diff --git a/backend/app/controllers/tag_descriptions_controller.rb b/backend/app/controllers/tag_descriptions_controller.rb
index 52859ac..726123f 100644
--- a/backend/app/controllers/tag_descriptions_controller.rb
+++ b/backend/app/controllers/tag_descriptions_controller.rb
@@ -46,7 +46,7 @@ class TagDescriptionsController < ApplicationController
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
     description = TagDescription.find_by(tag_id: params[:id], language_code: 'ja')
-    return head :not_found unless description
+    return create unless description
 
     TagDescriptionOperation.update!(
         tag: description.tag, body:, updated_by_user: current_user)
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index 9be0365..7919a24 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -464,7 +464,6 @@ class TagsController < ApplicationController
 
       old_name = tag.name(locale.language_code)
       name_changed = name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
       if tag.deprecated? == deprecated
         tag.update!(category:)
@@ -485,9 +484,7 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
-          name_changed:,
-          wiki_page:)
+          language_code: locale.language_code)
     end
 
     render json: TagRepr.base(tag.reload, language_code: locale.language_code)
@@ -518,7 +515,6 @@ class TagsController < ApplicationController
 
       old_name = tag.name(locale.language_code)
       name_changed = name.present? && name != old_name
-      wiki_page = tag.tag_name(locale.language_code)&.wiki_page if name_changed
 
       rename_tag_name!(locale, tag, name) if name_changed
       tag.update!(category:) if category.present?
@@ -532,9 +528,7 @@ class TagsController < ApplicationController
           tag,
           event_type: :update,
           created_by_user: current_user,
-          language_code: locale.language_code,
-          name_changed:,
-          wiki_page:)
+          language_code: locale.language_code)
     end
 
     render json: TagRepr.base(tag.reload, language_code: locale.language_code)
@@ -722,19 +716,8 @@ class TagsController < ApplicationController
             language_code:))
   end
 
-  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja',
-                          name_changed: false, wiki_page: nil
+  def record_tag_version! tag, event_type:, created_by_user:, language_code: 'ja'
     TagVersionRecorder.record!(tag:, event_type:, created_by_user:, language_code:)
-
-    return unless name_changed
-
-    wiki_page ||= tag.tag_name('ja')&.wiki_page
-    return unless wiki_page&.wiki_versions&.exists?
-
-    WikiVersionRecorder.record!(
-        page: wiki_page,
-        event_type: :update,
-        created_by_user:)
   end
 
   def validate_tag_rename locale, tag, name
diff --git a/backend/app/controllers/wiki_pages_controller.rb b/backend/app/controllers/wiki_pages_controller.rb
index 3973e48..60b7407 100644
--- a/backend/app/controllers/wiki_pages_controller.rb
+++ b/backend/app/controllers/wiki_pages_controller.rb
@@ -118,15 +118,23 @@ class WikiPagesController < ApplicationController
     return render_unprocessable_entity('タイトルは必須です．', field: :title) if title.blank?
     return render_unprocessable_entity('本文は必須です．', field: :body) if body.blank?
 
-    page = ApplicationRecord.transaction do
-      tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
-        name.script_code = 'Jpan'
-        name.primary_flg = true
-        name.auto_generated = false
-      end
+    page = if title.include?(':')
+      ApplicationRecord.transaction do
+        tag_name = TagName.find_or_create_by!(language_code: 'ja', name: title) do |name|
+          name.script_code = 'Jpan'
+          name.primary_flg = true
+          name.auto_generated = false
+        end
 
-      Wiki::Commit.create_content!(
-          tag_name:, body:, created_by_user: current_user, message:)
+        Wiki::Commit.create_legacy_content!(
+            tag_name:, body:, created_by_user: current_user, message:)
+      end
+    else
+      tag_name = TagName.find_by(language_code: 'ja', name: title)
+      return render_unprocessable_entity field: :title unless tag_name&.tag
+
+      TagDescriptionOperation.create!(
+          tag: tag_name.tag, body:, created_by_user: current_user, message:)
     end
 
