diff --git a/backend/packages/harness/deerflow/community/browser_automation/session.py b/backend/packages/harness/deerflow/community/browser_automation/session.py
index 36353a3b6..148b2052e 100644
--- a/backend/packages/harness/deerflow/community/browser_automation/session.py
+++ b/backend/packages/harness/deerflow/community/browser_automation/session.py
@@ -21,6 +21,7 @@ import os
 import threading
 import time
 from collections.abc import Callable, Coroutine
+from concurrent.futures import Future
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Any, Literal, TypeVar
 from urllib.parse import urlparse
@@ -172,6 +173,14 @@ def _is_playwright_timeout_error(exc: Exception) -> bool:
     return exc.__class__.__name__ == "TimeoutError" and exc.__class__.__module__.startswith("playwright.")
 
 
+def _consume_future_exception(future: asyncio.Future[Any]) -> None:
+    """Retrieve detached close errors; the concurrent-future callback logs them."""
+    if future.cancelled():
+        return
+    with contextlib.suppress(Exception):
+        future.exception()
+
+
 def redact_browser_url(url: str) -> str:
     """Drop query/fragment so a blocked-URL log line can't leak tokens/PII."""
     try:
@@ -198,7 +207,7 @@ class _PlaywrightLoopThread:
         future = asyncio.run_coroutine_threadsafe(coro, self._loop)
         return await asyncio.wrap_future(future)
 
-    def submit(self, coro: Coroutine[Any, Any, Any]) -> None:
+    def submit(self, coro: Coroutine[Any, Any, Any]) -> Future[Any]:
         """Schedule *coro* on the private loop without blocking the caller."""
         future = asyncio.run_coroutine_threadsafe(coro, self._loop)
 
@@ -209,6 +218,7 @@ class _PlaywrightLoopThread:
                 logger.debug("browser background task failed: %s", exc)
 
         future.add_done_callback(_log_failure)
+        return future
 
     def run_sync(self, coro: Coroutine[Any, Any, T], timeout: float | None = None) -> T:
         future = asyncio.run_coroutine_threadsafe(coro, self._loop)
@@ -849,8 +859,18 @@ class BrowserSession:
         with self._activity():
             await self._loop.run(self._dispatch_input(event))
 
+    def _submit_close(self) -> Future[Any]:
+        close_coro = self._close()
+        try:
+            return self._loop.submit(close_coro)
+        except Exception:
+            close_coro.close()
+            raise
+
     async def close(self) -> None:
-        await self._loop.run(self._close())
+        close_future = asyncio.wrap_future(self._submit_close())
+        close_future.add_done_callback(_consume_future_exception)
+        await asyncio.shield(close_future)
 
 
 class BrowserSessionManager:
@@ -1019,8 +1039,19 @@ class BrowserSessionManager:
             sessions = list(self._sessions.values())
             self._sessions.clear()
             self._last_used.clear()
+        close_futures: list[asyncio.Future[Any]] = []
         for session in sessions:
-            await session.close()
+            try:
+                close_future = asyncio.wrap_future(session._submit_close())
+            except Exception as exc:
+                logger.debug("browser session close submission failed: %s", exc)
+                continue
+            close_future.add_done_callback(_consume_future_exception)
+            close_futures.append(close_future)
+        if close_futures:
+            close_group = asyncio.gather(*close_futures)
+            close_group.add_done_callback(_consume_future_exception)
+            await asyncio.shield(close_group)
         return len(sessions)
 
