v0.6: DHCP tunnel transport with NOP heartbeat protocol

DhcpTunnelTest/Program.cs

@@ -0,0 +1,105 @@
+using System.Net;
+using System.Net.NetworkInformation;
+using System.Net.Sockets;
+using System.Text;
+
+// Args: [interface_ip] [interval_ms]
+// Defaults: auto-detect LAN IP, 50ms
+
+string localIp = args.Length > 0 ? args[0] : GetLanInterfaceIp() ?? "0.0.0.0";
+int intervalMs = args.Length > 1 && int.TryParse(args[1], out int iv) ? iv : 50;
+
+using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
+sock.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+sock.EnableBroadcast = true;
+
+var localEp = new IPEndPoint(IPAddress.Parse(localIp), 68);
+sock.Bind(localEp);
+
+Console.WriteLine($"Bound to {localEp} (SO_REUSEADDR)");
+Console.WriteLine("Sending NOPs + listening. Press Ctrl+C to stop.");
+Console.WriteLine();
+
+var cts = new CancellationTokenSource();
+var recvTask = Task.Run(() => ReceiveLoop(sock, cts.Token));
+
+var destEp = new IPEndPoint(IPAddress.Broadcast, 67);
+uint nonce = 0;
+
+while (!cts.Token.IsCancellationRequested)
+{
+    nonce++;
+    string msg = $"HKMSTR {nonce}\n";
+    byte[] payload = Encoding.UTF8.GetBytes(msg);
+
+    try
+    {
+        int sent = sock.SendTo(payload, destEp);
+        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] SENT n={nonce} {sent} bytes");
+    }
+    catch (Exception ex)
+    {
+        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] SEND FAILED: {ex.Message}");
+    }
+
+    try { Thread.Sleep(intervalMs); }
+    catch (OperationCanceledException) { break; }
+}
+
+cts.Cancel();
+await recvTask;
+
+static string? GetLanInterfaceIp()
+{
+    foreach (var nic in NetworkInterface.GetAllNetworkInterfaces())
+    {
+        if (nic.OperationalStatus != OperationalStatus.Up)
+            continue;
+        if (nic.NetworkInterfaceType == NetworkInterfaceType.Loopback)
+            continue;
+        if (nic.Description.Contains("WireGuard", StringComparison.OrdinalIgnoreCase))
+            continue;
+
+        foreach (var addr in nic.GetIPProperties().UnicastAddresses)
+        {
+            if (addr.Address.AddressFamily == AddressFamily.InterNetwork)
+            {
+                var ip = addr.Address.ToString();
+                if (ip.StartsWith("192.168.") || ip.StartsWith("10.") || ip.StartsWith("172."))
+                    return ip;
+            }
+        }
+    }
+    return null;
+}
+
+static void ReceiveLoop(Socket sock, CancellationToken ct)
+{
+    byte[] buffer = new byte[4096];
+    EndPoint fromEp = new IPEndPoint(IPAddress.Any, 0);
+
+    while (!ct.IsCancellationRequested)
+    {
+        int received;
+        try
+        {
+            if (!sock.Poll(500_000, SelectMode.SelectRead))
+                continue;
+            received = sock.ReceiveFrom(buffer, ref fromEp);
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV ERROR: {ex.Message}");
+            continue;
+        }
+
+        string text = Encoding.UTF8.GetString(buffer, 0, received).TrimEnd('\n', '\r');
+        if (!text.StartsWith("HKMSTR"))
+        {
+            Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV {received} bytes from {fromEp} (no magic)");
+            continue;
+        }
+
+        Console.WriteLine($"[{DateTime.Now:HH:mm:ss.fff}] RECV {received} bytes from {fromEp}: {text}");
+    }
+}

DhcpTunnelTest/Robovoice.DhcpTunnelTest.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Robovoice.App/AppConfig.cs

@@ -12,7 +12,7 @@ public sealed class AppConfig
     public int LengthScale { get; set; } = 100;
     public int NoiseWScale { get; set; } = 800;
     public bool MinimizeToTray { get; set; } = true;
-    public string ServerEndpoint { get; set; } = "127.0.0.1:5210";
+    public string InterfaceIp { get; set; } = string.Empty;
 
     public static string AppDataDir => Path.Combine(
         Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),

Robovoice.App/MainForm.Designer.cs

@@ -17,8 +17,7 @@ partial class MainForm
     private Button btnBrowseFile = null!;
     private Label lblFileName = null!;
     private Label lblServer = null!;
-    private TextBox txtServer = null!;
-    private Button btnConnect = null!;
+    private ComboBox cmbInterface = null!;
     private Label lblLineStatus = null!;
     private RichTextBox txtLog = null!;
     private CheckBox chkMinimizeToTray = null!;
@@ -58,8 +57,7 @@ partial class MainForm
         btnBrowseFile = new Button();
         lblFileName = new Label();
         lblServer = new Label();
-        txtServer = new TextBox();
-        btnConnect = new Button();
+        cmbInterface = new ComboBox();
         lblLineStatus = new Label();
         txtLog = new RichTextBox();
         chkMinimizeToTray = new CheckBox();
@@ -145,20 +143,15 @@ partial class MainForm
         lblFileName.ForeColor = Color.Gray;
 
         // lblServer
-        lblServer.Text = "Server:";
+        lblServer.Text = "Interface:";
         lblServer.Location = new Point(440, 48);
-        lblServer.Size = new Size(45, 23);
+        lblServer.Size = new Size(55, 23);
         lblServer.TextAlign = ContentAlignment.MiddleLeft;
 
-        // txtServer
-        txtServer.Location = new Point(488, 45);
-        txtServer.Size = new Size(110, 23);
-
-        // btnConnect
-        btnConnect.Text = "Connect";
-        btnConnect.Location = new Point(603, 44);
-        btnConnect.Size = new Size(60, 25);
-        btnConnect.UseVisualStyleBackColor = true;
+        // cmbInterface
+        cmbInterface.Location = new Point(498, 45);
+        cmbInterface.Size = new Size(165, 23);
+        cmbInterface.DropDownStyle = ComboBoxStyle.DropDownList;
 
