 = PostTag.create!(post: other_post, tag: tag2, created_user: member)
+      pt2.discard_by!(member)
+
+      # miss by tag
+      pt3 = PostTag.create!(post: post_record, tag: tag3, created_user: member)
+      pt3.discard_by!(member)
+
+      get '/posts/changes', params: { id: post_record.id, tag: tag2.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('changes', 'count')
+      expect(json['count']).to eq(1)
+
+      changes = json.fetch('changes')
+      expect(changes.size).to eq(1)
+      expect(changes[0]['change_type']).to eq('add')
+      expect(changes[0].dig('post', 'id')).to eq(post_record.id)
+      expect(changes[0].dig('tag', 'id')).to eq(tag2.id)
+    end
+
+    it 'returns empty history when tag does not match' do
+      tn2 = TagName.create!(name: 'history_tag_no_hit')
+      tag2 = Tag.create!(tag_name: tn2, category: :general)
+
+      get '/posts/changes', params: { tag: tag2.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('changes')).to eq([])
+      expect(json.fetch('count')).to eq(0)
     end
   end
 
@@ -2209,8 +2008,8 @@ RSpec.describe 'Posts API', type: :request do
     let(:oc_from) { Time.zone.local(2019, 12, 31, 0, 0, 0) }
     let(:oc_before) { Time.zone.local(2020, 1, 1, 0, 0, 0) }
 
-    let!(:tag_name2) { create(:tag_name, name: 'spec_tag_2') }
-    let!(:tag2) { create(:tag, primary_tag_name: tag_name2, category: :general) }
+    let!(:tag_name2) { TagName.create!(name: 'spec_tag_2') }
+    let!(:tag2) { Tag.create!(tag_name: tag_name2, category: :general) }
 
     def snapshot_tags(post)
       post.snapshot_tag_names.join(' ')
@@ -2225,7 +2024,6 @@ RSpec.describe 'Posts API', type: :request do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
-        tags_json: post.snapshot_tags_json,
         parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
@@ -2247,7 +2045,7 @@ RSpec.describe 'Posts API', type: :request do
     end
 
     let!(:v2) do
-      post_record.post_tags.find_by!(tag: tag).destroy!
+      post_record.post_tags.kept.find_by!(tag: tag).discard_by!(member)
       PostTag.create!(post: post_record, tag: tag2, created_user: member)
       post_record.update!(
         title: 'updated spec post',
@@ -2356,88 +2154,6 @@ RSpec.describe 'Posts API', type: :request do
       expect(first.fetch('created_at')).to eq(t_v1.iso8601)
     end
 
