Align ToolChoice with official OpenAI .NET SDK patterns

- ToolDefinition.Type: non-nullable with default ToolType.Function
- FunctionDefinition: Function and Name marked as required
- ToolChoice: factory methods (CreateAutoChoice, CreateNoneChoice,
  CreateRequiredChoice, CreateFunctionChoice) instead of static properties
- Update all callers in samples and tests
- Update sample Directory.Packages.props WinML version

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bmehta001

samples/cs/Directory.Packages.props

@@ -6,7 +6,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="Microsoft.AI.Foundry.Local" Version="0.9.0-dev" />
-    <PackageVersion Include="Microsoft.AI.Foundry.Local.WinML" Version="0.9.0-dev-20260324" />
+    <PackageVersion Include="Microsoft.AI.Foundry.Local.WinML" Version="0.9.0-dev" />
     <PackageVersion Include="Microsoft.Extensions.Logging" Version="9.0.10" />
     <PackageVersion Include="Microsoft.Extensions.Logging.Console" Version="9.0.10" />
     <PackageVersion Include="NAudio" Version="2.2.1" />

samples/cs/tool-calling-foundry-local-sdk/Program.cs

@@ -57,7 +57,7 @@ await model.DownloadAsync(progress =>
 
 // Get a chat client
 var chatClient = await model.GetChatClientAsync();
-chatClient.Settings.ToolChoice = ToolChoice.Required; // Force the model to make a tool call
+chatClient.Settings.ToolChoice = ToolChoice.CreateRequiredChoice(); // Force the model to make a tool call
 
 
 // Prepare messages
@@ -145,7 +145,7 @@ await model.DownloadAsync(progress =>
 
 // Set tool calling back to auto so that the model can decide whether to call
 // the tool again or continue the conversation based on the new user prompt
-chatClient.Settings.ToolChoice = ToolChoice.Auto;
+chatClient.Settings.ToolChoice = ToolChoice.CreateAutoChoice();
 
 
 // Run the next turn of the conversation

samples/cs/tutorial-tool-calling/Program.cs

@@ -134,7 +134,7 @@ await model.DownloadAsync(progress =>
 Console.WriteLine("Model loaded and ready.");
 
 var chatClient = await model.GetChatClientAsync();
-chatClient.Settings.ToolChoice = ToolChoice.Auto;
+chatClient.Settings.ToolChoice = ToolChoice.CreateAutoChoice();
 
 var messages = new List<ChatMessage>
 {

sdk/cs/src/OpenAI/ToolCallingTypes.cs

@@ -18,13 +18,13 @@ namespace Microsoft.AI.Foundry.Local.OpenAI;
 /// </summary>
 public class ToolDefinition
 {
-    /// <summary>The type of tool.</summary>
+    /// <summary>The type of tool. Defaults to <see cref="ToolType.Function"/>.</summary>
     [JsonPropertyName("type")]
-    public ToolType? Type { get; set; }
+    public ToolType Type { get; set; } = ToolType.Function;
 
     /// <summary>The function definition.</summary>
     [JsonPropertyName("function")]
-    public FunctionDefinition? Function { get; set; }
+    public required FunctionDefinition Function { get; set; }
 }
 
 /// <summary>
@@ -34,7 +34,7 @@ public class FunctionDefinition
 {
     /// <summary>The name of the function.</summary>
     [JsonPropertyName("name")]
-    public string? Name { get; set; }
+    public required string Name { get; set; }
 
     /// <summary>A description of what the function does.</summary>
     [JsonPropertyName("description")]
@@ -117,26 +117,35 @@ public class JsonSchema
 
 /// <summary>
 /// Controls which tool the model should use.
-/// Use static properties <see cref="None"/>, <see cref="Auto"/>, or <see cref="Required"/>
-/// for standard choices.
+/// Use static methods <see cref="CreateNoneChoice"/>, <see cref="CreateAutoChoice"/>,
+/// <see cref="CreateRequiredChoice"/>, or <see cref="CreateFunctionChoice(string)"/>.
 /// </summary>
 [JsonConverter(typeof(ToolChoiceConverter))]
 public class ToolChoice
 {
     /// <summary>The tool choice type.</summary>
-    public string? Type { get; set; }
+    public string? Type { get; internal set; }
 
