diff --git a/tests/agent/test_auxiliary_client_proxy_env.py b/tests/agent/test_auxiliary_client_proxy_env.py
new file mode 100644
index 00000000000..bde42ff815c
--- /dev/null
+++ b/tests/agent/test_auxiliary_client_proxy_env.py
@@ -0,0 +1,98 @@
+"""Regression guard: auxiliary OpenAI clients must use env-only proxy policy.
+
+On macOS, httpx with default ``trust_env=True`` reads system proxy settings
+via ``urllib.request.getproxies()`` but not the macOS proxy exception list.
+Auxiliary clients (vision, title generation, etc.) must mirror the main
+agent: explicit ``HTTPS_PROXY`` / ``NO_PROXY`` env vars only, via a custom
+keepalive transport that suppresses automatic system-proxy detection.
+"""
+from unittest.mock import patch
+
+import httpx
+
+from agent.auxiliary_client import _create_openai_client, _openai_http_client_kwargs
+from agent.process_bootstrap import _get_proxy_for_base_url
+
+
+def _pool_types(http_client) -> list:
+    return [
+        type(mount._pool).__name__
+        for mount in http_client._mounts.values()
+        if mount is not None and hasattr(mount, "_pool")
+    ]
+
+
+@patch("agent.auxiliary_client.OpenAI")
+def test_create_openai_client_routes_via_env_proxy(mock_openai, monkeypatch):
+    for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY",
+                "https_proxy", "http_proxy", "all_proxy", "NO_PROXY", "no_proxy"):
+        monkeypatch.delenv(key, raising=False)
+    monkeypatch.setenv("HTTPS_PROXY", "http://127.0.0.1:7897")
+
+    _create_openai_client(
+        api_key="test-key",
+        base_url="https://litellm.internal.example.com/v1",
+    )
+
+    http_client = mock_openai.call_args.kwargs.get("http_client")
+    assert isinstance(http_client, httpx.Client)
+    assert "HTTPProxy" in _pool_types(http_client)
+    http_client.close()
+
+
+@patch("agent.auxiliary_client.OpenAI")
+def test_create_openai_client_no_proxy_when_env_unset(mock_openai, monkeypatch):
+    for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY",
+                "https_proxy", "http_proxy", "all_proxy", "NO_PROXY", "no_proxy"):
+        monkeypatch.delenv(key, raising=False)
+
+    _create_openai_client(
+        api_key="test-key",
+        base_url="https://litellm.internal.example.com/v1",
+    )
+
+    http_client = mock_openai.call_args.kwargs.get("http_client")
+    assert isinstance(http_client, httpx.Client)
+    assert "HTTPProxy" not in _pool_types(http_client)
+    http_client.close()
+
+
+@patch("agent.auxiliary_client.OpenAI")
+def test_create_openai_client_ignores_macos_system_proxy(mock_openai, monkeypatch):
+    """System proxy from getproxies() must not apply when env vars are unset."""
+    for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY",
+                "https_proxy", "http_proxy", "all_proxy", "NO_PROXY", "no_proxy"):
+        monkeypatch.delenv(key, raising=False)
+
+    with patch(
+        "urllib.request.getproxies",
+        return_value={"http": "http://127.0.0.1:7897", "https": "http://127.0.0.1:7897"},
+    ):
+        _create_openai_client(
+            api_key="test-key",
+            base_url="https://litellm.internal.example.com/v1",
+        )
+
+    http_client = mock_openai.call_args.kwargs.get("http_client")
+    assert isinstance(http_client, httpx.Client)
+    assert "HTTPProxy" not in _pool_types(http_client)
+    http_client.close()
+
+
+def test_get_proxy_for_base_url_respects_no_proxy(monkeypatch):
+    for key in ("HTTPS_PROXY", "HTTP_PROXY", "ALL_PROXY",
+                "https_proxy", "http_proxy", "all_proxy", "NO_PROXY", "no_proxy"):
+        monkeypatch.delenv(key, raising=False)
+    monkeypatch.setenv("HTTPS_PROXY", "http://127.0.0.1:7897")
+    monkeypatch.setenv("NO_PROXY", "internal.example.com")
+
+    assert _get_proxy_for_base_url("https://litellm.internal.example.com/v1") is None
+    assert _get_proxy_for_base_url("https://api.openai.com/v1") == "http://127.0.0.1:7897"
+
+
+def test_openai_http_client_kwargs_async_mode():
+    kwargs = _openai_http_client_kwargs(
+        "https://litellm.internal.example.com/v1",
+        async_mode=True,
+    )
+    assert isinstance(kwargs["http_client"], httpx.AsyncClient)