#424

frontend/src/lib/help.test.ts

@@ -4,6 +4,36 @@ import { createHelpFixture } from '@/test/helpFixtures'
 
 
 describe ('Help file catalogue', () => {
+  it.each ([['ほーむ', 'ホーム'], ['ホーム', 'ほーむ'], ['ﾎｰﾑ', 'ホーム'],
+      ['ＡＢＣ', 'abc'], ['ｶﾞｲﾄﾞ', 'がいど']]) (
+      'normalises search text %s and %s identically', (query, text) => {
+	const { api } = createHelpFixture ()
+	expect (api.normaliseHelpSearchText (query)).toBe (api.normaliseHelpSearchText (text))
+      })
+
+  it.each ([['2026-10-02', null], ['2026-10-02.2', 2],
+      ['2026-10-02.3', 3], ['2026-10-02.10', 10]] as const) (
+      'separates the date and revision of %s', (edition, revision) => {
+	const { api } = createHelpFixture ()
+	expect (api.parseHelpEdition (edition)).toEqual ({ date: '2026-10-02', revision })
+	const date = api.helpEditionDate (edition)!
+	expect ([date.getFullYear (), date.getMonth (), date.getDate ()]).toEqual ([2026, 9, 2])
+      })
+
+  it.each (['missing', '2026-02-30', '2026-10-02.0', '2026-10-02.2.extra',
+      '2026-10-02.9007199254740992']) ('rejects invalid edition %s', edition => {
+    const { api } = createHelpFixture ()
+    expect (api.parseHelpEdition (edition)).toBeNull ()
+    expect (api.helpEditionDate (edition)).toBeNull ()
+  })
+
+  it ('compares numeric revision suffixes without losing the edition identifiers', () => {
+    const { api } = createHelpFixture ()
+    expect (['2026-10-02.10', '2026-10-02.3', '2026-10-02', '2026-10-02.2']
+	.sort (api.compareHelpEditions)).toEqual ([
+	'2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10'])
+  })
+
   it ('uses current_edition rather than the newest file, without YAML titles', async () => {
     const { api } = createHelpFixture ()
     expect ((await api.getHelpArticle ('guide'))?.languages.ja.currentEdition)

frontend/src/lib/help.ts

@@ -31,6 +31,42 @@ export type HelpDiff = {
     to: HelpEditionSource
     lines: HelpDiffLine[] }
 
+export type HelpEditionIdentifier = { date: string; revision: number | null }
+
+
+export const normaliseHelpSearchText = (value: string): string =>
+    value.normalize ('NFKC').toLowerCase ().replace (/[ァ-ヶヽヾ]/g,
+	character => String.fromCodePoint (character.codePointAt (0)! - 0x60))
+
+
+export const parseHelpEdition = (edition: string): HelpEditionIdentifier | null => {
+  const matched = edition.match (/^(\d{4}-\d{2}-\d{2})(?:\.([1-9]\d*))?$/)
+  if (matched == null)
+    return null
+  const date = new Date (matched[1])
+  const revision = matched[2] == null ? null : Number (matched[2])
+  if (Number.isNaN (date.getTime ()) || date.toISOString ().slice (0, 10) !== matched[1]
+      || (revision != null && !(Number.isSafeInteger (revision))))
+    return null
+  return { date: matched[1], revision }
+}
+
+
+export const compareHelpEditions = (a: string, b: string): number => {
+  const before = parseHelpEdition (a)
+  const after = parseHelpEdition (b)
+  if (before == null || after == null)
+    return a.localeCompare (b)
+  return before.date.localeCompare (after.date)
+      || (before.revision ?? 1) - (after.revision ?? 1)
+}
+
+
+export const helpEditionDate = (edition: string): Date | null => {
+  const parsed = parseHelpEdition (edition)
+  return parsed == null ? null : new Date (`${ parsed.date }T00:00:00`)
+}
+
 
 export const getHelpArticle = async (identifier: string): Promise<ArticleMeta | null> => {
   const { default: articles } = await import ('virtual:help/articles')

frontend/src/lib/tags.test.ts

@@ -72,11 +72,25 @@ describe ('tags API functions', () => {
     )
   })
 
