fix(sync): re-hydrate active trip store on reconnect/online (H1) (#1181)

setRefetchCallback was dead code, so on reconnect the queue flushed and Dexie
re-seeded but the open trip's Zustand store was never refreshed — a
collaborator's edits made while we were offline didn't appear until navigating
away and back.

- new tripStore.hydrateActiveTrip(): silent refresh of the active trip's
  collaborative state (days/places/packing/todo/budget/reservations/files),
  no resetTrip and no isLoading toggle so there's no splash on reconnect
- syncTriggers wires setRefetchCallback to it (WS layer awaits the flush hook
  first) and re-hydrates open trips after the online-event syncAll; cleared on
  unregister
- websocket exposes getActiveTrips() for the online-event path
- tests: refetch wiring + ordering, silent hydrate without reset/splash

client/tests/unit/sync/syncTriggers.test.ts

@@ -0,0 +1,76 @@
+/**
+ * syncTriggers — reconnect/online wiring (H1).
+ *
+ * Verifies the previously-dead refetch path is wired: on WS reconnect and on the
+ * `online` event the active trip's store is re-hydrated (after the queue flush).
+ */
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+
+const flush = vi.fn(() => Promise.resolve());
+const syncAll = vi.fn(() => Promise.resolve());
+const hydrate = vi.fn(() => Promise.resolve());
+
+let refetchCb: ((tripId: string) => void) | null = null;
+let preReconnect: (() => Promise<void>) | null = null;
+
+vi.mock('../../../src/sync/mutationQueue', () => ({
+  mutationQueue: { flush: () => flush() },
+}));
+vi.mock('../../../src/sync/tripSyncManager', () => ({
+  tripSyncManager: { syncAll: () => syncAll() },
+}));
+vi.mock('../../../src/api/websocket', () => ({
+  setPreReconnectHook: (fn: (() => Promise<void>) | null) => { preReconnect = fn; },
+  setRefetchCallback: (fn: ((tripId: string) => void) | null) => { refetchCb = fn; },
+  getActiveTrips: () => ['7'],
+}));
+vi.mock('../../../src/store/tripStore', () => ({
+  useTripStore: { getState: () => ({ hydrateActiveTrip: hydrate }) },
+}));
+
+import { registerSyncTriggers, unregisterSyncTriggers } from '../../../src/sync/syncTriggers';
+
+const flushMicrotasks = async () => {
+  for (let i = 0; i < 5; i++) await Promise.resolve();
+};
+
+beforeEach(() => {
+  flush.mockClear(); syncAll.mockClear(); hydrate.mockClear();
+  refetchCb = null; preReconnect = null;
+  Object.defineProperty(navigator, 'onLine', { value: true, writable: true, configurable: true });
+});
+
+afterEach(() => {
+  unregisterSyncTriggers();
+});
+
+describe('syncTriggers', () => {
+  it('registers a refetch callback that hydrates the active trip', () => {
+    registerSyncTriggers();
+    expect(refetchCb).toBeTypeOf('function');
+    refetchCb!('7');
+    expect(hydrate).toHaveBeenCalledWith('7');
+  });
+
+  it('also registers the pre-reconnect flush hook', () => {
+    registerSyncTriggers();
+    expect(preReconnect).toBeTypeOf('function');
+  });
+
+  it('clears both reconnect hooks on unregister', () => {
+    registerSyncTriggers();
+    unregisterSyncTriggers();
+    expect(refetchCb).toBeNull();
+    expect(preReconnect).toBeNull();
+  });
+
+  it('online event flushes, then re-seeds Dexie and re-hydrates active trips', async () => {
+    registerSyncTriggers();
+    window.dispatchEvent(new Event('online'));
+    await flushMicrotasks();
+
+    expect(flush).toHaveBeenCalled();
+    expect(syncAll).toHaveBeenCalled();
+    expect(hydrate).toHaveBeenCalledWith('7');
+  });
+});