fix: restrict provider URL detection to exact hostname matches

tests/agent/test_direct_provider_url_detection.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from run_agent import AIAgent
+
+
+def _agent_with_base_url(base_url: str) -> AIAgent:
+    agent = object.__new__(AIAgent)
+    agent.base_url = base_url
+    return agent
+
+
+def test_direct_openai_url_requires_openai_host():
+    agent = _agent_with_base_url("https://api.openai.com.example/v1")
+
+    assert agent._is_direct_openai_url() is False
+
+
+def test_direct_openai_url_ignores_path_segment_match():
+    agent = _agent_with_base_url("https://proxy.example.test/api.openai.com/v1")
+
+    assert agent._is_direct_openai_url() is False
+
+
+def test_direct_openai_url_accepts_native_host():
+    agent = _agent_with_base_url("https://api.openai.com/v1")
+
+    assert agent._is_direct_openai_url() is True