Improvements and tests for live transcription.

Decisions.md

@@ -174,19 +174,34 @@ up-to-30 s windows), so "live" is approximated by a **segment loop**:
 
 - **Capture (main thread):** `getUserMedia` → `AudioContext` at the device's
   native rate → an `AudioWorklet` chunker posts ~100 ms Float32 frames to the
-  main thread, which resamples them to 16 kHz with the existing pure
-  `resampleLinear` (D-012's documented fallback; adequate for speech).
-  The worklet module is loaded from a **Blob URL** built from an inline code
-  string — no extra served file, no build/service-worker changes, and it keeps
-  working offline. Where `audioWorklet`/Blob modules are unavailable
-  (older Safari), fall back to a `ScriptProcessorNode`. The context is *not*
-  forced to 16 kHz because Firefox cannot connect a `MediaStreamAudioSourceNode`
-  across sample rates.
+  main thread, which resamples them to 16 kHz with the pure, stateful
+  `StreamingResampler` (windowed-sinc low-pass; `resampleLinear` has no
+  anti-aliasing filter, so 48 kHz → 16 kHz decimation folded everything above
+  8 kHz into the speech band and measurably hurt accuracy — see
+  `tests/resampler.test.ts`). The worklet module is loaded from a **Blob URL**
+  built from an inline code string — no extra served file, no
+  build/service-worker changes, and it keeps working offline. Where
+  `audioWorklet`/Blob modules are unavailable (older Safari), fall back to a
+  `ScriptProcessorNode`. The context is *not* forced to 16 kHz because Firefox
+  cannot connect a `MediaStreamAudioSourceNode` across sample rates.
 - **Segmentation (pure, unit-tested):** a simple RMS energy gate
   (`src/lib/live.ts`) splits speech into segments: a segment starts at speech
   onset (with a short pre-roll), commits after a run of trailing silence or at
-  a max length (~25 s, under Whisper's 30 s window), and pure-silence audio is
+  a max length (under Whisper's 30 s window), and pure-silence audio is
   dropped entirely — Whisper hallucinates on silence, so never transcribe it.
+  Two accuracy refinements (2026-07-14): the gate has **hysteresis** (once a
+  segment is open, frames stay "speech" down to half the onset threshold, so
+  quiet phonemes don't fragment utterances), and a max-length commit is a
+  **soft cut** — it splits at the last sub-threshold frame in the trailing
+  window instead of mid-word at the hard cap, seeding the next segment with
+  the remainder (a mid-word cut corrupts the boundary word in both segments).
+  Dropped (near-silent) segments also clear any tentative text they produced,
+  so a hallucinated tentative pass can neither linger on screen nor be adopted
+  as the next segment's provisional text. Production tuning lives in
+  `LIVE_TUNING` (`src/lib/live.ts`), shared by `src/App.tsx` and the accuracy
+  harness (`tests/live-accuracy.test.ts` — tone-word oracle engine + WER, so
+  segmentation/scheduling/resampling accuracy is regression-tested under
+  `bun test` without a model).
   No ML VAD (e.g. Silero) until the energy gate proves insufficient in real use.
 - **Inference (existing worker, serialized):** the current segment is
   re-transcribed through the **existing** inference worker/pipeline on a