feat(i18n): tab auto titles follow the UI language

Titles are stored display text (layout templates, session snapshot,
broadcast registry), so a pane used to keep the wording of the language it
was opened in, and nextTerminalTitle could not even parse the number back
out of another language's pattern (numbering restarted, duplicates).

New pure module src/shared/terminalTitle.ts: resolution tries all four
languages' patterns, rendering uses the active one; i18n gains tFor(lang)
for off-language rendering. Workspace retitles auto-numbered local tabs in
place on language switch, snapshot restore and template apply; SSH panels
(user-typed connection names) are never touched. dockview's title-change
event propagates the new title to the broadcast registry and the snapshot
save with no extra wiring.

New test terminal-title.mjs (16 writer/reader language pairs, non-auto
title boundaries, gap filling); offline suite grows 17 -> 18.

src/renderer/src/workspace/Workspace.tsx

@@ -28,6 +28,7 @@ import 'dockview-react/dist/styles/dockview.css'
 
 import { connectPromptFor, type HostKeyPromptEvent, type SshConnection, type SshSecretOverride } from '@shared/connections'
 import { t } from '@shared/i18n'
+import { nextTerminalTitle, retitleAutoTitles } from '@shared/terminalTitle'
 import { ConnectionSidebar } from '../connections/ConnectionSidebar'
 import type { ConnectionSidebarHandle } from '../connections/ConnectionSidebar'
 import { ConnectFlow } from './ConnectFlow'
@@ -129,31 +130,6 @@ function restoreLayoutSnapshot(api: DockviewApi | undefined, snapshot: Serialize
   }
 }
 
-/**
- * "终端 N" titles fill the lowest free number among live panels: closing a
- * pane frees its number for the next new terminal, and a session restore can
- * no longer leave the numbering behind (the old in-memory counter restarted
- * at zero on launch and produced duplicate titles).
- */
-function nextTerminalTitle(existing: Iterable<string | undefined>): string {
-  const used = new Set<number>()
-  // The pattern is translated, so the number is read back through that same
-  // pattern (the `{n}` placeholder marks the digits) instead of a fixed one.
-  const [head, tail] = t('workspace.tab.terminalTitle', { n: '\u0000' }).split('\u0000')
-  const matcher = new RegExp(`^${escapeRegExp(head)}(\\d+)${escapeRegExp(tail ?? '')}$`)
-  for (const title of existing) {
-    const n = title?.match(matcher)?.[1]
-    if (n) used.add(Number(n))
-  }
-  let n = 1
-  while (used.has(n)) n++
-  return t('workspace.tab.terminalTitle', { n })
-}
-
-function escapeRegExp(text: string): string {
-  return text.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
-}
-
 function sessionIdOf(panel: IDockviewPanel | undefined): string | undefined {
   return (panel?.params as TerminalParams | undefined)?.sessionId
 }
@@ -457,6 +433,32 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
     setModeCounts((prev) => (prev.terminal === t && prev.ssh === s ? prev : { terminal: t, ssh: s }))
   }, [])
 