         // lblLineStatus
         lblLineStatus.Text = "";
@@ -277,8 +270,7 @@ partial class MainForm
         Controls.Add(btnBrowseFile);
         Controls.Add(lblFileName);
         Controls.Add(lblServer);
-        Controls.Add(txtServer);
-        Controls.Add(btnConnect);
+        Controls.Add(cmbInterface);
         Controls.Add(lblLineStatus);
         Controls.Add(lblNoise);
         Controls.Add(trkNoise);

Robovoice.App/MainForm.cs

@@ -2,7 +2,7 @@ using NAudio.Wave;
 using Robovoice.App;
 using Robovoice.Core;
 using Robovoice.Core.Voices;
-using Robovoice.Stt.Tcp;
+using Robovoice.Stt.Dhcp;
 using Robovoice.Tts.LibPiper;
 using System.Diagnostics;
 
@@ -16,7 +16,7 @@ internal sealed partial class MainForm : Form
 
     private LibPiperTtsEngine? _tts;
     private AudioOutput? _audioOutput;
-    private TcpSttSource? _sttSource;
+    private DhcpSttSource? _sttSource;
     private Orchestrator? _orchestrator;
     private PttHotkey? _pttHotkey;
     private NotifyIcon? _trayIcon;
@@ -61,7 +61,7 @@ internal sealed partial class MainForm : Form
         OnSliderScroll(null, EventArgs.Empty);
 
         chkMinimizeToTray.Checked = _config.MinimizeToTray;
-        txtServer.Text = _config.ServerEndpoint;
+        PopulateInterfaces();
 
         btnBrowseFile.Click += OnBrowseFile;
         btnTestVoice.Click += OnTestVoice;
@@ -71,8 +71,7 @@ internal sealed partial class MainForm : Form
         txtPttKey.KeyDown += OnPttKeyDown;
         cmbOutput.SelectedIndexChanged += OnOutputChanged;
         cmbVoice.SelectedIndexChanged += OnVoiceChanged;
-        txtServer.Leave += OnServerChanged;
-        btnConnect.Click += OnConnect;
+        cmbInterface.SelectedIndexChanged += OnInterfaceChanged;
 
         trkNoise.Scroll += OnSliderScroll;
         trkSpeed.Scroll += OnSliderScroll;
@@ -245,8 +244,9 @@ internal sealed partial class MainForm : Form
 
         if (_sttSource is null)
         {
-            _sttSource = new TcpSttSource { ServerEndpoint = txtServer.Text, Log = Log };
-            Log($"STT endpoint: {_sttSource.ServerEndpoint} (press Connect)");
+            string ifaceIp = cmbInterface.SelectedItem as string ?? "";
+            _sttSource = new DhcpSttSource { InterfaceIp = ifaceIp, Log = Log };
+            await _sttSource.StartAsync();
         }
 
         _orchestrator?.DisposeAsync().AsTask().Wait();
@@ -425,38 +425,57 @@ internal sealed partial class MainForm : Form
         SaveConfig();
     }
 
-    private void OnServerChanged(object? sender, EventArgs e)
+    private void PopulateInterfaces()
     {
-        if (_sttSource is not null)
+        cmbInterface.Items.Clear();
+        foreach (var (ip, name) in DhcpSttSource.GetAvailableInterfaces())
         {
-            _sttSource.ServerEndpoint = txtServer.Text;
-            Log($"Server endpoint: {txtServer.Text}");
-        }
-        SaveConfig();
+            cmbInterface.Items.Add(name);
+            cmbInterface.Items[^1] = name;
+            cmbInterface.Items[cmbInterface.Items.Count - 1] = name;
         }
 
-    private async void OnConnect(object? sender, EventArgs e)
+        if (!string.IsNullOrEmpty(_config.InterfaceIp))
         {
-        if (_sttSource is null)
+            for (int i = 0; i < cmbInterface.Items.Count; i++)
             {
-            Log("STT source not initialized.");
+                if (cmbInterface.Items[i] is string s && s.Contains(_config.InterfaceIp))
+                {
+                    cmbInterface.SelectedIndex = i;
                     return;
                 }
+            }
+        }
 
-        _sttSource.ServerEndpoint = txtServer.Text;
+        if (cmbInterface.Items.Count > 0)
+            cmbInterface.SelectedIndex = 0;
+    }
+
+    private void OnInterfaceChanged(object? sender, EventArgs e)
+    {
+        if (cmbInterface.SelectedItem is not string selected)
+            return;
+
+        string? ip = ExtractIpFromDisplay(selected);
+        if (ip is null) return;
+
+        _config.InterfaceIp = ip;
         SaveConfig();
-        btnConnect.Enabled = false;
-        try
+
+        if (_sttSource is not null)
         {
-            if (_sttSource.IsRunning)
-                await _sttSource.ReconnectAsync();
-            else
-                await _sttSource.StartAsync();
+            _sttSource.DisposeAsync().AsTask().Wait(2000);
+            _sttSource = null;
+            _ = InitializeEngineAsync();
         }
-        finally
+    }
+
+    private static string? ExtractIpFromDisplay(string display)
     {
-            btnConnect.Enabled = true;
-        }
+        int start = display.IndexOf('(');
+        int end = display.IndexOf(')');
+        if (start < 0 || end <= start) return null;
+        return display[(start + 1)..end];
     }
 
     private void SetupTray()
@@ -524,7 +543,7 @@ internal sealed partial class MainForm : Form
         _config.LengthScale = trkSpeed.Value;
         _config.NoiseWScale = trkNoiseW.Value;
         _config.MinimizeToTray = chkMinimizeToTray.Checked;
-        _config.ServerEndpoint = txtServer.Text;
+        _config.InterfaceIp = ExtractIpFromDisplay(cmbInterface.SelectedItem as string ?? "") ?? "";
         _config.Save();
     }
 

Robovoice.App/Robovoice.App.csproj

@@ -3,7 +3,7 @@
   <ItemGroup>
     <ProjectReference Include="..\Robovoice.Core\Robovoice.Core.csproj" />
     <ProjectReference Include="..\Robovoice.Tts.LibPiper\Robovoice.Tts.LibPiper.csproj" />
-    <ProjectReference Include="..\Robovoice.Stt.Tcp\Robovoice.Stt.Tcp.csproj" />
+    <ProjectReference Include="..\Robovoice.Stt.Dhcp\Robovoice.Stt.Dhcp.csproj" />
   </ItemGroup>
 
