Fix VAD — use processed_doa NaN as speech indicator

The auto-select beam always returns an angle (even for noise), so
VAD was always true. The processed_doa (index 0) is NaN when no
speech is present and a real angle when speech is detected.
Now: angle from auto-select beam, VAD from processed_doa being non-NaN.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

xvf3800.py

@@ -103,30 +103,28 @@ class XVF3800:
     def read_doa(self) -> tuple[int, bool]:
         """Read Direction of Arrival using the auto-select beam azimuth.
         Returns (angle 0-359 degrees, vad True/False).
-        Uses AUDIO_MGR_SELECTED_AZIMUTHS which tracks the active speaker."""
+
+        Uses AUDIO_MGR_SELECTED_AZIMUTHS which returns two values:
+          [0] processed_doa — NaN when no speech, real angle when speech detected (= VAD)
+          [1] auto_select_doa — always tracks strongest source, even noise (= angle)
+        """
         import math
 
-        # Read auto-select beam azimuth (2 floats: processed_doa, auto_select_doa)
         data = self._read_float(AUDIO_MGR_RESID, AUDIO_MGR_SELECTED_AZ_CMD, 2)
         if len(data) < 9:  # 1 status + 2*4 bytes
             return 0, False
 
         processed_doa, auto_select_doa = struct.unpack_from("<ff", data, 1)
 
-        # Use auto-select beam (index 1), fall back to processed (index 0)
+        # VAD: processed_doa is NaN when no speech, real value when speech
+        vad = not math.isnan(processed_doa)
+
+        # Angle: prefer auto-select beam (always has a value)
         if not math.isnan(auto_select_doa):
             angle_deg = math.degrees(auto_select_doa) % 360
-            vad = True
-        elif not math.isnan(processed_doa):
+        elif vad:
             angle_deg = math.degrees(processed_doa) % 360
-            vad = True
         else:
-            # Both NaN — no speech detected
-            # Fall back to simple DOA_VALUE
-            data2 = self._read_uint16(GPO_RESID, DOA_VALUE_CMD, 2)
-            if len(data2) >= 5:
-                angle, vad_flag = struct.unpack_from("<HH", data2, 1)
-                return angle % 360, bool(vad_flag)
             return 0, False
 
         return int(angle_deg) % 360, vad