OTEL trace support.

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableActivityExecutor.cs

@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using Microsoft.Agents.AI.Workflows;
@@ -40,18 +41,58 @@ internal static class DurableActivityExecutor
         string executorInput = inputWithState?.Input ?? input;
         Dictionary<string, string> sharedState = inputWithState?.State ?? [];
 
-        Executor executor = await binding.FactoryAsync(binding.Id).ConfigureAwait(false);
-        Type inputType = ResolveInputType(inputWithState?.InputTypeName, executor.InputTypes);
-        object typedInput = DeserializeInput(executorInput, inputType);
+        // Restore the orchestrator's trace context (workflow.run span) as the parent
+        // for spans created in the activity worker (e.g., executor.process).
+        // The Durable Task SDK propagates its own trace context (from scheduling time),
+        // not the orchestrator's Activity.Current. We bridge this gap by explicitly
+        // passing the traceparent through the activity input.
+        Activity? parentBridge = RestoreParentTraceContext(inputWithState?.TraceParent);
 
-        DurableWorkflowContext workflowContext = new(sharedState, executor);
-        object? result = await executor.ExecuteAsync(
-            typedInput,
-            new TypeId(inputType),
-            workflowContext,
-            cancellationToken).ConfigureAwait(false);
+        try
+        {
+            Executor executor = await binding.FactoryAsync(binding.Id).ConfigureAwait(false);
+            Type inputType = ResolveInputType(inputWithState?.InputTypeName, executor.InputTypes);
+            object typedInput = DeserializeInput(executorInput, inputType);
 
-        return SerializeActivityOutput(result, workflowContext);
+            DurableWorkflowContext workflowContext = new(sharedState, executor);
+            object? result = await executor.ExecuteAsync(
+                typedInput,
+                new TypeId(inputType),
+                workflowContext,
+                cancellationToken).ConfigureAwait(false);
+
+            return SerializeActivityOutput(result, workflowContext);
+        }
+        finally
+        {
+            parentBridge?.Dispose();
+        }
+    }
+
+    /// <summary>
+    /// Restores the orchestrator's trace context so that spans created in the activity worker
+    /// (like executor.process) appear as children of workflow.run in the trace hierarchy.
+    /// </summary>
+    /// <returns>A bridge activity that should be disposed when execution completes, or null if no context was provided.</returns>
+    private static Activity? RestoreParentTraceContext(string? traceParent)
+    {
+        if (traceParent is null)
+        {
+            return null;
+        }
+
+        if (!ActivityContext.TryParse(traceParent, null, out ActivityContext parentContext))
+        {
+            return null;
+        }
+
+        // StartActivity with an explicit parent context creates a sampled span whose parent
+        // is workflow.run. All subsequent spans (executor.process, message.send) created while
+        // this is Activity.Current will nest under it in the trace.
+        return DurableWorkflowInstrumentation.ActivitySource.StartActivity(
+            "executor.dispatch",
+            ActivityKind.Internal,
+            parentContext);
     }
 
     private static string SerializeActivityOutput(object? result, DurableWorkflowContext context)

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableActivityInput.cs

@@ -21,4 +21,10 @@ internal sealed class DurableActivityInput
     /// Gets or sets the shared state dictionary (scope-prefixed key -> serialized value).
     /// </summary>
     public Dictionary<string, string> State { get; set; } = [];
+
+    /// <summary>
+    /// Gets or sets the W3C traceparent of the orchestrator's workflow.run span,
+    /// used to establish parent-child trace hierarchy from the activity worker.
+    /// </summary>
+    public string? TraceParent { get; set; }
 }

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableExecutorDispatcher.cs

@@ -68,7 +68,8 @@ internal static class DurableExecutorDispatcher
         {
             Input = input,
             InputTypeName = inputTypeName,
-            State = sharedState
+            State = sharedState,
+            TraceParent = DurableWorkflowInstrumentation.WorkflowRunTraceParent.Value
         };
 
         string serializedInput = JsonSerializer.Serialize(activityInput, DurableWorkflowJsonContext.Default.DurableActivityInput);

