rsvp_occurrence_not_canonical· reason_code· applies to event_envelope, schema_validationpayload.occurrence is neither JSON null nor a canonical instance key (YYYY-MM-DD for all-day, YYYY-MM-DDTHH:MM:SS[Zone] for timed), including when its date component is not a real proleptic-Gregorian date. Receivers MUST reject instead of rewriting the key, since the typed current result subject derives from the signed value. See zh/models/calendar-event.md.