Twilio voice calls now get an AI transcript alongside the recording.
Once a call ends and its recording is stored, we transcribe it and show
the text under the audio player in the call bubble — the same experience
WhatsApp voice notes already have. Transcription runs on Captain and
consumes Captain response credits, so it only kicks in for accounts with
Captain enabled and audio transcriptions turned on.
## How to test
1. On an account with Captain enabled and Settings → Account → Audio
transcriptions on, make a call on a Twilio voice inbox and hang up.
2. Open the conversation. The voice call bubble shows the recording
player once Twilio delivers the recording.
3. Shortly after, the transcript appears under the player — no refresh
needed.
4. Turn audio transcriptions off (or exhaust Captain credits) and
repeat: the recording still appears, the transcript does not.
## What changed
- `Llm::SpeechToTextService` (new) — blob-in/text-out transcription
engine extracted from `Messages::AudioTranscriptionService`: size limit,
temp-file download, model resolution via `Llm::FeatureRouter`, the
OpenAI call, and Captain credit accounting. `.available_for?` holds the
shared gate.
- `Messages::AudioTranscriptionService` — now a thin wrapper over that
engine; its public contract is unchanged, so
`Captain::OpenAiMessageBuilderService` is unaffected.
- `Voice::CallTranscriptionService` / `Voice::CallTranscriptionJob`
(new) — transcribe `call.recording` into `calls.transcript`, then
rebroadcast the message so clients pick it up over the wire.
- `Voice::Provider::Twilio::RecordingAttachmentService` — enqueues the
job after the recording is attached.
The API and frontend needed no changes: `calls.transcript` already
existed, `_call.json.jbuilder` already serialized it, and
`VoiceCall.vue` already fed it to the audio chip. Nothing had ever
written the column.
Also wires `instrument_audio_transcription`, which existed but was never
called, so both transcription paths now emit LLM spans.
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