     /// <summary>Specifies a particular function to call.</summary>
-    public FunctionTool? Function { get; set; }
+    public FunctionTool? Function { get; internal set; }
+
+    /// <summary>Creates a choice indicating the model will not call any tool.</summary>
+    public static ToolChoice CreateNoneChoice() => new() { Type = "none" };
 
-    /// <summary>The model will not call any tool.</summary>
-    public static ToolChoice None => new() { Type = "none" };
+    /// <summary>Creates a choice indicating the model can choose whether to call a tool.</summary>
+    public static ToolChoice CreateAutoChoice() => new() { Type = "auto" };
 
-    /// <summary>The model can choose whether to call a tool.</summary>
-    public static ToolChoice Auto => new() { Type = "auto" };
+    /// <summary>Creates a choice indicating the model must call one or more tools.</summary>
+    public static ToolChoice CreateRequiredChoice() => new() { Type = "required" };
 
-    /// <summary>The model must call one or more tools.</summary>
-    public static ToolChoice Required => new() { Type = "required" };
+    /// <summary>Creates a choice indicating the model must call the specified function.</summary>
+    /// <exception cref="ArgumentNullException"><paramref name="functionName"/> is null.</exception>
+    /// <exception cref="ArgumentException"><paramref name="functionName"/> is empty.</exception>
+    public static ToolChoice CreateFunctionChoice(string functionName)
+    {
+        ArgumentNullException.ThrowIfNullOrEmpty(functionName, nameof(functionName));
+        return new() { Type = "function", Function = new FunctionTool { Name = functionName } };
+    }
 
     /// <summary>
     /// Specifies a specific function tool to call.

sdk/cs/test/FoundryLocal.Tests/ChatCompletionsTests.cs

@@ -1,4 +1,4 @@
-// --------------------------------------------------------------------------------------------------------------------
+// --------------------------------------------------------------------------------------------------------------------
 // <copyright company="Microsoft">
 //   Copyright (c) Microsoft. All rights reserved.
 // </copyright>
@@ -136,7 +136,7 @@ public async Task DirectTool_NoStreaming_Succeeds()
 
         chatClient.Settings.MaxTokens = 500;
         chatClient.Settings.Temperature = 0.0f; // for deterministic results
-        chatClient.Settings.ToolChoice = ToolChoice.Required; // Force the model to make a tool call
+        chatClient.Settings.ToolChoice = ToolChoice.CreateRequiredChoice(); // Force the model to make a tool call
 
         // Prepare messages and tools
         List<ChatMessage> messages =
@@ -202,7 +202,7 @@ public async Task DirectTool_NoStreaming_Succeeds()
 
         // Set tool calling back to auto so that the model can decide whether to call
         // the tool again or continue the conversation based on the new user prompt
-        chatClient.Settings.ToolChoice = ToolChoice.Auto;
+        chatClient.Settings.ToolChoice = ToolChoice.CreateAutoChoice();
 
         // Run the next turn of the conversation
         response = await chatClient.CompleteChatAsync(messages, tools).ConfigureAwait(false);
@@ -220,7 +220,7 @@ public async Task DirectTool_Streaming_Succeeds()
 
         chatClient.Settings.MaxTokens = 500;
         chatClient.Settings.Temperature = 0.0f; // for deterministic results
-        chatClient.Settings.ToolChoice = ToolChoice.Required; // Force the model to make a tool call
+        chatClient.Settings.ToolChoice = ToolChoice.CreateRequiredChoice(); // Force the model to make a tool call
 
         // Prepare messages and tools
         List<ChatMessage> messages =
@@ -306,7 +306,7 @@ public async Task DirectTool_Streaming_Succeeds()
 
         // Set tool calling back to auto so that the model can decide whether to call
         // the tool again or continue the conversation based on the new user prompt
-        chatClient.Settings.ToolChoice = ToolChoice.Auto;
+        chatClient.Settings.ToolChoice = ToolChoice.CreateAutoChoice();
 
         // Run the next turn of the conversation
         updates = chatClient.CompleteChatStreamingAsync(messages, tools, CancellationToken.None).ConfigureAwait(false);