   <ItemGroup>

Robovoice.Stt.Dhcp/DhcpSttSource.cs

@@ -0,0 +1,232 @@
+using System.Net;
+using System.Net.NetworkInformation;
+using System.Net.Sockets;
+using System.Text;
+using Robovoice.Core;
+
+namespace Robovoice.Stt.Dhcp;
+
+public sealed class DhcpSttSource : ISttSource
+{
+    private const string Magic = "HKMSTR";
+    private const int DhcpClientPort = 68;
+    private const int DhcpServerPort = 67;
+    private static readonly TimeSpan NopInterval = TimeSpan.FromMilliseconds(50);
+
+    private Socket? _sock;
+    private CancellationTokenSource? _cts;
+    private Task? _receiveTask;
+    private Task? _nopTask;
+    private EndPoint _broadcastEp = new IPEndPoint(IPAddress.Broadcast, DhcpServerPort);
+    private uint _nonce;
+    private bool _disposed;
+
+    public string InterfaceIp { get; set; } = string.Empty;
+
+    public Action<string>? Log { get; set; }
+
+    public event TranscriptEventHandler? TranscriptReceived;
+
+    public Task StartAsync(CancellationToken ct = default)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        if (_cts is not null)
+            return Task.CompletedTask;
+
+        string ip = string.IsNullOrEmpty(InterfaceIp) ? AutoDetectInterfaceIp() ?? "0.0.0.0" : InterfaceIp;
+
+        _sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
+        _sock.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, true);
+        _sock.EnableBroadcast = true;
+        _sock.Bind(new IPEndPoint(IPAddress.Parse(ip), DhcpClientPort));
+
+        Log?.Invoke($"STT: bound to {ip}:{DhcpClientPort}, broadcasting to :{DhcpServerPort}");
+
+        _cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+        _receiveTask = ReceiveLoopAsync(_cts.Token);
+        return Task.CompletedTask;
+    }
+
+    public async Task StopAsync(CancellationToken ct = default)
+    {
+        StopNop();
+
+        if (_cts is not null)
+            _cts.Cancel();
+
+        _sock?.Dispose();
+        _sock = null;
+
+        if (_receiveTask is not null)
+        {
+            try { await _receiveTask.WaitAsync(ct); }
+            catch { }
+            _receiveTask = null;
+        }
+
+        _cts?.Dispose();
+        _cts = null;
+    }
+
+    public void SendOn()
+    {
+        if (_cts is null)
+            return;
+
+        _nonce = 0;
+        SendNop();
+        _nopTask = NopLoopAsync(_cts.Token);
+    }
+
+    public void SendOff()
+    {
+        StopNop();
+        SendControl("HKMSTR:OFF");
+    }
+
+    private void StopNop()
+    {
+        if (_nopTask is not null)
+        {
+            try { _nopTask.Wait(2000); } catch { }
+            _nopTask = null;
+        }
+    }
+
+    private async Task NopLoopAsync(CancellationToken ct)
+    {
+        while (!ct.IsCancellationRequested)
+        {
+            try { await Task.Delay(NopInterval, ct); }
+            catch (OperationCanceledException) { break; }
+
+            SendNop();
+        }
+    }
+
+    private void SendNop()
+    {
+        _nonce++;
+        SendControl($"HKMSTR {_nonce}");
+    }
+
+    private void SendControl(string message)
+    {
+        if (_sock is null)
+            return;
+
+        try
+        {
+            byte[] payload = Encoding.UTF8.GetBytes(message + "\n");
+            _sock.SendTo(payload, _broadcastEp);
+        }
+        catch (Exception ex)
+        {
+            Log?.Invoke($"STT: send failed: {ex.Message}");
+        }
+    }
+
+    private async Task ReceiveLoopAsync(CancellationToken ct)
+    {
+        byte[] buffer = new byte[4096];
+        EndPoint fromEp = new IPEndPoint(IPAddress.Any, 0);
+
+        while (!ct.IsCancellationRequested)
+        {
+            int received;
+            try
+            {
+                if (!_sock!.Poll(500_000, SelectMode.SelectRead))
+                    continue;
+                received = _sock.ReceiveFrom(buffer, ref fromEp);
+            }
+            catch (OperationCanceledException)
+            {
+                break;
+            }
+            catch (ObjectDisposedException)
+            {
+                break;
+            }
+            catch (Exception ex)
+            {
+                Log?.Invoke($"STT: receive error: {ex.Message}");
+                continue;
+            }
+
+            string text = Encoding.UTF8.GetString(buffer, 0, received).TrimEnd('\n', '\r');
+            if (!text.StartsWith(Magic))
+                continue;
+
+            if (text.StartsWith("HKMSTR:P "))
+            {
+                string transcript = text["HKMSTR:P ".Length..];
+                TranscriptReceived?.Invoke(this, new TranscriptEventArgs
+                {
+                    Message = new TranscriptMessage(TranscriptType.Partial, transcript),
+                });
+            }
+            else if (text.StartsWith("HKMSTR:F "))
+            {
+                string transcript = text["HKMSTR:F ".Length..];
+                TranscriptReceived?.Invoke(this, new TranscriptEventArgs
+                {
+                    Message = new TranscriptMessage(TranscriptType.Final, transcript),
+                });
+            }
+        }
+    }
+
+    public static List<(string Ip, string Name)> GetAvailableInterfaces()
+    {
+        var result = new List<(string, string)>();
+
+        foreach (var nic in NetworkInterface.GetAllNetworkInterfaces())
+        {
+            if (nic.OperationalStatus != OperationalStatus.Up)
+                continue;
+            if (nic.NetworkInterfaceType == NetworkInterfaceType.Loopback)
+                continue;
+
+            string desc = nic.Description;
+            if (desc.Contains("WireGuard", StringComparison.OrdinalIgnoreCase))
+                continue;
+
+            foreach (var addr in nic.GetIPProperties().UnicastAddresses)
+            {
+                if (addr.Address.AddressFamily != AddressFamily.InterNetwork)
+                    continue;
+
+                string ip = addr.Address.ToString();
+                if (ip.StartsWith("192.168.") || ip.StartsWith("10.") ||
+                    ip.StartsWith("172.16.") || ip.StartsWith("172.17.") ||
+                    ip.StartsWith("172.18.") || ip.StartsWith("172.19.") ||
+                    ip.StartsWith("172.20.") || ip.StartsWith("172.21.") ||
+                    ip.StartsWith("172.22.") || ip.StartsWith("172.23.") ||
+                    ip.StartsWith("172.24.") || ip.StartsWith("172.25.") ||
+                    ip.StartsWith("172.26.") || ip.StartsWith("172.27.") ||
+                    ip.StartsWith("172.28.") || ip.StartsWith("172.29.") ||
+                    ip.StartsWith("172.30.") || ip.StartsWith("172.31."))
+                {
+                    result.Add((ip, $"{nic.Name} ({ip})"));
+                }
+            }
+        }
+
+        return result;
+    }
+
+    private static string? AutoDetectInterfaceIp()
+    {
+        foreach (var (ip, _) in GetAvailableInterfaces())
+            return ip;
+        return null;
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        if (_disposed) return;
+        await StopAsync();
+        _disposed = true;
+    }
+}

