event_id_digest_mismatch· reason_code· applies to event_envelopeSub-reason for schema_violation when the carried event_id does not equal the value re-derived from the Event's own canonical content per zh/conformance/encoding.md section 4.0. Receivers MUST re-derive and compare before using event_id for deduplication, indexing, routing, idempotency or authorization, and MUST NOT report this as proof_invalid: the distinct code is what localises cross-implementation canonical-JSON divergence and what prevents a forged event_id from entering the duplicate_conflict quarantine path.