fix(desktop): clear stale compaction status across session switches (#64127)

* fix(desktop): clear stale compaction status

Clear the compaction phase when a turn resumes with model or tool activity, and key response timers by session and turn so switching chats preserves elapsed time.\n\nSupersedes #48115 by porting its resumed-content approach to the current split stream hook and covering tool-first resumptions.\n\nCo-authored-by: liuhao1024 <sunsky.lau@gmail.com>

* fix(desktop): resume after thinking activity

* fix(desktop): clear turn timer on stop

apps/desktop/src/components/assistant-ui/thread/status.test.tsx

@@ -0,0 +1,56 @@
+import { act, cleanup, render, screen } from '@testing-library/react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { __resetElapsedTimerRegistryForTests } from '@/components/chat/activity-timer'
+import { I18nProvider } from '@/i18n'
+import { $activeSessionId, $turnStartedAt } from '@/store/session'
+
+import { ResponseLoadingIndicator } from './status'
+
+function renderIndicator() {
+  return render(
+    <I18nProvider configClient={null} initialLocale="en">
+      <ResponseLoadingIndicator />
+    </I18nProvider>
+  )
+}
+
+describe('ResponseLoadingIndicator timer', () => {
+  beforeEach(() => {
+    vi.useFakeTimers()
+    vi.setSystemTime(new Date('2026-01-01T00:00:00.000Z'))
+    __resetElapsedTimerRegistryForTests()
+  })
+
+  afterEach(() => {
+    cleanup()
+    $activeSessionId.set(null)
+    $turnStartedAt.set(null)
+    __resetElapsedTimerRegistryForTests()
+    vi.useRealTimers()
+  })
+
+  it('preserves each running session timer while switching between sessions', () => {
+    $activeSessionId.set('session-a')
+    $turnStartedAt.set(Date.now())
+    const sessionA = renderIndicator()
+
+    act(() => vi.advanceTimersByTime(5_000))
+    expect(screen.getByText('5s')).toBeTruthy()
+    sessionA.unmount()
+
+    $activeSessionId.set('session-b')
+    $turnStartedAt.set(Date.now())
+    const sessionB = renderIndicator()
+
+    act(() => vi.advanceTimersByTime(3_000))
+    expect(screen.getByText('3s')).toBeTruthy()
+    sessionB.unmount()
+
+    $activeSessionId.set('session-a')
+    $turnStartedAt.set(new Date('2026-01-01T00:00:00.000Z').getTime())
+    renderIndicator()
+
+    expect(screen.getByText('8s')).toBeTruthy()
+  })
+})

apps/desktop/src/components/assistant-ui/thread/status.tsx

@@ -11,6 +11,7 @@ import { cn } from '@/lib/utils'
 import { $backgroundResume } from '@/store/background-delegation'
 import { $compactionActive } from '@/store/compaction'
 import { $activeSessionAwaitingInput } from '@/store/prompts'
+import { $activeSessionId, $turnStartedAt } from '@/store/session'
 
 const StatusRow: FC<{ children: ReactNode; label: string } & React.ComponentPropsWithoutRef<'div'>> = ({
   children,
@@ -36,6 +37,13 @@ const CompactionHint: FC = () => (
   <span className="shimmer min-w-0 truncate text-muted-foreground/55">{COMPACTION_LABEL}</span>
 )
 
+function useActiveTurnTimerKey(): string | undefined {
+  const activeSessionId = useStore($activeSessionId)
+  const turnStartedAt = useStore($turnStartedAt)
+
+  return activeSessionId && turnStartedAt ? `turn:${activeSessionId}:${turnStartedAt}` : undefined
+}
+
 export const CenteredThreadSpinner: FC = () => {
   const { t } = useI18n()
 
@@ -59,7 +67,8 @@ export const CenteredThreadSpinner: FC = () => {
 
 export const ResponseLoadingIndicator: FC = () => {
   const { t } = useI18n()
-  const elapsed = useElapsedSeconds()
+  const timerKey = useActiveTurnTimerKey()
+  const elapsed = useElapsedSeconds(true, timerKey)
   const compacting = useStore($compactionActive)
 
   return (
@@ -134,6 +143,7 @@ export const StreamStallIndicator: FC = () => {
 
   const [stalled, setStalled] = useState(false)
   const compacting = useStore($compactionActive)
+  const turnTimerKey = useActiveTurnTimerKey()
   // A pending clarify / approval / sudo / secret means the turn is paused on the
   // user, not working — so don't resurrect the "thinking" timer while they
   // decide (matches the pet's awaitingInput pose taking priority over busy).
@@ -147,7 +157,7 @@ export const StreamStallIndicator: FC = () => {
   }, [activity])
 
   const active = (stalled || compacting) && !awaitingInput
-  const elapsed = useElapsedSeconds(active)
+  const elapsed = useElapsedSeconds(active, compacting ? turnTimerKey : undefined)
 
   if (!active) {
     return null