     render json: WikiPageRepr.base(page), status: :created
diff --git a/backend/app/services/tag_description_operation.rb b/backend/app/services/tag_description_operation.rb
index c6568de..f3d9ebc 100644
--- a/backend/app/services/tag_description_operation.rb
+++ b/backend/app/services/tag_description_operation.rb
@@ -20,11 +20,9 @@ class TagDescriptionOperation
                    base_revision_id: nil)
     ApplicationRecord.transaction do
       tag.lock!
-      description = TagDescription.lock.find_by(
+      description = TagDescription.lock.find_by!(
           tag_id: tag.id, language_code: LANGUAGE_CODE)
-      description&.lock!
-      tag_name = tag.tag_name(LANGUAGE_CODE)
-      page = WikiPage.lock.find_by!(tag_name:)
+      page = WikiPage.lock.find(description.id)
       revision = Wiki::CompatibilityWriter.update!(
           page:, body:, updated_by_user:, message:,
           base_revision_id:)
diff --git a/backend/app/services/wiki/commit.rb b/backend/app/services/wiki/commit.rb
index e1c37a5..1414307 100644
--- a/backend/app/services/wiki/commit.rb
+++ b/backend/app/services/wiki/commit.rb
@@ -42,10 +42,10 @@ module Wiki
     end
 
     def self.content! page:, body:, created_user:, message: nil, base_revision_id: nil
-      tag = page.tag_name.tag
-      if tag && page.tag_name.language_code == 'ja'
+      description = TagDescription.find_by(id: page.id)
+      if description
         return TagDescriptionOperation.update!(
-            tag:, body:, updated_by_user: created_user,
+            tag: description.tag, body:, updated_by_user: created_user,
             message:, base_revision_id:)
       end
 
diff --git a/backend/config/routes.rb b/backend/config/routes.rb
index c6664bc..7e3ab03 100644
--- a/backend/config/routes.rb
+++ b/backend/config/routes.rb
@@ -1,12 +1,4 @@
 Rails.application.routes.draw do
-  get 'tags/name/:name/description', to: 'tag_descriptions#show_by_title'
-
-  scope 'tags/:id/description', controller: :tag_descriptions do
-    get '', action: :show
-    post '', action: :create
-    put '', action: :update
-  end
-
   resources :nico_tags, path: 'tags/nico', only: [:index, :show, :update]
 
   scope 'tags/:parent_id/children', controller: :tag_children do
@@ -22,6 +14,7 @@ Rails.application.routes.draw do
 
       scope :name do
         get ':name/deerjikists', action: :deerjikists_by_name
+        get ':name/description', to: 'tag_descriptions#show_by_title'
         get ':name/materials', action: :materials_by_name
         get ':name', action: :show_by_name
       end
@@ -33,6 +26,9 @@ Rails.application.routes.draw do
 
       get :deerjikists
       put :deerjikists, action: :update_deerjikists
+
+      get :description, action: 'tag_descriptions#show'
+      put :description, action: 'tag_descriptions#update'
     end
   end
 
diff --git a/backend/spec/requests/tag_description_wiki_write_spec.rb b/backend/spec/requests/tag_description_wiki_write_spec.rb
index 5eb7323..798cffc 100644
--- a/backend/spec/requests/tag_description_wiki_write_spec.rb
+++ b/backend/spec/requests/tag_description_wiki_write_spec.rb
@@ -52,6 +52,58 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       expect(page.wiki_versions.last.body).to eq(version.body)
     end
 
+    ['missing_description', 'orphan_description'].each do |title|
+      it "rejects the bare title #{ title } without writing any resource" do
+        create(:tag_name, name: title) if title == 'orphan_description'
+        before_state = stored_state
+
+        post '/wiki', params: { title:, body: 'initial' }, headers: headers
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(json).to include('type' => 'validation_error')
+        expect(stored_state).to eq(before_state)
+      end
+    end
+
+    it 'creates a namespaced legacy Wiki resource without a Tag' do
+      expect do
+        post '/wiki', params: { title: 'Help:description_write', body: 'legacy' },
+             headers: headers
+      end.to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+          .and change(TagDescription, :count).by(0)
+          .and change(TagDescriptionVersion, :count).by(0)
+
+      expect(response).to have_http_status(:created)
+      page = WikiPage.find(json.fetch('id'))
+      expect(page.tag_name.tag).to be_nil
+      expect(page.body).to eq('legacy')
+      expect(page.current_revision.body).to eq('legacy')
+    end
+
+    it 'creates only legacy Wiki for a namespaced title with an existing Tag' do
+      namespaced_name = create(:tag_name, name: 'help:foo')
+      namespaced_tag = create(:tag, primary_tag_name: namespaced_name)
+
+      expect do
+        post '/wiki', params: { title: namespaced_name.name, body: 'legacy' },
+             headers: headers
+      end.to change(WikiPage, :count).by(1)
+          .and change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+          .and change(TagName, :count).by(0)
+          .and change(TagDescription, :count).by(0)
+          .and change(TagDescriptionVersion, :count).by(0)
+
+      expect(response).to have_http_status(:created)
+      page = WikiPage.find(json.fetch('id'))
+      expect(page).to have_attributes(tag_name_id: namespaced_name.id, body: 'legacy')
+      expect(page.tag_name.tag).to eq(namespaced_tag)
+      expect(page.current_revision.body).to eq('legacy')
+      expect(page.wiki_versions.last.body).to eq('legacy')
+    end
+
     [WikiPage, WikiRevision, WikiVersion, TagDescription, TagDescriptionVersion].each do |model|
       it "rolls back both systems when #{ model.name } persistence fails" do
         tag_name
@@ -101,6 +153,20 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       expect(page.wiki_versions.order(:version_no).last.body).to eq(version.body)
     end
 
