.NET: Add a CreateAIAgent extension method to IChatClient (#1223)

* Add a CreateAIAgent extension method to IChatClient

* Fix unit tests

* Add tests with null chat clients to ensure appropriate failure

* Switch to similar constructor

* Add ChatClientBuilder BuildAgent extensions

* Address code review comments.

dotnet/samples/GettingStarted/AgentProviders/Agent_With_ONNX/Program.cs

@@ -4,6 +4,7 @@
 // WARNING: ONNX doesn't support function calling, so any function tools passed to the agent will be ignored.
 
 using Microsoft.Agents.AI;
+using Microsoft.Extensions.AI;
 using Microsoft.ML.OnnxRuntimeGenAI;
 
 // E.g. C:\repos\Phi-4-mini-instruct-onnx\cpu_and_mobile\cpu-int4-rtn-block-32-acc-level-4
@@ -14,7 +15,7 @@ const string JokerInstructions = "You are good at telling jokes.";
 
 // Get a chat client for ONNX and use it to construct an AIAgent.
 using OnnxRuntimeGenAIChatClient chatClient = new(modelPath);
-AIAgent agent = new ChatClientAgent(chatClient, JokerInstructions, JokerName);
+AIAgent agent = chatClient.CreateAIAgent(JokerInstructions, JokerName);
 
 // Invoke the agent and output the text result.
 Console.WriteLine(await agent.RunAsync("Tell me a joke about a pirate."));

dotnet/samples/GettingStarted/AgentProviders/Agent_With_Ollama/Program.cs

@@ -3,6 +3,7 @@
 // This sample shows how to create and use a simple AI agent with Ollama as the backend.
 
 using Microsoft.Agents.AI;
+using Microsoft.Extensions.AI;
 using OllamaSharp;
 
 var endpoint = Environment.GetEnvironmentVariable("OLLAMA_ENDPOINT") ?? throw new InvalidOperationException("OLLAMA_ENDPOINT is not set.");
@@ -12,8 +13,8 @@ const string JokerName = "Joker";
 const string JokerInstructions = "You are good at telling jokes.";
 
 // Get a chat client for Ollama and use it to construct an AIAgent.
-using OllamaApiClient chatClient = new(new Uri(endpoint), modelName);
-AIAgent agent = new ChatClientAgent(chatClient, JokerInstructions, JokerName);
+AIAgent agent = new OllamaApiClient(new Uri(endpoint), modelName)
+    .CreateAIAgent(JokerInstructions, JokerName);
 
 // Invoke the agent and output the text result.
 Console.WriteLine(await agent.RunAsync("Tell me a joke about a pirate."));

dotnet/samples/GettingStarted/Agents/Agent_Step14_Middleware/Program.cs

@@ -10,6 +10,7 @@ using System.Text.RegularExpressions;
 using Azure.AI.OpenAI;
 using Azure.Identity;
 using Microsoft.Agents.AI;
+using Microsoft.Agents.AI.ChatClient;
 using Microsoft.Extensions.AI;
 
 // Get Azure AI Foundry configuration from environment variables
@@ -28,25 +29,21 @@ static string GetWeather([Description("The location to get the weather for.")] s
 static string GetDateTime()
     => DateTimeOffset.Now.ToString();
 
-// Adding middleware to the chat client level
-var chatClient = azureOpenAIClient.AsIChatClient()
+// Adding middleware to the chat client level and building an agent on top of it
+var originalAgent = azureOpenAIClient.AsIChatClient()
     .AsBuilder()
-        .Use(getResponseFunc: ChatClientMiddleware, getStreamingResponseFunc: null)
-    .Build();
-
-// For flexibility we create the agent without any middleware.
-var originalAgent = new ChatClientAgent(chatClient, new ChatClientAgentOptions(
+    .Use(getResponseFunc: ChatClientMiddleware, getStreamingResponseFunc: null)
+    .BuildAIAgent(
         instructions: "You are an AI assistant that helps people find information.",
-        // Agent level tools
-        tools: [AIFunctionFactory.Create(GetDateTime, name: nameof(GetDateTime))]));
+        tools: [AIFunctionFactory.Create(GetDateTime, name: nameof(GetDateTime))]);
 
 // Adding middleware to the agent level
 var middlewareEnabledAgent = originalAgent
     .AsBuilder()
-        .Use(FunctionCallMiddleware)
-        .Use(FunctionCallOverrideWeather)
-        .Use(PIIMiddleware, null)
-        .Use(GuardrailMiddleware, null)
+    .Use(FunctionCallMiddleware)
+    .Use(FunctionCallOverrideWeather)
+    .Use(PIIMiddleware, null)
+    .Use(GuardrailMiddleware, null)
     .Build();
 
 var thread = middlewareEnabledAgent.GetNewThread();
@@ -83,15 +80,15 @@ var optionsWithApproval = new ChatClientAgentRunOptions(new()
 {
     ChatClientFactory = (chatClient) => chatClient
         .AsBuilder()
-            .Use(PerRequestChatClientMiddleware, null) // Using the non-streaming for handling streaming as well
+        .Use(PerRequestChatClientMiddleware, null) // Using the non-streaming for handling streaming as well
         .Build()
 };
 
 // var response = middlewareAgent  // Using per-request middleware pipeline in addition to existing agent-level middleware
 var response = await originalAgent // Using per-request middleware pipeline without existing agent-level middleware
     .AsBuilder()
-        .Use(PerRequestFunctionCallingMiddleware)
-        .Use(ConsolePromptingApprovalMiddleware, null)
+    .Use(PerRequestFunctionCallingMiddleware)
+    .Use(ConsolePromptingApprovalMiddleware, null)
     .Build()
     .RunAsync("What's the current time and the weather in Seattle?", thread, optionsWithApproval);