The call site passes a null payload and carries the id in the documentId
column (matching FILE_UPLOADED), so the javadoc claiming Payload:
{"documentId": "uuid"} misdescribed the audit schema. Audit javadocs are the
contract forensic queries are written against.
Addresses @felix, @nora and @elicit review on PR #806.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>