direct_conversation_founding_unit_invalid· reason_code· applies to event_envelope, service_call, federation_transactionA Direct Conversation founding unit is not the closed caller-authored four-Event unit. Causes include a count other than four, wrong wire order, a missing peer or founder ak.member.state{join}, a missing ak.strand.create, a fifth Event, a mixed actor/pair/profile/Realm, any envelope field naming a predecessor Event inside the unit, an envelope realm_id that is not retype(events[0] event_id), a main_strand_id that is not retype(events[3] event_id), a founding_unit_digest that does not match the recomputed value, or any request field asserting a service-allocated identifier, reservation handle or materialization draft, or a genesis whose initial_join_rule, initial_discoverability or initial_history_access is not the create-locked closed, invite_only or since_join. Carried under failed_precondition on both the self and the peer path; the whole unit is rejected with zero writes. See zh/identity/contact-and-direct-conversation.md sections 5.5 and 6.1.