Fix Windows backend test compatibility (#1384)

* Fix Windows backend test compatibility

* Preserve ACP path style on Windows

* Fix installer import ordering

* Address review comments for Windows fixes

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/packages/harness/deerflow/community/aio_sandbox/aio_sandbox_provider.py

@@ -11,7 +11,6 @@ The provider itself handles:
 """
 
 import atexit
-import fcntl
 import hashlib
 import logging
 import os
@@ -20,6 +19,12 @@ import threading
 import time
 import uuid
 
+try:
+    import fcntl
+except ImportError:  # pragma: no cover - Windows fallback
+    fcntl = None  # type: ignore[assignment]
+    import msvcrt
+
 from deerflow.config import get_app_config
 from deerflow.config.paths import VIRTUAL_PATH_PREFIX, Paths, get_paths
 from deerflow.sandbox.sandbox import Sandbox
@@ -42,6 +47,24 @@ DEFAULT_REPLICAS = 3  # Maximum concurrent sandbox containers
 IDLE_CHECK_INTERVAL = 60  # Check every 60 seconds
 
 
+def _lock_file_exclusive(lock_file) -> None:
+    if fcntl is not None:
+        fcntl.flock(lock_file, fcntl.LOCK_EX)
+        return
+
+    lock_file.seek(0)
+    msvcrt.locking(lock_file.fileno(), msvcrt.LK_LOCK, 1)
+
+
+def _unlock_file(lock_file) -> None:
+    if fcntl is not None:
+        fcntl.flock(lock_file, fcntl.LOCK_UN)
+        return
+
+    lock_file.seek(0)
+    msvcrt.locking(lock_file.fileno(), msvcrt.LK_UNLCK, 1)
+
+
 class AioSandboxProvider(SandboxProvider):
     """Sandbox provider that manages containers running the AIO sandbox.
 
@@ -405,8 +428,10 @@ class AioSandboxProvider(SandboxProvider):
         lock_path = paths.thread_dir(thread_id) / f"{sandbox_id}.lock"
 
         with open(lock_path, "a", encoding="utf-8") as lock_file:
+            locked = False
             try:
-                fcntl.flock(lock_file, fcntl.LOCK_EX)
+                _lock_file_exclusive(lock_file)
+                locked = True
                 # Re-check in-process caches under the file lock in case another
                 # thread in this process won the race while we were waiting.
                 with self._lock:
@@ -440,7 +465,8 @@ class AioSandboxProvider(SandboxProvider):
 
                 return self._create_sandbox(thread_id, sandbox_id)
             finally:
-                fcntl.flock(lock_file, fcntl.LOCK_UN)
+                if locked:
+                    _unlock_file(lock_file)
 
     def _evict_oldest_warm(self) -> str | None:
         """Destroy the oldest container in the warm pool to free capacity.