fix(desktop): make the running-turn timer per-session

apps/desktop/src/app/session/hooks/use-message-stream.ts

@@ -451,7 +451,8 @@ export function useMessageStream({
             busy: false,
             needsInput: false,
             pendingBranchGroup: null,
-            streamId: null
+            streamId: null,
+            turnStartedAt: null
           }
         }
 
@@ -541,7 +542,8 @@ export function useMessageStream({
           pendingBranchGroup: null,
           awaitingResponse: false,
           busy: false,
-          needsInput: false
+          needsInput: false,
+          turnStartedAt: null
         }
       })
 
@@ -599,7 +601,8 @@ export function useMessageStream({
           sawAssistantPayload: true,
           awaitingResponse: false,
           busy: false,
-          needsInput: false
+          needsInput: false,
+          turnStartedAt: null
         }
       })
     },
@@ -683,7 +686,8 @@ export function useMessageStream({
               if (busy) {
                 return {
                   ...state,
-                  busy
+                  busy,
+                  turnStartedAt: state.turnStartedAt ?? Date.now()
                 }
               }
 
@@ -696,7 +700,8 @@ export function useMessageStream({
                 awaitingResponse: false,
                 busy,
                 pendingBranchGroup: null,
-                streamId: null
+                streamId: null,
+                turnStartedAt: null
               }
             })
           }
@@ -735,7 +740,8 @@ export function useMessageStream({
           busy: true,
           awaitingResponse: true,
           sawAssistantPayload: false,
-          interrupted: false
+          interrupted: false,
+          turnStartedAt: Date.now()
         }))
 
         if (isActiveEvent) {

apps/desktop/src/app/session/hooks/use-session-state-cache.test.tsx

@@ -0,0 +1,118 @@
+import { act, cleanup, render } from '@testing-library/react'
+import type { MutableRefObject } from 'react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { $turnStartedAt, setTurnStartedAt } from '@/store/session'
+
+import { useSessionStateCache } from './use-session-state-cache'
+
+type Cache = ReturnType<typeof useSessionStateCache>
+
+interface HarnessProps {
+  activeSessionId: string | null
+  onReady: (cache: Cache) => void
+  selectedStoredSessionId: string | null
+}
+
+function Harness({ activeSessionId, onReady, selectedStoredSessionId }: HarnessProps) {
+  const busyRef: MutableRefObject<boolean> = { current: false }
+  const cache = useSessionStateCache({
+    activeSessionId,
+    busyRef,
+    selectedStoredSessionId,
+    setAwaitingResponse: () => undefined,
+    setBusy: () => undefined,
+    setMessages: () => undefined
+  })
+
+  onReady(cache)
+
+  return null
+}
+
+describe('useSessionStateCache — per-session turn timer', () => {
+  beforeEach(() => {
+    // The view-sync flush runs on a real rAF in the browser path; in jsdom we
+    // want it synchronous so the global mirror is observable immediately. The
+    // hook closes over `window.requestAnimationFrame`, so stub that exact ref.
+    // Return null (not a handle) so the hook's `viewSyncRafRef.current = rAF(...)`
+    // assignment doesn't overwrite the null the synchronous callback just set —
+    // otherwise the ref reads truthy and the NEXT sync is suppressed (a real
+    // browser returns a handle but runs the callback async, so this race is a
+    // test-only artifact of firing synchronously).
+    vi.spyOn(window, 'requestAnimationFrame').mockImplementation((cb: FrameRequestCallback) => {
+      cb(0)
+
+      return null as unknown as number
+    })
+    setTurnStartedAt(null)
+  })
+
+  afterEach(() => {
+    cleanup()
+    vi.restoreAllMocks()
+    setTurnStartedAt(null)
+  })
+
+  it("keeps a background session's running turn clock and never mirrors it to the view", () => {
+    let cache!: Cache
+    // Active session is "fg-runtime"; the turn starts on the BACKGROUND session.
+    render(
+      <Harness activeSessionId="fg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="fg-stored" />
+    )
+
+    const startedAt = 1_700_000_000_000
+
+    act(() => {
+      cache.updateSessionState(
+        'bg-runtime',
+        state => ({ ...state, busy: true, turnStartedAt: startedAt }),
+        'bg-stored'
+      )
+    })
+
+    // The background session's own cache entry holds the clock...
+    expect(cache.sessionStateByRuntimeIdRef.current.get('bg-runtime')?.turnStartedAt).toBe(startedAt)
+    // ...but the global atom (statusbar timer) is untouched — a background turn
+    // must not drive the foreground timer.
+    expect($turnStartedAt.get()).toBeNull()
+  })
+
+  it("mirrors the focused session's turn clock into the global atom on view-sync", () => {
+    let cache!: Cache
+    render(<Harness activeSessionId="fg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="fg-stored" />)
+
+    const startedAt = 1_700_000_111_000
+
+    // A turn on the ACTIVE session stages into the view; the flush mirrors its
+    // turnStartedAt into the global atom the statusbar reads.
+    act(() => {
+      cache.updateSessionState(
+        'fg-runtime',
+        state => ({ ...state, busy: true, turnStartedAt: startedAt }),
+        'fg-stored'
+      )
+    })
+
+    expect($turnStartedAt.get()).toBe(startedAt)
+  })
+
+  it('clears the global clock when the focused turn ends', () => {
+    let cache!: Cache
+    render(<Harness activeSessionId="fg-runtime" onReady={c => (cache = c)} selectedStoredSessionId="fg-stored" />)
+
+    act(() => {
+      cache.updateSessionState(
+        'fg-runtime',
+        state => ({ ...state, busy: true, turnStartedAt: 1_700_000_222_000 }),
+        'fg-stored'
+      )
+    })
+    expect($turnStartedAt.get()).toBe(1_700_000_222_000)
+
+    act(() => {
+      cache.updateSessionState('fg-runtime', state => ({ ...state, busy: false, turnStartedAt: null }))
+    })
+    expect($turnStartedAt.get()).toBeNull()
+  })
+})

