✅ improve E2E test reliability on BrowserStack

[BenoitZugmeyer]

Motivation

E2E tests running on BrowserStack have been flaky due to high network latency between the remote browser and the local test server. Several issues compounded this:

• The idle wait duration was fixed at 500ms regardless of actual latency, causing waitForServersIdle() to return before all requests had arrived
• Requests sent by the browser could still be in-flight when waitForServersIdle() was called, making it return immediately despite pending network activity
• The browser was issuing spurious /favicon.ico requests that added noise to server idle tracking

Changes

• Measure browser-to-server latency once per worker before tests run, and use Math.max(500, latency * 1.5) as the idle wait duration
• waitForServersIdle() now waits idleWaitDuration ms upfront to let in-flight requests arrive before checking idle state
• Add a dedicated /flush route (replaces /ok?duration=200) that delays 200ms and returns HTML — used when navigating away to flush SDK events, including session replay Web Worker segments
• Suppress spurious /favicon.ico requests by embedding an empty favicon in all test pages
• Skip redundant flushEvents() in teardown when the page is already on /flush
• Stop the CI test run after the first failure (post-retries) to save time

Test instructions

Run the E2E tests on BrowserStack and verify that previously flaky tests pass consistently.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	178.84 KiB	178.84 KiB	0 B	0.00%	✅
Rum Profiler	6.16 KiB	6.16 KiB	0 B	0.00%	✅
Rum Recorder	27.03 KiB	27.03 KiB	0 B	0.00%	✅
Logs	56.36 KiB	56.36 KiB	0 B	0.00%	✅
Rum Slim	134.70 KiB	134.70 KiB	0 B	0.00%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0041	0.0066	+60.98%
RUM - add action	0.0135	0.0186	+37.78%
RUM - add error	0.0131	0.0171	+30.53%
RUM - add timing	0.0032	0.0033	+3.12%
RUM - start view	0.0136	0.0158	+16.18%
RUM - start/stop session replay recording	0.0008	0.0009	+12.50%
Logs - log message	0.0167	0.0178	+6.59%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	31.72 KiB	32.66 KiB	+966 B
RUM - add action	102.50 KiB	106.93 KiB	+4.43 KiB
RUM - add timing	32.67 KiB	32.62 KiB	-42 B
RUM - add error	106.81 KiB	107.49 KiB	+692 B
RUM - start/stop session replay recording	32.50 KiB	32.27 KiB	-235 B
RUM - start view	482.63 KiB	489.43 KiB	+6.81 KiB
Logs - log message	101.45 KiB	98.45 KiB	-3.00 KiB

🔗 RealWorld

[datadog-prod-us1-3]

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 77.01% (-0.01%)

_{This comment will be updated automatically if new data arrives.
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