Robovoice.Stt.Tcp/TcpSttSource.cs

@@ -1,253 +0,0 @@
-using System.Net;
-using System.Net.Sockets;
-using System.Text.Json;
-using System.Text.Json.Serialization;
-using Robovoice.Core;
-
-namespace Robovoice.Stt.Tcp;
-
-public sealed class TcpSttSource : ISttSource
-{
-    private TcpClient? _tcp;
-    private NetworkStream? _stream;
-    private StreamReader? _reader;
-    private StreamWriter? _writer;
-    private CancellationTokenSource? _cts;
-    private Task? _runTask;
-    private readonly object _sendLock = new();
-    private bool _disposed;
-
-    public string ServerEndpoint { get; set; } = "127.0.0.1:5210";
-
-    public bool IsRunning => _cts is not null;
-
-    public Action<string>? Log { get; set; }
-
-    public event TranscriptEventHandler? TranscriptReceived;
-
-    public Task StartAsync(CancellationToken ct = default)
-    {
-        ObjectDisposedException.ThrowIf(_disposed, this);
-        if (_cts is not null)
-            return Task.CompletedTask;
-
-        _cts = CancellationTokenSource.CreateLinkedTokenSource(ct);
-        _runTask = RunAsync(_cts.Token);
-        return Task.CompletedTask;
-    }
-
-    public async Task StopAsync(CancellationToken ct = default)
-    {
-        if (_cts is not null)
-            _cts.Cancel();
-
-        CleanupConnection();
-
-        if (_runTask is not null)
-        {
-            try { await _runTask.WaitAsync(ct); }
-            catch { }
-            _runTask = null;
-        }
-
-        _cts?.Dispose();
-        _cts = null;
-    }
-
-    private async Task RunAsync(CancellationToken ct)
-    {
-        while (!ct.IsCancellationRequested)
-        {
-            IPEndPoint? endpoint = ParseEndpoint(ServerEndpoint);
-            if (endpoint is null)
-            {
-                Log?.Invoke($"STT: invalid endpoint '{ServerEndpoint}'");
-                try { await Task.Delay(3000, ct); } catch { break; }
-                continue;
-            }
-
-            try
-            {
-                _tcp = new TcpClient();
-                using var connectCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
-                connectCts.CancelAfter(TimeSpan.FromSeconds(5));
-                await _tcp.ConnectAsync(endpoint.Address, endpoint.Port, connectCts.Token);
-
-                _stream = _tcp.GetStream();
-                _reader = new StreamReader(_stream, System.Text.Encoding.UTF8);
-                _writer = new StreamWriter(_stream, System.Text.Encoding.UTF8) { AutoFlush = true };
-
-                Log?.Invoke($"STT: connected to {ServerEndpoint}");
-
-                await ReceiveLoopAsync(ct);
-            }
-            catch (OperationCanceledException)
-            {
-                break;
-            }
-            catch (Exception ex)
-            {
-                Log?.Invoke($"STT: connection failed ({ex.Message}), retrying...");
-            }
-            finally
-            {
-                CleanupConnection();
-            }
-
-            if (!ct.IsCancellationRequested)
-            {
-                try { await Task.Delay(3000, ct); }
-                catch (OperationCanceledException) { break; }
-            }
-        }
-    }
-
-    private async Task ReceiveLoopAsync(CancellationToken ct)
-    {
-        while (!ct.IsCancellationRequested && _reader is not null)
-        {
-            string? line;
-            try
-            {
-                line = await _reader.ReadLineAsync(ct);
-            }
-            catch
-            {
-                break;
-            }
-
-            if (line is null)
-                break;
-
-            TranscriptMessage? message = ParseTranscriptLine(line);
-            if (message is null)
-                continue;
-
-            TranscriptReceived?.Invoke(this, new TranscriptEventArgs
-            {
-                Message = message,
-            });
-        }
-    }
-
-    public void SendOn()
-    {
-        SendControl("on");
-    }
-
-    public void SendOff()
-    {
-        SendControl("off");
-    }
-
-    public async Task ReconnectAsync(CancellationToken ct = default)
-    {
-        if (_cts is null)
-            return;
-
-        Log?.Invoke("STT: reconnecting...");
-        CleanupConnection();
-
-        try { await Task.Delay(500, ct); }
-        catch (OperationCanceledException) { return; }
-    }
-
-    private void SendControl(string evt)
-    {
-        lock (_sendLock)
-        {
-            if (_writer is null)
-                return;
-
-            try
-            {
-                _writer.WriteLine(JsonSerializer.Serialize(new ControlDto { Event = evt }));
-            }
-            catch
-            {
-                Log?.Invoke($"STT: failed to send '{evt}' (not connected?)");
-            }
-        }
-    }
-
-    private void CleanupConnection()
-    {
-        lock (_sendLock)
-        {
-            _writer?.Dispose();
-            _reader?.Dispose();
-            _stream?.Dispose();
-            _tcp?.Dispose();
-            _writer = null;
-            _reader = null;
-            _stream = null;
-            _tcp = null;
-        }
-    }
-
-    private static IPEndPoint? ParseEndpoint(string endpoint)
-    {
-        int colon = endpoint.LastIndexOf(':');
-        if (colon <= 0)
-            return null;
-
-        string host = endpoint[..colon];
-        if (!int.TryParse(endpoint[(colon + 1)..], out int port))
-            return null;
-
-        if (IPAddress.TryParse(host, out var addr))
-            return new IPEndPoint(addr, port);
-
-        try
-        {
-            var addresses = Dns.GetHostAddresses(host);
-            addr = addresses.FirstOrDefault(a => a.AddressFamily == AddressFamily.InterNetwork);
-            if (addr is null)
-                return null;
-            return new IPEndPoint(addr, port);
-        }
-        catch
-        {
-            return null;
-        }
-    }
-
-    private static TranscriptMessage? ParseTranscriptLine(string line)
-    {
-        if (string.IsNullOrWhiteSpace(line))
-            return null;
-
-        try
-        {
-            var dto = JsonSerializer.Deserialize<TransmitDto>(line);
-            if (dto is null)
-                return null;
-
-            var type = dto.Final ? TranscriptType.Final : TranscriptType.Partial;
-            return new TranscriptMessage(type, dto.Text ?? string.Empty);
-        }
-        catch (JsonException)
-        {
-            return null;
-        }
-    }
-
-    public async ValueTask DisposeAsync()
-    {
-        if (_disposed) return;
-        await StopAsync();
-        _disposed = true;
-    }
-}
-
-internal sealed class ControlDto
-{
-    [JsonPropertyName("event")]
-    public string Event { get; set; } = string.Empty;
-}
-
-internal sealed class TransmitDto
-{
-    public bool Final { get; set; }
-    public string Text { get; set; } = string.Empty;
-}

