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/tests/test_api_media.py

@@ -27,6 +27,7 @@ from sqlalchemy.pool import StaticPool
 
 from app.api import deps
 from app.api.main import app
+from app.config import get_settings
 from app.db.base import Base
 from app.db.models import Media
 
@@ -34,7 +35,7 @@ PNG_BYTES = b"\x89PNG\r\n\x1a\n fake image body"
 
 
 @pytest.fixture
-async def client(tmp_path: Path):
+async def client(tmp_path: Path, monkeypatch):
     """Yield an ``AsyncClient`` against ``app`` with a seeded in-memory DB.
 
     Seeds one ``Media`` row (``abc123``) pointing at a real PNG-bytes file
@@ -42,7 +43,15 @@ async def client(tmp_path: Path):
     deliberately missing on disk (to exercise the file-missing 404 path), plus
     a third (``nomime``) whose ``mime_type`` is NULL (to exercise the
     ext-derived content-type fallback).
+
+    ``MEDIA_DIR`` is pointed at ``tmp_path`` so the endpoint's path-traversal
+    sandbox check (file must live under ``Settings.media_dir``) admits the
+    seeded rows. The settings cache is cleared around the override so the new
+    value is picked up.
     """
+    monkeypatch.setenv("MEDIA_DIR", str(tmp_path))
+    get_settings.cache_clear()
+
     engine = create_async_engine(
         "sqlite+aiosqlite:///:memory:",
         poolclass=StaticPool,
@@ -104,6 +113,65 @@ async def client(tmp_path: Path):
     finally:
         app.dependency_overrides.clear()
         await engine.dispose()
+        get_settings.cache_clear()
+
+
+@pytest.fixture
+async def escape_client(tmp_path: Path, monkeypatch):
+    """Variant of :func:`client` that pins ``MEDIA_DIR`` to a sandbox subdir
+    while seeding a row whose ``local_path`` points OUTSIDE that sandbox.
+
+    Used to verify the path-traversal defense: an outside-sandbox file must be
+    refused with 404 even when it exists on disk and the row is otherwise valid.
+    """
+    sandbox = tmp_path / "media_dir"
+    sandbox.mkdir()
+    outside = tmp_path / "outside"
+    outside.mkdir()
+
+    monkeypatch.setenv("MEDIA_DIR", str(sandbox))
+    get_settings.cache_clear()
+
+    engine = create_async_engine(
+        "sqlite+aiosqlite:///:memory:",
+        poolclass=StaticPool,
+        connect_args={"check_same_thread": False},
+    )
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+    escape_file = outside / "secret.png"
+    escape_file.write_bytes(b"TOPSECRET")
+
+    SessionLocal = async_sessionmaker(engine, expire_on_commit=False)
+    async with SessionLocal() as session:
+        session.add(
+            Media(
+                media_hash="escape",
+                channel="wechat",
+                media_type="image",
+                original_url="https://wx.oss.yunkecn.com/x/secret.png",
+                local_path=str(escape_file),
+                size_bytes=len(b"TOPSECRET"),
+                mime_type="image/png",
+            )
+        )
+        await session.commit()
+
+    async def _override_session():
+        async with SessionLocal() as s:
+            yield s
+
+    app.dependency_overrides[deps.get_session] = _override_session
+    try:
+        async with AsyncClient(
+            transport=ASGITransport(app=app), base_url="http://test"
+        ) as ac:
+            yield ac
+    finally:
+        app.dependency_overrides.clear()
+        await engine.dispose()
+        get_settings.cache_clear()
 
 
 async def test_get_media_returns_bytes_with_content_type(client: AsyncClient):
@@ -145,3 +213,17 @@ async def test_get_media_falls_back_to_ext_when_mime_null(client: AsyncClient):
     assert r.status_code == 200
     assert r.headers["content-type"].startswith("image/webp")
     assert r.content == b"WEBPBYTES"
+
+
+async def test_get_media_refuses_path_outside_media_dir(escape_client: AsyncClient):
+    """A row whose local_path escapes media_dir is refused with 404 — even
+    though the file exists on disk and the row is otherwise valid.
+
+    Pins the path-traversal defense: a hostile or buggy ``local_path`` value
+    must never let the endpoint serve files outside the configured sandbox.
+    """
+    r = await escape_client.get("/api/media/escape")
+    assert r.status_code == 404
+    # The file must NOT be served — only the 404 JSON body is returned.
+    assert b"TOPSECRET" not in r.content
+    assert "media not found" in r.json()["detail"]