fix(browser-tests): fix flaky sessions route-lifecycle test by replacing timeout-based approach with sequential waitForSession

The test was flaky because getMultipleSentryEnvelopeRequests starts a 4000ms timeout
before page.goto, so the timeout could expire before all 4 session envelopes arrived.

Replaced with the robust sequential waitForSession pattern (used in start-session,
initial-scope, user tests) that deterministically waits for each session individually.

Co-Authored-By: Claude <noreply@anthropic.com>

Agent-Logs-Url: https://github.com/getsentry/sentry-javascript/sessions/443b2c75-cf14-4a37-8212-6a532959da82

Co-authored-by: Lms24 <8420481+Lms24@users.noreply.github.com>

Author: Copilot

dev-packages/browser-integration-tests/suites/sessions/route-lifecycle/test.ts

@@ -1,27 +1,30 @@
 import { expect } from '@playwright/test';
-import type { SerializedSession } from '@sentry/core/src';
 import { sentryTest } from '../../../utils/fixtures';
-import { getMultipleSentryEnvelopeRequests } from '../../../utils/helpers';
+import { waitForSession } from '../../../utils/helpers';
 
 sentryTest(
   'should start new sessions on pushState navigation with route lifecycle (default).',
   async ({ getLocalTestUrl, page }) => {
     const url = await getLocalTestUrl({ testDir: __dirname });
 
-    const sessionsPromise = getMultipleSentryEnvelopeRequests<SerializedSession>(page, 10, {
-      url,
-      envelopeType: 'session',
-      timeout: 4000,
-    });
+    const initSessionPromise = waitForSession(page, s => !!s.init && s.status === 'ok');
+    await page.goto(url);
+    const initSession = await initSessionPromise;
 
-    await page.waitForSelector('#navigate');
-
-    await page.locator('#navigate').click();
+    const session1Promise = waitForSession(page, s => !!s.init && s.status === 'ok' && s.sid !== initSession.sid);
     await page.locator('#navigate').click();
+    const session1 = await session1Promise;
+
+    const session2Promise = waitForSession(page, s => !!s.init && s.status === 'ok' && s.sid !== session1.sid);
     await page.locator('#navigate').click();
+    const session2 = await session2Promise;
 
-    const startedSessions = (await sessionsPromise).filter(session => session.init);
+    const session3Promise = waitForSession(page, s => !!s.init && s.status === 'ok' && s.sid !== session2.sid);
+    await page.locator('#navigate').click();
+    const session3 = await session3Promise;
 
-    expect(startedSessions.length).toBe(4);
+    // Verify we got 4 distinct init sessions (1 initial + 3 navigations)
+    const sids = new Set([initSession.sid, session1.sid, session2.sid, session3.sid]);
+    expect(sids.size).toBe(4);
   },
 );