Robovoice.slnx

@@ -2,6 +2,7 @@
   <Project Path="Robovoice.App/Robovoice.App.csproj" />
   <Project Path="Robovoice.Core/Robovoice.Core.csproj" />
   <Project Path="Robovoice.Stt.File/Robovoice.Stt.File.csproj" />
-  <Project Path="Robovoice.Stt.Tcp/Robovoice.Stt.Tcp.csproj" />
+  <Project Path="Robovoice.Stt.Dhcp/Robovoice.Stt.Dhcp.csproj" />
   <Project Path="Robovoice.Tts.LibPiper/Robovoice.Tts.LibPiper.csproj" />
+  <Project Path="DhcpTunnelTest/Robovoice.DhcpTunnelTest.csproj" />
 </Solution>

Server/NOTES.md

@@ -1,202 +1,232 @@
 # Server implementation notes
 
-The STT server listens for TCP connections from Robovoice, captures audio
-from a microphone when `on` is received, runs speech recognition (Moonshine),
-and sends transcript messages back over the same connection.
+The STT server listens on UDP port 67, receives NOP heartbeats and OFF
+messages from Robovoice, captures audio from a microphone, runs speech
+recognition (Moonshine), and sends transcript messages back to the client's
+source address.
 
 ## Architecture
 
 ```
-                         ┌── on/off (TCP, newline-delimited JSON)
+                         ┌── HKMSTR <nonce> (broadcast, every 50ms)
 Robovoice  ──────────────►│
                          │  STT Server
 Robovoice  ◄──────────────┤
-                         └── partial/final (TCP, newline-delimited JSON)
+                         └── HKMSTR:P/F <text> (unicast)
 ```
 
 The server:
-1. Listens on a TCP port (e.g. 5210)
-2. Accepts a connection from Robovoice
-3. Reads lines: waits for `{"event":"on"}`
-4. Records audio from the microphone
-5. Waits for `{"event":"off"}` (or a timeout)
-6. Runs STT on the captured audio
-7. Sends `{"final":true,"text":"..."}`\n back over the connection
+1. Listens on UDP :67
+2. First `HKMSTR <nonce>` → start recording
+3. `HKMSTR:OFF <nonce>` → stop recording, run STT
+4. 150ms with no NOPs → stop recording, run STT (backstop)
+5. Send `HKMSTR:F <text>` back to the client's source address:port
 
 ## Framing
 
-Every message is a single JSON object on one line, terminated by `\n`. No
-length prefix, no binary framing. Use `readline()` / `StreamReader.ReadLineAsync()`.
+All messages are newline-terminated UTF-8 text. No JSON, no binary framing.
+
+- `HKMSTR <nonce>` — NOP heartbeat (client → server)
+- `HKMSTR:OFF <nonce>` — stop signal (client → server)
+- `HKMSTR:P <text>` — partial transcript (server → client)
+- `HKMSTR:F <text>` — final transcript (server → client)
+
+The nonce is an incrementing integer for packet uniqueness only. Discard it.
 
