.NET: [Bug]: OpenTelemetry is not emitted when Agent is triggered through AGUI

[viul-sc]

Description

Create IChatClient:

string endpoint = _config.GetRequired("AZURE_OPENAI_ENDPOINT");
string deploymentName = _config.GetRequired("AZURE_OPENAI_DEPLOYMENT_NAME");
string apiKey = _config.GetRequired("AZURE_OPENAI_API_KEY");

AzureOpenAIClient azureOpenAIClient = new(new(endpoint), new ApiKeyCredential(apiKey));
IChatClient chatClient = azureOpenAIClient
    .GetChatClient(deploymentName)
    .AsIChatClient();
IChatClient otelChatClient = new ChatClientBuilder(chatClient)
    .UseOpenTelemetry(sourceName: _otelConfig.SourceName)
    .Build();

Create AIAgent:

AIAgent agent = _chatClient
    .AsAIAgent(
        name: Name,
        description: Description,
        instructions: Instructions,
        tools: _toolRepository.Tools)
    .AsBuilder()
    .UseOpenTelemetry(sourceName: _otelConfig.SourceName)
    .Build()

Trigger agent directrly - Otel is emitted:

agent.RunStreamingAsync("Tell me a joke about a pirate.")

Activity.TraceId:            84a8eedb8cbe1407ee0ed882abed7714
Activity.SpanId:             cb81234e17b71277
Activity.TraceFlags:         Recorded
Activity.DisplayName:        invoke_agent Orchestrator-Agent(39f55520b807458e96865cc3bb8502ee)
Activity.Kind:               Client
Activity.StartTime:          2026-02-06T09:47:18.9291545Z
Activity.Duration:           00:00:12.2744279
Activity.Tags:
    gen_ai.operation.name: invoke_agent
    gen_ai.request.model: gpt-5.2
    gen_ai.provider.name: openai
    server.address: oai-ai-viul-sandbox-swed.cognitiveservices.azure.com
    server.port: 443
    gen_ai.agent.id: 39f55520b807458e96865cc3bb8502ee
    gen_ai.agent.name: Orchestrator-Agent
    gen_ai.agent.description: Performs arithmetic calculations
    gen_ai.response.finish_reasons: ["stop"]
    gen_ai.response.id: chatcmpl-D6CiuhonjXur3lIEf3x6tVaqMbyF2
    gen_ai.response.model:
    gen_ai.usage.input_tokens: 75
    gen_ai.usage.output_tokens: 28
Instrumentation scope (ActivitySource):
    Name: a2a-poc
Resource associated with Activity:
    service.name: a2a-poc-service
    service.instance.id: 98570eeb-d4ed-4a55-ace5-1f29367966b4
    telemetry.sdk.name: opentelemetry
    telemetry.sdk.language: dotnet
    telemetry.sdk.version: 1.15.0

Setup AGUI server:

WebApplicationBuilder builder = WebApplication.CreateBuilder(args);
builder.Services.AddAGUI();
...
WebApplication app = builder.Build();
app.MapAGUI("/", agent);
await app.RunAsync();

Trigger through AGUI Client:

string serverUrl = "http://localhost:5001";
AGUIChatClient chatClient = new(new(), serverUrl);
AIAgent aguiAgent = chatClient.AsAIAgent();
aguiAgent.RunStreamingAsync("Tell me a joke about a pirate.");

Telemetry is not emitted.

Code Sample

Error Messages / Stack Traces

Package Versions

1.0.0-preview.260128.1

.NET Version

No response

Additional Context

No response

[viul-sc]

Results of intermediate investigation.

When calling the agent directly, the OTel Activity is not null:

When calling through AGUI, the Otel Activity is null:

[stephentoub]

In your repro you show doing this in the first case:
.UseOpenTelemetry
but not in the agui case.

[viul-sc]

aguiAgent is a proxy for accessing the original agent over the AGUI protocol. So the original agent should still emit the telemetry.

From what I see through debugging, UseOpenTelemetry creates a decorator of the original agent.
I.e., in the first case (working), the chain will be:

Client => OpenTelemetryAgent Decorator => ChatClientAgent => OpenTelemetryChatClient Decorator => ChatClient => OpenAIClient

In the second case (not working):

Client => AGUI Client => AGUI => OpenTelemetryAgent Decorator => ChatClientAgent => OpenTelemetryChatClient Decorator => ChatClient => OpenAIClient