direct_conversation_binding_invalid· reason_code· applies to event_envelope, auth_decision, state_resolutionThe ak.self.events.command.submit.v1 Direct Conversation binding-integrity stage rejected an ak.direct_conversation.bound Event because its issuer, pair key, authorization basis, Realm role, exact two-member set, main Strand, founding unit digest, or founding MLS references did not match accepted authoritative facts. The rejection occurs before result application, is atomic, and writes nothing; see contract-registry.json operation_registry.direct_conversation_admission_mappings.