+    it 'uses description identity even when its Wiki TagName no longer owns the Tag' do
+      tag_name.update_columns(tag_id: nil)
+
+      expect { update_description }
+          .to change(WikiRevision, :count).by(1)
+          .and change(WikiVersion, :count).by(1)
+          .and change(TagDescriptionVersion, :count).by(1)
+
+      expect(response).to have_http_status(:ok)
+      expect(description.reload).to have_attributes(body: 'after', version_no: 2)
+      expect(TagDescriptionVersion.find(page.reload.current_revision.id))
+          .to have_attributes(tag_id: tag.id, body: 'after', version_no: 2)
+    end
+
     it 'does not add body history for a title-only update' do
       revision_count = WikiRevision.count
       wiki_version_count = WikiVersion.count
@@ -111,10 +177,10 @@ RSpec.describe 'Tag description Wiki dual writes', type: :request do
       page_state = page.attributes
       description_state = description.attributes
 
-      update_description(body: 'before', title: 'description_renamed')
+      update_description(body: 'before', title: 'Help:description_renamed')
 
       expect(response).to have_http_status(:ok)
-      expect(tag_name.reload.name).to eq('description_renamed')
+      expect(tag_name.reload.name).to eq('Help:description_renamed')
       expect(WikiRevision.count).to eq(revision_count)
       expect(WikiVersion.count).to eq(wiki_version_count)
       expect(TagDescriptionVersion.count).to eq(description_version_count)
diff --git a/backend/spec/requests/tag_wiki_history_integrity_spec.rb b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
index a464c05..356e7e0 100644
--- a/backend/spec/requests/tag_wiki_history_integrity_spec.rb
+++ b/backend/spec/requests/tag_wiki_history_integrity_spec.rb
@@ -25,9 +25,10 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   describe 'PATCH /tags/:id' do
-    it 'records wiki_version when tag name changes and tag has wiki' do
+    it 'renames the current Wiki resource without adding body history' do
       tag = create_tag!(name: 'patch_tag_wiki_before')
       wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+      wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
       expect {
         patch "/tags/#{ tag.id }", params: {
@@ -35,23 +36,17 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
         }
       }
           .to change(TagVersion, :count).by(2)
-          .and change(WikiVersion, :count).by(1)
+          .and change(WikiVersion, :count).by(0)
 
       expect(response).to have_http_status(:ok)
 
       tag.reload
       wiki_page.reload
-      version = wiki_page.wiki_versions.order(:version_no).last
 
       expect(primary_tag_name_for(tag, 'ja').name).to eq('patch_tag_wiki_after')
       expect(wiki_page.title).to eq('patch_tag_wiki_after')
 
