.Net: Initial check-in for the A2A Agent implementation #12050

markwallace-microsoft · 2025-05-14T07:32:05Z

Motivation and Context

Description

Contribution Checklist

The code builds clean without any errors or warnings
The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
All unit tests pass, and I have added new tests where possible
I didn't break anyone 😄

markwallace-microsoft · 2025-06-19T13:36:35Z

@markwallace-microsoft great that you're working on this, I'm eager to try it!

Are there any major things that people should be aware of if they want to try it? When would this be likely to be merged to main?

Hi @hansmbakker
I'm hoping to get this merged and release early next week. The A2A protocol is still being developed so I would expect changes. So far the sample only supports the most basic functionality i.e., there is no support yet for long running tasks. But your feedback on what is the next most important thing to add would be much appreciated.

…wallace-microsoft/semantic-kernel into users/markwallace/a2a_agent

westey-m · 2025-06-20T17:00:52Z

dotnet/samples/Demos/A2AClientServer/A2AClient/A2AClient.csproj

+
+  <ItemGroup>
+    <PackageReference Include="SharpA2A.Core" />
+    <PackageReference Include="SharpA2A.AspNetCore" />


Do we need the asp.net package in the client? I would have expected it's only required for the server?

westey-m · 2025-06-20T17:08:04Z

dotnet/samples/Demos/A2AClientServer/A2AClient/HostClientAgent.cs

+
+            // Connect to the remote agents via A2A
+            var createAgentTasks = agentUrls.Select(agentUrl => this.CreateAgentAsync(agentUrl));
+            var agents = await Task.WhenAll(createAgentTasks);


Might be nice to also have a basic example where we are interacting directly with a single A2AAgent instance.
This multiagent sample is also great and we should keep it. I'm just thinking it might be easier for people to grasp a single agent one first.

I see you have a single agent demonstration under samples, so maybe this isn't necessary here then after all.

westey-m · 2025-06-20T17:30:18Z

dotnet/samples/Demos/A2AClientServer/README.md

+    resolution in SAP CRM and notify the customer via email within 2 business days, referencing the
+    original invoice and the credit memo number. Use the 'Formal Credit Notification' email
+    template."
+    Always reply with exactly this text:


Is this text intentionally repeated?

