fix(handler): 修复 gjson 迁移后的请求校验语义回退

- OpenAI handler: 添加 gjson.ValidBytes 校验 JSON 合法性；model 校验改为
  检查 gjson.String 类型而非仅判断非空（拒绝 model:123 等非法类型）；stream
  字段添加 True/False 类型检查；sjson.SetBytes 返回值显式处理错误
- Sora handler: 添加 gjson.ValidBytes 校验；model 校验同上改为类型检查；
  messages 校验从 Exists+Type==JSON 改为 IsArray+len>0（拒绝空数组和对象）
- 补充 TestOpenAIHandler_GjsonValidation 和更新 TestSoraHandler_ValidationExtraction
  覆盖新增的边界校验场景
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/handler/openai_gateway_handler.go

@@ -95,15 +95,26 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 
 	setOpsRequestContext(c, "", false, body)
 
-	// 使用 gjson 只读提取字段做校验，避免完整 Unmarshal
-	reqModel := gjson.GetBytes(body, "model").String()
-	reqStream := gjson.GetBytes(body, "stream").Bool()
+	// 校验请求体 JSON 合法性
+	if !gjson.ValidBytes(body) {
+		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "Failed to parse request body")
+		return
+	}
 
-	// 验证 model 必填
-	if reqModel == "" {
+	// 使用 gjson 只读提取字段做校验，避免完整 Unmarshal
+	modelResult := gjson.GetBytes(body, "model")
+	if !modelResult.Exists() || modelResult.Type != gjson.String || modelResult.String() == "" {
 		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "model is required")
 		return
 	}
+	reqModel := modelResult.String()
+
+	streamResult := gjson.GetBytes(body, "stream")
+	if streamResult.Exists() && streamResult.Type != gjson.True && streamResult.Type != gjson.False {
+		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "invalid stream field type")
+		return
+	}
+	reqStream := streamResult.Bool()
 
 	userAgent := c.GetHeader("User-Agent")
 	isCodexCLI := openai.IsCodexCLIRequest(userAgent) || (h.cfg != nil && h.cfg.Gateway.ForceCodexCLI)
@@ -111,7 +122,12 @@ func (h *OpenAIGatewayHandler) Responses(c *gin.Context) {
 		existingInstructions := gjson.GetBytes(body, "instructions").String()
 		if strings.TrimSpace(existingInstructions) == "" {
 			if instructions := strings.TrimSpace(service.GetOpenCodeInstructions()); instructions != "" {
-				body, _ = sjson.SetBytes(body, "instructions", instructions)
+				newBody, err := sjson.SetBytes(body, "instructions", instructions)
+				if err != nil {
+					h.errorResponse(c, http.StatusInternalServerError, "api_error", "Failed to process request")
+					return
+				}
+				body = newBody
 			}
 		}
 	}

backend/internal/handler/openai_gateway_handler_test.go

@@ -121,7 +121,11 @@ func TestOpenAIHandler_GjsonExtraction(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			body := []byte(tt.body)
-			model := gjson.GetBytes(body, "model").String()
+			modelResult := gjson.GetBytes(body, "model")
+			model := ""
+			if modelResult.Type == gjson.String {
+				model = modelResult.String()
+			}
 			stream := gjson.GetBytes(body, "stream").Bool()
 			require.Equal(t, tt.wantModel, model)
 			require.Equal(t, tt.wantStream, stream)
@@ -129,6 +133,38 @@ func TestOpenAIHandler_GjsonExtraction(t *testing.T) {
 	}
 }
 
+// TestOpenAIHandler_GjsonValidation 验证修复后的 JSON 合法性和类型校验
+func TestOpenAIHandler_GjsonValidation(t *testing.T) {
+	// 非法 JSON 被 gjson.ValidBytes 拦截
+	require.False(t, gjson.ValidBytes([]byte(`{invalid json`)))
+
+	// model 为数字 → 类型不是 gjson.String，应被拒绝
+	body := []byte(`{"model":123}`)
+	modelResult := gjson.GetBytes(body, "model")
+	require.True(t, modelResult.Exists())
+	require.NotEqual(t, gjson.String, modelResult.Type)
+
+	// model 为 null → 类型不是 gjson.String，应被拒绝
+	body2 := []byte(`{"model":null}`)
+	modelResult2 := gjson.GetBytes(body2, "model")
+	require.True(t, modelResult2.Exists())
+	require.NotEqual(t, gjson.String, modelResult2.Type)
+
+	// stream 为 string → 类型既不是 True 也不是 False，应被拒绝
+	body3 := []byte(`{"model":"gpt-4","stream":"true"}`)
+	streamResult := gjson.GetBytes(body3, "stream")
+	require.True(t, streamResult.Exists())
+	require.NotEqual(t, gjson.True, streamResult.Type)
+	require.NotEqual(t, gjson.False, streamResult.Type)
+
+	// stream 为 int → 同上
+	body4 := []byte(`{"model":"gpt-4","stream":1}`)
+	streamResult2 := gjson.GetBytes(body4, "stream")
+	require.True(t, streamResult2.Exists())
+	require.NotEqual(t, gjson.True, streamResult2.Type)
+	require.NotEqual(t, gjson.False, streamResult2.Type)
+}
+
 // TestOpenAIHandler_InstructionsInjection 验证 instructions 的 gjson/sjson 注入逻辑
 func TestOpenAIHandler_InstructionsInjection(t *testing.T) {
 	// 测试 1：无 instructions → 注入
@@ -148,4 +184,11 @@ func TestOpenAIHandler_InstructionsInjection(t *testing.T) {
 	body3 := []byte(`{"model":"gpt-4","instructions":"   "}`)
 	existing3 := strings.TrimSpace(gjson.GetBytes(body3, "instructions").String())
 	require.Empty(t, existing3)
+
+	// 测试 4：sjson.SetBytes 返回错误时不应 panic
+	// 正常 JSON 不会产生 sjson 错误，验证返回值被正确处理
+	validBody := []byte(`{"model":"gpt-4"}`)
+	result, setErr := sjson.SetBytes(validBody, "instructions", "hello")
+	require.NoError(t, setErr)
+	require.True(t, gjson.ValidBytes(result))
 }

