diff --git a/client/src/components/Settings/AccountTab.test.tsx b/client/src/components/Settings/AccountTab.test.tsx
index 85bdfd21e..8bd5d180a 100644
--- a/client/src/components/Settings/AccountTab.test.tsx
+++ b/client/src/components/Settings/AccountTab.test.tsx
@@ -10,6 +10,12 @@ import { buildUser, buildSettings } from '../../../tests/helpers/factories';
 import AccountTab from './AccountTab';
 import { ToastContainer } from '../shared/Toast';
 
+// Enabling or disabling MFA reloads the user, and loadUser registers the
+// background sync triggers: a 30 s heartbeat and window listeners that nothing
+// here unregisters, so they outlive the test and can fire, and log, while the
+// file's worker shuts down. Nothing here is about sync.
+vi.mock('../../sync/syncTriggers', () => ({ registerSyncTriggers: vi.fn(), unregisterSyncTriggers: vi.fn() }));
+
 beforeEach(() => {
   resetAllStores();
   server.use(
diff --git a/client/src/pages/LoginPage.test.tsx b/client/src/pages/LoginPage.test.tsx
index d78530cb8..cd88cbd1c 100644
--- a/client/src/pages/LoginPage.test.tsx
+++ b/client/src/pages/LoginPage.test.tsx
@@ -13,6 +13,18 @@ import LoginPage from './LoginPage';
 // made FE-PAGE-LOGIN-014 fail intermittently in CI while passing in isolation.
 vi.mock('./login/LoginWorld', () => ({ default: () => null }));
 
+// A successful sign-in registers the background sync triggers (a 30 s heartbeat
+// and window listeners that nothing here unregisters) and starts a full trip
+// sync it does not wait for. Left real, both outlive the test that started them
+// and can still be logging when the file's worker shuts down, which vitest
+// reports as an unhandled error although every test passed. Nothing here is
+// about sync.
+vi.mock('../sync/syncTriggers', () => ({ registerSyncTriggers: vi.fn(), unregisterSyncTriggers: vi.fn() }));
+vi.mock('../sync/tripSyncManager', async (importOriginal) => ({
+  ...(await importOriginal<typeof import('../sync/tripSyncManager')>()),
+  tripSyncManager: { syncAll: vi.fn(async () => {}) },
+}));
+
 // LoginPage uses inline styles for labels (no htmlFor/id pairing).
 // We find inputs by placeholder text.
 const EMAIL_PLACEHOLDER = 'your@email.com';
diff --git a/client/tests/helpers/msw/handlers/notifications.ts b/client/tests/helpers/msw/handlers/notifications.ts
index f009cee0f..aae795544 100644
--- a/client/tests/helpers/msw/handlers/notifications.ts
+++ b/client/tests/helpers/msw/handlers/notifications.ts
@@ -91,4 +91,9 @@ export const notificationHandlers = [
       },
     });
   }),
+
+  // A login and the notice host both start this fetch without waiting for it.
+  // Unhandled, MSW let it through to the network, where it could fail after the
+  // test had ended and log a warning into a worker that was shutting down.
+  http.get('/api/system-notices/active', () => HttpResponse.json([])),
 ];
diff --git a/client/tests/unit/mobile/settings/MSettingsAccount.test.tsx b/client/tests/unit/mobile/settings/MSettingsAccount.test.tsx
index 850e8400a..17d6a567f 100644
--- a/client/tests/unit/mobile/settings/MSettingsAccount.test.tsx
+++ b/client/tests/unit/mobile/settings/MSettingsAccount.test.tsx
@@ -22,6 +22,12 @@ vi.mock('react-router', async (importOriginal) => {
 
 vi.mock('@simplewebauthn/browser', () => ({ startRegistration: vi.fn() }));
 
+// Enabling or disabling MFA reloads the user, and loadUser registers the
+// background sync triggers: a 30 s heartbeat and window listeners that nothing
+// here unregisters, so they outlive the test and can fire, and log, while the
+// file's worker shuts down. Nothing here is about sync.
+vi.mock('../../../../src/sync/syncTriggers', () => ({ registerSyncTriggers: vi.fn(), unregisterSyncTriggers: vi.fn() }));
+
 const webauthn = startRegistration as unknown as ReturnType<typeof vi.fn>;
 
 const BACKUP_KEY = 'trek_mfa_backup_codes_pending';
diff --git a/client/tests/unit/stores/authStore.test.ts b/client/tests/unit/stores/authStore.test.ts
index 305bebe3b..1189fce87 100644
--- a/client/tests/unit/stores/authStore.test.ts
+++ b/client/tests/unit/stores/authStore.test.ts
@@ -20,6 +20,18 @@ const syncTriggers = vi.hoisted(() => ({
 }));
 vi.mock('../../../src/sync/syncTriggers', () => syncTriggers);
 
+// login, completeMfaLogin and register start a full trip sync they do not wait
+// for. Left real, it outlives the test that started it and can still be logging
+// when the file's worker shuts down, which vitest reports as an unhandled error
+// although every test passed (the authStore.push spec had the same flake). The
+// stub keeps the sync out and lets the tests assert that it was started.
+const tripSync = vi.hoisted(() => ({ syncAll: vi.fn(async () => {}) }));
+vi.mock('../../../src/sync/tripSyncManager', () => ({ tripSyncManager: tripSync }));
+
+// The notice store is not part of resetAllStores, and FE-STORE-AUTH-024 swaps
+// its fetch for a stub; each test starts from the real, unloaded store again.
+const initialNoticeState = useSystemNoticeStore.getState();
+
 // The user-scoped offline DB is real (fake-indexeddb); only the reopen step is
 // made failable so the "auth still succeeds when the DB won't open" path runs.
 const dbControl = vi.hoisted(() => ({ reopenFails: false, reopenedFor: null as number | string | null }));
@@ -37,6 +49,7 @@ vi.mock('../../../src/db/offlineDb', async (importOriginal) => {
 
 beforeEach(() => {
   resetAllStores();
+  useSystemNoticeStore.setState(initialNoticeState, true);
   vi.clearAllMocks();
   dbControl.reopenFails = false;
   dbControl.reopenedFor = null;
@@ -63,6 +76,7 @@ describe('authStore', () => {
       expect(state.isAuthenticated).toBe(true);
       expect(state.isLoading).toBe(false);
       expect(state.error).toBeNull();
+      expect(tripSync.syncAll).toHaveBeenCalledOnce();
     });
   });
 
@@ -194,6 +208,7 @@ describe('authStore', () => {
       expect(state.user).toEqual(user);
       expect(state.isAuthenticated).toBe(true);
       expect(state.isLoading).toBe(false);
+      expect(tripSync.syncAll).toHaveBeenCalledOnce();
     });
   });
 
@@ -273,6 +288,7 @@ describe('authStore', () => {
       expect(state.isAuthenticated).toBe(true);
       expect(state.isLoading).toBe(false);
       expect(connect).toHaveBeenCalledOnce();
+      expect(tripSync.syncAll).toHaveBeenCalledOnce();
     });
   });