-      expect(version).to have_attributes(
-        event_type: 'update',
-        title: 'patch_tag_wiki_after',
-        body: 'wiki body before',
-        created_by_user_id: member_user.id
-      )
+      expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
     end
 
     it 'does not record wiki_version when only category changes' do
@@ -79,9 +74,10 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
   end
 
   describe 'PUT /tags/:id' do
-    it 'records wiki_version when tag name changes and tag has wiki' do
+    it 'renames the current Wiki resource without adding body history' do
       tag = create_tag!(name: 'put_tag_wiki_before')
       wiki_page = create_wiki_for_tag!(tag:, body: 'wiki body before')
+      wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
       expect {
         put "/tags/#{ tag.id }", params: {
@@ -93,23 +89,17 @@ RSpec.describe 'Tag and wiki history integrity', type: :request do
         }
       }
           .to change(TagVersion, :count).by(2)
-          .and change(WikiVersion, :count).by(1)
+          .and change(WikiVersion, :count).by(0)
 
       expect(response).to have_http_status(:ok)
 
       tag.reload
       wiki_page.reload
-      version = wiki_page.wiki_versions.order(:version_no).last
 
       expect(primary_tag_name_for(tag, 'ja').name).to eq('put_tag_wiki_after')
       expect(wiki_page.title).to eq('put_tag_wiki_after')
 
-      expect(version).to have_attributes(
-        event_type: 'update',
-        title: 'put_tag_wiki_after',
-        body: 'wiki body before',
-        created_by_user_id: member_user.id
-      )
+      expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
     end
 
     it 'does not record wiki_version when only category changes' do
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index c8bfd54..0d0b75a 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -727,7 +727,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(tag.reload.category).to eq('general')
       end
 
-      it 'PATCH で tag の name を変更すると対応する wiki version を作成する' do
+      it 'PATCH の名称変更で Wiki の本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -735,24 +735,20 @@ RSpec.describe 'Tags API', type: :request do
                 created_by_user: member_user,
                 message: 'init')
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           patch "/tags/#{ tag.id }", params: {
             name: 'patch_wiki_renamed_tag',
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'patch_wiki_renamed_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('patch_wiki_renamed_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it 'tag の category だけを変更しても wiki version は作成しない' do
@@ -1380,7 +1376,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(system_tag.category).to eq(old_category)
       end
 
-      it 'wiki を持つ tag を更新すると wiki version も作成する' do
+      it 'Wiki を持つ Tag の名称変更で本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -1395,6 +1391,8 @@ RSpec.describe 'Tags API', type: :request do
           message: 'init'
         )
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           put "/tags/#{ tag.id }", params: {
             name: 'put_wiki_version_tag',
@@ -1405,18 +1403,12 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'put_wiki_version_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('put_wiki_version_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it 'wiki を持つ tag を旧 alias へ戻しても wiki を新しい正本名へ移す' do
@@ -1426,6 +1418,7 @@ RSpec.describe 'Tags API', type: :request do
                 body: 'wiki body before',
                 created_by_user: member_user,
                 message: 'init')
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
 
         expect {
           put "/tags/#{ tag.id }", params: {
@@ -1445,7 +1438,7 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(3)
-            .and change(WikiVersion, :count).by(2)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
@@ -1457,10 +1450,8 @@ RSpec.describe 'Tags API', type: :request do
         expect(TagName.find_by!(language_code: 'ja', name: 'put_wiki_roundtrip_b'))
             .to have_attributes(tag_id: tag.id, primary_flg: false)
 
-        versions = wiki_page.wiki_versions.order(:version_no).last(2)
-
-        expect(versions.map(&:event_type)).to eq(['update', 'update'])
-        expect(versions.map(&:title)).to eq(['put_wiki_roundtrip_b', 'spec_tag'])
+        expect(wiki_page.title).to eq('spec_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
 
       it '別名を他 tag から奪った場合、奪はれた側の tag version も作成する' do
@@ -1570,7 +1561,7 @@ RSpec.describe 'Tags API', type: :request do
         expect(TagImplication.where(tag:, parent_tag: child)).not_to exist
       end
 
-      it 'tag の name を変更すると対応する wiki version を作成する' do
+      it 'Tag の名称変更で Wiki の本文履歴を追加しない' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: primary_tag_name_for(tag, 'ja'),
@@ -1578,6 +1569,8 @@ RSpec.describe 'Tags API', type: :request do
                 created_by_user: member_user,
                 message: 'init')
 
+        wiki_history = wiki_page.wiki_versions.map(&:attributes)
+
         expect {
           put "/tags/#{ tag.id }", params: {
             name: 'put_wiki_renamed_tag',
@@ -1588,18 +1581,12 @@ RSpec.describe 'Tags API', type: :request do
           }
         }
             .to change(TagVersion, :count).by(2)
-            .and change(WikiVersion, :count).by(1)
+            .and change(WikiVersion, :count).by(0)
 
         expect(response).to have_http_status(:ok)
 
