Fix silence timeout never firing — gate on audio amplitude

on_audio was resetting the timer on every chunk including silence,
so the timeout never fired. Now passes the raw chunk and checks RMS;
only resets if energy is above 0.02 (speech, not ambient silence).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/stt.mjs

@@ -132,7 +132,7 @@ export class Stt {
 		let pending = Buffer.alloc(0)
 
 		mic.stdout.on('data', (chunk) => {
-			if (on_audio) on_audio()
+			if (on_audio) on_audio(chunk)
 			pending = Buffer.concat([pending, chunk])
 
 			// Feed complete VAD windows

query-demo.mjs

@@ -121,4 +121,12 @@ stt.listen(async (text) => {
 	accumulated = ''
 
 	await submit(query)
-}, { on_audio: () => { if (accumulated) reset_silence_timer() } })
+}, { on_audio: (chunk) => {
+	if (!accumulated) return
+	// Only reset silence timer if audio has significant energy (not silence)
+	const samples = new Int16Array(chunk.buffer, chunk.byteOffset, chunk.byteLength >> 1)
+	let sum = 0
+	for (let i = 0; i < samples.length; i++) sum += samples[i] * samples[i]
+	const rms = Math.sqrt(sum / samples.length) / 32768
+	if (rms > 0.02) reset_silence_timer()
+} })