Make it possible to construct the raw completion request from gRPC

.netconfig

@@ -165,4 +165,9 @@
     url = https://github.com/andrewlock/NetEscapades.Configuration/blob/master/src/NetEscapades.Configuration.Yaml/YamlConfigurationStreamParser.cs
     weak
 	sha = a1ec2c6746d96b4f6f140509aa68dcff09271146
-	etag = 9e5c6908edc34eb661d647671f79153d8f3a54ebdc848c8765c78d2715f2f657
+	etag = 9e5c6908edc34eb661d647671f79153d8f3a54ebdc848c8765c78d2715f2f657
+[file "src/Tests/Extensions/CallHelpers.cs"]
+	url = https://github.com/grpc/grpc-dotnet/blob/master/examples/Tester/Tests/Client/Helpers/CallHelpers.cs
+	sha = a04684ab2306e5a17bad26d3da69636b326cce14
+	etag = 7faacded709d2bede93356fd58b93af84884949f3bab098b8b8d121a03696449
+	weak

src/Extensions.Grok/Extensions.Grok.csproj

@@ -26,6 +26,7 @@
   <ItemGroup>
     <Compile Include="..\Extensions\Extensions\ChatOptionsExtensions.cs" Link="Extensions\ChatOptionsExtensions.cs" />
     <None Include="..\..\osmfeula.txt" Link="osmfeula.txt" PackagePath="OSMFEULA.txt" />
+    <InternalsVisibleTo Include="Tests"/>
   </ItemGroup>
 
 </Project>

src/Extensions.Grok/GrokChatClient.cs

@@ -15,8 +15,19 @@ class GrokChatClient : IChatClient
     readonly GrokClientOptions clientOptions;
 
     internal GrokChatClient(GrpcChannel channel, GrokClientOptions clientOptions, string defaultModelId)
+        : this(new ChatClient(channel), clientOptions, defaultModelId)
+    { }
+
+    /// <summary>
+    /// Test constructor.
+    /// </summary>
+    internal GrokChatClient(ChatClient client, string defaultModelId)
+        : this(client, new(), defaultModelId)
+    { }
+
+    GrokChatClient(ChatClient client, GrokClientOptions clientOptions, string defaultModelId)
     {
-        client = new ChatClient(channel);
+        this.client = client;
         this.clientOptions = clientOptions;
         this.defaultModelId = defaultModelId;
         metadata = new ChatClientMetadata("xai", clientOptions.Endpoint, defaultModelId);
@@ -97,7 +108,7 @@ public async Task<ChatResponse> GetResponseAsync(IEnumerable<ChatMessage> messag
         {
             ResponseId = response.Id,
             ModelId = response.Model,
-            CreatedAt = response.Created.ToDateTimeOffset(),
+            CreatedAt = response.Created?.ToDateTimeOffset(),
             FinishReason = lastOutput != null ? MapFinishReason(lastOutput.FinishReason) : null,
             Usage = MapToUsage(response.Usage),
         };
@@ -210,13 +221,16 @@ static CitationAnnotation MapCitation(string citation)
 
     GetCompletionsRequest MapToRequest(IEnumerable<ChatMessage> messages, ChatOptions? options)
     {
-        var request = new GetCompletionsRequest
+        var request = options?.RawRepresentationFactory?.Invoke(this) as GetCompletionsRequest ?? new GetCompletionsRequest()
         {
             // By default always include citations in the final output if available
             Include = { IncludeOption.InlineCitations },
             Model = options?.ModelId ?? defaultModelId,
         };
 
+        if (string.IsNullOrEmpty(request.Model))
+            request.Model = options?.ModelId ?? defaultModelId;
+
         if ((options?.EndUserId ?? clientOptions.EndUserId) is { } user) request.User = user;
         if (options?.MaxOutputTokens is { } maxTokens) request.MaxTokens = maxTokens;
         if (options?.Temperature is { } temperature) request.Temperature = temperature;

src/Tests/Extensions/CallHelpers.cs

@@ -0,0 +1,46 @@
+#region Copyright notice and license
+
+// Copyright 2019 The gRPC Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#endregion
+
+using Grpc.Core;
+
+namespace Tests.Client.Helpers
+{
+    static class CallHelpers
+    {
+        public static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(TResponse response)
+        {
+            return new AsyncUnaryCall<TResponse>(
+                Task.FromResult(response),
+                Task.FromResult(new Metadata()),
+                () => Status.DefaultSuccess,
+                () => new Metadata(),
+                () => { });
+        }
+
+        public static AsyncUnaryCall<TResponse> CreateAsyncUnaryCall<TResponse>(StatusCode statusCode)
+        {
+            var status = new Status(statusCode, string.Empty);
+            return new AsyncUnaryCall<TResponse>(
+                Task.FromException<TResponse>(new RpcException(status)),
+                Task.FromResult(new Metadata()),
+                () => status,
+                () => new Metadata(),
+                () => { });
+        }
+    }
+}

src/Tests/GrokTests.cs

@@ -4,7 +4,8 @@
 using Devlooped.Extensions.AI.Grok;
 using Devlooped.Grok;
 using Microsoft.Extensions.AI;
-using OpenAI.Realtime;
+using Moq;
+using Tests.Client.Helpers;
 using static ConfigurationExtensions;
 using OpenAIClientOptions = OpenAI.OpenAIClientOptions;
 
@@ -466,5 +467,40 @@ public async Task GrokStreamsUpdatesFromAllTools()
         Assert.True(typed.Price > 100);
     }
 
+    [Fact]
+    public async Task GrokCustomFactoryInvokedFromOptions()
+    {
+        var invoked = false;
+        var client = new Mock<Devlooped.Grok.Chat.ChatClient>(MockBehavior.Strict);
+        client.Setup(x => x.GetCompletionAsync(It.IsAny<GetCompletionsRequest>(), null, null, CancellationToken.None))
+            .Returns(CallHelpers.CreateAsyncUnaryCall(new GetChatCompletionResponse
+            {
+                Outputs =
+                {
+                    new CompletionOutput
+                    {
+                        Message = new CompletionMessage
+                        {
+                            Content = "Hey Cazzulino!"
+                        }
+                    }
+                }
+            }));
+
+        var grok = new GrokChatClient(client.Object, "grok-4-1-fast");
+        var response = await grok.GetResponseAsync("Hi, my internet alias is kzu. Lookup my real full name online.",
+            new GrokChatOptions
+            {
+                RawRepresentationFactory = (client) =>
+                {
+                    invoked = true;
+                    return new GetCompletionsRequest();
+                }
+            });
+
+        Assert.True(invoked);
+        Assert.Equal("Hey Cazzulino!", response.Text);
+    }
+
     record Response(DateOnly Today, string Release, decimal Price);
 }