Transcribe while recording, and run a hook when a recording starts

[TerrifiedBug]

What

• live_transcript (off by default; toggle under Recordings in Settings): a session also writes live.jsonl as it records. Every buffer the track files get is resampled to 16 kHz mono and accumulated per track; a timer that only exists while a session is live cuts a chunk when the speaker pauses (0.6 s under a quiet threshold) or, failing that, at the quietest 300 ms in the last 3 s once 10 s have built up. Each chunk goes through the daemon's already-loaded model and lands as one JSON line (speaker, start_ms, end_ms, text). The post-stop transcript is unchanged and remains the record.
• on_start: counterpart of on_stop, given the session folder the moment both tracks are recording. Both hooks share one launcher (Hook.swift) and both have a field in Settings.

Rules this keeps

• One loaded model: the live path borrows the daemon's Transcriber, same as the post-stop pass. No streaming checkpoint, no second resident model.
• Nothing runs while idle: the timer is created at session start and invalidated at stop.
• No new dependencies, no new processes.

Measured

yap bench --audio on parakeet-tdt-ctc-110m, 7 timed runs:

clip	p50	max
5 s	43 ms	48 ms
20 s	65 ms	71 ms

A chunk is 3 to 10 s of one speaker, so two tracks cost roughly 100 ms of ANE per 10 s of call, about 1%. Digital silence (the far side while you talk) is skipped before the model. A dictation press during a live session queues behind at most one chunk.

Tests

• LiveChunkerTests: the cut rules on synthetic audio (wait under 3 s, pause takes all, 10 s cuts after the quietest lull, final takes the tail, silence detection).
• LiveTranscriptTests: the whole path on real speech from say, through the recorder sink, the timer, the model and the file. Asserts a chunk is on disk while audio is still arriving and the final flush catches the tail. Skips when the model is not downloaded, so CI builds without it.
• Serializer order test updated for the new template key.

https://claude.ai/code/session_01TG4DEV5UyCPRFegrkNK3oE