 ## Python server with Moonshine
 
-[Moonshine](https://github.com/usefulsensors/moonshine) is a lightweight ASR
-model by Useful Sensors. Install with `pip install moonshine`.
-
 ```python
 import socket
-import json
+import threading
+import time
 import numpy as np
 import sounddevice as sd
 import moonshine
 
-LISTEN_PORT = 5210
+LISTEN_PORT = 67
+CLIENT_PORT = 68
 SAMPLE_RATE = 16000
+SILENCE_TIMEOUT = 0.150  # 150ms
 
 model = moonshine.MoonshineModel(model="moonshine/base")
 
-server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-server.bind(("0.0.0.0", LISTEN_PORT))
-server.listen(1)
+sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
+sock.bind(("0.0.0.0", LISTEN_PORT))
 
 print(f"STT server listening on :{LISTEN_PORT}")
 
-while True:
-    conn, addr = server.accept()
-    print(f"Client connected: {addr}")
+recording = False
+last_nop_time = 0
+client_addr = None
+audio_chunks = []
+lock = threading.Lock()
 
-    buf = ""
-    with conn:
+def monitor_silence():
+    """Backstop: stop recording if no NOPs for 150ms."""
+    global recording
     while True:
-            data = conn.recv(4096).decode("utf-8")
-            if not data:
-                break
-            buf += data
+        time.sleep(0.01)
+        with lock:
+            if recording and (time.monotonic() - last_nop_time) > SILENCE_TIMEOUT:
+                recording = False
+                threading.Thread(target=process_audio, daemon=True).start()
 
-            while "\n" in buf:
-                line, buf = buf.split("\n", 1)
-                msg = json.loads(line)
+threading.Thread(target=monitor_silence, daemon=True).start()
 
-                if msg.get("event") == "on":
-                    print("PTT on — recording")
+def process_audio():
+    global audio_chunks
+    with lock:
+        chunks = audio_chunks
         audio_chunks = []
+        addr = client_addr
 
-                    # Record until "off" or timeout
-                    conn.settimeout(0.1)
-                    while True:
-                        try:
-                            data2 = conn.recv(4096).decode("utf-8")
-                            if not data2:
-                                break
-                            buf += data2
-                            while "\n" in buf:
-                                line2, buf = buf.split("\n", 1)
-                                msg2 = json.loads(line2)
-                                if msg2.get("event") == "off":
-                                    break
-                        except socket.timeout:
-                            pass
+    if not chunks:
+        return
 
-                        chunk = sd.rec(int(SAMPLE_RATE * 0.1),
-                                      samplerate=SAMPLE_RATE,
-                                      channels=1, dtype="float32")
-                        sd.wait()
-                        audio_chunks.append(chunk.flatten())
-
-                    conn.settimeout(None)
-
-                    if not audio_chunks:
-                        continue
-
-                    audio = np.concatenate(audio_chunks)
+    audio = np.concatenate(chunks)
     print(f"Captured {len(audio)/SAMPLE_RATE:.1f}s")
 
     text = moonshine.transcribe(model, audio).strip()
 
     if text:
-                        print(f"Transcript: {text}")
-                        reply = json.dumps({"final": True, "text": text})
-                        conn.sendall((reply + "\n").encode("utf-8"))
+        print(f"Final: {text}")
+        reply = f"HKMSTR:F {text}\n".encode("utf-8")
+        sock.sendto(reply, addr)
     else:
         print("Empty transcript")
+
+while True:
+    data, addr = sock.recvfrom(4096)
+    text = data.decode("utf-8", errors="ignore").strip()
+
+    if not text.startswith("HKMSTR"):
+        continue
+
+    if text.startswith("HKMSTR:OFF"):
+        with lock:
+            if recording:
+                recording = False
+                threading.Thread(target=process_audio, daemon=True).start()
+        continue
+
+    if text.startswith("HKMSTR ") or text == "HKMSTR":
+        with lock:
+            client_addr = addr
+            last_nop_time = time.monotonic()
+
+            if not recording:
+                recording = True
+                audio_chunks = []
+                print(f"PTT on from {addr}")
+
+            # Capture 50ms of audio
+            chunk = sd.rec(int(SAMPLE_RATE * 0.05), samplerate=SAMPLE_RATE,
+                          channels=1, dtype="float32")
+            sd.wait()
+            audio_chunks.append(chunk.flatten())
 ```
 
 ## Python server with streaming partials
 
-For lower latency, send partial results while still recording:
+For live feedback, send partials while recording:
 
 ```python
 import socket
-import json
+import threading
+import time
 import numpy as np
 import sounddevice as sd
 import moonshine
 
-LISTEN_PORT = 5210
+LISTEN_PORT = 67
 SAMPLE_RATE = 16000
-CHUNK_DURATION = 0.5
+SILENCE_TIMEOUT = 0.150
+PARTIAL_INTERVAL = 0.5  # send partial every 500ms
 
 model = moonshine.MoonshineModel(model="moonshine/base")
 
-server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-server.bind(("0.0.0.0", LISTEN_PORT))
-server.listen(1)
+sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+sock.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
+sock.bind(("0.0.0.0", LISTEN_PORT))
 
 print(f"STT server listening on :{LISTEN_PORT}")
 
-while True:
-    conn, addr = server.accept()
-    print(f"Client connected: {addr}")
-    buf = ""
+recording = False
+last_nop_time = 0
+last_partial_time = 0
+client_addr = None
+audio_chunks = []
+lock = threading.Lock()
 
-    with conn:
-        while True:
-            data = conn.recv(4096).decode("utf-8")
-            if not data:
-                break
-            buf += data
+def capture_and_maybe_partial():
+    global last_partial_time
+    with lock:
+        if not recording:
+            return
 
-            while "\n" in buf:
-                line, buf = buf.split("\n", 1)
-                msg = json.loads(line)
-
-                if msg.get("event") != "on":
-                    continue
-
-                print("PTT on — recording")
-                audio_chunks = []
-
-                while True:
-                    try:
-                        conn.settimeout(CHUNK_DURATION)
-                        data2 = conn.recv(4096).decode("utf-8")
-                        if not data2:
-                            break
-                        buf += data2
-                        while "\n" in buf:
-                            line2, buf = buf.split("\n", 1)
-                            msg2 = json.loads(line2)
-                            if msg2.get("event") == "off":
-                                break
-                    except socket.timeout:
-                        pass
-
-                    chunk = sd.rec(int(SAMPLE_RATE * CHUNK_DURATION),
-                                  samplerate=SAMPLE_RATE,
+        chunk = sd.rec(int(SAMPLE_RATE * 0.05), samplerate=SAMPLE_RATE,
                       channels=1, dtype="float32")
         sd.wait()
         audio_chunks.append(chunk.flatten())
 
-                    # Send partial every few chunks
-                    if len(audio_chunks) % 4 == 0:
+        now = time.monotonic()
+        if now - last_partial_time > PARTIAL_INTERVAL:
+            last_partial_time = now
             partial_audio = np.concatenate(audio_chunks)
             partial_text = moonshine.transcribe(model, partial_audio).strip()
-                        if partial_text:
-                            reply = json.dumps({"final": False, "text": partial_text})
-                            conn.sendall((reply + "\n").encode("utf-8"))
+            if partial_text and client_addr:
+                reply = f"HKMSTR:P {partial_text}\n".encode("utf-8")
+                sock.sendto(reply, client_addr)
 
-                conn.settimeout(None)
+while True:
+    data, addr = sock.recvfrom(4096)
+    text = data.decode("utf-8", errors="ignore").strip()
 
-                if not audio_chunks:
+    if not text.startswith("HKMSTR"):
         continue
 
-                audio = np.concatenate(audio_chunks)
-                text = moonshine.transcribe(model, audio).strip()
+    if text.startswith("HKMSTR:OFF"):
+        with lock:
+            if recording:
+                recording = False
+                chunks = audio_chunks
+                audio_chunks = []
 
-                if text:
-                    print(f"Final: {text}")
-                    reply = json.dumps({"final": True, "text": text})
-                    conn.sendall((reply + "\n").encode("utf-8"))
+        if chunks:
+            audio = np.concatenate(chunks)
+            final_text = moonshine.transcribe(model, audio).strip()
+            if final_text:
+                reply = f"HKMSTR:F {final_text}\n".encode("utf-8")
+                sock.sendto(reply, addr)
+        continue
+
+    if text.startswith("HKMSTR") and not text.startswith("HKMSTR:"):
+        with lock:
+            client_addr = addr
+            last_nop_time = time.monotonic()
+
+            if not recording:
+                recording = True
+                audio_chunks = []
+                last_partial_time = time.monotonic()
+                print(f"PTT on from {addr}")
+
+        capture_and_maybe_partial()
+
+        # Check silence timeout
+        with lock:
+            if recording and (time.monotonic() - last_nop_time) > SILENCE_TIMEOUT:
+                recording = False
+                chunks = audio_chunks
+                audio_chunks = []
+
+        if 'chunks' in dir() and chunks:
+            audio = np.concatenate(chunks)
+            final_text = moonshine.transcribe(model, audio).strip()
+            if final_text:
+                reply = f"HKMSTR:F {final_text}\n".encode("utf-8")
+                sock.sendto(reply, addr)
 ```
 
