diff --git a/tests/unit/test_openai_compat.py b/tests/unit/test_openai_compat.py
index 0fa3d0a..497b062 100644
--- a/tests/unit/test_openai_compat.py
+++ b/tests/unit/test_openai_compat.py
@@ -1068,6 +1068,13 @@ class TestManagedReasoningOwnership:
 class TestDefaultClientFactory:
     """直接检查生产 factory，不用取证测试的另一套 factory 代替。"""
 
+    @pytest.fixture(autouse=True)
+    def isolate_proxy_environment(self, monkeypatch):
+        """离线构造测试不继承开发机代理；仍真实验证 trust_env 传递。"""
+        for key in ("HTTP_PROXY", "HTTPS_PROXY", "ALL_PROXY", "NO_PROXY"):
+            monkeypatch.delenv(key, raising=False)
+            monkeypatch.delenv(key.lower(), raising=False)
+
     @pytest.mark.parametrize("key", ["fake-a", "fake-b"])
     async def test_authorization_uses_source_api_key(self, key):
         from polygateway.transports.openai_compat import _default_client_factory