fix: 修复同 quantity 存在新用户和普通折扣档时老用户无法下单的问题

isNewUserOnlyForQuantity 原逻辑取第一条匹配记录即返回，
当同一 quantity 同时配置了 new_user_only=true 和 false 两档时，
结果依赖数组顺序，导致老用户/超24h用户触发 SubscribeNewUserOnly 错误。

修复：扫描所有同 quantity 档位，仅当存在 true 且无 false 兜底时才返回 true；
有 false 兜底则返回 false，老用户可正常购买并命中普通折扣档。

Co-Authored-By: claude-flow <ruv@ruv.net>

internal/logic/public/order/getDiscount.go

@@ -16,13 +16,23 @@ func getDiscount(discounts []types.SubscribeDiscount, inputMonths int64, isNewUs
 }
 
 // isNewUserOnlyForQuantity checks whether the matched discount tier has new_user_only enabled.
+// Returns true only when all matching tiers for the given quantity require new-user status
+// (i.e. no fallback tier with new_user_only=false exists). When both a new-user-only tier
+// and a general tier exist for the same quantity, non-new-users can still purchase via the
+// general tier, so this returns false.
 func isNewUserOnlyForQuantity(discounts []types.SubscribeDiscount, inputQuantity int64) bool {
-	for _, discount := range discounts {
-		if inputQuantity == discount.Quantity {
-			return discount.NewUserOnly
+	hasNewUserOnly := false
+	hasFallback := false
+	for _, d := range discounts {
+		if d.Quantity != inputQuantity {
+			continue
+		}
+		if d.NewUserOnly {
+			hasNewUserOnly = true
+		} else {
+			hasFallback = true
 		}
 	}
-
-	return false
+	return hasNewUserOnly && !hasFallback
 }
 

queue/logic/order/activateOrderLogic.go

@@ -1319,12 +1319,22 @@ func (l *ActivateOrderLogic) RedemptionActivate(ctx context.Context, orderInfo *
 }
 
 // isNewUserOnlyForQuantity checks whether the matched discount tier has new_user_only enabled.
+// Returns true only when all matching tiers for the given quantity require new-user status
+// (i.e. no fallback tier with new_user_only=false exists). When both a new-user-only tier
+// and a general tier exist for the same quantity, non-new-users can still purchase via the
+// general tier, so this returns false.
 func isNewUserOnlyForQuantity(discounts []internaltypes.SubscribeDiscount, inputQuantity int64) bool {
+	hasNewUserOnly := false
+	hasFallback := false
 	for _, d := range discounts {
-		if inputQuantity == d.Quantity {
-			return d.NewUserOnly
+		if d.Quantity != inputQuantity {
+			continue
+		}
+		if d.NewUserOnly {
+			hasNewUserOnly = true
+		} else {
+			hasFallback = true
 		}
 	}
-
-	return false
+	return hasNewUserOnly && !hasFallback
 }