-  it ('returns null when tag fetches fail', async () => {
+  it ('returns null for a missing named tag while retaining the ID helper contract', async () => {
-    api.apiGet.mockRejectedValueOnce (new Error ('missing'))
     api.apiGet.mockRejectedValueOnce (new Error ('missing'))
+    api.apiGet.mockRejectedValueOnce ({ isAxiosError: true, response: { status: 404 } })
 
     await expect (fetchTag ('1')).resolves.toBeNull ()
     await expect (fetchTagByName ('unknown')).resolves.toBeNull ()
   })
+
+  it.each ([403, 500]) ('propagates named tag HTTP %s', async status => {
+    const error = { isAxiosError: true, response: { status } }
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchTagByName ('ホーム')).rejects.toBe (error)
+  })
+
+  it ('propagates named tag network failures and encodes the name', async () => {
+    const error = new Error ('offline')
+    api.apiGet.mockRejectedValueOnce (error)
+    await expect (fetchTagByName ('名前/#%')).rejects.toBe (error)
+    expect (api.apiGet).toHaveBeenLastCalledWith (
+	`/tags/name/${ encodeURIComponent ('名前/#%') }`)
+  })
 })

frontend/src/lib/tags.ts

@@ -1,3 +1,5 @@
+import { isAxiosError } from 'axios'
+
 import { apiGet } from '@/lib/api'
 
 import type { Deerjikist,
@@ -68,11 +70,13 @@ export const fetchExternalTag = async (id: string): Promise<Tag | null> => {
 export const fetchTagByName = async (name: string): Promise<Tag | null> => {
   try
   {
-    return await apiGet (`/tags/name/${ name }`)
+    return await apiGet (`/tags/name/${ encodeURIComponent (name) }`)
   }
-  catch
+  catch (error)
   {
-    return null
+    if (isAxiosError (error) && error.response?.status === 404)
+      return null
+    throw error
   }
 }
 

frontend/src/pages/help/HelpChangesPage.test.tsx

@@ -41,6 +41,8 @@ describe ('Help global edition history', () => {
     expect (screen.getAllByRole ('columnheader').map (cell => cell.textContent))
 	.toEqual (['差分', 'タイトル', '有効開始年月日'])
     expect (container).not.toHaveTextContent ('未公開ホーム')
+    expect (container).not.toHaveTextContent ('Invalid Date')
+    expect (container.textContent).not.toMatch (/\d{1,2}:\d{2}/)
     expect (screen.getAllByRole ('link', { name: '差分' }).map (link =>
 	link.getAttribute ('href'))).toEqual ([
 	'/help/guide/diff?from=2026-10-02.3&to=2026-10-02.10',

frontend/src/pages/help/HelpChangesPage.tsx

@@ -8,7 +8,7 @@ import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
-import { getHelpChanges } from '@/lib/help'
+import { getHelpChanges, helpEditionDate } from '@/lib/help'
 import { helpKeys } from '@/lib/queryKeys'
 import { LIST_LIMIT_OPTIONS } from '@/lib/settings'
 import { dateString } from '@/lib/utils'
@@ -85,7 +85,7 @@ const HelpChangesPage: FC = () => {
 			  const diffQuery = new URLSearchParams ({
 			      from: entry.pred ?? '', to: entry.edition })
 			  const diffTo = `${ path }/diff?${ diffQuery.toString () }`
-			  const updatedAt = `${ entry.date }T00:00:00`
+			  const updatedAt = helpEditionDate (entry.edition)
 
 			  return (
 			      <tr key={`${ entry.identifier }/${ entry.edition }`}
@@ -102,7 +102,9 @@ const HelpChangesPage: FC = () => {
 				    {entry.title}
 				  </PrefetchLink>
 				</td>
-				<td className="p-2">{dateString (updatedAt, 'hour')}</td>
+				<td className="p-2">
+				  {updatedAt != null && dateString (updatedAt, 'hour')}
+				</td>
 			      </tr>)
 			})}
 		      </tbody>

frontend/src/pages/help/HelpDetailPage.test.tsx

@@ -37,6 +37,20 @@ const renderDetail = (route = '/help/guide') => renderWithProviders (
 describe ('Help details', () => {
   beforeEach (() => helpFixture.reset ())
 