 ## C# server skeleton
@@ -204,61 +234,99 @@ while True:
 ```csharp
 using System.Net;
 using System.Net.Sockets;
-using System.Text.Json;
+using System.Text;
 
-var listener = new TcpListener(IPAddress.Any, 5210);
-listener.Start();
+var sock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
+sock.Bind(new IPEndPoint(IPAddress.Any, 67));
 
-Console.WriteLine("STT server listening on :5210");
+Console.WriteLine("STT server listening on :67");
+
+byte[] buffer = new byte[4096];
+EndPoint fromEp = new IPEndPoint(IPAddress.Any, 0);
+bool recording = false;
+DateTime lastNop = DateTime.MinValue;
+List<float[]> audioChunks = new();
 
 while (true)
 {
-    var client = listener.AcceptTcpClient();
-    Console.WriteLine($"Client connected: {client.Client.RemoteEndPoint}");
-
-    using var stream = client.GetStream();
-    using var reader = new StreamReader(stream, Encoding.UTF8);
-    using var writer = new StreamWriter(stream, Encoding.UTF8) { AutoFlush = true };
-
-    string? line;
-    while ((line = reader.ReadLine()) is not null)
+    if (sock.Poll(50_000, SelectMode.SelectRead))
     {
-        var msg = JsonSerializer.Deserialize<Dictionary<string, string>>(line);
-        if (msg?["event"] != "on")
+        int received = sock.ReceiveFrom(buffer, ref fromEp);
+        string text = Encoding.UTF8.GetString(buffer, 0, received).TrimEnd('\n', '\r');
+
+        if (!text.StartsWith("HKMSTR"))
             continue;
 
-        Console.WriteLine("PTT on — recording");
-        // Capture audio...
-
-        // Read until "off"
-        while ((line = reader.ReadLine()) is not null)
+        if (text.StartsWith("HKMSTR:OFF"))
         {
-            msg = JsonSerializer.Deserialize<Dictionary<string, string>>(line);
-            if (msg?["event"] == "off")
-                break;
+            if (recording)
+            {
+                recording = false;
+                ProcessAndReply(audioChunks, fromEp);
+                audioChunks.Clear();
+            }
+            continue;
         }
 
-        // Run STT...
+        // NOP
+        lastNop = DateTime.UtcNow;
+        if (!recording)
+        {
+            recording = true;
+            audioChunks.Clear();
+            Console.WriteLine($"PTT on from {fromEp}");
+        }
+
+        // Capture 50ms audio here...
+        // audioChunks.Add(capturedChunk);
+
+        // Check silence timeout
+        if (recording && (DateTime.UtcNow - lastNop).TotalMilliseconds > 150)
+        {
+            recording = false;
+            ProcessAndReply(audioChunks, fromEp);
+            audioChunks.Clear();
+        }
+    }
+    else
+    {
+        // Timeout check even without incoming data
+        if (recording && (DateTime.UtcNow - lastNop).TotalMilliseconds > 150)
+        {
+            recording = false;
+            ProcessAndReply(audioChunks, fromEp);
+            audioChunks.Clear();
+        }
+    }
+}
+
+void ProcessAndReply(List<float[]> chunks, EndPoint client)
+{
+    if (chunks.Count == 0) return;
+
+    // Concatenate and run STT...
     string text = "recognized text here";
 
-        var reply = JsonSerializer.Serialize(new { final = true, text });
-        writer.WriteLine(reply);
+    if (!string.IsNullOrEmpty(text))
+    {
+        byte[] reply = Encoding.UTF8.GetBytes($"HKMSTR:F {text}\n");
+        sock.SendTo(reply, client);
     }
 }
 ```
 
 ## Tips
 
-- **One connection per client:** Robovoice maintains a single persistent TCP
-  connection. The server should handle one client at a time (or track
-  multiple if needed).
-- **Timeout:** implement a recording timeout in case the `off` message is
-  delayed or the client disconnects. 10–30 seconds is reasonable.
-- **Partials:** optional but improve UX — Robovoice logs them so the user
-  sees live feedback. Only `final` triggers TTS.
-- **Encoding:** always UTF-8. Every line is a UTF-8 JSON object terminated
-  by `\n`.
-- **Reconnection:** Robovoice auto-reconnects every 3 seconds if the
-  connection drops. The server just needs to accept new connections.
-- **Moonshine models:** `moonshine/base` (faster, less accurate) or
-  `moonshine/tiny` (fastest). Choose based on your hardware.
+- **Reply address:** always reply to the source endpoint of the last NOP.
+  The client binds to a specific IP on :68.
+- **Nonces:** discard them. They exist only to make each datagram unique.
+  Do not derive any meaning from nonce values.
+- **Silence timeout:** 150ms = 3 missed NOPs at 50ms intervals. If you
+  change the NOP interval on the client, adjust this accordingly.
+- **Partials:** optional. Send `HKMSTR:P <text>` while recording for live
+  feedback. Client logs them but only `HKMSTR:F` triggers TTS.
+- **Broadcast only for C→S:** the WireGuard killswitch only allows
+  outbound broadcast to 255.255.255.255:67. Unicast from client won't pass.
+- **Unicast OK for S→C:** the inbound WFP rule has no address restriction,
+  so unicast replies to :68 pass through.
+- **Moonshine models:** `moonshine/base` or `moonshine/tiny`.

