.NET: A2A agent (#520)

* add a2a agent

* Update dotnet/src/Microsoft.Extensions.AI.Agents.A2A/A2AAgent.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* address pr review feedback

* move unit tests for extension methods to the extensions folder

* address pr review comments

* address pr review comments

* address pr review feedback

* move a2a agent sample to console app

* remove unnecessary Ids set for new projects in the solution file

* remove unnecessary configuration

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

dotnet/samples/HowToCreateAnAIAgentByProvider/AIAgent_With_A2A/AIAgent_With_A2A.csproj

@@ -0,0 +1,22 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <LangVersion>12</LangVersion>
+
+    <Nullable>enable</Nullable>
+    <ImplicitUsings>disable</ImplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="A2A" />
+    <PackageReference Include="System.Net.ServerSentEvents" VersionOverride="10.0.0-preview.5.25277.114" />
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" VersionOverride="10.0.0-preview.5.25277.114" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\src\Microsoft.Extensions.AI.Agents.A2A\Microsoft.Extensions.AI.Agents.A2A.csproj" />
+  </ItemGroup>
+
+</Project>

dotnet/samples/HowToCreateAnAIAgentByProvider/AIAgent_With_A2A/Program.cs

@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft. All rights reserved.
+
+// This sample shows how to create and use a simple AI agent with an existing A2A agent.
+
+using System;
+using A2A;
+using Microsoft.Extensions.AI.Agents;
+using Microsoft.Extensions.AI.Agents.A2A;
+
+var a2aAgentHost = Environment.GetEnvironmentVariable("A2A_AGENT_HOST") ?? throw new InvalidOperationException("A2A_AGENT_HOST is not set.");
+
+// Initialize an A2ACardResolver to get an A2A agent card.
+A2ACardResolver agentCardResolver = new(new Uri(a2aAgentHost));
+
+// Create an instance of the AIAgent for an existing A2A agent specified by the agent card.
+AIAgent agent = await agentCardResolver.GetAIAgentAsync();
+
+// Invoke the agent and output the text result.
+AgentRunResponse response = await agent.RunAsync("Tell me a joke about a pirate.");
+Console.WriteLine(response);

dotnet/samples/HowToCreateAnAIAgentByProvider/AIAgent_With_A2A/README.md

@@ -0,0 +1,34 @@
+# Prerequisites
+
+Before you begin, ensure you have the following prerequisites:
+
+- .NET 8.0 SDK or later
+- Access to the A2A agent host service
+
+**Note**: These samples need to be run against a valid A2A server. If no A2A server is available, they can be run against the echo-agent that can be spun up locally by following the guidelines at: https://github.com/a2aproject/a2a-dotnet/blob/main/samples/AgentServer/README.md
+
+Set the following environment variables:
+
+```powershell
+$env:A2A_AGENT_HOST="https://your-a2a-agent-host" # Replace with your A2A agent host endpoint
+```
+
+## Advanced scenario
+
+This method can be used to create AI agents for A2A agents whose hosts support the [Direct Configuration / Private Discovery](https://github.com/a2aproject/A2A/blob/main/docs/topics/agent-discovery.md#3-direct-configuration--private-discovery) discovery mechanism.
+
+```csharp
+using A2A;
+using Microsoft.Extensions.AI.Agents;
+using Microsoft.Extensions.AI.Agents.A2A;
+
+// Create an A2AClient pointing to your `echo` A2A agent endpoint
+A2AClient a2aClient = new(new Uri("https://your-a2a-agent-host/echo"));
+
+// Create an AIAgent from the A2AClient
+AIAgent agent = a2aClient.GetAIAgent();
+
+// Run the agent
+AgentRunResponse response = await agent.RunAsync("Tell me a joke about a pirate.");
+Console.WriteLine(response);
+```

dotnet/samples/HowToCreateAnAIAgentByProvider/README.md

@@ -13,6 +13,7 @@ See the README.md for each sample for the prerequisites for that sample.
 
 |Sample|Description|
 |---|---|
+|[Creating an AIAgent with A2A](./AIAgent_With_A2A/)|This sample demonstrates how to create AIAgent for an existing A2A agent.|
 |[Creating an AIAgent with AzureFoundry](./AIAgent_With_AzureFoundry/)|This sample demonstrates how to create an Azure Foundry agent and expose it as an AIAgent|
 |[Creating an AIAgent with Azure OpenAI ChatCompletion](./AIAgent_With_AzureOpenAIChatCompletion/)|This sample demonstrates how to create an AIAgent using Azure OpenAI ChatCompletion as the underlying inference service|
 |[Creating an AIAgent with Azure OpenAI Responses](./AIAgent_With_AzureOpenAIResponses/)|This sample demonstrates how to create an AIAgent using Azure OpenAI Responses as the underlying inference service|