chore(bus): avoid stop thread hop

src/EventStore.Core.XUnit.Tests/Bus/MultiQueuedHandlerTests.cs

@@ -45,6 +45,53 @@ public void publishes_messages_without_a_synchronization_group_round_robin()
 		Assert.Equal([second], queues[1].Messages);
 	}
 
+	[Fact]
+	public async Task stop_waits_for_all_queues()
+	{
+		var queues = CreateQueues(2);
+		var firstStop = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+		var secondStop = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
+		queues[0].StopTask = firstStop.Task;
+		queues[1].StopTask = secondStop.Task;
+		var sut = new MultiQueuedHandler(queues.Length, i => queues[i]);
+
+		var stop = sut.Stop();
+		Assert.False(stop.IsCompleted);
+
+		firstStop.SetResult(null);
+		Assert.False(stop.IsCompleted);
+
+		secondStop.SetResult(null);
+		await stop;
+	}
+
+	[Fact]
+	public async Task stop_propagates_queue_stop_failures()
+	{
+		var queues = CreateQueues(2);
+		var failure = new InvalidOperationException("stop failed");
+		queues[0].StopTask = Task.FromException(failure);
+		var sut = new MultiQueuedHandler(queues.Length, i => queues[i]);
+
+		var ex = await Assert.ThrowsAsync<InvalidOperationException>(sut.Stop);
+
+		Assert.Same(failure, ex);
+	}
+
+	[Fact]
+	public async Task stop_attempts_all_queues_when_one_stop_throws_synchronously()
+	{
+		var queues = CreateQueues(2);
+		var failure = new InvalidOperationException("stop failed");
+		queues[0].StopException = failure;
+		var sut = new MultiQueuedHandler(queues.Length, i => queues[i]);
+
+		var ex = await Assert.ThrowsAsync<InvalidOperationException>(sut.Stop);
+
+		Assert.Same(failure, ex);
+		Assert.Equal(1, queues[1].StopCount);
+	}
+
 	private static RecordingQueuedHandler[] CreateQueues(int count)
 	{
 		var queues = new RecordingQueuedHandler[count];
@@ -67,11 +114,26 @@ private sealed class RecordingQueuedHandler(string name) : IQueuedHandler
 
 		public List<Message> Messages { get; } = [];
 
+		public Task StopTask { get; set; } = Task.CompletedTask;
+
+		public Exception StopException { get; set; }
+
+		public int StopCount { get; private set; }
+
 		public void Publish(Message message) => Messages.Add(message);
 
 		public Task Start() => Task.CompletedTask;
 
-		public Task Stop() => Task.CompletedTask;
+		public Task Stop()
+		{
+			StopCount++;
+			if (StopException is not null)
+			{
+				throw StopException;
+			}
+
+			return StopTask;
+		}
 
 		public void RequestStop()
 		{

src/EventStore.Core/Bus/MultiQueuedHandler.cs

@@ -48,7 +48,14 @@ public Task Stop()
 		var queues = _queues.Span;
 		for (int i = 0; i < queues.Length; ++i)
 		{
-			stopTasks[i] = Task.Run(queues[i].Stop);
+			try
+			{
+				stopTasks[i] = queues[i].Stop();
+			}
+			catch (Exception ex)
+			{
+				stopTasks[i] = Task.FromException(ex);
+			}
 		}
 
 		return Task.WhenAll(stopTasks);