#327

#63

#63

#63

#63

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #341

backend/app/controllers/application_controller.rb

@@ -1,14 +1,16 @@
 class ApplicationController < ActionController::API
+  before_action :reject_banned_ip_address!
   before_action :authenticate_user
+  before_action :reject_banned_user!
 
-  def current_user
-    @current_user
-  end
+  def current_user = @current_user
 
   private
 
   def authenticate_user
     code = request.headers['X-Transfer-Code'] || request.headers['HTTP_X_TRANSFER_CODE']
+    return if code.blank?
+
     @current_user = User.find_by(inheritance_code: code)
   end
 
@@ -22,4 +24,17 @@ class ApplicationController < ActionController::API
       s.in?(['', '1', 'true', 'on', 'yes'])
     end
   end
+
+  def reject_banned_ip_address!
+    ip_address = IpAddress.find_by(ip_address: IPAddr.new(request.remote_ip).hton)
+    return unless ip_address&.banned?
+
+    head :forbidden
+  end
+
+  def reject_banned_user!
+    return unless current_user&.banned?
+
+    head :forbidden
+  end
 end

backend/app/controllers/nico_tags_controller.rb

@@ -30,15 +30,22 @@ class NicoTagsController < ApplicationController
     id = params[:id].to_i
 
     tag = Tag.find(id)
-    return head :bad_request if tag.category != 'nico'
+    return head :bad_request unless tag.nico?
 
-    linked_tag_names = params[:tags].to_s.split(' ')
-    linked_tags = Tag.normalise_tags(linked_tag_names, with_tagme: false)
-    return head :bad_request if linked_tags.any? { |t| t.category == 'nico' }
+    linked_tag_names = params[:tags].to_s.split
+    linked_tags = Tag.normalise_tags!(linked_tag_names, with_tagme: false,
+                                                        with_no_deerjikist: false)
+    return head :bad_request if linked_tags.any? { |t| t.nico? }
+
+    ApplicationRecord.transaction do
+      TagVersioning.record_tag_snapshots!(linked_tags, created_by_user: current_user)
 
       tag.linked_tags = linked_tags
       tag.save!
 
+      NicoTagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+    end
+
     render json: tag.linked_tags.map { |t| TagRepr.base(t) }, status: :ok
   end
 end

backend/app/controllers/post_versions_controller.rb

@@ -0,0 +1,119 @@
+class PostVersionsController < ApplicationController
+  def index
+    post_id = params[:post].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
+
+    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
+            ON
+              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 AS prev_tags',
+                '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 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
+
+    versions = q.order(Arel.sql('post_versions.created_at DESC, post_versions.id DESC'))
+                .limit(limit)
+                .offset(offset)
+
+    render json: { versions: serialise_versions(versions), count: }
+  end
+
+  private
+
+  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|
+      cur_tags = split_tags(row.tags)
+      prev_tags = split_tags(row.attributes['prev_tags'])
+
+      {
+        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']
+        },
+        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
+        },
+        original_created_before: {
+          current: row.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 build_version_tags(cur_tags, prev_tags)
+    (cur_tags | prev_tags).map do |name|
+      type =
+        if cur_tags.include?(name) && prev_tags.include?(name)
+          'context'
+        elsif cur_tags.include?(name)
+          'added'
+        else
+          'removed'
+        end
+
+      {
+        name:,
+        type:
+      }
+    end
+  end
+
+  def split_tags(tags)
+    tags.to_s.split(/\s+/).reject(&:blank?)
+  end
+end

backend/app/controllers/posts_controller.rb

@@ -44,7 +44,7 @@ class PostsController < ApplicationController
         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(tags: { tag_name: :wiki_page })
+        .preload(tags: [:materials, { tag_name: :wiki_page }])
         .with_attached_thumbnail
 
     q = q.where('posts.url LIKE ?', "%#{ url }%") if url
@@ -95,7 +95,7 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts.preload(tags: { tag_name: :wiki_page })
+    post = filtered_posts.preload(tags: [:materials, { tag_name: :wiki_page }])
                          .order('RAND()')
                          .first
     return head :not_found unless post
@@ -104,12 +104,12 @@ class PostsController < ApplicationController
   end
 
   def show
-    post = Post.includes(tags: { tag_name: :wiki_page }).find_by(id: params[:id])
+    post = Post.includes(tags: [:materials, { tag_name: :wiki_page }]).find_by(id: params[:id])
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
                          .merge(tags: build_tag_tree_for(post.tags),
-                                related: post.related(limit: 20))
+                                related: PostRepr.many(post.related(limit: 20)))
   end
 
   def create
@@ -123,26 +123,36 @@ class PostsController < ApplicationController
     tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
+    parent_post_ids = parse_parent_post_ids
 
     post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
                     original_created_from:, original_created_before:)
-    post.thumbnail.attach(thumbnail)
+    post.thumbnail.attach(thumbnail) if thumbnail.present?
 
-    ActiveRecord::Base.transaction do
+    ApplicationRecord.transaction do
       post.save!
-      tags = Tag.normalise_tags(tag_names)
+
+      tags = Tag.normalise_tags!(tag_names)
+      TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
+
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      sync_parent_posts!(post, parent_post_ids)
+
       post.resized_thumbnail!
+
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: current_user)
     end
 
     post.reload
     render json: PostRepr.base(post), status: :created
-  rescue ActiveRecord::RecordInvalid
-    render json: { errors: post.errors.full_messages }, status: :unprocessable_entity
   rescue Tag::NicoTagNormalisationError
     head :bad_request
+  rescue ArgumentError => e
+    render json: { errors: [e.message] }, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   end
 
   def viewed
@@ -167,15 +177,24 @@ class PostsController < ApplicationController
     tag_names = params[:tags].to_s.split
     original_created_from = params[:original_created_from]
     original_created_before = params[:original_created_before]
+    parent_post_ids = parse_parent_post_ids
 
     post = Post.find(params[:id].to_i)
 
-    ActiveRecord::Base.transaction do
+    ApplicationRecord.transaction do
+      PostVersionRecorder.ensure_snapshot!(post, created_by_user: current_user)
+
       post.update!(title:, original_created_from:, original_created_before:)
-      tags = post.tags.where(category: 'nico').to_a +
-             Tag.normalise_tags(tag_names, with_tagme: false)
+
+      normalised_tags = Tag.normalise_tags!(tag_names, with_tagme: false)
+      TagVersioning.record_tag_snapshots!(normalised_tags, created_by_user: current_user)
+
+      tags = post.tags.nico.to_a + normalised_tags
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      sync_parent_posts!(post, parent_post_ids)
+
       PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
     end
 
@@ -183,10 +202,12 @@ class PostsController < ApplicationController
     json = post.as_json
     json['tags'] = build_tag_tree_for(post.tags)
     render json:, status: :ok
-  rescue ActiveRecord::RecordInvalid
-    render json: post.errors, status: :unprocessable_entity
   rescue Tag::NicoTagNormalisationError
     head :bad_request
+  rescue ArgumentError => e
+    render json: { errors: [e.message] }, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   end
 
   def changes
@@ -204,7 +225,7 @@ class PostsController < ApplicationController
     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: { tag_name: :wiki_page })
+                       tag: [:materials, { tag_name: :wiki_page }])
 
     events = []
     pts.each do |pt|
@@ -346,4 +367,41 @@ class PostsController < ApplicationController
 
     root_ids.filter_map { |id| build_node.call(id, []) }
   end
+
+  def parse_parent_post_ids
+    raise ArgumentError, 'parent_post_ids は必須です．' unless params.key?(:parent_post_ids)
+
+    params[:parent_post_ids].to_s.split.map { |token|
+      id = Integer(token, exception: false)
+      raise ArgumentError, "親投稿 Id. が不正です: #{ token }" if id.nil? || id <= 0
+
+      id
+    }.uniq
+  end
+
+  def sync_parent_posts! post, parent_post_ids
+    if parent_post_ids.include?(post.id)
+      post.errors.add(:base, '自分自身を親投稿にはできません．')
+      raise ActiveRecord::RecordInvalid, post
+    end
+
+    existing_ids = Post.where(id: parent_post_ids).pluck(:id)
+    missing_ids = parent_post_ids - existing_ids
+
+    if missing_ids.present?
+      post.errors.add(:base, "存在しない親投稿 ID があります: #{ missing_ids.join(' ') }")
+      raise ActiveRecord::RecordInvalid, post
+    end
+
+    current_ids = post.parent_posts.pluck(:id)
+
+    ids_to_add = parent_post_ids - current_ids
+    ids_to_remove = current_ids - parent_post_ids
+
+    PostImplication.where(post_id: post.id, parent_post_id: ids_to_remove).delete_all
+
+    ids_to_add.each do |parent_post_id|
+      PostImplication.create_or_find_by!(post_id: post.id, parent_post_id:)
+    end
+  end
 end

backend/app/controllers/tag_children_controller.rb

@@ -7,7 +7,16 @@ class TagChildrenController < ApplicationController
     child_id = params[:child_id]
     return head :bad_request if parent_id.blank? || child_id.blank?
 
-    Tag.find(parent_id).children << Tag.find(child_id) rescue nil
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return head :bad_request if parent.nico? || child.nico?
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
+
+      TagImplication.find_or_create_by!(parent_tag: parent, tag: child)
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
 
     head :no_content
   end
@@ -20,7 +29,16 @@ class TagChildrenController < ApplicationController
     child_id = params[:child_id]
     return head :bad_request if parent_id.blank? || child_id.blank?
 
-    Tag.find(parent_id).children.delete(Tag.find(child_id)) rescue nil
+    parent = Tag.find(parent_id)
+    child = Tag.find(child_id)
+    return head :bad_request if parent.nico? || child.nico?
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(child, created_by_user: current_user)
+
+      TagImplication.find_by(parent_tag: parent, tag: child)&.destroy!
+      TagVersionRecorder.record!(tag: child, event_type: :update, created_by_user: current_user)
+    end
 
     head :no_content
   end

backend/app/controllers/tag_versions_controller.rb

@@ -0,0 +1,92 @@
+class TagVersionsController < ApplicationController
+  def index
+    tag_id = params[:id].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
+
+    q = TagVersion.joins(<<~SQL.squish)
+          LEFT JOIN
+            tag_versions prev
+            ON
+              prev.tag_id = tag_versions.tag_id
+              AND prev.version_no = tag_versions.version_no - 1
+        SQL
+      .select('tag_versions.*', 'prev.name AS prev_name', 'prev.category AS prev_category',
+              '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
+
+    versions = q.order(Arel.sql('tag_versions.created_at DESC, tag_versions.id DESC'))
+                .limit(limit)
+                .offset(offset)
+
+    render json: { versions: serialise_versions(versions), count: }
+  end
+
+  private
+
+  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|
+      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'])
+
+      all_parent_tag_ids = (cur_parent_tag_ids | prev_parent_tag_ids)
+
+      tags_by_id =
+          Tag
+          .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]]),
+              type: h[:type] }
+          end
+
+      { tag_id: row.tag_id,
+        version_no: row.version_no,
+        event_type: row.event_type,
+        name: { current: row.name, prev: row.attributes['prev_name'] },
+        category: { current: row.category, prev: row.attributes['prev_category'] },
+        aliases: build_version_values(cur_aliases, prev_aliases, key: :name),
+        parent_tags:,
+        created_at: row.created_at.iso8601,
+        created_by_user: row.created_by_user_id &&
+                         { id: row.created_by_user_id,
+                           name: users_by_id[row.created_by_user_id] } }
+    end
+  end
+
+  def build_version_values cur_values, prev_values, key:
+    (cur_values | prev_values).map do |value|
+      type =
+          if cur_values.include?(value) && prev_values.include?(value)
+            'context'
+          elsif cur_values.include?(value)
+            'added'
+          else
+            'removed'
+          end
+
+      { key => value, type: }
+    end
+  end
+
+  def split_values(values) = values.to_s.split(/\s+/).reject(&:blank?)
+
+  def split_parent_tag_ids(values) = split_values(values).map(&:to_i)
+end

backend/app/controllers/tags_controller.rb

@@ -1,3 +1,7 @@
+require 'net/http'
+require 'uri'
+
+
 class TagsController < ApplicationController
   def index
     post_id = params[:post]
@@ -66,7 +70,7 @@ class TagsController < ApplicationController
             .offset(offset)
             .to_a
 
-    render json: { tags: TagRepr.base(tags), count: q.size }
+    render json: { tags: TagRepr.many(tags), count: q.size }
   end
 
   def with_depth
@@ -182,7 +186,8 @@ class TagsController < ApplicationController
              .find_by(id: params[:id])
     return head :not_found unless tag
 
-    render json: DeerjikistRepr.many(tag.deerjikists)
+    render json: { tag: TagRepr.base(tag),
+                   deerjikists: DeerjikistRepr.many(tag.deerjikists) }
   end
 
   def deerjikists_by_name
@@ -194,7 +199,31 @@ class TagsController < ApplicationController
              .find_by(tag_names: { name: })
     return head :not_found unless tag
 
-    render json: DeerjikistRepr.many(tag.deerjikists)
+    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?
+
+    tag = Tag.joins(:tag_name)
+             .includes(:tag_name, tag_name: :wiki_page)
+             .find_by(id: params[:id])
+    return head :not_found unless tag
+
+    ApplicationRecord.transaction do
+      tag.deerjikists = []
+      params[:_json].each do
+        platform = _1[:platform]
+        code = normalise_deerjikist_code(platform, _1[:code])
+        deerjikist = Deerjikist.find_or_initialize_by(platform:, code:)
+        deerjikist.tag = tag
+        deerjikist.save!
+      end
+    end
+
+    render json: DeerjikistRepr.many(tag.reload.deerjikists)
   end
 
   def materials_by_name
@@ -209,6 +238,60 @@ class TagsController < ApplicationController
     render json: build_tag_children(tag)
   end
 
+  def update_all
+    return head :unauthorized unless current_user
+    return head :forbidden unless current_user.gte_member?
+
+    tag = Tag.find_by(id: params[:id])
+    return head :not_found unless tag
+
+    name = params[:name].to_s.strip
+    category = params[:category].to_s.strip
+    return head :unprocessable_entity if name.blank? || category.blank?
+
+    if name != tag.name &&
+        tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
+      return render json: { error: 'システム・タグの名称は変更できません．' },
+                    status: :unprocessable_entity
+    end
+
+    if tag.nico? || category == 'nico'
+      return render json: { error: 'ニコタグは変更できません．' },
+                    status: :unprocessable_entity
+    end
+
+    alias_names = params[:aliases].to_s.split.uniq
+    parent_names = params[:parent_tags].to_s.split.uniq
+
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.update!(category:)
+      tag.tag_name.update!(name:)
+
+      alias_names << old_name if name_changed
+      alias_names.delete(name)
+
+      update_aliases!(tag, alias_names)
+      update_parent_tags!(tag, parent_names)
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
+    end
+
+    render json: TagRepr.base(tag.reload)
+  end
+
   def update
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
@@ -218,20 +301,37 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    if name.present?
-      tag.tag_name.update!(name:)
+    if tag.nico? || (category.present? && category == 'nico')
+      return render json: { error: 'ニコタグは変更できません．' },
+                    status: :unprocessable_entity
     end
 
-    if category.present?
-      tag.update!(category:)
+    ApplicationRecord.transaction do
+      TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
+
+      old_name = tag.name
+      name_changed = name.present? && name != old_name
+      wiki_page = tag.tag_name.wiki_page if name_changed
+
+      tag.tag_name.update!(name:) if name.present?
+      tag.update!(category:) if category.present?
+
+      tag.reload
+
+      record_tag_version!(
+          tag,
+          event_type: :update,
+          created_by_user: current_user,
+          name_changed:,
+          wiki_page:)
     end
 
-    render json: TagRepr.base(tag)
+    render json: TagRepr.base(tag.reload)
   end
 
   private
 
-  def build_tag_children(tag)
+  def build_tag_children tag
     material = tag.materials.first
     file = nil
     content_type = nil
@@ -244,4 +344,97 @@ class TagsController < ApplicationController
         children: tag.children.sort_by { _1.name }.map { build_tag_children(_1) },
         material: material.as_json&.merge(file:, content_type:))
   end
+
+  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.wiki_page
+    return unless wiki_page&.wiki_versions&.exists?
+
+    WikiVersionRecorder.record!(
+        page: wiki_page,
+        event_type: :update,
+        created_by_user:)
+  end
+
+  def update_aliases! tag, alias_names
+    alias_names = alias_names.uniq
+
+    affected_tags = [tag]
+
+    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.canonical&.tag
+    end
+
+    alias_names.each do |alias_name|
+      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)
+    end
+
+    current_aliases.each do |alias_tag_name|
+      next if alias_names.include?(alias_tag_name.name)
+
+      alias_tag_name.update!(canonical: nil)
+    end
+
+    alias_names.each do |alias_name|
+      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)
+    end
+  end
+
+  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
+
+    TagVersioning.record_tag_snapshots!((old_parent_tags + parent_tags).uniq,
+                                        created_by_user: current_user)
+
+    tag.reversed_tag_implications.destroy_all
+
+    parent_tags.each do |parent_tag|
+      next if parent_tag == tag
+
+      TagImplication.create!(tag:, parent_tag:)
+    end
+  end
+
+  def normalise_deerjikist_code platform, code
+    return code if platform != 'youtube' || code[0] != '@'
+
+    url = "https://www.youtube.com/#{ code }"
+
+    html = Net::HTTP.get(URI(url))
+
+    canonical = html[
+        /<link rel="canonical" href="https:\/\/www\.youtube\.com\/channel\/(UC[a-zA-Z0-9_-]{22})"/,
+        1]
+    return canonical if canonical
+
+    html[/"channelId":"(UC[a-zA-Z0-9_-]{22})"/, 1] || html[/\bUC[a-zA-Z0-9_-]{22}\b/]
+  rescue
+    nil
+  end
 end

backend/app/controllers/users_controller.rb

@@ -1,18 +1,22 @@
 class UsersController < ApplicationController
   def create
-    user = User.create!(inheritance_code: SecureRandom.uuid, role: 'guest')
+    user = nil
+    User.transaction do
+      user = User.create!(inheritance_code: SecureRandom.uuid, role: :guest)
+      attach_ip_address!(user)
+    end
+
     render json: { code: user.inheritance_code,
-                   user: user.slice(:id, :name, :inheritance_code, :role) }
+                   user: user.slice(:id, :name, :inheritance_code, :role) },
+           status: :created
   end
 
   def verify
-    ip_bin = IPAddr.new(request.remote_ip).hton
-    ip_address = IpAddress.find_or_create_by!(ip_address: ip_bin)
-
     user = User.find_by(inheritance_code: params[:code])
     return render json: { valid: false } unless user
+    return head :forbidden if user.banned?
 
-    UserIp.find_or_create_by!(user:, ip_address:)
+    attach_ip_address!(user)
 
     render json: { valid: true, user: user.slice(:id, :name, :inheritance_code, :role) }
   end
@@ -41,9 +45,18 @@ class UsersController < ApplicationController
     return head :bad_request if name.blank?
 
     if user.update(name:)
-      render json: user.slice(:id, :name, :inheritance_code, :role), status: :created
+      render json: user.slice(:id, :name, :inheritance_code, :role), status: :ok
     else
       render json: user.errors, status: :unprocessable_entity
     end
   end
+
+  private
+
+  def attach_ip_address! user
+    ip_bin = IPAddr.new(request.remote_ip).hton
+    ip_address = IpAddress.create_or_find_by!(ip_address: ip_bin)
+
+    UserIp.create_or_find_by!(user:, ip_address:)
+  end
 end

backend/app/controllers/wiki_pages_controller.rb

@@ -85,22 +85,24 @@ class WikiPagesController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
-    name = params[:title]&.strip
+    title = params[:title].to_s.strip
     body = params[:body].to_s
-
-    return head :unprocessable_entity if name.blank? || body.blank?
-
-    tag_name = TagName.find_undiscard_or_create_by!(name:)
-    page = WikiPage.new(tag_name:, created_user: current_user, updated_user: current_user)
-    if page.save
     message = params[:message].presence
-      Wiki::Commit.content!(page:, body:, created_user: current_user, message:)
+
+    return head :unprocessable_entity if title.blank? || body.blank?
+
+    tag_name = TagName.find_undiscard_or_create_by!(name: title)
+
+    page =
+        Wiki::Commit.create_content!(
+            tag_name:,
+            body:,
+            created_by_user: current_user,
+            message:)
 
     render json: WikiPageRepr.base(page), status: :created
-    else
-      render json: { errors: page.errors.full_messages },
-             status: :unprocessable_entity
-    end
+  rescue ActiveRecord::RecordInvalid, ActiveRecord::RecordNotUnique
+    head :unprocessable_entity
   end
 
   def update
@@ -113,12 +115,21 @@ class WikiPagesController < ApplicationController
     return head :unprocessable_entity if title.blank? || body.blank?
 
     page = WikiPage.find(params[:id])
-    base_revision_id = page.current_revision.id
+    base_revision_id = params[:base_revision_id].presence
 
-    if params[:title].present? && params[:title].strip != page.title
-      return head :unprocessable_entity
+    ApplicationRecord.transaction do
+      page.lock!
+
+      old_title = page.title
+
+      tag = Tag.find_by(tag_name_id: page.tag_name_id)
+
+      if tag && title != old_title
+        TagVersioning.ensure_snapshot!(tag, created_by_user: current_user)
       end
 
+      page.tag_name.update!(name: title) if title != old_title
+
       message = params[:message].presence
       Wiki::Commit.content!(page:,
                             body:,
@@ -126,6 +137,12 @@ class WikiPagesController < ApplicationController
                             message:,
                             base_revision_id:)
 
+      if tag && title != old_title
+        tag.reload
+        TagVersionRecorder.record!(tag:, event_type: :update, created_by_user: current_user)
+      end
+    end
+
     head :ok
   end
 

backend/app/models/ip_address.rb

@@ -1,6 +1,10 @@
 class IpAddress < ApplicationRecord
   validates :ip_address, presence: true, length: { maximum: 16 }
-  validates :banned, inclusion: { in: [true, false] }
 
-  has_many :users
+  has_many :user_ips, dependent: :destroy
+  has_many :users, through: :user_ips
+
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 end

backend/app/models/my_discard.rb

@@ -1,7 +1,11 @@
 module MyDiscard
   extend ActiveSupport::Concern
 
-  included { include Discard::Model }
+  included do
+    include Discard::Model
+
+    default_scope -> { kept }
+  end
 
   class_methods do
     def find_undiscard_or_create_by! attrs, &block

backend/app/models/nico_tag_version.rb

@@ -0,0 +1,7 @@
+class NicoTagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  validates :name, presence: true
+end

backend/app/models/post.rb

@@ -1,7 +1,6 @@
 class Post < ApplicationRecord
   require 'mini_magick'
 
-  belongs_to :parent, class_name: 'Post', optional: true, foreign_key: 'parent_id'
   belongs_to :uploaded_user, class_name: 'User', optional: true
 
   has_many :post_tags, dependent: :destroy, inverse_of: :post
@@ -13,6 +12,20 @@ class Post < ApplicationRecord
   has_many :post_similarities, dependent: :delete_all
   has_many :post_versions
 
+  has_many :parent_post_implications,
+           class_name: 'PostImplication',
+           foreign_key: :post_id,
+           dependent: :destroy,
+           inverse_of: :post
+  has_many :parents, through: :parent_post_implications, source: :parent_post
+
+  has_many :child_post_implications,
+           class_name: 'PostImplication',
+           foreign_key: :parent_post_id,
+           dependent: :destroy,
+           inverse_of: :parent_post
+  has_many :children, through: :child_post_implications, source: :post
+
   has_one_attached :thumbnail
 
   before_validation :normalise_url
@@ -22,17 +35,29 @@ class Post < ApplicationRecord
   validate :validate_original_created_range
   validate :url_must_be_http_url
 
+  def parent_posts = parents
+
+  def child_posts = children
+
+  def sibling_posts
+    parent_post_ids = parent_posts.order(:id).pluck(:id)
+
+    parent_post_ids.to_h { [_1, PostImplication.where(parent_post: _1).map(&:post)] }
+  end
+
   def as_json options = { }
-    super(options).merge({ thumbnail: thumbnail.attached? ?
+    super(options).merge(thumbnail: thumbnail.attached? ?
                                     Rails.application.routes.url_helpers.rails_blob_url(
                                         thumbnail, only_path: false) :
-                                      nil })
+                                    nil)
   rescue
     super(options).merge(thumbnail: nil)
   end
 
   def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
 
+  def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
+
   def related limit: nil
     ids = post_similarities.order(cos: :desc)
     ids = ids.limit(limit) if limit

backend/app/models/post_implication.rb

@@ -0,0 +1,19 @@
+class PostImplication < ApplicationRecord
+  self.primary_key = :post_id, :parent_post_id
+
+  belongs_to :post, inverse_of: :parent_post_implications
+  belongs_to :parent_post, class_name: 'Post', inverse_of: :child_post_implications
+
+  validates :post_id, presence: true, uniqueness: { scope: :parent_post_id }
+  validates :parent_post_id, presence: true
+
+  validate :parent_post_mustnt_be_itself
+
+  private
+
+  def parent_post_mustnt_be_itself
+    if parent_post_id == post_id
+      errors.add :parent_post_id, '親投稿に同じ投稿を設定することはできません．'
+    end
+  end
+end

backend/app/models/post_version.rb

@@ -1,29 +1,13 @@
 class PostVersion < ApplicationRecord
-  before_update do
-    raise ActiveRecord::ReadOnlyRecord, '版は更新できません．'
-  end
-
-  before_destroy do
-    raise ActiveRecord::ReadOnlyRecord, '版は削除できません．'
-  end
+  include VersionRecord
 
   belongs_to :post
   belongs_to :parent, class_name: 'Post', optional: true
-  belongs_to :created_by_user, class_name: 'User', optional: true
 
-  enum :event_type, { create: 'create',
-                      update: 'update',
-                      discard: 'discard',
-                      restore: 'restore' }, prefix: true, validate: true
-
-  validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
-  validates :event_type, presence: true, inclusion: { in: event_types.keys }
   validates :url, presence: true
 
   validate :validate_original_created_range
 
-  scope :chronological, -> { order(:version_no, :id) }
-
   private
 
   def validate_original_created_range

backend/app/models/tag.rb

@@ -8,8 +8,6 @@ class Tag < ApplicationRecord
     ;
   end
 
-  default_scope -> { kept }
-
   has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
@@ -36,6 +34,9 @@ class Tag < ApplicationRecord
   has_many :deerjikists, dependent: :delete_all
   has_many :materials
 
+  has_many :tag_versions
+  has_many :nico_tag_versions
+
   belongs_to :tag_name
   delegate :wiki_page, to: :tag_name
 
@@ -78,27 +79,18 @@ class Tag < ApplicationRecord
 
   def material_id = materials.first&.id
 
-  def self.tagme
-    @tagme ||= find_or_create_by_tag_name!('タグ希望', category: :meta)
-  end
+  def has_deerjikists = deerjikists.present?
 
-  def self.bot
-    @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
-  end
+  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.no_deerjikist
-    @no_deerjikist ||= find_or_create_by_tag_name!('ニジラー情報不詳', category: :meta)
-  end
-
-  def self.video
-    @video ||= find_or_create_by_tag_name!('動画', category: :meta)
-  end
-
-  def self.niconico
-    @niconico ||= find_or_create_by_tag_name!('ニコニコ', category: :meta)
-  end
-
-  def self.normalise_tags tag_names, with_tagme: true, deny_nico: true
+  def self.normalise_tags! tag_names, with_tagme: true,
+                                      with_no_deerjikist: true,
+                                      deny_nico: true
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
     end
@@ -112,7 +104,7 @@ class Tag < ApplicationRecord
     end
 
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
-    tags << Tag.no_deerjikist if tags.all? { |t| !(t.deerjikist?) }
+    tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
     tags.uniq(&:id)
   end
 
@@ -150,21 +142,25 @@ class Tag < ApplicationRecord
     retry
   end
 
-  def self.merge_tags! target_tag, source_tags
+  def self.merge_tags! target_tag, source_tags, created_by_user: nil
     target_tag => Tag
 
     affected_post_ids = Set.new
 
     Tag.transaction do
+      TagVersioning.ensure_snapshot!(target_tag, created_by_user:)
+
       Array(source_tags).compact.uniq.each do |source_tag|
         source_tag => Tag
 
         next if source_tag == target_tag
 
+        TagVersioning.ensure_snapshot!(source_tag, created_by_user:)
+
         source_tag.post_tags.kept.find_each do |source_pt|
           post_id = source_pt.post_id
           affected_post_ids << post_id
-          source_pt.discard_by!(nil)
+          source_pt.discard_by!(created_by_user)
           unless PostTag.kept.exists?(post_id:, tag: target_tag)
             PostTag.create!(post_id:, tag: target_tag)
           end
@@ -176,6 +172,7 @@ class Tag < ApplicationRecord
           raise ActiveRecord::RecordInvalid.new(source_tag_name)
         end
 
+        TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
         source_tag.discard!
 
         if source_tag.nico?
@@ -184,10 +181,13 @@ class Tag < ApplicationRecord
           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
 
       Post.where(id: affected_post_ids.to_a).find_each do |post|
-        PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user:)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user:)
       end
 
       # 投稿件数を再集計
@@ -197,6 +197,14 @@ class Tag < ApplicationRecord
     target_tag.reload
   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
+    linked_tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  end
+
   private
 
   def nico_tag_name_must_start_with_nico

backend/app/models/tag_name.rb

@@ -1,8 +1,6 @@
 class TagName < ApplicationRecord
   include MyDiscard
 
-  default_scope -> { kept }
-
   has_one :tag
   has_one :wiki_page
 

backend/app/models/tag_version.rb

@@ -0,0 +1,15 @@
+class TagVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :tag
+
+  enum :category, { deerjikist: 'deerjikist',
+                    meme: 'meme',
+                    character: 'character',
+                    general: 'general',
+                    material: 'material',
+                    meta: 'meta' }, validate: true
+
+  validates :name, presence: true
+  validates :category, presence: true
+end

backend/app/models/user.rb

@@ -4,7 +4,6 @@ class User < ApplicationRecord
   validates :name, length: { maximum: 255 }
   validates :inheritance_code, presence: true, length: { maximum: 64 }
   validates :role, presence: true, inclusion: { in: roles.keys }
-  validates :banned, inclusion: { in: [true, false] }
 
   has_many :created_posts,
            class_name: 'Post', foreign_key: :uploaded_user_id, dependent: :nullify
@@ -19,5 +18,10 @@ class User < ApplicationRecord
            class_name: 'WikiPage', foreign_key: :updated_user_id, dependent: :nullify
 
   def viewed?(post) = user_post_views.exists?(post_id: post.id)
+
   def gte_member? = member? || admin?
+
+  def banned? = banned_at.present?
+  def ban! = banned? || update!(banned_at: Time.current)
+  def unban! = update!(banned_at: nil)
 end

backend/app/models/version_record.rb

@@ -0,0 +1,19 @@
+module VersionRecord
+  extend ActiveSupport::Concern
+
+  def readonly? = persisted?
+
+  included do
+    belongs_to :created_by_user, class_name: 'User', optional: true
+
+    enum :event_type, { create: 'create',
+                        update: 'update',
+                        discard: 'discard',
+                        restore: 'restore' }, prefix: true, validate: true
+
+    validates :version_no, presence: true, numericality: { only_integer: true, greater_than: 0 }
+    validates :event_type, presence: true
+
+    scope :chronological, -> { order(:version_no, :id) }
+  end
+end

backend/app/models/wiki_page.rb

@@ -4,8 +4,6 @@ require 'set'
 class WikiPage < ApplicationRecord
   include MyDiscard
 
-  default_scope -> { kept }
-
   has_many :wiki_revisions, dependent: :destroy
   belongs_to :created_user, class_name: 'User'
   belongs_to :updated_user, class_name: 'User'
@@ -15,8 +13,11 @@ class WikiPage < ApplicationRecord
            foreign_key: :redirect_page_id,
            dependent: :nullify
 
+  has_many :wiki_versions
+
   belongs_to :tag_name
   validates :tag_name, presence: true
+  validates :body, presence: true
 
   def title = tag_name.name
 
@@ -26,11 +27,6 @@ class WikiPage < ApplicationRecord
 
   def current_revision = wiki_revisions.order(id: :desc).first
 
-  def body
-    rev = current_revision
-    rev.body if rev&.content?
-  end
-
   def resolve_redirect limit: 10
     page = self
     visited = Set.new

backend/app/models/wiki_version.rb

@@ -0,0 +1,8 @@
+class WikiVersion < ApplicationRecord
+  include VersionRecord
+
+  belongs_to :wiki_page
+
+  validates :title, presence: true
+  validates :body, presence: true
+end

backend/app/representations/post_repr.rb

@@ -2,7 +2,8 @@
 
 
 module PostRepr
-  BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE } }.freeze
+  BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE },
+           methods: [:parent_posts, :child_posts, :sibling_posts] }.freeze
 
   module_function
 

backend/app/representations/tag_repr.rb

@@ -3,15 +3,14 @@
 
 module TagRepr
   BASE = { only: [:id, :category, :post_count, :created_at, :updated_at],
-           methods: [:name, :has_wiki, :material_id] }.freeze
+           methods: [:name, :has_wiki, :material_id, :has_deerjikists] }.freeze
 
   module_function
 
   def base tag
-    tag.as_json(BASE)
+    tag.as_json(BASE).merge(aliases: tag.snapshot_aliases,
+                            parents: tag.parents.map { _1.as_json(BASE) })
   end
 
-  def many tags
-    tags.map { |t| base(t) }
-  end
+  def many(tags) = tags.map { |t| base(t) }
 end

backend/app/services/nico_tag_version_recorder.rb

@@ -0,0 +1,19 @@
+class NicoTagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  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 = :tag
+
+  def snapshot_attributes
+    { name: @record.name, linked_tags: @record.snapshot_linked_tag_names.join(' ') }
+  end
+end

backend/app/services/post_version_recorder.rb

@@ -1,57 +1,31 @@
-class PostVersionRecorder
+class PostVersionRecorder < VersionRecorder
   def self.record! post:, event_type:, created_by_user:
     new(post:, event_type:, created_by_user:).record!
   end
 
   def initialize post:, event_type:, created_by_user:
-    @post = post
-    @event_type = event_type
-    @created_by_user = created_by_user
+    super(record: post, event_type:, created_by_user:)
   end
 
-  def record!
-    @post.with_lock do
-      latest = @post.post_versions.order(version_no: :desc).first
-      attrs = snapshot_attributes
+  def self.ensure_snapshot! post, created_by_user:
+    return if post.post_versions.exists?
 