+  it.each (['2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10']) (
+      'displays a date without inventing a time for edition %s', async edition => {
+	const { container } = renderDetail (`/help/guide?edition=${ edition }`)
+	await screen.findByRole ('heading')
+	expect (container).toHaveTextContent ('10月2日')
+	expect (container).not.toHaveTextContent ('Invalid Date')
+	expect (container.textContent).not.toMatch (/\d{1,2}:\d{2}/)
+	const revision = edition.split ('.')[1]
+	if (revision != null)
+	  expect (container).toHaveTextContent (` .${ revision }`)
+	expect (helpFixture.modules[`../../help/guide/editions/ja/${ edition }.mdx`])
+	    .toHaveBeenCalled ()
+      })
+
   it ('displays current_edition H1 and body even when newer files exist', async () => {
     renderDetail ()
     expect (await screen.findByRole ('heading', { name: 'ホーム第十版' }))
@@ -70,6 +84,7 @@ describe ('Help details', () => {
   })
 
   it.each (['/help/missing', '/help/guide?edition=missing',
+      '/help/guide?edition=2026-02-30', '/help/guide?edition=2026-10-02.2.extra',
       '/help/guide?edition=2026-10-02.11']) (
       'shows NotFound without redirecting %s', async route => {
 	renderDetail (route)

frontend/src/pages/help/HelpDetailPage.tsx

@@ -5,7 +5,10 @@ import { useLocation, useParams } from 'react-router-dom'
 import PrefetchLink from '@/components/PrefetchLink'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
-import { getHelpArticle, getHelpEditionContent } from '@/lib/help'
+import { getHelpArticle,
+	 getHelpEditionContent,
+	 helpEditionDate,
+	 parseHelpEdition } from '@/lib/help'
 import { dateString } from '@/lib/utils'
 import { helpKeys } from '@/lib/queryKeys'
 import NotFound from '@/pages/NotFound'
@@ -31,6 +34,8 @@ const HelpDetailPage: FC = () => {
   const languageMeta = article?.languages[language]
 
   const edition = requestedEdition ?? languageMeta?.currentEdition
+  const editionInfo = parseHelpEdition (edition ?? '')
+  const editionDate = helpEditionDate (edition ?? '')
 
   const editions = languageMeta?.publishedEditions ?? []
 
@@ -42,7 +47,7 @@ const HelpDetailPage: FC = () => {
       : undefined
 
   const { data: current, isSuccess, isError } = useQuery ({
-      enabled: edition != null && editions.includes (edition),
+      enabled: edition != null && editionInfo != null && editions.includes (edition),
       queryKey: helpKeys.edition (identifier, language, edition ?? ''),
       queryFn: () => getHelpEditionContent (identifier, language, edition ?? ''),
       staleTime: Infinity })
@@ -51,6 +56,7 @@ const HelpDetailPage: FC = () => {
       && (article == null
 	  || languageMeta == null
 	  || edition == null
+	  || editionInfo == null
 	  || !(editions.includes (edition))))
     return <NotFound/>
 
@@ -76,7 +82,10 @@ const HelpDetailPage: FC = () => {
 		  </PrefetchLink>)
 	       : '(最古)'}
 
-	      <span>{dateString (edition, 'hour')}</span>
+	      <span>
+		{editionDate != null && dateString (editionDate, 'hour')}
+		{editionInfo?.revision != null && ` .${ editionInfo.revision }`}
+	      </span>
 
