fix(listener): reclaim soft-deleted names so UNIQUE(name) can be reused

backend/internal/listener/service.go

@@ -123,6 +123,9 @@ func (s *Service) Delete(id uint) error {
 	if err := s.db.Delete(&models.Listener{}, id).Error; err != nil {
 		return fmt.Errorf("failed to delete listener: %w", err)
 	}
+	// Soft-delete keeps the row; rename so UNIQUE(name) can be reused immediately.
+	freed := fmt.Sprintf("%s__deleted_%d", previous.Name, id)
+	_ = s.db.Unscoped().Model(&models.Listener{}).Where("id = ?", id).Update("name", freed).Error
 	if err := s.regenerateConfigLocked(); err != nil {
 		if rollbackErr := s.db.Unscoped().Save(&previous).Error; rollbackErr != nil {
 			return fmt.Errorf("%v; rollback deleted listener failed: %w", err, rollbackErr)
@@ -145,17 +148,33 @@ func (s *Service) ensureUniqueName(candidate *models.Listener) error {
 	if name == "" {
 		return fmt.Errorf("listener name is required")
 	}
-	var count int64
+	// Only live rows should block create/update. Soft-deleted rows still occupy
+	// the SQLite UNIQUE index, so reclaim those names first.
+	var active int64
 	q := s.db.Model(&models.Listener{}).Where("name = ?", name)
 	if candidate.ID != 0 {
 		q = q.Where("id <> ?", candidate.ID)
 	}
-	if err := q.Count(&count).Error; err != nil {
+	if err := q.Count(&active).Error; err != nil {
 		return fmt.Errorf("check listener name uniqueness: %w", err)
 	}
-	if count > 0 {
+	if active > 0 {
 		return fmt.Errorf("listener name %q already exists", name)
 	}
+	var soft []models.Listener
+	sq := s.db.Unscoped().Where("name = ? AND deleted_at IS NOT NULL", name)
+	if candidate.ID != 0 {
+		sq = sq.Where("id <> ?", candidate.ID)
+	}
+	if err := sq.Find(&soft).Error; err != nil {
+		return fmt.Errorf("check soft-deleted listener names: %w", err)
+	}
+	for _, row := range soft {
+		newName := fmt.Sprintf("%s__deleted_%d", name, row.ID)
+		if err := s.db.Unscoped().Model(&models.Listener{}).Where("id = ?", row.ID).Update("name", newName).Error; err != nil {
+			return fmt.Errorf("reclaim soft-deleted name %q: %w", name, err)
+		}
+	}
 	return nil
 }