Transcript status callback
Sent to your `status_url` when the call's transcription is ready.
`calling.transcript.completed` includes the transcribed text;
`calling.transcript.failed` means the call could not be transcribed.
Status callbacks are advisory, best-effort notifications — delivery can be delayed or fail silently, so don't gate time-critical actions on receiving one. See [Status callback reliability](/docs/platform/webhooks#status-callback-reliability).