refactor(antigravity): 提取并同步 Schema 清理逻辑至 schema_cleaner.go

主要变更：
1. 重构代码结构：
   - 将 CleanJSONSchema 及其相关辅助函数从 request_transformer.go 提取到独立的 schema_cleaner.go 文件中，实现逻辑解耦。

2. 逻辑优化与修正：
   - 参考 Antigravity-Manager (json_schema.rs) 的实现逻辑，修正了 Schema 清洗策略。

backend/internal/service/antigravity_gateway_service.go

@@ -1320,6 +1320,14 @@ func (s *AntigravityGatewayService) ForwardGemini(ctx context.Context, c *gin.Co
 		return nil, err
 	}
 
+	// 清理 Schema
+	if cleanedBody, err := cleanGeminiRequest(injectedBody); err == nil {
+		injectedBody = cleanedBody
+		log.Printf("[Antigravity] Cleaned request schema in forwarded request for account %s", account.Name)
+	} else {
+		log.Printf("[Antigravity] Failed to clean schema: %v", err)
+	}
+
 	// 包装请求
 	wrappedBody, err := s.wrapV1InternalRequest(projectID, mappedModel, injectedBody)
 	if err != nil {
@@ -1752,6 +1760,19 @@ func (s *AntigravityGatewayService) handleGeminiStreamingResponse(c *gin.Context
 					if u := extractGeminiUsage(parsed); u != nil {
 						usage = u
 					}
+					// Check for MALFORMED_FUNCTION_CALL
+					if candidates, ok := parsed["candidates"].([]any); ok && len(candidates) > 0 {
+						if cand, ok := candidates[0].(map[string]any); ok {
+							if fr, ok := cand["finishReason"].(string); ok && fr == "MALFORMED_FUNCTION_CALL" {
+								log.Printf("[Antigravity] MALFORMED_FUNCTION_CALL detected in forward stream")
+								if content, ok := cand["content"]; ok {
+									if b, err := json.Marshal(content); err == nil {
+										log.Printf("[Antigravity] Malformed content: %s", string(b))
+									}
+								}
+							}
+						}
+					}
 				}
 
 				if firstTokenMs == nil {
@@ -1901,6 +1922,20 @@ func (s *AntigravityGatewayService) handleGeminiStreamToNonStreaming(c *gin.Cont
 				usage = u
 			}
 
+			// Check for MALFORMED_FUNCTION_CALL
+			if candidates, ok := parsed["candidates"].([]any); ok && len(candidates) > 0 {
+				if cand, ok := candidates[0].(map[string]any); ok {
+					if fr, ok := cand["finishReason"].(string); ok && fr == "MALFORMED_FUNCTION_CALL" {
+						log.Printf("[Antigravity] MALFORMED_FUNCTION_CALL detected in forward non-stream collect")
+						if content, ok := cand["content"]; ok {
+							if b, err := json.Marshal(content); err == nil {
+								log.Printf("[Antigravity] Malformed content: %s", string(b))
+							}
+						}
+					}
+				}
+			}
+
 			// 保留最后一个有 parts 的响应
 			if parts := extractGeminiParts(parsed); len(parts) > 0 {
 				lastWithParts = parsed
@@ -2541,3 +2576,55 @@ func isImageGenerationModel(model string) bool {
 		modelLower == "gemini-2.5-flash-image-preview" ||
 		strings.HasPrefix(modelLower, "gemini-2.5-flash-image-")
 }
+
+// cleanGeminiRequest 清理 Gemini 请求体中的 Schema
+func cleanGeminiRequest(body []byte) ([]byte, error) {
+	var payload map[string]any
+	if err := json.Unmarshal(body, &payload); err != nil {
+		return nil, err
+	}
+
+	modified := false
+
+	// 1. 清理 Tools
+	if tools, ok := payload["tools"].([]any); ok && len(tools) > 0 {
+		for _, t := range tools {
+			toolMap, ok := t.(map[string]any)
+			if !ok {
+				continue
+			}
+
+			// function_declarations (snake_case) or functionDeclarations (camelCase)
+			var funcs []any
+			if f, ok := toolMap["functionDeclarations"].([]any); ok {
+				funcs = f
+			} else if f, ok := toolMap["function_declarations"].([]any); ok {
+				funcs = f
+			}
+
+			if len(funcs) == 0 {
+				continue
+			}
+
+			for _, f := range funcs {
+				funcMap, ok := f.(map[string]any)
+				if !ok {
+					continue
+				}
+
+				if params, ok := funcMap["parameters"].(map[string]any); ok {
+					antigravity.DeepCleanUndefined(params)
+					cleaned := antigravity.CleanJSONSchema(params)
+					funcMap["parameters"] = cleaned
+					modified = true
+				}
+			}
+		}
+	}
+
+	if !modified {
+		return body, nil
+	}
+
+	return json.Marshal(payload)
+}