Extend the admin report spec to assert the full stored object and step
fields, and add a spec covering the queued object and lastAttemptFailed,
so a wrong JSON tag in toExplainDTO fails a test instead of shipping.
Exposes core/artwork.Explain over GET /api/artwork/explain?kind=&id=,
reporting stored trace and queue state without ever walking the chain
live, so the response can only leak history the server already has.