Add entity operation trace span creation

Create trace spans for entity operation execution in OnRunEntityBatchAsync,
using the trace context propagated from the parent orchestration. This
completes the distributed tracing story for entities by making entity
operations visible in trace viewers.

- Add EntityOperation constant to TraceActivityConstants
- Add StartTraceActivityForEntityOperation to TraceHelper
- Create span with entity metadata tags in GrpcDurableTaskWorker.Processor

Author: cgillum

src/Shared/Grpc/Tracing/TraceActivityConstants.cs

@@ -24,6 +24,11 @@ static class TraceActivityConstants
     /// </summary>
     public const string Event = "event";
 
+    /// <summary>
+    /// The name of the activity that represents entity operation execution.
+    /// </summary>
+    public const string EntityOperation = "entity_operation";
+
     /// <summary>
     /// The name of the activity that represents timer operations.
     /// </summary>

src/Shared/Grpc/Tracing/TraceHelper.cs

@@ -156,6 +156,58 @@ static class TraceHelper
         return newActivity;
     }
 
+    /// <summary>
+    /// Starts a new trace activity for executing an entity operation.
+    /// </summary>
+    /// <param name="entityName">The name of the entity.</param>
+    /// <param name="operationName">The name of the operation being executed.</param>
+    /// <param name="instanceId">The instance ID of the entity.</param>
+    /// <param name="traceParent">The W3C traceparent header value from the parent orchestration.</param>
+    /// <param name="traceState">The W3C tracestate header value from the parent orchestration.</param>
+    /// <returns>
+    /// Returns a newly started <see cref="Activity"/> with entity operation metadata, or null if tracing is not enabled.
+    /// </returns>
+    public static Activity? StartTraceActivityForEntityOperation(
+        string entityName,
+        string? operationName,
+        string instanceId,
+        string? traceParent,
+        string? traceState)
+    {
+        if (traceParent is null || !ActivityContext.TryParse(
+                traceParent,
+                traceState,
+                out ActivityContext activityContext))
+        {
+            return null;
+        }
+
+        string spanName = string.IsNullOrEmpty(operationName)
+            ? $"{TraceActivityConstants.EntityOperation}:{entityName}"
+            : $"{TraceActivityConstants.EntityOperation}:{entityName}:{operationName}";
+
+        Activity? newActivity = ActivityTraceSource.StartActivity(
+            spanName,
+            kind: ActivityKind.Server,
+            parentContext: activityContext);
+
+        if (newActivity == null)
+        {
+            return null;
+        }
+
+        newActivity.SetTag(Schema.Task.Type, TraceActivityConstants.EntityOperation);
+        newActivity.SetTag(Schema.Task.Name, entityName);
+        newActivity.SetTag(Schema.Task.InstanceId, instanceId);
+
+        if (!string.IsNullOrEmpty(operationName))
+        {
+            newActivity.SetTag("durabletask.entity.operation", operationName);
+        }
+
+        return newActivity;
+    }
+
     /// <summary>
     /// Emits a new trace activity for a (task) activity that successfully completes.
     /// </summary>

src/Worker/Grpc/GrpcDurableTaskWorker.Processor.cs

@@ -865,6 +865,15 @@ async Task OnRunEntityBatchAsync(
             var coreEntityId = DTCore.Entities.EntityId.FromString(batchRequest.InstanceId!);
             EntityId entityId = new(coreEntityId.Name, coreEntityId.Key);
 
+            // Start a trace span for entity operation execution using the first operation's trace context.
+            OperationRequest? firstOp = batchRequest.Operations?.FirstOrDefault();
+            using Activity? traceActivity = TraceHelper.StartTraceActivityForEntityOperation(
+                entityId.Name,
+                firstOp?.Operation,
+                batchRequest.InstanceId!,
+                firstOp?.TraceContext?.TraceParent,
+                firstOp?.TraceContext?.TraceState);
+
             TaskName name = new(entityId.Name);
 
             EntityBatchResult? batchResult;
@@ -913,6 +922,8 @@ async Task OnRunEntityBatchAsync(
                 {
                     FailureDetails = new FailureDetails(frameworkException),
                 };
+
+                traceActivity?.SetStatus(ActivityStatusCode.Error, frameworkException.Message);
             }
 
             P.EntityBatchResult response = batchResult.ToEntityBatchResult(