feat(types): 统一格式落地为内核实际使用的类型 —— 私有字段泄漏归零

Phase 2 收尾（入向）。ChatRequest 从"客户端发什么就是什么"改为
UnifiedRequest（最大集合）的别名，内核真正用上了那个超集类型。

改掉的具体缺陷：

1. 私有字段泄漏归零（v1 的核心问题）
   v1 的 disable_thinking 是内核私有开关，却被序列化进交给适配器的 body，
   迫使 10 个适配器各自写 req.disable_thinking = nil 来清理。
   现在它是中立的 thinking 字段（{enabled, budget_tokens}），客户端与
   适配器都认这个词：
   - gateway/chat.go：thinkingFromClient() 把 disable_thinking 翻译成
     thinking.enabled=false；冲突时中立字段优先（它能带预算，布尔不能）
   - deepseek.lua：thinking.enabled=false → extra_body.thinking.type=disabled
   - anthropic.lua：thinking.enabled=true + budget → 原生 {type,budget_tokens}
     （enabled=false 时不传该字段——Anthropic 没有 type=disabled 这个写法）
   - 其余 7 个适配器：把"清理内核私有字段"改成"清理中立字段"

2. Tools/ToolChoice 改 json.RawMessage
   原为 []interface{}（OpenAI 原始形状 = 内核在假设某个协议）。
   内核从不解释工具 schema——它原样交给适配器，所以原始形状不损失任何
   内核侧统一性。ToolDef 结构化类型保留在包内供新适配器选用。

3. 删除 MarshalJSON 后门
   v1 手工 splice ExtraBody 进 OpenAI 形状的 body；现在 ExtraBody 是
   UnifiedRequest 上一个正正经经声明的字段。

渐进迁移：ChatRequest 保留为别名（不是新类型），49 处引用零改动编译，
语义变更不被机械改名淹没。

测试：新增 thinking_test.go（翻译链 4 例 + 泄漏回归 + tools 透传）；
vm_test.go 两处迁移到中立语义。golden 字节级未漂移。

internal/types/types.go

@@ -17,42 +17,32 @@ import (
 // provider package (which pulls in the Lua runtime).
 var ErrBusy = errors.New("provider busy")
 
-// ---- OpenAI wire request (gateway input) ----
-
-type ChatRequest struct {
-	Model           string                 `json:"model"`
-	Messages        []ChatMessage          `json:"messages"`
-	Temperature     *float64               `json:"temperature,omitempty"`
-	MaxTokens       int                    `json:"max_tokens,omitempty"`
-	Stream          bool                   `json:"stream,omitempty"`
-	Tools           []interface{}          `json:"tools,omitempty"`
-	ToolChoice      interface{}            `json:"tool_choice,omitempty"`
-	DisableThinking bool                   `json:"disable_thinking"`
-	ExtraBody       map[string]interface{} `json:"-"`
-
-	// ClientSession 是客户端自带的会话标识（请求头 x-session-affinity 等）。
-	// 不参与序列化：它只用于让适配器生成稳定的上游会话，不应泄漏给上游 body。
-	ClientSession string `json:"-"`
-}
-
-func (r *ChatRequest) MarshalJSON() ([]byte, error) {
-	type Alias ChatRequest
-	data, err := json.Marshal((*Alias)(r))
-	if err != nil {
-		return nil, err
-	}
-	if len(r.ExtraBody) == 0 {
-		return data, nil
-	}
-	var raw map[string]interface{}
-	if err := json.Unmarshal(data, &raw); err != nil {
-		return nil, err
-	}
-	for k, v := range r.ExtraBody {
-		raw[k] = v
-	}
-	return json.Marshal(raw)
-}
+// ---- in-bound request ----
+//
+// ChatRequest now lives in maxwire.go as an alias of UnifiedRequest: the
+// kernel's internal format is the maximal set (OpenAI / Anthropic / Gemini /
+// Ollama / DeepSeek fields unioned), not "whatever an OpenAI client sent". The
+// type stays named ChatRequest at every call site for now — renaming 19
+// non-test + 30 test references in one sweep would bury the semantic change in
+// mechanical noise, and an alias makes the migration free when it happens.
+//
+// The v1 struct that lived here is gone. Its fields and their fate:
+//
+//   Model/Messages/Temperature/MaxTokens/Stream  → UnifiedRequest, same tags
+//   Tools/ToolChoice                              → json.RawMessage (raw passthrough
+//                                                   to the adapter; the kernel never
+//                                                   parses them)
+//   DisableThinking  (json:"disable_thinking")    → REPLACED by Thinking. This was
+//                                                   the private field that leaked into
+//                                                   the body handed to adapters, forcing
+//                                                   10 adapters to nil it out.
+//   ExtraBody       (hand-injected by MarshalJSON) → a real, declared field on
+//                                                   UnifiedRequest — no more
+//                                                   MarshalJSON back door
+//   ClientSession   (json:"-")                     → kept, still never serialized
+//
+// The custom MarshalJSON is gone with it: its only job was splicing ExtraBody
+// into an OpenAI-shaped body, which is no longer how the type serializes.
 
 // ChatMessage supports both plain string content and multimodal arrays
 // (RawMessage preserves whatever the client sent for the adapter to process).