 	      {succ
 	       ? (

frontend/src/pages/help/HelpListPage.test.tsx

@@ -52,4 +52,65 @@ describe ('Help search', () => {
     expect (await screen.findByRole ('alert')).toHaveTextContent ('fixture loading failed')
     expect (screen.queryByRole ('link', { name: 'ホーム第十版' })).not.toBeInTheDocument ()
   })
+
+  it ('sorts edition suffixes numerically and displays their date without a time', async () => {
+    const editions = ['2026-10-02', '2026-10-02.2', '2026-10-02.3', '2026-10-02.10']
+    helpFixture.assets.search.default.ja = editions.map ((edition, index) => ({
+	identifier: `article-${ index }`, edition, title: `article-${ index }`, body: '' }))
+    const { container } = renderWithProviders (<HelpListPage/>, { route: '/help' })
+    await screen.findByText ('4 件')
+    expect (Array.from (container.querySelectorAll ('tbody a'), link => link.textContent))
+	.toEqual (['article-3', 'article-2', 'article-1', 'article-0'])
+    const dates = Array.from (container.querySelectorAll ('tbody tr'), row =>
+	row.children[1].textContent)
+    expect (dates).toHaveLength (4)
+    dates.forEach (date => {
+      expect (date).toContain ('10月2日')
+      expect (date).not.toContain ('Invalid Date')
+      expect (date).not.toMatch (/\d{1,2}:\d{2}/)
+    })
+  })
+
+  it.each ([['ホーム', 'ほーむ', '', true], ['ほーむ', 'ホーム', '', true],
+      ['ホーム', 'ﾎｰﾑ', '', true], ['ホーム', '', 'ホーム', true],
+      ['ホーム', 'ほーむ', 'ﾎｰﾑ', true], ['ホーム', 'ほーむ', '不一致', false]] as const) (
+      'searches title %s with %s and body with %s', async (title, query, text, found) => {
+	const entry = { identifier: 'guide', edition: '2026-10-02.10',
+	    title, body: 'ほーむの案内' }
+	helpFixture.assets.search.default.ja = [entry]
+	const params = new URLSearchParams ({ title: query, text })
+	renderWithProviders (<HelpListPage/>, { route: `/help?${ params }` })
+	await screen.findByText (`${ found ? 1 : 0 } 件`)
+	if (found)
+	  expect (screen.getByRole ('link', { name: title })).toHaveAttribute ('href', '/help/guide')
+	else
+	  expect (screen.queryByRole ('link', { name: title })).not.toBeInTheDocument ()
+	expect (entry).toEqual ({ identifier: 'guide', edition: '2026-10-02.10',
+	    title, body: 'ほーむの案内' })
+      })
+
+  // ai_ci equality is documented by MySQL; these are not captured DB sort results.
+  it.each (['asc', 'desc']) ('uses identifier ties for MySQL ai_ci title order %s',
+      async direction => {
+	helpFixture.assets.search.default.ja = [
+	    { identifier: 'alpha', edition: '2026-10-02', title: 'Éclair', body: '' },
+	    { identifier: 'beta', edition: '2026-10-02', title: 'eclair', body: '' }]
+	const { container } = renderWithProviders (<HelpListPage/>, {
+	    route: `/help?order=title:${ direction }` })
+	await screen.findByText ('2 件')
+	expect (Array.from (container.querySelectorAll ('tbody a'), link =>
+	    link.getAttribute ('href'))).toEqual (['/help/alpha', '/help/beta'])
+      })
+
+  it.each (['asc', 'desc']) ('ignores title case before identifier ties in order %s',
+      async direction => {
+	helpFixture.assets.search.default.ja = [
+	    { identifier: 'alpha', edition: '2026-10-02', title: 'home', body: '' },
+	    { identifier: 'beta', edition: '2026-10-02', title: 'HOME', body: '' }]
+	const { container } = renderWithProviders (<HelpListPage/>, {
+	    route: `/help?order=title:${ direction }` })
+	await screen.findByText ('2 件')
+	expect (Array.from (container.querySelectorAll ('tbody a'), link =>
+	    link.getAttribute ('href'))).toEqual (['/help/alpha', '/help/beta'])
+      })
 })

frontend/src/pages/help/HelpListPage.tsx

@@ -10,7 +10,10 @@ import PageTitle from '@/components/common/PageTitle'
 import Pagination from '@/components/common/Pagination'
 import MainArea from '@/components/layout/MainArea'
 import { SITE_TITLE } from '@/config'
-import { getHelpSearchEntries } from '@/lib/help'
+import { compareHelpEditions,
+	 getHelpSearchEntries,
+	 helpEditionDate,
+	 normaliseHelpSearchText } from '@/lib/help'
 import { helpKeys } from '@/lib/queryKeys'
 import { LIST_LIMIT_OPTIONS } from '@/lib/settings'
 import { dateString, inputClass } from '@/lib/utils'
@@ -55,22 +58,20 @@ const HelpSearchPage: FC = () => {
   }, [conditions.title, conditions.text])
 
