feat(browser)!: Switch default browser session lifecycle mode to page (#21245)

#### Summary

- Default browserSessionIntegration session lifecycle is now page
instead of route. One session per page load; soft navigations no longer
start new sessions unless lifecycle: 'route' is set.

#### Checklist
-  If you've added code that should be tested, please add tests.
- Link an issue if there is one related to your pull request. If no
issue is linked, one will be auto-generated and linked.

Closes : #21241

---------

Co-authored-by: Martin Sonnberger <martin.sonnberger@sentry.io>

Author: nehaprasad-dev

dev-packages/browser-integration-tests/suites/sessions/initial-scope/init.js

@@ -5,6 +5,7 @@ window.Sentry = Sentry;
 Sentry.init({
   dsn: 'https://public@dsn.ingest.sentry.io/1337',
   release: '0.1',
+  integrations: [Sentry.browserSessionIntegration({ lifecycle: 'route' })],
   initialScope: {
     user: {
       id: '1337',

dev-packages/browser-integration-tests/suites/sessions/page-lifecycle/init.js

@@ -5,5 +5,4 @@ window.Sentry = Sentry;
 Sentry.init({
   dsn: 'https://public@dsn.ingest.sentry.io/1337',
   release: '0.1',
-  integrations: [Sentry.browserSessionIntegration({ lifecycle: 'page' })],
 });

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

@@ -8,7 +8,7 @@ import {
   waitForSession,
 } from '../../../utils/helpers';
 
-sentryTest('starts a session on pageload with page lifecycle.', async ({ getLocalTestUrl, page }) => {
+sentryTest('starts a session on pageload with page lifecycle (default).', async ({ getLocalTestUrl, page }) => {
   const url = await getLocalTestUrl({ testDir: __dirname });
 
   const sessionPromise = waitForSession(page, s => !!s.init && s.status === 'ok');
@@ -32,7 +32,7 @@ sentryTest('starts a session on pageload with page lifecycle.', async ({ getLoca
 });
 
 sentryTest(
-  "doesn't start a new session on pushState navigation with page lifecycle.",
+  "doesn't start a new session on pushState navigation with page lifecycle (default).",
   async ({ getLocalTestUrl, page }) => {
     const url = await getLocalTestUrl({ testDir: __dirname });
 

dev-packages/browser-integration-tests/suites/sessions/route-lifecycle/init.js

@@ -5,4 +5,5 @@ window.Sentry = Sentry;
 Sentry.init({
   dsn: 'https://public@dsn.ingest.sentry.io/1337',
   release: '0.1',
+  integrations: [Sentry.browserSessionIntegration({ lifecycle: 'route' })],
 });

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

@@ -3,7 +3,7 @@ import { sentryTest } from '../../../utils/fixtures';
 import { waitForSession } from '../../../utils/helpers';
 
 sentryTest(
-  'should start new sessions on pushState navigation with route lifecycle (default).',
+  'should start new sessions on pushState navigation with route lifecycle.',
   async ({ getLocalTestUrl, page }) => {
     const url = await getLocalTestUrl({ testDir: __dirname });
 

dev-packages/browser-integration-tests/suites/sessions/start-session/init.js

@@ -0,0 +1,9 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '0.1',
+  integrations: [Sentry.browserSessionIntegration({ lifecycle: 'route' })],
+});

dev-packages/browser-integration-tests/suites/sessions/user/init.js

@@ -0,0 +1,9 @@
+import * as Sentry from '@sentry/browser';
+
+window.Sentry = Sentry;
+
+Sentry.init({
+  dsn: 'https://public@dsn.ingest.sentry.io/1337',
+  release: '0.1',
+  integrations: [Sentry.browserSessionIntegration({ lifecycle: 'route' })],
+});

packages/browser/src/integrations/browsersession.ts

@@ -7,13 +7,11 @@ interface BrowserSessionOptions {
   /**
    * Controls the session lifecycle - when new sessions are created.
    *
-   * - `'route'`: A session is created on page load and on every navigation.
-   *   This is the default behavior.
    * - `'page'`: A session is created once when the page is loaded. Session is not
-   *   updated on navigation. This is useful for webviews or single-page apps where
-   *   URL changes should not trigger new sessions.
+   *   updated on navigation. This is the default behavior.
+   * - `'route'`: A session is created on page load and on every navigation.
    *
-   * @default 'route'
+   * @default 'page'
    */
   lifecycle?: 'route' | 'page';
 }
@@ -25,7 +23,7 @@ interface BrowserSessionOptions {
  * Note: In order for session tracking to work, you need to set up Releases: https://docs.sentry.io/product/releases/
  */
 export const browserSessionIntegration = defineIntegration((options: BrowserSessionOptions = {}) => {
-  const lifecycle = options.lifecycle ?? 'route';
+  const lifecycle = options.lifecycle ?? 'page';
 
   return {
     name: 'BrowserSession' as const,

packages/browser/test/integrations/browsersession.test.ts

@@ -147,8 +147,7 @@ describe('browserSessionIntegration', () => {
   });
 
   it('does not re-send the navigation session when navigation happens before the deferred initial capture', () => {
-    // Default lifecycle is 'route', which also registers the navigation handler.
-    setupBrowserSession();
+    setupBrowserSession({ lifecycle: 'route' });
 
     // The initial capture is deferred, so nothing is sent synchronously.
     expect(SentryCore.captureSession).not.toHaveBeenCalled();
@@ -165,7 +164,7 @@ describe('browserSessionIntegration', () => {
   });
 
   it('still captures a session on navigation that happens after the initial capture', () => {
-    setupBrowserSession();
+    setupBrowserSession({ lifecycle: 'route' });
 
     vi.runAllTimers();
     expect(SentryCore.captureSession).toHaveBeenCalledTimes(1);