fix(messages): 聊天记录大对话超时——DESC首屏+keyset游标+群聊直达索引

用户报:聊天记录多时「聊天记录加载失败：请求失败 (ECONNABORTED)」(2026-09-07)。
服务器 EXPLAIN ANALYZE 实测两级根因:
- 单聊 1 万条:ASC 末页 OFFSET 10486 逐条回表 2515ms(DESC LIMIT 15ms,167 倍);
- 群聊 16,290 条:查询刻意不带 owner(chat_group 去重后 owner 错位),现有
  (channel,owner,room,timestamp) 索引被 owner 挡住,退化到 room 单列索引+
  filter+filesort——count 4.7s/首页 5.1s/末页 10.7s;真凶群 53132846289@chatroom
  40,863 条,三段串行 ~40s 必撞前端 axios 15s 超时。

修法(不动共享 MySQL 配置,沿用既往修复模式):
1. 迁移 e6f7a8b9c0d1:message 补 (channel, room_id, timestamp) 索引,群查询
   seek+排序直达+覆盖 count;模型侧双声明防 autogenerate 反 DROP。
2. /api/messages 加 order=asc|desc(默认 asc 不变)与 before_ts/before_id
   keyset 游标(成对,单传 422)——排序列 (timestamp,msg_id) 全序,平手按
   msg_id 决胜,游标页恒 O(page_size)。
3. 前端 ChatMain/ChatTimeline 首屏改「order=desc 取最新 50 反转」单请求
   (原 page1 拿 total+深 OFFSET 末页两请求),「加载更多」改游标上翻;
   hasMoreOlder=已加载<总数。SessionPane 搜索等 order=asc 默认路径不受影响。

本地实测(37,532 条群):desc 首页 0.39s、游标上翻 0.24s,浏览器真机
渲染+上翻 150 条无错。测试 8 增(desc/游标/平手边界/422/窗口叠加/
前端流程不变式),全量 601 绿。

Co-Authored-By: Claude Code <noreply@anthropic.com>

yunke-server/app/api/routers/messages.py

@@ -12,10 +12,20 @@ Read-only query over the mirrored ``message`` table. Filters:
   see ``_MSG_TYPE_FILTER``). Unknown values are rejected with 422.
 * ``q``                    — substring match on ``text`` (``%``/``_`` escaped
   as literals).
+* ``order``                — ``asc`` (default, oldest-first timeline) /
+  ``desc`` (newest-first; 聊天窗首屏「取最新一页」用它,反向索引扫描恒
+  O(page_size),避开 ASC 深 OFFSET 逐行回表——2026-09-07 实测 1 万条对话
+  末页 2.5s、4 万条群 10.7s 撞前端 15s 超时)。
+* ``before_ts``/``before_id`` — keyset 游标(成对,可选):只取严格早于
+  ``(before_ts, before_id)`` 的消息(排序列 (timestamp, msg_id) 全序,
+  平手按 msg_id 决胜)。「加载更多」上翻历史用它,每页恒 O(page_size);
+  两参必须成对,单传任一 422。
 
-Ordered by ``timestamp asc`` so the timeline renders oldest-first. The index
-``ix_message_channel_owner_talker_time`` covers the hot path
-``(channel, owner_account_id, talker_id, timestamp)``.
+Ordered by ``(timestamp, msg_id)`` in the requested direction. The index
+``ix_message_channel_owner_talker_time`` covers the 1:1 hot path
+``(channel, owner_account_id, talker_id, timestamp)``; group queries filter
+``channel + room_id`` without owner(群聊 owner 错位,见 ChatMain queryFor),
+served by ``ix_message_channel_room_time``.
 """
 
 from __future__ import annotations
@@ -23,7 +33,7 @@ from __future__ import annotations
 from typing import Annotated, Literal
 
 import sqlalchemy as sa
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.api.deps import get_session
@@ -70,8 +80,16 @@ async def list_messages(
     end: Annotated[int | None, Query(ge=0)] = None,
     msg_type: Annotated[MsgTypeParam | None, Query()] = None,
     q: Annotated[str | None, Query()] = None,
+    order: Annotated[Literal["asc", "desc"], Query()] = "asc",
+    before_ts: Annotated[int | None, Query(ge=0)] = None,
+    before_id: Annotated[str | None, Query()] = None,
 ) -> Page[MessageOut]:
-    """List messages for a timeline (ordered by ``timestamp asc``)."""
+    """List messages for a timeline (ordered by ``(timestamp, msg_id)``)."""
+    if (before_ts is None) != (before_id is None):
+        raise HTTPException(
+            status_code=422, detail="before_ts 与 before_id 必须成对使用"
+        )
+
     conditions = []
     if channel is not None:
         conditions.append(Message.channel == channel)
@@ -91,20 +109,30 @@ async def list_messages(
         # LIKE 通配符转义: %/_ 按字面匹配
         escaped = q.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
         conditions.append(Message.text.like(f"%{escaped}%", escape="\\"))
+    if before_ts is not None:
+        # keyset 游标:严格早于 (before_ts, before_id) 的全序前缀,平手按
+        # msg_id 决胜——与 order_by 同一全序,翻页无缝
+        conditions.append(
+            sa.or_(
+                Message.timestamp < before_ts,
+                sa.and_(Message.timestamp == before_ts, Message.msg_id < before_id),
+            )
+        )
 
     total_stmt = sa.select(sa.func.count()).select_from(Message)
     if conditions:
         total_stmt = total_stmt.where(*conditions)
     total = (await session.execute(total_stmt)).scalar_one()
 
+    ts_order = (
+        Message.timestamp.desc() if order == "desc" else Message.timestamp.asc()
+    )
+    id_order = Message.msg_id.desc() if order == "desc" else Message.msg_id.asc()
     list_stmt = sa.select(Message)
     if conditions:
         list_stmt = list_stmt.where(*conditions)
     list_stmt = (
-        list_stmt.order_by(
-            sa.nullslast(Message.timestamp.asc()),
-            Message.msg_id.asc(),
-        )
+        list_stmt.order_by(sa.nullslast(ts_order), id_order)
         .limit(page_size)
         .offset((page - 1) * page_size)
     )