+  /**
+   * Re-render every auto-numbered tab title in the active language, keeping its
+   * number. Idempotent — a title already in the active language is left alone.
+   *
+   * Titles are stored display text (they ride along in layout templates, the
+   * session snapshot and the broadcast registry) and outlive a language switch,
+   * so without this a pane keeps the wording of the language it was opened in.
+   *
+   * SSH panes are excluded: their title is the connection name the user typed,
+   * and a connection named "Terminal 3" must not be renamed behind their back.
+   *
+   * `setTitle` fires dockview's title-change event, which is all the rest needs:
+   * `TerminalPanel` re-registers the broadcast title, the tab component
+   * re-renders, the sidebar list refreshes and the snapshot save is scheduled
+   * (a panel title change forwards into the dockview's layout-change event).
+   */
+  const retitleAutoPanels = useCallback((): void => {
+    retitleAutoTitles(
+      [terminalApiRef.current, sshApiRef.current].flatMap((api) =>
+        (api?.panels ?? []).filter(
+          (panel) => (panel.params as TerminalParams | undefined)?.sessionKind !== 'ssh'
+        )
+      )
+    )
+  }, [])
+
   /** Focus a local terminal panel from the sidebar (terminal dockview). */
   const onFocusPanel = useCallback((panelId: string): void => {
     const panel = terminalApiRef.current?.getPanel(panelId)
@@ -996,6 +998,11 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
       const renames = new Map([...terminalLayout.renames, ...sshLayout.renames])
       await rebindSessionPanels(terminal, snapshot, true, renames)
       await rebindSessionPanels(ssh, snapshot, true, renames)
+      // A snapshot is written in whatever language was active at the time, so
+      // render its auto titles in the current language before anything compares
+      // them: the dedup below then sees "终端 3" and "Terminal 3" as the one
+      // collision they are instead of letting both through.
+      retitleAutoPanels()
       // Retitle duplicates left over from the old counter bug (the snapshot it
       // wrote keeps colliding titles forever otherwise): the first panel keeps
       // the title, later ones get the lowest free number.
@@ -1006,13 +1013,13 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
       const seenTitles = new Set<string>()
       for (const p of [...(terminal?.panels ?? []), ...(ssh?.panels ?? [])]) {
         if ((p.params as TerminalParams | undefined)?.sessionKind === 'ssh') continue
-        const t = p.title ?? ''
-        if (!t) continue
-        if (seenTitles.has(t)) {
+        const title = p.title ?? ''
+        if (!title) continue
+        if (seenTitles.has(title)) {
           const fresh = nextTerminalTitle(seenTitles)
           p.setTitle(fresh)
           seenTitles.add(fresh)
-        } else seenTitles.add(t)
+        } else seenTitles.add(title)
       }
       lastLocalCwdRef.current = snapshot.lastLocalCwd ?? lastLocalCwdRef.current
       useWorkspaceModeStore.getState().setMode(snapshot.mode)
@@ -1020,7 +1027,7 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
       recomputeLocalPanels()
       return true
     },
-    [rebindSessionPanels, recountAll, recomputeLocalPanels]
+    [rebindSessionPanels, recountAll, recomputeLocalPanels, retitleAutoPanels]
   )
 
   const handleApplyTemplate = useCallback(
@@ -1119,6 +1126,11 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
       if (terminalApiRef.current) await rebindRestoredPanels(terminalApiRef.current)
       if (sshApiRef.current) await rebindRestoredPanels(sshApiRef.current)
 
+      // A template carries the tab titles it was saved with, which may be in
+      // another language (or written by a build whose language the user has
+      // since switched away from).
+      retitleAutoPanels()
+
       // Old sessions are unreachable after the layout swap — kill them.
       for (const sid of previousSessions) killSession(sid)
       recountAll()
@@ -1126,7 +1138,7 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
       const mode = useWorkspaceModeStore.getState().mode
       activePanelRef.current = apiOfMode(mode, terminalApiRef.current, sshApiRef.current)?.activePanel
     },
-    [killSession, message, rebindRestoredPanels, recountAll, recomputeLocalPanels]
+    [killSession, message, rebindRestoredPanels, recountAll, recomputeLocalPanels, retitleAutoPanels]
   )
 
   const handleDeleteTemplate = useCallback(async (meta: LayoutMetaLike): Promise<void> => {
@@ -1156,6 +1168,20 @@ export default function Workspace({ onOpenSettings }: WorkspaceProps): React.JSX
   // are translated at build time, so `language` has to be a dependency or a
   // language switch would leave stale menu text behind.
   const language = useSettingsStore((s) => s.settings.system.language)
+
+  // Auto tab titles are stored display text, so they have to be re-rendered on
+  // a language switch — the rest of the UI re-renders itself. Skipped on mount
+  // (a boot pass has not restored any panel yet, and a restored title is
+  // retitled by the pass itself) and on every settings echo that leaves the
+  // language untouched, which is the common case.
+  const lastLanguageRef = useRef<string | undefined>(undefined)
+  useEffect(() => {
+    if (lastLanguageRef.current === language) return
+    const changed = lastLanguageRef.current !== undefined
+    lastLanguageRef.current = language
+    if (changed) retitleAutoPanels()
+  }, [language, retitleAutoPanels])
+
   const layoutMenu = useMemo<MenuProps>(
     () => ({
       items: [