fix(security): 路径穿越防护+导出行数上限+并发同步锁(3 critical/important)

- media.py: GET /api/media/{hash} 现强制 file 必须位于 Settings.media_dir
  沙箱内(resolve + relative_to),杜绝 local_path 越权读取任意文件。
- export.py: /api/export/chat-html 加 EXPORT_MAX_ROWS=5000 硬上限(.limit()),
  超出时仅渲染前 5000 条并插入 .export-warning 横幅,防止 OOM。
- scheduler.py: _safe_run 增加 SyncRun advisory lock(60min TTL),发现同
  entity 存在 status='running' 且在 TTL 内的记录即返回 skipped SyncResult;
  同时为本轮 stake 一行 wrapping SyncRun,让并发 CLI/scheduler/手动触发
  能相互避让。崩溃场景由 TTL 自动恢复。
- tests: 新增 path-traversal 拒绝/export 截断警告/advisory lock skip+TTL
  恢复 5 个测试;test_api_media 的 fixture 改为 MEDIA_DIR=tmp_path 以适配
  新沙箱语义。

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

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

@@ -21,6 +21,13 @@ router = APIRouter(prefix="/api/export", tags=["export"])
 
 SessionDep = Annotated[AsyncSession, Depends(get_session)]
 
+# Hard cap on rows an HTML export will load + render. An account-wide export
+# with no date range can match millions of messages; rendering all of them in
+# memory risks OOM. The cap is a safety valve, not a tight budget — at 5k rows
+# the HTML is already unwieldy in any browser. When hit, the response carries
+# a visible warning banner so the operator knows to narrow the date range.
+EXPORT_MAX_ROWS = 5000
+
 
 def _ts_text(ts: int | None) -> str:
     if not ts:
@@ -73,7 +80,14 @@ def _render_media(m) -> str:
     return ""
 
 
-def _render_chat_html(rows: list[Message], channel: str, owner: str, peer: str) -> str:
+def _render_chat_html(
+    rows: list[Message],
+    channel: str,
+    owner: str,
+    peer: str,
+    *,
+    warning: str = "",
+) -> str:
     bubbles = []
     for m in rows:
         side = "right" if m.is_send else "left"
@@ -90,6 +104,7 @@ def _render_chat_html(rows: list[Message], channel: str, owner: str, peer: str)
 <title>{title}</title><style>
 body{{font-family:-apple-system,Segoe UI,sans-serif;background:#f5f5f5;margin:0;padding:16px}}
 h1{{font-size:16px;margin:0 0 12px}}
+.export-warning{{background:#fff3cd;border:1px solid #ffeeba;color:#856404;padding:8px 12px;border-radius:4px;margin:0 0 12px;font-size:13px}}
 .bubble{{max-width:70%;margin:6px 0;padding:8px 12px;border-radius:8px;clear:both}}
 .bubble.right{{float:right;background:#95ec69;text-align:right}}
 .bubble.left{{float:left;background:#fff}}
@@ -98,7 +113,7 @@ h1{{font-size:16px;margin:0 0 12px}}
 .bubble .media{{margin-top:4px;font-size:13px}}
 .bubble .media audio,.bubble .media video,.bubble .media img{{display:block;max-width:100%}}
 .bubble .media .dur{{font-size:12px;color:#666;margin-left:4px}}
-</style></head><body><h1>{title}</h1>
+</style></head><body>{warning}<h1>{title}</h1>
 {''.join(bubbles) or '<p>暂无消息</p>'}
 </body></html>"""
 
@@ -132,9 +147,21 @@ async def export_chat_html(
         q = q.where(Message.timestamp >= start)
     if end is not None:
         q = q.where(Message.timestamp <= end)
-    q = q.order_by(sa.nullslast(Message.timestamp.asc()), Message.msg_id.asc())
+    q = q.order_by(sa.nullslast(Message.timestamp.asc()), Message.msg_id.asc()).limit(
+        EXPORT_MAX_ROWS
+    )
     rows = (await session.execute(q)).scalars().all()
-    html = _render_chat_html(list(rows), channel, owner_account_id, peer)
+    # If we filled the cap there may be more rows beyond it — surface a visible
+    # warning so the operator knows the export was truncated and can re-run
+    # with a tighter date range.
+    capped = len(rows) >= EXPORT_MAX_ROWS
+    warning = (
+        f'<div class="export-warning">⚠️ 结果超过 {EXPORT_MAX_ROWS} 条，'
+        f'仅导出前 {EXPORT_MAX_ROWS} 条。请缩小日期范围。</div>'
+        if capped
+        else ""
+    )
+    html = _render_chat_html(list(rows), channel, owner_account_id, peer, warning=warning)
     safe = peer or "all"
     filename = f"chat-{channel}-{owner_account_id}-{safe}.html".replace("@", "_").replace("/", "_")
     return Response(