test(mesh): stampede callers on dedicated threads — arrival gate must not depend on thread-pool injection

tests/Server/ZB.MOM.WW.OtOpcUa.ControlPlane.Tests/Communication/MeshPskProviderTests.cs

@@ -296,13 +296,16 @@ public sealed class MeshPskProviderTests
         var resolver = new FakeSecretResolver { Value = "stored-psk", ResolveDelay = TimeSpan.FromMilliseconds(50) };
         var provider = CreateProvider(resolver);
 
-        var callers = Enumerable.Range(0, Callers).Select(_ => Task.Run(() =>
+        // LongRunning gives each caller a dedicated thread: reaching the arrival gate must not
+        // depend on thread-pool injection, which is rate-limited and made this flake on a
+        // contended box (the gate timed out before all 16 pool threads existed).
+        var callers = Enumerable.Range(0, Callers).Select(_ => Task.Factory.StartNew(() =>
         {
             arrived.Signal();
             start.Wait();
             provider.TryGetPsk("SITE-A", out var psk).ShouldBeTrue();
             return psk;
-        })).ToArray();
+        }, CancellationToken.None, TaskCreationOptions.LongRunning, TaskScheduler.Default)).ToArray();
 
         arrived.Wait(TimeSpan.FromSeconds(10)).ShouldBeTrue("all callers should reach the start gate");
         start.Set();