-        version = wiki_page.reload.wiki_versions.order(:version_no).last
-
-        expect(version).to have_attributes(
-          event_type: 'update',
-          title: 'put_wiki_renamed_tag',
-          body: 'wiki body before',
-          created_by_user_id: member_user.id
-        )
+        expect(wiki_page.reload.title).to eq('put_wiki_renamed_tag')
+        expect(wiki_page.wiki_versions.reload.map(&:attributes)).to eq(wiki_history)
       end
     end
   end
diff --git a/backend/spec/requests/wiki_history_integrity_spec.rb b/backend/spec/requests/wiki_history_integrity_spec.rb
index db365c6..50de843 100644
--- a/backend/spec/requests/wiki_history_integrity_spec.rb
+++ b/backend/spec/requests/wiki_history_integrity_spec.rb
@@ -21,7 +21,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_create_atomic',
+               title: 'Help:wiki_history_create_atomic',
                body: "a\nb\nc",
                message: 'initial commit',
              },
@@ -37,7 +37,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       revision = page.current_revision
       version = page.wiki_versions.order(:version_no).last
 
-      expect(page.title).to eq('wiki_history_create_atomic')
+      expect(page.title).to eq('Help:wiki_history_create_atomic')
       expect(page.body).to eq("a\nb\nc")
 
       expect(revision).to be_content
@@ -47,7 +47,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect(version).to have_attributes(
         version_no: 1,
         event_type: 'create',
-        title: 'wiki_history_create_atomic',
+        title: 'Help:wiki_history_create_atomic',
         body: "a\nb\nc",
         reason: 'initial commit',
         created_by_user_id: user.id
@@ -58,7 +58,7 @@ RSpec.describe 'Wiki history integrity', type: :request do
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_blank_body',
+               title: 'Help:wiki_history_blank_body',
                body: "\r\n\r\n",
                message: 'blank',
              },
@@ -67,16 +67,17 @@ RSpec.describe 'Wiki history integrity', type: :request do
           .not_to change(WikiPage, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
-      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_blank_body' })).not_to exist
+      expect(WikiPage.joins(:tag_name)
+          .where(tag_names: { name: 'Help:wiki_history_blank_body' })).not_to exist
     end
 
     it 'returns 422 and creates no partial page when title already exists' do
-      create_wiki_page(title: 'wiki_history_duplicate_title', body: 'first')
+      create_wiki_page(title: 'Help:wiki_history_duplicate_title', body: 'first')
 
       expect {
         post '/wiki',
              params: {
-               title: 'wiki_history_duplicate_title',
+               title: 'Help:wiki_history_duplicate_title',
                body: 'second',
                message: 'duplicate',
              },
@@ -85,7 +86,8 @@ RSpec.describe 'Wiki history integrity', type: :request do
           .not_to change(WikiPage, :count)
 
       expect(response).to have_http_status(:unprocessable_entity)
-      expect(WikiPage.joins(:tag_name).where(tag_names: { name: 'wiki_history_duplicate_title' }).count).to eq(1)
+      expect(WikiPage.joins(:tag_name)
+          .where(tag_names: { name: 'Help:wiki_history_duplicate_title' }).count).to eq(1)
     end
   end
 
diff --git a/backend/spec/requests/wiki_spec.rb b/backend/spec/requests/wiki_spec.rb
index bbd1c22..5a4eeae 100644
--- a/backend/spec/requests/wiki_spec.rb
+++ b/backend/spec/requests/wiki_spec.rb
@@ -111,7 +111,7 @@ RSpec.describe 'Wiki API', type: :request do
     context 'when success' do
       it 'creates wiki_page and first content revision' do
         expect do
-          post endpoint, params: { title: 'TestPage', body: "a\nb\nc", message: 'init' },
+          post endpoint, params: { title: 'Help:TestPage', body: "a\nb\nc", message: 'init' },
                          headers: auth_headers(member)
         end
             .to change(WikiPage, :count).by(1)
@@ -121,7 +121,7 @@ RSpec.describe 'Wiki API', type: :request do
         expect(response).to have_http_status(:created)
 
         page_id = json.fetch('id')
-        expect(json.fetch('title')).to eq('TestPage')
+        expect(json.fetch('title')).to eq('Help:TestPage')
 