-      return latest if @event_type == :update && latest && same_snapshot?(latest, attrs)
-
-      PostVersion.create!(
-          post: @post,
-          version_no: (latest&.version_no || 0) + 1,
-          event_type: @event_type,
-          title: attrs[:title],
-          url: attrs[:url],
-          thumbnail_base: attrs[:thumbnail_base],
-          tags: attrs[:tags],
-          parent: attrs[:parent],
-          original_created_from: attrs[:original_created_from],
-          original_created_before: attrs[:original_created_before],
-          created_at: Time.current,
-          created_by_user: @created_by_user)
-    end
+    record!(post:, event_type: :create, created_by_user:)
   end
 
   private
 
-  def snapshot_attributes
-    { title: @post.title,
-      url: @post.url,
-      thumbnail_base: @post.thumbnail_base,
-      tags: @post.snapshot_tag_names.join(' '),
-      parent: @post.parent,
-      original_created_from: @post.original_created_from,
-      original_created_before: @post.original_created_before }
-  end
+  def version_class = PostVersion
+  def version_association = :post_versions
+  def record_key = :post
 
-  def same_snapshot? version, attrs
-    true &&
-        version.title == attrs[:title] &&
-        version.url == attrs[:url] &&
-        version.thumbnail_base == attrs[:thumbnail_base] &&
-        version.tags == attrs[:tags] &&
-        version.parent_id == attrs[:parent]&.id &&
-        version.original_created_from == attrs[:original_created_from] &&
-        version.original_created_before == attrs[:original_created_before]
+  def snapshot_attributes
+    { title: @record.title,
+      url: @record.url,
+      thumbnail_base: @record.thumbnail_base,
+      tags: @record.snapshot_tag_names.join(' '),
+      parent_post_ids: @record.snapshot_parent_post_ids.join(' '),
+      original_created_from: @record.original_created_from,
+      original_created_before: @record.original_created_before }
   end
 end

backend/app/services/tag_version_recorder.rb

@@ -0,0 +1,22 @@
+class TagVersionRecorder < VersionRecorder
+  def self.record! tag:, event_type:, created_by_user:
+    new(tag:, event_type:, created_by_user:).record!
+  end
+
+  def initialize tag:, event_type:, created_by_user:
+    super(record: tag, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = TagVersion
+  def version_association = :tag_versions
+  def record_key = :tag
+
+  def snapshot_attributes
+    { name: @record.name,
+      category: @record.category,
+      aliases: @record.snapshot_aliases.join(' '),
+      parent_tag_ids: @record.snapshot_parent_tag_ids.join(' ') }
+  end
+end

backend/app/services/tag_versioning.rb

@@ -0,0 +1,38 @@
+class TagVersioning
+  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:
+    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:)
+    end
+  end
+
+  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
+
+    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:)
+    end
+  end
+end

backend/app/services/version_recorder.rb

@@ -0,0 +1,62 @@
+class VersionRecorder
+  EVENT_TYPES = ['create', 'update', 'discard', 'restore'].freeze
+
+  def initialize record:, event_type:, created_by_user:
+    @record = record
+    @event_type = event_type.to_s
+    @created_by_user = created_by_user
+
+    validate_event_type!
+  end
+
+  def record!
+    raise "#{ record_class.name } must be persisted" unless @record.persisted?
+
+    ApplicationRecord.transaction do
+      @record = record_class.unscoped.lock.find(@record.id)
+      latest = latest_version
+
+      if !(latest) && @event_type != 'create'
+        raise "#{ version_class.name } first event must be create"
+      end
+
+      if @event_type == 'create' && latest
+        raise "#{ version_class.name } create event already exists"
+      end
+
+      attrs = snapshot_attributes
+
+      return latest if @event_type == 'update' && latest && same_snapshot?(latest, attrs)
+
+      version_class.create!(base_attributes(latest).merge(record_key => @record).merge(attrs))
+    end
+  end
+
+  private
+
+  def latest_version = versions.order(version_no: :desc).first
+
+  def versions = @record.public_send(version_association)
+
+  def base_attributes latest
+    { version_no: (latest&.version_no || 0) + 1,
+      event_type: @event_type,
+      created_at: Time.current,
+      created_by_user: @created_by_user }
+  end
+
+  def same_snapshot?(version, attrs) = attrs.all? { |k, v| version.public_send(k) == v }
+
+  def validate_event_type!
+    return if EVENT_TYPES.include?(@event_type)
+
+    raise ArgumentError, "Invalid event_type: #{ @event_type }"
+  end
+
+  def version_class = raise NotImplementedError
+  def version_association = raise NotImplementedError
+  def record_key = raise NotImplementedError
+  def snapshot_attributes = raise NotImplementedError
+
+  def record_class = @record.class
+end

backend/app/services/wiki/commit.rb

@@ -7,6 +7,31 @@ module Wiki
       ;
     end
 
+    def self.create_content! tag_name:, body:, created_by_user:, message: nil
+      normalised = normalise_body(body)
+
+      page = WikiPage.new(tag_name:,
+                          body: normalised,
+                          created_user: created_by_user,
+                          updated_user: created_by_user)
+
+      if normalised.blank?
+        page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, page
+      end
+
+      ActiveRecord::Base.transaction do
+        page.save!
+
+        new(page:, created_user: created_by_user).content!(
+            body: normalised,
+            message:,
+            base_revision_id: nil)
+
+        page
+      end
+    end
+
     def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
       new(page:, created_user:).content!(body:, message:, base_revision_id:)
     end
@@ -21,7 +46,12 @@ module Wiki
     end
 
     def content! body:, message:, base_revision_id:
-      normalised = normalise_body(body)
+      normalised = self.class.normalise_body(body)
+      if normalised.blank?
+        @page.errors.add(:body, :blank)
+        raise ActiveRecord::RecordInvalid, @page
+      end
+
       lines = split_lines(normalised)
 
       line_shas = lines.map { |line| Digest::SHA256.hexdigest(line) }
@@ -37,10 +67,19 @@ module Wiki
           current_id = @page.wiki_revisions.maximum(:id)
           if current_id && current_id != base_revision_id.to_i
             raise Conflict,
-                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
+                "競合が発生してゐます" +
+                "（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
           end
         end
 
+        @page.update!(body: normalised)
+
+        WikiVersionRecorder.record!(
+            page: @page,
+            event_type: @page.wiki_versions.exists? ? :update : :create,
+            reason: message,
+            created_by_user: @created_user)
+
         rev = WikiRevision.create!(
             wiki_page:        @page,
             base_revision_id:,
@@ -54,65 +93,45 @@ module Wiki
         rows = line_ids.each_with_index.map do |line_id, pos|
           { wiki_revision_id: rev.id, wiki_line_id: line_id, position: pos }
         end
-        WikiRevisionLine.insert_all!(rows)
+        WikiRevisionLine.insert_all!(rows) if rows.any?
 
         rev
       end
     end
 
-    def redirect! redirect_page:, message:, base_revision_id:
-      ActiveRecord::Base.transaction do
-        @page.lock!
+    def redirect!(redirect_page:, message:, base_revision_id:) = raise '廃止しました．'
 
-        if base_revision_id.present?
-          current_id = @page.wiki_revisions.maximum(:id)
-          if current_id && current_id != base_revision_id.to_i
-            raise Conflict,
-                "競合が発生してゐます（現在の Id.：#{ current_id }，ベース Id.：#{ base_revision_id }）．"
-          end
-        end
-
-        WikiRevision.create!(
-            wiki_page:        @page,
-            base_revision_id:,
-            created_user:     @created_user,
-            kind:             :redirect,
-            redirect_page:,
-            message:,
-            lines_count:      0,
-            tree_sha256:      nil)
-      end
+    def self.normalise_body body
+      s = body.to_s
+      s.gsub!(/\r\n?/, "\n")
+      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
+      s.gsub(/\n+$/, '')
     end
 
     private
 
-    def normalise_body body
-      s = body.to_s
-      s.gsub!("\r\n", "\n")
-      s.encode('UTF-8', invalid: :replace, undef: :replace, replace: '🖕')
-    end
-
-    def split_lines body
-      body.split("\n")
-    end
+    def split_lines(body) = body.split("\n")
 
     def upsert_lines! lines, line_shas
       now = Time.current
 
       id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
 
-      missing_rows = []
+      missing_by_sha = { }
+
       line_shas.each_with_index do |sha, i|
         next if id_by_sha.key?(sha)
+        next if missing_by_sha.key?(sha)
 
-        missing_rows << { sha256:     sha,
+        missing_by_sha[sha] = {
+            sha256:     sha,
             body:       lines[i],
             created_at: now,
             updated_at: now }
       end
 
-      if missing_rows.any?
-        WikiLine.upsert_all(missing_rows)
+      if missing_by_sha.any?
+        WikiLine.upsert_all(missing_by_sha.values)
         id_by_sha = WikiLine.where(sha256: line_shas).pluck(:sha256, :id).to_h
       end
 

backend/app/services/wiki_version_recorder.rb

@@ -0,0 +1,21 @@
+class WikiVersionRecorder < VersionRecorder
+  def self.record! page:, event_type:, reason: nil, created_by_user:
+    new(page:, event_type:, reason:, created_by_user:).record!
+  end
+
+  def initialize page:, event_type:, reason: nil, created_by_user:
+    @reason = reason
+    super(record: page, event_type:, created_by_user:)
+  end
+
+  private
+
+  def version_class = WikiVersion
+  def version_association = :wiki_versions
+  def record_key = :wiki_page
+
+  def snapshot_attributes = {
+      title: @record.title,
+      body: @record.body,
+      reason: @reason }
+end

backend/app/services/youtube/api_client.rb

@@ -0,0 +1,73 @@
+require 'json'
+require 'net/http'
+require 'uri'
+
+
+module Youtube
+  class ApiClient
+    ENDPOINT = 'https://www.googleapis.com/youtube/v3'
+
+    def initialize api_key: ENV.fetch('YOUTUBE_API_KEY')
+      @api_key = api_key
+    end
+
+    def search_videos q:, published_after: nil, published_before: nil, page_token: nil
+      get_json('/search', {
+          part:           'snippet',
+          type:           'video',
+          q:,
+          order:          'date',
+          maxResults:     50,
+          regionCode:     'JP',
+          relevanceLanguage: 'ja',
+          publishedAfter: published_after&.iso8601,
+          publishedBefore: published_before&.iso8601,
+          pageToken:      page_token }.compact)
+    end
+
+    def videos ids
+      return { 'items' => [] } if ids.empty?
+
+      get_json('/videos', part: 'snippet,status,contentDetails', id: ids.join(','))
+    end
+
+    def playlist_items playlist_id:, page_token: nil
+      get_json('/playlistItems', {
+          part:       'snippet,contentDetails,status',
+          playlistId: playlist_id,
+          maxResults: 50,
+          pageToken:  page_token }.compact)
+    end
+
+    def channel id: nil, handle: nil
+      raise ArgumentError, 'id or handle is required' if id.present? == handle.present?
+
+      params = { part: 'snippet,contentDetails' }
+      params[:id] = id if id.present?
+      params[:forHandle] = handle if handle.present?
+
+      get_json('/channels', params)
+    end
+
+    private
+
+    def get_json path, params
+      uri = URI(ENDPOINT + path)
+      uri.query = URI.encode_www_form(params.merge(key: @api_key))
+
+      response = Net::HTTP.start(uri.host,
+                                 uri.port,
+                                 use_ssl: true,
+                                 open_timeout: 10,
+                                 read_timeout: 30) do |http|
+        http.get(uri)
+      end
+
+      unless response.is_a?(Net::HTTPSuccess)
+        raise "YouTube API error: #{ response.code } #{ response.body }"
+      end
+
+      JSON.parse(response.body)
+    end
+  end
+end

backend/app/services/youtube/sync.rb

@@ -0,0 +1,168 @@
+require 'open-uri'
+require 'set'
+require 'time'
+
+
+module Youtube
+  class Sync
+    def initialize client: ApiClient.new
+      @client = client
+    end
+
+    def sync!
+      video_ids = discover_video_ids
+      return if video_ids.empty?
+
+      video_ids.each_slice(50) do |ids|
+        @client.videos(ids).fetch('items', []).each do |item|
+          sync_video!(VideoItem.new(item))
+        end
+      end
+    end
+
+    private
+
+    def discover_video_ids
+      ids = Set.new
+
+      query_terms.each do |q|
+        response = @client.search_videos(q:, published_after: sync_since)
+
+        response.fetch('items', []).each do |item|
+          video_id = item.dig('id', 'videoId')
+          ids << video_id if video_id.present?
+        end
+      end
+
+      playlist_ids.each do |playlist_id|
+        each_playlist_item(playlist_id) do |item|
+          video_id = item.dig('contentDetails', 'videoId')
+          video_id ||= item.dig('snippet', 'resourceId', 'videoId')
+
+          ids << video_id if video_id.present?
+        end
+      end
+
+      ids.to_a
+    end
+
+    def sync_video! video
+      post = Post.where('url REGEXP ?', youtube_url_regexp(video.id)).first
+
+      original_created_from = video.published_at.change(sec: 0)
+      original_created_before = original_created_from + 1.minute
+
+      post_created = false
+      post_changed = false
+
+      if post
+        post.assign_attributes(title: video.title,
+                               original_created_from:,
+                               original_created_before:,
+                               thumbnail_base: video.thumbnail_url)
+
+        post_changed = post.changed?
+        post.save! if post_changed
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+      else
+        post_created = true
+        post = Post.create!(
+            title: video.title,
+            url: video.url,
+            thumbnail_base: video.thumbnail_url,
+            uploaded_user_id: nil,
+            original_created_from:,
+            original_created_before:)
+
+        attach_thumbnail_if_needed!(post, video.thumbnail_url)
+
+        sync_post_tags!(post, [Tag.tagme.id, Tag.bot.id, Tag.youtube.id, Tag.video.id])
+      end
+
+      kept_tag_ids = post.tags.pluck(:id).to_set
+      desired_tag_ids = kept_tag_ids.to_a
+
+      deerjikist = Deerjikist.find_by(platform: :youtube, code: video.channel_id)
+      if deerjikist
+        desired_tag_ids.delete(Tag.no_deerjikist.id)
+        desired_tag_ids << deerjikist.tag_id
+      elsif post.tags.where(category: :deerjikist).none?
+        desired_tag_ids << Tag.no_deerjikist.id
+      end
+
+      desired_tag_ids.uniq!
+
+      sync_post_tags!(post, desired_tag_ids, current_tag_ids: kept_tag_ids)
+
+      if post_created
+        PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
+      elsif post_changed || kept_tag_ids != desired_tag_ids.to_set
+        PostVersionRecorder.ensure_snapshot!(post, created_by_user: nil)
+        PostVersionRecorder.record!(post:, event_type: :update, created_by_user: nil)
+      end
+    end
+
+    def sync_post_tags! post, desired_tag_ids, current_tag_ids: nil
+      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
+      to_remove = current_tag_ids - desired_tag_ids
+
+      Tag.where(id: to_add.to_a).find_each do |tag|
+        begin
+          PostTag.create!(post:, tag:)
+        rescue ActiveRecord::RecordNotUnique
+          ;
+        end
+      end
+
+      PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
+        pt.discard_by!(nil)
+      end
+    end
+
+    def attach_thumbnail_if_needed! post, thumbnail_url
+      return if post.thumbnail.attached?
+      return if thumbnail_url.blank?
+
+      post.thumbnail.attach(
+          io:           URI.open(thumbnail_url),
+          filename:     File.basename(URI.parse(thumbnail_url).path),
+          content_type: 'image/jpeg')
+
+      post.resized_thumbnail!
+    end
+
+    def youtube_url_regexp id
+      escaped = Regexp.escape(id)
+      "(youtube\\.com/watch\\?v=#{ escaped }|youtu\\.be/#{ escaped })([^A-Za-z0-9_-]|$)"
+    end
+
+    def query_terms = ['ぼざろクリーチャーシリーズ', '伊地知ニジカ', '伊地知虹鹿']
+
+    def playlist_ids
+      ['PLrOch4zHkI5vu29b-f9umUQQ4tQkuWLPX',
+       'PLrOch4zHkI5vOK0RaytQq6PbucxQkkL0K',
+       'PLrOch4zHkI5tdwm9vSegiDQJOM-hgpcOC']
+    end
+
+    def sync_since = 14.days.ago
+
+    def each_playlist_item playlist_id
+      page_token = nil
+
+      loop do
+        response = @client.playlist_items(playlist_id:, page_token:)
+
+        response.fetch('items', []).each do |item|
+          yield item
+        end
+
+        page_token = response['nextPageToken']
+        break if page_token.blank?
+      end
+    end
+  end
+end

backend/app/services/youtube/video_item.rb

@@ -0,0 +1,32 @@
+require 'time'
+
+
+module Youtube
+  class VideoItem
+    attr_reader :id, :title, :channel_id, :published_at, :thumbnail_url, :raw_tags
+
+    def initialize item
+      snippet = item.fetch('snippet')
+
+      @id = item.fetch('id')
+      @title = snippet['title']
+      @channel_id = snippet['channelId']
+      @published_at = Time.iso8601(snippet['publishedAt'])
+      @thumbnail_url = pick_thumbnail(snippet['thumbnails'] || { })
+      @raw_tags = snippet['tags'] || []
+    end
+
+    def url = "https://www.youtube.com/watch?v=#{ @id }"
+
+    private
+
+    def pick_thumbnail thumbnails
+      ['maxres', 'standard', 'high', 'medium', 'default'].each do |key|
+        url = thumbnails.dig(key, 'url')
+        return url if url.present?
+      end
+
+      nil
+    end
+  end
+end

backend/config/routes.rb

@@ -6,10 +6,11 @@ Rails.application.routes.draw do
     delete ':child_id', action: :destroy
   end
 
-  resources :tags, only: [:index, :show, :update] do
+  resources :tags, only: [:index, :show] do
     collection do
       get :autocomplete
       get :'with-depth', action: :with_depth
+      get :versions, to: 'tag_versions#index'
 
       scope :name do
         get ':name/deerjikists', action: :deerjikists_by_name
@@ -19,7 +20,11 @@ Rails.application.routes.draw do
     end
 
     member do
+      put '', action: :update_all
+      patch '', action: :update
+
       get :deerjikists
+      put :deerjikists, action: :update_deerjikists
     end
   end
 
@@ -49,6 +54,7 @@ Rails.application.routes.draw do
     collection do
       get :random
       get :changes
+      get :versions, to: 'post_versions#index'
     end
 
     member do

backend/config/schedule.rb

@@ -1,12 +1,27 @@
 env :PATH, '/root/.rbenv/shims:/root/.rbenv/bin:/usr/local/bin:/usr/bin:/bin'
 
+set :path, '/var/www/btrc-hub/backend'
+set :environment, 'production'
 set :output, standard: '/var/log/btrc_hub_nico_sync.log',
              error:    '/var/log/btrc_hub_nico_sync_err.log'
 
-every 1.day, at: '3:00 pm' do
+job_type :rake,
+         'cd :path && set -a && . /etc/btrc-hub/backend.env && set +a && ' \
+         ':environment_variable=:environment bundle exec rake :task --silent :output'
+
+every 1.day, at: '11:00 am' do
   rake 'nico:sync', environment: 'production'
 end
 
 every 1.day, at: '0:00 am' do
   rake 'post_similarity:calc', environment: 'production'
+  rake 'tag_similarity:calc', environment: 'production'
+end
+
+every 1.day, at: '7:50 am' do
+  rake 'nico:export', environment: 'production'
+end
+
+every :hour do
+  rake 'post:sync', environment: 'production'
 end

backend/config/storage.yml

@@ -13,3 +13,4 @@ r2:
   secret_access_key: <%= ENV['R2_SECRET_ACCESS_KEY'] %>
   bucket: <%= ENV['R2_BUCKET'] %>
   region: auto
+  request_checksum_calculation: when_required

backend/db/migrate/20260409123700_create_post_versions.rb

@@ -2,15 +2,15 @@ require 'set'
 
 
 class CreatePostVersions < ActiveRecord::Migration[8.0]
-  class Post < ApplicationRecord
+  class Post < ActiveRecord::Base
     self.table_name = 'posts'
   end
 
-  class PostTag < ApplicationRecord
+  class PostTag < ActiveRecord::Base
     self.table_name = 'post_tags'
   end
 
-  class PostVersion < ApplicationRecord
+  class PostVersion < ActiveRecord::Base
     self.table_name = 'post_versions'
   end
 

backend/db/migrate/20260419035400_create_tag_versions.rb

@@ -0,0 +1,156 @@
+class CreateTagVersions < ActiveRecord::Migration[8.0]
+  class Tag < ActiveRecord::Base
+    self.table_name = 'tags'
+  end
+
+  class TagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  class TagImplication < ActiveRecord::Base
+    self.table_name = 'tag_implications'
+  end
+
+  class TagVersion < ActiveRecord::Base
+    self.table_name = 'tag_versions'
+  end
+
+  class NicoTagVersion < ActiveRecord::Base
+    self.table_name = 'nico_tag_versions'
+  end
+
+  class NicoTagRelation < ActiveRecord::Base
+    self.table_name = 'nico_tag_relations'
+  end
+
+  def up
+    create_table :tag_versions do |t|
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :name, null: false
+      t.string :category, null: false
+      t.text :aliases, null: false
+      t.text :parent_tag_ids, null: false
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }, index: false
+
+      t.index [:tag_id, :version_no], unique: true
+      t.index :created_at
+      t.index [:tag_id, :created_at], order: { created_at: :desc }
+      t.index [:created_by_user_id, :created_at], order: { created_at: :desc }
+      t.check_constraint 'version_no > 0',
+                         name: 'tag_versions_version_no_positive'
+    end
+
+    create_table :nico_tag_versions do |t|
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :name, null: false
+      t.text :linked_tags, null: false
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }, index: false
+
+      t.index [:tag_id, :version_no], unique: true
+      t.index :created_at
+      t.index [:tag_id, :created_at], order: { created_at: :desc }
+      t.index [:created_by_user_id, :created_at], order: { created_at: :desc }
+      t.check_constraint 'version_no > 0',
+                         name: 'nico_tag_versions_version_no_positive'
+    end
+
+    TagVersion.reset_column_information
+    say_with_time 'Backfilling tag_versions' do
+      Tag.where(discarded_at: nil)
+         .where.not(category: 'nico')
+         .find_in_batches(batch_size: 500) do |tags|
+        tag_ids = tags.map(&:id)
+
+        tag_implication_rows_by_tag_id =
+            TagImplication
+            .where(tag_id: tag_ids)
+            .pluck(:tag_id, :parent_tag_id)
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        tag_name_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+            .where(tags: { id: tag_ids })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object({ }) do |row, h|
+              h[row[0]] = row[1]
+            end
+
+        tag_alias_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.canonical_id')
+            .where(tags: { id: tag_ids })
+            .where(tag_names: { discarded_at: nil })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        TagVersion.insert_all(tags.map { |tag|
+          { tag_id: tag.id,
+            version_no: 1,
+            event_type: 'create',
+            name: tag_name_rows_by_tag_id[tag.id],
+            category: tag.category,
+            aliases: tag_alias_rows_by_tag_id[tag.id].sort.join(' '),
+            parent_tag_ids: tag_implication_rows_by_tag_id[tag.id].sort.join(' '),
+            created_at: tag.created_at,
+            created_by_user_id: nil }
+        })
+      end
+    end
+
+    NicoTagVersion.reset_column_information
+    say_with_time 'Backfilling nico_tag_versions' do
+      Tag.where(discarded_at: nil, category: 'nico')
+         .find_in_batches(batch_size: 500) do |tags|
+        tag_ids = tags.map(&:id)
+
+        tag_name_rows_by_tag_id =
+            TagName
+            .joins('INNER JOIN tags ON tags.tag_name_id = tag_names.id')
+            .where(tags: { id: tag_ids })
+            .pluck('tags.id', 'tag_names.name')
+            .each_with_object({ }) do |row, h|
+              h[row[0]] = row[1]
+            end
+
+        nico_tag_relation_rows_by_tag_id =
+            NicoTagRelation
+            .joins('INNER JOIN tags nico_tags ON nico_tags.id = nico_tag_relations.nico_tag_id')
+            .joins('INNER JOIN tags linked_tags ON linked_tags.id = nico_tag_relations.tag_id')
+            .joins('INNER JOIN tag_names ON tag_names.id = linked_tags.tag_name_id')
+            .where(nico_tags: { id: tag_ids })
+            .where(linked_tags: { discarded_at: nil })
+            .where(tag_names: { discarded_at: nil })
+            .pluck('nico_tags.id', 'tag_names.name')
+            .each_with_object(Hash.new { |h, k| h[k] = [] }) do |row, h|
+              h[row[0]] << row[1]
+            end
+
+        NicoTagVersion.insert_all(tags.map { |tag|
+          { tag_id: tag.id,
+            version_no: 1,
+            event_type: 'create',
+            name: tag_name_rows_by_tag_id[tag.id],
+            linked_tags: nico_tag_relation_rows_by_tag_id[tag.id].sort.join(' '),
+            created_at: tag.created_at,
+            created_by_user_id: nil }
+        })
+      end
+    end
+  end
+
+  def down
+    drop_table :nico_tag_versions
+    drop_table :tag_versions
+  end
+end

backend/db/migrate/20260426120600_create_wiki_versions.rb

@@ -0,0 +1,91 @@
+class CreateWikiVersions < ActiveRecord::Migration[8.0]
+  class WikiPage < ActiveRecord::Base
+    self.table_name = 'wiki_pages'
+  end
+
+  class WikiRevision < ActiveRecord::Base
+    self.table_name = 'wiki_revisions'
+  end
+
+  class WikiRevisionLine < ActiveRecord::Base
+    self.table_name = 'wiki_revision_lines'
+  end
+
+  class WikiLine < ActiveRecord::Base
+    self.table_name = 'wiki_lines'
+  end
+
+  class WikiVersion < ActiveRecord::Base
+    self.table_name = 'wiki_versions'
+  end
+
+  class TagName < ActiveRecord::Base
+    self.table_name = 'tag_names'
+  end
+
+  def up
+    add_column :wiki_pages, :body, :text, after: :tag_name_id
+
+    create_table :wiki_versions do |t|
+      t.references :wiki_page, null: false, foreign_key: true
+      t.integer :version_no, null: false
+      t.string :event_type, null: false
+      t.string :title, null: false
+      t.text :body, null: false
+      t.text :reason
+      t.datetime :created_at, null: false
+      t.references :created_by_user, foreign_key: { to_table: :users }
+
+      t.index [:wiki_page_id, :version_no], unique: true
+      t.check_constraint 'version_no > 0',
+                         name: 'wiki_versions_version_no_positive'
+      t.check_constraint "event_type IN ('create', 'update', 'discard', 'restore')",
+                         name: 'wiki_versions_event_type_valid'
+    end
+
+    WikiPage.reset_column_information
+    WikiVersion.reset_column_information
+
+    say_with_time 'Backfilling wiki_versions' do
+      WikiPage.find_each do |page|
+        base_revision_id = nil
+        version_no = 1
+        title = TagName.find(page.tag_name_id).name
+        body = nil
+        loop do
+          rev = WikiRevision.where(wiki_page_id: page.id).find_by(base_revision_id:)
+          break unless rev
+
+          body = WikiRevisionLine.where(wiki_revision_id: rev.id).order(:position).map { |wrl|
+            WikiLine.find(wrl.wiki_line_id).body
+          }.join("\n")
+
+          WikiVersion.create!(
+              wiki_page_id: page.id,
+              version_no:,
+              event_type: version_no == 1 ? 'create' : 'update',
+              title:,
+              body:,
+              reason: rev.message,
+              created_at: rev.created_at,
+              created_by_user_id: rev.created_user_id)
+
+          version_no += 1
+          base_revision_id = rev.id
+        end
+        if body
+          page.update!(body:)
+        else
+          page.destroy!
+        end
+      end
+    end
+
+    change_column_null :wiki_pages, :body, false
+  end
+
+  def down
+    drop_table :wiki_versions
+    remove_column :wiki_pages, :body
+  end
+end

backend/db/migrate/20260427214800_create_post_implications.rb

@@ -0,0 +1,24 @@
+class CreatePostImplications < ActiveRecord::Migration[8.0]
+  def up
+    create_table :post_implications, primary_key: [:post_id, :parent_post_id] do |t|
+      t.references :post, null: false, foreign_key: true, index: false
+      t.references :parent_post, null: false, foreign_key: { to_table: :posts }
+      t.timestamps
+
+      t.check_constraint 'post_id <> parent_post_id',
+                         name: 'chk_post_implications_no_self'
+    end
+
+    add_column :post_versions, :parent_post_ids, :text, null: false, after: :parent_id
+    remove_column :post_versions, :parent_id, :bigint
+    remove_reference :posts, :parent, foreign_key: { to_table: :posts }
+  end
+
+  def down
+    add_reference :posts, :parent, foreign_key: { to_table: :posts }, after: :thumbnail_base
+    add_column :post_versions, :parent_id, :bigint, after: :post_id
+    remove_column :post_versions, :parent_post_ids, :text
+
+    drop_table :post_implications
+  end
+end

backend/db/migrate/20260501153900_rename_banned_to_banned_at_in_users_and_ip_addresses.rb

@@ -0,0 +1,16 @@
+class RenameBannedToBannedAtInUsersAndIpAddresses < ActiveRecord::Migration[8.0]
+  def up
+    [:users, :ip_addresses].each do
+      add_column _1, :banned_at, :datetime, after: :banned
+      add_index _1, :banned_at
+      remove_column _1, :banned
+    end
+  end
+
+  def down
+    [:ip_addresses, :users].each do
+      add_column _1, :banned, :boolean, null: false, default: false, after: :banned_at
+      remove_column _1, :banned_at
+    end
+  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_04_09_123700) do
+ActiveRecord::Schema[8.0].define(version: 2026_05_01_153900) 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
@@ -50,9 +50,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
 
   create_table "ip_addresses", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.binary "ip_address", limit: 16, null: false
-    t.boolean "banned", default: false, null: false
+    t.datetime "banned_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    t.index ["banned_at"], name: "index_ip_addresses_on_banned_at"
     t.index ["ip_address"], name: "index_ip_addresses_on_ip_address", unique: true
   end
 
@@ -104,6 +105,30 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["tag_id"], name: "index_nico_tag_relations_on_tag_id"
   end
 
+  create_table "nico_tag_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.text "linked_tags", null: false
+    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", 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|
+    t.bigint "post_id", null: false
+    t.bigint "parent_post_id", null: false
+    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
@@ -140,13 +165,12 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
     t.text "tags", null: false
-    t.bigint "parent_id"
+    t.text "parent_post_ids", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
     t.datetime "created_at", null: false
     t.bigint "created_by_user_id"
     t.index ["created_by_user_id"], name: "index_post_versions_on_created_by_user_id"
-    t.index ["parent_id"], name: "index_post_versions_on_parent_id"
     t.index ["post_id", "version_no"], name: "index_post_versions_on_post_id_and_version_no", unique: true
     t.index ["post_id"], name: "index_post_versions_on_post_id"
     t.check_constraint "`event_type` in (_utf8mb4'create',_utf8mb4'update',_utf8mb4'discard',_utf8mb4'restore')", name: "post_versions_event_type_valid"
@@ -157,13 +181,11 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "title"
     t.string "url", limit: 768, null: false
     t.string "thumbnail_base", limit: 2000
-    t.bigint "parent_id"
     t.bigint "uploaded_user_id"
     t.datetime "created_at", null: false
     t.datetime "original_created_from"
     t.datetime "original_created_before"
     t.datetime "updated_at", null: false
-    t.index ["parent_id"], name: "index_posts_on_parent_id"
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
   end
@@ -216,6 +238,23 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["target_tag_id"], name: "index_tag_similarities_on_target_tag_id"
   end
 
+  create_table "tag_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "tag_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "name", null: false
+    t.string "category", null: false
+    t.text "aliases", null: false
+    t.text "parent_tag_ids", null: false
+    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", 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|
     t.bigint "tag_name_id", null: false
     t.string "category", default: "general", null: false
@@ -294,9 +333,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.string "name"
     t.string "inheritance_code", limit: 64, null: false
     t.string "role", null: false
-    t.boolean "banned", default: false, null: false
+    t.datetime "banned_at"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
+    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|
@@ -322,6 +362,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
 
   create_table "wiki_pages", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "tag_name_id", null: false
+    t.text "body", null: false
     t.bigint "created_user_id", null: false
     t.bigint "updated_user_id", null: false
     t.datetime "created_at", null: false
@@ -364,6 +405,22 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
     t.index ["wiki_page_id"], name: "index_wiki_revisions_on_wiki_page_id"
   end
 
