focus_mismatch· reason_code· applies to service_call, auth_decisionMedia token exchange (ak.self.call.media.exchange.issue_token.v1) requested a `focus_id` different from the already-committed `ak.call.state.session_focus`. Token issuer MUST reject; clients MUST re-target the established focus rather than retrying with the original preference. See zh/crypto-media/media-service-binding.md §3 and §5.