功能：发货链接支持永久有效，默认 TTL=0

- DELIVERY_LINK_TTL_MINUTES 设为 0 或负数时链接永久有效（expires_at 存 NULL），
  默认值由 120 改为 0，本地 .env 同步改为永久
- 新增 delivery_link_generated_at 列区分从未生成与永久链接，兼容历史数据
- 永久链接授权仅校验 HMAC 签名、不校验过期（exp=0），作废/恢复语义不变
- 前端链接有效期列对永久链接显示"永久有效"

backend/internal/service/delivery.go

@@ -73,8 +73,9 @@ func NewDeliveryService(fulfillment *FulfillmentService, bffBaseURL, channel, li
 	if linkSecret == "" {
 		linkSecret = "affiliate-dash-delivery-link-secret"
 	}
-	if linkTTLMinutes <= 0 {
-		linkTTLMinutes = 120
+	// linkTTLMinutes <= 0 表示链接永久有效（0 为默认值）。
+	if linkTTLMinutes < 0 {
+		linkTTLMinutes = 0
 	}
 	return &DeliveryService{
 		fulfillment: fulfillment,
@@ -133,11 +134,11 @@ type DeliveryBindResult struct {
 }
 
 type DeliveryLinkResult struct {
-	OrderNo     string    `json:"order_no"`
-	DeliveryURL string    `json:"delivery_url"`
-	ExpiresAt   time.Time `json:"expires_at"`
-	Exp         int64     `json:"exp"`
-	Sign        string    `json:"sign"`
+	OrderNo     string     `json:"order_no"`
+	DeliveryURL string     `json:"delivery_url"`
+	ExpiresAt   *time.Time `json:"expires_at,omitempty"` // null 表示永久有效
+	Exp         int64      `json:"exp"`
+	Sign        string     `json:"sign"`
 }
 
 type DeliverySubmitResult struct {
@@ -627,7 +628,12 @@ func (s *DeliveryService) GetOrCreateDeliveryLink(merchantID uint, orderNo, requ
 	}
 	// 复用未过期链接：已交付/发货中订单也允许查看兑换结果或进度，仅停止发放新链接。
 	if order.DeliveryLinkExpiresAt != nil && order.DeliveryLinkExpiresAt.After(now) {
-		return s.buildDeliveryLinkResult(order.OrderNo, order.DeliveryLinkExpiresAt.UTC().Truncate(time.Second), requestBaseURL), nil
+		expiresAt := order.DeliveryLinkExpiresAt.UTC().Truncate(time.Second)
+		return s.buildDeliveryLinkResult(order.OrderNo, &expiresAt, requestBaseURL), nil
+	}
+	// 永久有效链接（已生成、未作废、无有效期）直接复用，不重复生成。
+	if order.DeliveryLinkGeneratedAt != nil && order.DeliveryLinkExpiresAt == nil {
+		return s.buildDeliveryLinkResult(order.OrderNo, nil, requestBaseURL), nil
 	}
 	// 仅待发货（含可重试的发货失败）订单能生成或续期新链接。
 	canShip, reason := CanFulfill(order)
@@ -637,12 +643,17 @@ func (s *DeliveryService) GetOrCreateDeliveryLink(merchantID uint, orderNo, requ
 		}
 		return nil, newDeliveryHTTPError(http.StatusBadRequest, reason)
 	}
-	expiresAt := now.Add(s.linkTTL).UTC().Truncate(time.Second)
+	var expiresAt *time.Time
+	if s.linkTTL > 0 {
+		value := now.Add(s.linkTTL).UTC().Truncate(time.Second)
+		expiresAt = &value
+	}
 	if err := s.fulfillment.db.Model(&model.FulfillmentOrder{}).
 		Where("id = ?", order.ID).
 		Updates(map[string]interface{}{
-			"delivery_link_expires_at": expiresAt,
-			"delivery_link_revoked_at": nil,
+			"delivery_link_expires_at":   expiresAt,
+			"delivery_link_revoked_at":   nil,
+			"delivery_link_generated_at": now,
 		}).Error; err != nil {
 		return nil, err
 	}
@@ -689,22 +700,34 @@ func (s *DeliveryService) RestoreDeliveryLink(merchantID, actorUserID uint, orde
 		}
 		return nil, newDeliveryHTTPError(http.StatusBadRequest, reason)
 	}
-	expiresAt := time.Now().UTC().Add(s.linkTTL).Truncate(time.Second)
-	if order.DeliveryLinkExpiresAt != nil && expiresAt.Equal(order.DeliveryLinkExpiresAt.UTC().Truncate(time.Second)) {
-		expiresAt = expiresAt.Add(time.Second)
+	now := time.Now().UTC()
+	var expiresAt *time.Time
+	if s.linkTTL > 0 {
+		value := now.Add(s.linkTTL).Truncate(time.Second)
+		if order.DeliveryLinkExpiresAt != nil && value.Equal(order.DeliveryLinkExpiresAt.UTC().Truncate(time.Second)) {
+			value = value.Add(time.Second)
+		}
+		expiresAt = &value
 	}
 	if err := s.fulfillment.db.Transaction(func(tx *gorm.DB) error {
 		if err := tx.Model(&model.FulfillmentOrder{}).
 			Where("id = ?", order.ID).
 			Updates(map[string]interface{}{
-				"delivery_link_expires_at": expiresAt,
-				"delivery_link_revoked_at": nil,
+				"delivery_link_expires_at":   expiresAt,
+				"delivery_link_revoked_at":   nil,
+				"delivery_link_generated_at": now,
 			}).Error; err != nil {
 			return err
 		}
-		return writeAudit(tx, &merchantID, optionalUint(actorUserID), nil, "delivery_link.restore", "fulfillment_order", order.OrderNo, map[string]interface{}{
-			"expires_at": timeutil.FormatAPITime(expiresAt),
-		})
+		metadata := map[string]interface{}{
+			"generated_at": timeutil.FormatAPITime(now),
+		}
+		if expiresAt != nil {
+			metadata["expires_at"] = timeutil.FormatAPITime(*expiresAt)
+		} else {
+			metadata["permanent"] = true
+		}
+		return writeAudit(tx, &merchantID, optionalUint(actorUserID), nil, "delivery_link.restore", "fulfillment_order", order.OrderNo, metadata)
 	}); err != nil {
 		return nil, err
 	}