   const results = useMemo (() => {
-    const titleQuery = conditions.title.trim ().normalize ('NFKC').toLowerCase ()
+    const titleQuery = normaliseHelpSearchText (conditions.title.trim ())
-    const textQuery = conditions.text.trim ().normalize ('NFKC').toLowerCase ()
+    const textQuery = normaliseHelpSearchText (conditions.text.trim ())
     const [field, direction] = order.split (':')
 
     return (
 	entries.filter (entry => (
 	    (!(titleQuery)
-	     || entry.title.normalize ('NFKC').toLowerCase ().includes (titleQuery))
+	     || normaliseHelpSearchText (entry.title).includes (titleQuery))
 	    && (!(textQuery)
-		|| entry.body.normalize ('NFKC').toLowerCase ().includes (textQuery))))
+		|| normaliseHelpSearchText (entry.body).includes (textQuery))))
 	.sort ((a, b) => {
-	  const [dateA, revisionA = '1'] = a.edition.split ('.')
-	  const [dateB, revisionB = '1'] = b.edition.split ('.')
 	  const comparison = field === 'title'
 	      ? a.title.localeCompare (b.title, 'ja')
-	      : (dateA.localeCompare (dateB) || Number (revisionA) - Number (revisionB))
+	      : compareHelpEditions (a.edition, b.edition)
 
 	  return (direction === 'asc' ? comparison : -comparison)
 	      || a.identifier.localeCompare (b.identifier)
@@ -180,7 +181,7 @@ const HelpSearchPage: FC = () => {
 		      </thead>
 		      <tbody>
 			{pageResults.map (entry => {
-			  const updatedAt = new Date (entry.edition.replace (/\..*$/, ''))
+			  const updatedAt = helpEditionDate (entry.edition)
 
 			  return (
 			      <tr key={entry.identifier}
@@ -192,7 +193,9 @@ const HelpSearchPage: FC = () => {
 				    {entry.title}
 				  </PrefetchLink>
 				</td>
-				<td className="p-2">{dateString (updatedAt, 'hour')}</td>
+				<td className="p-2">
+				  {updatedAt != null && dateString (updatedAt, 'hour')}
+				</td>
 			      </tr>)
 			})}
 		      </tbody>

frontend/src/pages/wiki/WikiDetailPage.test.tsx

@@ -1,14 +1,18 @@
-import { screen } from '@testing-library/react'
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
 import { Route, Routes } from 'react-router-dom'
-import { describe, expect, it, vi } from 'vitest'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
 
+import { apiPost } from '@/lib/api'
+import { getHelpTitleIndex } from '@/lib/help'
 import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
-import { buildTag, buildWikiPage } from '@/test/factories'
+import WikiNewPage from '@/pages/wiki/WikiNewPage'
+import { buildTag, buildUser, buildWikiPage } from '@/test/factories'
 import { renderWithProviders } from '@/test/render'
 
 const wikiApi = vi.hoisted (() => ({
   fetchWikiPage:        vi.fn (),
   fetchWikiPageByTitle: vi.fn (),
+  fetchWikiPages:       vi.fn (),
 }))
 
 const tagsApi = vi.hoisted (() => ({
@@ -22,8 +26,93 @@ const postsApi = vi.hoisted (() => ({
 vi.mock ('@/lib/wiki', () => wikiApi)
 vi.mock ('@/lib/tags', () => tagsApi)
 vi.mock ('@/lib/posts', () => postsApi)
+vi.mock ('@/lib/help', () => ({ getHelpTitleIndex: vi.fn () }))
+vi.mock ('@/lib/api', () => ({ apiPost: vi.fn () }))
+vi.mock ('@/components/ui/use-toast', () => ({ toast: vi.fn () }))
+vi.mock ('react-markdown-editor-lite', () => ({
+    default: ({ value, onChange }: {
+	value: string
+	onChange: (event: { text: string }) => void }) => (
+	    <textarea aria-label="本文エディタ" value={value}
+		onChange={event => onChange ({ text: event.target.value })}/>) }))
 