+  create_table "wiki_versions", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "wiki_page_id", null: false
+    t.integer "version_no", null: false
+    t.string "event_type", null: false
+    t.string "title", null: false
+    t.text "body", null: false
+    t.text "reason"
+    t.datetime "created_at", null: false
+    t.bigint "created_by_user_id"
+    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"
   add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
   add_foreign_key "material_versions", "materials"
@@ -377,6 +434,10 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) 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"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
   add_foreign_key "post_tags", "posts"
@@ -384,9 +445,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   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", "posts", column: "parent_id"
   add_foreign_key "post_versions", "users", column: "created_by_user_id"
-  add_foreign_key "posts", "posts", column: "parent_id"
   add_foreign_key "posts", "users", column: "uploaded_user_id"
   add_foreign_key "settings", "users"
   add_foreign_key "tag_implications", "tags"
@@ -394,6 +453,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) 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"
   add_foreign_key "theatre_comments", "users"
@@ -417,4 +478,6 @@ ActiveRecord::Schema[8.0].define(version: 2026_04_09_123700) do
   add_foreign_key "wiki_revisions", "wiki_pages"
   add_foreign_key "wiki_revisions", "wiki_pages", column: "redirect_page_id"
   add_foreign_key "wiki_revisions", "wiki_revisions", column: "base_revision_id"
+  add_foreign_key "wiki_versions", "users", column: "created_by_user_id"
+  add_foreign_key "wiki_versions", "wiki_pages"
 end

backend/lib/tasks/export_nico.rake

@@ -0,0 +1,23 @@
+namespace :nico do
+  desc 'ニコニコ DB 逆連携'
+  task export: :environment do
+    require 'open3'
+
+    mysql_user = ENV.fetch('MYSQL_USER')
+    mysql_pass = ENV.fetch('MYSQL_PASS')
+    nizika_nico_path = ENV.fetch('NIZIKA_NICO_PATH')
+
+    videos = Post.where('url LIKE ?', '%nicovideo.jp/watch/%').pluck(:url).filter_map {
+      _1[%r{nicovideo\.jp/watch/([^/?#]+)}, 1]
+    }.uniq
+
+    next if videos.empty?
+
+    _, stderr, status = Open3.capture3(
+        { 'MYSQL_USER' => mysql_user, 'MYSQL_PASS' => mysql_pass },
+        'python3', '-m', 'tracked_videos.put_bulk_upsert', *videos,
+        chdir: nizika_nico_path)
+
+    raise stderr unless status.success?
+  end
+end

backend/lib/tasks/sync_nico.rake

@@ -115,6 +115,10 @@ namespace :nico do
       datum['tags'].each do |raw|
         name = TagNameSanitisationRule.sanitise("nico:#{ raw }")
         tag = Tag.find_or_create_by_tag_name!(name, category: :nico)
+
+        event_type = tag.nico_tag_versions.exists? ? :update : :create
+        NicoTagVersionRecorder.record!(tag:, event_type:, created_by_user: nil)
+
         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
@@ -149,6 +153,7 @@ namespace :nico do
       if post_created
         PostVersionRecorder.record!(post:, event_type: :create, created_by_user: nil)
       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
     end

backend/lib/tasks/sync_posts.rake

@@ -0,0 +1,6 @@
+namespace :post do
+  desc '投稿同期（ニコニコ以外）'
+  task sync: :environment do
+    Youtube::Sync.new.sync!
+  end
+end

backend/spec/factories/ip_addresses.rb

@@ -0,0 +1,10 @@
+FactoryBot.define do
+  factory :ip_address do
+    ip_address { IPAddr.new('203.0.113.10').hton }
+    banned_at { nil }
+
+    trait :banned do
+      banned_at { Time.current }
+    end
+  end
+end

backend/spec/factories/users.rb

@@ -1,15 +1,24 @@
 FactoryBot.define do
   factory :user do
-    name { "test-user" }
+    name { nil }
     inheritance_code { SecureRandom.uuid }
-    role { "guest" }
+    role { 'guest' }
+    banned_at { nil }
+
+    trait :guest do
+      role { 'guest' }
+    end
 
     trait :member do
-      role { "member" }
+      role { 'member' }
     end
 
     trait :admin do
       role { 'admin' }
     end
+
+    trait :banned do
+      banned_at { Time.current }
+    end
   end
 end

backend/spec/factories/wiki_pages.rb

@@ -3,5 +3,7 @@ FactoryBot.define do
     title { "TestPage" }
     association :created_user, factory: :user
     association :updated_user, factory: :user
+
+    body { ' ' }
   end
 end

backend/spec/models/post_implication_spec.rb

@@ -0,0 +1,51 @@
+require 'rails_helper'
+
+RSpec.describe PostImplication, type: :model do
+  let!(:post_record) do
+    Post.create!(
+      title: 'post',
+      url: 'https://example.com/post-implication-post'
+    )
+  end
+
+  let!(:parent_post) do
+    Post.create!(
+      title: 'parent post',
+      url: 'https://example.com/post-implication-parent'
+    )
+  end
+
+  it 'is valid with post and parent_post' do
+    implication = described_class.new(
+      post: post_record,
+      parent_post:
+    )
+
+    expect(implication).to be_valid
+  end
+
+  it 'does not allow same post as parent_post' do
+    implication = described_class.new(
+      post: post_record,
+      parent_post: post_record
+    )
+
+    expect(implication).not_to be_valid
+    expect(implication.errors[:parent_post_id]).to be_present
+  end
+
+  it 'does not allow duplicate pair' do
+    described_class.create!(
+      post: post_record,
+      parent_post:
+    )
+
+    duplicate = described_class.new(
+      post: post_record,
+      parent_post:
+    )
+
+    expect(duplicate).not_to be_valid
+    expect(duplicate.errors[:post_id]).to be_present
+  end
+end

backend/spec/models/post_version_spec.rb

@@ -19,7 +19,7 @@ RSpec.describe PostVersion, type: :model do
       url: post_record.url,
       thumbnail_base: post_record.thumbnail_base,
       tags: post_record.snapshot_tag_names.join(' '),
-      parent: post_record.parent,
+      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,
       created_at: Time.current,

backend/spec/models/tag_spec.rb

@@ -107,11 +107,13 @@ RSpec.describe Tag, type: :model do
     context 'when the source tag_name has a wiki_page' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
       let!(:wiki_page) do
-        WikiPage.create!(
+        admin = create_admin_user!
+
+        Wiki::Commit.create_content!(
             tag_name: source_tag_name,
-          created_user: create_admin_user!,
-          updated_user: create_admin_user!
-        )
+            body: 'source wiki body',
+            created_by_user: admin,
+            message: 'init')
       end
 
       it 'rolls back the transaction' do
@@ -159,7 +161,7 @@ RSpec.describe Tag, type: :model do
         url: post.url,
         thumbnail_base: post.thumbnail_base,
         tags: snapshot_tags(post),
-        parent: post.parent,
+        parent_post_ids: post.snapshot_parent_post_ids.join(' '),
         original_created_from: post.original_created_from,
         original_created_before: post.original_created_before,
         created_at: Time.current,

backend/spec/models/version_record_spec.rb

@@ -0,0 +1,74 @@
+require 'rails_helper'
+
+RSpec.describe VersionRecord, type: :model do
+  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: tag.name,
+      category: tag.category,
+      aliases: '',
+      parent_tag_ids: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.update!(name: 'changed')
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'prevents TagVersion destroy' do
+    version = TagVersion.create!(
+      tag: tag,
+      version_no: 1,
+      event_type: 'create',
+      name: tag.name,
+      category: tag.category,
+      aliases: '',
+      parent_tag_ids: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.destroy!
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'makes NicoTagVersion read only after create' do
+    version = NicoTagVersion.create!(
+      tag: nico_tag,
+      version_no: 1,
+      event_type: 'create',
+      name: nico_tag.name,
+      linked_tags: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.update!(name: 'nico:changed')
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+
+  it 'prevents NicoTagVersion destroy' do
+    version = NicoTagVersion.create!(
+      tag: nico_tag,
+      version_no: 1,
+      event_type: 'create',
+      name: nico_tag.name,
+      linked_tags: '',
+      created_at: Time.current,
+      created_by_user: nil
+    )
+
+    expect {
+      version.destroy!
+    }.to raise_error(ActiveRecord::ReadOnlyRecord)
+  end
+end

backend/spec/requests/nico_tags_spec.rb

@@ -14,6 +14,7 @@ RSpec.describe 'NicoTags', type: :request do
 
   describe 'PATCH /tags/nico/:id' do
     let(:member) { create(:user, :member) }
+    let(:admin) { create(:user, :admin) }
     let(:nico_tag) { create(:tag, :nico) }
 
     it '401 when not logged in' do
@@ -34,5 +35,59 @@ RSpec.describe 'NicoTags', type: :request do
       patch "/tags/nico/#{non_nico.id}", params: { tags: 'a b' }
       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_name = TagName.create!(name: 'nico:nico_tags_spec_source')
+      nico_tag = Tag.create!(tag_name: nico_tag_name, category: :nico)
+
+      linked_a_name = TagName.create!(name: 'nico_linked_a')
+      linked_a = Tag.create!(tag_name: linked_a_name, category: :general)
+
+      linked_b_name = TagName.create!(name: 'nico_linked_b')
+      linked_b = Tag.create!(tag_name: linked_b_name, category: :general)
+
+      TagVersioning.ensure_snapshot!(nico_tag, created_by_user: admin)
+
+      expect {
+        patch "/tags/nico/#{nico_tag.id}", params: {
+          tags: "  #{linked_a.name}\n#{linked_b.name}  "
+        }
+      }.to change(TagVersion, :count).by(2)
+       .and change(NicoTagVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      names = json.map { |t| t['name'] }
+      expect(names).to match_array(['nico_linked_a', 'nico_linked_b'])
+
+      linked_versions = TagVersion.where(tag: [linked_a, linked_b]).order(:tag_id)
+      expect(linked_versions.map(&:event_type)).to eq(['create', 'create'])
+      expect(linked_versions.map(&:created_by_user_id)).to all(eq(admin.id))
+
+      versions = nico_tag.reload.nico_tag_versions.order(:version_no)
+      expect(versions.map(&:event_type)).to eq(['create', 'update'])
+      expect(versions.last.linked_tags.split).to match_array([
+        'nico_linked_a',
+        'nico_linked_b'
+      ])
+      expect(versions.last.created_by_user_id).to eq(admin.id)
+    end
+
+    it '400 when linked tag normalises to nico tag' do
+      sign_in_as(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: 'linked_ng_alias' }
+      }.not_to change(NicoTagVersion, :count)
+
+      expect(response).to have_http_status(:bad_request)
+    end
   end
 end

backend/spec/requests/posts_spec.rb

@@ -1,8 +1,8 @@
-include ActiveSupport::Testing::TimeHelpers
-
 require 'rails_helper'
 require 'set'
 
+include ActiveSupport::Testing::TimeHelpers
+
 RSpec.describe 'Posts API', type: :request do
   # create / update で thumbnail.attach は走るが、
   # resized_thumbnail! が MiniMagick 依存でコケやすいので request spec ではスタブしとくのが無難。
@@ -15,6 +15,31 @@ RSpec.describe 'Posts API', type: :request do
     Rack::Test::UploadedFile.new(StringIO.new('dummy'), 'image/jpeg', original_filename: 'dummy.jpg')
   end
 
+  def post_write_params params = { }
+    { parent_post_ids: '' }.merge(params)
+  end
+
+  def create_parent_post! title:, url:
+    Post.create!(title:, url:)
+  end
+
+  def create_post_version_for! post
+    PostVersion.create!(
+      post:,
+      version_no: 1,
+      event_type: 'create',
+      title: post.title,
+      url: post.url,
+      thumbnail_base: post.thumbnail_base,
+      tags: post.snapshot_tag_names.join(' '),
+      parent_post_ids: post.snapshot_parent_post_ids.join(' '),
+      original_created_from: post.original_created_from,
+      original_created_before: post.original_created_before,
+      created_at: post.created_at,
+      created_by_user: post.uploaded_user
+    )
+  end
+
   let!(:tag_name) { TagName.create!(name: 'spec_tag') }
   let!(:tag)      { Tag.create!(tag_name: tag_name, category: :general) }
 
@@ -457,6 +482,65 @@ RSpec.describe 'Posts API', type: :request do
         expect(json).to have_key('viewed')
         expect([true, false]).to include(json['viewed'])
       end
+
+      context 'when post has parent, child, and sibling posts' do
+        let!(:parent_post) do
+          create_parent_post!(
+            title: 'shared parent post',
+            url: 'https://example.com/shared-parent-post'
+          )
+        end
+
+        let!(:child_post) do
+          Post.create!(
+            title: 'child post',
+            url: 'https://example.com/show-child-post'
+          )
+        end
+
+        let!(:sibling_post) do
+          Post.create!(
+            title: 'sibling post',
+            url: 'https://example.com/show-sibling-post'
+          )
+        end
+
+        before do
+          PostImplication.create!(
+            post: post_record,
+            parent_post:
+          )
+
+          PostImplication.create!(
+            post: child_post,
+            parent_post: post_record
+          )
+
+          PostImplication.create!(
+            post: sibling_post,
+            parent_post:
+          )
+        end
+
+        it 'returns parent_posts, child_posts, and sibling_posts' do
+          get "/posts/#{post_record.id}"
+
+          expect(response).to have_http_status(:ok)
+
+          parent_ids = json.fetch('parent_posts').map { |p| p.fetch('id') }
+          child_ids = json.fetch('child_posts').map { |p| p.fetch('id') }
+
+          expect(parent_ids).to include(parent_post.id)
+          expect(child_ids).to include(child_post.id)
+
+          sibling_posts_by_parent = json.fetch('sibling_posts')
+          siblings = sibling_posts_by_parent.fetch(parent_post.id.to_s)
+
+          sibling_ids = siblings.map { |p| p.fetch('id') }
+          expect(sibling_ids).to include(post_record.id)
+          expect(sibling_ids).to include(sibling_post.id)
+        end
+      end
     end
 
     context 'when post does not exist' do
@@ -475,25 +559,28 @@ RSpec.describe 'Posts API', type: :request do
 
     it '401 when not logged in' do
       sign_out
-      post '/posts', params: { title: 't', url: 'https://example.com/x', tags: 'a', thumbnail: dummy_upload }
+      post '/posts', params: post_write_params(title: 't', url: 'https://example.com/x', tags: 'a',
+                                               thumbnail: dummy_upload)
+
       expect(response).to have_http_status(:unauthorized)
     end
 
     it '403 when not member' do
       sign_in_as(create(:user, role: 'guest'))
-      post '/posts', params: { title: 't', url: 'https://example.com/x', tags: 'a', thumbnail: dummy_upload }
+      post '/posts', params: post_write_params(title: 't', url: 'https://example.com/x', tags: 'a',
+                                               thumbnail: dummy_upload)
       expect(response).to have_http_status(:forbidden)
     end
 
     it '201 and creates post + tags when member' do
       sign_in_as(member)
 
-      post '/posts', params: {
+      post '/posts', params: post_write_params(
         title: 'new post',
         url: 'https://example.com/new',
         tags: 'spec_tag', # 既存タグ名を投げる
         thumbnail: dummy_upload
-      }
+      )
 
       expect(response).to have_http_status(:created)
       expect(json).to include('id', 'title', 'url')
@@ -507,12 +594,12 @@ RSpec.describe 'Posts API', type: :request do
     it '201 and creates post + tags when member and tags have aliases' do
       sign_in_as(member)
 
-      post '/posts', params: {
+      post '/posts', params: post_write_params(
         title: 'new post',
         url: 'https://example.com/new',
         tags: 'manko', # 既存タグ名を投げる
         thumbnail: dummy_upload
-      }
+      )
 
       expect(response).to have_http_status(:created)
       expect(json).to include('id', 'title', 'url')
@@ -533,13 +620,14 @@ RSpec.describe 'Posts API', type: :request do
       it 'return 400' do
         sign_in_as(member)
 
-        post '/posts', params: {
+        post '/posts', params: post_write_params(
           title: 'new post',
-            url: 'https://example.com/nico_tag',
+          url: 'https://example.com/nico-tag-post',
           tags: 'nico:nico_tag',
-            thumbnail: dummy_upload }
+          thumbnail: dummy_upload
+        )
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:bad_request), response.body
       end
     end
 
@@ -547,11 +635,11 @@ RSpec.describe 'Posts API', type: :request do
       it 'returns 422' do
         sign_in_as(member)
 
-        post '/posts', params: {
+        post '/posts', params: post_write_params(
             title: 'new post',
             url: '   ',
             tags: 'spec_tag', # 既存タグ名を投げる
-            thumbnail: dummy_upload }
+            thumbnail: dummy_upload)
 
         expect(response).to have_http_status(:unprocessable_entity)
       end
@@ -561,16 +649,156 @@ RSpec.describe 'Posts API', type: :request do
       it 'returns 422' do
         sign_in_as(member)
 
-        post '/posts', params: {
+        post '/posts', params: post_write_params(
             title: 'new post',
             url: 'ぼざクリタグ広場',
             tags: 'spec_tag', # 既存タグ名を投げる
-          thumbnail: dummy_upload
-        }
+            thumbnail: dummy_upload)
 
         expect(response).to have_http_status(:unprocessable_entity)
       end
     end
+
+    context 'when parent_post_ids is provided' do
+      let!(:parent_post_1) do
+        create_parent_post!(
+          title: 'parent post 1',
+          url: 'https://example.com/parent-post-1'
+        )
+      end
+
+      let!(:parent_post_2) do
+        create_parent_post!(
+          title: 'parent post 2',
+          url: 'https://example.com/parent-post-2'
+        )
+      end
+
+      it 'creates post implications for parent posts' do
+        sign_in_as(member)
+
+        expect {
+          post '/posts', params: {
+              title: 'child post',
+              url: 'https://example.com/child-post',
+              tags: 'spec_tag',
+              parent_post_ids: "#{parent_post_1.id} #{parent_post_2.id}",
+              thumbnail: dummy_upload }
+        }.to change(PostImplication, :count).by(2)
+
+        expect(response).to have_http_status(:created)
+
+        created_post = Post.find(json.fetch('id'))
+        expect(created_post.parent_posts.order(:id).pluck(:id)).to eq(
+          [parent_post_1.id, parent_post_2.id].sort
+        )
+
+        expect(PostImplication.exists?(
+          post_id: created_post.id,
+          parent_post_id: parent_post_1.id
+        )).to be(true)
+
+        expect(PostImplication.exists?(
+          post_id: created_post.id,
+          parent_post_id: parent_post_2.id
+        )).to be(true)
+      end
+
+      it 'deduplicates parent_post_ids' do
+        sign_in_as(member)
+
+        expect {
+          post '/posts', params: post_write_params(
+            title: 'dedup child post',
+            url: 'https://example.com/dedup-child-post',
+            tags: 'spec_tag',
+            parent_post_ids: "#{parent_post_1.id} #{parent_post_1.id}",
+            thumbnail: dummy_upload
+          )
+        }.to change(PostImplication, :count).by(1)
+
+        expect(response).to have_http_status(:created)
+
+        created_post = Post.find(json.fetch('id'))
+        expect(created_post.parent_posts.pluck(:id)).to eq([parent_post_1.id])
+      end
+
+      it 'records parent_post_ids in post version' do
+        sign_in_as(member)
+
+        post '/posts', params: post_write_params(
+          title: 'versioned child post',
+          url: 'https://example.com/versioned-child-post',
+          tags: 'spec_tag',
+          parent_post_ids: "#{parent_post_1.id} #{parent_post_2.id}",
+          thumbnail: dummy_upload
+        )
+
+        expect(response).to have_http_status(:created)
+
+        created_post = Post.find(json.fetch('id'))
+        version = PostVersion.find_by!(post: created_post, version_no: 1)
+
+        expect(version.parent_post_ids.split.map(&:to_i)).to eq(
+          [parent_post_1.id, parent_post_2.id].sort
+        )
+      end
+    end
+
+    context 'when parent_post_ids is missing' do
+      it 'returns 422' do
+        sign_in_as(member)
+
+        expect {
+          post '/posts', params: {
+              title: 'missing parent_post_ids',
+              url: 'https://example.com/missing-parent-post-ids',
+              tags: 'spec_tag',
+              thumbnail: dummy_upload }
+        }.not_to change(Post, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to be_present
+      end
+    end
+
+    context 'when parent_post_ids includes invalid token' do
+      it 'returns 422 and does not create post' do
+        sign_in_as(member)
+
+        expect {
+          post '/posts', params: post_write_params(
+            title: 'invalid parent ids',
+            url: 'https://example.com/invalid-parent-ids',
+            tags: 'spec_tag',
+            parent_post_ids: 'abc',
+            thumbnail: dummy_upload
+          )
+        }.not_to change(Post, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to be_present
+      end
+    end
+
+    context 'when parent_post_ids includes nonexistent post id' do
+      it 'returns 422 and does not create post implication' do
+        sign_in_as(member)
+
+        expect {
+          post '/posts', params: post_write_params(
+            title: 'missing parent post',
+            url: 'https://example.com/missing-parent-post',
+            tags: 'spec_tag',
+            parent_post_ids: '999999999',
+            thumbnail: dummy_upload
+          )
+        }.not_to change(PostImplication, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to be_present
+      end
+    end
   end
 
   describe 'PUT /posts/:id' do
@@ -578,13 +806,13 @@ RSpec.describe 'Posts API', type: :request do
 
     it '401 when not logged in' do
       sign_out
-      put "/posts/#{post_record.id}", params: { title: 'updated', tags: 'spec_tag' }
+      put "/posts/#{post_record.id}", params: post_write_params(title: 'updated', tags: 'spec_tag')
       expect(response).to have_http_status(:unauthorized)
     end
 
     it '403 when not member' do
       sign_in_as(create(:user, role: 'guest'))
-      put "/posts/#{post_record.id}", params: { title: 'updated', tags: 'spec_tag' }
+      put "/posts/#{post_record.id}", params: post_write_params(title: 'updated', tags: 'spec_tag')
       expect(response).to have_http_status(:forbidden)
     end
 
@@ -595,10 +823,9 @@ RSpec.describe 'Posts API', type: :request do
       tn2 = TagName.create!(name: 'spec_tag_2')
       Tag.create!(tag_name: tn2, category: :general)
 
-      put "/posts/#{post_record.id}", params: {
+      put "/posts/#{post_record.id}", params: post_write_params(
           title: 'updated title',
-        tags: 'spec_tag_2'
-      }
+          tags: 'spec_tag_2')
 
       expect(response).to have_http_status(:ok)
       expect(json).to have_key('tags')
@@ -619,11 +846,178 @@ RSpec.describe 'Posts API', type: :request do
       it 'return 400' do
         sign_in_as(member)
 
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'nico:nico_tag'
+        )
+
+        expect(response).to have_http_status(:bad_request), response.body
+      end
+    end
+
+    context 'when parent_post_ids is provided' do
+      let!(:old_parent_post) do
+        create_parent_post!(
+          title: 'old parent post',
+          url: 'https://example.com/old-parent-post'
+        )
+      end
+
+      let!(:new_parent_post_1) do
+        create_parent_post!(
+          title: 'new parent post 1',
+          url: 'https://example.com/new-parent-post-1'
+        )
+      end
+
+      let!(:new_parent_post_2) do
+        create_parent_post!(
+          title: 'new parent post 2',
+          url: 'https://example.com/new-parent-post-2'
+        )
+      end
+
+      before do
+        PostImplication.create!(
+          post: post_record,
+          parent_post: old_parent_post
+        )
+      end
+
+      it 'replaces parent posts' do
+        sign_in_as(member)
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: "#{new_parent_post_1.id} #{new_parent_post_2.id}"
+        )
+
+        expect(response).to have_http_status(:ok)
+
+        expect(post_record.reload.parent_posts.order(:id).pluck(:id)).to eq(
+          [new_parent_post_1.id, new_parent_post_2.id].sort
+        )
+
+        expect(PostImplication.exists?(
+          post_id: post_record.id,
+          parent_post_id: old_parent_post.id
+        )).to be(false)
+      end
+
+      it 'clears parent posts when parent_post_ids is blank' do
+        sign_in_as(member)
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: ''
+        )
+
+        expect(response).to have_http_status(:ok)
+        expect(post_record.reload.parent_posts).to be_empty
+      end
+
+      it 'records changed parent_post_ids in post version' do
+        sign_in_as(member)
+        create_post_version_for!(post_record.reload)
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: "#{new_parent_post_1.id} #{new_parent_post_2.id}"
+        )
+
+        expect(response).to have_http_status(:ok)
+
+        version = post_record.reload.post_versions.order(:version_no).last
+
+        expect(version.version_no).to eq(2)
+        expect(version.parent_post_ids.split.map(&:to_i)).to eq(
+          [new_parent_post_1.id, new_parent_post_2.id].sort
+        )
+      end
+    end
+
+    context 'when parent_post_ids is missing' do
+      it 'returns 422' do
+        sign_in_as(member)
+
         put "/posts/#{post_record.id}", params: {
             title: 'updated title',
-            tags: 'nico:nico_tag' }
+            tags: 'spec_tag' }
 
-        expect(response).to have_http_status(:bad_request)
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json.fetch('errors')).to be_present
+      end
+    end
+
+    context 'when parent_post_ids includes invalid token' do
+      it 'returns 422 and does not change parent posts' do
+        sign_in_as(member)
+
+        parent_post = create_parent_post!(
+          title: 'valid parent post',
+          url: 'https://example.com/valid-parent-post'
+        )
+
+        PostImplication.create!(
+          post: post_record,
+          parent_post:
+        )
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: 'abc'
+        )
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(post_record.reload.parent_posts.pluck(:id)).to eq([parent_post.id])
+      end
+    end
+
+    context 'when parent_post_ids includes nonexistent post id' do
+      it 'returns 422 and does not change parent posts' do
+        sign_in_as(member)
+
+        parent_post = create_parent_post!(
+          title: 'existing parent post',
+          url: 'https://example.com/existing-parent-post'
+        )
+
+        PostImplication.create!(
+          post: post_record,
+          parent_post:
+        )
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: '999999999'
+        )
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(post_record.reload.parent_posts.pluck(:id)).to eq([parent_post.id])
+      end
+    end
+
+    context 'when parent_post_ids includes self id' do
+      it 'returns 422 and does not create self implication' do
+        sign_in_as(member)
+
+        put "/posts/#{post_record.id}", params: post_write_params(
+          title: 'updated title',
+          tags: 'spec_tag',
+          parent_post_ids: post_record.id.to_s
+        )
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(PostImplication.exists?(
+          post_id: post_record.id,
+          parent_post_id: post_record.id
+        )).to be(false)
       end
     end
   end
@@ -756,6 +1150,218 @@ RSpec.describe 'Posts API', type: :request do
     end
   end
 
+  describe 'GET /posts/versions' do
+    let(:member) { create(:user, :member, name: 'version member') }
+
+    let(:t_v1) { Time.zone.local(2020, 1, 1, 12, 0, 0) }
+    let(:t_v2) { Time.zone.local(2020, 1, 2, 12, 0, 0) }
+    let(:t_other) { Time.zone.local(2020, 1, 3, 12, 0, 0) }
+
+    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) { 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(' ')
+    end
+
+    def create_post_version! post, version_no:, event_type:, created_by_user:, created_at:
+      PostVersion.create!(
+        post:,
+        version_no:,
+        event_type:,
+        title: post.title,
+        url: post.url,
+        thumbnail_base: post.thumbnail_base,
+        tags: snapshot_tags(post),
+        parent_post_ids: post.snapshot_parent_post_ids.join(' '),
+        original_created_from: post.original_created_from,
+        original_created_before: post.original_created_before,
+        created_at:,
+        created_by_user:
+      )
+    end
+
+    let!(:v1) do
+      travel_to(t_v1) do
+        create_post_version!(
+          post_record,
+          version_no: 1,
+          event_type: 'create',
+          created_by_user: member,
+          created_at: t_v1
+        )
+      end
+    end
+
+    let!(:v2) do
+      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',
+        original_created_from: oc_from,
+        original_created_before: oc_before
+      )
+
+      travel_to(t_v2) do
+        create_post_version!(
+          post_record.reload,
+          version_no: 2,
+          event_type: 'update',
+          created_by_user: member,
+          created_at: t_v2
+        )
+      end
+    end
+
+    let!(:other_post_version) do
+      other_post = Post.create!(
+        title: 'other versioned post',
+        url: 'https://example.com/other-versioned'
+      )
+      PostTag.create!(post: other_post, tag: tag)
+
+      travel_to(t_other) do
+        create_post_version!(
+          other_post,
+          version_no: 1,
+          event_type: 'create',
+          created_by_user: member,
+          created_at: t_other
+        )
+      end
+    end
+
+    it 'returns versions for the specified post in reverse chronological order' do
+      get '/posts/versions', params: { post: post_record.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('versions', 'count')
+      expect(json.fetch('count')).to eq(2)
+
+      versions = json.fetch('versions')
+      expect(versions.map { |v| v['post_id'] }.uniq).to eq([post_record.id])
+      expect(versions.map { |v| v['version_no'] }).to eq([2, 1])
+
+      latest = versions.first
+      expect(latest).to include(
+        'post_id' => post_record.id,
+        'version_no' => 2,
+        'event_type' => 'update',
+        'created_by_user' => {
+          'id' => member.id,
+          'name' => member.name
+        }
+      )
+
+      expect(latest.fetch('title')).to eq(
+        'current' => 'updated spec post',
+        'prev' => 'spec post'
+      )
+      expect(latest.fetch('url')).to eq(
+        'current' => 'https://example.com/spec',
+        'prev' => 'https://example.com/spec'
+      )
+      expect(latest.fetch('thumbnail')).to eq(
+        'current' => nil,
+        'prev' => nil
+      )
+      expect(latest.fetch('thumbnail_base')).to eq(
+        'current' => nil,
+        'prev' => nil
+      )
+      expect(latest.fetch('tags')).to include(
+        { 'name' => 'spec_tag_2', 'type' => 'added' },
+        { 'name' => 'spec_tag', 'type' => 'removed' }
+      )
+      expect(latest.fetch('original_created_from')).to eq(
+        'current' => oc_from.iso8601,
+        'prev' => nil
+      )
+      expect(latest.fetch('original_created_before')).to eq(
+        'current' => oc_before.iso8601,
+        'prev' => nil
+      )
+      expect(latest.fetch('created_at')).to eq(t_v2.iso8601)
+
+      first = versions.second
+      expect(first).to include(
+        'post_id' => post_record.id,
+        'version_no' => 1,
+        'event_type' => 'create',
+        'created_by_user' => {
+          'id' => member.id,
+          'name' => member.name
+        }
+      )
+      expect(first.fetch('title')).to eq(
+        'current' => 'spec post',
+        'prev' => nil
+      )
+      expect(first.fetch('tags')).to include(
+        { 'name' => 'spec_tag', 'type' => 'added' }
+      )
+      expect(first.fetch('created_at')).to eq(t_v1.iso8601)
+    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 }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('count')).to eq(1)
+
+      versions = json.fetch('versions')
+      expect(versions.size).to eq(1)
+      expect(versions[0]['post_id']).to eq(post_record.id)
+      expect(versions[0]['version_no']).to eq(2)
+      expect(versions[0]['tags']).to include(
+        { 'name' => 'spec_tag_2', 'type' => 'added' }
+      )
+    end
+
+    it 'filters versions by tag when the tag exists in either current or previous snapshot' do
+      get '/posts/versions', params: { post: post_record.id, tag: tag.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('count')).to eq(2)
+
+      versions = json.fetch('versions')
+      expect(versions.map { |v| v['post_id'] }).to all(eq(post_record.id))
+      expect(versions.map { |v| v['version_no'] }).to eq([2, 1])
+
+      latest = versions[0]
+      first = versions[1]
+
+      expect(latest['tags']).to include(
+        { 'name' => 'spec_tag', 'type' => 'removed' }
+      )
+      expect(first['tags']).to include(
+        { 'name' => 'spec_tag', 'type' => 'added' }
+      )
+    end
+
+    it 'returns empty when tag does not exist' do
+      get '/posts/versions', params: { tag: 999_999_999 }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('versions')).to eq([])
+      expect(json.fetch('count')).to eq(0)
+    end
+
+    it 'clamps page and limit to at least 1' do
+      get '/posts/versions', params: { post: post_record.id, page: 0, limit: 0 }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('count')).to eq(2)
+
+      versions = json.fetch('versions')
+      expect(versions.size).to eq(1)
+      expect(versions[0]['version_no']).to eq(2)
+    end
+  end
+
   describe 'POST /posts/:id/viewed' do
     let(:user) { create(:user) }
 
@@ -803,33 +1409,15 @@ RSpec.describe 'Posts API', type: :request do
       post.snapshot_tag_names.join(' ')
     end
 
-    def create_post_version_for!(post)
-      PostVersion.create!(
-        post: post,
-        version_no: 1,
-        event_type: 'create',
-        title: post.title,
-        url: post.url,
-        thumbnail_base: post.thumbnail_base,
-        tags: snapshot_tags(post),
-        parent: post.parent,
-        original_created_from: post.original_created_from,
-        original_created_before: post.original_created_before,
-        created_at: post.created_at,
-        created_by_user: post.uploaded_user
-      )
-    end
-
     it 'creates version 1 on POST /posts' do
       sign_in_as(member)
 
       expect do
-        post '/posts', params: {
+        post '/posts', params: post_write_params(
             title: 'versioned post',
             url: 'https://example.com/versioned-post',
             tags: 'spec_tag',
-          thumbnail: dummy_upload
-        }
+            thumbnail: dummy_upload)
       end.to change(PostVersion, :count).by(1)
 
       expect(response).to have_http_status(:created)
@@ -852,10 +1440,9 @@ RSpec.describe 'Posts API', type: :request do
       Tag.create!(tag_name: tag_name2, category: :general)
 
       expect do
-        put "/posts/#{post_record.id}", params: {
+        put "/posts/#{post_record.id}", params: post_write_params(
             title: 'updated title',
-          tags: 'spec_tag_2'
-        }
+            tags: 'spec_tag_2')
       end.to change(PostVersion, :count).by(1)
 
       expect(response).to have_http_status(:ok)
@@ -870,15 +1457,15 @@ RSpec.describe 'Posts API', type: :request do
 
     it 'does not create a new version on PUT /posts/:id when snapshot is unchanged' do
       sign_in_as(member)
-      create_post_version_for!(post_record)
 
