fix: 空评论列表 500，并完善撤回审计与角色说明

空切片 JSON 统一为数组；撤回保留正文供站长阅读，成员侧居中提示与重新编辑；头像支持拖放；角色弹窗补全职责说明并汇入封禁。

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

backend/service/chat.go

@@ -153,6 +153,10 @@ func (s *ChatService) toViews(rooms []model.ChatRoom, userID uint) []RoomView {
 	unread := s.unreadCounts(userID, ids)
 	views := make([]RoomView, 0, len(rooms))
 	for _, r := range rooms {
+		// 会话列表预览不向前台下发已撤回正文
+		if r.LastMessage != nil && r.LastMessage.RecalledAt != nil {
+			r.LastMessage.Content = ""
+		}
 		v := RoomView{ChatRoom: r, UnreadCount: unread[r.ID]}
 		if r.IsDefault {
 			v.Pinned = true
@@ -887,7 +891,7 @@ func (s *ChatService) ListMessages(userID, roomID, beforeID uint, size int, over
 		q = q.Where("id < ?", beforeID)
 	}
 	var msgs []model.ChatMessage
-	if err := q.Order("id DESC").Limit(size + 1).Preload("Sender").Find(&msgs).Error; err != nil {
+	if err := q.Order("id DESC").Limit(size + 1).Preload("Sender").Preload("Recaller").Find(&msgs).Error; err != nil {
 		return nil, false, err
 	}
 	hasMore := len(msgs) > size
@@ -897,7 +901,7 @@ func (s *ChatService) ListMessages(userID, roomID, beforeID uint, size int, over
 	for i, j := 0, len(msgs)-1; i < j; i, j = i+1, j-1 {
 		msgs[i], msgs[j] = msgs[j], msgs[i]
 	}
-	// 对非监管者清空已撤回正文
+	// 已撤回正文：仅监管者（站长/超管）保留，供聊天界面审计展示；普通成员清空
 	if !oversee {
 		for i := range msgs {
 			if msgs[i].RecalledAt != nil {
@@ -908,7 +912,7 @@ func (s *ChatService) ListMessages(userID, roomID, beforeID uint, size int, over
 	return msgs, hasMore, nil
 }
 
-// RecallMessage 撤回消息：群主可撤自己的；监管者可撤任意；标记 RecalledAt 不清行
+// RecallMessage 撤回消息：群主可撤自己的；监管者可撤任意；标记 RecalledAt，正文保留供审计
 func (s *ChatService) RecallMessage(operatorID, roomID, messageID uint, oversee bool) (*model.ChatMessage, error) {
 	if _, err := s.getRoom(roomID); err != nil {
 		return nil, err
@@ -935,17 +939,16 @@ func (s *ChatService) RecallMessage(operatorID, roomID, messageID uint, oversee
 		}
 	}
 	now := time.Now()
+	// 只打撤回标记，保留正文供站长审计；前台 ListMessages 对非监管者置空 content
 	if err := s.db.Model(&msg).Updates(map[string]interface{}{
 		"recalled_at": now,
 		"recalled_by": operatorID,
-		"content":     "",
 	}).Error; err != nil {
 		return nil, err
 	}
 	msg.RecalledAt = &now
 	msg.RecalledBy = operatorID
-	msg.Content = ""
-	_ = s.db.Preload("Sender").First(&msg, msg.ID)
+	_ = s.db.Preload("Sender").Preload("Recaller").First(&msg, msg.ID)
 	return &msg, nil
 }