Handle test cancellation in diffenginetray

src/DiffEngineTray.Tests/PiperTest.cs

@@ -1,3 +1,6 @@
+using System.Net;
+using System.Net.Sockets;
+
 public class PiperTest :
     IDisposable
 {
@@ -64,6 +67,36 @@ public async Task Move()
         await Verify(received);
     }
 
+    [Test]
+    public async Task ClientDisconnectsAbruptly()
+    {
+        DeletePayload? received = null;
+        var source = new CancelSource();
+        var task = PiperServer.Start(_ => { }, s => received = s, source.Token);
+
+        // Connect and immediately close with RST (no data sent),
+        // simulating a client that was canceled mid-connection.
+        using (var client = new TcpClient())
+        {
+            await client.ConnectAsync(IPAddress.Loopback, PiperClient.Port);
+            // Linger with timeout 0 causes a RST (forcible close) on Close
+            client.LingerState = new(true, 0);
+        }
+
+        // Give the server time to process the abrupt disconnect
+        await Task.Delay(500);
+
+        // Server should still work after the abrupt disconnect
+        await PiperClient.SendDeleteAsync("Foo", source.Token);
+        await Task.Delay(1000, source.Token);
+        source.Cancel();
+        await task;
+
+        // Verify the server recovered and processed the subsequent valid message
+        Assert.NotNull(received);
+        Assert.Equal("Foo", received!.File);
+    }
+
     [Test]
     public async Task SendOnly()
     {

src/DiffEngineTray/PiperServer.cs

@@ -35,6 +35,11 @@ public static async Task Start(
                     //when task is cancelled socket is disposed
                     break;
                 }
+                catch (IOException exception)
+                    when (exception.InnerException is SocketException { SocketErrorCode: SocketError.ConnectionReset })
+                {
+                    //client disconnected abruptly, e.g. test was canceled
+                }
                 catch (Exception exception)
                 {
                     if (cancel.IsCancellationRequested)
@@ -58,6 +63,7 @@ static async Task Handle(TcpListener listener, Action<MovePayload> move, Action<
         {
             using var client = await listener.AcceptTcpClientAsync(cancel);
             using var reader = new StreamReader(client.GetStream());
+
             var payload = await reader.ReadToEndAsync(cancel);
 
             if (payload.Contains("\"Type\":\"Move\"") ||