 describe ('WikiDetailPage', () => {
+  beforeEach (() => {
+    wikiApi.fetchWikiPageByTitle.mockReset ().mockResolvedValue (null)
+    wikiApi.fetchWikiPages.mockReset ().mockResolvedValue ([])
+    tagsApi.fetchTagByName.mockReset ().mockResolvedValue (null)
+    postsApi.fetchPosts.mockReset ().mockResolvedValue ({ posts: [], count: 0 })
+    vi.mocked (getHelpTitleIndex).mockReset ().mockResolvedValue ({ })
+    vi.mocked (apiPost).mockReset ()
+  })
+
+  it ('offers creation for an existing tag after the Help lookup completes', async () => {
+    let finish!: (index: Record<string, string[]>) => void
+    const pending = new Promise<Record<string, string[]>> (resolve => {
+      finish = resolve
+    })
+    vi.mocked (getHelpTitleIndex).mockReturnValueOnce (pending)
+    tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: '既存タグ', hasWiki: false }))
+    renderWithProviders (
+	<Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	{ route: `/wiki/${ encodeURIComponent ('既存タグ') }` })
+    await waitFor (() => expect (getHelpTitleIndex).toHaveBeenCalled ())
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+    await act (async () => finish ({ }))
+    expect (await screen.findByRole ('link', { name: '新規作成してください' }))
+	.toHaveAttribute ('href', `/wiki/new?title=${ encodeURIComponent ('既存タグ') }`)
+  })
+
+  it ('creates a tag description through the existing form and displays its content', async () => {
+    const page = buildWikiPage ({ title: '既存タグ', body: '説明文',
+	resourceType: 'tag_description' })
+    tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: page.title, hasWiki: false }))
+    vi.mocked (apiPost).mockResolvedValueOnce (page)
+    renderWithProviders (
+	<Routes>
+	  <Route path="/wiki/new" element={<WikiNewPage user={buildUser ({ role: 'member' })}/>}/>
+	  <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+	</Routes>, { route: `/wiki/${ encodeURIComponent (page.title) }` })
+    fireEvent.click (await screen.findByRole ('link', { name: '新規作成してください' }))
+    await screen.findByRole ('heading', { name: '新規 Wiki ページ' })
+    wikiApi.fetchWikiPageByTitle.mockResolvedValue (page)
+    expect (screen.getAllByRole ('textbox')[0]).toHaveValue (page.title)
+    fireEvent.change (screen.getByRole ('textbox', { name: '本文エディタ' }), {
+	target: { value: page.body } })
+    fireEvent.click (screen.getByRole ('button', { name: '追加' }))
+    expect (await screen.findByText (page.body)).toBeInTheDocument ()
+    const form = vi.mocked (apiPost).mock.calls[0][1] as FormData
+    expect (form.get ('title')).toBe (page.title)
+    expect (form.get ('body')).toBe (page.body)
+    expect (apiPost).toHaveBeenCalledWith ('/wiki', form,
+	{ headers: { 'Content-Type': 'multipart/form-data' } })
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+  })
+
+  it ('shows NotFound when neither a tag nor a Help title exists', async () => {
+    renderWithProviders (
+	<Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	{ route: '/wiki/missing' })
+    expect (await screen.findByText ('404')).toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+  })
+
+  it.each (['403', '500', 'offline']) ('keeps Wiki error %s distinct from missing content',
+      async message => {
+	wikiApi.fetchWikiPageByTitle.mockRejectedValue (new Error (message))
+	tagsApi.fetchTagByName.mockResolvedValue (buildTag ({ name: '既存タグ' }))
+	renderWithProviders (
+	    <Routes><Route path="/wiki/:title" element={<WikiDetailPage/>}/></Routes>,
+	    { route: `/wiki/${ encodeURIComponent ('既存タグ') }` })
+	expect (await screen.findByRole ('alert')).toHaveTextContent (message)
+	expect (getHelpTitleIndex).not.toHaveBeenCalled ()
+	expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	    .not.toBeInTheDocument ()
+      })
+
   it ('renders deprecated state outside the wiki title link', async () => {
     wikiApi.fetchWikiPageByTitle.mockResolvedValueOnce (buildWikiPage ({
       title:        '旧タグ',

frontend/src/pages/wiki/WikiDetailPage.tsx

@@ -1,4 +1,4 @@
-import { useQuery, useQueryClient } from '@tanstack/react-query'
+import { useQuery } from '@tanstack/react-query'
 import { useEffect, useMemo } from 'react'
 import { Helmet } from 'react-helmet-async'
 import { useLocation, useNavigate, useParams } from 'react-router-dom'
@@ -29,48 +29,39 @@ const WikiDetailPage: FC = () => {
 
   const location = useLocation ()
   const navigate = useNavigate ()
-  const queryClient = useQueryClient ()
 
   const defaultTag = useMemo (() => ({ name: title, category: 'general' } as Tag), [title])
 
   const query = new URLSearchParams (location.search)
   const version = query.get ('version') || undefined
 
