fix: keep retrying a lost push subscription, at most every 15 minutes #1147

Recreating the subscription removed the account's stored id before the
replacement was created and verified, and the resync now requires that
id. One interrupted or timed-out attempt (up to 75 seconds of
verification) therefore ended recovery for that account for good. The
id now stays until a verified replacement overwrites it.

A failed resync also forgot its timestamp, so every return to the tab
reran the whole enable. It now waits 15 minutes before the next try.

lib/__tests__/web-push.test.ts

@@ -306,7 +306,27 @@ describe('resyncWebPush', () => {
     vi.stubGlobal('fetch', vi.fn().mockRejectedValue(new Error('offline')));
     expect(await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false })).toBe(false);
     installFetch({});
-    expect(await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false })).toBe(true);
+    // Not on the very next tab focus...
+    expect(await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false })).toBe(false);
+    // ...but a quarter of an hour later.
+    const later = Date.now() + 16 * 60_000;
+    vi.spyOn(Date, 'now').mockReturnValue(later);
+    try {
+      expect(await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false })).toBe(true);
+    } finally {
+      vi.mocked(Date.now).mockRestore();
+    }
+  });
+
+  it('keeps the opt-in when recreating the subscription fails', async () => {
+    localStorage.setItem(SUB_KEY, 'push-old');
+    localStorage.setItem(DEVICE_KEY, THIS_DEVICE);
+    // The server lost the old subscription, and creating a new one fails.
+    const client = makeClient([]);
+    vi.mocked(client.createPushSubscription).mockRejectedValue(new Error('server down'));
+    installFetch({});
+    expect(await resyncWebPush({ client, relayBaseUrl: RELAY, inboxOnly: false })).toBe(false);
+    expect(localStorage.getItem(SUB_KEY)).toBe('push-old');
   });
 
   it('re-syncs an enabled registration and installs the missing filter', async () => {

lib/web-push.ts

@@ -526,7 +526,9 @@ export async function enableWebPush(
       }
       await params.client.destroyPushSubscription(storedServerId).catch(() => undefined);
     }
-    localStorage.removeItem(subIdKey);
+    // The stored id stays until the replacement is verified below: it is
+    // what tells resyncWebPush this account opted in, so dropping it here
+    // would end recovery for good after one interrupted attempt.
   }
 
   // Reap leftover subscriptions that would otherwise starve the new one's
@@ -719,6 +721,8 @@ export async function isWebPushEnabled(accountId: string): Promise<boolean> {
 // 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;
+// After a failed attempt: soon again, but not on every return to the tab.
+const RESYNC_RETRY_MS = 15 * 60 * 1000;
 const lastResyncAt = new Map<string, number>();
 
 export interface ResyncWebPushParams {
@@ -762,8 +766,9 @@ export async function resyncWebPush(params: ResyncWebPushParams): Promise<boolea
     });
     return true;
   } catch {
-    // A failed attempt must not wait a day for the next one.
-    lastResyncAt.delete(accountId);
+    // A failed attempt must not wait a day for the next one, nor rerun the
+    // whole enable on every tab focus.
+    lastResyncAt.set(accountId, Date.now() - RESYNC_INTERVAL_MS + RESYNC_RETRY_MS);
     return false;
   }
 }