#411

backend/app/controllers/materials_controller.rb

@@ -236,10 +236,10 @@ class MaterialsController < ApplicationController
     nil
   end
 
-  def resolve_material_tag! locale, tag_name_raw
-    tag_name = TagName.find_or_create_by!(language_code: locale.language_code,
-                                          name: tag_name_raw)
-    tag_name.tag || Tag.create!(tag_name:, 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

backend/app/controllers/posts_controller.rb

@@ -308,7 +308,6 @@ 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]
@@ -330,8 +329,7 @@ class PostsController < ApplicationController
         base_snapshot = post_snapshot_from_version(base_version)
         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:,
@@ -360,7 +358,7 @@ 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
@@ -687,11 +685,11 @@ class PostsController < ApplicationController
     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, deny_deprecated: true,
-                                           with_sections: true) =>
+    Tag.normalise_tags!(tag_names, with_tagme: false, deny_deprecated: true,
+                                        with_sections: true) =>
         { tags:, sections: }
 
     tags = Tag.expand_parent_tags(tags).reject(&:deprecated?)
@@ -827,7 +825,7 @@ 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],
@@ -835,10 +833,10 @@ 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,
-                        deny_deprecated: true,
-                        with_sections: true) => { tags: editable_tags, sections: }
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false,
+                                               deny_deprecated: true,
+                                               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

backend/app/controllers/tags_controller.rb

@@ -573,7 +573,7 @@ class TagsController < ApplicationController
       return false
     end
 
-    target_tag_name = TagName.find_by(name:)
+    target_tag_name = TagName.with_discarded.find_by(name:)
     return true if target_tag_name.nil?
     return true if target_tag_name.canonical_id?
 
@@ -585,14 +585,17 @@ class TagsController < ApplicationController
     return if name == tag.name
 
     current_tag_name = tag.tag_name
-    target_tag_name = TagName.find_by(name:)
+    target_tag_name = TagName.with_discarded.find_by(name:)
 
     if target_tag_name.nil?
       current_tag_name.update!(name:)
       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:
@@ -602,9 +605,11 @@ class TagsController < ApplicationController
       TagVersioning.ensure_snapshot!(old_owner_tag, created_by_user: current_user)
     end
 
+    promoted_tag_name.undiscard! if promoted_tag_name.discarded?
     promoted_tag_name.update!(canonical: nil)
 
-    TagName.where(canonical_id: current_tag_name.id)
+    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: promoted_tag_name)
@@ -635,7 +640,7 @@ class TagsController < ApplicationController
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_or_create_by!(name: alias_name)
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
       affected_tags << alias_tag_name.canonical&.tag
     end
 
@@ -650,7 +655,7 @@ class TagsController < ApplicationController
     end
 
     alias_names.each do |alias_name|
-      alias_tag_name = TagName.find_or_create_by!(name: alias_name)
+      alias_tag_name = TagName.find_undiscard_or_create_by!(name: alias_name)
       alias_tag_name.update!(canonical: tag.tag_name)
     end
 

backend/app/controllers/wiki_pages_controller.rb

@@ -94,7 +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!(name: title)
+    tag_name = TagName.find_undiscard_or_create_by!(name: title)
 
     page =
         Wiki::Commit.create_content!(

backend/app/models/language.rb

@@ -1,3 +0,0 @@
-class Language < ApplicationRecord
-  has_many :languages, class_name: 'Locale', foreign_key: :language_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),
-                      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/post.rb

@@ -63,19 +63,16 @@ class Post < ApplicationRecord
   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,

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
@@ -52,7 +54,6 @@ class Tag < ApplicationRecord
   has_many :tag_versions
   has_many :nico_tag_versions
 
-  has_many :tag_names
   belongs_to :tag_name
   delegate :wiki_page, to: :tag_name
 
