transcription_artifact_pipeline_bypassed· reason_code· applies to service_callA backend attempted to deliver a transcription artifact outside the Arkret-side blob pipeline, or used a key not derived from the MLS-Exporter label `ak.rtc-transcript-key/v1` (e.g. reused the SFrame / recording label or an empty Context). Clients MUST fail closed. See zh/crypto-media/call-state.md §5.1 and zh/crypto-media/media-service-binding.md §8.1.