Transcription edits a composer draft. It does not submit an agent turn. Audio is temporary client input, and only normal message submission sends the resulting text. The current implementation transcribes locally on supported iOS devices; environment-backed transcription is not implemented.
The shared controller owns the operation while the client supplies capture and transcription. Preparation binds the transcriber and resolved locale for the whole recording. Draft ownership, text, and revision are captured before recording and checked before insertion, so a late transcript cannot overwrite a draft that was edited or replaced.
Cancellation invalidates a result immediately, but resources stay owned until the underlying work settles. Apple's native transcription call cannot be interrupted once started. Releasing the session or deleting its recording when the abort signal fires would race that work. The transcription contract therefore requires implementations to settle only after their work has stopped; the Apple binding checks cancellation between native calls and discards late results.