WIP: preserve failed Codex job issue-242-hhdxc839

Refs #454

## Automated implementation (requires human review)
[SidebarComponent.tsx](frontend/src/components/layout/SidebarComponent.tsx) の1行を修正しました。`overflow-y-auto` を `md` 以上に限定し、スマホでサゼストがサイドバーの領域外で切られる原因を取り除きました。

差分を確認済みです。指定に従い、テスト・lint・ビルドは未実行です。実画面でのスマホ表示とPC表示の確認も未実施です。

## Automated review (not a guarantee of correctness)
```text
The change restricts sidebar scrolling to medium and larger viewports. No actionable regression was identified in the current diff.

```

## Verification
- Tests/builds/migrations were not authorized and were not invoked by the controller.
- Codex was instructed not to run them; its command transcript should be inspected.
- Do not merge before manual acceptance and required checks.

---------

Co-authored-by: Codex Night Worker <codex-night@localhost>
Reviewed-on: #456
Co-authored-by: テツノニジカ <969+codex-bot@noreply.localhost>

backend/db/migrate/20261115000000_add_post_count_index_to_tags.rb

@@ -0,0 +1,5 @@
+class AddPostCountIndexToTags < ActiveRecord::Migration[8.0]
+  def change
+    add_index :tags, :post_count
+  end
+end

backend/db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_10_15_010000) do
+ActiveRecord::Schema[8.0].define(version: 2026_11_15_000000) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -630,6 +630,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_10_15_010000) do
     t.integer "post_count", default: 0, null: false
     t.integer "version_no", null: false
     t.index ["deprecated_at"], name: "index_tags_on_deprecated_at"
+    t.index ["post_count"], name: "index_tags_on_post_count"
     t.check_constraint "(`deprecated_at` is null) or (`category` <> _utf8mb4'nico')", name: "chk_tags_deprecated_at_not_nico"
     t.check_constraint "`version_no` > 0", name: "chk_tags_version_no_positive"
   end

backend/spec/models/tag_spec.rb

@@ -2,6 +2,19 @@ require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
   include WikiRecords
+
+  describe 'post_count index' do
+    it 'has a non-unique index on post_count alone' do
+      indexes = described_class.connection.indexes(described_class.table_name)
+
+      expect(indexes).to include(
+          have_attributes(
+              name: 'index_tags_on_post_count',
+              columns: ['post_count'],
+              unique: false))
+    end
+  end
+
   describe '#has_description?' do
     let(:tag) { create(:tag) }
 

frontend/src/components/PostFormTagsArea.tsx

@@ -36,13 +36,10 @@ const replaceToken = (value: string, start: number, end: number, text: string) =
 type Props = Omit<ComponentPropsWithoutRef<'textarea'>, 'value' | 'onChange' | 'onBlur'> & {
     tags:     string
     setTags:  (tags: string) => void
-    label?:   ReactNode
     errors?:  ReactNode[] }
 
 
-const PostFormTagsArea: FC<Props> = (
-    { tags, setTags, label: fieldLabel, errors, ...rest },
-) => {
+const PostFormTagsArea: FC<Props> = ({ tags, setTags, errors, ...rest }) => {
   const { label } = useUITranslation ('navigation')
   const locale = useLocale ()
   const ref = useRef<HTMLTextAreaElement> (null)
@@ -120,10 +117,7 @@ const PostFormTagsArea: FC<Props> = (
   }, [locale])
 
   return (
-      <FormField
-	  className="relative w-full"
-	  label={fieldLabel ?? label ('tags')}
-	  messages={errors}>
+      <FormField className="relative w-full" label={label ('tags')} messages={errors}>
 	{({ describedBy, invalid }) => (
 	    <>
 	      <TextArea

frontend/src/components/layout/SidebarComponent.test.tsx

@@ -70,6 +70,16 @@ describe ('SidebarComponent', () => {
     vi.spyOn (HTMLElement.prototype, 'hasPointerCapture').mockReturnValue (true)
   })
 
+  it ('limits sidebar scrolling to desktop to avoid clipping mobile suggestions', () => {
+    renderSidebar ()
+
+    // jsdom has no layout; guard the responsive classes responsible for clipping.
+    const sidebar = screen.getByText ('Sidebar body')
+
+    expect (sidebar).not.toHaveClass ('overflow-y-auto')
+    expect (sidebar).toHaveClass ('md:overflow-y-auto')
+  })
+
   it ('uses maxWidth without applying the container main-width reserve twice', async () => {
     localStorage.setItem ('sidebar:test-sidebar:left:width', '700')
     const onWidthChange = vi.fn ()

frontend/src/components/layout/SidebarComponent.tsx

@@ -339,7 +339,7 @@ const SidebarComponent: FC<Props> = ({
 	  </style>
 	</Helmet>
 
-	<div className="h-full overflow-y-auto p-4 sidebar">
+	<div className="h-full md:overflow-y-auto p-4 sidebar">
 	  {children}
 	</div>
 

frontend/src/pages/tags/NicoTagListPage.test.tsx

@@ -162,13 +162,12 @@ describe ('NicoTagListPage', () => {
     })
   })
 
