test(feishu): restore the loop default executor torn down by the dedup test

The regression test swaps in a torn-down default executor but never
restores the pristine one, leaking the poisoned executor to anything
sharing the loop. Save/restore via the private slot because
set_default_executor() rejects None, which is exactly the pristine
(lazy-creation) state. Also apply ruff format to the file.

tests/gateway/test_feishu_sdk_executor.py

@@ -8,6 +8,7 @@ ThreadPoolExecutor and recreates it on demand if it has been shut down.
 
 Covers: #10849, #111020
 """
+
 import asyncio
 import concurrent.futures
 import json
@@ -60,7 +61,9 @@ async def test_run_blocking_executes_on_owned_pool():
 
 
 @pytest.mark.asyncio
-async def test_is_duplicate_flush_survives_default_executor_teardown(tmp_path, monkeypatch):
+async def test_is_duplicate_flush_survives_default_executor_teardown(
+    tmp_path, monkeypatch
+):
     """The inbound dedup flush must not ride the loop's default executor.
 
     After the adapter's background event loop dies, its teardown shuts the
@@ -73,8 +76,11 @@ async def test_is_duplicate_flush_survives_default_executor_teardown(tmp_path, m
     from gateway.config import PlatformConfig
 
     adapter = FeishuAdapter(PlatformConfig())
+    loop = asyncio.get_running_loop()
+    # Save/restore via the private slot: set_default_executor() rejects None, but the
+    # pristine state is exactly "no default executor set yet" (lazy creation on first use).
+    original_executor = loop._default_executor
     try:
-        loop = asyncio.get_running_loop()
         torn_down = concurrent.futures.ThreadPoolExecutor(max_workers=1)
         loop.set_default_executor(torn_down)
         torn_down.shutdown(wait=True)
@@ -85,9 +91,10 @@ async def test_is_duplicate_flush_survives_default_executor_teardown(tmp_path, m
 
         # The dedup gate must still admit the message and flush it to disk.
         assert await adapter._is_duplicate("om_after_executor_teardown") is False
-        state = json.loads((tmp_path / "feishu_seen_message_ids.json").read_text(encoding="utf-8"))
+        state = json.loads(
+            (tmp_path / "feishu_seen_message_ids.json").read_text(encoding="utf-8")
+        )
         assert "om_after_executor_teardown" in state["message_ids"]
     finally:
+        loop._default_executor = original_executor
         adapter._shutdown_sdk_executor()
-
-