-  const { data: wikiPage, isLoading: loading, isSuccess, isFetching } = useQuery ({
+  const { data: wikiPage, isLoading: loading, isSuccess, isFetching, error } = useQuery ({
       enabled:  Boolean (title) && !(/^\d+$/.test (title)),
       queryKey: wikiKeys.show (title, { version }),
       queryFn:  () => fetchWikiPageByTitle (title, { version }) })
 
+  const missingWiki = isSuccess && !(isFetching) && wikiPage == null
+  const { data: titleIndex, isPending: lookupPending,
+	  isFetching: lookupFetching, error: lookupError } = useQuery ({
+      enabled: missingWiki,
+      queryKey: helpKeys.titles ('ja'),
+      queryFn: () => getHelpTitleIndex ('ja'),
+      staleTime: Infinity })
+  const lookupTitle = title.trim ().normalize ('NFKC').toLowerCase ().replace (/^ヘルプ:/, '')
+  const identifiers = useMemo (() => (
+      (titleIndex != null && Object.hasOwn (titleIndex, lookupTitle))
+      ? titleIndex[lookupTitle] : []), [titleIndex, lookupTitle])
+
   useEffect (() => {
-    if (!(isSuccess) || isFetching || wikiPage != null)
+    if (missingWiki && !(lookupFetching) && lookupError == null && identifiers.length === 1)
-      return
+      navigate (`/help/${ encodeURIComponent (identifiers[0]) }`, { replace: true })
-
+  }, [missingWiki, lookupFetching, lookupError, identifiers, navigate])
-    let active = true
-    const lookupTitle = title.trim ().normalize ('NFKC').toLowerCase ().replace (/^ヘルプ:/, '')
-
-    void queryClient.fetchQuery ({
-	queryKey: helpKeys.titles ('ja'),
-	queryFn: () => getHelpTitleIndex ('ja'),
-	staleTime: Infinity }).then (index => {
-      if (!(active))
-	return
-
-      const identifiers = Object.hasOwn (index, lookupTitle) ? index[lookupTitle] : []
-      if (identifiers.length === 1)
-	navigate (`/help/${ encodeURIComponent (identifiers[0]) }`, { replace: true })
-    }).catch (() => {
-      // A failed Help lookup leaves the original missing Wiki URL in place.
-    })
-
-    return () => {
-      active = false
-    }
-  }, [isSuccess, isFetching, wikiPage, title, version, queryClient, navigate])
 
   const effectiveTitle = wikiPage?.title ?? title
   const deprecated = wikiPage?.deprecatedAt != null
 
-  const { data: tag } = useQuery ({
+  const { data: tag, isPending: tagPending,
+	  isFetching: tagFetching, error: tagError } = useQuery ({
       enabled:  Boolean (effectiveTitle),
       queryKey: tagsKeys.show (effectiveTitle),
       queryFn:  () => fetchTagByName (effectiveTitle) })
@@ -121,7 +112,15 @@ const WikiDetailPage: FC = () => {
     }
   }, [title, navigate])
 
-  if (isSuccess && wikiPage == null)
+  const displayError = error ?? (missingWiki ? lookupError ?? tagError : null)
+  if (displayError != null)
+    return <MainArea><p role="alert">{displayError.message}</p></MainArea>
+
+  const waiting = loading || (isFetching && wikiPage == null)
+      || (missingWiki && (lookupPending || lookupFetching || tagPending
+			  || (tagFetching && tag == null) || identifiers.length === 1))
+
+  if (missingWiki && !(waiting) && (tag == null || version != null))
     return <NotFound/>
 
   return (
@@ -157,7 +156,7 @@ const WikiDetailPage: FC = () => {
 		     {...(version && { to: `/wiki/${ encodeURIComponent (title) }` })}/>
 	    {deprecated && <span>（廃止）</span>}
 	  </h1>
-	  {loading ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
+	  {waiting ? <div>Loading...</div> : <WikiBody title={title} body={wikiPage?.body}/>}
 
