diff --git a/src/RioJoy.Core/Output/SendInputSink.cs b/src/RioJoy.Core/Output/SendInputSink.cs
index a5c116d..33f1b26 100644
--- a/src/RioJoy.Core/Output/SendInputSink.cs
+++ b/src/RioJoy.Core/Output/SendInputSink.cs
@@ -70,12 +70,8 @@ public sealed class SendInputSink : IInputSink
         Send(input);
     }
 
-    private static void Send(INPUT input)
-    {
-        Span<INPUT> inputs = stackalloc INPUT[1];
-        inputs[0] = input;
-        SendInput(1, inputs, Marshal.SizeOf<INPUT>());
-    }
+    private static void Send(INPUT input) =>
+        SendInput(1, new[] { input }, Marshal.SizeOf<INPUT>());
 
     // --- Win32 interop --------------------------------------------------------
 
@@ -130,7 +126,7 @@ public sealed class SendInputSink : IInputSink
     }
 
     [DllImport("user32.dll", SetLastError = true)]
-    private static extern uint SendInput(uint nInputs, Span<INPUT> pInputs, int cbSize);
+    private static extern uint SendInput(uint nInputs, INPUT[] pInputs, int cbSize);
 
     [DllImport("user32.dll")]
     private static extern uint MapVirtualKey(uint uCode, uint uMapType);
diff --git a/src/RioJoy.Core/RioRuntime.cs b/src/RioJoy.Core/RioRuntime.cs
index 1759a8f..867a3ee 100644
--- a/src/RioJoy.Core/RioRuntime.cs
+++ b/src/RioJoy.Core/RioRuntime.cs
@@ -20,6 +20,7 @@ public sealed class RioRuntime : IRioCommandSink, IDisposable
     private readonly InputRouter _router;
     private readonly ILampSink _lamp;
     private bool _started;
+    private bool _lampsInitialized;
 
     public RioRuntime(
         RioSerialLink link,
@@ -61,18 +62,23 @@ public sealed class RioRuntime : IRioCommandSink, IDisposable
     /// <summary>Raised for each board/lamp status item in a <see cref="RioCommand.CheckReply"/>.</summary>
     public event Action<CheckStatus>? CheckReceived;
 
-    /// <summary>Subscribe to the link and set all lamps to their idle state.</summary>
+    /// <summary>
+    /// Subscribe to the link. Lit lamps are dimmed on the first reply from the board
+    /// (<see cref="EnsureLampsInitialized"/>) rather than here: lamp commands sent in
+    /// the first milliseconds after the DTR reset (on port open) are dropped before
+    /// the board finishes booting, so the idle-dim state never takes.
+    /// </summary>
     public void Start()
     {
         if (_started)
             return;
         _started = true;
+        _lampsInitialized = false;
 
         _link.PacketReceived += OnPacket;
         _link.AnalogReceived += OnAnalog;
         _link.VersionReceived += OnVersion;
         _link.CheckReceived += OnCheck;
-        _router.InitializeLamps();
     }
 
     /// <summary>Unsubscribe from the link.</summary>
@@ -97,19 +103,37 @@ public sealed class RioRuntime : IRioCommandSink, IDisposable
     /// <summary>Invoke a RIO command directly (e.g. from the tray menu).</summary>
     public void Trigger(RioCommandCode command) => ((IRioCommandSink)this).Execute(command);
 
+    // Once the board replies (alive after the reset), set every lit button to dim.
+    private void EnsureLampsInitialized()
+    {
+        if (_lampsInitialized)
+            return;
+        _lampsInitialized = true;
+        _router.InitializeLamps();
+    }
+
     private void OnAnalog(AnalogReport report)
     {
+        EnsureLampsInitialized();
         AxisOutputs axes = _calibrator.Update(report);
-        _joystick.SetAxis(JoyAxis.X, axes.X);
-        _joystick.SetAxis(JoyAxis.Y, axes.Y);
-        _joystick.SetAxis(JoyAxis.Z, axes.Z);
-        _joystick.SetAxis(JoyAxis.Rx, axes.Rx);
-        _joystick.SetAxis(JoyAxis.Ry, axes.Ry);
-        _joystick.SetAxis(JoyAxis.Rz, axes.Rz);
+        try
+        {
+            _joystick.SetAxis(JoyAxis.X, axes.X);
+            _joystick.SetAxis(JoyAxis.Y, axes.Y);
+            _joystick.SetAxis(JoyAxis.Z, axes.Z);
+            _joystick.SetAxis(JoyAxis.Rx, axes.Rx);
+            _joystick.SetAxis(JoyAxis.Ry, axes.Ry);
+            _joystick.SetAxis(JoyAxis.Rz, axes.Rz);
+        }
+        catch
+        {
+            // Output is best-effort: a faulty joystick sink must not kill the link.
+        }
     }
 
