fix: renew push subscriptions before Stalwart's 7-day expiry

Bulwark asks for a 90-day push subscription, but Stalwart clamps
`expires` to 7 days. The background renewal ran once per page load,
so a tab or installed app left open for more than a week let the
subscription lapse and notifications stopped without a hint.

The renewal now runs at most once a day instead of once per load, and
also when the tab comes back to the foreground.

components/push-notification-prompt.tsx

@@ -118,11 +118,19 @@ export function PushNotificationPrompt() {
   // live registration stale.
   useEffect(() => {
     if (!policyLoaded || !isAuthenticated || !client || !accountId || isDemoMode) return;
-    void resyncWebPush({
-      client,
-      relayBaseUrl,
-      accountLabel: username ?? undefined,
-    });
+    const resync = () => {
+      void resyncWebPush({
+        client,
+        relayBaseUrl,
+        accountLabel: username ?? undefined,
+      });
+    };
+    resync();
+    // A long-open tab comes back to the foreground: renew the subscription
+    // before the server's 7-day expiry (resyncWebPush runs at most daily).
+    const onVisible = () => { if (document.visibilityState === 'visible') resync(); };
+    document.addEventListener('visibilitychange', onVisible);
+    return () => document.removeEventListener('visibilitychange', onVisible);
   }, [accountId, client, isAuthenticated, isDemoMode, policyLoaded, relayBaseUrl, username]);
 
   useEffect(() => {

lib/__tests__/web-push.test.ts

@@ -234,16 +234,22 @@ describe('resyncWebPush', () => {
     expect(client.createPushSubscription).not.toHaveBeenCalled();
   });
 
-  it('runs at most once per account per page load', async () => {
+  it('runs at most once a day per account', async () => {
     localStorage.setItem(DEVICE_KEY, THIS_DEVICE);
     localStorage.setItem(SUB_KEY, 'push-old');
     const client = makeClient([sub('push-old', THIS_DEVICE)], { emailPushCapability: true });
     installFetch({});
+    const now = vi.spyOn(Date, 'now').mockReturnValue(1_000_000);
 
     expect(await resyncWebPush({ client, relayBaseUrl: RELAY })).toBe(true);
     expect(await resyncWebPush({ client, relayBaseUrl: RELAY })).toBe(false);
-
     expect(client.listPushSubscriptions).toHaveBeenCalledTimes(1);
+
+    // A tab left open past a day renews again, before Stalwart's 7-day expiry.
+    now.mockReturnValue(1_000_000 + 25 * 60 * 60 * 1000);
+    expect(await resyncWebPush({ client, relayBaseUrl: RELAY })).toBe(true);
+    expect(client.listPushSubscriptions).toHaveBeenCalledTimes(2);
+    now.mockRestore();
   });
 
   it('swallows failures instead of surfacing them to the app', async () => {

lib/web-push.ts

@@ -651,10 +651,13 @@ export async function isWebPushEnabled(accountId: string): Promise<boolean> {
   return sub !== null && localStorage.getItem(subscriptionIdKey(accountId)) !== null;
 }
 
-// Accounts already re-synced during this page load. One pass per account is
-// plenty: the subscription only drifts between sessions (expiry, a client
-// update that changed what we subscribe to, a recreated Junk mailbox).
-const resyncedAccountIds = new Set<string>();
+// When each account was last re-synced during this page load. Once a day is
+// enough for the drift between sessions (a client update that changed what
+// we subscribe to, a recreated Junk mailbox), but not only once: Stalwart
+// clamps `expires` to 7 days, so a tab or installed app left open for a
+// week would otherwise let the subscription lapse and push stop silently.
+const RESYNC_INTERVAL_MS = 24 * 60 * 60 * 1000;
+const lastResyncAt = new Map<string, number>();
 
 export interface ResyncWebPushParams {
   client: IJMAPClient;
@@ -676,10 +679,12 @@ export async function resyncWebPush(params: ResyncWebPushParams): Promise<boolea
   } catch {
     return false;
   }
-  if (!accountId || resyncedAccountIds.has(accountId)) return false;
+  if (!accountId) return false;
+  const last = lastResyncAt.get(accountId);
+  if (last !== undefined && Date.now() - last < RESYNC_INTERVAL_MS) return false;
   try {
     if (!(await isWebPushEnabled(accountId))) return false;
-    resyncedAccountIds.add(accountId);
+    lastResyncAt.set(accountId, Date.now());
     await enableWebPush({
       client: params.client,
       relayBaseUrl: params.relayBaseUrl,
@@ -693,5 +698,5 @@ export async function resyncWebPush(params: ResyncWebPushParams): Promise<boolea
 
 // Test hook: forget which accounts were re-synced during this page load.
 export function resetWebPushResyncState(): void {
-  resyncedAccountIds.clear();
+  lastResyncAt.clear();
 }