-      expect do
-        put "/posts/#{post_record.id}", params: {
+      PostTag.create!(post: post_record, tag: Tag.no_deerjikist)
+      create_post_version_for!(post_record.reload)
+
+      expect {
+        put "/posts/#{post_record.id}", params: post_write_params(
             title: post_record.title,
-          tags: 'spec_tag'
-        }
-      end.not_to change(PostVersion, :count)
-
+            tags: 'spec_tag')
+      }.not_to change(PostVersion, :count)
       expect(response).to have_http_status(:ok)
 
       version = post_record.reload.post_versions.order(:version_no).last
@@ -891,12 +1478,11 @@ RSpec.describe 'Posts API', type: :request do
       sign_in_as(member)
 
       expect do
-        post '/posts', params: {
+        post '/posts', params: post_write_params(
             title: 'invalid post',
             url: 'ぼざクリタグ広場',
             tags: 'spec_tag',
-          thumbnail: dummy_upload
-        }
+            thumbnail: dummy_upload)
       end.not_to change(PostVersion, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
@@ -907,15 +1493,60 @@ RSpec.describe 'Posts API', type: :request do
       create_post_version_for!(post_record)
 
       expect do
-        put "/posts/#{post_record.id}", params: {
+        put "/posts/#{post_record.id}", params: post_write_params(
             title: 'updated title',
             tags: 'spec_tag',
             original_created_from: Time.zone.local(2020, 1, 2, 0, 0, 0).iso8601,
-          original_created_before: Time.zone.local(2020, 1, 1, 0, 0, 0).iso8601
-        }
+            original_created_before: Time.zone.local(2020, 1, 1, 0, 0, 0).iso8601)
       end.not_to change(PostVersion, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
     end
   end
+
+  describe 'tag versioning from post write actions' do
+    let(:member) { create(:user, :member) }
+
+    it 'creates tag snapshot for normalised tags on POST /posts' do
+      sign_in_as(member)
+
+      expect {
+        post '/posts', params: post_write_params(
+            title: 'tag versioned post',
+            url: 'https://example.com/tag-versioned-post',
+            tags: 'spec_tag',
+            thumbnail: dummy_upload)
+      }.to change { tag.reload.tag_versions.count }.by(1)
+
+      expect(response).to have_http_status(:created)
+
+      version = tag.reload.tag_versions.order(:version_no).last
+      expect(version.version_no).to eq(1)
+      expect(version.event_type).to eq('create')
+      expect(version.name).to eq('spec_tag')
+      expect(version.category).to eq('general')
+      expect(version.created_by_user_id).to eq(member.id)
+    end
+
+    it 'creates tag snapshot for normalised tags on PUT /posts/:id' do
+      sign_in_as(member)
+
+      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(
+            title: 'updated title',
+            tags: 'spec_tag_2')
+      }.to change { tag2.reload.tag_versions.count }.by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      version = tag2.reload.tag_versions.order(:version_no).last
+      expect(version.version_no).to eq(1)
+      expect(version.event_type).to eq('create')
+      expect(version.name).to eq('spec_tag_2')
+      expect(version.created_by_user_id).to eq(member.id)
+    end
+  end
 end

backend/spec/requests/tag_children_spec.rb

@@ -58,15 +58,47 @@ RSpec.describe "TagChildren", type: :request do
       end
     end
 
-    context "when Tag.find raises (invalid ids) it still returns 204" do
+    context "when Tag.find raises (invalid ids)" do
       before { stub_current_user(admin) }
 
       let(:parent_id) { -1 }
       let(:child_id) { -1 }
 
-      it "returns 204 (rescue nil)" do
+      it "returns 404" do
         do_request
-        expect(response).to have_http_status(:no_content)
+        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
@@ -116,17 +148,57 @@ RSpec.describe "TagChildren", type: :request do
 
         expect(response).to have_http_status(:no_content)
       end
+
+      it 'records create and update versions for child tag' do
+        expect {
+          do_request
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:no_content)
+
+        versions = child.reload.tag_versions.order(:version_no)
+        expect(versions.map(&:event_type)).to eq(['create', 'update'])
+        expect(versions.first.parent_tag_ids.split).to include(parent.id.to_s)
+        expect(versions.second.parent_tag_ids).to eq('')
+        expect(versions.second.created_by_user_id).to eq(admin.id)
+      end
     end
 
-    context "when Tag.find raises (invalid ids) it still returns 204" do
+    context "when Tag.find raises (invalid ids)" do
       before { stub_current_user(admin) }
 
       let(:parent_id) { -1 }
       let(:child_id) { -1 }
 
-      it "returns 204 (rescue nil)" do
+      it "returns 404" do
         do_request
-        expect(response).to have_http_status(:no_content)
+        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

backend/spec/requests/tag_versions_spec.rb

@@ -0,0 +1,243 @@
+require 'rails_helper'
+
+RSpec.describe 'TagVersions API', type: :request do
+  let(:member) { create(:user, :member, name: 'version member') }
+
+  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, 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) }
+  let(:t_other) { Time.zone.local(2020, 1, 3, 12, 0, 0) }
+
+  def create_tag_version!(
+    tag:,
+    version_no:,
+    event_type:,
+    name:,
+    category:,
+    aliases: [],
+    parent_tags: [],
+    created_by_user:,
+    created_at:
+  )
+    TagVersion.create!(
+      tag: tag,
+      version_no: version_no,
+      event_type: event_type,
+      name: name,
+      category: category,
+      aliases: Array(aliases).join(' '),
+      parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
+      created_by_user: created_by_user,
+      created_at: created_at
+    )
+  end
+
+  let!(:v1) do
+    create_tag_version!(
+      tag: tag,
+      version_no: 1,
+      event_type: 'create',
+      name: 'old_tag_name',
+      category: 'general',
+      aliases: ['alias_shared', 'alias_old'],
+      parent_tags: [parent_shared, parent_old],
+      created_by_user: member,
+      created_at: t_v1
+    )
+  end
+
+  let!(:v2) do
+    create_tag_version!(
+      tag: tag,
+      version_no: 2,
+      event_type: 'update',
+      name: 'new_tag_name',
+      category: 'meme',
+      aliases: ['alias_shared', 'alias_new'],
+      parent_tags: [parent_shared, parent_new],
+      created_by_user: member,
+      created_at: t_v2
+    )
+  end
+
+  let!(:other_v1) do
+    create_tag_version!(
+      tag: other_tag,
+      version_no: 1,
+      event_type: 'create',
+      name: 'other_tag_name',
+      category: 'general',
+      aliases: ['other_alias'],
+      parent_tags: [other_parent],
+      created_by_user: member,
+      created_at: t_other
+    )
+  end
+
+  describe 'GET /tags/versions' do
+    it 'returns all versions in reverse chronological order when id is omitted' do
+      get '/tags/versions'
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('versions', 'count')
+      expect(json.fetch('count')).to eq(3)
+
+      versions = json.fetch('versions')
+
+      expect(versions.map { |v| [v['tag_id'], v['version_no']] }).to eq([
+        [other_tag.id, 1],
+        [tag.id, 2],
+        [tag.id, 1]
+      ])
+    end
+
+    it 'returns versions for the specified tag with diffs' do
+      get '/tags/versions', params: { id: tag.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to include('versions', 'count')
+      expect(json.fetch('count')).to eq(2)
+
+      versions = json.fetch('versions')
+      expect(versions.map { |v| v['tag_id'] }.uniq).to eq([tag.id])
+      expect(versions.map { |v| v['version_no'] }).to eq([2, 1])
+
+      latest = versions.first
+      expect(latest).to include(
+        'tag_id' => tag.id,
+        'version_no' => 2,
+        'event_type' => 'update',
+        'created_by_user' => {
+          'id' => member.id,
+          'name' => member.name
+        }
+      )
+
+      expect(latest.fetch('name')).to eq(
+        'current' => 'new_tag_name',
+        'prev' => 'old_tag_name'
+      )
+      expect(latest.fetch('category')).to eq(
+        'current' => 'meme',
+        'prev' => 'general'
+      )
+      expect(latest.fetch('aliases')).to include(
+        { 'name' => 'alias_shared', 'type' => 'context' },
+        { 'name' => 'alias_new', 'type' => 'added' },
+        { 'name' => 'alias_old', 'type' => 'removed' }
+      )
+      expect(latest.fetch('parent_tags')).to include(
+        a_hash_including(
+          'type' => 'context',
+          'tag' => a_hash_including(
+            'id' => parent_shared.id
+          )
+        ),
+        a_hash_including(
+          'type' => 'added',
+          'tag' => a_hash_including(
+            'id' => parent_new.id
+          )
+        ),
+        a_hash_including(
+          'type' => 'removed',
+          'tag' => a_hash_including(
+            'id' => parent_old.id
+          )
+        )
+      )
+      expect(latest.fetch('created_at')).to eq(t_v2.iso8601)
+
+      first = versions.second
+      expect(first).to include(
+        'tag_id' => tag.id,
+        'version_no' => 1,
+        'event_type' => 'create',
+        'created_by_user' => {
+          'id' => member.id,
+          'name' => member.name
+        }
+      )
+      expect(first.fetch('name')).to eq(
+        'current' => 'old_tag_name',
+        'prev' => nil
+      )
+      expect(first.fetch('category')).to eq(
+        'current' => 'general',
+        'prev' => nil
+      )
+      expect(first.fetch('aliases')).to include(
+        { 'name' => 'alias_shared', 'type' => 'added' },
+        { 'name' => 'alias_old', 'type' => 'added' }
+      )
+      expect(first.fetch('parent_tags')).to include(
+        a_hash_including(
+          'type' => 'added',
+          'tag' => a_hash_including(
+            'id' => parent_shared.id
+          )
+        ),
+        a_hash_including(
+          'type' => 'added',
+          'tag' => a_hash_including(
+            'id' => parent_old.id
+          )
+        )
+      )
+      expect(first.fetch('created_at')).to eq(t_v1.iso8601)
+    end
+
+    it 'returns empty when the specified tag has no versions' do
+      fresh_tag = create(:tag, name: 'no_versions_tag', category: :general)
+
+      get '/tags/versions', params: { id: fresh_tag.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('versions')).to eq([])
+      expect(json.fetch('count')).to eq(0)
+    end
+
+    it 'clamps page and limit to at least 1' do
+      get '/tags/versions', params: { id: tag.id, page: 0, limit: 0 }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('count')).to eq(2)
+
+      versions = json.fetch('versions')
+      expect(versions.size).to eq(1)
+      expect(versions.first['version_no']).to eq(2)
+    end
+
+    it 'does not create tag versions by wiki updates when tag has no versions yet' do
+      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!(
+              tag_name: wiki_tag_name,
+              body: 'before',
+              created_by_user: member,
+              message: 'init')
+
+      Wiki::Commit.content!(
+          page: wiki_page,
+          body: 'after',
+          created_user: member,
+          message: 'edit',
+          base_revision_id: wiki_page.current_revision.id)
+
+      get '/tags/versions', params: { id: wiki_tag.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json.fetch('versions')).to eq([])
+      expect(json.fetch('count')).to eq(0)
+    end
+  end
+end

backend/spec/requests/tag_wiki_history_integrity_spec.rb

@@ -0,0 +1,160 @@
+require 'rails_helper'
+
+RSpec.describe 'Tag and wiki history integrity', type: :request do
+  let(:member_user) { create(:user, role: 'member') }
+
+  def stub_current_user user
+    allow_any_instance_of(ApplicationController).to receive(:current_user).and_return(user)
+  end
+
+  def create_tag! name:, category: :general
+    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: tag.tag_name,
+        body:,
+        created_by_user: user,
+        message: 'init')
+  end
+
+  before do
+    stub_current_user(member_user)
+  end
+
+  describe 'PATCH /tags/:id' do
+    it 'records wiki_version when tag name changes and tag has wiki' do
+      tag = create_tag!(name: 'patch_tag_wiki_before')
+      wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+
+      expect {
+        patch "/tags/#{ tag.id }", params: {
+          name: 'patch_tag_wiki_after',
+        }
+      }
+          .to change(TagVersion, :count).by(2)
+          .and change(WikiVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      tag.reload
+      wiki_page.reload
+      version = wiki_page.wiki_versions.order(:version_no).last
+
+      expect(tag.name).to eq('patch_tag_wiki_after')
+      expect(wiki_page.title).to eq('patch_tag_wiki_after')
+
+      expect(version).to have_attributes(
+        event_type: 'update',
+        title: 'patch_tag_wiki_after',
+        body: 'wiki body before',
+        created_by_user_id: member_user.id
+      )
+    end
+
+    it 'does not record wiki_version when only category changes' do
+      tag = create_tag!(name: 'patch_tag_category_only')
+      wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+
+      before_wiki_versions = wiki_page.wiki_versions.count
+
+      expect {
+        patch "/tags/#{ tag.id }", params: {
+          category: 'meme',
+        }
+      }
+          .to change(TagVersion, :count).by(2)
+
+      expect(response).to have_http_status(:ok)
+
+      tag.reload
+      wiki_page.reload
+
+      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
+  end
+
+  describe 'PUT /tags/:id' do
+    it 'records wiki_version when tag name changes and tag has wiki' do
+      tag = create_tag!(name: 'put_tag_wiki_before')
+      wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+
+      expect {
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_tag_wiki_after',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+      }
+          .to change(TagVersion, :count).by(2)
+          .and change(WikiVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      tag.reload
+      wiki_page.reload
+      version = wiki_page.wiki_versions.order(:version_no).last
+
+      expect(tag.name).to eq('put_tag_wiki_after')
+      expect(wiki_page.title).to eq('put_tag_wiki_after')
+
+      expect(version).to have_attributes(
+        event_type: 'update',
+        title: 'put_tag_wiki_after',
+        body: 'wiki body before',
+        created_by_user_id: member_user.id
+      )
+    end
+
+    it 'does not record wiki_version when only category changes' do
+      tag = create_tag!(name: 'put_tag_category_only')
+      wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+
+      before_wiki_versions = wiki_page.wiki_versions.count
+
+      expect {
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_tag_category_only',
+          category: 'meme',
+          aliases: '',
+          parent_tags: '',
+        }
+      }
+          .to change(TagVersion, :count).by(2)
+
+      expect(response).to have_http_status(:ok)
+
+      tag.reload
+      wiki_page.reload
+
+      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
+
+    it 'does not record wiki_version when only aliases change' do
+      tag = create_tag!(name: 'put_tag_alias_only')
+      wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+
+      before_wiki_versions = wiki_page.wiki_versions.count
+
+      expect {
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_tag_alias_only',
+          category: 'general',
+          aliases: 'put_tag_alias_only_alias',
+          parent_tags: '',
+        }
+      }
+          .to change(TagVersion, :count).by(2)
+
+      expect(response).to have_http_status(:ok)
+      expect(wiki_page.reload.wiki_versions.count).to eq(before_wiki_versions)
+    end
+  end
+end

backend/spec/requests/tags_deerjikists_spec.rb

@@ -8,8 +8,10 @@ RSpec.describe 'Tags deerjikists API', type: :request do
 
   let!(:tag) { create(:tag, category: :deerjikist) }
 
+  let(:member) { create(:user, :member) }
+  let(:guest) { create(:user, role: :guest) }
+
   before do
-    # show_by_name / deerjikists_by_name 用に名前を固定
     tag.tag_name.update!(name: 'deerjika')
   end
 
@@ -21,10 +23,20 @@ RSpec.describe 'Tags deerjikists API', type: :request do
     let(:tag_id) { tag.id }
 
     context 'when tag exists and has no deerjikists' do
-      it 'returns 200 and empty array' do
+      it 'returns 200 with tag and empty deerjikists array' do
         do_request
+
         expect(response).to have_http_status(:ok)
-        expect(json).to eq([])
+
+        expect(json).to be_a(Hash)
+
+        expect(json['tag']).to be_a(Hash)
+        expect(json['tag']['id']).to eq(tag.id)
+        expect(json['tag']['name']).to eq('deerjika')
+        expect(json['tag']['category']).to eq('deerjikist')
+        expect(json['tag']['has_deerjikists']).to eq(false)
+
+        expect(json['deerjikists']).to eq([])
       end
     end
 
@@ -34,14 +46,24 @@ RSpec.describe 'Tags deerjikists API', type: :request do
         Deerjikist.create!(platform: platform2, code: code2, tag: tag)
       end
 
-      it 'returns 200 and deerjikists array' do
+      it 'returns 200 with tag and deerjikists array' do
         do_request
+
         expect(response).to have_http_status(:ok)
 
-        expect(json).to be_a(Array)
-        expect(json.size).to eq(2)
+        expect(json).to be_a(Hash)
 
-        expect(json.map { |h| [h['platform'], h['code']] }).to contain_exactly(
+        expect(json['tag']).to be_a(Hash)
+        expect(json['tag']['id']).to eq(tag.id)
+        expect(json['tag']['name']).to eq('deerjika')
+        expect(json['tag']['category']).to eq('deerjikist')
+        expect(json['tag']['has_deerjikists']).to eq(true)
+
+        expect(json['deerjikists']).to be_a(Array)
+        expect(json['deerjikists'].size).to eq(2)
+
+        expect(json['deerjikists'].map { |h| [h['platform'], h['code']] })
+          .to contain_exactly(
             [platform1, code1],
             [platform2, code2],
           )
@@ -53,6 +75,7 @@ RSpec.describe 'Tags deerjikists API', type: :request do
 
       it 'returns 404' do
         do_request
+
         expect(response).to have_http_status(:not_found)
       end
     end
@@ -70,6 +93,7 @@ RSpec.describe 'Tags deerjikists API', type: :request do
 
       it 'returns 400' do
         do_request
+
         expect(response).to have_http_status(:bad_request)
       end
     end
@@ -79,23 +103,209 @@ RSpec.describe 'Tags deerjikists API', type: :request do
 
       it 'returns 404' do
         do_request
+
         expect(response).to have_http_status(:not_found)
       end
     end
 
+    context 'when tag exists and has no deerjikists' do
+      it 'returns 200 with tag and empty deerjikists array' do
+        do_request
+
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to be_a(Hash)
+
+        expect(json['tag']).to be_a(Hash)
+        expect(json['tag']['id']).to eq(tag.id)
+        expect(json['tag']['name']).to eq('deerjika')
+        expect(json['tag']['category']).to eq('deerjikist')
+        expect(json['tag']['has_deerjikists']).to eq(false)
+
+        expect(json['deerjikists']).to eq([])
+      end
+    end
+
     context 'when tag exists and has deerjikists' do
       before do
         Deerjikist.create!(platform: platform1, code: code1, tag: tag)
       end
 
-      it 'returns 200 and deerjikists array' do
+      it 'returns 200 with tag and deerjikists array' do
         do_request
+
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to be_a(Hash)
+
+        expect(json['tag']).to be_a(Hash)
+        expect(json['tag']['id']).to eq(tag.id)
+        expect(json['tag']['name']).to eq('deerjika')
+        expect(json['tag']['category']).to eq('deerjikist')
+        expect(json['tag']['has_deerjikists']).to eq(true)
+
+        expect(json['deerjikists']).to be_a(Array)
+        expect(json['deerjikists'].size).to eq(1)
+
+        expect(json['deerjikists'][0]['platform']).to eq(platform1)
+        expect(json['deerjikists'][0]['code']).to eq(code1)
+      end
+    end
+  end
+
+  describe 'PUT /tags/:id/deerjikists' do
+    subject(:do_request) do
+      put "/tags/#{tag_id}/deerjikists", params: payload, as: :json
+    end
+
+    let(:tag_id) { tag.id }
+    let(:payload) do
+      [
+        { platform: platform1, code: code1 },
+        { platform: platform2, code: code2 },
+      ]
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        do_request
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      before do
+        sign_in_as guest
+      end
+
+      it 'returns 403' do
+        do_request
+
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when tag does not exist' do
+      let(:tag_id) { 9_999_999 }
+
+      before do
+        sign_in_as member
+      end
+
+      it 'returns 404' do
+        do_request
+
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+
+    context 'when logged in as member' do
+      before do
+        sign_in_as member
+      end
+
+      context 'when tag has no deerjikists' do
+        it 'creates deerjikists and returns deerjikists array' do
+          expect {
+            do_request
+          }.to change { Deerjikist.where(tag: tag).count }.from(0).to(2)
+
           expect(response).to have_http_status(:ok)
 
+          expect(json).to be_a(Array)
+          expect(json.map { |h| [h['platform'], h['code']] })
+            .to contain_exactly(
+              [platform1, code1],
+              [platform2, code2],
+            )
+
+          expect(Deerjikist.where(tag: tag).map { |d| [d.platform, d.code] })
+            .to contain_exactly(
+              [platform1, code1],
+              [platform2, code2],
+            )
+        end
+      end
+
+      context 'when tag already has deerjikists' do
+        before do
+          Deerjikist.create!(platform: platform1, code: 'old-code-1', tag: tag)
+          Deerjikist.create!(platform: platform2, code: 'old-code-2', tag: tag)
+        end
+
+        it 'replaces deerjikists and returns deerjikists array' do
+          do_request
+
+          expect(response).to have_http_status(:ok)
+
+          expect(Deerjikist.where(tag: tag).map { |d| [d.platform, d.code] })
+            .to contain_exactly(
+              [platform1, code1],
+              [platform2, code2],
+            )
+
+          expect(Deerjikist.exists?(platform: platform1, code: 'old-code-1')).to eq(false)
+          expect(Deerjikist.exists?(platform: platform2, code: 'old-code-2')).to eq(false)
+
+          expect(json).to be_a(Array)
+          expect(json.map { |h| [h['platform'], h['code']] })
+            .to contain_exactly(
+              [platform1, code1],
+              [platform2, code2],
+            )
+        end
+      end
+
+      context 'when payload is empty array' do
+        let(:payload) { [] }
+
+        before do
+          Deerjikist.create!(platform: platform1, code: code1, tag: tag)
+          Deerjikist.create!(platform: platform2, code: code2, tag: tag)
+        end
+
+        it 'clears deerjikists and returns empty array' do
+          expect {
+            do_request
+          }.to change { Deerjikist.where(tag: tag).count }.from(2).to(0)
+
+          expect(response).to have_http_status(:ok)
+          expect(json).to eq([])
+        end
+      end
+
+      context 'when youtube code is handle' do
+        let(:channel_id) { 'UCabcdefghijklmnopqrstuv' }
+        let(:payload) do
+          [
+            { platform: 'youtube', code: '@deerjika' },
+          ]
+        end
+
+        before do
+          allow(Net::HTTP).to receive(:get).and_return(
+            %(<link rel="canonical" href="https://www.youtube.com/channel/#{channel_id}">),
+          )
+        end
+
+        it 'normalises youtube handle to channel id' do
+          expect {
+            do_request
+          }.to change { Deerjikist.where(tag: tag).count }.from(0).to(1)
+
+          expect(response).to have_http_status(:ok)
+
+          expect(Net::HTTP).to have_received(:get)
+
+          expect(Deerjikist.exists?(platform: 'youtube', code: channel_id, tag: tag))
+            .to eq(true)
+
           expect(json).to be_a(Array)
           expect(json.size).to eq(1)
-        expect(json[0]['platform']).to eq(platform1)
-        expect(json[0]['code']).to eq(code1)
+          expect(json[0]['platform']).to eq('youtube')
+          expect(json[0]['code']).to eq(channel_id)
+        end
       end
     end
   end

backend/spec/requests/tags_spec.rb

@@ -1,7 +1,6 @@
 require 'cgi'
 require 'rails_helper'
 
-
 RSpec.describe 'Tags API', type: :request do
   let!(:tn) { TagName.create!(name: 'spec_tag') }
   let!(:tag) { Tag.create!(tag_name: tn, category: :general) }
@@ -197,6 +196,30 @@ RSpec.describe 'Tags API', type: :request do
       expect(response_tags.size).to eq(1)
       expect(response_names).to eq(['norm_a'])
     end
+
+    it 'returns aliases and parent tags' do
+      parent_tag = Tag.create!(
+        tag_name: TagName.create!(name: 'index_parent_tag'),
+        category: :meme
+      )
+      TagImplication.create!(tag:, parent_tag:)
+
+      get '/tags', params: { name: 'spec_tag' }
+
+      expect(response).to have_http_status(:ok)
+
+      row = response_tags.find { |t| t['name'] == 'spec_tag' }
+
+      expect(row['aliases']).to include('unko')
+      expect(row['parents'].map { |t| t['name'] }).to include('index_parent_tag')
+
+      parent = row['parents'].find { |t| t['name'] == 'index_parent_tag' }
+      expect(parent).to include(
+        'id' => parent_tag.id,
+        'name' => 'index_parent_tag',
+        'category' => 'meme'
+      )
+    end
   end
 
   describe 'GET /tags/:id' do
@@ -220,6 +243,28 @@ RSpec.describe 'Tags API', type: :request do
         expect(json).to have_key('created_at')
         expect(json).to have_key('updated_at')
       end
+
+      it 'returns aliases and parent tags' do
+        parent_tag = Tag.create!(
+          tag_name: TagName.create!(name: 'show_parent_tag'),
+          category: :character
+        )
+        TagImplication.create!(tag:, parent_tag:)
+
+        request
+
+        expect(response).to have_http_status(:ok)
+
+        expect(json['aliases']).to include('unko')
+        expect(json['parents'].map { |t| t['name'] }).to include('show_parent_tag')
+
+        parent = json['parents'].find { |t| t['name'] == 'show_parent_tag' }
+        expect(parent).to include(
+          'id' => parent_tag.id,
+          'name' => 'show_parent_tag',
+          'category' => 'character'
+        )
+      end
     end
 
     context 'when tag does not exist' do
@@ -359,14 +404,120 @@ RSpec.describe 'Tags API', type: :request do
         expect(tag.category).to eq('meta')
       end
 
-      it '存在しない id だと RecordNotFound になる（通常は 404）' do
+      it '存在しない id なら 404 を返す' do
         patch '/tags/999999999', params: { name: 'x' }
-        expect(response.status).to be_in([404, 500])
+        expect(response).to have_http_status(:not_found)
       end
 
-      it 'バリデーションで update! が失敗したら（通常は 422 か 500）' do
+      it 'nico category への変更は 422 を返す' do
         patch "/tags/#{tag.id}", params: { name: 'new', category: 'nico' }
-        expect(response.status).to be_in([422, 500])
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(tag.reload.name).to eq('spec_tag')
+        expect(tag.category).to eq('general')
+      end
+
+      it 'creates initial and update tag versions when name and category change' do
+        expect {
+          patch "/tags/#{tag.id}", params: { name: 'new_tag_name', category: 'meme' }
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+
+        versions = tag.reload.tag_versions.order(:version_no)
+
+        expect(versions.map(&:event_type)).to eq(['create', 'update'])
+
+        expect(versions.first.name).to eq('spec_tag')
+        expect(versions.first.category).to eq('general')
+        expect(versions.first.aliases.split).to include('unko')
+
+        expect(versions.second.name).to eq('new_tag_name')
+        expect(versions.second.category).to eq('meme')
+        expect(versions.second.created_by_user_id).to eq(member_user.id)
+      end
+
+      it 'returns 422 when changing normal tag category to nico' do
+        expect {
+          patch "/tags/#{tag.id}", params: { category: 'nico' }
+        }.not_to change(TagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(tag.reload.category).to eq('general')
+      end
+
+      it 'returns 422 when updating nico tag name' do
+        nico_tag_name = TagName.create!(name: 'nico:tags_spec_source')
+        nico_tag = Tag.create!(tag_name: nico_tag_name, category: :nico)
+
+        expect {
+          patch "/tags/#{ nico_tag.id }", params: { name: 'nico:tags_spec_renamed' }
+        }.not_to change(NicoTagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(nico_tag.reload.name).to eq('nico:tags_spec_source')
+        expect(nico_tag.category).to eq('nico')
+      end
+
+      it 'returns 422 when changing nico tag category to normal category' do
+        nico_tag_name = TagName.create!(name: 'nico:category_change_ng')
+        nico_tag = Tag.create!(tag_name: nico_tag_name, category: :nico)
+
+        expect {
+          patch "/tags/#{nico_tag.id}", params: { category: 'general' }
+        }.not_to change(NicoTagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(nico_tag.reload.category).to eq('nico')
+      end
+
+      it 'PATCH で tag の name を変更すると対応する wiki version を作成する' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'wiki body before',
+                created_by_user: member_user,
+                message: 'init')
+
+        expect {
+          patch "/tags/#{ tag.id }", params: {
+            name: 'patch_wiki_renamed_tag',
+          }
+        }
+            .to change(TagVersion, :count).by(2)
+            .and change(WikiVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        version = wiki_page.reload.wiki_versions.order(:version_no).last
+
+        expect(version).to have_attributes(
+          event_type: 'update',
+          title: 'patch_wiki_renamed_tag',
+          body: 'wiki body before',
+          created_by_user_id: member_user.id
+        )
+      end
+
+      it 'tag の category だけを変更しても wiki version は作成しない' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'wiki body before',
+                created_by_user: member_user,
+                message: 'init')
+
+        before_wiki_version_count = wiki_page.reload.wiki_versions.count
+
+        expect {
+          patch "/tags/#{ tag.id }", params: {
+            category: 'meme',
+          }
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+        expect(wiki_page.reload.wiki_versions.count).to eq(before_wiki_version_count)
       end
     end
   end
@@ -510,4 +661,397 @@ RSpec.describe 'Tags API', type: :request do
       expect(response).to have_http_status(:not_found)
     end
   end
+
+  describe 'PUT /tags/:id' do
+    context '未ログイン' do
+      before { stub_current_user(nil) }
+
+      it '401 を返す' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'new',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'ログインしてゐるが member でない' do
+      before { stub_current_user(non_member_user) }
+
+      it '403 を返す' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'new',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'member' do
+      before { stub_current_user(member_user) }
+
+      it '存在しない id なら 404 を返す' do
+        put '/tags/999999999', params: {
+          name: 'new',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:not_found)
+      end
+
+      it 'name が空なら 422 を返す' do
+        put "/tags/#{ tag.id }", params: {
+          name: '',
+          category: 'general',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(tag.reload.name).to eq('spec_tag')
+      end
+
+      it 'category が空なら 422 を返す' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'new',
+          category: '',
+          aliases: '',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(tag.reload.name).to eq('spec_tag')
+        expect(tag.category).to eq('general')
+      end
+
+      it 'name, category, aliases, parent tags をまとめて更新できる' do
+        old_parent = Tag.create!(
+          tag_name: TagName.create!(name: 'put_old_parent'),
+          category: :general
+        )
+        kept_parent = Tag.create!(
+          tag_name: TagName.create!(name: 'put_kept_parent'),
+          category: :general
+        )
+        TagImplication.create!(tag:, parent_tag: old_parent)
+        TagImplication.create!(tag:, parent_tag: kept_parent)
+
+        put "/tags/#{ tag.id }", params: {
+          name: 'put_renamed_tag',
+          category: 'meme',
+          aliases: 'put_alias_a put_alias_b put_alias_a',
+          parent_tags: 'put_kept_parent put_new_parent',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+
+        expect(tag.name).to eq('put_renamed_tag')
+        expect(tag.category).to eq('meme')
+
+        expect(TagName.find_by(name: 'put_alias_a').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by(name: 'put_alias_b').canonical).to eq(tag.tag_name)
+
+        old_name_alias = TagName.find_by(name: 'spec_tag')
+        expect(old_name_alias).to be_present
+        expect(old_name_alias.canonical).to eq(tag.tag_name)
+
+        expect(alias_tn.reload.canonical).to be_nil
+
+        expect(tag.parents.map(&:name)).to contain_exactly(
+          'put_kept_parent',
+          'put_new_parent'
+        )
+
+        expect(TagImplication.where(tag:, parent_tag: old_parent)).not_to exist
+
+        expect(json['name']).to eq('put_renamed_tag')
+        expect(json['category']).to eq('meme')
+        expect(json['aliases']).to contain_exactly(
+          'put_alias_a',
+          'put_alias_b',
+          'spec_tag'
+        )
+        expect(json['parents'].map { |t| t['name'] }).to contain_exactly(
+          'put_kept_parent',
+          'put_new_parent'
+        )
+      end
+
+      it 'aliases に現在名を指定しても alias には残さない' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'spec_tag',
+          category: 'general',
+          aliases: 'spec_tag put_alias_self_test',
+          parent_tags: '',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        tag.reload
+
+        expect(TagName.find_by(name: 'put_alias_self_test').canonical).to eq(tag.tag_name)
+        expect(json['aliases']).to include('put_alias_self_test')
+        expect(json['aliases']).not_to include('spec_tag')
+      end
+
+      it 'parent_tags に自分自身を指定しても自己参照は作らない' do
+        put "/tags/#{ tag.id }", params: {
+          name: 'spec_tag',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: 'spec_tag',
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        expect(TagImplication.where(tag:, parent_tag: tag)).not_to exist
+        expect(tag.reload.parents).to eq([])
+      end
+
+      it 'initial and update tag versions を作成する' do
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'put_versioned_tag',
+            category: 'meta',
+            aliases: '',
+            parent_tags: '',
+          }
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+
+        versions = tag.reload.tag_versions.order(:version_no)
+
+        expect(versions.map(&:event_type)).to eq(['create', 'update'])
+
+        expect(versions.first.name).to eq('spec_tag')
+        expect(versions.first.category).to eq('general')
+        expect(versions.first.aliases.split).to include('unko')
+
+        expect(versions.second.name).to eq('put_versioned_tag')
+        expect(versions.second.category).to eq('meta')
+        expect(versions.second.aliases.split).to include('spec_tag')
+        expect(versions.second.created_by_user_id).to eq(member_user.id)
+      end
+
+      it 'parent tag の snapshot も作成する' do
+        old_parent = Tag.create!(
+          tag_name: TagName.create!(name: 'put_snapshot_old_parent'),
+          category: :general
+        )
+        new_parent = Tag.create!(
+          tag_name: TagName.create!(name: 'put_snapshot_new_parent'),
+          category: :general
+        )
+        TagImplication.create!(tag:, parent_tag: old_parent)
+
+        put "/tags/#{ tag.id }", params: {
+          name: 'spec_tag',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: new_parent.name,
+        }
+
+        expect(response).to have_http_status(:ok)
+
+        expect(old_parent.reload.tag_versions.map(&:event_type)).to include('create')
+        expect(new_parent.reload.tag_versions.map(&:event_type)).to include('create')
+      end
+
+      it 'normal tag を nico category には変更できない' do
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'spec_tag',
+            category: 'nico',
+            aliases: '',
+            parent_tags: '',
+          }
+        }.not_to change(TagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(tag.reload.name).to eq('spec_tag')
+        expect(tag.category).to eq('general')
+      end
+
+      it 'nico tag は更新できない' do
+        nico_tag = Tag.create!(
+          tag_name: TagName.create!(name: 'nico:put_update_all_ng'),
+          category: :nico
+        )
+
+        expect {
+          put "/tags/#{ nico_tag.id }", params: {
+            name: 'nico:put_update_all_renamed',
+            category: 'nico',
+            aliases: '',
+            parent_tags: '',
+          }
+        }.not_to change(NicoTagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(nico_tag.reload.name).to eq('nico:put_update_all_ng')
+        expect(nico_tag.category).to eq('nico')
+      end
+
+      it 'system tag の name は変更できない' do
+        system_tag = Tag.tagme
+        old_name = system_tag.name
+        old_category = system_tag.category
+
+        expect {
+          put "/tags/#{ system_tag.id }", params: {
+            name: 'put_system_tag_renamed',
+            category: old_category,
+            aliases: '',
+            parent_tags: '',
+          }
+        }.not_to change(TagVersion, :count)
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(system_tag.reload.name).to eq(old_name)
+        expect(system_tag.category).to eq(old_category)
+      end
+
+      it 'wiki を持つ tag を更新すると wiki version も作成する' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'wiki body before',
+                created_by_user: member_user,
+                message: 'init')
+
+        Wiki::Commit.content!(
+          page: wiki_page,
+          body: 'wiki body before',
+          created_user: member_user,
+          message: 'init'
+        )
+
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'put_wiki_version_tag',
+            category: 'meme',
+            aliases: 'unko',
+            parent_tags: '',
+          }
+        }
+            .to change(TagVersion, :count).by(2)
+            .and change(WikiVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        version = wiki_page.reload.wiki_versions.order(:version_no).last
+
+        expect(version).to have_attributes(
+          event_type: 'update',
+          title: 'put_wiki_version_tag',
+          body: 'wiki body before',
+          created_by_user_id: member_user.id
+        )
+      end
+
+      it '別名を他 tag から奪った場合、奪はれた側の tag version も作成する' do
+        old_owner = Tag.create!(
+          tag_name: TagName.create!(name: 'put_alias_old_owner'),
+          category: :general
+        )
+        stolen_alias = TagName.create!(
+          name: 'put_stolen_alias',
+          canonical: old_owner.tag_name
+        )
+
+        expect(old_owner.tag_name.aliases.map(&:name)).to include('put_stolen_alias')
+
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'spec_tag',
+            category: 'general',
+            aliases: 'unko put_stolen_alias',
+            parent_tags: '',
+          }
+        }
+            .to change { tag.reload.tag_versions.count }.by(2)
+            .and change { old_owner.reload.tag_versions.count }.by(2)
+
+        expect(response).to have_http_status(:ok)
+
+        expect(stolen_alias.reload.canonical).to eq(tag.tag_name)
+        expect(old_owner.reload.tag_name.aliases.map(&:name)).not_to include('put_stolen_alias')
+
+        old_owner_versions = old_owner.tag_versions.order(:version_no)
+
+        expect(old_owner_versions.first.event_type).to eq('create')
+        expect(old_owner_versions.first.aliases.split).to include('put_stolen_alias')
+
+        expect(old_owner_versions.second.event_type).to eq('update')
+        expect(old_owner_versions.second.aliases.split).not_to include('put_stolen_alias')
+      end
+
+      it 'parent_tags に指定すると循環する tag は 422 にする' do
+        pending '#332 で対応予定'
+
+        child = Tag.create!(
+          tag_name: TagName.create!(name: 'put_cycle_child'),
+          category: :general
+        )
+
+        TagImplication.create!(tag: child, parent_tag: tag)
+
+        put "/tags/#{ tag.id }", params: {
+          name: 'spec_tag',
+          category: 'general',
+          aliases: 'unko',
+          parent_tags: child.name,
+        }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+
+        expect(TagImplication.where(tag:, parent_tag: child)).not_to exist
+      end
+
+      it 'tag の name を変更すると対応する wiki version を作成する' do
+        wiki_page =
+            Wiki::Commit.create_content!(
+                tag_name: tag.tag_name,
+                body: 'wiki body before',
+                created_by_user: member_user,
+                message: 'init')
+
+        expect {
+          put "/tags/#{ tag.id }", params: {
+            name: 'put_wiki_renamed_tag',
+            category: 'general',
+            aliases: 'unko',
+            parent_tags: '',
+          }
+        }
+            .to change(TagVersion, :count).by(2)
+            .and change(WikiVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        version = wiki_page.reload.wiki_versions.order(:version_no).last
+
+        expect(version).to have_attributes(
+          event_type: 'update',
+          title: 'put_wiki_renamed_tag',
+          body: 'wiki body before',
+          created_by_user_id: member_user.id
+        )
+      end
+    end
+  end
 end

