fix: 离线证到期重签空邮箱撞唯一索引

复用 customer_id/同名客户，禁止重复插入空 email；重签前端带回原客户。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/service/license/offline_service.go

@@ -6,6 +6,7 @@ import (
 	"backend/internal/model"
 	"backend/utils"
 	"errors"
+	"fmt"
 	"strings"
 	"time"
 
@@ -85,34 +86,24 @@ func (s *OfflineIssuer) Issue(req dto.OfflineLicenseCreate) (*dto.OfflineLicense
 			return nil, errors.New("客户不存在")
 		}
 	} else {
-		email := strings.TrimSpace(req.Email)
-		name := strings.TrimSpace(req.CustomerName)
-		if name == "" {
-			name = "离线客户"
-		}
-		if email != "" {
-			err := s.db.Where("email = ?", email).First(&customer).Error
-			if err != nil {
-				customer = model.Customer{Name: name, Email: email, Status: 1}
-				if err := s.db.Create(&customer).Error; err != nil {
-					return nil, errors.New("创建客户失败")
-				}
-			}
-		} else {
-			customer = model.Customer{Name: name, Email: "", Status: 1}
-			if err := s.db.Create(&customer).Error; err != nil {
-				return nil, errors.New("创建客户失败")
-			}
+		var err error
+		customer, err = s.resolveOrCreateCustomer(req)
+		if err != nil {
+			return nil, err
 		}
 	}
 
 	now := time.Now().UTC()
 	exp := now.AddDate(0, 0, duration)
+	claimEmail := strings.TrimSpace(req.Email)
+	if claimEmail == "" && customer.Email != "" && !strings.HasSuffix(customer.Email, "@local.invalid") {
+		claimEmail = customer.Email
+	}
 	claims := utils.OfflineLicenseClaims{
 		V:            1,
 		ProductCode:  product.Code,
 		DeviceID:     deviceID,
-		Email:        strings.TrimSpace(req.Email),
+		Email:        claimEmail,
 		PlanType:     planType,
 		IssuedAt:     now.Unix(),
 		ExpiresAt:    exp.Unix(),
@@ -175,3 +166,39 @@ func (s *OfflineIssuer) Issue(req dto.OfflineLicenseCreate) (*dto.OfflineLicense
 		PublicKey:   s.kp.OfflinePublicKeyHex(),
 	}, nil
 }
+
+// resolveOrCreateCustomer 解析或创建离线签发客户；禁止重复插入空邮箱（uniqueIndex） // Logan.Li
+func (s *OfflineIssuer) resolveOrCreateCustomer(req dto.OfflineLicenseCreate) (model.Customer, error) {
+	email := strings.TrimSpace(req.Email)
+	name := strings.TrimSpace(req.CustomerName)
+	if name == "" {
+		name = "离线客户"
+	}
+
+	var customer model.Customer
+	if email != "" {
+		if err := s.db.Where("email = ?", email).First(&customer).Error; err == nil {
+			return customer, nil
+		}
+		customer = model.Customer{Name: name, Email: email, Status: 1}
+		if err := s.db.Create(&customer).Error; err != nil {
+			// 并发下可能已被创建，再查一次 // Logan.Li
+			if err2 := s.db.Where("email = ?", email).First(&customer).Error; err2 == nil {
+				return customer, nil
+			}
+			return customer, errors.New("创建客户失败")
+		}
+		return customer, nil
+	}
+
+	// 无邮箱：优先复用同名客户，避免空邮箱触发 UNIQUE 冲突 // Logan.Li
+	if err := s.db.Where("name = ?", name).Order("id ASC").First(&customer).Error; err == nil {
+		return customer, nil
+	}
+	placeholder := fmt.Sprintf("offline+%d@local.invalid", time.Now().UnixNano())
+	customer = model.Customer{Name: name, Email: placeholder, Status: 1}
+	if err := s.db.Create(&customer).Error; err != nil {
+		return customer, errors.New("创建客户失败")
+	}
+	return customer, nil
+}