feat(search): FTS5 trigram全文索引(中文搜索3.95s→0.003s,1300倍)

- message_fts 外部内容虚拟表+trigram分词(中文子串可MATCH,无需分词库)
- 3个触发器随ORM upsert自动同步索引(抓取器零改动)
- 搜索路由:≥3字走FTS MATCH,<3字/MySQL回退LIKE
- 实测:搜「大众途安」56条,LIKE全扫3.95s→FTS 0.003s;索引+300MB
- 7个新测试(建表幂等/触发器同步/中文匹配/短查询回退/未建索引回退),426绿

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

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

@@ -57,7 +57,91 @@ async def _search_messages(
     start: int | None,
     end: int | None,
 ) -> Page[MessageOut]:
-    """Run the message search. Caller validates ``q``."""
+    """Run the message search. Caller validates ``q``.
+
+    **FTS 加速(2026-08-21)**: 建了 ``message_fts``(trigram) 索引且查询
+    ≥3 字时走 MATCH(毫秒级);否则回退 LIKE 全扫(675k 行约 4s)。
+    两路径结果一致(FTS join 回 message 表后套同样的过滤/排序)。
+    """
+    from app.db.fts import fts_available
+
+    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)
+    return await _search_messages_like(session, q, page, page_size, channel, start, end)
+
+
+async def _search_messages_fts(
+    session: AsyncSession,
+    q: str,
+    page: int,
+    page_size: int,
+    channel: str | None,
+    start: int | None,
+    end: int | None,
+) -> Page[MessageOut]:
+    """FTS trigram MATCH 路径 — join 回 message 表套过滤/排序/分页。"""
+    conds = ['message_fts MATCH :fts_q']
+    params: dict[str, Any] = {"fts_q": f'"{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)
+
+    total = (
+        await session.execute(
+            sa.text(
+                f"SELECT count(*) FROM message m "
+                f"JOIN message_fts f ON m.rowid = f.rowid WHERE {where}"
+            ),
+            params,
+        )
+    ).scalar_one()
+
+    id_rows = (
+        await session.execute(
+            sa.text(
+                f"SELECT m.msg_id FROM message m "
+                f"JOIN message_fts f ON m.rowid = f.rowid WHERE {where} "
+                f"ORDER BY m.timestamp DESC, m.msg_id ASC "
+                f"LIMIT :lim OFFSET :off"
+            ),
+            {**params, "lim": page_size, "off": (page - 1) * page_size},
+        )
+    ).scalars().all()
+
+    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,
+    page: int,
+    page_size: int,
+    channel: str | None,
+    start: int | None,
+    end: int | None,
+) -> Page[MessageOut]:
+    """LIKE 全扫路径(未建 FTS 索引 / 查询 <3 字 / MySQL)。"""
     conditions: list[Any] = [Message.text.like(f"%{q}%")]
     if channel is not None:
         conditions.append(Message.channel == channel)