backend/spec/requests/users_spec.rb

@@ -1,110 +1,266 @@
-require "rails_helper"
+require 'rails_helper'
 
+RSpec.describe 'Users', type: :request do
+  let(:remote_ip) { '203.0.113.10' }
 
-RSpec.describe "Users", type: :request do
-  describe "POST /users" do
-    it "creates guest user and returns code" do
-      post "/users"
-      expect(response).to have_http_status(:ok)
-      expect(json["code"]).to be_present
-      expect(json["user"]["role"]).to eq("guest")
+  before do
+    allow_any_instance_of(ActionDispatch::Request)
+      .to receive(:remote_ip)
+      .and_return(remote_ip)
+  end
+
+  def auth_headers(user)
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
+  describe 'POST /users' do
+    it 'creates guest user, IpAddress and UserIp, and returns code' do
+      expect {
+        post '/users'
+      }.to change(User, :count).by(1)
+        .and change(IpAddress, :count).by(1)
+        .and change(UserIp, :count).by(1)
+
+      expect(response).to have_http_status(:created)
+      expect(json['code']).to be_present
+      expect(json['user']['role']).to eq('guest')
+
+      user = User.last
+      ip_address = IpAddress.find_by(ip_address: IPAddr.new(remote_ip).hton)
+
+      expect(user.role).to eq('guest')
+      expect(ip_address).to be_present
+      expect(UserIp.exists?(user:, ip_address:)).to eq(true)
+    end
+
+    it 'returns 403 and does not create user when current IP address is banned' do
+      IpAddress.create!(
+        ip_address: IPAddr.new(remote_ip).hton,
+        banned_at: Time.current
+      )
+
+      expect {
+        post '/users'
+      }.not_to change(User, :count)
+
+      expect(response).to have_http_status(:forbidden)
+      expect(UserIp.count).to eq(0)
     end
   end
 
-  describe "POST /users/code/renew" do
-    it "returns 401 when not logged in" do
-      sign_out
-      post "/users/code/renew"
-      expect(response).to have_http_status(:unauthorized)
-    end
-  end
+  describe 'POST /users/code/renew' do
+    it 'returns 401 when not logged in' do
+      post '/users/code/renew'
 
-  describe "PUT /users/:id" do
-    let(:user) { create(:user, name: "old-name", role: "guest") }
-
-    it "returns 401 when current_user id mismatch" do
-      sign_in_as(create(:user))
-      put "/users/#{user.id}", params: { name: "new-name" }
       expect(response).to have_http_status(:unauthorized)
     end
 
-    it "returns 400 when name is blank" do
-      sign_in_as(user)
-      put "/users/#{user.id}", params: { name: "   " }
+    it 'returns 403 when current user is banned' do
+      user = create(:user, :banned)
+
+      post '/users/code/renew', headers: auth_headers(user)
+
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it 'returns 403 when current IP address is banned' do
+      user = create(:user)
+
+      IpAddress.create!(
+        ip_address: IPAddr.new(remote_ip).hton,
+        banned_at: Time.current
+      )
+
+      post '/users/code/renew', headers: auth_headers(user)
+
+      expect(response).to have_http_status(:forbidden)
+    end
+  end
+
+  describe 'PUT /users/:id' do
+    let(:user) { create(:user, name: 'old-name', role: 'guest') }
+
+    it 'returns 401 when current_user id mismatch' do
+      other_user = create(:user)
+
+      put "/users/#{user.id}",
+          params: { name: 'new-name' },
+          headers: auth_headers(other_user)
+
+      expect(response).to have_http_status(:unauthorized)
+    end
+
+    it 'returns 400 when name is blank' do
+      put "/users/#{user.id}",
+          params: { name: '   ' },
+          headers: auth_headers(user)
+
       expect(response).to have_http_status(:bad_request)
     end
 
-    it "updates name and returns 201 with user slice" do
-      sign_in_as(user)
-      put "/users/#{user.id}", params: { name: "new-name" }
+    it 'updates name and returns user slice' do
+      put "/users/#{user.id}",
+          params: { name: 'new-name' },
+          headers: auth_headers(user)
 
-      expect(response).to have_http_status(:created)
-      expect(json["id"]).to eq(user.id)
-      expect(json["name"]).to eq("new-name")
+      expect(response).to have_http_status(:ok)
+      expect(json['id']).to eq(user.id)
+      expect(json['name']).to eq('new-name')
 
       user.reload
-      expect(user.name).to eq("new-name")
+      expect(user.name).to eq('new-name')
+    end
+
+    it 'returns 403 when current user is banned' do
+      user.update!(banned_at: Time.current)
+
+      put "/users/#{user.id}",
+          params: { name: 'new-name' },
+          headers: auth_headers(user)
+
+      expect(response).to have_http_status(:forbidden)
+
+      user.reload
+      expect(user.name).to eq('old-name')
+    end
+
+    it 'returns 403 when current IP address is banned' do
+      IpAddress.create!(
+        ip_address: IPAddr.new(remote_ip).hton,
+        banned_at: Time.current
+      )
+
+      put "/users/#{user.id}",
+          params: { name: 'new-name' },
+          headers: auth_headers(user)
+
+      expect(response).to have_http_status(:forbidden)
+
+      user.reload
+      expect(user.name).to eq('old-name')
     end
   end
 
-  describe "POST /users/verify" do
-    it "returns valid:false when code not found" do
-      post "/users/verify", params: { code: "nope" }
+  describe 'POST /users/verify' do
+    it 'returns valid:false when code not found' do
+      post '/users/verify', params: { code: 'nope' }
+
       expect(response).to have_http_status(:ok)
-      expect(json["valid"]).to eq(false)
+      expect(json['valid']).to eq(false)
     end
 
-    it "creates IpAddress and UserIp, and returns valid:true with user slice" do
-      user = create(:user, inheritance_code: SecureRandom.uuid, role: "guest")
+    it 'returns 403 when current IP address is banned' do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: 'guest')
 
-      # request.remote_ip を固定
-      allow_any_instance_of(ActionDispatch::Request).to receive(:remote_ip).and_return("203.0.113.10")
+      IpAddress.create!(
+        ip_address: IPAddr.new(remote_ip).hton,
+        banned_at: Time.current
+      )
 
       expect {
-        post "/users/verify", params: { code: user.inheritance_code }
+        post '/users/verify', params: { code: user.inheritance_code }
+      }.not_to change(UserIp, :count)
+
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it 'returns 403 when verified user is banned' do
+      user = create(
+        :user,
+        :banned,
+        inheritance_code: SecureRandom.uuid,
+        role: 'guest'
+      )
+
+      expect {
+        post '/users/verify', params: { code: user.inheritance_code }
+      }.not_to change(UserIp, :count)
+
+      expect(response).to have_http_status(:forbidden)
+    end
+
+    it 'creates IpAddress and UserIp, and returns valid:true with user slice' do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: 'guest')
+
+      expect {
+        post '/users/verify', params: { code: user.inheritance_code }
       }.to change(UserIp, :count).by(1)
+        .and change(IpAddress, :count).by(1)
 
       expect(response).to have_http_status(:ok)
-      expect(json["valid"]).to eq(true)
-      expect(json["user"]["id"]).to eq(user.id)
-      expect(json["user"]["inheritance_code"]).to eq(user.inheritance_code)
-      expect(json["user"]["role"]).to eq("guest")
+      expect(json['valid']).to eq(true)
+      expect(json['user']['id']).to eq(user.id)
+      expect(json['user']['inheritance_code']).to eq(user.inheritance_code)
+      expect(json['user']['role']).to eq('guest')
 
-      # ついでに IpAddress もできてることを確認（ipの保存形式がバイナリでも count で見れる）
-      expect(IpAddress.count).to be >= 1
+      ip_address = IpAddress.find_by(ip_address: IPAddr.new(remote_ip).hton)
+      expect(ip_address).to be_present
+      expect(UserIp.exists?(user:, ip_address:)).to eq(true)
     end
 
-    it "is idempotent for same user+ip (does not create duplicate UserIp)" do
-      user = create(:user, inheritance_code: SecureRandom.uuid, role: "guest")
-      allow_any_instance_of(ActionDispatch::Request).to receive(:remote_ip).and_return("203.0.113.10")
+    it 'is idempotent for same user and same IP address' do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: 'guest')
 
-      post "/users/verify", params: { code: user.inheritance_code }
+      post '/users/verify', params: { code: user.inheritance_code }
       expect(response).to have_http_status(:ok)
 
       expect {
-        post "/users/verify", params: { code: user.inheritance_code }
+        post '/users/verify', params: { code: user.inheritance_code }
       }.not_to change(UserIp, :count)
 
       expect(response).to have_http_status(:ok)
-      expect(json["valid"]).to eq(true)
+      expect(json['valid']).to eq(true)
+    end
+
+    it 'creates another UserIp for same user and different IP address' do
+      user = create(:user, inheritance_code: SecureRandom.uuid, role: 'guest')
+
+      post '/users/verify', params: { code: user.inheritance_code }
+      expect(response).to have_http_status(:ok)
+
+      allow_any_instance_of(ActionDispatch::Request)
+        .to receive(:remote_ip)
+        .and_return('203.0.113.11')
+
+      expect {
+        post '/users/verify', params: { code: user.inheritance_code }
+      }.to change(UserIp, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(json['valid']).to eq(true)
     end
   end
 
-  describe "GET /users/me" do
-    it "returns 404 when code not found" do
-      get "/users/me", params: { code: "nope" }
+  describe 'GET /users/me' do
+    it 'returns 404 when code not found' do
+      get '/users/me', params: { code: 'nope' }
+
       expect(response).to have_http_status(:not_found)
     end
 
-    it "returns user slice when found" do
-      user = create(:user, inheritance_code: SecureRandom.uuid, name: "me", role: "guest")
-      get "/users/me", params: { code: user.inheritance_code }
+    it 'returns user slice when found' do
+      user = create(:user, inheritance_code: SecureRandom.uuid, name: 'me', role: 'guest')
+
+      get '/users/me', params: { code: user.inheritance_code }
 
       expect(response).to have_http_status(:ok)
-      expect(json["id"]).to eq(user.id)
-      expect(json["name"]).to eq("me")
-      expect(json["inheritance_code"]).to eq(user.inheritance_code)
-      expect(json["role"]).to eq("guest")
+      expect(json['id']).to eq(user.id)
+      expect(json['name']).to eq('me')
+      expect(json['inheritance_code']).to eq(user.inheritance_code)
+      expect(json['role']).to eq('guest')
+    end
+
+    it 'returns 403 when current IP address is banned' do
+      user = create(:user, inheritance_code: SecureRandom.uuid)
+
+      IpAddress.create!(
+        ip_address: IPAddr.new(remote_ip).hton,
+        banned_at: Time.current
+      )
+
+      get '/users/me', params: { code: user.inheritance_code }
+
+      expect(response).to have_http_status(:forbidden)
     end
   end
 end

backend/spec/requests/wiki_body_search_pending_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki body search', type: :request do
+  let!(:user) { create_member_user! }
+
+  it 'searches wiki pages by body text' do
+    pending '#336 で対応予定'
+
+    Wiki::Commit.create_content!(
+        tag_name: TagName.create!(name: 'wiki_body_search_hit'),
+        body: 'unique body keyword for wiki search',
+        created_by_user: user,
+        message: 'init')
+
+    Wiki::Commit.create_content!(
+        tag_name: TagName.create!(name: 'wiki_body_search_miss'),
+        body: 'ordinary body',
+        created_by_user: user,
+        message: 'init')
+
+    get '/wiki/search', params: { body: 'unique body keyword' }
+
+    expect(response).to have_http_status(:ok)
+    expect(json.map { |page| page['title'] }).to include('wiki_body_search_hit')
+    expect(json.map { |page| page['title'] }).not_to include('wiki_body_search_miss')
+  end
+end

backend/spec/requests/wiki_conflict_spec.rb

@@ -0,0 +1,42 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki conflict handling', type: :request do
+  let!(:user) { create_member_user! }
+
+  def auth_headers user
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
+  it 'returns 409 when base_revision_id is stale' do
+    page =
+        Wiki::Commit.create_content!(
+            tag_name: TagName.create!(name: 'wiki_conflict_request'),
+            body: 'first',
+            created_by_user: user,
+            message: 'init')
+
+    stale_id = page.current_revision.id
+
+    Wiki::Commit.content!(
+        page:,
+        body: 'second',
+        created_user: user,
+        message: 'other edit',
+        base_revision_id: stale_id)
+
+    put "/wiki/#{ page.id }",
+        params: {
+          title: 'wiki_conflict_request',
+          body: 'third',
+          message: 'stale',
+          base_revision_id: stale_id,
+        },
+        headers: auth_headers(user)
+
+    expect(response).to have_http_status(:conflict)
+
+    page.reload
+    expect(page.body).to eq('second')
+    expect(page.current_revision.message).to eq('other edit')
+  end
+end

backend/spec/requests/wiki_history_integrity_spec.rb

@@ -0,0 +1,196 @@
+require 'cgi'
+require 'rails_helper'
+
+RSpec.describe 'Wiki history integrity', type: :request do
+  let!(:user) { create_member_user! }
+
+  def auth_headers user
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
+  def create_wiki_page title:, body: 'body', message: 'init', user: self.user
+    Wiki::Commit.create_content!(
+        tag_name: TagName.create!(name: title),
+        body:,
+        created_by_user: user,
+        message:)
+  end
+
+  describe 'POST /wiki' do
+    it 'creates wiki_page, wiki_revision, and wiki_version atomically' do
+      expect {
+        post '/wiki',
+             params: {
+               title: 'wiki_history_create_atomic',
+               body: "a\nb\nc",
+               message: 'initial commit',
+             },
+             headers: auth_headers(user)
+      }
+          .to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+
+      expect(response).to have_http_status(:created)
+
+      page = WikiPage.find(json.fetch('id'))
+      revision = page.current_revision
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.title).to eq('wiki_history_create_atomic')
+      expect(page.body).to eq("a\nb\nc")
+
+      expect(revision).to be_content
+      expect(revision.message).to eq('initial commit')
+      expect(revision.lines_count).to eq(3)
+
+      expect(version).to have_attributes(
+        version_no: 1,
+        event_type: 'create',
+        title: 'wiki_history_create_atomic',
+        body: "a\nb\nc",
+        reason: 'initial commit',
+        created_by_user_id: user.id
+      )
+    end
+
+    it 'returns 422 and creates nothing when normalised body is blank' do
+      expect {
+        post '/wiki',
+             params: {
+               title: 'wiki_history_blank_body',
+               body: "\r\n\r\n",
+               message: 'blank',
+             },
+             headers: auth_headers(user)
+      }
+          .not_to change(WikiPage, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_blank_body' })).not_to exist
+    end
+
+    it 'returns 422 and creates no partial page when title already exists' do
+      create_wiki_page(title: 'wiki_history_duplicate_title', body: 'first')
+
+      expect {
+        post '/wiki',
+             params: {
+               title: 'wiki_history_duplicate_title',
+               body: 'second',
+               message: 'duplicate',
+             },
+             headers: auth_headers(user)
+      }
+          .not_to change(WikiPage, :count)
+
+      expect(response).to have_http_status(:unprocessable_entity)
+      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_duplicate_title' }).count).to eq(1)
+    end
+  end
+
+  describe 'PUT /wiki/:id' do
+    it 'updates body and records wiki_revision and wiki_version' do
+      page = create_wiki_page(title: 'wiki_history_update_body', body: 'before')
+      current_id = page.current_revision.id
+
+      expect {
+        put "/wiki/#{ page.id }",
+            params: {
+              title: 'wiki_history_update_body',
+              body: 'after',
+              message: 'edit body',
+              base_revision_id: current_id,
+            },
+            headers: auth_headers(user)
+      }
+          .to change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      page.reload
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.title).to eq('wiki_history_update_body')
+      expect(page.body).to eq('after')
+
+      expect(version).to have_attributes(
+        event_type: 'update',
+        title: 'wiki_history_update_body',
+        body: 'after',
+        reason: 'edit body',
+        created_by_user_id: user.id
+      )
+    end
+
+    it 'renames title and records wiki_version with new title' do
+      page = create_wiki_page(title: 'wiki_history_rename_before', body: 'before')
+      current_id = page.current_revision.id
+
+      expect {
+        put "/wiki/#{ page.id }",
+            params: {
+              title: 'wiki_history_rename_after',
+              body: 'after',
+              message: 'rename',
+              base_revision_id: current_id,
+            },
+            headers: auth_headers(user)
+      }
+          .to change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+
+      page.reload
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.title).to eq('wiki_history_rename_after')
+      expect(page.body).to eq('after')
+
+      expect(version).to have_attributes(
+        event_type: 'update',
+        title: 'wiki_history_rename_after',
+        body: 'after',
+        reason: 'rename',
+        created_by_user_id: user.id
+      )
+    end
+
+    it 'does not change title, body, revision, or version on stale base_revision_id' do
+      page = create_wiki_page(title: 'wiki_history_conflict_page', body: 'first')
+      stale_id = page.current_revision.id
+
+      Wiki::Commit.content!(
+          page:,
+          body: 'second',
+          created_user: user,
+          message: 'other edit',
+          base_revision_id: stale_id)
+
+      page.reload
+      current_title = page.title
+      current_body = page.body
+      revision_count = page.wiki_revisions.count
+      version_count = page.wiki_versions.count
+
+      put "/wiki/#{ page.id }",
+          params: {
+            title: 'wiki_history_conflict_renamed',
+            body: 'third',
+            message: 'stale edit',
+            base_revision_id: stale_id,
+          },
+          headers: auth_headers(user)
+
+      expect(response).to have_http_status(:conflict)
+
+      page.reload
+      expect(page.title).to eq(current_title)
+      expect(page.body).to eq(current_body)
+      expect(page.wiki_revisions.count).to eq(revision_count)
+      expect(page.wiki_versions.count).to eq(version_count)
+    end
+  end
+end

backend/spec/requests/wiki_restore_pending_spec.rb

@@ -0,0 +1,37 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki restore', type: :request do
+  let!(:user) { create_member_user! }
+
+  def auth_headers user
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
+  it 'restores wiki page to previous version' do
+    pending '#337 で対応予定'
+
+    page =
+        Wiki::Commit.create_content!(
+            tag_name: TagName.create!(name: 'wiki_restore_page'),
+            body: 'v1',
+            created_by_user: user,
+            message: 'init')
+
+    v1 = page.wiki_versions.order(:version_no).last
+
+    Wiki::Commit.content!(
+        page:,
+        body: 'v2',
+        created_user: user,
+        message: 'edit',
+        base_revision_id: page.current_revision.id)
+
+    post "/wiki/#{ page.id }/restore",
+         params: { version_no: v1.version_no },
+         headers: auth_headers(user)
+
+    expect(response).to have_http_status(:ok)
+    expect(page.reload.body).to eq('v1')
+    expect(page.wiki_versions.order(:version_no).last.event_type).to eq('restore')
+  end
+end

backend/spec/requests/wiki_spec.rb

@@ -4,13 +4,19 @@ require 'securerandom'
 
 
 RSpec.describe 'Wiki API', type: :request do
+  def auth_headers(user)
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
   let!(:user) { create_member_user! }
 
   let!(:tn) { TagName.create!(name: 'spec_wiki_title') }
   let!(:page) do
-    WikiPage.create!(tag_name: tn, created_user: user, updated_user: user).tap do |p|
-      Wiki::Commit.content!(page: p, body: 'init', created_user: user, message: 'init')
-    end
+    Wiki::Commit.create_content!(
+        tag_name: tn,
+        body: 'init',
+        created_by_user: user,
+        message: 'init')
   end
 
   describe 'GET /wiki' do
@@ -37,6 +43,7 @@ RSpec.describe 'Wiki API', type: :request do
     context 'when wiki page exists' do
       it 'returns wiki page with title' do
         request
+
         expect(response).to have_http_status(:ok)
 
         expect(json).to include(
@@ -50,6 +57,7 @@ RSpec.describe 'Wiki API', type: :request do
 
       it 'returns 404' do
         request
+
         expect(response).to have_http_status(:not_found)
       end
     end
@@ -99,25 +107,34 @@ RSpec.describe 'Wiki API', type: :request do
         end
             .to change(WikiPage, :count).by(1)
             .and change(WikiRevision, :count).by(1)
+            .and change(WikiVersion, :count).by(1)
 
         expect(response).to have_http_status(:created)
 
         page_id = json.fetch('id')
         expect(json.fetch('title')).to eq('TestPage')
 
-        page = WikiPage.find(page_id)
-        rev = page.current_revision
+        created_page = WikiPage.find(page_id)
+        version = created_page.wiki_versions.order(:version_no).last
+
+        expect(version).to have_attributes(
+          version_no: 1,
+          event_type: 'create',
+          title: 'TestPage',
+          body: "a\nb\nc",
+          created_by_user_id: member.id
+        )
+
+        rev = created_page.current_revision
         expect(rev).to be_present
         expect(rev).to be_content
         expect(rev.message).to eq('init')
 
-        # body が復元できること
-        expect(page.body).to eq("a\nb\nc")
+        expect(created_page.body).to eq("a\nb\nc")
 
-        # 行数とリレーションの整合
         expect(rev.lines_count).to eq(3)
         expect(rev.wiki_revision_lines.order(:position).pluck(:position)).to eq([0, 1, 2])
-        expect(rev.wiki_lines.pluck(:body)).to match_array(%w[a b c])
+        expect(rev.wiki_lines.pluck(:body)).to match_array(['a', 'b', 'c'])
       end
 
       it 'reuses existing WikiLine rows by sha256' do
@@ -135,6 +152,41 @@ RSpec.describe 'Wiki API', type: :request do
         # "a" の WikiLine が増殖しない（1行のはず）
         expect(WikiLine.where(body: 'a').count).to eq(1)
       end
+
+      it 'deduplicates duplicated new lines before upsert' do
+        duplicated = 'duplicated_line_for_wiki_line_upsert_spec'
+
+        post endpoint,
+             params: { title: 'DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
+             headers: auth_headers(member)
+
+        expect(response).to have_http_status(:created)
+
+        page = WikiPage.find(json.fetch('id'))
+        rev = page.current_revision
+
+        expect(rev.lines_count).to eq(2)
+        expect(WikiLine.where(body: duplicated).count).to eq(1)
+        expect(rev.wiki_revision_lines.count).to eq(2)
+        expect(rev.wiki_revision_lines.pluck(:wiki_line_id).uniq.size).to eq(1)
+      end
+
+      it 'normalises CRLF and strips trailing newlines' do
+        post endpoint,
+             params: { title: 'NormalisedBody', body: "a\r\nb\r\n\r\n", message: 'normalise' },
+             headers: auth_headers(member)
+
+        expect(response).to have_http_status(:created)
+
+        page = WikiPage.find(json.fetch('id'))
+        rev = page.current_revision
+        version = page.wiki_versions.order(:version_no).last
+
+        expect(page.body).to eq("a\nb")
+        expect(version.body).to eq("a\nb")
+        expect(rev.lines_count).to eq(2)
+        expect(rev.wiki_lines.order('wiki_revision_lines.position').map(&:body)).to eq(['a', 'b'])
+      end
     end
   end
 
@@ -146,17 +198,14 @@ RSpec.describe 'Wiki API', type: :request do
       { 'X-Transfer-Code' => user.inheritance_code }
     end
 
-    #let!(:page) { create(:wiki_page, title: 'TestPage') }
-    let!(:page) do
-      build(:wiki_page, title: 'TestPage').tap do |p|
-        puts p.errors.full_messages unless p.valid?
-        p.save!
-      end
-    end
+    let!(:test_tag_name) { TagName.create!(name: 'TestPage') }
 
-    before do
-      # 初期版を 1 つ作っておく（更新が“2版目”になるように）
-      Wiki::Commit.content!(page: page, body: "a\nb", created_user: member, message: 'init')
+    let!(:page) do
+      Wiki::Commit.create_content!(
+          tag_name: test_tag_name,
+          body: "a\nb",
+          created_by_user: member,
+          message: 'init')
     end
 
     context 'when not logged in' do
@@ -182,14 +231,6 @@ RSpec.describe 'Wiki API', type: :request do
             headers: auth_headers(member)
         expect(response).to have_http_status(:unprocessable_entity)
       end
-
-      it 'returns 422 when title mismatched (if you forbid rename here)' do
-        put "/wiki/#{page.id}",
-            params: { title: 'OtherTitle', body: 'x' },
-            headers: auth_headers(member)
-        # 君の controller 例だと title 変更は 422 にしてた
-        expect(response).to have_http_status(:unprocessable_entity)
-      end
     end
 
     context 'when success' do
@@ -200,7 +241,18 @@ RSpec.describe 'Wiki API', type: :request do
           put "/wiki/#{page.id}",
               params: { title: 'TestPage', body: "x\ny", message: 'edit', base_revision_id: current_id },
               headers: auth_headers(member)
-        end.to change(WikiRevision, :count).by(1)
+        end
+            .to change(WikiRevision, :count).by(1)
+            .and change(WikiVersion, :count).by(1)
+
+        version = page.wiki_versions.order(:version_no).last
+
+        expect(version).to have_attributes(
+          event_type: 'update',
+          title: 'TestPage',
+          body: "x\ny",
+          created_by_user_id: member.id
+        )
 
         expect(response).to have_http_status(:ok)
 
@@ -211,25 +263,60 @@ RSpec.describe 'Wiki API', type: :request do
         expect(page.body).to eq("x\ny")
         expect(rev.base_revision_id).to eq(current_id)
       end
+
+      it 'wiki body だけを変更しても tag version は作成しない' do
+        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,
+            event_type: :create,
+            created_by_user: member)
+
+        linked_page =
+            Wiki::Commit.create_content!(
+                tag_name: linked_tag_name,
+                body: 'before',
+                created_by_user: member,
+                message: 'init')
+
+        current_id = linked_page.current_revision.id
+        before_count = linked_tag.reload.tag_versions.count
+
+        expect {
+          put "/wiki/#{ linked_page.id }",
+              params: {
+                title: 'wiki_body_only_tag',
+                body: 'after',
+                message: 'edit',
+                base_revision_id: current_id,
+              },
+              headers: auth_headers(member)
+        }
+            .to change(WikiRevision, :count).by(1)
+            .and change(WikiVersion, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+        expect(linked_tag.reload.tag_versions.count).to eq(before_count)
+      end
     end
 
-    # TODO: コンフリクト未実装のため，実装したらコメント外す．
-    # context 'when conflict' do
-    #   it 'returns 409 when base_revision_id mismatches' do
-    #     # 先に別ユーザ（同じ member でもOK）が 1 回更新して先頭を進める
-    #     Wiki::Commit.content!(page: page, body: "zzz", created_user: member, message: 'other edit')
-    #     page.reload
+    context 'when conflict' do
+      it 'returns 409 when base_revision_id mismatches' do
+        # 先に別ユーザ（同じ member でもOK）が 1 回更新して先頭を進める
+        Wiki::Commit.content!(page: page, body: "zzz", created_user: member, message: 'other edit')
+        page.reload
 
-    #     stale_id = page.wiki_revisions.order(:id).first.id # わざと古い id
-    #     put "/wiki/#{page.id}",
-    #         params: { title: 'TestPage', body: 'x', base_revision_id: stale_id },
-    #         headers: auth_headers(member)
+        stale_id = page.wiki_revisions.order(:id).first.id # わざと古い id
+        put "/wiki/#{page.id}",
+            params: { title: 'TestPage', body: 'x', base_revision_id: stale_id },
+            headers: auth_headers(member)
 
-    #     expect(response).to have_http_status(:conflict)
-    #     json = JSON.parse(response.body)
-    #     expect(json['error']).to eq('conflict')
-    #   end
-    # end
+        expect(response).to have_http_status(:conflict)
+        json = JSON.parse(response.body)
+        expect(json['error']).to eq('conflict')
+      end
+    end
 
     context 'when page not found' do
       it 'returns 404' do
@@ -261,14 +348,17 @@ RSpec.describe 'Wiki API', type: :request do
 
   describe 'GET /wiki/search' do
     before do
-      # 追加で検索ヒット用
-      TagName.create!(name: 'spec_wiki_title_2')
-      WikiPage.create!(tag_name: TagName.find_by!(name: 'spec_wiki_title_2'),
-                       created_user: user, updated_user: user)
+      Wiki::Commit.create_content!(
+          tag_name: TagName.create!(name: 'spec_wiki_title_2'),
+          body: 'search body 2',
+          created_by_user: user,
+          message: 'init')
 
