API v2: validation error instead of HTTP 200 for ignored fields

PUT /sale accepts fields it does not process (e.g. a nested CreditNotes array, or a changed Type) and returns HTTP 200 with the unchanged record. The integration believes the change succeeded.

Request: return a 400 error, or at least a warning in the response, when the payload contains fields the endpoint ignores or cannot change.

Use case: silent no-ops force every integration to re-read the record after each write to detect failed changes.