fix(threads): preserve selectedThreadId on cold-boot identity hydration (#1196)

app/src/providers/CoreStateProvider.tsx

@@ -28,7 +28,7 @@ import {
 import { socketService } from '../services/socketService';
 import { store } from '../store';
 import { resetUserScopedState } from '../store/resetActions';
-import { clearAllThreads, loadThreads } from '../store/threadSlice';
+import { loadThreads, resetThreadCachesPreservingSelection } from '../store/threadSlice';
 import { getActiveUserId, setActiveUserId } from '../store/userScopedStorage';
 import {
   openhumanUpdateAnalyticsSettings,
@@ -257,7 +257,12 @@ export default function CoreStateProvider({ children }: { children: ReactNode })
       !isLogout
     ) {
       const threadReloadRequestId = requestId;
-      store.dispatch(clearAllThreads());
+      // Reset the in-memory thread caches (rows from a pre-auth bucket — see
+      // #1157) but preserve the redux-persisted `selectedThreadId` so a
+      // reload of an already-authed user resumes the user's last-viewed
+      // thread (#1168). The Conversations mount effect falls back to "most
+      // recent" if the persisted id is no longer in the reloaded list.
+      store.dispatch(resetThreadCachesPreservingSelection());
       void store
         .dispatch(loadThreads())
         .unwrap()

app/src/providers/__tests__/CoreStateProvider.identityFlip.test.tsx

@@ -153,9 +153,13 @@ describe('CoreStateProvider — identity flip cleanup (#900)', () => {
     setActiveSpy.mockRestore();
   });
 
-  it('seed matches next user (no restart) but identity hydrates null→B: clears threads and reloads (#1157)', async () => {
+  it('seed matches next user (no restart) but identity hydrates null→B: resets thread caches (preserving selection) and reloads (#1157, #1168)', async () => {
     userScopedStorage.setActiveUserId('B');
     fetchSnapshot.mockResolvedValue(makeSnapshot({ userId: 'B', sessionToken: 'tokB' }));
+    // Seed a persisted selection that should survive the boot-time reset so
+    // the user resumes their last-viewed thread instead of falling through
+    // to "most recent".
+    store.dispatch(threadSlice.setSelectedThread('thr-persisted'));
     const dispatchSpy = vi.spyOn(store, 'dispatch');
     const loadThreadsSpy = vi.spyOn(threadSlice, 'loadThreads');
 
@@ -173,10 +177,22 @@ describe('CoreStateProvider — identity flip cleanup (#900)', () => {
     expect(
       dispatchSpy.mock.calls.some(([action]) => {
         if (!action || typeof action !== 'object' || !('type' in action)) return false;
-        return (action as { type: string }).type === threadSlice.clearAllThreads().type;
+        return (
+          (action as { type: string }).type ===
+          threadSlice.resetThreadCachesPreservingSelection().type
+        );
       })
     ).toBe(true);
+    // The legacy `clearAllThreads` (which nulls selectedThreadId) must NOT
+    // be dispatched on this boot path — that was the #1168 regression.
+    expect(
+      dispatchSpy.mock.calls.some(([action]) => {
+        if (!action || typeof action !== 'object' || !('type' in action)) return false;
+        return (action as { type: string }).type === threadSlice.clearAllThreads().type;
+      })
+    ).toBe(false);
     expect(loadThreadsSpy).toHaveBeenCalled();
+    expect(store.getState().thread.selectedThreadId).toBe('thr-persisted');
 
     dispatchSpy.mockRestore();
     loadThreadsSpy.mockRestore();

app/src/store/threadSlice.ts

@@ -279,6 +279,19 @@ const threadSlice = createSlice({
       state.activeThreadId = null;
       state.welcomeThreadId = null;
     },
+    // Like `clearAllThreads` but keeps `selectedThreadId`. Used on the
+    // post-bootstrap identity-observation path (#1168 + #1157): we need to
+    // drop pre-auth in-memory thread rows but the persisted last-viewed
+    // thread id is still valid for the reloaded user, so preserving it lets
+    // the Conversations effect resume that thread instead of falling
+    // through to "most recent".
+    resetThreadCachesPreservingSelection: state => {
+      state.threads = [];
+      state.messagesByThreadId = {};
+      state.messages = [];
+      state.activeThreadId = null;
+      state.welcomeThreadId = null;
+    },
     // [#1123] True no-op — welcome-agent onboarding replaced by Joyride walkthrough.
     // Kept to avoid breaking existing imports; state.welcomeThreadId is never
     // mutated because the welcome-agent flow no longer runs.
@@ -350,6 +363,7 @@ export const {
   clearSelectedThread,
   setActiveThread,
   clearAllThreads,
+  resetThreadCachesPreservingSelection,
   setWelcomeThreadId,
 } = threadSlice.actions;