-      TagName.create!(name: 'unrelated_title')
-      WikiPage.create!(tag_name: TagName.find_by!(name: 'unrelated_title'),
-                       created_user: user, updated_user: user)
+      Wiki::Commit.create_content!(
+          tag_name: TagName.create!(name: 'unrelated_title'),
+          body: 'unrelated body',
+          created_by_user: user,
+          message: 'init')
     end
 
     it 'returns up to 20 pages filtered by title like' do
@@ -278,7 +368,9 @@ RSpec.describe 'Wiki API', type: :request do
       expect(json).to be_an(Array)
 
       titles = json.map { |p| p['title'] }
-      expect(titles).to include('spec_wiki_title', 'spec_wiki_title_2')
+
+      expect(titles).to include('spec_wiki_title')
+      expect(titles).to include('spec_wiki_title_2')
       expect(titles).not_to include('unrelated_title')
     end
 
@@ -329,7 +421,12 @@ 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 = TagName.create!(name: 'spec_no_rev')
-      p2 = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
+      # 異常データ: revision 無し WikiPage を直接作る
+      p2 = WikiPage.create!(
+          tag_name: tn2,
+          body: 'init',
+          created_user: user,
+          updated_user: user)
 
       get "/wiki/changes?id=#{p2.id}"
       expect(response).to have_http_status(:ok)
@@ -398,29 +495,68 @@ RSpec.describe 'Wiki API', type: :request do
       expect(json['older_revision_id']).to eq(rev_a.id)
       expect(json['newer_revision_id']).to eq(page.current_revision.id)
     end
-
-    it 'returns 422 when "to" is redirect revision' do
-      # redirect revision を作る
-      tn2 = TagName.create!(name: 'redirect_target')
-      target = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
-
-      Wiki::Commit.redirect!(page: page, redirect_page: target, created_user: user, message: 'redir')
-      redirect_rev = page.current_revision
-      expect(redirect_rev).to be_redirect
-
-      get "/wiki/#{page.id}/diff?from=#{rev_a.id}&to=#{redirect_rev.id}"
-      expect(response).to have_http_status(:unprocessable_entity)
   end
 
-    it 'returns 422 when "from" is redirect revision' do
-      tn2 = TagName.create!(name: 'redirect_target2')
-      target = WikiPage.create!(tag_name: tn2, created_user: user, updated_user: user)
+  describe 'Wiki::Commit.redirect!' do
+    it 'raises because redirect revisions are deprecated' do
+      target_tag_name = TagName.create!(name: 'redirect_deprecated_target')
+      target =
+          Wiki::Commit.create_content!(
+              tag_name: target_tag_name,
+              body: 'target',
+              created_by_user: user,
+              message: 'init')
 
-      Wiki::Commit.redirect!(page: page, redirect_page: target, created_user: user, message: 'redir2')
-      redirect_rev = page.current_revision
+      expect {
+        Wiki::Commit.redirect!(
+          page: page,
+          redirect_page: target,
+          created_user: user,
+          message: 'redirect',
+          base_revision_id: page.current_revision.id
+        )
+      }.to raise_error(RuntimeError, '廃止しました．')
+    end
+  end
 
-      get "/wiki/#{page.id}/diff?from=#{redirect_rev.id}&to=#{rev_b.id}"
-      expect(response).to have_http_status(:unprocessable_entity)
-    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 = 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!(
+            tag_name: linked_tag_name,
+            body: 'before',
+            created_by_user: user,
+            message: 'init')
+
+    current_id = linked_page.current_revision.id
+
+    expect {
+      put "/wiki/#{ linked_page.id }",
+          params: {
+            title: 'wiki_linked_tag_for_version_renamed',
+            body: 'after',
+            message: 'rename',
+            base_revision_id: current_id,
+          },
+          headers: auth_headers(user)
+    }
+        .to change(WikiRevision, :count).by(1)
+        .and change(WikiVersion, :count).by(1)
+        .and change { linked_tag.reload.tag_versions.count }.by(2)
+
+    expect(response).to have_http_status(:ok)
+
+    linked_tag.reload
+    expect(linked_tag.name).to eq('wiki_linked_tag_for_version_renamed')
+
+    versions = linked_tag.tag_versions.order(:version_no)
+
+    expect(versions.first.event_type).to eq('create')
+    expect(versions.first.name).to eq('wiki_linked_tag_for_version')
+
+    expect(versions.second.event_type).to eq('update')
+    expect(versions.second.name).to eq('wiki_linked_tag_for_version_renamed')
   end
 end

backend/spec/requests/wiki_title_collision_spec.rb

@@ -0,0 +1,62 @@
+require 'rails_helper'
+
+RSpec.describe 'Wiki title collision', type: :request do
+  let!(:user) { create_member_user! }
+
+  def auth_headers user
+    { 'X-Transfer-Code' => user.inheritance_code }
+  end
+
+  def create_wiki_page title:, body:
+    Wiki::Commit.create_content!(
+        tag_name: TagName.create!(name: title),
+        body:,
+        created_by_user: user,
+        message: 'init')
+  end
+
+  it 'returns 422 when renaming wiki title to existing title' do
+    source = create_wiki_page(title: 'wiki_collision_source', body: 'source body')
+    create_wiki_page(title: 'wiki_collision_target', body: 'target body')
+
+    source_revision_count = source.wiki_revisions.count
+    source_version_count = source.wiki_versions.count
+    old_title = source.title
+    old_body = source.body
+
+    put "/wiki/#{ source.id }",
+        params: {
+          title: 'wiki_collision_target',
+          body: 'new body',
+          message: 'rename collision',
+          base_revision_id: source.current_revision.id,
+        },
+        headers: auth_headers(user)
+
+    expect(response).to have_http_status(:unprocessable_entity)
+
+    source.reload
+
+    expect(source.title).to eq(old_title)
+    expect(source.body).to eq(old_body)
+    expect(source.wiki_revisions.count).to eq(source_revision_count)
+    expect(source.wiki_versions.count).to eq(source_version_count)
+  end
+
+  it 'returns 422 when creating wiki with existing title' do
+    create_wiki_page(title: 'wiki_collision_create', body: 'already exists')
+
+    expect {
+      post '/wiki',
+           params: {
+             title: 'wiki_collision_create',
+             body: 'new body',
+             message: 'duplicate create',
+           },
+           headers: auth_headers(user)
+    }
+        .not_to change(WikiPage, :count)
+
+    expect(response).to have_http_status(:unprocessable_entity)
+  end
+end

backend/spec/services/wiki/commit_integrity_spec.rb

@@ -0,0 +1,173 @@
+require 'digest'
+require 'rails_helper'
+
+RSpec.describe Wiki::Commit do
+  let(:user) { create_member_user! }
+
+  def create_page title:, body: 'initial body'
+    described_class.create_content!(
+        tag_name: TagName.create!(name: title),
+        body:,
+        created_by_user: user,
+        message: 'init')
+  end
+
+  describe '.create_content!' do
+    it 'creates page, revision, and version with normalised body' do
+      expect {
+        described_class.create_content!(
+            tag_name: TagName.create!(name: 'commit_integrity_create'),
+            body: "a\r\nb\r\n\r\n",
+            created_by_user: user,
+            message: 'init')
+      }
+          .to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+
+      page = WikiPage.joins(:tag_name).find_by!(tag_names: { name: 'commit_integrity_create' })
+      revision = page.current_revision
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.body).to eq("a\nb")
+      expect(revision.lines_count).to eq(2)
+      expect(version.body).to eq("a\nb")
+      expect(version.reason).to eq('init')
+    end
+
+    it 'rejects body that becomes blank after normalisation' do
+      tag_name = TagName.create!(name: 'commit_integrity_blank')
+
+      expect {
+        described_class.create_content!(
+            tag_name:,
+            body: "\r\n\r\n",
+            created_by_user: user,
+            message: 'blank')
+      }
+          .to raise_error(ActiveRecord::RecordInvalid)
+
+      expect(WikiPage.where(tag_name:)).not_to exist
+    end
+  end
+
+  describe '.content!' do
+    it 'updates page body, revision, and version' do
+      page = create_page(title: 'commit_integrity_update', body: 'before')
+      current_id = page.current_revision.id
+
+      expect {
+        described_class.content!(
+            page:,
+            body: 'after',
+            created_user: user,
+            message: 'edit',
+            base_revision_id: current_id)
+      }
+          .to change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+
+      page.reload
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.body).to eq('after')
+      expect(version.body).to eq('after')
+      expect(version.reason).to eq('edit')
+    end
+
+    it 'does not record tag_version on body-only wiki update' do
+      tag_name = TagName.create!(name: 'commit_integrity_linked_tag')
+      tag = Tag.create!(tag_name:, category: :general)
+
+      page =
+          described_class.create_content!(
+              tag_name:,
+              body: 'before',
+              created_by_user: user,
+              message: 'init')
+
+      TagVersionRecorder.record!(
+          tag:,
+          event_type: :create,
+          created_by_user: user)
+
+      before_count = tag.reload.tag_versions.count
+
+      described_class.content!(
+          page:,
+          body: 'after',
+          created_user: user,
+          message: 'edit',
+          base_revision_id: page.current_revision.id)
+
+      expect(tag.reload.tag_versions.count).to eq(before_count)
+    end
+
+    it 'raises conflict and leaves page, revision, and version unchanged' do
+      page = create_page(title: 'commit_integrity_conflict', body: 'first')
+      stale_id = page.current_revision.id
+
+      described_class.content!(
+          page:,
+          body: 'second',
+          created_user: user,
+          message: 'second',
+          base_revision_id: stale_id)
+
+      page.reload
+      before_body = page.body
+      before_revision_count = page.wiki_revisions.count
+      before_version_count = page.wiki_versions.count
+
+      expect {
+        described_class.content!(
+            page:,
+            body: 'third',
+            created_user: user,
+            message: 'stale',
+            base_revision_id: stale_id)
+      }
+          .to raise_error(Wiki::Commit::Conflict)
+
+      page.reload
+      expect(page.body).to eq(before_body)
+      expect(page.wiki_revisions.count).to eq(before_revision_count)
+      expect(page.wiki_versions.count).to eq(before_version_count)
+    end
+
+    it 'deduplicates duplicated missing wiki lines' do
+      page = create_page(title: 'commit_integrity_dedup', body: 'before')
+      duplicated = 'commit_integrity_duplicate_line'
+
+      described_class.content!(
+          page:,
+          body: "#{ duplicated }\n#{ duplicated }",
+          created_user: user,
+          message: 'dedup',
+          base_revision_id: page.current_revision.id)
+
+      revision = page.reload.current_revision
+
+      expect(WikiLine.where(body: duplicated).count).to eq(1)
+      expect(revision.wiki_revision_lines.count).to eq(2)
+      expect(revision.wiki_revision_lines.pluck(:wiki_line_id).uniq.size).to eq(1)
+    end
+  end
+
+  describe '.redirect!' do
+    it 'raises because redirect revisions are deprecated' do
+      page = create_page(title: 'commit_integrity_redirect_source', body: 'source')
+      target = create_page(title: 'commit_integrity_redirect_target', body: 'target')
+
+      expect {
+        described_class.redirect!(
+            page:,
+            redirect_page: target,
+            created_user: user,
+            message: 'redirect',
+            base_revision_id: page.current_revision.id)
+      }
+          .to raise_error(RuntimeError, '廃止しました．')
+    end
+  end
+end

backend/spec/services/wiki/commit_spec.rb

@@ -0,0 +1,150 @@
+require 'rails_helper'
+
+RSpec.describe Wiki::Commit do
+  let(:user) { create_member_user! }
+
+  def create_page(title: 'commit_spec_page', body: 'initial body')
+    tag_name = TagName.create!(name: title)
+
+    Wiki::Commit.create_content!(
+        tag_name:,
+        body:,
+        created_by_user: user,
+        message: 'init')
+  end
+
+  describe '.content!' do
+    it 'stores normalised body in wiki_pages and wiki_versions' do
+      page = create_page(title: 'commit_normalised_page')
+
+      described_class.content!(
+        page:,
+        body: "a\r\nb\r\n\r\n",
+        created_user: user,
+        message: 'init'
+      )
+
+      page.reload
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(page.body).to eq("a\nb")
+      expect(version.body).to eq("a\nb")
+      expect(page.current_revision.lines_count).to eq(2)
+    end
+
+    it 'deduplicates duplicated missing wiki lines before upsert' do
+      page = create_page(title: 'commit_duplicate_line_page')
+      duplicated = 'commit_duplicate_line'
+
+      described_class.content!(
+        page:,
+        body: "#{ duplicated }\n#{ duplicated }",
+        created_user: user,
+        message: 'init'
+      )
+
+      page.reload
+
+      expect(WikiLine.where(body: duplicated).count).to eq(1)
+      expect(page.current_revision.lines_count).to eq(2)
+      expect(page.current_revision.wiki_revision_lines.count).to eq(2)
+    end
+
+    it 'raises conflict when base_revision_id is stale' do
+      page = create_page(title: 'commit_conflict_page')
+
+      first = described_class.content!(
+        page:,
+        body: 'first',
+        created_user: user,
+        message: 'first'
+      )
+
+      described_class.content!(
+        page:,
+        body: 'second',
+        created_user: user,
+        message: 'second',
+        base_revision_id: first.id
+      )
+
+      expect {
+        described_class.content!(
+          page:,
+          body: 'third',
+          created_user: user,
+          message: 'third',
+          base_revision_id: first.id
+        )
+      }.to raise_error(Wiki::Commit::Conflict)
+    end
+
+    it 'does not record tag version when corresponding tag has no versions' do
+      tag_name = TagName.create!(name: 'commit_linked_tag_without_versions')
+      tag = Tag.create!(tag_name:, category: :general)
+
+      page =
+          described_class.create_content!(
+              tag_name:,
+              body: 'before',
+              created_by_user: user,
+              message: 'init')
+
+      expect(tag.reload.tag_versions.count).to eq(0)
+
+      current_revision_id = page.current_revision.id
+
+      expect {
+        described_class.content!(
+            page:,
+            body: 'after',
+            created_user: user,
+            message: 'edit',
+            base_revision_id: current_revision_id)
+      }.to change(WikiVersion, :count).by(1)
+
+      expect(tag.reload.tag_versions.count).to eq(0)
+    end
+
+    it 'does not record tag version when corresponding tag has no versions' do
+      tag_name = TagName.create!(name: 'commit_linked_tag_without_versions')
+      tag = Tag.create!(tag_name:, category: :general)
+
+      page =
+          described_class.create_content!(
+              tag_name:,
+              body: 'before',
+              created_by_user: user,
+              message: 'init')
+
+      current_revision_id = page.current_revision.id
+
+      expect {
+        described_class.content!(
+            page:,
+            body: 'after',
+            created_user: user,
+            message: 'edit',
+            base_revision_id: current_revision_id)
+      }.to change(WikiVersion, :count).by(1)
+
+      expect(tag.reload.tag_versions.count).to eq(0)
+    end
+  end
+
+  describe '.redirect!' do
+    it 'raises because redirect revisions are deprecated' do
+      page = create_page(title: 'commit_redirect_source')
+      target = create_page(title: 'commit_redirect_target')
+
+      expect {
+        described_class.redirect!(
+          page:,
+          redirect_page: target,
+          created_user: user,
+          message: 'redirect'
+        )
+      }.to raise_error(RuntimeError, '廃止しました．')
+    end
+  end
+end

backend/spec/services/wiki_version_recorder_spec.rb

@@ -0,0 +1,99 @@
+require 'rails_helper'
+
+RSpec.describe WikiVersionRecorder do
+  let(:user) { create_member_user! }
+
+  def create_page title:, body: 'body'
+    Wiki::Commit.create_content!(
+        tag_name: TagName.create!(name: title),
+        body:,
+        created_by_user: user,
+        message: 'init')
+  end
+
+  describe '.record!' do
+    it 'records title, body, reason, user, and version number' do
+      page = create_page(title: 'wiki_version_recorder_basic', body: 'body')
+
+      expect {
+        described_class.record!(
+            page:,
+            event_type: :update,
+            reason: 'manual reason',
+            created_by_user: user)
+      }
+          .to change { page.reload.wiki_versions.count }.by(1)
+
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(version).to have_attributes(
+        version_no: 2,
+        event_type: 'update',
+        title: 'wiki_version_recorder_basic',
+        body: 'body',
+        reason: 'manual reason',
+        created_by_user_id: user.id
+      )
+    end
+
+    it 'does not create duplicated update version for identical snapshot' do
+      page = create_page(title: 'wiki_version_recorder_duplicate', body: 'body')
+
+      described_class.record!(
+          page:,
+          event_type: :update,
+          reason: nil,
+          created_by_user: user)
+
+      before_count = page.reload.wiki_versions.count
+
+      described_class.record!(
+          page:,
+          event_type: :update,
+          reason: nil,
+          created_by_user: user)
+
+      expect(page.reload.wiki_versions.count).to eq(before_count)
+    end
+
+    it 'creates update version when title changes' do
+      page = create_page(title: 'wiki_version_recorder_title_before', body: 'body')
+      page.tag_name.update!(name: 'wiki_version_recorder_title_after')
+
+      expect {
+        described_class.record!(
+            page:,
+            event_type: :update,
+            reason: 'rename',
+            created_by_user: user)
+      }
+          .to change { page.reload.wiki_versions.count }.by(1)
+
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(version.title).to eq('wiki_version_recorder_title_after')
+      expect(version.body).to eq('body')
+      expect(version.reason).to eq('rename')
+    end
+
+    it 'creates update version when body changes' do
+      page = create_page(title: 'wiki_version_recorder_body', body: 'before')
+      page.update!(body: 'after')
+
+      expect {
+        described_class.record!(
+            page:,
+            event_type: :update,
+            reason: 'body',
+            created_by_user: user)
+      }
+          .to change { page.reload.wiki_versions.count }.by(1)
+
+      version = page.wiki_versions.order(:version_no).last
+
+      expect(version.title).to eq('wiki_version_recorder_body')
+      expect(version.body).to eq('after')
+      expect(version.reason).to eq('body')
+    end
+  end
+end

backend/spec/services/youtube/api_client_spec.rb

@@ -0,0 +1,130 @@
+require 'rails_helper'
+
+RSpec.describe Youtube::ApiClient do
+  let(:api_key) { 'test-api-key' }
+  let(:client) { described_class.new(api_key:) }
+
+  describe '#search_videos' do
+    it 'calls YouTube search API with expected params' do
+      published_after = Time.zone.parse('2026-05-01 00:00:00')
+      published_before = Time.zone.parse('2026-05-02 00:00:00')
+
+      expect(client).to receive(:get_json).with(
+        '/search',
+        {
+          part: 'snippet',
+          type: 'video',
+          q: 'ぼざろクリーチャー',
+          order: 'date',
+          maxResults: 50,
+          regionCode: 'JP',
+          relevanceLanguage: 'ja',
+          publishedAfter: published_after.iso8601,
+          publishedBefore: published_before.iso8601,
+          pageToken: 'NEXT'
+        }
+      ).and_return({ 'items' => [] })
+
+      client.search_videos(
+        q: 'ぼざろクリーチャー',
+        published_after:,
+        published_before:,
+        page_token: 'NEXT'
+      )
+    end
+
+    it 'omits nil optional params' do
+      expect(client).to receive(:get_json).with(
+        '/search',
+        hash_excluding(:publishedAfter, :publishedBefore, :pageToken)
+      ).and_return({ 'items' => [] })
+
+      client.search_videos(q: 'ぼざろクリーチャー')
+    end
+  end
+
+  describe '#videos' do
+    it 'returns empty items when ids are empty' do
+      expect(client).not_to receive(:get_json)
+
+      expect(client.videos([])).to eq({ 'items' => [] })
+    end
+
+    it 'calls videos API with comma separated ids' do
+      expect(client).to receive(:get_json).with(
+        '/videos',
+        {
+          part: 'snippet,status,contentDetails',
+          id: 'video-1,video-2'
+        }
+      ).and_return({ 'items' => [] })
+
+      client.videos(['video-1', 'video-2'])
+    end
+  end
+
+  describe '#playlist_items' do
+    it 'calls playlistItems API with page token' do
+      expect(client).to receive(:get_json).with(
+        '/playlistItems',
+        {
+          part: 'snippet,contentDetails,status',
+          playlistId: 'PL123',
+          maxResults: 50,
+          pageToken: 'NEXT'
+        }
+      ).and_return({ 'items' => [] })
+
+      client.playlist_items(playlist_id: 'PL123', page_token: 'NEXT')
+    end
+
+    it 'omits page token when nil' do
+      expect(client).to receive(:get_json).with(
+        '/playlistItems',
+        {
+          part: 'snippet,contentDetails,status',
+          playlistId: 'PL123',
+          maxResults: 50
+        }
+      ).and_return({ 'items' => [] })
+
+      client.playlist_items(playlist_id: 'PL123')
+    end
+  end
+
+  describe '#channel' do
+    it 'calls channels API by id' do
+      expect(client).to receive(:get_json).with(
+        '/channels',
+        {
+          part: 'snippet,contentDetails',
+          id: 'UC123'
+        }
+      ).and_return({ 'items' => [] })
+
+      client.channel(id: 'UC123')
+    end
+
+    it 'calls channels API by handle' do
+      expect(client).to receive(:get_json).with(
+        '/channels',
+        {
+          part: 'snippet,contentDetails',
+          forHandle: '@some_handle'
+        }
+      ).and_return({ 'items' => [] })
+
+      client.channel(handle: '@some_handle')
+    end
+
+    it 'raises when neither id nor handle is given' do
+      expect { client.channel }.to raise_error(ArgumentError, 'id or handle is required')
+    end
+
+    it 'raises when both id and handle are given' do
+      expect do
+        client.channel(id: 'UC123', handle: '@some_handle')
+      end.to raise_error(ArgumentError, 'id or handle is required')
+    end
+  end
+end

backend/spec/services/youtube/sync_spec.rb

@@ -0,0 +1,310 @@
+require 'rails_helper'
+
+RSpec.describe Youtube::Sync do
+  let(:client) { instance_double(Youtube::ApiClient) }
+  let(:sync) { described_class.new(client:) }
+
+  before do
+    allow(PostVersionRecorder).to receive(:record!)
+    allow(PostVersionRecorder).to receive(:ensure_snapshot!)
+    allow(sync).to receive(:attach_thumbnail_if_needed!)
+  end
+
+  describe '#sync!' do
+    it 'returns without fetching video details when no video ids are discovered' do
+      allow(sync).to receive(:query_terms).and_return([])
+      allow(sync).to receive(:playlist_ids).and_return([])
+
+      expect(client).not_to receive(:videos)
+
+      sync.sync!
+    end
+
+    it 'discovers ids from search and all playlist pages' do
+      allow(sync).to receive(:query_terms).and_return(['ぼざろクリーチャー'])
+      allow(sync).to receive(:playlist_ids).and_return(['PL123'])
+      allow(sync).to receive(:sync_since).and_return(Time.zone.parse('2026-05-01 00:00:00'))
+
+      allow(client).to receive(:search_videos).with(
+        q: 'ぼざろクリーチャー',
+        published_after: Time.zone.parse('2026-05-01 00:00:00')
+      ).and_return({
+        'items' => [
+          {
+            'id' => {
+              'videoId' => 'search-video-1'
+            }
+          }
+        ]
+      })
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: nil
+      ).and_return({
+        'items' => [
+          {
+            'contentDetails' => {
+              'videoId' => 'playlist-video-1'
+            }
+          }
+        ],
+        'nextPageToken' => 'NEXT'
+      })
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: 'NEXT'
+      ).and_return({
+        'items' => [
+          {
+            'snippet' => {
+              'resourceId' => {
+                'videoId' => 'playlist-video-2'
+              }
+            }
+          }
+        ]
+      })
+
+      expect(client).to receive(:videos).with(
+        satisfy do |ids|
+          ids.sort == ['playlist-video-1', 'playlist-video-2', 'search-video-1']
+        end
+      ).and_return({ 'items' => [] })
+
+      sync.sync!
+    end
+
+    it 'creates a YouTube post with default tags and no_deerjikist when no deerjikist mapping exists' do
+      Tag.tagme
+      Tag.bot
+      Tag.youtube
+      Tag.video
+      Tag.no_deerjikist
+
+      allow(sync).to receive(:query_terms).and_return([])
+      allow(sync).to receive(:playlist_ids).and_return(['PL123'])
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: nil
+      ).and_return({
+        'items' => [
+          {
+            'contentDetails' => {
+              'videoId' => 'video-1'
+            }
+          }
+        ]
+      })
+
+      allow(client).to receive(:videos).with(['video-1']).and_return({
+        'items' => [
+          youtube_video_item(
+            id: 'video-1',
+            title: 'YouTube テスト動画',
+            channel_id: 'UC_NO_MAPPING'
+          )
+        ]
+      })
+
+      expect do
+        sync.sync!
+      end.to change(Post, :count).by(1)
+
+      post = Post.find_by!(url: 'https://www.youtube.com/watch?v=video-1')
+      tag_ids = post.tags.pluck(:id)
+
+      expect(post.title).to eq('YouTube テスト動画')
+      expect(post.uploaded_user_id).to be_nil
+      expect(post.original_created_from).to eq(Time.zone.parse('2026-05-01 12:34:00'))
+      expect(post.original_created_before).to eq(Time.zone.parse('2026-05-01 12:35:00'))
+
+      expect(tag_ids).to include(Tag.tagme.id)
+      expect(tag_ids).to include(Tag.bot.id)
+      expect(tag_ids).to include(Tag.youtube.id)
+      expect(tag_ids).to include(Tag.video.id)
+      expect(tag_ids).to include(Tag.no_deerjikist.id)
+
+      expect(PostVersionRecorder).to have_received(:record!).with(
+        post:,
+        event_type: :create,
+        created_by_user: nil
+      )
+    end
+
+    it 'uses deerjikist tag when channel id is mapped' do
+      Tag.tagme
+      Tag.bot
+      Tag.youtube
+      Tag.video
+      Tag.no_deerjikist
+
+      deerjikist_tag = Tag.find_or_create_by_tag_name!('テスト投稿者', category: :deerjikist)
+      Deerjikist.create!(
+        platform: 'youtube',
+        code: 'UC_MAPPED',
+        tag: deerjikist_tag
+      )
+
+      allow(sync).to receive(:query_terms).and_return([])
+      allow(sync).to receive(:playlist_ids).and_return(['PL123'])
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: nil
+      ).and_return({
+        'items' => [
+          {
+            'contentDetails' => {
+              'videoId' => 'video-1'
+            }
+          }
+        ]
+      })
+
+      allow(client).to receive(:videos).with(['video-1']).and_return({
+        'items' => [
+          youtube_video_item(
+            id: 'video-1',
+            title: 'YouTube テスト動画',
+            channel_id: 'UC_MAPPED'
+          )
+        ]
+      })
+
+      sync.sync!
+
+      post = Post.find_by!(url: 'https://www.youtube.com/watch?v=video-1')
+      tag_ids = post.tags.pluck(:id)
+
+      expect(tag_ids).to include(deerjikist_tag.id)
+      expect(tag_ids).not_to include(Tag.no_deerjikist.id)
+    end
+
+    it 'removes no_deerjikist when deerjikist mapping is added later' do
+      Tag.no_deerjikist
+
+      post = Post.create!(
+        title: '旧タイトル',
+        url: 'https://www.youtube.com/watch?v=video-1',
+        uploaded_user_id: nil,
+        original_created_from: Time.zone.parse('2026-05-01 00:00:00'),
+        original_created_before: Time.zone.parse('2026-05-01 00:01:00')
+      )
+      PostTag.create!(post:, tag: Tag.no_deerjikist)
+
+      deerjikist_tag = Tag.find_or_create_by_tag_name!('後から判明した投稿者', category: :deerjikist)
+      Deerjikist.create!(
+        platform: 'youtube',
+        code: 'UC_MAPPED_LATER',
+        tag: deerjikist_tag
+      )
+
+      allow(sync).to receive(:query_terms).and_return([])
+      allow(sync).to receive(:playlist_ids).and_return(['PL123'])
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: nil
+      ).and_return({
+        'items' => [
+          {
+            'contentDetails' => {
+              'videoId' => 'video-1'
+            }
+          }
+        ]
+      })
+
+      allow(client).to receive(:videos).with(['video-1']).and_return({
+        'items' => [
+          youtube_video_item(
+            id: 'video-1',
+            title: '新タイトル',
+            channel_id: 'UC_MAPPED_LATER'
+          )
+        ]
+      })
+
+      sync.sync!
+
+      post.reload
+      tag_ids = post.tags.pluck(:id)
+
+      expect(post.title).to eq('新タイトル')
+      expect(tag_ids).to include(deerjikist_tag.id)
+      expect(tag_ids).not_to include(Tag.no_deerjikist.id)
+
+      expect(PostVersionRecorder).to have_received(:ensure_snapshot!).with(
+        post,
+        created_by_user: nil
+      )
+      expect(PostVersionRecorder).to have_received(:record!).with(
+        post:,
+        event_type: :update,
+        created_by_user: nil
+      )
+    end
+
+    it 'matches existing youtu.be URL and does not create duplicate post' do
+      post = Post.create!(
+        title: '旧タイトル',
+        url: 'https://youtu.be/video-1',
+        uploaded_user_id: nil,
+        original_created_from: Time.zone.parse('2026-05-01 00:00:00'),
+        original_created_before: Time.zone.parse('2026-05-01 00:01:00')
+      )
+
+      allow(sync).to receive(:query_terms).and_return([])
+      allow(sync).to receive(:playlist_ids).and_return(['PL123'])
+
+      allow(client).to receive(:playlist_items).with(
+        playlist_id: 'PL123',
+        page_token: nil
+      ).and_return({
+        'items' => [
+          {
+            'contentDetails' => {
+              'videoId' => 'video-1'
+            }
+          }
+        ]
+      })
+
+      allow(client).to receive(:videos).with(['video-1']).and_return({
+        'items' => [
+          youtube_video_item(
+            id: 'video-1',
+            title: '新タイトル',
+            channel_id: 'UC_NO_MAPPING'
+          )
+        ]
+      })
+
+      expect do
+        sync.sync!
+      end.not_to change(Post, :count)
+
+      expect(post.reload.title).to eq('新タイトル')
+    end
+  end
+
+  def youtube_video_item(id:, title:, channel_id:)
+    {
+      'id' => id,
+      'snippet' => {
+        'title' => title,
+        'channelId' => channel_id,
+        'publishedAt' => '2026-05-01T12:34:56Z',
+        'thumbnails' => {
+          'high' => {
+            'url' => "https://img.youtube.com/#{id}.jpg"
+          }
+        },
+        'tags' => ['tag-a', 'tag-b']
+      }
+    }
+  end
+end

backend/spec/services/youtube/video_item_spec.rb

@@ -0,0 +1,93 @@
+require 'rails_helper'
+
+RSpec.describe Youtube::VideoItem do
+  describe '#initialize' do
+    it 'extracts fields from YouTube video API item' do
+      item = {
+        'id' => 'video-1',
+        'snippet' => {
+          'title' => 'テスト動画',
+          'channelId' => 'UC123',
+          'publishedAt' => '2026-05-01T12:34:56Z',
+          'tags' => ['tag-a', 'tag-b'],
+          'thumbnails' => {
+            'high' => {
+              'url' => 'https://img.youtube.com/high.jpg'
+            },
+            'medium' => {
+              'url' => 'https://img.youtube.com/medium.jpg'
+            }
+          }
+        }
+      }
+
+      video = described_class.new(item)
+
+      expect(video.id).to eq('video-1')
+      expect(video.title).to eq('テスト動画')
+      expect(video.channel_id).to eq('UC123')
+      expect(video.published_at).to eq(Time.iso8601('2026-05-01T12:34:56Z'))
+      expect(video.thumbnail_url).to eq('https://img.youtube.com/high.jpg')
+      expect(video.raw_tags).to eq(['tag-a', 'tag-b'])
+      expect(video.url).to eq('https://www.youtube.com/watch?v=video-1')
+    end
+
+    it 'uses highest priority thumbnail' do
+      item = {
+        'id' => 'video-1',
+        'snippet' => {
+          'title' => 'テスト動画',
+          'channelId' => 'UC123',
+          'publishedAt' => '2026-05-01T12:34:56Z',
+          'thumbnails' => {
+            'default' => {
+              'url' => 'https://img.youtube.com/default.jpg'
+            },
+            'standard' => {
+              'url' => 'https://img.youtube.com/standard.jpg'
+            },
+            'maxres' => {
+              'url' => 'https://img.youtube.com/maxres.jpg'
+            }
+          }
+        }
+      }
+
+      video = described_class.new(item)
+
+      expect(video.thumbnail_url).to eq('https://img.youtube.com/maxres.jpg')
+    end
+
+    it 'falls back to empty raw tags' do
+      item = {
+        'id' => 'video-1',
+        'snippet' => {
+          'title' => 'テスト動画',
+          'channelId' => 'UC123',
+          'publishedAt' => '2026-05-01T12:34:56Z',
+          'thumbnails' => {}
+        }
+      }
+
+      video = described_class.new(item)
+
+      expect(video.raw_tags).to eq([])
+    end
+
+    it 'returns nil thumbnail when no thumbnail exists' do
+      item = {
+        'id' => 'video-1',
+        'snippet' => {
+          'title' => 'テスト動画',
+          'channelId' => 'UC123',
+          'publishedAt' => '2026-05-01T12:34:56Z',
+          'thumbnails' => {}
+        }
+      }
+
+      video = described_class.new(item)
+
+      expect(video.thumbnail_url).to be_nil
+    end
+  end
+end

backend/spec/support/test_records.rb

@@ -2,14 +2,12 @@ module TestRecords
   def create_member_user!
     User.create!(name: 'spec user',
                  inheritance_code: SecureRandom.hex(16),
-                 role: 'member',
-                 banned: false)
+                 role: 'member')
   end
 
   def create_admin_user!
     User.create!(name: 'spec admin',
                  inheritance_code: SecureRandom.hex(16),
-                 role: 'admin',
-                 banned: false)
+                 role: 'admin')
   end
 end

