[s2x]

What changed

The polling watcher test selects files by traversal order and checks a complete sweep. It no longer assumes a file name is in the first tick. The coverage artifact name is now available after a test failure.

Closes #1122

How it was tested

• Full PHPUnit and coverage suites on Linux PHP 8.3: 2,651 tests, 84.89% line coverage.
• Polling watcher tests on Linux PHP 8.2 and macOS PHP 8.5.
• Coverage and workflow gate tests, composer lint, and actionlint.
• Checked matrix artifact names locally. GitHub CI and actual failure-path upload remain to be verified.

Checklist

• Tests added or updated, and all checks pass locally
• CHANGELOG.md updated under [Unreleased] (not applicable: test and CI changes only)
• Documentation updated (not applicable)
• Everything is written in English
• The PR title is a Conventional Commit