Root cause: commits e6d48e6 and e085621 stored ci.yml with JSON-escaped
content (literal \n sequences, leading double-quote) instead of proper
YAML with actual newlines. All CI runs failed with "workflow file issue"
before any job could start.
Fix: restore from pre-corruption base (2517164), apply intended changes:
- concurrency.cancel-in-progress: true → false (queue rather than cancel)
- changes job: runs-on ubuntu-latest (frees mac mini for real work)
PR #1242 intent preserved, corruption from API commit removed.
bcf7f93281