fix(redeem): 用户兑换历史不返回备注

- 用户侧 RedeemCode DTO 移除 notes 字段，避免泄露内部备注\n- 新增 AdminRedeemCode，并调整管理员兑换码接口继续返回 notes\n- 增加 /api/v1/redeem/history 契约测试，确保用户侧响应不包含 notes

backend/internal/handler/admin/redeem_handler.go

@@ -54,9 +54,9 @@ func (h *RedeemHandler) List(c *gin.Context) {
 		return
 	}
 
-	out := make([]dto.RedeemCode, 0, len(codes))
+	out := make([]dto.AdminRedeemCode, 0, len(codes))
 	for i := range codes {
-		out = append(out, *dto.RedeemCodeFromService(&codes[i]))
+		out = append(out, *dto.RedeemCodeFromServiceAdmin(&codes[i]))
 	}
 	response.Paginated(c, out, total, page, pageSize)
 }
@@ -76,7 +76,7 @@ func (h *RedeemHandler) GetByID(c *gin.Context) {
 		return
 	}
 
-	response.Success(c, dto.RedeemCodeFromService(code))
+	response.Success(c, dto.RedeemCodeFromServiceAdmin(code))
 }
 
 // Generate handles generating new redeem codes
@@ -100,9 +100,9 @@ func (h *RedeemHandler) Generate(c *gin.Context) {
 		return
 	}
 
-	out := make([]dto.RedeemCode, 0, len(codes))
+	out := make([]dto.AdminRedeemCode, 0, len(codes))
 	for i := range codes {
-		out = append(out, *dto.RedeemCodeFromService(&codes[i]))
+		out = append(out, *dto.RedeemCodeFromServiceAdmin(&codes[i]))
 	}
 	response.Success(c, out)
 }
@@ -163,7 +163,7 @@ func (h *RedeemHandler) Expire(c *gin.Context) {
 		return
 	}
 
-	response.Success(c, dto.RedeemCodeFromService(code))
+	response.Success(c, dto.RedeemCodeFromServiceAdmin(code))
 }
 
 // GetStats handles getting redeem code statistics

backend/internal/handler/dto/mappers.go

@@ -304,7 +304,24 @@ func RedeemCodeFromService(rc *service.RedeemCode) *RedeemCode {
 	if rc == nil {
 		return nil
 	}
-	return &RedeemCode{
+	out := redeemCodeFromServiceBase(rc)
+	return &out
+}
+
+// RedeemCodeFromServiceAdmin converts a service RedeemCode to DTO for admin users.
+// It includes notes - user-facing endpoints must not use this.
+func RedeemCodeFromServiceAdmin(rc *service.RedeemCode) *AdminRedeemCode {
+	if rc == nil {
+		return nil
+	}
+	return &AdminRedeemCode{
+		RedeemCode: redeemCodeFromServiceBase(rc),
+		Notes:     rc.Notes,
+	}
+}
+
+func redeemCodeFromServiceBase(rc *service.RedeemCode) RedeemCode {
+	return RedeemCode{
 		ID:           rc.ID,
 		Code:         rc.Code,
 		Type:         rc.Type,
@@ -312,7 +329,6 @@ func RedeemCodeFromService(rc *service.RedeemCode) *RedeemCode {
 		Status:       rc.Status,
 		UsedBy:       rc.UsedBy,
 		UsedAt:       rc.UsedAt,
-		Notes:        rc.Notes,
 		CreatedAt:    rc.CreatedAt,
 		GroupID:      rc.GroupID,
 		ValidityDays: rc.ValidityDays,

backend/internal/handler/dto/types.go

@@ -193,7 +193,6 @@ type RedeemCode struct {
 	Status    string     `json:"status"`
 	UsedBy    *int64     `json:"used_by"`
 	UsedAt    *time.Time `json:"used_at"`
-	Notes     string     `json:"notes"`
 	CreatedAt time.Time  `json:"created_at"`
 
 	GroupID      *int64 `json:"group_id"`
@@ -203,6 +202,14 @@ type RedeemCode struct {
 	Group *Group `json:"group,omitempty"`
 }
 
+// AdminRedeemCode 是管理员接口使用的 redeem code DTO（包含 notes 等字段）。
+// 注意：普通用户接口不得返回 notes 等内部信息。
+type AdminRedeemCode struct {
+	RedeemCode
+
+	Notes string `json:"notes"`
+}
+
 // UsageLog 是普通用户接口使用的 usage log DTO（不包含管理员字段）。
 type UsageLog struct {
 	ID        int64  `json:"id"`