feat: decouple billing correctness from usage log batching

backend/internal/handler/sora_gateway_handler.go

@@ -399,17 +399,19 @@ func (h *SoraGatewayHandler) ChatCompletions(c *gin.Context) {
 
 		userAgent := c.GetHeader("User-Agent")
 		clientIP := ip.GetClientIP(c)
+		requestPayloadHash := service.HashUsageRequestPayload(body)
 
 		// 使用量记录通过有界 worker 池提交，避免请求热路径创建无界 goroutine。
 		h.submitUsageRecordTask(func(ctx context.Context) {
 			if err := h.gatewayService.RecordUsage(ctx, &service.RecordUsageInput{
-				Result:       result,
-				APIKey:       apiKey,
-				User:         apiKey.User,
-				Account:      account,
-				Subscription: subscription,
-				UserAgent:    userAgent,
-				IPAddress:    clientIP,
+				Result:             result,
+				APIKey:             apiKey,
+				User:               apiKey.User,
+				Account:            account,
+				Subscription:       subscription,
+				UserAgent:          userAgent,
+				IPAddress:          clientIP,
+				RequestPayloadHash: requestPayloadHash,
 			}); err != nil {
 				logger.L().With(
 					zap.String("component", "handler.sora_gateway.chat_completions"),