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/handler/chat.go

@@ -98,7 +98,7 @@ func (h *Handlers) ListChatRooms(c *gin.Context) {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "获取会话列表失败"})
 		return
 	}
-	c.JSON(http.StatusOK, gin.H{"rooms": rooms, "total": total, "page": page, "size": size})
+	c.JSON(http.StatusOK, gin.H{"rooms": nonNilSlice(rooms), "total": total, "page": page, "size": size})
 }
 
 // GetChatRoom 群详情（公开非成员可预览；私密非成员 404）
@@ -273,7 +273,7 @@ func (h *Handlers) ListChatMembers(c *gin.Context) {
 		c.JSON(chatErrToStatus(err), gin.H{"error": err.Error()})
 		return
 	}
-	c.JSON(http.StatusOK, gin.H{"members": list})
+	c.JSON(http.StatusOK, gin.H{"members": nonNilSlice(list)})
 }
 
 // KickChatMember 群主踢人
@@ -315,7 +315,7 @@ func (h *Handlers) ListChatMessages(c *gin.Context) {
 		c.JSON(chatErrToStatus(err), gin.H{"error": err.Error()})
 		return
 	}
-	c.JSON(http.StatusOK, gin.H{"messages": msgs, "has_more": hasMore})
+	c.JSON(http.StatusOK, gin.H{"messages": nonNilSlice(msgs), "has_more": hasMore})
 }
 
 // SendChatMessage 发消息
@@ -387,16 +387,30 @@ func (h *Handlers) RecallChatMessage(c *gin.Context) {
 		c.JSON(chatErrToStatus(err), gin.H{"error": err.Error()})
 		return
 	}
+	data := gin.H{
+		"id":          msg.ID,
+		"room_id":     roomID,
+		"sender_id":   msg.SenderID,
+		"recalled_by": msg.RecalledBy,
+		"recalled_at": msg.RecalledAt,
+	}
+	if msg.Recaller != nil && msg.Recaller.ID > 0 {
+		data["recaller"] = gin.H{
+			"id":       msg.Recaller.ID,
+			"username": msg.Recaller.Username,
+			"nickname": msg.Recaller.Nickname,
+			"avatar":   msg.Recaller.Avatar,
+			"role":     msg.Recaller.Role,
+		}
+	}
 	h.Hub.BroadcastRoom(realtime.RoomChat(roomID), realtime.Envelope{
 		Type: realtime.EventChatRecalled,
-		Data: gin.H{
-			"id":          msg.ID,
-			"room_id":     roomID,
-			"sender_id":   msg.SenderID,
-			"recalled_by": msg.RecalledBy,
-			"recalled_at": msg.RecalledAt,
-		},
+		Data: data,
 	})
+	// 监管者保留正文供界面展示；撤回者本人保留正文供「重新编辑」；其余不回传
+	if !oversee && msg.SenderID != claims.ID {
+		msg.Content = ""
+	}
 	c.JSON(http.StatusOK, gin.H{"message": msg})
 }
 
@@ -444,7 +458,7 @@ func (h *Handlers) SearchChatUsers(c *gin.Context) {
 		c.JSON(http.StatusInternalServerError, gin.H{"error": "搜索失败"})
 		return
 	}
-	c.JSON(http.StatusOK, gin.H{"users": users})
+	c.JSON(http.StatusOK, gin.H{"users": nonNilSlice(users)})
 }
 
 // ChatUnreadSummary 未读汇总