Per RFC-WS-6 §Q3 v1.3 addition 2.
- Added 'failure_response_code' to FormSubmission $fillable + 'string' cast.
Plain string (not enum) — the exception subclass on
form_submission_action_failures is the canonical classification source;
this column is a denormalised mirror for response-shape rendering.
- Factory fluent state method withFailureResponseCode() with documentation
of the four valid values.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>