.NET: Add OpenTelemetry Chat Client to harness stack (#6961)

* Add OpenTelemetry Chat Client to harness stack

* Address PR comments

dotnet/src/Microsoft.Agents.AI.Harness/HarnessAgent.cs

@@ -190,6 +190,11 @@ public sealed class HarnessAgent : DelegatingAIAgent
             }
         }
 
+        CompactionProvider? compactionProvider = compactionStrategy is not null
+            ? new CompactionProvider(compactionStrategy, loggerFactory: loggerFactory)
+            : null;
+
+        // Build ChatHistoryProvider
         ChatHistoryProvider chatHistoryProvider = options?.ChatHistoryProvider
             ?? (compactionStrategy is not null
                 ? new InMemoryChatHistoryProvider(new InMemoryChatHistoryProviderOptions
@@ -198,6 +203,7 @@ public sealed class HarnessAgent : DelegatingAIAgent
                 })
                 : new InMemoryChatHistoryProvider());
 
+        // Build instructions
         string harnessInstructions = options?.HarnessInstructions ?? DefaultInstructions;
         string? agentInstructions = options?.ChatOptions?.Instructions;
 
@@ -209,14 +215,11 @@ public sealed class HarnessAgent : DelegatingAIAgent
             (false, false) => $"{harnessInstructions}\n\n{agentInstructions}",
         };
 
+        // Build Chat Options & context providers
         ChatOptions chatOptions = BuildChatOptions(options, instructions, options?.MaxOutputTokens);
-
-        CompactionProvider? compactionProvider = compactionStrategy is not null
-            ? new CompactionProvider(compactionStrategy, loggerFactory: loggerFactory)
-            : null;
-
         IEnumerable<AIContextProvider> contextProviders = BuildContextProviders(options, loggerFactory);
 
+        // Build ChatClient stack
         ChatClientBuilder chatClientBuilder = chatClient.AsBuilder();
 
         if (options?.DisableNonApprovalRequiredFunctionBypassing is not true)
@@ -224,7 +227,7 @@ public sealed class HarnessAgent : DelegatingAIAgent
             chatClientBuilder.UseNonApprovalRequiredFunctionBypassing();
         }
 
-        ChatClientBuilder pipeline = chatClientBuilder
+        chatClientBuilder = chatClientBuilder
             .UseFunctionInvocation(loggerFactory, configure: options?.MaximumIterationsPerRequest is int maxIterations
                 ? ficc => ficc.MaximumIterationsPerRequest = maxIterations
                 : null)
@@ -233,10 +236,16 @@ public sealed class HarnessAgent : DelegatingAIAgent
 
         if (compactionProvider is not null)
         {
-            pipeline = pipeline.UseAIContextProviders(compactionProvider);
+            chatClientBuilder = chatClientBuilder.UseAIContextProviders(compactionProvider);
         }
 
-        return pipeline
+        if (options?.DisableOpenTelemetry is not true)
+        {
+            chatClientBuilder = chatClientBuilder.UseOpenTelemetry(sourceName: options?.OpenTelemetrySourceName);
+        }
+
+        // Build Chat Client Agent
+        return chatClientBuilder
             .BuildAIAgent(new ChatClientAgentOptions
             {
                 Id = options?.Id,

dotnet/tests/Microsoft.Agents.AI.Harness.UnitTests/HarnessAgentTests.cs

@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft. All rights reserved.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -844,6 +846,90 @@ public class HarnessAgentTests
         Assert.NotNull(agent.GetService<OpenTelemetryAgent>());
     }
 
+    /// <summary>
+    /// Verify that the inner agent's ChatClient pipeline includes OpenTelemetryChatClient when
+    /// OpenTelemetry is enabled, so model calls are traced in addition to the agent-level
+    /// <see cref="OpenTelemetryAgent"/> wrapper.
+    /// </summary>
+    [Fact]
+    public void Pipeline_IncludesOpenTelemetryChatClientWhenEnabled()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+        var options = CreateAllDisabledOptions();
+        options.DisableOpenTelemetry = false;
+
+        // Act
+        var agent = new HarnessAgent(chatClient, options);
+        var innerAgent = agent.GetService<ChatClientAgent>();
+
+        // Assert
+        Assert.NotNull(innerAgent);
+        Assert.NotNull(innerAgent!.ChatClient.GetService<OpenTelemetryChatClient>());
+    }
+
+    /// <summary>
+    /// Verify that the inner agent's ChatClient pipeline excludes OpenTelemetryChatClient when
+    /// OpenTelemetry is disabled.
+    /// </summary>
+    [Fact]
+    public void Pipeline_ExcludesOpenTelemetryChatClientWhenDisabled()
+    {
+        // Arrange
+        var chatClient = new Mock<IChatClient>().Object;
+
+        // Act
+        var agent = new HarnessAgent(chatClient, CreateAllDisabledOptions());
+        var innerAgent = agent.GetService<ChatClientAgent>();
+
+        // Assert
+        Assert.NotNull(innerAgent);
+        Assert.Null(innerAgent!.ChatClient.GetService<OpenTelemetryChatClient>());
+    }
+
+    /// <summary>
+    /// Verify that the chat-client-level OpenTelemetry instrumentation emits a chat span under the
+    /// configured <see cref="HarnessAgentOptions.OpenTelemetrySourceName"/>, proving both that the
+    /// ChatClient pipeline is instrumented and that the source name is propagated.
+    /// </summary>
+    [Fact]
+    public async Task OpenTelemetry_ChatClientEmitsChatSpanUnderConfiguredSourceNameAsync()
+    {
+        // Arrange
+        var sourceName = Guid.NewGuid().ToString();
+        var activities = new ConcurrentQueue<Activity>();
+        using var listener = new ActivityListener
+        {
+            ShouldListenTo = source => source.Name == sourceName,
+            Sample = (ref ActivityCreationOptions<ActivityContext> _) => ActivitySamplingResult.AllDataAndRecorded,
+            ActivityStopped = activities.Enqueue,
+        };
+        ActivitySource.AddActivityListener(listener);
+
+        var mockClient = new Mock<IChatClient>();
+        mockClient
+            .Setup(c => c.GetResponseAsync(
+                It.IsAny<IEnumerable<ChatMessage>>(),
+                It.IsAny<ChatOptions>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new ChatResponse(new ChatMessage(ChatRole.Assistant, "Hello!")));
+
+        var options = CreateAllDisabledOptions();
+        options.DisableOpenTelemetry = false;
+        options.OpenTelemetrySourceName = sourceName;
+
+        var agent = new HarnessAgent(mockClient.Object, options);
+        var session = await agent.CreateSessionAsync();
+
+        // Act
+        await agent.RunAsync([new ChatMessage(ChatRole.User, "Hi")], session);
+
+        // Assert
+        Assert.Contains(
+            activities,
+            a => string.Equals(a.GetTagItem("gen_ai.operation.name") as string, "chat", StringComparison.Ordinal));
+    }
+
     #endregion
 
     #region Feature: WebSearch