-    context 'with external tag history' do
-      let(:external_id) { tag.id }
-      let(:external) { create(:external_tag, id: external_id) }
-      let(:external_post) { create(:post) }
-
-      before do
-        PostExternalTag.create!(post: external_post, external_tag: external)
-        PostVersionRecorder.record!(
-            post: external_post, event_type: :create, created_by_user: member)
-
-        unrelated_post = create(:post)
-        PostExternalTag.create!(post: unrelated_post, external_tag: create(:external_tag))
-        PostVersionRecorder.record!(
-            post: unrelated_post, event_type: :create, created_by_user: member)
-      end
-
-      it 'prefers Tag over ExternalTag for the legacy tag parameter' do
-        get '/posts/versions', params: { tag: tag.id }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(3)
-        expect(json.fetch('versions').map { [_1.fetch('post_id'), _1.fetch('version_no')] })
-            .to contain_exactly(
-                [post_record.id, 1], [post_record.id, 2], [other_post_version.post_id, 1])
-      end
-
-      it 'explicitly filters ExternalTag even when its id collides with Tag' do
-        get '/posts/versions', params: { external_tag: external.id }
-
-        expect(response).to have_http_status(:ok)
-        expect(json.fetch('count')).to eq(1)
-        expect(json.fetch('versions')).to contain_exactly(
-            a_hash_including('post_id' => external_post.id, 'version_no' => 1))
-      end
-
-      # Temporary compatibility shim until the frontend sends external_tag explicitly.
-      context 'with legacy tag fallback and no internal Tag with the external id' do
-        let(:external_id) { Tag.maximum(:id).to_i + 10_000 }
-
-        it 'falls back to ExternalTag for the legacy tag parameter' do
-          expect(Tag.exists?(external.id)).to be(false)
-
-          get '/posts/versions', params: { tag: external.id }
-
-          expect(response).to have_http_status(:ok)
-          expect(json.fetch('count')).to eq(1)
-          expect(json.fetch('versions')).to contain_exactly(
-              a_hash_including('post_id' => external_post.id, 'version_no' => 1))
-        end
-
-        [:tag, :external_tag].each do |parameter|
-          it "includes external removal history through the legacy API's #{ parameter }" do
-            external_post.post_external_tags.destroy_all
-            PostVersionRecorder.record!(
-                post: external_post.reload, event_type: :update, created_by_user: member)
-
-            get '/posts/versions', params: { parameter => external.id }
-
-            expect(response).to have_http_status(:ok)
-            expect(json.fetch('count')).to eq(2)
-            expect(json.fetch('versions')).to contain_exactly(
-                a_hash_including('post_id' => external_post.id, 'version_no' => 1),
-                a_hash_including('post_id' => external_post.id, 'version_no' => 2))
-          end
-        end
-      end
-    end
-
-    it 'can render history containing external identifiers' do
-      PostExternalTag.create!(post: post_record, external_tag: create(:external_tag))
-      post_record.update_columns(version_no: 2)
-      PostVersionRecorder.record!(post: post_record,
-                                  event_type: :update, created_by_user: member)
-
-      get '/posts/versions', params: { post: post_record.id }
-
-      expect(response).to have_http_status(:ok)
-      expect(json.fetch('count')).to eq(3)
-      expect(json.fetch('versions').first.fetch('tags')).to include(
-          'name' => primary_tag_name_for(tag2, 'ja').name, 'type' => 'context')
-    end
-
     it 'filters versions by tag when the current snapshot includes the tag' do
       get '/posts/versions', params: { post: post_record.id, tag: tag2.id }
 
@@ -2568,8 +2284,8 @@ RSpec.describe 'Posts API', type: :request do
       sign_in_as(member)
       base_version = create_post_version_for!(post_record)
 
-      tag_name2 = create(:tag_name, name: 'spec_tag_2')
-      create(:tag, primary_tag_name: tag_name2, category: :general)
+      tag_name2 = TagName.create!(name: 'spec_tag_2')
+      Tag.create!(tag_name: tag_name2, category: :general)
 
       expect do
         put "/posts/#{post_record.id}", params: post_write_params(
@@ -2733,8 +2449,8 @@ RSpec.describe 'Posts API', type: :request do
 
       base_version = create_post_version_for!(post_record.reload)
 
-      tag_name2 = create(:tag_name, name: 'spec_tag_2')
-      tag2 = create(:tag, primary_tag_name: tag_name2, category: :general)
+      tag_name2 = TagName.create!(name: 'spec_tag_2')
+      tag2 = Tag.create!(tag_name: tag_name2, category: :general)
 
       expect {
         put "/posts/#{post_record.id}", params: post_write_params(

backend/spec/requests/tag_children_spec.rb

@@ -80,6 +80,38 @@ RSpec.describe "TagChildren", type: :request do
         expect(response).to have_http_status(:not_found)
       end
     end
+
+    context 'when parent is nico' do
+      before { stub_current_user(admin) }
+
+      let!(:parent) { create(:tag, :nico, name: 'nico:parent_ng') }
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it 'returns 400 and does not create relation' do
+        expect {
+          do_request
+        }.not_to change(TagImplication, :count)
+
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+
+    context 'when child is nico' do
+      before { stub_current_user(admin) }
+
+      let!(:child) { create(:tag, :nico, name: 'nico:child_ng') }
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it 'returns 400 and does not create relation' do
+        expect {
+          do_request
+        }.not_to change(TagImplication, :count)
+
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
   end
 
