Add SIGTERM signal handling to CTRLPlusCCancellationTokenSource

Co-authored-by: nohwnd <5735905+nohwnd@users.noreply.github.com>

Author: Copilot

src/Platform/Microsoft.Testing.Platform/Services/CTRLPlusCCancellationTokenSource.cs

@@ -11,6 +11,10 @@ internal sealed class CTRLPlusCCancellationTokenSource : ITestApplicationCancell
     private readonly CancellationTokenSource _cancellationTokenSource = new();
     private readonly ILogger? _logger;
 
+#if NETCOREAPP
+    private PosixSignalRegistration? _sigTermRegistration;
+#endif
+
     public CTRLPlusCCancellationTokenSource(IConsole? console = null, ILogger? logger = null)
     {
         if (console is not null && !IsCancelKeyPressNotSupported())
@@ -19,7 +23,38 @@ public CTRLPlusCCancellationTokenSource(IConsole? console = null, ILogger? logge
         }
 
         _logger = logger;
+
+#if NETCOREAPP
+        // Register for SIGTERM signals if not running on WASI
+        if (!OperatingSystem.IsWasi())
+        {
+            try
+            {
+                _sigTermRegistration = PosixSignalRegistration.Create(PosixSignal.SIGTERM, HandlePosixSignal);
+            }
+            catch (Exception ex)
+            {
+                _logger?.LogWarning($"Failed to register SIGTERM signal handler: {ex}");
+            }
+        }
+#endif
+    }
+
+#if NETCOREAPP
+    private void HandlePosixSignal(PosixSignalContext context)
+    {
+        context.Cancel = true;
+        try
+        {
+            _cancellationTokenSource.Cancel();
+            _logger?.LogInformation("Received SIGTERM signal, cancellation requested.");
+        }
+        catch (AggregateException ex)
+        {
+            _logger?.LogWarning($"Exception during SIGTERM signal handling:\n{ex}");
+        }
     }
+#endif
 
     [SupportedOSPlatformGuard("android")]
     [SupportedOSPlatformGuard("ios")]
@@ -51,7 +86,12 @@ private void OnConsoleCancelKeyPressed(object? sender, ConsoleCancelEventArgs e)
     }
 
     public void Dispose()
-        => _cancellationTokenSource.Dispose();
+    {
+#if NETCOREAPP
+        _sigTermRegistration?.Dispose();
+#endif
+        _cancellationTokenSource.Dispose();
+    }
 
     public void Cancel()
         => _cancellationTokenSource.Cancel();