diff --git a/backend/app/core/background.py b/backend/app/core/background.py
new file mode 100644
index 00000000..2f47ea7c
--- /dev/null
+++ b/backend/app/core/background.py
@@ -0,0 +1,28 @@
+"""进程里「发出去就不管」的后台任务（推送通知、评测收尾的清理）：留着引用免得被回收，测试和关停时等它们做完。"""
+
+from __future__ import annotations
+
+import asyncio
+from typing import Any
+
+
+async def drain(tasks: set[asyncio.Future[Any]]) -> None:
+    """等 tasks 里本事件循环上的任务都做完。
+
+    已经做完的直接从集合里摘掉，不等它们自己的 discard 回调：done 回调排在任务所在的事件循环上，那个循环要是已经不转了（测试里
+    每个测试一个事件循环，前一个测试末尾刚做完的推送）回调就永远不跑、任务一直留在集合里。以前的写法 `while tasks: await
+    gather(*tasks)` 碰上这种集合，gather 拿到的全是做完了的、立刻返回，await 不让出事件循环，就在这里空转——CPU 打满、整个
+    进程卡死（PostgreSQL 全量里 test_personal_apps 收尾时出现过）。别的事件循环上还没做完的等不到（不在这个循环上），不等；
+    那个循环已经关了的一并摘掉。"""
+    loop = asyncio.get_running_loop()
+    while True:
+        for task in list(tasks):
+            if task.done() or (task.get_loop() is not loop and task.get_loop().is_closed()):
+                tasks.discard(task)
+        mine = [task for task in tasks if task.get_loop() is loop]
+        if not mine:
+            return
+        await asyncio.gather(*mine, return_exceptions=True)
+
+
+__all__ = ["drain"]
diff --git a/backend/app/eval/cleanup.py b/backend/app/eval/cleanup.py
index a52a947e..956b37f2 100644
--- a/backend/app/eval/cleanup.py
+++ b/backend/app/eval/cleanup.py
@@ -119,8 +119,10 @@ def spawn(suite_id: str) -> None:
 
 async def drain() -> None:
     """等后台的清理做完（测试、关停用）。"""
-    while _background:
-        await asyncio.gather(*list(_background), return_exceptions=True)
+    from app.core.background import drain as drain_tasks
+
+    # 不写成 while _background: await gather(...)：别的事件循环上做完、还没摘掉的任务会让那样的循环空转（core/background）
+    await drain_tasks(_background)
 
 
 __all__ = ["clean_suite", "drain", "keep_set", "spawn"]
diff --git a/backend/app/notify/service.py b/backend/app/notify/service.py
index 17366503..211c35ff 100644
--- a/backend/app/notify/service.py
+++ b/backend/app/notify/service.py
@@ -121,8 +121,10 @@ def spawn(coro: Coroutine[Any, Any, Any]) -> None:
 
 async def drain() -> None:
     """等后台的推送都推完（测试、关停用）。"""
-    while _background:
-        await asyncio.gather(*list(_background), return_exceptions=True)
+    from app.core.background import drain as drain_tasks
+
+    # 不写成 while _background: await gather(...)：别的事件循环上做完、还没摘掉的任务会让那样的循环空转（core/background）
+    await drain_tasks(_background)
 
 
 async def personal_url_problem(url: str) -> str | None:
diff --git a/backend/tests/test_background_drain.py b/backend/tests/test_background_drain.py
new file mode 100644
index 00000000..4aab03af
--- /dev/null
+++ b/backend/tests/test_background_drain.py
@@ -0,0 +1,81 @@
+"""core/background.drain：等后台任务做完，碰上别的事件循环上做完、还没摘掉的任务不空转。
+
+以前 notify.service.drain、eval.cleanup.drain 写的是 `while _background: await gather(*_background)`：前一个测试的事件循环上
+刚做完的推送，done 回调（从集合里摘掉）排在那个已经不转的循环上、永远不跑；gather 拿到的全是做完了的、立刻返回，await 不让出
+事件循环，于是空转、整个测试进程卡死（PostgreSQL 全量里 test_personal_apps 收尾时出现过两次）。空转时事件循环也转不动，
+asyncio.wait_for 的超时救不了，所以这里在另一个线程里跑、按线程等。
+"""
+
+from __future__ import annotations
+
+import asyncio
+import threading
+from typing import Any
+
+import pytest
+
+from app.core import background
+from app.eval import cleanup
+from app.notify import service
+
+
+def _finished_on_a_dead_loop(tasks: set[asyncio.Future[Any]]) -> asyncio.Future[Any]:
+    """在另一个事件循环上做完、但 discard 回调没跑过的任务：照 spawn 的写法登记，结果设上（回调排进那个循环），循环不转就关。"""
+    other = asyncio.new_event_loop()
+    fut = other.create_future()
+    tasks.add(fut)
+    fut.add_done_callback(tasks.discard)
+    fut.set_result(None)
+    other.close()
+    return fut
+
+
+def _returns_within(seconds: float, make: Any) -> bool:
+    done = threading.Event()
+
+    def go() -> None:
+        asyncio.run(make())
+        done.set()
+
+    threading.Thread(target=go, daemon=True).start()
+    return done.wait(seconds)
+
+
+@pytest.mark.parametrize("module", [service, cleanup], ids=["notify", "eval-cleanup"])
+def test_drain_does_not_spin_on_tasks_finished_on_another_loop(module):
+    stale = _finished_on_a_dead_loop(module._background)
+    try:
+        assert _returns_within(5, module.drain), "drain 卡住了（空转）"
+        assert stale not in module._background, "做完了的摘掉"
+    finally:
+        module._background.discard(stale)
+
+
+def test_drain_waits_for_this_loops_tasks_and_skips_other_loops_pending_ones():
+    tasks: set[asyncio.Future[Any]] = set()
+    other = asyncio.new_event_loop()
+    pending_elsewhere = other.create_future()      # 别的循环上没做完的：等不到，不等
+    tasks.add(pending_elsewhere)
+    seen: list[str] = []
+
+    async def scenario() -> None:
+        async def slow() -> None:
+            await asyncio.sleep(0.05)
+            seen.append("slow")
+
+        task = asyncio.get_running_loop().create_task(slow())
+        tasks.add(task)
+        task.add_done_callback(tasks.discard)
+        await background.drain(tasks)
+        seen.append("drained")
+
+    try:
+        assert _returns_within(5, scenario)
+        assert seen == ["slow", "drained"], "本循环上的等它做完"
+        assert pending_elsewhere in tasks, "循环还开着的别人的任务留着"
+        other.close()
+        assert _returns_within(5, lambda: background.drain(tasks))
+        assert tasks == set(), "循环关了的一并摘掉"
+    finally:
+        if not other.is_closed():
+            other.close()