The SHA-pinned versions from the security hardening commit referenced non-existent commit hashes, causing the workflow to fail with 'unable to resolve action'. Switch to standard major version tags (v4, v3, v2, v6, v5) which are the recommended approach for GitHub-maintained and well-known actions. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>