@@ -102,20 +103,18 @@ 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,
-                           with_no_deerjikist: true,
-                           deny_nico: true,
-                           deny_deprecated: false,
-                           with_sections: false
+  def self.normalise_tags! tag_names, with_tagme: true,
+                                      with_no_deerjikist: true,
+                                      deny_nico: true,
+                                      deny_deprecated: false,
+                                      with_sections: false
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
     end
@@ -144,7 +143,7 @@ class Tag < ApplicationRecord
 
       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]
         end
@@ -232,23 +231,13 @@ 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
-    unless tag
-      tag = Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) do
-        _1.category = category
-      end
-    end
-
-    tag
   rescue ActiveRecord::RecordNotUnique
     retry
   end
@@ -284,10 +273,10 @@ class Tag < ApplicationRecord
         end
 
         TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
-        source_tag.destroy!
+        source_tag.discard!
 
         if source_tag.nico?
-          source_tag_name.destroy!
+          source_tag_name.discard!
         else
           source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
                                          updated_at: Time.current)
@@ -308,7 +297,7 @@ class Tag < ApplicationRecord
     target_tag.reload
   end
 
-  def snapshot_aliases = tag_name.aliases.order(:name).pluck(:name)
+  def snapshot_aliases = tag_name.aliases.kept.order(:name).pluck(:name)
 
   def snapshot_parent_tag_ids = parents.order(:id).pluck(:id)
 

backend/app/models/tag_name.rb

@@ -1,5 +1,7 @@
 class TagName < ApplicationRecord
-  belongs_to :tag
+  include MyDiscard
+
+  has_one :tag
   has_one :wiki_page
 
   belongs_to :canonical, class_name: 'TagName', optional: true
@@ -21,12 +23,6 @@ class TagName < ApplicationRecord
     names.map { |name| tns[name]&.canonical&.name || name }.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 }"
-  end
-
   private
 
   def canonical_must_be_canonical

backend/app/models/tag_name_sanitisation_rule.rb

@@ -32,7 +32,7 @@ class TagNameSanitisationRule < ApplicationRecord
             elsif source_tag
               source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
             end
-            tn.destroy!
+            tn.discard!
 
             next
           end

backend/db/migrate/20260919000000_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/20260919010000_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/20260919020000_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/20260919030000_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/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/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_21_030000) do
+ActiveRecord::Schema[8.0].define(version: 2026_09_21_010000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -72,6 +72,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.index ["correct_post_id"], name: "index_gekanator_games_on_correct_post_id"
     t.index ["guessed_post_id"], name: "index_gekanator_games_on_guessed_post_id"
     t.index ["user_id"], name: "index_gekanator_games_on_user_id"
+    t.check_constraint "`question_count` >= 0", name: "chk_gekanator_games_question_count_nonnegative"
   end
 
   create_table "gekanator_question_examples", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -274,9 +275,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_at"], name: "index_nico_tag_versions_on_created_at"
-    t.index ["created_by_user_id", "created_at"], name: "index_nico_tag_versions_on_created_by_user_id_and_created_at"
-    t.index ["tag_id", "created_at"], name: "index_nico_tag_versions_on_tag_id_and_created_at"
+    t.index ["created_by_user_id", "created_at"], name: "index_nico_tag_versions_on_created_by_user_id_and_created_at", order: { created_at: :desc }
+    t.index ["tag_id", "created_at"], name: "index_nico_tag_versions_on_tag_id_and_created_at", order: { created_at: :desc }
     t.index ["tag_id", "version_no"], name: "index_nico_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "nico_tag_versions_version_no_positive"
   end
 
   create_table "post_implications", primary_key: ["post_id", "parent_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -285,13 +287,14 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["parent_post_id"], name: "index_post_implications_on_parent_post_id"
+    t.check_constraint "`post_id` <> `parent_post_id`", name: "chk_post_implications_no_self"
   end
 
   create_table "post_similarities", primary_key: ["post_id", "target_post_id"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "target_post_id", null: false
     t.float "cos", null: false
-    t.index ["post_id", "cos"], name: "index_post_similarities_on_post_id_and_cos"
+    t.index ["post_id", "cos"], name: "index_post_similarities_on_post_id_and_cos", order: { cos: :desc }
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
@@ -347,6 +350,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.index ["post_id"], name: "index_post_versions_on_post_id"
     t.index ["video_ms", "post_id"], name: "idx_post_versions_video_ms_post_id"
     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\":{\"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}}',`tags_json`)", name: "chk_post_versions_tags_json_schema"
   end
 
