feat: enhance error handling in GeminiHelper and streamline response processing

- Added status code mapping handling in GeminiHelper to reset status codes based on response.
- Removed redundant candidate check in GeminiTextGenerationHandler to simplify response processing.

relay/channel/gemini/relay-gemini-native.go

@@ -35,19 +35,6 @@ func GeminiTextGenerationHandler(c *gin.Context, resp *http.Response, info *rela
 		return nil, service.OpenAIErrorWrapper(err, "unmarshal_response_body_failed", http.StatusInternalServerError)
 	}
 
-	// 检查是否有候选响应
-	if len(geminiResponse.Candidates) == 0 {
-		return nil, &dto.OpenAIErrorWithStatusCode{
-			Error: dto.OpenAIError{
-				Message: "No candidates returned",
-				Type:    "server_error",
-				Param:   "",
-				Code:    500,
-			},
-			StatusCode: resp.StatusCode,
-		}
-	}
-
 	// 计算使用量（基于 UsageMetadata）
 	usage := dto.Usage{
 		PromptTokens:     geminiResponse.UsageMetadata.PromptTokenCount,

relay/relay-gemini.go

@@ -165,8 +165,23 @@ func GeminiHelper(c *gin.Context) (openaiErr *dto.OpenAIErrorWithStatusCode) {
 		return service.OpenAIErrorWrapperLocal(err, "do_request_failed", http.StatusInternalServerError)
 	}
 
+	statusCodeMappingStr := c.GetString("status_code_mapping")
+
+	var httpResp *http.Response
+	if resp != nil {
+		httpResp = resp.(*http.Response)
+		relayInfo.IsStream = relayInfo.IsStream || strings.HasPrefix(httpResp.Header.Get("Content-Type"), "text/event-stream")
+		if httpResp.StatusCode != http.StatusOK {
+			openaiErr = service.RelayErrorHandler(httpResp, false)
+			// reset status code 重置状态码
+			service.ResetStatusCode(openaiErr, statusCodeMappingStr)
+			return openaiErr
+		}
+	}
+
 	usage, openaiErr := adaptor.DoResponse(c, resp.(*http.Response), relayInfo)
 	if openaiErr != nil {
+		service.ResetStatusCode(openaiErr, statusCodeMappingStr)
 		return openaiErr
 	}