Server/PROTOCOL.md

@@ -1,70 +1,111 @@
-# Robovoice TCP STT Protocol
+# Robovoice DHCP Tunnel Protocol
 
 ## Overview
 
-Robovoice acts as a **client**: it connects to a remote STT server over TCP,
-sends control messages when the user presses/releases the PTT key, and
-receives transcript messages back. The STT server captures audio from a
-microphone, runs speech recognition (Moonshine), and sends transcripts back
-over the same connection.
+Robovoice communicates with a remote STT server by tunneling through the
+DHCP UDP ports (68→67). This exploits a common killswitch exception: VPN
+software (e.g. WireGuard) blocks all traffic except DHCP, which is allowed
+for network connectivity maintenance.
 
 ```
-[Robovoice client] --TCP--> [STT server :5210]
-     │                            │
-     ├── {"event":"on"}\n  ──────►│
-     │                            ├── capture audio
-     ├── {"event":"off"}\n ──────►│
-     │                            ├── run STT
-     │◄── {"final":true,...}\n ──┤
+[Robovoice client] --broadcast UDP :68→:67--> [STT server]
+[Robovoice client] <--unicast UDP :67→:68-- [STT server]
 ```
 
+The client broadcasts NOP heartbeats while PTT is held. The server starts
+recording on the first NOP and stops when it receives OFF or when 150ms
+pass with no NOPs.
+
 ## Transport
 
-- **Protocol:** TCP (reliable, ordered, connection-oriented)
-- **Server endpoint:** configurable in Robovoice UI (default `127.0.0.1:5210`)
-- **Framing:** newline-delimited JSON (NDJSON) — each message is a single
-  UTF-8 JSON object terminated by `\n`
-- **Auto-reconnect:** if the connection drops, Robovoice retries every 3
-  seconds until the server is available
+- **Protocol:** UDP (connectionless, unreliable)
+- **Client → Server:** broadcast, source port 68, dest port 67
+- **Server → Client:** unicast, source port 67, dest port 68
+- **Client binds:** to a specific LAN interface IP on port 68 (with
+  `SO_REUSEADDR` to coexist with the Windows DHCP service)
+- **No connection state** — purely fire-and-forget datagrams
 
-## Control messages (client → server)
+## Wire format
 
-Sent by Robovoice when the user presses/releases the PTT key.
+All messages are plain text, newline-terminated (`\n`). Every message starts
+with the 6-byte magic `HKMSTR` to distinguish our traffic from real DHCP.
 
-```json
-{"event": "on"}
+### Client → Server
+
+**NOP (heartbeat while PTT held):**
+```
+HKMSTR <nonce>\n
+```
+Sent every 50ms while PTT is held. The nonce is an incrementing unsigned
+integer that makes each datagram unique. The server discards it — it's
+purely for packet uniqueness, not for any protocol logic.
+
+**OFF (PTT released):**
+```
+HKMSTR:OFF <nonce>\n
+```
+Sent once when PTT is released. This is the fast-stop signal. If lost, the
+150ms timeout acts as a backstop.
+
+### Server → Client
+
+**Partial transcript:**
+```
+HKMSTR:P <text>\n
+```
+Intermediate recognition result. Fire-and-forget. Client logs it but does
+not act on it.
+
+**Final transcript:**
+```
+HKMSTR:F <text>\n
+```
+Complete utterance. Client feeds this to the TTS engine.
+
+## Server state machine
+
+```
+                    ┌──────────────────────────────────────────┐
+                    │                                          │
+                    ▼                                          │
+              ┌──────────┐  first NOP   ┌──────────────┐       │
+              │  IDLE    │ ──────────► │  RECORDING   │       │
+              └──────────┘             └──────────────┘       │
+                                           │      │           │
+                                   OFF     │      │ 150ms     │
+                                   recv'd  │      │ silence   │
+                                           ▼      ▼           │
+                                       ┌─────────────┐        │
+                                       │  PROCESSING │        │
+                                       └─────────────┘        │
+                                            │                 │
+                                     STT    │                 │
+                                     done   │                 │
+                                            ▼                 │
+                                       send HKMSTR:F ─────────┘
 ```
 
-```json
-{"event": "off"}
-```
+- **IDLE → RECORDING:** first NOP received, start mic capture
+- **RECORDING → PROCESSING:** OFF received, OR 150ms since last NOP
+- **PROCESSING → IDLE:** STT done, send `HKMSTR:F <text>`
 
-| Field   | Type   | Description                        |
-|---------|--------|------------------------------------|
-| `event` | string | `"on"` (PTT pressed) or `"off"` (PTT released) |
+## Timing
 
-## Transcript messages (server → client)
+| Parameter | Value | Purpose |
+|-----------|-------|---------|
+| NOP interval | 50ms | Heartbeat frequency while PTT held |
+| Silence timeout | 150ms | Stop recording if no NOPs (3 missed = lost OFF) |
+| NOP bandwidth | ~20 msg/s × ~20 bytes | ~400 bytes/s — negligible |
 
-Sent by the server back to Robovoice over the same TCP connection.
+## Why this works
 
-```json
-{"final": false, "text": "hello world"}
-```
-
-```json
-{"final": true, "text": "hello world how are you"}
-```
-
-| Field   | Type    | Required | Description                                      |
-|---------|---------|----------|--------------------------------------------------|
-| `final` | bool    | yes      | `true` = final result, `false` = partial         |
-| `text`  | string  | yes      | The transcript text (may be empty for partials)  |
-
-### Semantics
-
-- **`final: false`** — intermediate recognition result (partial). Robovoice
-  logs these but does not act on them (only `final` triggers TTS).
-- **`final: true`** — complete utterance. Robovoice feeds this to the TTS
-  engine and speaks it.
-
-Malformed JSON or unknown field values are silently dropped by the client.
+1. **Outbound broadcast `:68→:67` to `255.255.255.255`** passes the
+   WireGuard WFP killswitch (DHCP exception matches this exact pattern)
+2. **Inbound `:67→:68`** has no address restriction in the WFP rule, so
+   unicast replies pass through
+3. **Binding to a specific interface IP** (not `0.0.0.0`) wins unicast
+   delivery over the Windows DHCP client service
+4. **NOP spam** ensures the ON message gets through even at 5% packet loss
+   (3 consecutive NOPs = ~0.01% drop probability)
+5. **150ms timeout** is the backstop for lost OFF — at 50ms intervals, 3
+   consecutive NOPs must all be lost to false-stop