@@ -365,6 +370,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.index ["url"], name: "index_posts_on_url", unique: true
     t.index ["video_ms", "id"], name: "idx_posts_video_ms_id"
     t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_posts_video_ms_positive"
+    t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
   create_table "settings", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -372,12 +378,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.string "theme", default: "system", null: false
-    t.string "display_density", default: "comfortable", null: false
-    t.string "font_size", default: "normal", null: false
-    t.integer "post_list_limit", default: 50, null: false
-    t.string "post_list_order", default: "created_at_desc", null: false
-    t.string "viewed_post_display", default: "show", null: false
-    t.boolean "tag_autocomplete_nico", default: true, null: false
     t.string "auto_fetch_title", default: "manual", null: false
     t.string "auto_fetch_thumbnail", default: "manual", null: false
     t.string "wiki_editor_mode", default: "split", null: false
@@ -409,7 +409,9 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.bigint "canonical_id"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.datetime "discarded_at"
     t.index ["canonical_id"], name: "index_tag_names_on_canonical_id"
+    t.index ["discarded_at"], name: "index_tag_names_on_discarded_at"
     t.index ["name"], name: "index_tag_names_on_name", unique: true
   end
 
@@ -417,7 +419,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.bigint "tag_id", null: false
     t.bigint "target_tag_id", null: false
     t.float "cos", null: false
-    t.index ["tag_id", "cos"], name: "index_tag_similarities_on_tag_id_and_cos"
+    t.index ["tag_id", "cos"], name: "index_tag_similarities_on_tag_id_and_cos", order: { cos: :desc }
     t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
   end
 
@@ -433,9 +435,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     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"
-    t.index ["tag_id", "created_at"], name: "index_tag_versions_on_tag_id_and_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 }
     t.index ["tag_id", "version_no"], name: "index_tag_versions_on_tag_id_and_version_no", unique: true
+    t.check_constraint "`version_no` > 0", name: "tag_versions_version_no_positive"
   end
 
   create_table "tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -445,10 +448,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) 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"
   end
 
   create_table "theatre_comments", primary_key: ["theatre_id", "no"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -615,11 +621,13 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "discarded_at"
+    t.integer "next_asset_no", default: 1, null: false
     t.integer "version_no", null: false
     t.index ["created_user_id"], name: "index_wiki_pages_on_created_user_id"
     t.index ["discarded_at"], name: "index_wiki_pages_on_discarded_at"
     t.index ["tag_name_id"], name: "index_wiki_pages_on_tag_name_id", unique: true
     t.index ["updated_user_id"], name: "index_wiki_pages_on_updated_user_id"
+    t.check_constraint "`version_no` > 0", name: "chk_wiki_pages_version_no_positive"
   end
 
   create_table "wiki_revision_lines", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
@@ -664,6 +672,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
     t.index ["created_by_user_id"], name: "index_wiki_versions_on_created_by_user_id"
     t.index ["wiki_page_id", "version_no"], name: "index_wiki_versions_on_wiki_page_id_and_version_no", unique: true
     t.index ["wiki_page_id"], name: "index_wiki_versions_on_wiki_page_id"
+    t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "wiki_versions_event_type_valid"
+    t.check_constraint "`version_no` > 0", name: "wiki_versions_version_no_positive"
   end
 
