fix(audio): open stereo mics at native channel count (#673)

Prefer 2ch before 1ch when PortAudio reports two or more input
channels. Intel SOF digital mics (the Raptor Lake device in #666)
often only support stereo at the PCM; opening them as converted
mono can abort with heap corruption right after capture starts.

Mono-only devices are still never probed with 2 channels (#567).

src/vocalinux/speech_recognition/recognition_manager.py

@@ -501,9 +501,18 @@ def _open_capture_stream(audio, device_index: Optional[int] = None) -> tuple[int
 
     # Never probe stereo on a device that reports a single input channel
     # (opening with more channels than supported is itself a known
-    # PortAudio/ALSA corruption trigger).
+    # PortAudio/ALSA corruption trigger). Stereo-capable devices must be
+    # opened at their native layout first: Intel SOF DMICs (Raptor Lake
+    # "Digital Microphone", etc.) often only support 2ch at the PCM, and
+    # PortAudio can abort with heap corruption if open() accepts a converted
+    # 1ch stream and the callback then overruns (#666).
     reported_channels = int(device_info.get("maxInputChannels", 0) or 0)
-    channel_options = [1] if reported_channels == 1 else [1, 2]
+    if reported_channels == 1:
+        channel_options = [1]
+    elif reported_channels >= 2:
+        channel_options = [2, 1]
+    else:
+        channel_options = [1, 2]
 
     bluetooth = _is_bluetooth_device(device_name)
     # Brief settle helps BlueZ/Pulse release SCO between failed open attempts.

tests/test_recognition_manager_device_config.py

@@ -334,6 +334,59 @@ class TestAudioDeviceDetection(unittest.TestCase):
             assert stream is mock_stream
             assert mock_audio.open.call_count == 1
 
+    def test_open_capture_stream_stereo_device_prefers_native_channels(self):
+        """Stereo devices must be opened 2ch-first, not converted mono (#666).
+
+        Intel SOF digital mics report maxInputChannels=2. Opening them as
+        1ch can succeed then abort in PortAudio's callback with
+        ``free(): corrupted unsorted chunks``.
+        """
+        mock_audio = MagicMock()
+        mock_stream = MagicMock()
+        mock_audio.open.return_value = mock_stream
+        mock_audio.get_device_info_by_index.return_value = {
+            "name": "Raptor Lake-P/U/H cAVS Digital Microphone",
+            "defaultSampleRate": 48000,
+            "maxInputChannels": 2,
+        }
+        mock_pyaudio = MagicMock(paInt16=8)
+
+        with patch.dict("sys.modules", {"pyaudio": mock_pyaudio}):
+            channels, rate, stream = _open_capture_stream(mock_audio, 18)
+
+        assert channels == 2
+        assert rate == 48000
+        assert stream is mock_stream
+        assert mock_audio.open.call_count == 1
+        assert mock_audio.open.call_args.kwargs.get("channels") == 2
+
+    def test_open_capture_stream_stereo_device_falls_back_to_mono(self):
+        """If native stereo open fails, still try mono on a 2ch-reporting device."""
+        mock_audio = MagicMock()
+        mock_stream = MagicMock()
+
+        def open_side_effect(**kwargs):
+            if kwargs.get("channels") == 2:
+                raise IOError("[Errno -9998] Invalid number of channels")
+            return mock_stream
+
+        mock_audio.open.side_effect = open_side_effect
+        mock_audio.get_device_info_by_index.return_value = {
+            "name": "USB Microphone",
+            "defaultSampleRate": 48000,
+            "maxInputChannels": 2,
+        }
+        mock_pyaudio = MagicMock(paInt16=8)
+
+        with patch.dict("sys.modules", {"pyaudio": mock_pyaudio}):
+            channels, rate, stream = _open_capture_stream(mock_audio, 0)
+
+        assert channels == 1
+        assert rate == 48000
+        assert stream is mock_stream
+        assert mock_audio.open.call_args.kwargs.get("channels") == 1
+        assert any(call.kwargs.get("channels") == 2 for call in mock_audio.open.call_args_list)
+
     def test_open_capture_stream_mono_device_never_probes_stereo(self):
         """Mono-only devices must never be opened with 2 channels.