 	  {(!(version) && posts.length > 0) && (
 	      <div className="not-prose">

frontend/src/pages/wiki/WikiHelpCompatibility.test.tsx

@@ -1,8 +1,9 @@
-import { screen, waitFor } from '@testing-library/react'
+import { act, fireEvent, screen, waitFor } from '@testing-library/react'
-import { Route, Routes, useLocation } from 'react-router-dom'
+import { Route, Routes, useLocation, useNavigate } from 'react-router-dom'
 import { beforeEach, describe, expect, it, vi } from 'vitest'
 
 import { apiGet } from '@/lib/api'
+import * as help from '@/lib/help'
 import HelpDetailPage from '@/pages/help/HelpDetailPage'
 import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
 import { buildWikiPage } from '@/test/factories'
@@ -17,7 +18,14 @@ vi.mock ('@/lib/posts', () => ({ fetchPosts: async () => ({ posts: [], count: 0
 
 const Location = () => {
   const location = useLocation ()
-  return <output data-testid="location">{location.pathname}{location.search}</output>
+  const navigate = useNavigate ()
+  return (
+      <>
+	<output data-testid="location">{location.pathname}{location.search}</output>
+	<button onClick={() => navigate (`/wiki/${ encodeURIComponent ('該当なし') }`)}>
+	  switch title
+	</button>
+      </>)
 }
 
 
@@ -92,6 +100,36 @@ describe ('Legacy Wiki to Help compatibility', () => {
     expect (screen.getByTestId ('location')).toHaveTextContent (route)
   })
 
+  it ('waits for title lookup and does not redirect a later Wiki URL using an old title',
+      async () => {
+	let finish!: (index: Record<string, string[]>) => void
+	const pending = new Promise<Record<string, string[]>> (resolve => {
+	  finish = resolve
+	})
+	const lookup = vi.spyOn (help, 'getHelpTitleIndex').mockReturnValueOnce (pending)
+	renderWiki ('ホーム')
+	await waitFor (() => expect (lookup).toHaveBeenCalled ())
+	expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+	fireEvent.click (screen.getByRole ('button', { name: 'switch title' }))
+	await waitFor (() => expect (apiGet).toHaveBeenCalledWith (
+	    `/wiki/title/${ encodeURIComponent ('該当なし') }`, expect.anything ()))
+	await act (async () => finish ({ 'ホーム': ['guide'] }))
+	await screen.findByText ('404')
+	expect (screen.getByTestId ('location'))
+	    .toHaveTextContent (`/wiki/${ encodeURIComponent ('該当なし') }`)
+      })
+
+  it ('does not treat a Wiki network failure as a missing Wiki', async () => {
+    vi.mocked (apiGet).mockRejectedValueOnce (new Error ('offline'))
+    const { route } = renderWiki ('ホーム')
+    expect (await screen.findByRole ('alert')).toHaveTextContent ('offline')
+    expect (screen.getByTestId ('location')).toHaveTextContent (route)
+    expect (helpFixture.loads.titles).not.toHaveBeenCalled ()
+    expect (screen.queryByText ('404')).not.toBeInTheDocument ()
+    expect (screen.queryByRole ('link', { name: '新規作成してください' }))
+	.not.toBeInTheDocument ()
+  })
+
   it.each ([403, 500]) ('does not redirect HTTP %s to Help', async status => {
     vi.mocked (apiGet).mockRejectedValueOnce ({ isAxiosError: true, response: { status } })
     const { route, queryClient } = renderWiki ('ホーム')

frontend/src/pages/wiki/WikiNewPage.tsx

@@ -59,7 +59,7 @@ const WikiNewPage: FC<Props> = ({ user }) => {
       const data = await apiPost<WikiPage> ('/wiki', formData,
 				  { headers: { 'Content-Type': 'multipart/form-data' } })
       toast ({ title: '投稿成功!' })
-      navigate (`/wiki/${ data.title }`)
+      navigate (`/wiki/${ encodeURIComponent (data.title) }`)
     }
     catch (e)
     {