feat(search): MySQL ngram FULLTEXT分支(LIKE 13.5s→索引毫秒级;索引缺失自动回退LIKE)

MySQL LIKE 全扫698k行13.5s撞axios 15s超时→前端ERR_ABORTED;
MATCH...AGAINST(ngram)毫秒级;本地C盘不足索引待服务器建
(索引SQL: CREATE FULLTEXT INDEX ft_msg_text ON message(text) WITH PARSER ngram)

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

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

@@ -65,6 +65,12 @@ async def _search_messages(
     """
     from app.db.fts import fts_available
 
+    if session.bind is not None and session.bind.dialect.name == "mysql":
+        # MySQL: ngram FULLTEXT 索引(LIKE 全扫 698k 行要 13.5s,2026-08-22 实测
+        # 撞 axios 15s 超时前端 ERR_ABORTED);索引不存在时自动回退 LIKE
+        return await _search_messages_mysql(
+            session, q, page, page_size, channel, start, end
+        )
     use_fts = len(q) >= 3 and await fts_available(session)
     if use_fts:
         return await _search_messages_fts(session, q, page, page_size, channel, start, end)
@@ -132,6 +138,60 @@ async def _search_messages_fts(
     return Page(items=items, total=total, page=page, page_size=page_size)
 
 
+async def _search_messages_mysql(
+    session: AsyncSession,
+    q: str,
+    page: int,
+    page_size: int,
+    channel: str | None,
+    start: int | None,
+    end: int | None,
+) -> Page[MessageOut]:
+    """MySQL ngram FULLTEXT MATCH 路径;索引缺失自动回退 LIKE。"""
+    conds = ["MATCH(m.text) AGAINST(:ftq IN NATURAL LANGUAGE MODE)"]
+    params: dict[str, Any] = {"ftq": q}
+    if channel is not None:
+        conds.append("m.channel = :ch")
+        params["ch"] = channel
+    if start is not None:
+        conds.append("m.timestamp >= :s")
+        params["s"] = start
+    if end is not None:
+        conds.append("m.timestamp <= :e")
+        params["e"] = end
+    where = " AND ".join(conds)
+
+    try:
+        total = (
+            await session.execute(
+                sa.text(f"SELECT count(*) FROM message m WHERE {where}"), params
+            )
+        ).scalar_one()
+        id_rows = (
+            await session.execute(
+                sa.text(
+                    f"SELECT m.msg_id FROM message m WHERE {where} "
+                    f"ORDER BY m.timestamp DESC, m.msg_id ASC LIMIT :lim OFFSET :off"
+                ),
+                {**params, "lim": page_size, "off": (page - 1) * page_size},
+            )
+        ).scalars().all()
+    except Exception:
+        # 索引不存在(部署早期) → 回退 LIKE
+        return await _search_messages_like(session, q, page, page_size, channel, start, end)
+
+    items: list[MessageOut] = []
+    if id_rows:
+        rows = (
+            await session.execute(
+                sa.select(Message).where(Message.msg_id.in_(list(id_rows)))
+            )
+        ).scalars().all()
+        by_id = {r.msg_id: r for r in rows}
+        items = [MessageOut.model_validate(by_id[mid]) for mid in id_rows if mid in by_id]
+    return Page(items=items, total=total, page=page, page_size=page_size)
+
+
 async def _search_messages_like(
     session: AsyncSession,
     q: str,