   add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
@@ -688,6 +698,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) 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"
@@ -696,6 +707,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
   add_foreign_key "materials", "users", column: "updated_by_user_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_implications", "posts"
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
@@ -714,6 +726,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
   add_foreign_key "tag_names", "tag_names", column: "canonical_id"
   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"
@@ -740,6 +753,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_09_21_030000) do
   add_foreign_key "user_post_views", "posts"
   add_foreign_key "user_post_views", "users"
   add_foreign_key "user_theme_slots", "users"
+  add_foreign_key "wiki_assets", "users", column: "created_by_user_id"
+  add_foreign_key "wiki_assets", "wiki_pages"
   add_foreign_key "wiki_pages", "tag_names"
   add_foreign_key "wiki_pages", "users", column: "created_user_id"
   add_foreign_key "wiki_pages", "users", column: "updated_user_id"

backend/spec/db/delete_discarded_tags_spec.rb

@@ -1,123 +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
-    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/models/tag_name_sanitisation_rule_spec.rb

@@ -57,7 +57,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
 
       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
@@ -75,27 +75,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
         described_class.apply!
         expected_tag_name_id = existing.canonical_id || existing.id
         expect(source_tag.reload.tag_name_id).to eq(expected_tag_name_id)
-        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!(:alias_name) do
-        TagName.create!(name: 'foobar', canonical: existing_tag.tag_name)
-      end
-      let!(:source) do
-        TagName.create!(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 canonical tag' do
-        described_class.apply!
-
-        expect(TagName.unscoped.exists?(source.id)).to be(false)
-        expect(alias_name.reload.canonical).to eq(existing_tag.tag_name)
-        expect(Tag.find(existing_tag.id)).to eq(existing_tag)
+        expect(TagName.exists?(source_tag_name_id)).to be(false)
       end
     end
 
@@ -112,15 +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(existing_tag.reload.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_spec.rb

@@ -173,47 +173,6 @@ RSpec.describe Tag, type: :model do
     end
   end
 
-  describe '.find_or_create_by_tag_name!' do
-    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!(
-            '  lookup_new  ', category: :character)
-      }.to change(Tag, :count).by(1).and change(TagName, :count).by(1)
-
-      expect(tag.name).to eq('lookup_new')
-      expect(tag.category).to eq('character')
-    end
-
-    it 'reuses the canonical tag for an alias without changing its category' do
-      tag = create(:tag, category: :character)
-      alias_name = TagName.create!(name: 'lookup_alias', canonical: tag.tag_name)
-      found = nil
-
-      expect {
-        found = described_class.find_or_create_by_tag_name!(
-            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')
-    end
-
-    it 'creates a tag for an existing canonical name reached through an alias' do
-      canonical = create(:tag_name)
-      alias_name = TagName.create!(name: 'lookup_alias', canonical:)
-      tag = nil
-
-      expect {
-        tag = described_class.find_or_create_by_tag_name!(
-            alias_name.name, category: :general)
-      }.to change(Tag, :count).by(1).and change(TagName, :count).by(0)
-
-      expect(tag.tag_name).to eq(canonical)
-    end
-  end
-
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
@@ -226,14 +185,17 @@ RSpec.describe Tag, type: :model do
     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 'deletes the source link, links the target, and aliases the discarded source tag' do
         described_class.merge_tags!(target_tag, [source_tag])
 
         target_link = PostTag.find_by(post: post_record, tag: target_tag)
 
         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.reload.post_count).to eq(0)
+
+        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
@@ -256,76 +218,17 @@ RSpec.describe Tag, type: :model do
 
         expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
         expect(target_links).to contain_exactly(target_post_tag)
+        expect(source_tag.reload.post_count).to eq(0)
         expect(PostTagSection.where(post: post_record, tag: source_tag)).to be_empty
         expect(target_post_tag.reload.sections).to contain_exactly(target_section)
 
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(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 = source_tag.name
-      source_alias = TagName.create!(name: 'merge_alias', canonical: source_tag_name)
-      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).to have_attributes(
-          name: source_name, aliases: source_alias.name, created_by_user: user)
-      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'])
-      expect(target_versions.last.aliases.split).to eq([source_name])
-    end
-
-    it 'deletes source relationships while preserving unrelated relationships' do
-      parent = create(:tag)
-      child = create(:tag)
-      nico_tag = create(:tag, :nico)
-      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) }
 
