fix(mobile): retain structured transcript during reconnect

mobile/src/session/use-mobile-structured-agent-session.test.tsx

@@ -803,4 +803,22 @@ describe('useMobileStructuredAgentSession', () => {
     expect(hook?.session.messages).toHaveLength(1)
     expect(hook?.session.status).toBe('ready')
   })
+
+  it('keeps the transcript visible while a reconnect is loading', async () => {
+    await act(async () => {
+      renderer = create(createElement(Harness, { connected: true }))
+    })
+    await vi.waitFor(() => expect(listener).toEqual(expect.any(Function)))
+    act(() => listener?.(snapshotWithMessage()))
+    expect(hook?.session.messages).toHaveLength(1)
+
+    await act(async () => {
+      renderer?.update(createElement(Harness, { connected: false }))
+    })
+    await act(async () => {
+      renderer?.update(createElement(Harness, { connected: true }))
+    })
+
+    expect(hook?.session.messages).toHaveLength(1)
+  })
 })

mobile/src/session/use-mobile-structured-agent-state.ts

@@ -40,6 +40,7 @@ export function useMobileStructuredAgentState(args: {
   const [state, setState] = useState<StructuredAgentSessionState>(EMPTY_STRUCTURED_AGENT_SESSION)
   const [loadingOlder, setLoadingOlder] = useState(false)
   const stateRef = useRef(state)
+  const sessionIdentityRef = useRef<{ client: RpcClient; sessionId: string } | null>(null)
   useLayoutEffect(() => {
     stateRef.current = state
   }, [state])
@@ -50,6 +51,7 @@ export function useMobileStructuredAgentState(args: {
 
   useEffect(() => {
     if (!client || !sessionId || !enabled) {
+      sessionIdentityRef.current = null
       setState(EMPTY_STRUCTURED_AGENT_SESSION)
       setLoadingOlder(false)
       return
@@ -60,6 +62,14 @@ export function useMobileStructuredAgentState(args: {
       // nor empty-state copy, so the chat reads as gone rather than offline.
       return
     }
+    const sessionChanged =
+      sessionIdentityRef.current?.client !== client ||
+      sessionIdentityRef.current?.sessionId !== sessionId
+    sessionIdentityRef.current = { client, sessionId }
+    if (sessionChanged) {
+      // Do not leak the previous tab's transcript while the new session loads.
+      setState(EMPTY_STRUCTURED_AGENT_SESSION)
+    }
     apply({ type: 'loading' })
     const holderId = structuredAgentSessionHolderId('mobile-chat')
     let cancelled = false

src/shared/structured-agent-session-reducer.ts

@@ -95,7 +95,8 @@ export function reduceStructuredAgentSession(
   action: StructuredAgentSessionAction
 ): StructuredAgentSessionState {
   if (action.type === 'loading') {
-    return { ...EMPTY_STRUCTURED_AGENT_SESSION, status: 'loading' }
+    // Keep the last transcript visible while a reconnect rehydrates the stream.
+    return { ...state, status: 'loading', error: undefined }
   }
   if (action.type === 'error') {
     return { ...state, status: 'error', error: action.message }