 
diff --git a/backend/tests/test_browser_close_cancellation.py b/backend/tests/test_browser_close_cancellation.py
new file mode 100644
index 000000000..75738d72c
--- /dev/null
+++ b/backend/tests/test_browser_close_cancellation.py
@@ -0,0 +1,194 @@
+from __future__ import annotations
+
+import asyncio
+from concurrent.futures import Future
+from typing import Any, cast
+
+import pytest
+
+import deerflow.community.browser_automation.session as session_module
+from deerflow.community.browser_automation.session import BrowserSession, BrowserSessionManager
+
+
+class _ControllablePrivateLoop:
+    """Model the cancellation boundary between a caller loop and Playwright's loop."""
+
+    def __init__(self) -> None:
+        self.cleanup_futures: list[Future[None]] = []
+        self.run_cancelled = False
+
+    async def run(self, coro: Any) -> None:
+        # Current main awaits the private-loop proxy directly, so caller
+        # cancellation propagates through wrap_future and cancels cleanup.
+        coro.close()
+        try:
+            await asyncio.Future()
+        except asyncio.CancelledError:
+            self.run_cancelled = True
+            raise
+
+    def submit(self, coro: Any) -> Future[None]:
+        # The fixed close path hands cleanup to the private loop and awaits its
+        # concurrent future behind a shield. Closing the coroutine here avoids
+        # needing Playwright in this focused lifecycle test.
+        coro.close()
+        cleanup_future: Future[None] = Future()
+        self.cleanup_futures.append(cleanup_future)
+        return cleanup_future
+
+
+class _FailingPrivateLoop(_ControllablePrivateLoop):
+    def __init__(self) -> None:
+        super().__init__()
+        self.submitted_coro: Any | None = None
+
+    def submit(self, coro: Any) -> Future[None]:
+        self.submitted_coro = coro
+        raise RuntimeError("private loop closed")
+
+
+def _session(loop: _ControllablePrivateLoop) -> BrowserSession:
+    return BrowserSession(
+        cast(Any, loop),
+        headless=True,
+        timeout_ms=1000,
+        viewport={"width": 1000, "height": 500},
+    )
+
+
+@pytest.mark.asyncio
+async def test_browser_close_caller_cancellation_does_not_cancel_private_cleanup() -> None:
+    loop = _ControllablePrivateLoop()
+    session = _session(loop)
+
+    close_task = asyncio.create_task(session.close())
+    await asyncio.sleep(0)
+
+    close_task.cancel("caller stopped")
+    with pytest.raises(asyncio.CancelledError):
+        await close_task
+
+    assert not loop.run_cancelled
+    assert len(loop.cleanup_futures) == 1
+    assert not loop.cleanup_futures[0].cancelled()
+
+    loop.cleanup_futures[0].set_result(None)
+    await asyncio.sleep(0)
+
+
+def test_submit_close_closes_coroutine_when_submission_fails() -> None:
+    loop = _FailingPrivateLoop()
+    session = _session(loop)
+
+    with pytest.raises(RuntimeError, match="private loop closed"):
+        session._submit_close()
+
+    assert loop.submitted_coro is not None
+    assert loop.submitted_coro.cr_frame is None
+
+
+@pytest.mark.asyncio
+async def test_manager_close_session_cancellation_keeps_detached_cleanup_running() -> None:
+    loop = _ControllablePrivateLoop()
+    session = _session(loop)
+    manager = BrowserSessionManager()
+    manager._sessions["thread-a"] = session
+    manager._last_used["thread-a"] = 0.0
+
+    close_task = asyncio.create_task(manager.close_session("thread-a"))
+    await asyncio.sleep(0)
+
+    assert "thread-a" not in manager._sessions
+    assert len(loop.cleanup_futures) == 1
+
+    close_task.cancel("request stopped")
+    with pytest.raises(asyncio.CancelledError):
+        await close_task
+
+    assert not loop.cleanup_futures[0].cancelled()
+    loop.cleanup_futures[0].set_result(None)
+    await asyncio.sleep(0)
+
+
+@pytest.mark.asyncio
+async def test_manager_close_all_submits_every_cleanup_before_cancellable_wait() -> None:
+    loop = _ControllablePrivateLoop()
+    manager = BrowserSessionManager()
+    manager._sessions.update({"thread-a": _session(loop), "thread-b": _session(loop)})
+    manager._last_used.update({"thread-a": 0.0, "thread-b": 0.0})
+
+    close_task = asyncio.create_task(manager.close_all_sessions())
+    await asyncio.sleep(0)
+
+    assert manager._sessions == {}
+    assert len(loop.cleanup_futures) == 2
+
+    close_task.cancel("shutdown interrupted")
+    with pytest.raises(asyncio.CancelledError):
+        await close_task
+
+    assert all(not future.cancelled() for future in loop.cleanup_futures)
+    for future in loop.cleanup_futures:
+        future.set_result(None)
+    await asyncio.sleep(0)
+
+
+@pytest.mark.asyncio
+async def test_manager_close_all_continues_after_sync_submission_failure() -> None:
+    failing_loop = _FailingPrivateLoop()
+    healthy_loop = _ControllablePrivateLoop()
+    manager = BrowserSessionManager()
+    manager._sessions.update({"broken": _session(failing_loop), "healthy": _session(healthy_loop)})
+    manager._last_used.update({"broken": 0.0, "healthy": 0.0})
+
+    close_task = asyncio.create_task(manager.close_all_sessions())
+    await asyncio.sleep(0)
+
+    assert manager._sessions == {}
+    assert len(healthy_loop.cleanup_futures) == 1
+    assert failing_loop.submitted_coro is not None
+    assert failing_loop.submitted_coro.cr_frame is None
+
+    healthy_loop.cleanup_futures[0].set_result(None)
+    assert await close_task == 2
+
+
+@pytest.mark.asyncio
+async def test_manager_close_all_consumes_group_failure_after_caller_cancellation(monkeypatch: pytest.MonkeyPatch) -> None:
+    loop = _ControllablePrivateLoop()
+    manager = BrowserSessionManager()
+    manager._sessions["thread-a"] = _session(loop)
+    manager._last_used["thread-a"] = 0.0
+
+    original_gather = asyncio.gather
+    original_consume = session_module._consume_future_exception
+    group_future: asyncio.Future[Any] | None = None
+    consumed: list[asyncio.Future[Any]] = []
+
+    def tracking_gather(*aws: Any, **kwargs: Any) -> asyncio.Future[Any]:
+        nonlocal group_future
+        group_future = cast(asyncio.Future[Any], original_gather(*aws, **kwargs))
+        return group_future
+
+    def recording_consume(future: asyncio.Future[Any]) -> None:
+        consumed.append(future)
+        original_consume(future)
+
+    monkeypatch.setattr(asyncio, "gather", tracking_gather)
+    monkeypatch.setattr(session_module, "_consume_future_exception", recording_consume)
+
+    close_task = asyncio.create_task(manager.close_all_sessions())
+    await asyncio.sleep(0)
+    assert group_future is not None
+
+    close_task.cancel("shutdown interrupted")
+    with pytest.raises(asyncio.CancelledError):
+        await close_task
+
+    loop.cleanup_futures[0].set_exception(RuntimeError("teardown failed"))
+    await asyncio.sleep(0)
+    await asyncio.sleep(0)
+    await asyncio.sleep(0)
+
+    assert group_future.done()
+    assert group_future in consumed