   describe "DELETE /tag_children" do
@@ -154,5 +186,31 @@ RSpec.describe "TagChildren", type: :request do
         expect(response).to have_http_status(:not_found)
       end
     end
+
+    context 'when parent is nico' do
+      before { stub_current_user(admin) }
+
+      let!(:parent) { create(:tag, :nico, name: 'nico:parent_ng_delete') }
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it 'returns 400' do
+        do_request
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
+
+    context 'when child is nico' do
+      before { stub_current_user(admin) }
+
+      let!(:child) { create(:tag, :nico, name: 'nico:child_ng_delete') }
+      let(:parent_id) { parent.id }
+      let(:child_id) { child.id }
+
+      it 'returns 400' do
+        do_request
+        expect(response).to have_http_status(:bad_request)
+      end
+    end
   end
 end

backend/spec/requests/tag_versions_spec.rb

@@ -3,13 +3,13 @@ require 'rails_helper'
 RSpec.describe 'TagVersions API', type: :request do
   let(:member) { create(:user, :member, name: 'version member') }
 
-  let!(:tag) { create(:tag, primary_name: 'tag_versions_target', category: :general) }
-  let!(:other_tag) { create(:tag, primary_name: 'tag_versions_other', category: :general) }
+  let!(:tag) { create(:tag, name: 'tag_versions_target', category: :general) }
+  let!(:other_tag) { create(:tag, name: 'tag_versions_other', category: :general) }
 
-  let!(:parent_shared) { create(:tag, primary_name: 'parent_shared', category: :general) }
-  let!(:parent_old) { create(:tag, primary_name: 'parent_old', category: :general) }
-  let!(:parent_new) { create(:tag, primary_name: 'parent_new', category: :general) }
-  let!(:other_parent) { create(:tag, primary_name: 'other_parent', category: :general) }
+  let!(:parent_shared) { create(:tag, name: 'parent_shared', category: :general) }
+  let!(:parent_old) { create(:tag, name: 'parent_old', category: :general) }
+  let!(:parent_new) { create(:tag, name: 'parent_new', category: :general) }
+  let!(:other_parent) { create(:tag, name: 'other_parent', category: :general) }
 
   let(:t_v1) { Time.zone.local(2020, 1, 1, 12, 0, 0) }
   let(:t_v2) { Time.zone.local(2020, 1, 2, 12, 0, 0) }
@@ -36,12 +36,6 @@ RSpec.describe 'TagVersions API', type: :request do
             category: category,
             deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
-            names: [{ language_code: 'ja', name:, script_code: 'Jpan',
-                      primary_flg: true,
-                      auto_generated: false }] + Array(aliases).map { |alias_name|
-              { language_code: 'ja', name: alias_name, script_code: 'Jpan',
-                primary_flg: false, auto_generated: false }
-            },
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
             created_at: created_at)
@@ -217,7 +211,7 @@ RSpec.describe 'TagVersions API', type: :request do
     end
 
     it 'returns empty when the specified tag has no versions' do
-      fresh_tag = create(:tag, primary_name: 'no_versions_tag', category: :general)
+      fresh_tag = create(:tag, name: 'no_versions_tag', category: :general)
 
       get '/tags/versions', params: { id: fresh_tag.id }
 
@@ -238,8 +232,8 @@ RSpec.describe 'TagVersions API', type: :request do
     end
 
     it 'does not create tag versions by wiki updates when tag has no versions yet' do
-      wiki_tag_name = create(:tag_name, name: 'tag_versions_from_wiki')
-      wiki_tag = create(:tag, primary_tag_name: wiki_tag_name, category: :general)
+      wiki_tag_name = TagName.create!(name: 'tag_versions_from_wiki')
+      wiki_tag = Tag.create!(tag_name: wiki_tag_name, category: :general)
 
