fix(plip): VAD calib for quiet voice + ring stop

Recalibrate the capture VAD to the quiet handset voice: onset 1.4%->0.7%
FS (was never triggering -> 'no sustained voice'), silence 0.6%->0.34%
FS and end-of-speech window 600->900 ms so a whole sentence is held
instead of cut mid-phrase. Also force slic_ring_stop() on incoming
pickup so the physical bell always stops when answered (phone.c/slic.c
s_ringing could desync, leaving the bell ringing through the call).

plip_voice/main/audio.c

@@ -599,19 +599,14 @@ int audio_capture_wav(uint8_t *out, size_t out_max, int max_ms, int silence_ms)
     const int max_frames     = (max_ms     / 20);
     const int silence_frames = (silence_ms / 20);
 
-    /* VAD thresholds (raw S16). Tuned for the SLIC handset mic at +24 dB PGA:
-     * speech peaks ~5 % FS / RMS ~1-2 %, noise floor ~0.6 %. Onset must sit
-     * between (catch quiet speech), silence ABOVE the noise floor (so the turn
-     * ends when the caller stops instead of running to max_ms). */
-    /* Measured on the SLIC handset (DC-blocked): speech body sits ~1 % FS RMS
-     * with peaks ~18 %, noise floor ~0.3 %. The previous silence threshold
-     * (1.2 %) was ABOVE the speech body, so the recorder classified the
-     * caller's own voice as silence and cut the turn after ~0.6 s → empty STT.
-     * Onset must clear noise (3-frame sustained confirm also guards it); silence
-     * must sit between the noise floor and the speech body so the turn ends only
-     * on a real pause. */
-    const int32_t  vad_onset_rms_sq   = 450 * 450;   /* ~1.4% FS² — speech onset above noise */
-    const int32_t  vad_silence_rms_sq = 200 * 200;   /* ~0.6% FS² — below speech body, above noise floor */
+    /* Calibrated to the QUIET handset voice (DC-blocked: body 0.16-0.8 % FS RMS,
+     * loud syllables ~2-4 %, noise floor ~0.3 %). The old onset (1.4 %) NEVER
+     * triggered → "no sustained voice"; the old silence (0.6 %) sat ABOVE the
+     * body → cut mid-sentence. Now: onset catches a real syllable just above the
+     * floor (3-frame confirm guards clicks); silence sits just above the floor so
+     * the turn ends only on a true pause, holding the whole sentence. */
+    const int32_t  vad_onset_rms_sq   = 230 * 230;   /* ~0.70% FS² — quiet-voice onset */
+    const int32_t  vad_silence_rms_sq = 110 * 110;   /* ~0.34% FS² — just above noise floor */
 
     int  silent_frames = 0;
     int  total_frames  = 0;

plip_voice/main/conversation.c

@@ -47,7 +47,9 @@
 #define CAPTURE_MAX_IRAM    (128 * 1024)
 #define CAPTURE_MAX_MS_PSRAM  8000
 #define CAPTURE_MAX_MS_IRAM   4000
-#define CAPTURE_SILENCE_MS     600   /* end-of-speech VAD: shorter = snappier reply (was 800) */
+#define CAPTURE_SILENCE_MS     900   /* end-of-speech: needs to ride through brief
+                                      * mid-sentence pauses so a whole phrase is
+                                      * captured (quiet handset voice). 900 ms. */
 #define REPLY_POLL_MS          200   /* interval for checking hook during playback */
 #define REPLY_PLAYBACK_EXTRA_MS 500  /* safety margin added to computed WAV duration */
 #define BETWEEN_TURNS_MS       300   /* short pause between capture rounds */
@@ -124,6 +126,10 @@ static void enter_incoming_greet(void)
 {
     s_incoming_armed = false;
     phone_ring_stop();
+    slic_ring_stop();   /* belt-and-suspenders: kill the physical bell directly in
+                         * case phone.c's s_ringing flag desynced from slic.c's
+                         * (otherwise phone_ring_stop early-returns and the bell
+                         * keeps ringing through the answered call). */
     tones_stop();
     dialer_reset();
     s_offhook = true;