feat(browser): Check for clock drift on page lifecycle events

Also check on `freeze`/`resume` (Chromium only) and `pagehide`/`pageshow`
(back/forward cache). This makes the time origin correction happen at the
pause, not at the next regular timestamp call.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: Lms24

packages/browser/src/client.ts

@@ -162,8 +162,17 @@ export class BrowserClient extends Client<BrowserClientOptions> {
           });
         }
       });
+
+      // `freeze` and `resume` are only fired by Chromium browsers. Other browsers never fire them, so these listeners
+      // are no-ops there.
+      WINDOW.document.addEventListener('freeze', () => timestampInSeconds());
+      WINDOW.document.addEventListener('resume', () => timestampInSeconds());
     }
 
+    // Pages restored from the back/forward cache were paused while they were cached.
+    WINDOW.addEventListener?.('pagehide', () => timestampInSeconds());
+    WINDOW.addEventListener?.('pageshow', () => timestampInSeconds());
+
     if (userInfo) {
       this.on('beforeSendSession', addAutoIpAddressToSession);
     }

packages/browser/test/client.test.ts

@@ -63,6 +63,20 @@ describe('BrowserClient', () => {
     expect(SentryCore.timestampInSeconds).toHaveBeenCalled();
   });
 
+  it.each([
+    ['freeze', () => WINDOW.document],
+    ['resume', () => WINDOW.document],
+    ['pagehide', () => WINDOW],
+    ['pageshow', () => WINDOW],
+  ])('checks the clocks for drift on %s', (eventName, getTarget) => {
+    client = new BrowserClient(getDefaultBrowserClientOptions());
+    vi.mocked(SentryCore.timestampInSeconds).mockClear();
+
+    getTarget().dispatchEvent(new Event(eventName));
+
+    expect(SentryCore.timestampInSeconds).toHaveBeenCalled();
+  });
+
   it('does not flush outcomes when sendClientReports is disabled but still flushes the client', async () => {
     client = new BrowserClient(getDefaultBrowserClientOptions({ sendClientReports: false }));
     const flushSpy = vi.spyOn(client, 'flush').mockReturnValue(Promise.resolve(true) as any);