Fix delayed message null activity

src/NServiceBus.AcceptanceTests/Core/OpenTelemetry/Traces/When_incoming_message_was_delayed.cs

@@ -11,6 +11,24 @@
 
 public class When_incoming_message_was_delayed : OpenTelemetryAcceptanceTest // assuming W3C trace!
 {
+    [Test]
+    public async Task By_sendoptions_Should_create_new_trace_and_set_current_activity()
+    {
+        var context = await Scenario.Define<Context>()
+            .WithEndpoint<TestEndpoint>(b => b
+                .When(s =>
+                {
+                    var sendOptions = new SendOptions();
+                    sendOptions.DelayDeliveryWith(TimeSpan.FromMilliseconds(100));
+                    sendOptions.RouteToThisEndpoint();
+                    return s.Send(new DelayedMessage(), sendOptions);
+                }))
+            .Done(c => c.DelayedMessageReceived)
+            .Run();
+
+        Assert.That(context.DelayedMessageCurrentActivityId, Is.Not.Null, "delayed message current activityId is not null");
+    }
+
     [Test]
     public async Task By_sendoptions_Should_create_new_trace_and_link_to_send()
     {
@@ -141,6 +159,10 @@ class Context : ScenarioContext
         public string IncomingMessageId { get; set; }
         public string ReplyMessageId { get; set; }
         public bool IncomingMessageReceived { get; set; }
+        public bool DelayedMessageReceived { get; set; }
+#nullable enable
+        public string? DelayedMessageCurrentActivityId { get; set; }
+#nullable disable
     }
     class SagaContext : ScenarioContext
     {
@@ -162,6 +184,7 @@ public Task Handle(IncomingMessage message, IMessageHandlerContext context)
             {
                 testContext.IncomingMessageId = context.MessageId;
                 testContext.IncomingMessageReceived = true;
+                //testContext.IncomingMessageCurrentActivityId = Activity.Current?.Id;
                 return context.Reply(new ReplyMessage());
             }
         }
@@ -198,6 +221,20 @@ public Task Handle(ReplyMessage message, IMessageHandlerContext context)
                 return Task.CompletedTask;
             }
         }
+
+        class DelayedMessageHandler : IHandleMessages<DelayedMessage>
+        {
+            Context testContext;
+
+            public DelayedMessageHandler(Context testContext) => this.testContext = testContext;
+
+            public Task Handle(DelayedMessage message, IMessageHandlerContext context)
+            {
+                testContext.DelayedMessageReceived = true;
+                testContext.DelayedMessageCurrentActivityId = Activity.Current?.Id;
+                return Task.CompletedTask;
+            }
+        }
     }
 
     class SagaOtelEndpoint : EndpointConfigurationBuilder
@@ -286,6 +323,10 @@ public class MessageToBeRetried : IMessage
     {
     }
 
+    public class DelayedMessage : IMessage
+    {
+    }
+
     public class IncomingMessage : IMessage
     {
     }

src/NServiceBus.Core/OpenTelemetry/Tracing/ActivityFactory.cs

@@ -35,7 +35,8 @@ public Activity StartIncomingPipelineActivity(MessageContext context)
             {
                 // create a new trace or root activity
                 ActivityLink[] links = [new ActivityLink(sendSpanContext)];
-                activity = ActivitySources.Main.StartActivity(name: ActivityNames.IncomingMessageActivityName, ActivityKind.Consumer, CreateNewRootActivityContext(), tags: null, links: links);
+                //pass in traceFlags of current activity, otherwise the activity returned is null
+                activity = ActivitySources.Main.StartActivity(name: ActivityNames.IncomingMessageActivityName, ActivityKind.Consumer, CreateNewRootActivityContext(sendSpanContext.TraceFlags), tags: null, links: links);
             }
             else
             {
@@ -69,7 +70,7 @@ public Activity StartIncomingPipelineActivity(MessageContext context)
     /// <summary>
     /// This could be cleaned up once a dedicated API is created, see https://github.com/dotnet/runtime/issues/65528
     /// </summary>
-    static ActivityContext CreateNewRootActivityContext() => new(Activity.TraceIdGenerator is null ? ActivityTraceId.CreateRandom() : Activity.TraceIdGenerator(), default, default, default);
+    static ActivityContext CreateNewRootActivityContext(ActivityTraceFlags traceFlags) => new(Activity.TraceIdGenerator is null ? ActivityTraceId.CreateRandom() : Activity.TraceIdGenerator(), default, traceFlags, default);
 
     public Activity StartOutgoingPipelineActivity(string activityName, string displayName, IBehaviorContext outgoingContext)
     {