S2c D5 completion: schema_version_at_open column + drift semantics.
- Migration 2026_04_22_100002 adds unsignedInteger schema_version_at_open.
Recorded by FormSubmissionService::createDraft at the moment the
portal first renders the form.
- PublicFormSubmissionResource.schema_drift now compares
schema_version_at_open vs schema_version_at_submit (or
schema.version for active drafts) so organiser edits during an
open draft surface as drift on subsequent PUT/submit responses.
- PublicFormSubmissionController::update routes through
FormSubmissionService::saveDraft so auto_save_count increments
and the FormSubmissionDraftUpdated event fires per PUT.
- bootstrap/app.php: FormRequest ValidationException on
/api/v1/public/forms/* is now re-wrapped into the D6 envelope with
code=VALIDATION_FAILED, so public endpoints emit one consistent
error shape regardless of layer.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>