test(wpt): retry WPT server startup on port conflicts or timeout

[trivikr]

This relates to...

Fixes: #5184

Rationale

The WPT server binds to several randomly-assigned ephemeral ports (for https-local, http-local, etc.). On busy CI runners, these can collide with ports already in use, causing the server to exit with code 1 before all readiness checks pass. This is non-deterministic and depends on what else is running on the host.

Changes

• Extract server startup logic into a startWPTServer() function
• Wrap it in a retry loop (up to 3 attempts, 2-second delay between retries) so a fresh attempt picks different random ports
• Deduplicate the server URL string into a WPT_SERVER_URL constant
• Use setTimeout from node:timers/promises for the retry delay

Features

N/A

Bug Fixes

Fixes intermittent WPT test failures on CI where the Python WPT server exits before becoming ready due to ephemeral port collisions ([Errno 98] Address already in use) or readiness timeouts.

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (4f8f814) to head (709c819).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5215   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files         110      110           
  Lines       36366    36366           
=======================================
  Hits        33922    33922           
  Misses       2444     2444           

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[mcollina]

lgtm