rsvp_basis_malformed· reason_code· applies to event_envelope, schema_validationentry.schedule_basis_refs does not carry exactly one well-formed ak:event: typed id: it is empty, holds more than one item, repeats an item, or the item is not a valid typed Event id. This shape admission is decidable from the payload field alone, without resolving the referenced Event, and MUST reject rather than pend. See zh/models/calendar-event.md section 8.1.