       wiki_page =
           Wiki::Commit.create_content!(

backend/spec/requests/tag_wiki_history_integrity_spec.rb

@@ -8,13 +8,13 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   def create_tag! name:, category: :general
-    tag_name = create(:tag_name, name:)
-    create(:tag, primary_tag_name: tag_name, category:)
+    tag_name = TagName.create!(name:)
+    Tag.create!(tag_name:, category:)
   end
 
   def create_wiki_for_tag! tag:, body: 'wiki body', user: member_user
     Wiki::Commit.create_content!(
-        tag_name: primary_tag_name_for(tag, 'ja'),
+        tag_name: tag.tag_name,
         body:,
         created_by_user: user,
         message: 'init')
@@ -43,7 +43,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       wiki_page.reload
       version = wiki_page.wiki_versions.order(:version_no).last
 
-      expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_wiki_after')
+      expect(tag.name).to eq('patch_tag_wiki_after')
       expect(wiki_page.title).to eq('patch_tag_wiki_after')
 
       expect(version).to have_attributes(
@@ -72,7 +72,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       tag.reload
       wiki_page.reload
 
-      expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_category_only')
+      expect(tag.name).to eq('patch_tag_category_only')
       expect(tag.category).to eq('meme')
       expect(wiki_page.wiki_versions.count).to eq(before_wiki_versions)
     end
@@ -101,7 +101,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       wiki_page.reload
       version = wiki_page.wiki_versions.order(:version_no).last
 
-      expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_wiki_after')
+      expect(tag.name).to eq('put_tag_wiki_after')
       expect(wiki_page.title).to eq('put_tag_wiki_after')
 
       expect(version).to have_attributes(
@@ -134,7 +134,7 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
       tag.reload
       wiki_page.reload
 
-      expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_category_only')
+      expect(tag.name).to eq('put_tag_category_only')
       expect(tag.category).to eq('meme')
       expect(wiki_page.wiki_versions.count).to eq(before_wiki_versions)
     end

backend/spec/requests/tags_deerjikists_spec.rb

@@ -12,7 +12,7 @@ RSpec.describe 'Tags deerjikists API', type: :request do
   let(:guest) { create(:user, role: :guest) }
 
   before do
-    primary_tag_name_for(tag, 'ja').update!(name: 'deerjika')
+    tag.tag_name.update!(name: 'deerjika')
   end
 
   describe 'GET /tags/:id/deerjikists' do
@@ -226,14 +226,6 @@ RSpec.describe 'Tags deerjikists API', type: :request do
               [platform2, code2],
             )
         end
-
-        it 'locks the tag before replacing the complete list' do
-          expect_any_instance_of(Tag).to receive(:lock!).and_call_original
-
-          do_request
-
-          expect(response).to have_http_status(:ok)
-        end
       end
 
       context 'when tag already has deerjikists' do
@@ -307,81 +299,6 @@ RSpec.describe 'Tags deerjikists API', type: :request do
         end
       end
 
