test: guard custom reasoning roots at the transport boundary

tests/unit/test_openai_compat.py

@@ -1115,3 +1115,31 @@ class TestDefaultClientFactory:
             assert client.trust_env is trust_env
         finally:
             await client.aclose()
+
+
+@pytest.mark.parametrize("key", ["depth.key", "off_control", "switch"])
+async def test_custom_profile_raw_roots_cannot_override_managed_intent(key):
+    registry = {
+        "custom": ProviderProfile(
+            name="custom",
+            thinking=ThinkingWire(
+                off={"off_control": False}, on_base={"switch": True}, effort_key="depth.key"
+            ),
+            strip_think_tags=False,
+        )
+    }
+    sent = []
+    transport = _transport_for(
+        lambda request: sent.append(request) or _sse_stream(_chunk(content="x")), registry=registry
+    )
+    try:
+        with pytest.raises(RequestRejectedError, match="冲突"):
+            await _complete(
+                transport,
+                _source(provider="custom"),
+                reasoning_effort=Effort.HIGH,
+                overlay={key: True},
+            )
+        assert sent == []
+    finally:
+        await transport.aclose()