优化实时聊天：稳定 WS、按 seq 增量同步，并修复访客评价推送

- 客服/访客 WebSocket 不再因切换会话反复重连，断线自动恢复
- 新增 after_seq 增量拉取，重连与消息空洞时 catch-up
- 结束会话同时推送给访客，预览页可弹出评价并支持兜底状态同步

server/internal/handler/widget.go

@@ -479,15 +479,61 @@ func (h *WidgetHandler) GetMessages(c *gin.Context) {
 		c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "会话参数错误"})
 		return
 	}
-	if _, ok := loadVisitorSession(c, uint(sessionID), visitorTokenFromRequest(c, "")); !ok {
+	session, ok := loadVisitorSession(c, uint(sessionID), visitorTokenFromRequest(c, ""))
+	if !ok {
 		return
 	}
 
+	afterSeq := 0
+	if raw := strings.TrimSpace(c.Query("after_seq")); raw != "" {
+		parsed, err := strconv.Atoi(raw)
+		if err != nil || parsed < 0 {
+			c.JSON(http.StatusBadRequest, gin.H{"code": 400, "message": "after_seq 无效"})
+			return
+		}
+		afterSeq = parsed
+	}
+
+	limit := 200
+	if raw := strings.TrimSpace(c.Query("limit")); raw != "" {
+		if parsed, err := strconv.Atoi(raw); err == nil && parsed > 0 {
+			if parsed > 500 {
+				parsed = 500
+			}
+			limit = parsed
+		}
+	}
+
+	query := model.DB.Where("session_id = ?", sessionID)
+	if afterSeq > 0 {
+		query = query.Where("seq > ?", afterSeq)
+	}
+
 	var messages []model.Message
-	if err := model.DB.Where("session_id = ?", sessionID).Order("seq asc").Find(&messages).Error; err != nil {
+	if err := query.Order("seq asc").Limit(limit).Find(&messages).Error; err != nil {
 		c.JSON(http.StatusInternalServerError, gin.H{"code": 500, "message": "查询消息失败"})
 		return
 	}
 
-	c.JSON(http.StatusOK, gin.H{"code": 0, "data": messages})
+	var maxSeq int
+	if err := model.DB.Model(&model.Message{}).
+		Where("session_id = ?", sessionID).
+		Select("COALESCE(MAX(seq), 0)").
+		Scan(&maxSeq).Error; err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"code": 500, "message": "查询消息失败"})
+		return
+	}
+
+	hasMore := len(messages) >= limit && (len(messages) == 0 || messages[len(messages)-1].Seq < maxSeq)
+	c.JSON(http.StatusOK, gin.H{
+		"code": 0,
+		"data": gin.H{
+			"messages":           messages,
+			"after_seq":          afterSeq,
+			"max_seq":            maxSeq,
+			"has_more":           hasMore,
+			"session_status":     session.Status,
+			"satisfaction_score": session.SatisfactionScore,
+		},
+	})
 }