         created_page = WikiPage.find(page_id)
         version = created_page.wiki_versions.order(:version_no).last
@@ -129,7 +129,7 @@ RSpec.describe 'Wiki API', type: :request do
         expect(version).to have_attributes(
           version_no: 1,
           event_type: 'create',
-          title: 'TestPage',
+          title: 'Help:TestPage',
           body: "a\nb\nc",
           created_by_user_id: member.id
         )
@@ -151,7 +151,7 @@ RSpec.describe 'Wiki API', type: :request do
         WikiLine.create!(sha256: Digest::SHA256.hexdigest('a'), body: 'a', created_at: Time.current, updated_at: Time.current)
 
         post endpoint,
-             params: { title: 'Reuse', body: "a\na" },
+             params: { title: 'Help:Reuse', body: "a\na" },
              headers: auth_headers(member)
 
         page = WikiPage.find(JSON.parse(response.body).fetch('id'))
@@ -166,7 +166,7 @@ RSpec.describe 'Wiki API', type: :request do
         duplicated = 'duplicated_line_for_wiki_line_upsert_spec'
 
         post endpoint,
-             params: { title: 'DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
+             params: { title: 'Help:DuplicateNewLine', body: "#{ duplicated }\n#{ duplicated }" },
              headers: auth_headers(member)
 
         expect(response).to have_http_status(:created)
@@ -182,7 +182,8 @@ RSpec.describe 'Wiki API', type: :request do
 
       it 'normalises CRLF and strips trailing newlines' do
         post endpoint,
-             params: { title: 'NormalisedBody', body: "a\r\nb\r\n\r\n", message: 'normalise' },
+             params: { title: 'Help:NormalisedBody',
+                       body: "a\r\nb\r\n\r\n", message: 'normalise' },
              headers: auth_headers(member)
 
         expect(response).to have_http_status(:created)
diff --git a/backend/spec/requests/wiki_title_collision_spec.rb b/backend/spec/requests/wiki_title_collision_spec.rb
index f78f987..a8df14b 100644
--- a/backend/spec/requests/wiki_title_collision_spec.rb
+++ b/backend/spec/requests/wiki_title_collision_spec.rb
@@ -44,12 +44,12 @@ RSpec.describe 'Wiki title collision', type: :request do
   end
 
   it 'returns 422 when creating wiki with existing title' do
-    create_wiki_page(title: 'wiki_collision_create', body: 'already exists')
+    create_wiki_page(title: 'Help:wiki_collision_create', body: 'already exists')
 
     expect {
       post '/wiki',
            params: {
-             title: 'wiki_collision_create',
+             title: 'Help:wiki_collision_create',
              body: 'new body',
              message: 'duplicate create',
            },
diff --git a/backend/spec/requests/wiki_unmigrated_contract_spec.rb b/backend/spec/requests/wiki_unmigrated_contract_spec.rb
index 1029b0f..9cd106b 100644
--- a/backend/spec/requests/wiki_unmigrated_contract_spec.rb
+++ b/backend/spec/requests/wiki_unmigrated_contract_spec.rb
@@ -14,6 +14,25 @@ RSpec.describe 'Unmigrated Wiki compatibility', type: :request do
 
   before { expect(TagDescription.exists?(id: page.id)).to be(false) }
 
+  it 'keeps a Tag-linked legacy page in the legacy domain when its title changes' do
+    create(:tag, primary_tag_name: tag_name)
+
+    expect do
+      put "/wiki/#{ page.id }",
+          params: { title: 'legacy_tag_renamed', body: 'changed legacy body',
+                    message: 'legacy rename', base_revision_id: last_revision.id },
+          headers: { 'X-Transfer-Code' => user.inheritance_code }
+    end.to change(WikiRevision, :count).by(1)
+        .and change(WikiVersion, :count).by(1)
+        .and change(TagDescription, :count).by(0)
+        .and change(TagDescriptionVersion, :count).by(0)
+
+    expect(response).to have_http_status(:ok)
+    expect(page.reload).to have_attributes(body: 'changed legacy body')
+    expect(page.title).to eq('legacy_tag_renamed')
+    expect(page.current_revision).to have_attributes(message: 'legacy rename')
+  end
+
   it 'shows legacy current and historical content by ID' do
     get "/wiki/#{ page.id }"
     expect(response).to have_http_status(:ok)