fix(browser): re-read document.referrer when buffered value is empty

On iOS Safari, document.referrer is not yet populated when the snippet
captures BufferedPageContext. This causes context.page.referrer to be
empty in all Segment calls for the session.

Re-read document.referrer in popPageContext() when the buffered value
is empty.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: abueide

packages/browser/src/core/buffer/__tests__/index.test.ts

@@ -5,6 +5,7 @@ import {
   flushAnalyticsCallsInNewTask,
   PreInitMethodCallBuffer,
   PreInitMethodName,
+  popPageContext,
 } from '..'
 import { Analytics } from '../../analytics'
 import { Context } from '../../context'
@@ -13,6 +14,7 @@ import { User } from '../../user'
 import { getBufferedPageCtxFixture } from '../../../test-helpers/fixtures'
 import * as GlobalAnalytics from '../../../lib/global-analytics-helper'
 import { setVersionType } from '../../../lib/version-type'
+import { BufferedPageContextDiscriminant } from '../../page'
 
 describe(PreInitMethodCallBuffer, () => {
   beforeEach(() => {
@@ -359,6 +361,47 @@ describe(AnalyticsBuffered, () => {
   })
 })
 
+describe(popPageContext, () => {
+  const makeBPC = (referrer: string) => ({
+    __t: BufferedPageContextDiscriminant,
+    c: undefined,
+    p: '/',
+    u: 'https://example.com/',
+    s: '',
+    t: 'Test',
+    r: referrer,
+  })
+
+  function withDocumentReferrer(value: string, fn: () => void) {
+    const original = document.referrer
+    Object.defineProperty(document, 'referrer', { value, configurable: true })
+    try {
+      fn()
+    } finally {
+      Object.defineProperty(document, 'referrer', {
+        value: original,
+        configurable: true,
+      })
+    }
+  }
+
+  it('should use fresh document.referrer when buffered referrer is empty', () => {
+    withDocumentReferrer('https://www.google.com/', () => {
+      const args: unknown[] = [makeBPC('')]
+      const result = popPageContext(args)
+      expect(result!.referrer).toBe('https://www.google.com/')
+    })
+  })
+
+  it('should not override when both buffered and document.referrer are empty', () => {
+    withDocumentReferrer('', () => {
+      const args: unknown[] = [makeBPC('')]
+      const result = popPageContext(args)
+      expect(result!.referrer).toBe('')
+    })
+  })
+})
+
 describe(callAnalyticsMethod, () => {
   let ajs!: Analytics
   let resolveSpy!: jest.Mock<any, any>

packages/browser/src/core/buffer/index.ts

@@ -107,7 +107,16 @@ export const flushAnalyticsCallsInNewTask = (
 export const popPageContext = (args: unknown[]): PageContext | undefined => {
   if (hasBufferedPageContextAsLastArg(args)) {
     const ctx = args.pop() as BufferedPageContext
-    return createPageContext(ctx)
+    const pageCtx = createPageContext(ctx)
+    // Re-read referrer if the buffered value is empty (iOS Safari timing issue)
+    if (
+      !pageCtx.referrer &&
+      typeof document !== 'undefined' &&
+      document.referrer
+    ) {
+      return { ...pageCtx, referrer: document.referrer }
+    }
+    return pageCtx
   }
 }