apps/desktop/src/app/session/hooks/use-session-state-cache.ts

@@ -5,7 +5,7 @@ import type { ChatMessage } from '@/lib/chat-messages'
 import { preserveLocalAssistantErrors } from '@/lib/chat-messages'
 import { createClientSessionState } from '@/lib/chat-runtime'
 import { setMutableRef } from '@/lib/mutable-ref'
-import { $busy, $messages, noteSessionActivity, setSessionAttention, setSessionWorking } from '@/store/session'
+import { $busy, $messages, noteSessionActivity, setSessionAttention, setSessionWorking, setTurnStartedAt } from '@/store/session'
 
 import type { ClientSessionState } from '../../types'
 
@@ -92,6 +92,10 @@ export function useSessionStateCache({
     setBusy(pending.state.busy)
     setMutableRef(busyRef, pending.state.busy)
     setAwaitingResponse(pending.state.awaitingResponse)
+    // Mirror the focused session's per-session turn clock into the global
+    // atom the statusbar timer reads. Keeps a backgrounded turn's elapsed
+    // time intact on focus instead of zeroing it (the "timer restarts" bug).
+    setTurnStartedAt(pending.state.turnStartedAt)
   }, [busyRef, setAwaitingResponse, setBusy, setMessages])
 
   const syncSessionStateToView = useCallback(

apps/desktop/src/app/types.ts

@@ -91,4 +91,9 @@ export interface ClientSessionState {
   /** A blocking clarify prompt is waiting on the user for this session. Drives
    *  the sidebar "needs input" indicator; cleared when the turn resumes/ends. */
   needsInput: boolean
+  /** Epoch ms the current turn started, or null when idle. Per-session so a
+   *  background turn's elapsed timer keeps counting while another session is
+   *  focused, and switching sessions doesn't zero a still-running turn's clock.
+   *  The global $turnStartedAt mirrors whichever session is currently viewed. */
+  turnStartedAt: number | null
 }

apps/desktop/src/lib/chat-runtime.ts

@@ -46,7 +46,8 @@ export function createClientSessionState(
     sawAssistantPayload: false,
     pendingBranchGroup: null,
     interrupted: false,
-    needsInput: false
+    needsInput: false,
+    turnStartedAt: null
   }
 }