Leverage overload resolution attribute to direct compiler

We want our overload to take precedence over the built-in MEAI to provider smarter casting for your clients.

Author: kzu

src/AI.CodeAnalysis/ChatClientExtensions.cs

@@ -7,6 +7,9 @@
 /// </summary>
 static class ChatClientExtensions
 {
+#if NET9_0_OR_GREATER
+    [System.Runtime.CompilerServices.OverloadResolutionPriorityAttribute(100)]
+#endif
     /// <summary>Gets an <see cref="IChatClient"/> for use with this <see cref="ChatClient"/>.</summary>
     public static IChatClient AsIChatClient(this ChatClient client) =>
         client as IChatClient ?? OpenAIClientExtensions.AsIChatClient(client);

src/AI.Tests/OpenAITests.cs

@@ -1,4 +1,5 @@
-using System.Text.Json.Nodes;
+using System.ClientModel;
+using System.Text.Json.Nodes;
 using Devlooped.Extensions.AI.OpenAI;
 using Microsoft.Extensions.AI;
 using OpenAI;
@@ -9,6 +10,18 @@ namespace Devlooped.Extensions.AI;
 
 public class OpenAITests(ITestOutputHelper output)
 {
+    [SecretsFact("OPENAI_API_KEY")]
+    public void CanGetAsIChatClient()
+    {
+        var inner = new OpenAIClient(new ApiKeyCredential(Configuration["OPENAI_API_KEY"]!),
+            new OpenAIClientOptions
+            {
+                //Endpoint = new Uri("https://api.x.ai/v1"),
+            }).GetChatClient("grok-4").AsIChatClient();
+
+        Assert.NotNull(inner);
+    }
+
     [SecretsFact("OPENAI_API_KEY")]
     public async Task OpenAISwitchesModel()
     {