westey-m · 2025-06-20T17:30:48Z

dotnet/samples/Demos/A2AClientServer/A2AClient/README.md

+
+1. Run the A2A client:
+    ```bash
+    cd A2AClient


Here we are already in the A2AClient directory

westey-m · 2025-06-20T17:37:19Z

dotnet/src/Agents/A2A/A2AAgent.cs

+    /// <param name="client">A2AClient instance to associate with the agent.</param>
+    /// <param name="agentCard">AgentCard instance associated ith the agent.</param>


Suggested change

/// <param name="client">A2AClient instance to associate with the agent.</param>

/// <param name="agentCard">AgentCard instance associated ith the agent.</param>

/// <param name="client"><see cref="A2AClient"/> instance to associate with the agent.</param>

/// <param name="agentCard"><see cref="AgentCard"/> instance associated with the agent.</param>

westey-m · 2025-06-20T17:39:56Z

dotnet/src/Agents/A2A/A2AAgent.cs

+        }
+    }
+
+    private async IAsyncEnumerable<AgentResponseItem<ChatMessageContent>> InvokeAgentAsync(string name, ChatMessageContent message, A2AAgentThread thread, AgentInvokeOptions options, [EnumeratorCancellation] CancellationToken cancellationToken)


I don't see the name param being used in the method. Am I missing something?

westey-m · 2025-06-20T17:41:24Z

dotnet/src/Agents/A2A/A2AAgent.cs

+        this.AgentCard = agentCard;
+        this.Name = agentCard.Name;
+        this.Description = agentCard.Description;


It doesn't look like these are required to ensure the functioning of the Agent. Could we make agentCard optional?

dmytrostruk · 2025-06-20T17:11:26Z

dotnet/samples/Demos/A2AClientServer/A2AClient/Program.cs

+            .Build();
+        var apiKey = configRoot["A2AClient:ApiKey"] ?? throw new ArgumentException("A2AClient:ApiKey must be provided");
+        var modelId = configRoot["A2AClient:ModelId"] ?? "gpt-4.1";
+        var agentUrls = configRoot["A2AClient:AgentUrls"] ?? "http://localhost:5000/ http://localhost:5001/ http://localhost:5002/";


nit: Wondering if comma separator or ; will work as well here, since space separator is a little bit unclear.

dmytrostruk · 2025-06-20T17:20:09Z

dotnet/samples/Demos/A2AClientServer/A2AServer/Plugins/CurrencyPlugin.cs

+        this._httpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
+
+        // Create a retry policy for transient HTTP errors
+        this._retryPolicy = Policy


nit: I would configure retry policy on HttpClient level, so CurrencyPlugin will be decoupled from HTTP-related logic, but since it's a demo app, it's not critical, so feel free to skip.

westey-m · 2025-06-20T17:52:31Z

dotnet/src/Agents/A2A/A2AAgent.cs

+    {
+        Verify.NotNull(messages);
+
+        foreach (var message in messages)


Mmm, this is interesting. In the CopilotChatAgent we concatenate the input messages and invoke once where here we invoke for each message.
For inference type agents we invoke once with all messages too, so they are processed in one go. Not sure if we want to follow that approach everywhere.

westey-m · 2025-06-20T17:54:23Z

dotnet/src/Agents/A2A/A2AAgent.cs

+        };
+
+        A2AResponse response = await this.Client.SendMessageAsync(messageSendParams).ConfigureAwait(false);
+        if (response is AgentTask agentTask)


What's an AgentTask?

westey-m · 2025-06-20T17:58:14Z

dotnet/src/Agents/A2A/A2AAgentThread.cs

+    /// <summary>
+    /// Gets the session id of the current thread.
+    /// </summary>
+    public string SessionId { get; init; }


Do we need SessionId as well if we already have id?

westey-m · 2025-06-20T18:09:15Z

dotnet/src/Agents/A2A/A2AHostAgent.cs

+    /// Attach the <see cref="A2AAgent"/> to the provided <see cref="ITaskManager"/>
+    /// </summary>
+    /// <param name="taskManager"></param>
+    public void Attach(ITaskManager taskManager)


Looks like you need a new TaskManager instance for each agent instance. Do we think it would be necessary to add the same agent to multiple task managers? It doesn't look like that's supported since we only have one taskmanager field here.
It might be easier for the consumer if we just wrapped the TaskManager in the A2AHostAgent, so that the consumer doesn't have to know about it.
And maybe add an extension method for just mapping an Agent like this:

app.MapA2A(myA2AHostAgent);

westey-m · 2025-06-20T18:11:45Z

dotnet/samples/Demos/A2AClientServer/A2AServer/AzureAI/AzureAIHostAgent.cs

+
+namespace A2A;
+
+internal abstract class AzureAIHostAgent : A2AHostAgent


Instead of inheriting from A2AHostAgent also consider instantiating an A2AHostAgent with an Agent instance, so it is just a standalone utility. Forcing users to inherit from A2AHostAgent to get the adapter functionality seems somewhat opinionated to me.
I can see a case where we may just want to support:

var myA2AAgent = myAgent.ToA2AAgent(card); app.MapA2A(myA2AAgent);

westey-m · 2025-06-20T18:16:46Z

dotnet/src/Agents/A2A/Properties/AssemblyInfo.cs

+using System.Diagnostics.CodeAnalysis;
+
+// This assembly is currently experimental.
+[assembly: Experimental("SKEXP0110")]


Isn't this implied by it being alpha?

Initial check-in for the A2A Agent implementation

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markwallace-microsoft requested a review from a team as a code owner May 14, 2025 07:32

markwallace-microsoft added the .NET Issue or Pull requests regarding .NET code label May 14, 2025

Merge branch 'main' into users/markwallace/a2a_agent

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tommasodotNET mentioned this pull request Jun 13, 2025

.Net: Remote Chat Completion Agent Demo #11554

Closed

4 tasks

ultrasimulation mentioned this pull request Jun 17, 2025

.Net: New Feature: Remote Agent and Agent Orchestration (A2A) #12488

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markwallace-microsoft added 2 commits June 19, 2025 10:05

Upgrade to latest SharpA2A

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…wallace-microsoft/semantic-kernel into users/markwallace/a2a_agent

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		/// <param name="client">A2AClient instance to associate with the agent.</param>
		/// <param name="agentCard">AgentCard instance associated ith the agent.</param>


		namespace A2A;

		internal abstract class AzureAIHostAgent : A2AHostAgent

.Net: Initial check-in for the A2A Agent implementation #12050

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markwallace-microsoft commented May 14, 2025

Motivation and Context

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markwallace-microsoft commented Jun 19, 2025

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