fix: refresh the widgets when the app goes to the background #52

Leaving the app scheduled the widget refresh with a zero-delay timer.
React Native pauses JS timers while the activity is in the background
(timers in the bridgeless runtime have no immediate path for a zero
delay), so the refresh only ran once the app came back or a widget task
happened to start. Switching accounts and pressing Home left the
widgets on the previous account's mail. The refresh now starts directly
from the app state change.

src/widgets/__tests__/sync.test.ts

@@ -0,0 +1,32 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+const refreshSnapshot = vi.hoisted(() => vi.fn(async () => undefined));
+vi.mock('../build', () => ({ refreshSnapshot, readRegistry: vi.fn() }));
+vi.mock('../render', () => ({ hasPlacedWidgets: vi.fn(async () => true), redrawAll: vi.fn(async () => undefined) }));
+vi.mock('../state', () => ({ replaceAll: vi.fn() }));
+
+const { handleAppState } = await import('../sync');
+
+afterEach(() => {
+  vi.useRealTimers();
+  refreshSnapshot.mockClear();
+});
+
+describe('widget sync', () => {
+  it('refreshes when the app goes to the background without waiting for a timer', async () => {
+    // React Native pauses JS timers while the activity is in the background,
+    // so not even a zero-delay timer may stand between leaving the app and
+    // the refresh. Fake timers that never advance stand in for that.
+    vi.useFakeTimers();
+    handleAppState('background');
+    for (let i = 0; i < 10; i++) await Promise.resolve();
+    expect(refreshSnapshot).toHaveBeenCalledTimes(1);
+  });
+
+  it('leaves the app coming back to the scheduled refreshes', async () => {
+    vi.useFakeTimers();
+    handleAppState('active');
+    for (let i = 0; i < 10; i++) await Promise.resolve();
+    expect(refreshSnapshot).not.toHaveBeenCalled();
+  });
+});

src/widgets/sync.ts

@@ -35,6 +35,18 @@ function schedule(delayMs: number, urgent = false): void {
   timer = setTimeout(() => { void run(); }, wait);
 }
 
+/**
+ * Leaving the app is the most likely moment to glance at a widget, so the
+ * widgets refresh right then. Not through a timer: React Native pauses JS
+ * timers while the app is in the background, so even a zero-delay timer
+ * would only fire when the app comes back.
+ */
+export function handleAppState(next: string): void {
+  if (next !== 'background') return;
+  if (timer) clearTimeout(timer);
+  void run();
+}
+
 /** Start following app state; returns the cleanup. No-op off Android. */
 export function startWidgetSync(): () => void {
   if (Platform.OS !== 'android') return () => {};
@@ -61,9 +73,7 @@ export function startWidgetSync(): () => void {
       }
     }),
   ];
-  const appState = AppState.addEventListener('change', (next) => {
-    if (next === 'background') schedule(0, true);
-  });
+  const appState = AppState.addEventListener('change', handleAppState);
   return () => {
     for (const unsubscribe of unsubscribers) unsubscribe();
     appState.remove();