     private void OnPacket(RioPacket packet)
     {
+        EnsureLampsInitialized();
         ReadOnlySpan<byte> p = packet.Payload.Span;
         switch (packet.Command)
         {
@@ -131,10 +155,17 @@ public sealed class RioRuntime : IRioCommandSink, IDisposable
     // Route the event through the input pipeline and notify any live-activity listener.
     private void Activity(int address, bool pressed)
     {
-        if (pressed)
-            _router.Press(address);
-        else
-            _router.Release(address);
+        try
+        {
+            if (pressed)
+                _router.Press(address);
+            else
+                _router.Release(address);
+        }
+        catch
+        {
+            // Output is best-effort: a faulty sink must never kill the serial link.
+        }
 
         // Light the button on the RIO even when it is unmapped (the router only lamps
         // mapped lamp-buttons), so the editor's check-function workflow always responds.
diff --git a/tests/RioJoy.Core.Tests/Output/SendInputSinkTests.cs b/tests/RioJoy.Core.Tests/Output/SendInputSinkTests.cs
new file mode 100644
index 0000000..5cc04ad
--- /dev/null
+++ b/tests/RioJoy.Core.Tests/Output/SendInputSinkTests.cs
@@ -0,0 +1,21 @@
+using RioJoy.Core.Output;
+using Xunit;
+
+namespace RioJoy.Core.Tests.Output;
+
+public class SendInputSinkTests
+{
+    [Fact]
+    public void SendInput_DoesNotThrow_OnMarshalling()
+    {
+        var sink = new SendInputSink();
+
+        // A zero relative mouse move is a no-op, but it exercises the same SendInput
+        // INPUT[] marshalling path that previously threw MarshalDirectiveException with
+        // a Span<INPUT> parameter — which killed the serial read thread when a button
+        // with output enabled was pressed.
+        Exception? ex = Record.Exception(() => sink.MouseMove(0, 0));
+
+        Assert.Null(ex);
+    }
+}
diff --git a/tests/RioJoy.Core.Tests/RioRuntimeTests.cs b/tests/RioJoy.Core.Tests/RioRuntimeTests.cs
index 4380b95..4bdafba 100644
--- a/tests/RioJoy.Core.Tests/RioRuntimeTests.cs
+++ b/tests/RioJoy.Core.Tests/RioRuntimeTests.cs
@@ -72,6 +72,40 @@ public class RioRuntimeTests
         await run;
     }
 
+    [Fact]
+    public async Task LitLamps_Dimmed_OnFirstBoardReply_NotOnStart()
+    {
+        var fake = new FakeTransport();
+        var link = new RioSerialLink(fake, new RioSerialLinkOptions { AutoPollAnalog = false });
+        var recorder = new RecordingSink();
+
+        var map = new RioInputMap { [0x05] = new RioMapEntry(0x9001) }; // lit joystick button
+        using var runtime = new RioRuntime(link, map, recorder, recorder);
+        runtime.Start();
+
+        using var cts = new CancellationTokenSource();
+        Task run = link.RunAsync(cts.Token);
+
+        // Nothing is sent on Start: lamp commands would be dropped during the board's
+        // post-reset boot, so no write happens until the board first replies.
+        await Assert.ThrowsAnyAsync<OperationCanceledException>(
+            () => fake.NextWriteAsync(TimeSpan.FromMilliseconds(150)));
+
+        // A reply proves the board is alive → the lit lamp is dimmed.
+        fake.Enqueue(PacketBuilder.Build(RioCommand.AnalogReply, new byte[10]));
+
+        bool dimmed = false;
+        for (int i = 0; i < 8 && !dimmed; i++)
+        {
+            byte[] w = await fake.NextWriteAsync(TimeSpan.FromSeconds(2));
+            dimmed = w.Length >= 3 && w[0] == (byte)RioCommand.LampRequest && w[1] == 0x05;
+        }
+        Assert.True(dimmed, "expected a LampRequest dimming address 0x05 after the first reply");
+
+        cts.Cancel();
+        await run;
+    }
+
     [Fact]
     public async Task ButtonActivity_FiresForPressAndRelease_EvenWhenUnmapped()
     {