@@ -335,7 +238,7 @@ RSpec.describe Tag, type: :model do
         target_link = PostTag.find_by(post: post_record, tag: target_tag)
 
         expect(Tag.find(target_tag.id)).to be_present
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
         expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
         expect(target_link).to be_present
         expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
@@ -360,7 +263,7 @@ 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)
@@ -368,8 +271,7 @@ RSpec.describe Tag, type: :model do
         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.canonical_id).to eq(target_tag.tag_name_id)
+        expect(Tag.with_discarded.find(source_tag.id)).to be_discarded
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -386,23 +288,17 @@ 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 = earlier_source.tag_name
+      it 'rolls back the transaction' do
         source_section = create(:post_tag_section, post: post_record,
                                                    tag: source_tag,
                                                    begin_ms: 1000, end_ms: 2000)
 
         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.canonical_id).to be_nil
-        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(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(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
@@ -413,45 +309,21 @@ RSpec.describe Tag, type: :model do
     end
 
     context 'when merging a nico source tag' do
-      let!(:target_tag) do
-        create(:tag, category: :nico, tag_name: create(:tag_name, name: 'nico:foo'))
-      end
-      let!(:source_tag) do
-        create(:tag, category: :nico, tag_name: create(:tag_name, name: 'nico:bar'))
-      end
+      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 'deletes the source tag and name instead of keeping an alias' do
+      it 'discards the source tag_name instead of aliasing it' do
         described_class.merge_tags!(target_tag, [source_tag])
 
-        expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
+        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
-
-      it 'keeps nico history while deleting source links and allows recreating the name' do
-        linked_tag = create(:tag)
-        NicoTagRelation.create!(nico_tag: source_tag, tag: linked_tag)
-        kept_relation = NicoTagRelation.create!(nico_tag: target_tag, tag: linked_tag)
-        user = create_member_user!
-        source_name = source_tag.name
-
-        described_class.merge_tags!(target_tag, [source_tag], created_by_user: user)
-
-        expect(NicoTagRelation.all).to contain_exactly(kept_relation)
-        versions = NicoTagVersion.where(tag_id: source_tag.id).order(:version_no)
-        expect(versions.pluck(:version_no, :event_type))
-            .to eq([[1, 'create'], [2, 'discard']])
-        expect(versions.last).to have_attributes(
-            name: source_name, linked_tags: linked_tag.name, created_by_user: user)
-
-        recreated = described_class.find_or_create_by_tag_name!(source_name, category: :nico)
-
-        expect(recreated.id).not_to eq(source_tag.id)
-        expect(recreated.tag_name_id).not_to eq(source_tag_name_id)
-        expect(recreated.nico_tag_versions).to be_empty
-        expect(versions.reload.size).to eq(2)
-      end
     end
 
     def snapshot_tags(post)

backend/spec/requests/posts_spec.rb

@@ -1252,7 +1252,9 @@ RSpec.describe 'Posts API', type: :request do
 
     context 'when nico tag already exists in tags' do
       before do
-        Tag.find_or_create_by_tag_name!('nico:nico_tag', category: :nico)
+        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
@@ -1578,7 +1580,9 @@ RSpec.describe 'Posts API', type: :request do
 
     context 'when nico tag already exists in tags' do
       before do
-        Tag.find_or_create_by_tag_name!('nico:nico_tag', category: :nico)
+        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

backend/spec/tasks/nico_sync_spec.rb

@@ -8,7 +8,8 @@ RSpec.describe 'nico:sync' do
   end
 
   def create_tag!(name, category:)
-    Tag.find_or_create_by_tag_name!(name, category:)
+    tn = TagName.find_undiscard_or_create_by!(name: name.to_s.strip)
+    Tag.find_undiscard_or_create_by!(tag_name_id: tn.id) { |t| t.category = category }
   end
 
   def link_nico_to_tag!(nico_tag, tag)