feat: 新增方案 C 的 Handoff 路由宿主，并让抽城市支持自然语言。

把图 JSON 编译成 CreateHandoffBuilderWith + WithHandoff；Agent 固定 Id 以免交接工具名错位；DeepSeek 关闭 thinking，避免多轮丢掉 reasoning_content 导致 400。

MAF1.Core/Utils/AgentFactory.cs

@@ -15,6 +15,7 @@ namespace MAF1.Utils;
 public sealed class AgentFactory
 {
     private readonly ChatClient _chatClient;
+    private readonly bool _disableDeepSeekThinking;
 
     public AgentFactory(LlmOptions options)
     {
@@ -33,6 +34,8 @@ public sealed class AgentFactory
             ? DefaultModelFor(options.Endpoint)
             : options.Model;
 
+        _disableDeepSeekThinking = LooksLikeDeepSeek(options.Endpoint);
+
         if (LooksLikeAzureOpenAI(options.Endpoint))
         {
             Console.Error.WriteLine($"使用 Azure OpenAI: {options.Endpoint}  部署: {model}");
@@ -48,14 +51,34 @@ public sealed class AgentFactory
         }
 
         Console.Error.WriteLine($"使用 OpenAI 兼容接口: {clientOptions.Endpoint?.ToString() ?? "https://api.openai.com/v1"}  模型: {model}");
+        if (_disableDeepSeekThinking)
+        {
+            Console.Error.WriteLine("已关闭 DeepSeek thinking，避免 Handoff 多轮丢掉 reasoning_content 导致 HTTP 400。");
+        }
+
         _chatClient = new OpenAIClient(new ApiKeyCredential(options.ApiKey), clientOptions)
             .GetChatClient(model);
     }
 
-    /// <summary>把 ChatClient 包成 Microsoft.Agents.AI 的 AIAgent，并挂上 tools。</summary>
-    public AIAgent CreateAgent(string name, string instructions, IList<AITool>? tools = null)
+    /// <summary>把 ChatClient 包成 Microsoft.Agents.AI 的 AIAgent，并挂上 tools。Id 固定为 name，Handoff 工具才是 handoff_to_n1。</summary>
+    public AIAgent CreateAgent(string name, string instructions, IList<AITool>? tools = null, string? description = null)
     {
-        return _chatClient.AsAIAgent(instructions: instructions, name: name, tools: tools);
+        ChatOptions chatOptions = new()
+        {
+            Instructions = instructions,
+            Tools = tools,
+        };
+        ChatClientAgentOptions options = new()
+        {
+            Id = name,
+            Name = name,
+            Description = description,
+            ChatOptions = chatOptions,
+        };
+        return _chatClient.AsAIAgent(options, clientFactory: inner =>
+            _disableDeepSeekThinking
+                ? new ConfigureOptionsChatClient(inner, DeepSeekThinking.Disable)
+                : inner);
     }
 
     /// <summary>合并配置文件和环境变量。插件进程里环境变量通常由宿主写入。</summary>
@@ -78,6 +101,10 @@ public sealed class AgentFactory
         return "gpt-4o-mini";
     }
 
+    private static bool LooksLikeDeepSeek(string? endpoint)
+        => !string.IsNullOrWhiteSpace(endpoint)
+            && endpoint.Contains("deepseek", StringComparison.OrdinalIgnoreCase);
+
     private static bool LooksLikeAzureOpenAI(string? endpoint)
     {
         if (string.IsNullOrWhiteSpace(endpoint) || !Uri.TryCreate(endpoint, UriKind.Absolute, out Uri? uri))

MAF1.Core/Utils/DeepSeekThinking.cs

@@ -0,0 +1,28 @@
+using System.ClientModel.Primitives;
+using System.Text.Json;
+using Microsoft.Extensions.AI;
+using OpenAI.Chat;
+
+namespace MAF1.Utils;
+
+/// <summary>
+/// DeepSeek V4 默认开 thinking。Handoff 多轮带 tools 时必须回传 reasoning_content，
+/// 客户端会丢掉该字段导致 HTTP 400。请求里关闭 thinking 即可。
+/// </summary>
+internal static class DeepSeekThinking
+{
+    public static void Disable(ChatOptions options)
+    {
+        options.RawRepresentationFactory = _ =>
+        {
+            ChatCompletionOptions raw = new();
+#pragma warning disable SCME0001
+            raw.Patch.Set("$.thinking"u8, BinaryData.FromObjectAsJson(new Dictionary<string, string>
+            {
+                ["type"] = "disabled",
+            }));
+#pragma warning restore SCME0001
+            return raw;
+        };
+    }
+}