fix: remove unnecessary async blocking in ProcessExit handler (#4854)

TUnit.Core/EngineCancellationToken.cs

@@ -82,9 +82,11 @@ private void OnProcessExit(object? sender, EventArgs e)
         {
             CancellationTokenSource.Cancel();
 
-            // Give After hooks a brief moment to execute via registered callbacks
-            // ProcessExit has limited time, so we can only wait briefly
-            Task.Delay(TimeSpan.FromMilliseconds(500)).GetAwaiter().GetResult();
+            // Give After hooks a brief moment to execute via registered callbacks.
+            // ProcessExit has limited time (~3s on Windows), so we can only wait briefly.
+            // Thread.Sleep is appropriate here: we're on a synchronous event handler thread
+            // and just need a simple delay — no need to involve the task scheduler.
+            Thread.Sleep(500);
         }
     }
 

TUnit.Core/Executors/DedicatedThreadExecutor.cs

@@ -361,7 +361,11 @@ public override void Send(SendOrPostCallback d, object? state)
                     await tcs.Task.ConfigureAwait(false);
                 });
 
-                // This wait is safe because it's on a Task.Run thread without SynchronizationContext
+                // This blocking wait is intentional and safe from deadlocks because:
+                // 1. We verified above that the current thread is NOT the dedicated thread
+                // 2. The work is posted to the dedicated thread's queue via Post()
+                // 3. waitTask runs via Task.Run without a SynchronizationContext, so no context capture
+                // 4. SynchronizationContext.Send is synchronous by API contract — blocking is required
                 waitTask.GetAwaiter().GetResult();
             }
         }