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableStreamingWorkflowRun.cs

@@ -23,6 +23,7 @@ namespace Microsoft.Agents.AI.DurableTask.Workflows;
 internal sealed class DurableStreamingWorkflowRun : IStreamingWorkflowRun
 {
     private readonly DurableTaskClient _client;
+    private readonly Activity? _runActivity;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="DurableStreamingWorkflowRun"/> class.
@@ -30,11 +31,13 @@ internal sealed class DurableStreamingWorkflowRun : IStreamingWorkflowRun
     /// <param name="client">The durable task client for orchestration operations.</param>
     /// <param name="instanceId">The unique instance ID for this orchestration run.</param>
     /// <param name="workflow">The workflow being executed.</param>
-    internal DurableStreamingWorkflowRun(DurableTaskClient client, string instanceId, Workflow workflow)
+    /// <param name="runActivity">The workflow.run activity to stop when the workflow completes.</param>
+    internal DurableStreamingWorkflowRun(DurableTaskClient client, string instanceId, Workflow workflow, Activity? runActivity = null)
     {
         this._client = client;
         this.RunId = instanceId;
         this.WorkflowName = workflow.Name ?? string.Empty;
+        this._runActivity = runActivity;
     }
 
     /// <inheritdoc/>

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowClient.cs

@@ -1,5 +1,6 @@
 // Copyright (c) Microsoft. All rights reserved.
 
+using System.Diagnostics;
 using Microsoft.Agents.AI.Workflows;
 using Microsoft.DurableTask;
 using Microsoft.DurableTask.Client;
@@ -40,7 +41,20 @@ internal sealed class DurableWorkflowClient : IWorkflowClient
             throw new ArgumentException("Workflow must have a valid Name property.", nameof(workflow));
         }
 
-        DurableWorkflowInput<TInput> workflowInput = new() { Input = input };
+        // Start workflow.run at the client level so its span ID is stable across orchestrator
+        // replays. The Durable Task orchestrator re-executes from the top on each replay,
+        // creating new Activity objects that are abandoned when the method suspends. By creating
+        // workflow.run here and propagating its context via TraceParent, activity worker spans
+        // consistently reference a properly exported parent span.
+        Activity? runActivity = DurableWorkflowInstrumentation.ActivitySource.StartActivity("workflow.run");
+        runActivity?.SetTag("workflow.id", workflow.StartExecutorId)
+            .SetTag("workflow.name", workflow.Name);
+
+        DurableWorkflowInput<TInput> workflowInput = new()
+        {
+            Input = input,
+            TraceParent = runActivity?.Id ?? Activity.Current?.Id
+        };
 
         string instanceId = await this._client.ScheduleNewOrchestrationInstanceAsync(
             orchestratorName: WorkflowNamingHelper.ToOrchestrationFunctionName(workflow.Name),
@@ -48,7 +62,9 @@ internal sealed class DurableWorkflowClient : IWorkflowClient
             options: runId is not null ? new StartOrchestrationOptions(runId) : null,
             cancellation: cancellationToken).ConfigureAwait(false);
 
-        return new DurableWorkflowRun(this._client, instanceId, workflow.Name);
+        runActivity?.SetTag("run.id", instanceId);
+
+        return new DurableWorkflowRun(this._client, instanceId, workflow.Name, runActivity);
     }
 
     /// <inheritdoc/>
@@ -74,7 +90,15 @@ internal sealed class DurableWorkflowClient : IWorkflowClient
             throw new ArgumentException("Workflow must have a valid Name property.", nameof(workflow));
         }
 
