core/config+agent: OpenAI provider_tools for hosted Responses tools

Merge opaque tool dicts (web_search, file_search, …) into POST /responses; local ToolRegistry unchanged.

tests/test_runtime/test_client_factory.py

@@ -24,6 +24,19 @@ def test_openai_provider_defaults_base_url() -> None:
     client = create_client(provider)
     assert isinstance(client, ResponsesChatClient)
     assert hasattr(client, "chat_completions")
+    assert client._provider_tools == []
+
+
+def test_openai_provider_tools_passed_to_wrapper() -> None:
+    from plyngent.agent.responses_client import ResponsesChatClient
+
+    provider = OpenAIProvider(
+        access_key_or_token="sk-test",
+        provider_tools=[{"type": "web_search"}],
+    )
+    client = create_client(provider)
+    assert isinstance(client, ResponsesChatClient)
+    assert client._provider_tools == [{"type": "web_search"}]
 
 
 def test_openai_compatible_requires_url() -> None: