Live wakeword loop: PortAudio input + queue + threshold detection

Replaces the Task 3 smoke-test Program.cs with the full inference loop:
- PA_ALSA_PLUGHW=1 and ORT_LOGGING_LEVEL=3 via both Environment.SetEnvironmentVariable
  and Libc.setenv (P/Invoke) per the Test 1 findings.md env-var gotcha.
- OrtEnv.CreateInstanceWithOptions with ORT_LOGGING_LEVEL_ERROR to suppress
  early GPU-discovery warnings from device_discovery.cc in ORT 1.26.0
  (the env var alone does not silence these; CreateInstanceWithOptions does).
- Callback-driven PortAudio input stream at 16 kHz / Int16 / 1280 frames/block.
- BlockingCollection<short[]>(16) queue; per-call new short[1280] allocation (no races).
- Main loop: Take() -> WakewordModel.Predict() -> threshold >= 0.5 with 1.0s cooldown
  -> DETECTED alexa score=... t=...s. No beep (Task 5 adds it).
- Console.CancelKeyPress -> cts.Cancel() -> graceful stream.Stop() + model.Dispose()
  + PortAudio.Terminate().

tests/02-wakeword-cs/Program.cs

@@ -1,22 +1,137 @@
+using System.Collections.Concurrent;
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using Microsoft.ML.OnnxRuntime;
+using PortAudioSharp;
 using WakewordProbe;
+using Stream = PortAudioSharp.Stream;
+
+const int SampleRate = WakewordModel.SampleRate;
+const int Channels = 1;
+const uint BlockFrames = WakewordModel.FrameSamples; // 1280
+const float Threshold = 0.5f;
+const double CooldownSeconds = 1.0;
+
+// .NET-side mirror for any readers that go through Environment.GetEnvironmentVariable,
+// AND libc setenv so PortAudio / onnxruntime (which use getenv()) see the values.
+Environment.SetEnvironmentVariable("PA_ALSA_PLUGHW", "1");
+Libc.setenv("PA_ALSA_PLUGHW", "1", 1);
+Environment.SetEnvironmentVariable("ORT_LOGGING_LEVEL", "3");
+Libc.setenv("ORT_LOGGING_LEVEL", "3", 1);
+// ORT 1.26.0: the env var does NOT suppress early GPU-discovery warnings from device_discovery.cc.
+// CreateInstanceWithOptions sets the log level at OrtEnv creation time, before EP discovery runs.
+var ortEnvOpts = new EnvironmentCreationOptions { logId = "WakewordProbe", logLevel = OrtLoggingLevel.ORT_LOGGING_LEVEL_ERROR };
+OrtEnv.CreateInstanceWithOptions(ref ortEnvOpts);
+
+PortAudio.Initialize();
+WakewordModel? model = null;
+try
+{
+    int device = FindUsbDevice();
+    Console.WriteLine($"Using device {device} ('{PortAudio.GetDeviceInfo(device).name}')");
 
-string modelsDir = Path.Combine(AppContext.BaseDirectory, "models");
     Console.WriteLine("Loading WakewordModel...");
     var t0 = DateTime.UtcNow;
-using var model = new WakewordModel(
+    string modelsDir = Path.Combine(AppContext.BaseDirectory, "models");
+    model = new WakewordModel(
         Path.Combine(modelsDir, "melspectrogram.onnx"),
         Path.Combine(modelsDir, "embedding_model.onnx"),
         Path.Combine(modelsDir, "alexa.onnx"));
     Console.WriteLine($"Loaded in {(DateTime.UtcNow - t0).TotalSeconds:0.00}s.");
 