-      context 'when platform is outside the enum' do
-        let(:payload) do
-          [
-            { platform: 'invalid', code: code1 },
-          ]
-        end
-
-        it 'returns 422 with an indexed platform error without changing the list' do
-          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
-
-          expect {
-            do_request
-          }.not_to change { Deerjikist.where(tag: tag).map { |d| [d.platform, d.code] } }
-
-          expect(response).to have_http_status(:unprocessable_entity)
-          expect(json.fetch('errors')).to include(
-            'deerjikists.0.platform' => [be_present],
-          )
-        end
-      end
-
-      context 'when a requested deerjikist belongs to another tag' do
-        let!(:other_tag) { create(:tag, category: :deerjikist) }
-        let!(:owned_deerjikist) do
-          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
-        end
-        let!(:conflicting_deerjikist) do
-          Deerjikist.create!(platform: platform2, code: code2, tag: other_tag)
-        end
-        let(:payload) do
-          [
-            { platform: 'nico', code: 'new-code' },
-            { platform: platform2, code: code2 },
-          ]
-        end
-
-        before do
-          primary_tag_name_for(other_tag, 'ja').update!(name: 'existing-deerjikist')
-        end
-
-        it 'returns an indexed 422 error and rolls back the complete replacement' do
-          expect {
-            do_request
-          }.not_to change { Deerjikist.order(:platform, :code).pluck(:platform, :code, :tag_id) }
-
-          expect(response).to have_http_status(:unprocessable_entity)
-          expect(json.fetch('errors')).to include(
-            'deerjikists.1.code' => [include('existing-deerjikist')],
-          )
-          expect(owned_deerjikist.reload.tag_id).to eq(tag.id)
-          expect(conflicting_deerjikist.reload.tag_id).to eq(other_tag.id)
-        end
-      end
-
-      context 'when a requested deerjikist already belongs to the same tag' do
-        let!(:existing_deerjikist) do
-          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
-        end
-        let(:payload) do
-          [
-            { platform: platform1, code: code1 },
-          ]
-        end
-
-        it 'keeps the existing row' do
-          expect {
-            do_request
-          }.not_to change { existing_deerjikist.reload.created_at }
-
-          expect(response).to have_http_status(:ok)
-          expect(Deerjikist.where(tag: tag).pluck(:platform, :code))
-            .to eq([[platform1, code1]])
-        end
-      end
-
       context 'when youtube code is handle' do
         let(:channel_id) { 'UCabcdefghijklmnopqrstuv' }
         let(:payload) do

backend/spec/requests/theatres_spec.rb

@@ -396,7 +396,7 @@ RSpec.describe 'Theatres API', type: :request do
     end
 
     it 'finalizes skip when votes reach majority and stores voters and tag snapshots' do
-      tag = create(:tag, primary_name: 'skip-target')
+      tag = create(:tag, name: 'skip-target')
       PostTag.create!(post: niconico_post, tag:)
 
       TheatreSkipVote.create!(theatre:, post: niconico_post, user: member)
@@ -503,7 +503,7 @@ RSpec.describe 'Theatres API', type: :request do
     end
 
     it 'returns tag penalties and candidate weights for the current watchers' do
-      tag = create(:tag, primary_name: 'heavy-tag')
+      tag = create(:tag, name: 'heavy-tag')
       PostTag.create!(post: second_niconico_post, tag:)
       event = TheatreSkipEvent.create!(
         theatre:,

backend/spec/requests/wiki_conflict_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe 'Wiki conflict handling', type: :request do
   it 'returns 409 when base_revision_id is stale' do
     page =
         Wiki::Commit.create_content!(
-            tag_name: create(:tag_name, name: 'wiki_conflict_request'),
+            tag_name: TagName.create!(name: 'wiki_conflict_request'),
             body: 'first',
             created_by_user: user,
             message: 'init')

backend/spec/requests/wiki_history_integrity_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
 
   def create_wiki_page title:, body: 'body', message: 'init', user: self.user
     Wiki::Commit.create_content!(
-        tag_name: create(:tag_name, name: title),
+        tag_name: TagName.create!(name: title),
         body:,
         created_by_user: user,
         message:)

backend/spec/requests/wiki_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe 'Wiki API', type: :request do
 
   let!(:user) { create_member_user! }
 
-  let!(:tn) { create(:tag_name, name: 'spec_wiki_title') }
+  let!(:tn) { TagName.create!(name: 'spec_wiki_title') }
   let!(:page) do
     Wiki::Commit.create_content!(
         tag_name: tn,
@@ -19,10 +19,11 @@ RSpec.describe 'Wiki API', type: :request do
         message: 'init')
   end
   let!(:tag) do
-    create(:tag,
-        primary_tag_name: tn,
+    Tag.create!(
+      tag_name: tn,
       category: :general,
-        deprecated_at: Time.zone.local(2026, 6, 1))
+      deprecated_at: Time.zone.local(2026, 6, 1)
+    )
   end
 
   describe 'GET /wiki' do
@@ -207,7 +208,7 @@ RSpec.describe 'Wiki API', type: :request do
       { 'X-Transfer-Code' => user.inheritance_code }
     end
 