-  it ('saves links after completing the tag at the cursor', async () => {
+  it ('updates links from a tag card', async () => {
     api.apiGet
       .mockResolvedValueOnce ({
         tags:  [buildNicoTag ({ id: 7, name: 'nico:source' })],
         count: 1,
       })
-      .mockResolvedValueOnce ([buildTag ({ id: 8, name: '連携先', postCount: 3 })])
       .mockResolvedValueOnce ({
         tags: [
           buildNicoTag ({
@@ -184,24 +183,8 @@ describe ('NicoTagListPage', () => {
     renderPage ()
 
     fireEvent.click (await screen.findByRole ('button', { name: '編集' }))
-    const textarea = screen.getByLabelText ('連携する広場タグ')
-    fireEvent.change (textarea, { target: { value: '既存 連携\n後続' } })
-    fireEvent.focus (textarea)
-    fireEvent.select (textarea, {
-	target: { selectionStart: 4, selectionEnd: 4 } })
-
-    await waitFor (() => {
-      expect (api.apiGet).toHaveBeenCalledWith (
-	  '/tags/autocomplete',
-	  { locale: 'ja', params: { q: '連携', nico: '0' },
-	    signal: expect.any (AbortSignal) })
-    })
-    fireEvent.mouseDown (await screen.findByText ('連携先'))
-
-    expect (textarea).toHaveValue ('既存 連携先 \n後続')
-    await waitFor (() => {
-      expect ((textarea as HTMLTextAreaElement).selectionStart).toBe (7)
-      expect ((textarea as HTMLTextAreaElement).selectionEnd).toBe (7)
+    fireEvent.change (screen.getByLabelText ('連携する広場タグ'), {
+      target: { value: '連携先' },
     })
     fireEvent.click (screen.getByRole ('button', { name: '保存' }))
 
@@ -212,8 +195,6 @@ describe ('NicoTagListPage', () => {
           { locale: 'ja', headers: { 'Content-Type': 'multipart/form-data' } },
       )
     })
-    const payload = api.apiPut.mock.calls[0][1] as FormData
-    expect (payload.get ('tags')).toBe ('既存 連携先 \n後続')
     expect (await screen.findByText ('1 件')).toBeInTheDocument ()
   })
 

frontend/src/pages/tags/NicoTagListPage.tsx

@@ -6,10 +6,11 @@ import { useLocation } from 'react-router-dom'
 import { useLocale, useLocaleNavigate } from '@/lib/useLocale'
 import TagLink from '@/components/TagLink'
 import SortHeader from '@/components/SortHeader'
-import PostFormTagsArea from '@/components/PostFormTagsArea'
+import FieldError from '@/components/common/FieldError'
 import FormField from '@/components/common/FormField'
 import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
+import TextArea from '@/components/common/TextArea'
 import useDialogue from '@/lib/dialogues/useDialogue'
 import MainArea from '@/components/layout/MainArea'
 import { toast } from '@/components/ui/use-toast'
@@ -356,18 +357,21 @@ const NicoTagListPage: FC<Props> = ({ user }) => {
 					       dark:bg-rose-950/30">
 				  <td colSpan={editable ? 5 : 4} className="p-3">
 				    <div className="space-y-2">
-				      <PostFormTagsArea
+				      <label htmlFor={`nico-links-${ tag.id }`}
+					     className="block text-sm font-semibold">
+					{label ('nico.tagsToLink')}
+				      </label>
+				      <TextArea
 					  id={`nico-links-${ tag.id }`}
-					  label={label ('nico.tagsToLink')}
-					  aria-label={message ('nico.tagsToLink').text}
-					  tags={rawTags[tag.id] ?? ''}
-					  errors={errors}
+					  value={rawTags[tag.id] ?? ''}
+					  invalid={(errorsByTagId[tag.id] ?? []).length > 0}
 					  className="min-h-24 resize-y"
 					  placeholder={message ('nico.tagsPlaceholder').text}
 					  lang={message ('nico.tagsPlaceholder').language}
-					  setTags={value => setRawTags (rawTags => ({
+					  onChange={e => setRawTags (rawTags => ({
 					      ...rawTags,
-					      [tag.id]: value}))}/>
+					      [tag.id]: e.target.value}))}/>
+				      <FieldError messages={errors}/>
 				      <div className="flex justify-end gap-2">
 					<button
 					    type="button"

frontend/src/pages/tags/TagDetailPage.test.tsx

@@ -35,6 +35,10 @@ const renderPage = () =>
 describe ('TagDetailPage', () => {
   beforeEach (() => {
     vi.clearAllMocks ()
+    tagsApi.fetchTag.mockReset ()
+    api.apiPut.mockReset ()
+    api.isApiError.mockReset ()
+    toastApi.toast.mockReset ()
     api.isApiError.mockReturnValue (false)
   })
 
@@ -51,8 +55,11 @@ describe ('TagDetailPage', () => {
   })
 
   it ('submits edited tag fields', async () => {
-    tagsApi.fetchTag.mockResolvedValueOnce (buildTag ({ id: 7, name: 'old' }))
-    api.apiPut.mockResolvedValueOnce (buildTag ({ id: 7, name: 'new', aliases: ['alias'] }))
+    const updatedTag = buildTag ({ id: 7, name: 'new', aliases: ['alias'] })
+    tagsApi.fetchTag
+	.mockResolvedValue (updatedTag)
+	.mockResolvedValueOnce (buildTag ({ id: 7, name: 'old' }))
+    api.apiPut.mockResolvedValueOnce (updatedTag)
 
     renderPage ()