-// Smoke test: feed 50 frames of silence (1280 zero samples each).
+    var queue = new BlockingCollection<short[]>(boundedCapacity: 16);
-// Expect every score to be 0f (warmup gate + no signal).
+    using var cts = new CancellationTokenSource();
-var silentFrame = new short[WakewordModel.FrameSamples];
+    Console.CancelKeyPress += (_, e) => { e.Cancel = true; cts.Cancel(); };
-int nonZero = 0;
+
-for (int i = 0; i < 50; i++)
+    var inParams = new StreamParameters
     {
-    float s = model.Predict(silentFrame);
+        device = device,
-    if (s != 0f) nonZero++;
+        channelCount = Channels,
+        sampleFormat = SampleFormat.Int16,
+        suggestedLatency = PortAudio.GetDeviceInfo(device).defaultLowInputLatency,
+        hostApiSpecificStreamInfo = IntPtr.Zero,
+    };
+
+    Stream.Callback callback = (IntPtr input, IntPtr _, uint frameCount,
+        ref StreamCallbackTimeInfo _2, StreamCallbackFlags status, IntPtr _3) =>
+    {
+        if (status.HasFlag(StreamCallbackFlags.InputOverflow))
+            Console.Error.WriteLine("[status] input overflow");
+
+        if (frameCount != BlockFrames)
+        {
+            Console.Error.WriteLine($"[status] unexpected callback frameCount={frameCount} (want {BlockFrames})");
+            return StreamCallbackResult.Continue;
+        }
+
+        var frame = new short[BlockFrames];
+        unsafe
+        {
+            short* src = (short*)input.ToPointer();
+            fixed (short* dst = &frame[0])
+                Buffer.MemoryCopy(src, dst, BlockFrames * sizeof(short), BlockFrames * sizeof(short));
+        }
+        if (!queue.TryAdd(frame, 0))
+            Console.Error.WriteLine("[status] consumer behind, dropping frame");
+        return StreamCallbackResult.Continue;
+    };
+
+    using var stream = new Stream(
+        inParams, null, SampleRate, BlockFrames, StreamFlags.NoFlag, callback, IntPtr.Zero);
+    stream.Start();
+    Console.WriteLine("Listening. Say 'alexa'. Ctrl-C to exit.");
+
+    var sw = Stopwatch.StartNew();
+    TimeSpan lastTrigger = TimeSpan.FromSeconds(-CooldownSeconds);
+
+    try
+    {
+        while (!cts.IsCancellationRequested)
+        {
+            short[] frame = queue.Take(cts.Token);
+            float score = model.Predict(frame);
+            var now = sw.Elapsed;
+            if (score >= Threshold && (now - lastTrigger).TotalSeconds >= CooldownSeconds)
+            {
+                Console.WriteLine($"DETECTED alexa score={score:0.000} t={now.TotalSeconds:0.0}s");
+                lastTrigger = now;
+                // Beep is added in Task 5.
+            }
+        }
+    }
+    catch (OperationCanceledException) { /* Ctrl-C path */ }
+
+    stream.Stop();
+    Console.WriteLine("\nbye");
+}
+finally
+{
+    model?.Dispose();
+    PortAudio.Terminate();
+}
+
+static int FindUsbDevice()
+{
+    int count = PortAudio.DeviceCount;
+    for (int i = 0; i < count; i++)
+    {
+        var info = PortAudio.GetDeviceInfo(i);
+        if (info.name.ToLowerInvariant().Contains("usb") && info.maxInputChannels >= 1)
+            return i;
+    }
+    Console.Error.WriteLine("USB audio device not found. Devices:");
+    for (int i = 0; i < count; i++)
+    {
+        var info = PortAudio.GetDeviceInfo(i);
+        Console.Error.WriteLine(
+            $"  [{i}] {info.name} in={info.maxInputChannels} out={info.maxOutputChannels}");
+    }
+    Environment.Exit(1);
+    return -1; // unreachable
+}
+
+static class Libc
+{
+    [DllImport("libc", EntryPoint = "setenv")]
+    public static extern int setenv(string name, string value, int overwrite);
 }
-Console.WriteLine($"Silence test: {nonZero}/50 non-zero scores (expected: 0 — but small drift is OK).");
-Console.WriteLine("Predict pipeline ran without throwing.");