aead_nonce_counter_replay· reason_code· applies to event_envelope, encodingAn AEAD-encrypted payload (encrypted_payload, blob attachment, to_device, etc.) repeated a per-(key_ref, epoch, device_id) counter already seen by the receiver. The receiver MUST reject the payload before AEAD decryption to prevent attempted nonce reuse against a valid sender device. See zh/crypto-media/media-and-blob.md §3.1 and zh/conformance/encoding.md §10.1.