backend/internal/handler/sora_gateway_handler.go

@@ -106,13 +106,22 @@ func (h *SoraGatewayHandler) ChatCompletions(c *gin.Context) {
 
 	setOpsRequestContext(c, "", false, body)
 
+	// 校验请求体 JSON 合法性
+	if !gjson.ValidBytes(body) {
+		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "Failed to parse request body")
+		return
+	}
+
 	// 使用 gjson 只读提取字段做校验，避免完整 Unmarshal
-	reqModel := gjson.GetBytes(body, "model").String()
-	if reqModel == "" {
+	modelResult := gjson.GetBytes(body, "model")
+	if !modelResult.Exists() || modelResult.Type != gjson.String || modelResult.String() == "" {
 		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "model is required")
 		return
 	}
-	if !gjson.GetBytes(body, "messages").Exists() || gjson.GetBytes(body, "messages").Type != gjson.JSON {
+	reqModel := modelResult.String()
+
+	msgsResult := gjson.GetBytes(body, "messages")
+	if !msgsResult.IsArray() || len(msgsResult.Array()) == 0 {
 		h.errorResponse(c, http.StatusBadRequest, "invalid_request_error", "messages is required")
 		return
 	}

backend/internal/handler/sora_gateway_handler_test.go

@@ -440,18 +440,35 @@ func TestSoraHandler_StreamForcing(t *testing.T) {
 func TestSoraHandler_ValidationExtraction(t *testing.T) {
 	// model 缺失
 	body := []byte(`{"messages":[{"role":"user","content":"test"}]}`)
-	model := gjson.GetBytes(body, "model").String()
-	require.Empty(t, model)
+	modelResult := gjson.GetBytes(body, "model")
+	require.True(t, !modelResult.Exists() || modelResult.Type != gjson.String || modelResult.String() == "")
+
+	// model 为数字 → 类型不是 gjson.String，应被拒绝
+	body1b := []byte(`{"model":123,"messages":[{"role":"user","content":"test"}]}`)
+	modelResult1b := gjson.GetBytes(body1b, "model")
+	require.True(t, modelResult1b.Exists())
+	require.NotEqual(t, gjson.String, modelResult1b.Type)
 
 	// messages 缺失
 	body2 := []byte(`{"model":"sora"}`)
-	require.False(t, gjson.GetBytes(body2, "messages").Exists())
+	require.False(t, gjson.GetBytes(body2, "messages").IsArray())
 
-	// messages 不是 JSON 数组
+	// messages 不是 JSON 数组（字符串）
 	body3 := []byte(`{"model":"sora","messages":"not array"}`)
-	msgResult := gjson.GetBytes(body3, "messages")
-	require.True(t, msgResult.Exists())
-	require.NotEqual(t, gjson.JSON, msgResult.Type) // string 类型，不是 JSON 数组
+	require.False(t, gjson.GetBytes(body3, "messages").IsArray())
+
+	// messages 是对象而非数组 → IsArray 返回 false
+	body4 := []byte(`{"model":"sora","messages":{}}`)
+	require.False(t, gjson.GetBytes(body4, "messages").IsArray())
+
+	// messages 是空数组 → IsArray 为 true 但 len==0，应被拒绝
+	body5 := []byte(`{"model":"sora","messages":[]}`)
+	msgsResult := gjson.GetBytes(body5, "messages")
+	require.True(t, msgsResult.IsArray())
+	require.Equal(t, 0, len(msgsResult.Array()))
+
+	// 非法 JSON 被 gjson.ValidBytes 拦截
+	require.False(t, gjson.ValidBytes([]byte(`{invalid`)))
 }
 
 // TestGenerateOpenAISessionHash_WithBody 验证 generateOpenAISessionHash 的 body/header 解析逻辑