-        DurableWorkflowInput<TInput> workflowInput = new() { Input = input };
+        Activity? runActivity = DurableWorkflowInstrumentation.ActivitySource.StartActivity("workflow.run");
+        runActivity?.SetTag("workflow.id", workflow.StartExecutorId)
+            .SetTag("workflow.name", workflow.Name);
+
+        DurableWorkflowInput<TInput> workflowInput = new()
+        {
+            Input = input,
+            TraceParent = runActivity?.Id ?? Activity.Current?.Id
+        };
 
         string instanceId = await this._client.ScheduleNewOrchestrationInstanceAsync(
             orchestratorName: WorkflowNamingHelper.ToOrchestrationFunctionName(workflow.Name),
@@ -82,7 +106,9 @@ internal sealed class DurableWorkflowClient : IWorkflowClient
             options: runId is not null ? new StartOrchestrationOptions(runId) : null,
             cancellation: cancellationToken).ConfigureAwait(false);
 
-        return new DurableStreamingWorkflowRun(this._client, instanceId, workflow);
+        runActivity?.SetTag("run.id", instanceId);
+
+        return new DurableStreamingWorkflowRun(this._client, instanceId, workflow, runActivity);
     }
 
     /// <inheritdoc/>

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowInput.cs

@@ -13,4 +13,11 @@ internal sealed class DurableWorkflowInput<TInput>
     /// Gets the workflow input data.
     /// </summary>
     public required TInput Input { get; init; }
+
+    /// <summary>
+    /// Gets or sets the W3C traceparent of the client-side workflow.run span.
+    /// Propagated through the orchestration to activity workers so that executor spans
+    /// appear as children of workflow.run in the trace hierarchy.
+    /// </summary>
+    public string? TraceParent { get; set; }
 }

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowInstrumentation.cs

@@ -13,4 +13,10 @@ internal static class DurableWorkflowInstrumentation
     /// The shared <see cref="ActivitySource"/> used by all durable workflow components.
     /// </summary>
     internal static readonly ActivitySource ActivitySource = new("Microsoft.Agents.AI.DurableTask.Workflows");
+
+    /// <summary>
+    /// Carries the W3C traceparent of the client-side workflow.run span through the
+    /// orchestrator's async call chain so it can be included in activity inputs.
+    /// </summary>
+    internal static readonly AsyncLocal<string?> WorkflowRunTraceParent = new();
 }

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowRun.cs

@@ -15,6 +15,7 @@ internal sealed class DurableWorkflowRun : IAwaitableWorkflowRun
 {
     private readonly DurableTaskClient _client;
     private readonly List<WorkflowEvent> _eventSink = [];
+    private Activity? _runActivity;
     private int _lastBookmark;
 
     /// <summary>
@@ -23,11 +24,13 @@ internal sealed class DurableWorkflowRun : IAwaitableWorkflowRun
     /// <param name="client">The durable task client for orchestration operations.</param>
     /// <param name="instanceId">The unique instance ID for this orchestration run.</param>
     /// <param name="workflowName">The name of the workflow being executed.</param>
-    internal DurableWorkflowRun(DurableTaskClient client, string instanceId, string workflowName)
+    /// <param name="runActivity">The workflow.run activity to stop when the workflow completes.</param>
+    internal DurableWorkflowRun(DurableTaskClient client, string instanceId, string workflowName, Activity? runActivity = null)
     {
         this._client = client;
         this.RunId = instanceId;
         this.WorkflowName = workflowName;
+        this._runActivity = runActivity;
     }
 
     /// <inheritdoc/>
@@ -48,33 +51,42 @@ internal sealed class DurableWorkflowRun : IAwaitableWorkflowRun
     /// <exception cref="InvalidOperationException">Thrown when the workflow was terminated or ended with an unexpected status.</exception>
     public async ValueTask<TResult?> WaitForCompletionAsync<TResult>(CancellationToken cancellationToken = default)
     {
-        OrchestrationMetadata metadata = await this._client.WaitForInstanceCompletionAsync(
-            this.RunId,
-            getInputsAndOutputs: true,
-            cancellation: cancellationToken).ConfigureAwait(false);
-
-        if (metadata.RuntimeStatus == OrchestrationRuntimeStatus.Completed)
+        try
         {
-            return DurableStreamingWorkflowRun.ExtractResult<TResult>(metadata.SerializedOutput);
-        }
+            OrchestrationMetadata metadata = await this._client.WaitForInstanceCompletionAsync(
+                this.RunId,
+                getInputsAndOutputs: true,
+                cancellation: cancellationToken).ConfigureAwait(false);
 