backend/spec/tasks/nico_export_spec.rb

@@ -0,0 +1,100 @@
+require 'rails_helper'
+require 'rake'
+require 'open3'
+
+RSpec.describe 'nico:export' do
+  let(:task) { Rake::Task['nico:export'] }
+  let(:success_status) { instance_double(Process::Status, success?: true) }
+  let(:failure_status) { instance_double(Process::Status, success?: false) }
+
+  def create_post(url)
+    Post.create!(url:)
+  end
+
+  before(:all) do
+    Rails.application.load_tasks unless Rake::Task.task_defined?('nico:export')
+  end
+
+  before do
+    task.reenable
+
+    allow(ENV).to receive(:fetch).with('MYSQL_USER').and_return('mysql-user')
+    allow(ENV).to receive(:fetch).with('MYSQL_PASS').and_return('mysql-pass')
+    allow(ENV).to receive(:fetch).with('NIZIKA_NICO_PATH').and_return('/srv/nizika-nico')
+  end
+
+  describe 'export' do
+    it 'exports nicovideo ids to shared nico DB' do
+      create_post('https://www.nicovideo.jp/watch/sm12345?ref=foo')
+      create_post('https://www.nicovideo.jp/watch/so67890#comments')
+      create_post('https://www.nicovideo.jp/watch/nm24680')
+      create_post('https://example.com/watch/sm99999')
+
+      expect(Open3).to receive(:capture3) do |env, *args, **kwargs|
+        expect(env).to eq(
+          {
+            'MYSQL_USER' => 'mysql-user',
+            'MYSQL_PASS' => 'mysql-pass',
+          },
+        )
+
+        expect(args.take(3)).to eq(
+          [
+            'python3',
+            '-m',
+            'tracked_videos.put_bulk_upsert',
+          ],
+        )
+
+        expect(args.drop(3)).to contain_exactly(
+          'sm12345',
+          'so67890',
+          'nm24680',
+        )
+
+        expect(kwargs).to eq(chdir: '/srv/nizika-nico')
+
+        ['', '', success_status]
+      end
+
+      task.invoke
+    end
+
+    it 'deduplicates video ids' do
+      create_post('https://www.nicovideo.jp/watch/sm12345')
+      create_post('https://www.nicovideo.jp/watch/sm12345?from=1')
+
+      expect(Open3).to receive(:capture3) do |_env, *args, **_kwargs|
+        expect(args.drop(3)).to eq(['sm12345'])
+
+        ['', '', success_status]
+      end
+
+      task.invoke
+    end
+
+    it 'does not call python when there are no nicovideo posts' do
+      create_post('https://example.com/watch/sm12345')
+
+      expect(Open3).not_to receive(:capture3)
+
+      task.invoke
+    end
+
+    it 'raises stderr when python command fails' do
+      create_post('https://www.nicovideo.jp/watch/sm12345')
+
+      allow(Open3).to receive(:capture3).and_return(
+        [
+          '',
+          'bulk upsert failed',
+          failure_status,
+        ],
+      )
+
+      expect {
+        task.invoke
+      }.to raise_error(RuntimeError, 'bulk upsert failed')
+    end
+  end
+end

backend/spec/tasks/nico_sync_spec.rb

@@ -104,7 +104,7 @@ RSpec.describe "nico:sync" do
       url: post.url,
       thumbnail_base: post.thumbnail_base,
       tags: snapshot_tags(post),
-      parent: post.parent,
+      parent_post_ids: post.snapshot_parent_post_ids.join(' '),
       original_created_from: post.original_created_from,
       original_created_before: post.original_created_before,
       created_at: Time.current,
@@ -214,4 +214,108 @@ RSpec.describe "nico:sync" do
     expect(version.event_type).to eq('create')
     expect(version.tags).to eq(snapshot_tags(post.reload))
   end
+
+  it '新規 nico tag に nico tag version を作る' do
+    Tag.bot
+    Tag.tagme
+    Tag.niconico
+    Tag.video
+    Tag.no_deerjikist
+
+    stub_python([{
+      'code' => 'sm9',
+      'title' => 't',
+      'tags' => ['AAA'],
+      'uploaded_at' => '2026-01-01 12:34:56'
+    }])
+
+    allow(URI).to receive(:open).and_return(StringIO.new('<html></html>'))
+
+    expect {
+      run_rake_task('nico:sync')
+    }.to change(NicoTagVersion, :count).by(1)
+
+    nico_tag = Tag.joins(:tag_name).find_by!(tag_names: { name: 'nico:AAA' })
+    version = nico_tag.nico_tag_versions.order(:version_no).last
+
+    expect(version.version_no).to eq(1)
+    expect(version.event_type).to eq('create')
+    expect(version.name).to eq('nico:AAA')
+    expect(version.created_by_user).to be_nil
+  end
+
+  it '既存 post に version が無い場合は create snapshot を補う' do
+    post = Post.create!(
+      title: 'old',
+      url: 'https://www.nicovideo.jp/watch/sm9',
+      uploaded_user: nil
+    )
+
+    kept_general = create_tag!('spec_kept_without_version', category: 'general')
+    PostTag.create!(post: post, tag: kept_general)
+
+    Tag.bot
+    Tag.tagme
+    Tag.no_deerjikist
+
+    stub_python([{
+      'code' => 'sm9',
+      'title' => 'changed title',
+      'tags' => ['AAA'],
+      'uploaded_at' => '2026-01-01 12:34:56'
+    }])
+
+    allow(URI).to receive(:open).and_return(StringIO.new('<html></html>'))
+
+    expect {
+      run_rake_task('nico:sync')
+    }.to change { post.reload.post_versions.count }.by(1)
+
+    versions = post.reload.post_versions.order(:version_no)
+
+    expect(versions.map(&:event_type)).to eq(['create'])
+    expect(versions.first.title).to eq('changed title')
+    expect(versions.first.tags).to eq(snapshot_tags(post.reload))
+  end
+
+  it '既存 version がある post には update version を作る' do
+    post = Post.create!(
+      title: 'old',
+      url: 'https://www.nicovideo.jp/watch/sm9',
+      uploaded_user: nil
+    )
+
+    kept_general = create_tag!('spec_kept_with_version', category: 'general')
+    PostTag.create!(post: post, tag: kept_general)
+
+    PostVersionRecorder.record!(
+      post: post,
+      event_type: :create,
+      created_by_user: nil
+    )
+
+    Tag.bot
+    Tag.tagme
+    Tag.no_deerjikist
+
+    stub_python([{
+      'code' => 'sm9',
+      'title' => 'changed title',
+      'tags' => ['AAA'],
+      'uploaded_at' => '2026-01-01 12:34:56'
+    }])
+
+    allow(URI).to receive(:open).and_return(StringIO.new('<html></html>'))
+
+    expect {
+      run_rake_task('nico:sync')
+    }.to change { post.reload.post_versions.count }.by(1)
+
+    versions = post.reload.post_versions.order(:version_no)
+
+    expect(versions.map(&:event_type)).to eq(['create', 'update'])
+    expect(versions.first.title).to eq('old')
+    expect(versions.second.title).to eq('changed title')
+    expect(versions.second.tags).to eq(snapshot_tags(post.reload))
+  end
 end

backend/spec/tasks/post_sync_spec.rb

@@ -0,0 +1,25 @@
+require 'rails_helper'
+require 'rake'
+
+RSpec.describe 'post:sync' do
+  around do |example|
+    original_application = Rake.application
+    Rake.application = Rake::Application.new
+
+    Rake::Task.define_task(:environment)
+    load Rails.root.join('lib/tasks/sync_posts.rake')
+
+    example.run
+  ensure
+    Rake.application = original_application
+  end
+
+  it 'runs Youtube::Sync' do
+    sync = instance_double(Youtube::Sync)
+
+    expect(Youtube::Sync).to receive(:new).once.and_return(sync)
+    expect(sync).to receive(:sync!).once
+
+    Rake::Task['post:sync'].invoke
+  end
+end

frontend/src/App.tsx

@@ -10,6 +10,7 @@ import RouteBlockerOverlay from '@/components/RouteBlockerOverlay'
 import TopNav from '@/components/TopNav'
 import { Toaster } from '@/components/ui/toaster'
 import { apiPost, isApiError } from '@/lib/api'
+import DeerjikistDetailPage from '@/pages/deerjikists/DeerjikistDetailPage'
 import MaterialBasePage from '@/pages/materials/MaterialBasePage'
 import MaterialDetailPage from '@/pages/materials/MaterialDetailPage'
 import MaterialListPage from '@/pages/materials/MaterialListPage'
@@ -26,6 +27,8 @@ import PostNewPage from '@/pages/posts/PostNewPage'
 import PostSearchPage from '@/pages/posts/PostSearchPage'
 import ServiceUnavailable from '@/pages/ServiceUnavailable'
 import SettingPage from '@/pages/users/SettingPage'
+import TagDetailPage from '@/pages/tags/TagDetailPage'
+import TagHistoryPage from '@/pages/tags/TagHistoryPage'
 import TagListPage from '@/pages/tags/TagListPage'
 import TheatreDetailPage from '@/pages/theatres/TheatreDetailPage'
 import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
@@ -55,7 +58,10 @@ const RouteTransitionWrapper = ({ user, setUser }: {
 	  <Route path="/posts/:id" element={<PostDetailRoute user={user}/>}/>
 	  <Route path="/posts/changes" element={<PostHistoryPage/>}/>
 	  <Route path="/tags" element={<TagListPage/>}/>
+	  <Route path="/tags/:id" element={<TagDetailPage/>}/>
+	  <Route path="/tags/:id/deerjikists" element={<DeerjikistDetailPage/>}/>
 	  <Route path="/tags/nico" element={<NicoTagListPage user={user}/>}/>
+	  <Route path="/tags/changes" element={<TagHistoryPage/>}/>
 	  <Route path="/theatres/:id" element={<TheatreDetailPage/>}/>
 	  <Route path="/materials" element={<MaterialBasePage/>}>
 	    <Route index element={<MaterialListPage/>}/>

frontend/src/components/DraggableDroppableTagRow.tsx

@@ -90,7 +90,9 @@ export default (({ tag, nestLevel, pathKey, parentTagId, suppressClickRef, sp }:
 	  className={cn ('rounded select-none', over && 'ring-2 ring-offset-2')}
 	  {...attributes}
 	  {...listeners}>
-	<motion.div layoutId={`tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
+	<motion.div
+	    transition={{ layout: { duration: .2, ease: 'easeOut' } }}
+	    layoutId={`tag-${ sp ? 'sp-' : '' }${ tag.id }`}>
 	  <TagLink tag={tag} nestLevel={nestLevel}/>
 	</motion.div>
       </div>)

frontend/src/components/PostEditForm.tsx

@@ -4,6 +4,7 @@ import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import Label from '@/components/common/Label'
 import { Button } from '@/components/ui/button'
+import { toast } from '@/components/ui/use-toast'
 import { apiPut } from '@/lib/api'
 
 import type { FC } from 'react'
@@ -35,20 +36,34 @@ export default (({ post, onSave }: Props) => {
       useState<string | null> (post.originalCreatedBefore)
   const [originalCreatedFrom, setOriginalCreatedFrom] =
       useState<string | null> (post.originalCreatedFrom)
-  const [title, setTitle] = useState (post.title)
+  const [parentPostIds, setParentPostIds] =
+      useState ((post.parentPosts ?? []).map (p => p.id).join (' '))
   const [tags, setTags] = useState<string> ('')
+  const [title, setTitle] = useState (post.title)
 
   const handleSubmit = async () => {
+    try
+    {
       const data = await apiPut<Post> (
 	  `/posts/${ post.id }`,
-	{ title, tags, original_created_from: originalCreatedFrom,
+	  { title, tags, parent_post_ids: parentPostIds,
+	    original_created_from: originalCreatedFrom,
 	    original_created_before: originalCreatedBefore },
 	  { headers: { 'Content-Type': 'multipart/form-data' } })
       onSave ({ ...post,
 		title:                  data.title,
 		tags:                   data.tags,
+		parentPosts:            data.parentPosts,
+		childPosts:             data.childPosts,
+		siblingPosts:           data.siblingPosts,
 		originalCreatedFrom:    data.originalCreatedFrom,
 		originalCreatedBefore:  data.originalCreatedBefore } as Post)
+      toast ({ description: '更新しました．' })
+    }
+    catch
+    {
+      toast ({ description: '更新はできなかったよ……' })
+    }
   }
 
   useEffect (() => {
@@ -62,10 +77,20 @@ export default (({ post, onSave }: Props) => {
 	  <Label>タイトル</Label>
 	  <input type="text"
 		 className="w-full border rounded p-2"
-		 value={title}
+		 value={title ?? ''}
 		 onChange={ev => setTitle (ev.target.value)}/>
 	</div>
 
+	{/* 親投稿 */}
+	<div>
+	  <Label>親投稿</Label>
+	  <input
+	      type="text"
+	      value={parentPostIds}
+	      onChange={e => setParentPostIds (e.target.value)}
+	      className="w-full border p-2 rounded"/>
+	</div>
+
 	{/* タグ */}
 	<PostFormTagsArea tags={tags} setTags={setTags}/>
 

frontend/src/components/PostList.tsx

@@ -3,6 +3,7 @@ import { useRef } from 'react'
 import { useLocation } from 'react-router-dom'
 
 import PrefetchLink from '@/components/PrefetchLink'
+import { cn } from '@/lib/utils'
 import { useSharedTransitionStore } from '@/stores/sharedTransitionStore'
 
 import type { FC, MouseEvent } from 'react'
@@ -39,8 +40,10 @@ export default (({ posts, onClick }: Props) => {
 		<motion.div
 		    ref={cardRef}
 		    layoutId={layoutId}
-		    className="w-full h-full overflow-hidden rounded-xl shadow
-			       transform-gpu will-change-transform"
+		    className={cn ('w-full h-full overflow-hidden rounded-xl shadow',
+				   'transform-gpu will-change-transform',
+				   (post.childPosts ?? []).length > 0 && 'outline-4 outline-green-500',
+				   (post.parentPosts ?? []).length > 0 && 'ring-4 ring-yellow-500')}
 		    whileHover={{ scale: 1.02 }}
 		    onLayoutAnimationStart={() => {
 		      if (!(cardRef.current))

frontend/src/components/TagDetailSidebar.tsx

@@ -313,7 +313,9 @@ export default (({ post, sp }: Props) => {
 	  {CATEGORIES.map ((cat: Category) => ((tags[cat] ?? []).length > 0 || dragging) && (
 	      <div className="my-3" key={cat}>
 		<SubsectionTitle>
-		  <motion.div layoutId={`tag-${ sp ? 'sp-' : '' }${ cat }`}>
+		  <motion.div
+		      layoutId={`tag-${ sp ? 'sp-' : '' }${ cat }`}
+		      transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
 		    {CATEGORY_NAMES[cat]}
 		  </motion.div>
 		</SubsectionTitle>
@@ -325,7 +327,9 @@ export default (({ post, sp }: Props) => {
 		</ul>
 	      </div>))}
 	  {post && (
-	      <motion.div layoutId={`post-info-${ sp }`}>
+	      <motion.div
+		  layoutId={`post-info-${ sp }`}
+		  transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
 		<SectionTitle>情報</SectionTitle>
 		<ul>
 		  <li>Id.: {post.id}</li>

frontend/src/components/TagLink.tsx

@@ -45,9 +45,9 @@ export default (({ tag,
       <>
 	{(linkFlg && withWiki) && (
 	    <span className="mr-1">
-	      {(tag.materialId != null || tag.hasWiki)
+	      {(tag.materialId != null || tag.hasWiki || tag.hasDeerjikists)
 	       ? (
-		  tag.materialId == null
+		  tag.materialId == null && !(tag.hasDeerjikists)
 		  ? (
 		      <PrefetchLink
 			  to={`/wiki/${ encodeURIComponent (tag.name) }`}
@@ -55,11 +55,19 @@ export default (({ tag,
 			?
 		      </PrefetchLink>)
 		  : (
+		      tag.materialId != null
+		      ? (
 			  <PrefetchLink
 			      to={`/materials/${ tag.materialId }`}
 			      className={linkClass}>
 			    ?
-		      </PrefetchLink>))
+			  </PrefetchLink>)
+		      : (
+			  <PrefetchLink
+			      to={`/tags/${ tag.id }/deerjikists`}
+			      className={linkClass}>
+			    ?
+			  </PrefetchLink>)))
 	       : (
 		  ['character', 'material'].includes (tag.category)
 		  ? (
@@ -70,6 +78,16 @@ export default (({ tag,
 			  title={`${ tag.name } 素材情報が存在しません．`}>
 			!
 		      </PrefetchLink>)
+		  : (
+		      tag.category === 'deerjikist'
+		      ? (
+			  <PrefetchLink
+			      to={`/tags/${ tag.id }/deerjikists`}
+			      className="animate-[wiki-blink_.25s_steps(2,end)_infinite]
+					 dark:animate-[wiki-blink-dark_.25s_steps(2,end)_infinite]"
+			      title={`${ tag.name } に関する情報が存在しません．`}>
+			    !
+			  </PrefetchLink>)
 		      : (
 			  <PrefetchLink
 			      to={`/wiki/${ encodeURIComponent (tag.name) }`}
@@ -77,7 +95,7 @@ export default (({ tag,
 					 dark:animate-[wiki-blink-dark_.25s_steps(2,end)_infinite]"
 			      title={`${ tag.name } Wiki が存在しません．`}>
 			    !
-		      </PrefetchLink>))}
+			  </PrefetchLink>)))}
 	    </span>)}
 	{nestLevel > 0 && (
 	    <span

frontend/src/components/TopNav.tsx

@@ -8,7 +8,7 @@ import PrefetchLink from '@/components/PrefetchLink'
 import TopNavUser from '@/components/TopNavUser'
 import { WikiIdBus } from '@/lib/eventBus/WikiIdBus'
 import { tagsKeys, wikiKeys } from '@/lib/queryKeys'
-import { fetchTagByName } from '@/lib/tags'
+import { fetchTag, fetchTagByName } from '@/lib/tags'
 import { cn } from '@/lib/utils'
 import { fetchWikiPage } from '@/lib/wiki'
 
@@ -29,6 +29,8 @@ export const menuOutline = ({ tag, wikiId, user, pathName }: {
   const wikiPageFlg = Boolean (/^\/wiki\/(?!new|changes)[^\/]+/.test (pathName) && wikiId)
   const wikiTitle = pathName.split ('/')[2] ?? ''
 
+  const tagFlg = /^\/tags\/\d+/.test (pathName)
+
   return [
       { name: '広場', to: '/posts', subMenu: [
 	  { name: '一覧', to: '/posts' },
@@ -38,10 +40,15 @@ export const menuOutline = ({ tag, wikiId, user, pathName }: {
 	  { name: 'ヘルプ', to: '/wiki/ヘルプ:広場' }] },
       { name: 'タグ', to: '/tags', subMenu: [
 	  { name: 'マスタ', to: '/tags' },
-	  { name: '別名タグ', to: '/tags/aliases', visible: false },
-	  { name: '上位タグ', to: '/tags/implications', visible: false },
 	  { name: 'ニコニコ連携', to: '/tags/nico' },
-	  { name: 'ヘルプ', to: '/wiki/ヘルプ:タグ' }] },
+	  { name: '履歴', to: '/tags/changes' },
+	  { name: 'ヘルプ', to: '/wiki/ヘルプ:タグ' },
+	  { component: <Separator/>, visible: tagFlg },
+	  { name: `広場 (${ postCount || 0 })`,
+	    to: `/posts?tags=${ encodeURIComponent (tag?.name ?? '') }`,
+	    visible: tagFlg },
+	  { name: '履歴', to: `/tags/changes?id=${ tag?.id }`,
+	    visible: tagFlg && tag?.category !== 'nico' }] },
       { name: '素材', to: '/materials', visible: false, subMenu: [
 	  { name: '一覧', to: '/materials' },
 	  { name: '検索', to: '/materials/search', visible: false }, 
@@ -114,12 +121,14 @@ export default (({ user }: Props) => {
       queryKey: wikiKeys.show (wikiIdStr, { }),
       queryFn: () => fetchWikiPage (wikiIdStr, { }) })
 
-  const effectiveTitle = wikiPage?.title ?? ''
+  const tagFlg = /^\/tags\/\d+/.test (location.pathname)
+  const effectiveTitle = (tagFlg ? location.pathname.split ('/')[2] : wikiPage?.title) ?? ''
 
   const { data: tag } = useQuery ({
       enabled: Boolean (effectiveTitle),
       queryKey: tagsKeys.show (effectiveTitle),
-      queryFn: () => fetchTagByName (effectiveTitle) })
+      queryFn: () => (tagFlg ? fetchTag : fetchTagByName) (effectiveTitle) })
+
 
   const menu = menuOutline ({ tag, wikiId, user, pathName: location.pathname })
   const visibleMenu = menu.filter ((item): item is MenuVisibleItem => item.visible ?? true)

frontend/src/consts.ts

@@ -1,4 +1,4 @@
-import type { Category } from 'types'
+import type { Category, Platform } from 'types'
 
 export const LIGHT_COLOUR_SHADE = 800
 export const DARK_COLOUR_SHADE = 300
@@ -31,6 +31,11 @@ export const FETCH_POSTS_ORDER_FIELDS = [
     'updated_at',
     ] as const
 
+export const PLATFORMS = ['nico', 'youtube'] as const
+
+export const PLATFORM_NAMES: Record<Platform, string> =
+    { nico: 'ニコニコ', youtube: 'YouTube' } as const
+
 export const TAG_COLOUR = {
     deerjikist: 'rose',
     meme:       'purple',

frontend/src/lib/posts.ts

@@ -1,6 +1,6 @@
 import { apiDelete, apiGet, apiPost } from '@/lib/api'
 
-import type { FetchPostsParams, Post, PostTagChange } from '@/types'
+import type { FetchPostsParams, Post, PostVersion } from '@/types'
 
 
 export const fetchPosts = async (
@@ -29,15 +29,15 @@ export const fetchPost = async (id: string): Promise<Post> => await apiGet (`/po
 
 
 export const fetchPostChanges = async (
-    { id, tag, page, limit }: {
-	id?:    string
+    { post, tag, page, limit }: {
+	post?:  string
 	tag?:   string
 	page:   number
 	limit:  number },
 ): Promise<{
-    changes:  PostTagChange[]
+    versions: PostVersion[]
     count:    number }> =>
-	await apiGet ('/posts/changes', { params: { ...(id && { id }),
+	await apiGet ('/posts/versions', { params: { ...(post && { post }),
 						     ...(tag && { tag }),
 						     page, limit } })
 

frontend/src/lib/prefetchers.ts

@@ -3,7 +3,7 @@ import { match } from 'path-to-regexp'
 
 import { fetchPost, fetchPosts, fetchPostChanges } from '@/lib/posts'
 import { postsKeys, tagsKeys, wikiKeys } from '@/lib/queryKeys'
-import { fetchTagByName, fetchTag, fetchTags } from '@/lib/tags'
+import { fetchTagByName, fetchTag, fetchTagChanges, fetchTags } from '@/lib/tags'
 import { fetchWikiPage,
 	 fetchWikiPageByTitle,
 	 fetchWikiPages } from '@/lib/wiki'
@@ -14,6 +14,7 @@ type Prefetcher = (qc: QueryClient, url: URL) => Promise<void>
 
 const mPost = match<{ id: string }> ('/posts/:id')
 const mWiki = match<{ title: string }> ('/wiki/:title')
+const mTag = match<{ id: string }> ('/tags/:id')
 
 
 const prefetchWikiPagesIndex: Prefetcher = async (qc, url) => {
@@ -169,6 +170,30 @@ const prefetchTagsIndex: Prefetcher = async (qc, url) => {
 }
 
 
+const prefetchTagShow: Prefetcher = async (qc, url) => {
+  const m = mTag (url.pathname)
+  if (!(m))
+    return
+
+  const { id } = m.params
+
+  await qc.prefetchQuery ({
+      queryKey: tagsKeys.show (id),
+      queryFn:  () => fetchTag (id) })
+}
+
+
+const prefetchTagChanges: Prefetcher = async (qc, url) => {
+  const id = url.searchParams.get ('id')
+  const page = Number (url.searchParams.get ('page') || 1)
+  const limit = Number (url.searchParams.get ('limit') || 20)
+
+  await qc.prefetchQuery ({
+      queryKey: tagsKeys.changes ({ ...(id && { id }), page, limit }),
+      queryFn: () => fetchTagChanges ({ ...(id && { id }), page, limit }) })
+}
+
+
 export const routePrefetchers: { test: (u: URL) => boolean; run: Prefetcher }[] = [
     { test: u => ['/', '/posts', '/posts/search'].includes (u.pathname),
       run: prefetchPostsIndex },
@@ -180,7 +205,11 @@ export const routePrefetchers: { test: (u: URL) => boolean; run: Prefetcher }[]
     { test: u => (!(['/wiki/new', '/wiki/changes'].includes (u.pathname))
 		  && Boolean (mWiki (u.pathname))),
       run: prefetchWikiPageShow },
-    { test: u => u.pathname === '/tags', run: prefetchTagsIndex }]
+    { test: u => u.pathname === '/tags', run: prefetchTagsIndex },
+    { test: u => (!(['/tags/nico', '/tags/changes'].includes (u.pathname))
+		  && Boolean (mTag (u.pathname))),
+      run: prefetchTagShow },
+    { test: u => u.pathname === '/tags/changes', run: prefetchTagChanges }]
 
 
 export const prefetchForURL = async (qc: QueryClient, urlLike: string): Promise<void> => {

frontend/src/lib/queryKeys.ts

@@ -5,13 +5,16 @@ export const postsKeys = {
     index:    (p: FetchPostsParams) => ['posts', 'index', p] as const,
     show:     (id: string) => ['posts', id] as const,
     related:  (id: string) => ['related', id] as const,
-    changes:  (p: { id?: string; tag?: string; page: number; limit: number }) =>
+    changes:  (p: { post?: string; tag?: string; page: number; limit: number }) =>
 		  ['posts', 'changes', p] as const }
 
 export const tagsKeys = {
     root:         ['tags'] as const,
     index:        (p: FetchTagsParams) => ['tags', 'index', p] as const,
-    show:   (name: string) => ['tags', name] as const }
+    show:         (name: string) => ['tags', name] as const,
+    changes:      (p: { id?: string; page: number; limit: number }) =>
+		      ['tags', 'changes', p] as const,
+    deerjikists:  (id: string) => ['tags', 'deerjikists', id] as const }
 
 export const wikiKeys = {
     root:   ['wiki'] as const,

frontend/src/lib/tags.ts

@@ -1,6 +1,6 @@
 import { apiGet } from '@/lib/api'
 
-import type { FetchTagsParams, Tag } from '@/types'
+import type { Deerjikist, FetchTagsParams, Tag, TagVersion } from '@/types'
 
 
 export const fetchTags = async (
@@ -45,3 +45,20 @@ export const fetchTagByName = async (name: string): Promise<Tag | null> => {
     return null
   }
 }
+
+
+export const fetchTagChanges = async (
+    { id, page, limit }: {
+	id?:    string
+	page:   number
+	limit:  number },
+): Promise<{
+    versions: TagVersion[]
+    count:    number }> =>
+	await apiGet ('/tags/versions', { params: { ...(id && { id }), page, limit } })
+
+
+export const fetchDeerjikistsByTag = async (
+    id: string,
+): Promise<{ tag: Tag; deerjikists: Deerjikist[]}> =>
+    await apiGet (`/tags/${ id }/deerjikists`)

frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx

@@ -0,0 +1,155 @@
+import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { useEffect, useState } from 'react'
+import { useParams } from 'react-router-dom'
+
+import TagLink from '@/components/TagLink'
+import Label from '@/components/common/Label'
+import PageTitle from '@/components/common/PageTitle'
+import MainArea from '@/components/layout/MainArea'
+import { toast } from '@/components/ui/use-toast'
+import { PLATFORM_NAMES, PLATFORMS } from '@/consts'
+import { apiPut } from '@/lib/api'
+import { tagsKeys } from '@/lib/queryKeys'
+import { fetchDeerjikistsByTag } from '@/lib/tags'
+import { cn } from '@/lib/utils'
+
+import type { FC, FormEvent } from 'react'
+
+import type { Deerjikist, Platform } from '@/types'
+
+
+export default (() => {
+  const { id } = useParams ()
+  const tagId = String (id ?? '')
+  const tagKey = tagsKeys.deerjikists (tagId)
+
+  const { data: qData, isLoading: loading } =
+      useQuery ({ queryKey: tagKey, queryFn: () => fetchDeerjikistsByTag (tagId) })
+  const tag = qData?.tag
+  const deerjikists = qData?.deerjikists ?? []
+
+  const [data, setData] =
+      useState<(Omit<Deerjikist, 'platform'> & { platform: Platform | null })[]> ([])
+  const [disabled, setDisabled] = useState (true)
+
+  const qc = useQueryClient ()
+
+  const handleSubmit = async (e: FormEvent) => {
+    e.preventDefault ()
+
+    try
+    {
+      setDisabled (true)
+
+      setData (await apiPut<Deerjikist[]> (`/tags/${ id }/deerjikists`, data))
+      qc.invalidateQueries ({ queryKey: tagsKeys.root })
+
+      toast ({ description: '更新しました．' })
+    }
+    catch
+    {
+      toast ({ title: '更新失敗', description: '入力内容を確認してください．' })
+    }
+    finally
+    {
+      setDisabled (false)
+    }
+  }
+
+  useEffect (() => {
+    if (!(tag))
+      {
+	setDisabled (true)
+	return
+      }
+
+    setData (deerjikists)
+    setDisabled (false)
+  }, [tag, deerjikists])
+
+  return (
+      <MainArea>
+	{(loading || !(tag)) ? 'Loading...' : (
+	    <div className="max-w-xl">
+	      <PageTitle>
+		<TagLink tag={tag} withWiki={false} withCount={false}/>
+	      </PageTitle>
+
+	      <form onSubmit={handleSubmit} className="my-4 space-y-2">
+		{data.map ((datum, i) => (
+		    <fieldset key={i} className="min-w-0 rounded-lg border border-gray-300
+						 dark:border-gray-700 p-4">
+		      <legend className="px-2 text-sm font-semibold text-gray-700
+					 dark:text-gray-300">
+			<button
+			    type="button"
+			    disabled={disabled}
+			    onClick={() => setData (prev => [...prev.slice (0, i),
+							     ...prev.slice (i + 1)])}>
+			  #{i + 1}
+			</button>
+		      </legend>
+
+		      {/* プラットフォーム */}
+		      <div>
+			<Label>プラットフォーム</Label>
+			<select
+			    className="w-full border p-2 rounded"
+			    disabled={disabled}
+			    value={datum.platform ?? ''}
+			    onChange={e => setData (prev => {
+			      const rtn = [...prev]
+			      rtn[i] = { ...rtn[i],
+					 platform: (e.target.value || null) as Platform | null }
+			      return rtn
+			    })}>
+			  <option value="">&nbsp;</option>
+			  {PLATFORMS.map (p => (
+			      <option key={p} value={p}>
+				{PLATFORM_NAMES[p]}
+			      </option>))}
+			</select>
+		      </div>
+
+		      {/* コード */}
+		      <div>
+			<Label>コード</Label>
+			<input
+			    type="text"
+			    disabled={disabled}
+			    className="w-full border p-2 rounded"
+			    value={datum.code}
+			    onChange={e => setData (prev => {
+			      const rtn = [...prev]
+			      rtn[i] = { ...rtn[i], code: e.target.value }
+			      return rtn
+			    })}/>
+		      </div>
+		    </fieldset>
+		))}
+
+		<div className="py-3">
+		  <button
+		      type="button"
+		      disabled={disabled}
+		      onClick={() => setData (prev => [...prev, { platform: null, code: '' }])}>
+		    +
+		  </button>
+		</div>
+
+		<div className="py-3">
+		  <button
+		      type="submit"
+		      disabled={disabled}
+		      className={cn ('px-4 py-2 rounded',
+				     (disabled
+				      ? 'text-gray-300 bg-gray-500'
+				      : 'text-white bg-blue-500'))}>
+		    更新
+		  </button>
+		</div>
+	      </form>
+	    </div>
+	)}
+      </MainArea>)
+}) satisfies FC

frontend/src/pages/posts/PostDetailPage.tsx

@@ -21,7 +21,7 @@ import ServiceUnavailable from '@/pages/ServiceUnavailable'
 
 import type { FC } from 'react'
 
-import type { NiconicoViewerHandle, User } from '@/types'
+import type { NiconicoViewerHandle, Post, User } from '@/types'
 
 type Props = { user: User | null }
 
@@ -96,7 +96,7 @@ export default (({ user }: Props) => {
       <div className="md:flex md:flex-1 overflow-y-auto md:overflow-y-hidden">
 	<Helmet>
 	  {(post?.thumbnail || post?.thumbnailBase) && (
-	      <meta name="thumbnail" content={post.thumbnail || post.thumbnailBase}/>)}
+	      <meta name="thumbnail" content={post.thumbnail! || post.thumbnailBase!}/>)}
 	  {post && <title>{`${ post.title || post.url } | ${ SITE_TITLE }`}</title>}
 	</Helmet>
 
