fix: 修复gpt->claude转换无法命中codex缓存问题

backend/internal/service/openai_gateway_service.go

@@ -3646,6 +3646,13 @@ type OpenAIRecordUsageInput struct {
 // RecordUsage records usage and deducts balance
 func (s *OpenAIGatewayService) RecordUsage(ctx context.Context, input *OpenAIRecordUsageInput) error {
 	result := input.Result
+
+	// 跳过所有 token 均为零的用量记录——上游未返回 usage 时不应写入数据库
+	if result.Usage.InputTokens == 0 && result.Usage.OutputTokens == 0 &&
+		result.Usage.CacheCreationInputTokens == 0 && result.Usage.CacheReadInputTokens == 0 {
+		return nil
+	}
+
 	apiKey := input.APIKey
 	user := input.User
 	account := input.Account