-        if (metadata.RuntimeStatus == OrchestrationRuntimeStatus.Failed)
-        {
-            if (metadata.FailureDetails is not null)
+            if (metadata.RuntimeStatus == OrchestrationRuntimeStatus.Completed)
             {
-                // Use TaskFailedException to preserve full failure details including stack trace and inner exceptions
-                throw new TaskFailedException(
-                    taskName: this.WorkflowName,
-                    taskId: 0,
-                    failureDetails: metadata.FailureDetails);
+                this._runActivity?.AddEvent(new ActivityEvent("workflow.completed"));
+                return DurableStreamingWorkflowRun.ExtractResult<TResult>(metadata.SerializedOutput);
+            }
+
+            if (metadata.RuntimeStatus == OrchestrationRuntimeStatus.Failed)
+            {
+                if (metadata.FailureDetails is not null)
+                {
+                    // Use TaskFailedException to preserve full failure details including stack trace and inner exceptions
+                    throw new TaskFailedException(
+                        taskName: this.WorkflowName,
+                        taskId: 0,
+                        failureDetails: metadata.FailureDetails);
+                }
+
+                throw new InvalidOperationException(
+                    $"Workflow '{this.WorkflowName}' (RunId: {this.RunId}) failed without failure details.");
             }
 
             throw new InvalidOperationException(
-                $"Workflow '{this.WorkflowName}' (RunId: {this.RunId}) failed without failure details.");
+                $"Workflow '{this.WorkflowName}' (RunId: {this.RunId}) ended with unexpected status: {metadata.RuntimeStatus}");
+        }
+        finally
+        {
+            this._runActivity?.Dispose();
+            this._runActivity = null;
         }
-
-        throw new InvalidOperationException(
-            $"Workflow '{this.WorkflowName}' (RunId: {this.RunId}) ended with unexpected status: {metadata.RuntimeStatus}");
     }
 
     /// <summary>

dotnet/src/Microsoft.Agents.AI.DurableTask/Workflows/DurableWorkflowRunner.cs

@@ -44,7 +44,6 @@
 //  Superstep 5 — loop exits (no pending messages)
 //    GetFinalResult returns resultE
 
-using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
 using Microsoft.Agents.AI.DurableTask.Workflows.EdgeRouters;
@@ -116,23 +115,12 @@ internal sealed class DurableWorkflowRunner
         // Extract input - the start executor determines the expected input type from its own InputTypes
         object input = workflowInput.Input;
 
-        string result = await RunSuperstepLoopAsync(context, workflow, edgeMap, input, logger).ConfigureAwait(true);
+        // Store the client-side workflow.run traceparent so activity dispatchers can include it
+        // in activity inputs. This avoids creating workflow.run in the orchestrator, where the
+        // replay model causes Activities to be abandoned on each re-invocation.
+        DurableWorkflowInstrumentation.WorkflowRunTraceParent.Value = workflowInput.TraceParent;
 
-        // Emit the workflow.run span after the superstep loop completes.
-        // Durable Task orchestrations replay the method from the top, where context.IsReplaying
-        // is true. It only transitions to false during forward progress (after all cached activity
-        // results are replayed). By emitting here — after RunSuperstepLoopAsync — we are guaranteed
-        // to be in non-replay mode, so the span is always captured exactly once.
-        if (!context.IsReplaying)
-        {
-            using Activity? activity = DurableWorkflowInstrumentation.ActivitySource.StartActivity("workflow.run");
-            activity?.SetTag("workflow.id", workflow.StartExecutorId)
-                .SetTag("workflow.name", workflowName)
-                .SetTag("run.id", instanceId)
-                .AddEvent(new ActivityEvent("workflow.completed"));
-        }
-
-        return result;
+        return await RunSuperstepLoopAsync(context, workflow, edgeMap, input, logger).ConfigureAwait(true);
     }
 
     private Workflow GetWorkflowOrThrow(string orchestrationName)