Fix macOS PR builds failing with hashFiles broken symlink error

[Copilot]

Fixes #issue_number

Description

macOS PR builds fail during cache restoration with:

hashFiles('.build/packagelockhash') failed. Fail to hash files under directory '/Users/runner/work/vscode/vscode'

GitHub Actions' hashFiles() function errors when encountering broken symlinks during directory traversal—a known runner issue particularly affecting macOS.

Changes

• Broken symlink cleanup: Added find command to remove broken symlinks before hashFiles() calls, optimized to skip node_modules
• Cache key verification: Added validation that .build/packagelockhash and .build/builtindepshash files are created and non-empty
• Debug output: Log cache key hashes for troubleshooting

Modified steps in .github/workflows/pr-darwin-test.yml:

• Prepare node_modules cache key
• Prepare built-in extensions cache key

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Mac OS PR builds fail with 'The template is not valid'</issue_title>
<issue_description>E.g. https://github.com/microsoft/vscode/actions/runs/19597747630/job/56124714358?pr=278624

Error: The template is not valid. microsoft/vscode/.github/workflows/pr-darwin-test.yml@7fbb6cfc7f88ab49739d74ce2aced0e8f7b1fe00 (Line: 42, Col: 16): hashFiles('.build/packagelockhash') failed. Fail to hash files under directory '/Users/runner/work/vscode/vscode'

</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Mac OS PR builds fail with 'The template is not valid' #278961

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