A bare '?' in YAML is an explicit-key indicator for a null key, which
produced a job with an empty name (p.Jobs[""]) — a parser invariant
violation caught by FuzzParseBytes.
ParseBytes now returns an error when keyNode.Value is empty.
Failing corpus entry retained as a seed so CI exercises this path.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