-    let!(:test_tag_name) { create(:tag_name, name: 'TestPage') }
+    let!(:test_tag_name) { TagName.create!(name: 'TestPage') }
 
     let!(:page) do
       Wiki::Commit.create_content!(
@@ -274,8 +275,8 @@ RSpec.describe 'Wiki API', type: :request do
       end
 
       it 'wiki body だけを変更しても tag version は作成しない' do
-        linked_tag_name = create(:tag_name, name: 'wiki_body_only_tag')
-        linked_tag = create(:tag, primary_tag_name: linked_tag_name, category: :general)
+        linked_tag_name = TagName.create!(name: 'wiki_body_only_tag')
+        linked_tag = Tag.create!(tag_name: linked_tag_name, category: :general)
 
         TagVersionRecorder.record!(
             tag: linked_tag,
@@ -358,13 +359,13 @@ RSpec.describe 'Wiki API', type: :request do
   describe 'GET /wiki/search' do
     before do
       Wiki::Commit.create_content!(
-          tag_name: create(:tag_name, name: 'spec_wiki_title_2'),
+          tag_name: TagName.create!(name: 'spec_wiki_title_2'),
           body: 'search body 2',
           created_by_user: user,
           message: 'init')
 
       Wiki::Commit.create_content!(
-          tag_name: create(:tag_name, name: 'unrelated_title'),
+          tag_name: TagName.create!(name: 'unrelated_title'),
           body: 'unrelated body',
           created_by_user: user,
           message: 'init')
@@ -433,7 +434,7 @@ RSpec.describe 'Wiki API', type: :request do
 
     it 'returns empty array when page has no revisions and filtered by id' do
       # 別ページを作って revision 無し
-      tn2 = create(:tag_name, name: 'spec_no_rev')
+      tn2 = TagName.create!(name: 'spec_no_rev')
       # 異常データ: revision 無し WikiPage を直接作る
       p2 = WikiPage.create!(
           tag_name: tn2,
@@ -513,7 +514,7 @@ RSpec.describe 'Wiki API', type: :request do
 
   describe 'Wiki::Commit.redirect!' do
     it 'raises because redirect revisions are deprecated' do
-      target_tag_name = create(:tag_name, name: 'redirect_deprecated_target')
+      target_tag_name = TagName.create!(name: 'redirect_deprecated_target')
       target =
           Wiki::Commit.create_content!(
               tag_name: target_tag_name,
@@ -534,8 +535,8 @@ RSpec.describe 'Wiki API', type: :request do
   end
 
   it 'wiki title を変更すると対応する tag の version を作成する' do
-    linked_tag_name = create(:tag_name, name: 'wiki_linked_tag_for_version')
-    linked_tag = create(:tag, primary_tag_name: linked_tag_name, category: :general)
+    linked_tag_name = TagName.create!(name: 'wiki_linked_tag_for_version')
+    linked_tag = Tag.create!(tag_name: linked_tag_name, category: :general)
 
     linked_page =
         Wiki::Commit.create_content!(
@@ -563,8 +564,7 @@ RSpec.describe 'Wiki API', type: :request do
     expect(response).to have_http_status(:ok)
 
     linked_tag.reload
-    expect(primary_tag_name_for(linked_tag, 'ja').name)
-        .to eq('wiki_linked_tag_for_version_renamed')
+    expect(linked_tag.name).to eq('wiki_linked_tag_for_version_renamed')
 
     versions = linked_tag.tag_versions.order(:version_no)
 

backend/spec/requests/wiki_title_collision_spec.rb

@@ -9,7 +9,7 @@ RSpec.describe 'Wiki title collision', type: :request do
 
   def create_wiki_page title:, body:
     Wiki::Commit.create_content!(
-        tag_name: create(:tag_name, name: title),
+        tag_name: TagName.create!(name: title),
         body:,
         created_by_user: user,
         message: 'init')