@@ -108,6 +108,34 @@ export default (({ user }: Props) => {
 	  {post
 	   ? (
 	      <>
+		{(post.childPosts ?? []).length > 0 && (
+		    <div className="mb-4 bg-green-200 dark:bg-green-800 text-sm p-2 rounded-md">
+		      <p>この投稿には {post.childPosts!.length} 件の子投稿があります．</p>
+		      <PostList posts={[{ ...post, childPosts: [{ } as Post] },
+					...post.childPosts!.map (p => ({
+					    ...p, parentPosts: [{ } as Post] }))]}/>
+		    </div>
+		)}
+		{(post.parentPosts ?? []).map (pp => {
+		  const siblings = post.siblingPosts?.[String (pp.id) as `${ number }`]
+		  if (!(siblings))
+		    return
+
+		  return (
+		      <div
+			  key={pp.id}
+			  className="mb-4 bg-yellow-200 dark:bg-yellow-800 text-sm p-2 rounded-md">
+			<p>
+			  この投稿には 1 件の親投稿{
+			      siblings.length > 1
+			      && `と ${ siblings.length - 1 } 件の姉妹投稿`}があります．
+			</p>
+			<PostList posts={[{ ...pp, childPosts: [{ } as Post] },
+					  ...siblings.map (p => ({
+					      ...p, parentPosts: [{ } as Post] }))]}/>
+		      </div>)
+		})}
+
 		{(post.thumbnail || post.thumbnailBase) && (
 		    <motion.div
 			layoutId={`page-${ id }`}
@@ -116,7 +144,7 @@ export default (({ user }: Props) => {
 			initial={{ opacity: 1 }}
 			animate={{ opacity: 0 }}
 			transition={{ duration: .2, ease: 'easeOut' }}>
-		      <img src={post.thumbnail || post.thumbnailBase}
+		      <img src={post.thumbnail || post.thumbnailBase || undefined}
 			   alt={post.title || post.url}
 			   title={post.title || post.url || undefined}
 			   className="object-cover w-full h-full"/>
@@ -146,7 +174,6 @@ export default (({ user }: Props) => {
 					       (prev: any) => newPost ?? prev)
 			      qc.invalidateQueries ({ queryKey: postsKeys.root })
 			      qc.invalidateQueries ({ queryKey: tagsKeys.root })
-			      toast ({ description: '更新しました．' })
 			    }}/>
 		      </Tab>)}
 		</TabGroup>

frontend/src/pages/posts/PostHistoryPage.tsx

@@ -1,4 +1,4 @@
-import { useQuery } from '@tanstack/react-query'
+import { useQuery, useQueryClient } from '@tanstack/react-query'
 import { motion } from 'framer-motion'
 import { useEffect } from 'react'
 import { Helmet } from 'react-helmet-async'
@@ -9,15 +9,30 @@ import PrefetchLink from '@/components/PrefetchLink'
 import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
 import MainArea from '@/components/layout/MainArea'
+import { toast } from '@/components/ui/use-toast'
 import { SITE_TITLE } from '@/config'
+import { apiPut } from '@/lib/api'
 import { fetchPostChanges } from '@/lib/posts'
 import { postsKeys, tagsKeys } from '@/lib/queryKeys'
 import { fetchTag } from '@/lib/tags'
-import { cn, dateString } from '@/lib/utils'
+import { cn, dateString, originalCreatedAtString } from '@/lib/utils'
 
 import type { FC } from 'react'
 
 
+const renderDiff = (diff: { current: string | null; prev: string | null }) => (
+    <>
+      {(diff.prev && diff.prev !== diff.current) && (
+	  <>
+	    <del className="text-red-600 dark:text-red-400">
+	      {diff.prev}
+	    </del>
+	    {diff.current && <br/>}
+	  </>)}
+      {diff.current}
+    </>)
+
+
 export default (() => {
   const location = useLocation ()
   const query = new URLSearchParams (location.search)
@@ -36,15 +51,17 @@ export default (() => {
       : { data: null }
 
   const { data, isLoading: loading } = useQuery ({
-      queryKey: postsKeys.changes ({ ...(id && { id }),
+      queryKey: postsKeys.changes ({ ...(id && { post: id }),
 				     ...(tagId && { tag: tagId }),
 				     page, limit }),
-      queryFn:  () => fetchPostChanges ({ ...(id && { id }),
+      queryFn:  () => fetchPostChanges ({ ...(id && { post: id }),
 					  ...(tagId && { tag: tagId }),
 					  page, limit }) })
-  const changes = data?.changes ?? []
+  const changes = data?.versions ?? []
   const totalPages = data ? Math.ceil (data.count / limit) : 0
 
+  const qc = useQueryClient ()
+
   useEffect (() => {
     document.querySelector ('table')?.scrollIntoView ({ behavior: 'smooth' })
   }, [location.search])
@@ -65,76 +82,203 @@ export default (() => {
 
 	{loading ? 'Loading...' : (
 	    <>
-	      <table className="table-auto w-full border-collapse">
+	      <div className="overflow-x-auto">
+		<table className="w-full min-w-[1200px] table-fixed border-collapse">
+		  <colgroup>
+		    {/* 投稿 */}
+		    <col className="w-64"/>
+		    {/* 版 */}
+		    <col className="w-40"/>
+		    {/* タイトル */}
+		    <col className="w-96"/>
+		    {/* URL */}
+		    <col className="w-96"/>
+		    {/* タグ */}
+		    <col className="w-[48rem]"/>
+		    {/* TODO: 親投稿 */}
+		    {/* <col className="w-[48rem]"/> */}
+		    {/* オリジナルの投稿日時 */}
+		    <col className="w-96"/>
+		    {/* 更新日時 */}
+		    <col className="w-64"/>
+		    {/* (差戻ボタン) */}
+		    <col className="w-20"/>
+		  </colgroup>
+
 		  <thead className="border-b-2 border-black dark:border-white">
 		    <tr>
 		      <th className="p-2 text-left">投稿</th>
-		    <th className="p-2 text-left">変更</th>
-		    <th className="p-2 text-left">日時</th>
+		      <th className="p-2 text-left">版</th>
+		      <th className="p-2 text-left">タイトル</th>
+		      <th className="p-2 text-left">URL</th>
+		      <th className="p-2 text-left">タグ</th>
+		      {/* TODO: 親投稿の履歴 */}
+		      {/* <th className="p-2 text-left">親投稿</th> */}
+		      <th className="p-2 text-left">オリジナルの投稿日時</th>
+		      <th className="p-2 text-left">更新日時</th>
+		      <th className="p-2"/>
 		    </tr>
 		  </thead>
+
 		  <tbody>
 		    {changes.map ((change, i) => {
-		    const withPost = i === 0 || change.post.id !== changes[i - 1].post.id
+		      const withPost = i === 0 || change.postId !== changes[i - 1].postId
 		      if (withPost)
 			{
 			  rowsCnt = 1
 			  for (let j = i + 1;
 			       (j < changes.length
-			      && change.post.id === changes[j].post.id);
+				&& change.postId === changes[j].postId);
 			       ++j)
 			    ++rowsCnt
 			}
 
-		    let layoutId: string | undefined = `page-${ change.post.id }`
+		      let layoutId: string | undefined = `page-${ change.postId }`
 		      if (layoutIds.includes (layoutId))
 			layoutId = undefined
 		      else
 			layoutIds.push (layoutId)
 
 		      return (
-			<tr key={`${ change.timestamp }-${ change.post.id }-${ change.tag?.id }`}
+			  <tr key={`${ change.postId }.${ change.versionNo }`}
 			      className={cn ('even:bg-gray-100 dark:even:bg-gray-700',
 					     withPost && 'border-t')}>
 			    {withPost && (
 				<td className="align-top p-2 bg-white dark:bg-[#242424] border-r"
 				    rowSpan={rowsCnt}>
-				<PrefetchLink to={`/posts/${ change.post.id }`}>
+				  <PrefetchLink to={`/posts/${ change.postId }`}>
 				    <motion.div
 					layoutId={layoutId}
-				      transition={{ type: 'spring',
-						    stiffness: 500,
-						    damping: 40,
-						    mass: .5 }}>
-				    <img src={change.post.thumbnail
-					      || change.post.thumbnailBase
+					transition={{ layout: { duration: .2, ease: 'easeOut' } }}>
+				      <img src={change.thumbnail.current
+						|| change.thumbnailBase.current
 						|| undefined}
-					 alt={change.post.title || change.post.url}
-					 title={change.post.title || change.post.url || undefined}
+					   alt={change.title.current || change.url.current}
+					   title={change.title.current || change.url.current || undefined}
 					   className="w-40"/>
 				    </motion.div>
 				  </PrefetchLink>
 				</td>)}
+			    <td className="p-2">{change.postId}.{change.versionNo}</td>
+			    <td className="p-2 break-all">{renderDiff (change.title)}</td>
+			    <td className="p-2 break-all">{renderDiff (change.url)}</td>
 			    <td className="p-2">
-			    {change.tag
-			     ? <TagLink tag={change.tag} withWiki={false} withCount={false}/>
-			     : '(マスタ削除済のタグ) '}
-			    {`を${ change.changeType === 'add' ? '記載' : '消除' }`}
+			      {change.tags.map ((tag, i) => (
+				  tag.type === 'added'
+				  ? (
+				      <ins
+					  key={i}
+					  className="mr-2 text-green-600 dark:text-green-400">
+					{tag.name}
+				      </ins>)
+				  : (
+				      tag.type === 'removed'
+				      ? (
+					  <del
+					      key={i}
+					      className="mr-2 text-red-600 dark:text-red-400">
+					    {tag.name}
+					  </del>)
+				      : (
+					  <span key={i} className="mr-2">
+					    {tag.name}
+					  </span>))))}
+			    </td>
+			    {/* TODO: 親投稿の履歴 */}
+			    {/* <td className="p-2">
+			      {change.parentPosts.map ((pp, i) => (
+				  pp.type === 'added'
+				  ? (
+				      <ins
+					  key={i}
+					  className="mr-2 text-green-600 dark:text-green-400">
+					{pp.title}
+				      </ins>)
+				  : (
+				      pp.type === 'removed'
+				      ? (
+					  <del
+					      key={i}
+					      className="mr-2 text-red-600 dark:text-red-400">
+					    {pp.title}
+					  </del>)
+				      : (
+					  <span key={i} className="mr-2">
+					    {pp.title}
+					  </span>))))}
+			    </td> */}
+			    <td className="p-2">
+			      {change.versionNo === 1
+			       ? originalCreatedAtString (change.originalCreatedFrom.current,
+							  change.originalCreatedBefore.current)
+			       : renderDiff ({
+				  current: originalCreatedAtString (
+					       change.originalCreatedFrom.current,
+					       change.originalCreatedBefore.current),
+				  prev: originalCreatedAtString (
+					    change.originalCreatedFrom.prev,
+					    change.originalCreatedBefore.prev) })}
 			    </td>
 			    <td className="p-2">
-			    {change.user
+			      {change.createdByUser
 			       ? (
-				<PrefetchLink to={`/users/${ change.user.id }`}>
-				  {change.user.name}
+				  <PrefetchLink to={`/users/${ change.createdByUser.id }`}>
+				    {change.createdByUser.name
+				     || `名もなきニジラー（#${ change.createdByUser.id }）`}
 				  </PrefetchLink>)
 			       : 'bot 操作'}
 			      <br/>
-			    {dateString (change.timestamp)}
+			      {dateString (change.createdAt)}
+			    </td>
+			    <td className="p-2">
+			      <a
+				  href="#"
+				  onClick={async e => {
+				    e.preventDefault ()
+
+				    if (!(confirm (
+					`『${ change.title.current
+					      || change.url.current }』を版 ${
+					change.versionNo } に差戻します．\nよろしいですか?`)))
+				      return
+
+				    try
+				    {
+				      await apiPut (
+					  `/posts/${ change.postId }`,
+					  { title: change.title.current,
+					    tags: change.tags
+						  .filter (t => t.type !== 'removed')
+						  .map (t => t.name)
+						  .filter (t => t.slice (0, 5) !== 'nico:')
+						  .join (' '),
+					    parent_post_ids:
+						(change.parentPosts ?? [])
+						.filter (p => p.type !== 'removed')
+						.map (p => p.id)
+						.join (' '),
+					    original_created_from:
+						change.originalCreatedFrom.current,
+					    original_created_before:
+						change.originalCreatedBefore.current })
+
+				      qc.invalidateQueries ({ queryKey: postsKeys.root })
+				      qc.invalidateQueries ({ queryKey: tagsKeys.root })
+				      toast ({ description: '差戻しました．' })
+				    }
+				    catch
+				    {
+				      toast ({ description: '差戻に失敗……' })
+				    }
+				  }}>
+				復元
+			      </a>
 			    </td>
 			  </tr>)
 		    })}
 		  </tbody>
 		</table>
+	      </div>
 
 	      <Pagination page={page} totalPages={totalPages}/>
 	    </>)}

frontend/src/pages/posts/PostNewPage.tsx

@@ -29,6 +29,7 @@ export default (({ user }: Props) => {
 
   const [originalCreatedBefore, setOriginalCreatedBefore] = useState<string | null> (null)
   const [originalCreatedFrom, setOriginalCreatedFrom] = useState<string | null> (null)
+  const [parentPostIds, setParentPostIds] = useState ('')
   const [tags, setTags] = useState ('')
   const [thumbnailAutoFlg, setThumbnailAutoFlg] = useState (true)
   const [thumbnailFile, setThumbnailFile] = useState<File | null> (null)
@@ -46,6 +47,7 @@ export default (({ user }: Props) => {
     formData.append ('title', title)
     formData.append ('url', url)
     formData.append ('tags', tags)
+    formData.append ('parent_post_ids', parentPostIds)
     if (thumbnailFile)
       formData.append ('thumbnail', thumbnailFile)
     if (originalCreatedFrom)
@@ -177,6 +179,16 @@ export default (({ user }: Props) => {
 		     className="mt-2 max-h-48 rounded border"/>)}
 	  </div>
 
+	  {/* 親投稿 */}
+	  <div>
+	    <Label>親投稿</Label>
+	    <input
+		type="text"
+		value={parentPostIds}
+		onChange={e => setParentPostIds (e.target.value)}
+		className="w-full border p-2 rounded"/>
+	  </div>
+
 	  {/* タグ */}
 	  <PostFormTagsArea tags={tags} setTags={setTags}/>
 

frontend/src/pages/posts/PostSearchPage.tsx

@@ -289,7 +289,7 @@ export default (() => {
 		    {results.map (row => (
 			<tr key={row.id} className="even:bg-gray-100 dark:even:bg-gray-700">
 			  <td className="p-2">
-			    <PrefetchLink to={`/posts/${ row.id }`} title={row.title}>
+			    <PrefetchLink to={`/posts/${ row.id }`} title={row.title || undefined}>
 			      <motion.div
 				  layoutId={`page-${ row.id }`}
 				  transition={{ type: 'spring',
@@ -304,7 +304,7 @@ export default (() => {
 			    </PrefetchLink>
 			  </td>
 			  <td className="p-2 truncate">
-			    <PrefetchLink to={`/posts/${ row.id }`} title={row.title}>
+			    <PrefetchLink to={`/posts/${ row.id }`} title={row.title || undefined}>
 			      {row.title}
 			    </PrefetchLink>
 			  </td>

frontend/src/pages/tags/TagDetailPage.tsx

@@ -0,0 +1,158 @@
+import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { useEffect, useState } from 'react'
+import { useParams } from 'react-router-dom'
+
+import TagLink from '@/components/TagLink'
+import Label from '@/components/common/Label'
+import PageTitle from '@/components/common/PageTitle'
+import MainArea from '@/components/layout/MainArea'
+import { toast } from '@/components/ui/use-toast'
+import { CATEGORIES, CATEGORY_NAMES } from '@/consts'
+import { apiPut } from '@/lib/api'
+import { postsKeys, tagsKeys } from '@/lib/queryKeys'
+import { fetchTag } from '@/lib/tags'
+import { cn } from '@/lib/utils'
+
+import type { FC, FormEvent } from 'react'
+
+import type { Category, Tag } from '@/types'
+
+
+export default (() => {
+  const { id } = useParams ()
+  const tagId = String (id ?? '')
+  const tagKey = tagsKeys.show (tagId)
+
+  const { data: tag, isLoading: loading } = useQuery ({
+      queryKey: tagKey,
+      queryFn: () => fetchTag (tagId) })
+
+  const [name, setName] = useState ('')
+  const [category, setCategory] = useState<Category> ('general')
+  const [aliases, setAliases] = useState ('')
+  const [parentTags, setParentTags] = useState ('')
+  const [disabled, setDisabled] = useState (true)
+
+  const qc = useQueryClient ()
+
+  const handleSubmit = async (e: FormEvent) => {
+    e.preventDefault ()
+
+    const formData = new FormData
+    formData.append ('name', name)
+    formData.append ('category', category)
+    formData.append ('aliases', aliases)
+    formData.append ('parent_tags', parentTags)
+
+    try
+    {
+      const data = await apiPut<Tag> (`/tags/${ id }`, formData)
+
+      setName (data.name)
+      setCategory (data.category as Category)
+      setAliases (data.aliases.join (' '))
+      setParentTags (data.parents.map (t => t.name).join (' '))
+
+      qc.invalidateQueries ({ queryKey: postsKeys.root })
+      qc.invalidateQueries ({ queryKey: tagsKeys.root })
+      toast ({ description: '更新しました．' })
+    }
+    catch
+    {
+      toast ({ description: '更新に失敗しました．' })
+    }
+  }
+
+  useEffect (() => {
+    if (!(tag))
+      {
+	setDisabled (true)
+	return
+      }
+
+    setName (tag.name)
+    setCategory (tag.category as Category)
+    setAliases (tag.aliases.join (' '))
+    setParentTags (tag.parents.map (t => t.name).join (' '))
+    setDisabled (tag.category === 'nico')
+  }, [tag])
+
+  return (
+      <MainArea>
+	{(loading || !(tag)) ? 'Loading...' : (
+	    <div className="max-w-xl">
+	      <PageTitle>
+		<TagLink
+		    tag={tag}
+		    withWiki={false}
+		    withCount={false}/>
+	      </PageTitle>
+
+	      <form onSubmit={handleSubmit} className="my-4 space-y-2">
+		{/* 名称 */}
+		<div>
+		  <Label>名称</Label>
+		  {/* TODO: 補完に対応させる */}
+		  <input
+		      type="text"
+		      disabled={disabled}
+		      value={name}
+		      onChange={e => setName (e.target.value)}
+		      className="w-full border p-2 rounded"/>
+		</div>
+
+		{/* カテゴリ */}
+		<div>
+		  <Label>カテゴリ</Label>
+		  <select
+		      disabled={disabled}
+		      value={category ?? ''}
+		      onChange={e => setCategory(e.target.value as Category)}
+		      className="w-full border p-2 rounded">
+		    {CATEGORIES.filter (cat => tag.category === 'nico' || cat !== 'nico')
+			       .map (cat => (
+			<option key={cat} value={cat}>
+			  {CATEGORY_NAMES[cat]}
+			</option>))}
+		  </select>
+		</div>
+
+		{/* 別名 */}
+		<div>
+		  <Label>別名</Label>
+		  {/* TODO: 補完に対応させる */}
+		  <input
+		      type="text"
+		      disabled={disabled}
+		      value={aliases}
+		      onChange={e => setAliases (e.target.value)}
+		      className="w-full border p-2 rounded"/>
+		</div>
+
+		{/* 上位タグ */}
+		<div>
+		  <Label>上位タグ</Label>
+		  {/* TODO: 補完に対応させる */}
+		  <input
+		      type="text"
+		      disabled={disabled}
+		      value={parentTags}
+		      onChange={e => setParentTags (e.target.value)}
+		      className="w-full border p-2 rounded"/>
+		</div>
+
+		<div className="py-3">
+		  <button
+		      type="submit"
+		      disabled={disabled}
+		      className={cn ('px-4 py-2 rounded',
+				     (disabled
+				      ? 'text-gray-300 bg-gray-500'
+				      : 'text-white bg-blue-500'))}>
+		    更新
+		  </button>
+		</div>
+	      </form>
+	    </div>)}
+      </MainArea>)
+}) satisfies FC

frontend/src/pages/tags/TagHistoryPage.tsx

@@ -0,0 +1,212 @@
+import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { useEffect } from 'react'
+import { Helmet } from 'react-helmet-async'
+import { useLocation } from 'react-router-dom'
+
+import PrefetchLink from '@/components/PrefetchLink'
+import PageTitle from '@/components/common/PageTitle'
+import Pagination from '@/components/common/Pagination'
+import MainArea from '@/components/layout/MainArea'
+import { toast } from '@/components/ui/use-toast'
+import { SITE_TITLE } from '@/config'
+import { CATEGORY_NAMES } from '@/consts'
+import { apiPut } from '@/lib/api'
+import { postsKeys, tagsKeys } from '@/lib/queryKeys'
+import { fetchTagChanges } from '@/lib/tags'
+import { cn, dateString } from '@/lib/utils'
+
+import type { FC } from 'react'
+
+
+const renderDiff = (diff: { current: string | null; prev: string | null }) => (
+    <>
+      {(diff.prev && diff.prev !== diff.current) && (
+	  <>
+	    <del className="text-red-600 dark:text-red-400">
+	      {diff.prev}
+	    </del>
+	    {diff.current && <br/>}
+	  </>)}
+      {diff.current}
+    </>)
+
+
+export default (() => {
+  const location = useLocation ()
+  const query = new URLSearchParams (location.search)
+  const id = query.get ('id')
+  const page = Number (query.get ('page') ?? 1)
+  const limit = Number (query.get ('limit') ?? 20)
+
+  const { data, isLoading: loading } = useQuery ({
+      queryKey: tagsKeys.changes ({ ...(id && { id }), page, limit }),
+      queryFn:  () => fetchTagChanges ({ ...(id && { id }), page, limit }) })
+  const changes = data?.versions ?? []
+  const totalPages = data ? Math.ceil (data.count / limit) : 0
+
+  const qc = useQueryClient ()
+
+  useEffect (() => {
+    document.querySelector ('table')?.scrollIntoView ({ behavior: 'smooth' })
+  }, [location.search])
+
+  return (
+      <MainArea>
+	<Helmet>
+	  <title>{`タグ定義変更履歴 | ${ SITE_TITLE }`}</title>
+	</Helmet>
+
+	<PageTitle>
+	  タグ定義変更履歴
+	  {id && <>: タグ {<PrefetchLink to={`/tags/${ id }`}>#{id}</PrefetchLink>}</>}
+	</PageTitle>
+
+	{loading ? 'Loading...' : (
+	    <>
+	      <div className="overflow-x-auto">
+		<table className="w-full min-w-[1200px] table-fixed border-collapse">
+		  <colgroup>
+		    {/* 版 */}
+		    <col className="w-40"/>
+		    {/* 名称 */}
+		    <col className="w-96"/>
+		    {/* カテゴリ */}
+		    <col className="w-96"/>
+		    {/* 別名 */}
+		    <col className="w-[48rem]"/>
+		    {/* 上位タグ */}
+		    <col className="w-96"/>
+		    {/* 更新日時 */}
+		    <col className="w-64"/>
+		    {/* (差戻ボタン) */}
+		    <col className="w-20"/>
+		  </colgroup>
+
+		  <thead className="border-b-2 border-black dark:border-white">
+		    <tr>
+		      <th className="p-2 text-left">版</th>
+		      <th className="p-2 text-left">名称</th>
+		      <th className="p-2 text-left">カテゴリ</th>
+		      <th className="p-2 text-left">別名</th>
+		      <th className="p-2 text-left">上位タグ</th>
+		      <th className="p-2 text-left">更新日時</th>
+		      <th className="p-2"/>
+		    </tr>
+		  </thead>
+
+		  <tbody>
+		    {changes.map (change => (
+			<tr key={`${ change.tagId }.${ change.versionNo }`}
+			    className={cn ('even:bg-gray-100 dark:even:bg-gray-700')}>
+			  <td className="p-2">{change.tagId}.{change.versionNo}</td>
+			  <td className="p-2 break-all">{renderDiff (change.name)}</td>
+			  <td className="p-2 break-all">
+			    {renderDiff ({
+				current: CATEGORY_NAMES[change.category.current],
+				prev: (change.category.prev
+				       && CATEGORY_NAMES[change.category.prev]) })}
+			  </td>
+			  <td className="p-2">
+			    {change.aliases.map ((tag, i) => (
+				tag.type === 'added'
+				? (
+				    <ins
+					key={i}
+					className="mr-2 text-green-600 dark:text-green-400">
+				      {tag.name}
+				    </ins>)
+				: (
+				    tag.type === 'removed'
+				    ? (
+					<del
+					    key={i}
+					    className="mr-2 text-red-600 dark:text-red-400">
+					  {tag.name}
+					</del>)
+				    : (
+					<span key={i} className="mr-2">
+					  {tag.name}
+					</span>))))}
+			  </td>
+			  <td className="p-2">
+			    {change.parentTags.map ((tag, i) => (
+				tag.type === 'added'
+				? (
+				    <ins
+					key={i}
+					className="mr-2 text-green-600 dark:text-green-400">
+				      {tag.tag.name}
+				    </ins>)
+				: (
+				    tag.type === 'removed'
+				    ? (
+					<del
+					    key={i}
+					    className="mr-2 text-red-600 dark:text-red-400">
+					  {tag.tag.name}
+					</del>)
+				    : (
+					<span key={i} className="mr-2">
+					  {tag.tag.name}
+					</span>))))}
+			  </td>
+			  <td className="p-2">
+			    {change.createdByUser
+			     ? (
+				<PrefetchLink to={`/users/${ change.createdByUser.id }`}>
+				  {change.createdByUser.name
+				   || `名もなきニジラー（#${ change.createdByUser.id }）`}
+				</PrefetchLink>)
+			     : 'bot 操作'}
+			    <br/>
+			    {dateString (change.createdAt)}
+			  </td>
+			  <td className="p-2">
+			    <a
+				href="#"
+				onClick={async e => {
+				  e.preventDefault ()
+
+				  if (!(confirm (
+				      `タグ『${ change.name.current }』を版 ${
+				      change.versionNo } に差戻します．\nよろしいですか?`)))
+				    return
+
+				  try
+				  {
+				    await apiPut (
+					`/tags/${ change.tagId }`,
+					{ name: change.name.current,
+					  category: change.category.current,
+					  aliases:
+					      change.aliases
+					      .filter (t => t.type !== 'removed')
+					      .map (t => t.name)
+					      .join (' '),
+					  parent_tags:
+					      change.parentTags
+					      .filter (t => t.type !== 'removed')
+					      .map (t => t.tag.name)
+					      .join (' ') })
+
+				    qc.invalidateQueries ({ queryKey: postsKeys.root })
+				    qc.invalidateQueries ({ queryKey: tagsKeys.root })
+				    toast ({ description: '差戻しました．' })
+				  }
+				  catch
+				  {
+				    toast ({ description: '差戻に失敗……' })
+				  }
+				}}>
+			      復元
+			    </a>
+			  </td>
+			</tr>))}
+		  </tbody>
+		</table>
+	      </div>
+
+	      <Pagination page={page} totalPages={totalPages}/>
+	    </>)}
+      </MainArea>)
+}) satisfies FC

frontend/src/pages/tags/TagListPage.tsx

@@ -205,13 +205,15 @@ export default (() => {
 	{loading ? 'Loading...' : (results.length > 0 ? (
 	    <div className="mt-4">
 	      <div className="overflow-x-auto">
-		<table className="w-full min-w-[1200px] table-fixed border-collapse">
+		<table className="w-full min-w-[2000px] table-fixed border-collapse">
 		  <colgroup>
 		    <col className="w-72"/>
-		    <col className="w-48"/>
 		    <col className="w-16"/>
-		    <col className="w-44"/>
-		    <col className="w-44"/>
+		    <col className="w-48"/>
+		    <col className="w-72"/>
+		    <col className="w-48"/>
+		    <col className="w-56"/>
+		    <col className="w-56"/>
 		    <col className="w-16"/>
 		  </colgroup>
 
@@ -224,13 +226,6 @@ export default (() => {
 			    currentOrder={order}
 			    defaultDirection={defaultDirection}/>
 		      </th>
-		      <th className="p-2 text-left whitespace-nowrap">
-			<SortHeader<FetchTagsOrderField>
-			    by="category"
-			    label="カテゴリ"
-			    currentOrder={order}
-			    defaultDirection={defaultDirection}/>
-		      </th>
 		      <th className="p-2 text-left whitespace-nowrap">
 			<SortHeader<FetchTagsOrderField>
 			    by="post_count"
@@ -238,6 +233,15 @@ export default (() => {
 			    currentOrder={order}
 			    defaultDirection={defaultDirection}/>
 		      </th>
+		      <th className="p-2 text-left whitespace-nowrap">
+			<SortHeader<FetchTagsOrderField>
+			    by="category"
+			    label="カテゴリ"
+			    currentOrder={order}
+			    defaultDirection={defaultDirection}/>
+		      </th>
+		      <th className="p-2 text-left whitespace-nowrap">別名</th>
+		      <th className="p-2 text-left whitespace-nowrap">上位タグ</th>
 		      <th className="p-2 text-left whitespace-nowrap">
 			<SortHeader<FetchTagsOrderField>
 			    by="created_at"
@@ -260,10 +264,23 @@ export default (() => {
 		    {results.map (row => (
 			<tr key={row.id} className="even:bg-gray-100 dark:even:bg-gray-700">
 			  <td className="p-2">
-			    <TagLink tag={row} withCount={false}/>
+			    <TagLink
+				tag={row}
+				to={`/tags/${ encodeURIComponent (row.id) }`}
+				withCount={false}/>
 			  </td>
-			  <td className="p-2">{CATEGORY_NAMES[row.category]}</td>
 			  <td className="p-2 text-right">{row.postCount}</td>
+			  <td className="p-2">{CATEGORY_NAMES[row.category]}</td>
+			  <td className="p-2">{row.aliases.join (' ')}</td>
+			  <td className="p-2">
+			    {row.parents.map (t => (
+				<span key={t.id} className="mr-2">
+				  <TagLink
+				      tag={t}
+				      withWiki={false}
+				      withCount={false}/>
+				</span>))}
+			  </td>
 			  <td className="p-2">{dateString (row.createdAt)}</td>
 			  <td className="p-2">{dateString (row.updatedAt)}</td>
 			  <td className="p-2">

frontend/src/pages/wiki/WikiDetailPage.tsx

@@ -114,13 +114,15 @@ export default () => {
 		     {...(version && { to: `/wiki/${ encodeURIComponent (title) }` })}/>
 	  </h1>
 	  {loading ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
-	</article>
 
 	  {(!(version) && posts.length > 0) && (
+	      <div className="not-prose">
 		<TabGroup>
 		  <Tab name="広場">
 		    <PostList posts={posts}/>
 		  </Tab>
-	    </TabGroup>)}
+		</TabGroup>
+	      </div>)}
+	</article>
       </MainArea>)
 }

frontend/src/types.ts

@@ -1,5 +1,6 @@
 import { CATEGORIES,
 	 FETCH_POSTS_ORDER_FIELDS,
+	 PLATFORMS,
 	 USER_ROLES,
 	 ViewFlagBehavior } from '@/consts'
 
@@ -7,6 +8,8 @@ import type { ReactNode } from 'react'
 
 export type Category = typeof CATEGORIES[number]
 
+export type Deerjikist = { platform: Platform; code: string }
+
 export type FetchPostsOrder = `${ FetchPostsOrderField }:${ 'asc' | 'desc' }`
 
 export type FetchPostsOrderField = typeof FETCH_POSTS_ORDER_FIELDS[number]
@@ -114,20 +117,25 @@ export type NiconicoViewerHandle = {
     showComments: () => void
     hideComments: () => void }
 
+export type Platform = typeof PLATFORMS[number]
+
 export type Post = {
     id:                     number
     url:                    string
-    title:                  string
-    thumbnail:              string
-    thumbnailBase:          string
+    title:                  string | null
+    thumbnail:              string | null
+    thumbnailBase:          string | null
     tags:                   Tag[]
+    parentPosts?:           Post[]
+    childPosts?:            Post[]
+    siblingPosts?:          Record<`${ number }`, Post[]>
     viewed:                 boolean
     related:                Post[]
     originalCreatedFrom:    string | null
     originalCreatedBefore:  string | null
     createdAt:              string
     updatedAt:              string
-    uploadedUser:           { id: number; name: string } | null }
+    uploadedUser:           { id: number; name: string | null } | null }
 
 export type PostTagChange = {
     post:       Post
@@ -136,6 +144,24 @@ export type PostTagChange = {
     changeType: 'add' | 'remove'
     timestamp:  string }
 
+export type PostVersion = {
+    postId:                 number
+    versionNo:              number
+    eventType:              'create' | 'update' | 'discard' | 'restore'
+    title:                  { current: string | null; prev: string | null }
+    url:                    { current: string; prev: string | null }
+    thumbnail:              { current: string | null; prev: string | null }
+    thumbnailBase:          { current: string | null; prev: string | null }
+    tags:                   { name: string
+			      type: 'context' | 'added' | 'removed' }[]
+    parentPosts:            { id: number
+			      title: string
+			      type: 'context' | 'added' | 'removed' }[]
+    originalCreatedFrom:    { current: string | null; prev: string | null }
+    originalCreatedBefore:  { current: string | null; prev: string | null }
+    createdAt:              string
+    createdByUser:          { id: number; name: string | null } | null }
+
 export type SubMenuComponentItem = {
     component:  ReactNode
     visible:    boolean }
@@ -151,14 +177,28 @@ export type Tag = {
     id:             number
     name:           string
     category:       Category
+    aliases:        string[]
+    parents:        Tag[]
     postCount:      number
     createdAt:      string
     updatedAt:      string
     hasWiki:        boolean
-    materialId:     number
+    materialId:     number | null
+    hasDeerjikists: boolean
     children?:      Tag[]
     matchedAlias?:  string | null }
 
+export type TagVersion = {
+    tagId:                  number
+    versionNo:              number
+    eventType:              'create' | 'update' | 'discard' | 'restore'
+    name:                   { current: string; prev: string | null }
+    category:               { current: Category; prev: Category | null }
+    aliases:                { name: string; type: 'context' | 'added' | 'removed' }[]
+    parentTags:             { tag: Tag; type: 'context' | 'added' | 'removed' }[]
+    createdAt:              string
+    createdByUser:          { id: number; name: string | null } | null }
+
 export type Theatre = {
     id:             number
     name:           string | null