fix: audit findings - PUT response rechargeURL, NaN guard, debug logs

- Add BalanceLowNotifyRechargeURL to admin PUT response (fixes save-then-stale)
- Add ?? 1 guard for account_rate_multiplier in UsageTable else branch
- Downgrade high-frequency notify logs from Info to Debug
- Extract "Sub2API" magic string to defaultSiteName constant

backend/cmd/server/VERSION

@@ -1 +1 @@
-0.1.110.42
+0.1.110.43

backend/internal/handler/admin/setting_handler.go

@@ -1072,6 +1072,7 @@ func (h *SettingHandler) UpdateSettings(c *gin.Context) {
 		EnableCCHSigning:                     updatedSettings.EnableCCHSigning,
 		BalanceLowNotifyEnabled:              updatedSettings.BalanceLowNotifyEnabled,
 		BalanceLowNotifyThreshold:            updatedSettings.BalanceLowNotifyThreshold,
+		BalanceLowNotifyRechargeURL:          updatedSettings.BalanceLowNotifyRechargeURL,
 		AccountQuotaNotifyEnabled:            updatedSettings.AccountQuotaNotifyEnabled,
 		AccountQuotaNotifyEmails:             dto.NotifyEmailEntriesFromService(updatedSettings.AccountQuotaNotifyEmails),
 		PaymentEnabled:                       updatedPaymentCfg.Enabled,

backend/internal/service/balance_notify_service.go

@@ -21,6 +21,8 @@ const (
 	quotaDimDaily  = "daily"
 	quotaDimWeekly = "weekly"
 	quotaDimTotal  = "total"
+
+	defaultSiteName = "Sub2API"
 )
 
 // quotaDimLabels maps dimension names to display labels.
@@ -79,7 +81,7 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 
 	globalEnabled, globalThreshold, rechargeURL := s.getBalanceNotifyConfig(ctx)
 	if !globalEnabled {
-		slog.Info("CheckBalanceAfterDeduction: global notify disabled", "user_id", user.ID)
+		slog.Debug("CheckBalanceAfterDeduction: global notify disabled", "user_id", user.ID)
 		return
 	}
 
@@ -100,7 +102,7 @@ func (s *BalanceNotifyService) CheckBalanceAfterDeduction(ctx context.Context, u
 	}
 
 	newBalance := oldBalance - cost
-	slog.Info("CheckBalanceAfterDeduction: crossing check",
+	slog.Debug("CheckBalanceAfterDeduction: crossing check",
 		"user_id", user.ID,
 		"old_balance", oldBalance,
 		"new_balance", newBalance,
@@ -324,7 +326,7 @@ func (s *BalanceNotifyService) getAccountQuotaNotifyEmails(ctx context.Context)
 func (s *BalanceNotifyService) getSiteName(ctx context.Context) string {
 	name, err := s.settingRepo.GetValue(ctx, SettingKeySiteName)
 	if err != nil || name == "" {
-		return "Sub2API"
+		return defaultSiteName
 	}
 	return name
 }

backend/internal/service/gateway_service.go

@@ -7555,7 +7555,7 @@ func notifyBalanceLow(p *postUsageBillingParams, deps *billingDeps, result *Usag
 	}
 
 	oldBalance := resolveOldBalance(p, result)
-	slog.Info("notifyBalanceLow: calling CheckBalanceAfterDeduction",
+	slog.Debug("notifyBalanceLow: calling CheckBalanceAfterDeduction",
 		"user_id", p.User.ID,
 		"old_balance", oldBalance,
 		"cost", p.Cost.ActualCost,
@@ -7599,7 +7599,7 @@ func notifyAccountQuota(p *postUsageBillingParams, deps *billingDeps, result *Us
 	if result != nil {
 		quotaState = result.QuotaState
 	}
-	slog.Info("notifyAccountQuota: calling CheckAccountQuotaAfterIncrement",
+	slog.Debug("notifyAccountQuota: calling CheckAccountQuotaAfterIncrement",
 		"account_id", p.Account.ID,
 		"account_cost", accountCost,
 		"has_quota_state", quotaState != nil,

frontend/src/components/admin/usage/UsageTable.vue

@@ -155,7 +155,7 @@
               </div>
             </div>
             <div v-if="row.account_rate_multiplier != null" class="mt-0.5 text-[11px] text-gray-400">
-              A ${{ (row.account_stats_cost != null ? row.account_stats_cost * (row.account_rate_multiplier ?? 1) : row.total_cost * row.account_rate_multiplier).toFixed(6) }}
+              A ${{ (row.account_stats_cost != null ? row.account_stats_cost * (row.account_rate_multiplier ?? 1) : row.total_cost * (row.account_rate_multiplier ?? 1)).toFixed(6) }}
             </div>
           </div>
         </template>