fix(llm): use the OpenAI Responses API only for native endpoints

The Responses API exists only on native OpenAI. When the openai provider is
pointed at a custom base_url (a proxy, gateway, or local server that speaks only
Chat Completions), keep the Responses API off so the call does not fail.

tests/test_openai_responses_base_url.py

@@ -0,0 +1,43 @@
+"""The Responses API only exists on native OpenAI; a custom base_url on the
+openai provider must fall back to Chat Completions (#1024)."""
+
+from __future__ import annotations
+
+import pytest
+
+from tradingagents.llm_clients.openai_client import (
+    OpenAIClient,
+    _is_native_openai_base_url,
+)
+
+
+@pytest.mark.unit
+class NativeBaseUrlTests:
+    def test_unset_is_native(self):
+        assert _is_native_openai_base_url(None) is True
+        assert _is_native_openai_base_url("") is True
+
+    def test_openai_hosts_are_native(self):
+        assert _is_native_openai_base_url("https://api.openai.com/v1") is True
+        assert _is_native_openai_base_url("api.openai.com/v1") is True
+
+    def test_custom_endpoints_are_not_native(self):
+        assert _is_native_openai_base_url("http://localhost:1234/v1") is False
+        assert _is_native_openai_base_url("https://my-gateway.example.com/v1") is False
+        assert _is_native_openai_base_url("https://api.openai.com.evil.com/v1") is False
+
+
+@pytest.mark.unit
+class ResponsesApiSelectionTests:
+    def test_native_openai_enables_responses_api(self, monkeypatch):
+        monkeypatch.setenv("OPENAI_API_KEY", "sk-test")
+        llm = OpenAIClient("gpt-5.5", provider="openai").get_llm()
+        assert getattr(llm, "use_responses_api", False) is True
+
+    def test_custom_base_url_disables_responses_api(self, monkeypatch):
+        monkeypatch.setenv("OPENAI_API_KEY", "sk-test")
+        llm = OpenAIClient(
+            "gpt-5.5", base_url="http://localhost:1234/v1", provider="openai"
+        ).get_llm()
+        # use_responses_api should be absent/False so the client speaks Chat Completions.
+        assert getattr(llm, "use_responses_api", False) is False

tradingagents/llm_clients/openai_client.py

@@ -1,6 +1,7 @@
 import os
 from dataclasses import dataclass
-from typing import Any, Optional
+from typing import Any
+from urllib.parse import urlparse
 
 from langchain_core.messages import AIMessage
 from langchain_openai import ChatOpenAI
@@ -84,7 +85,7 @@ class DeepSeekChatOpenAI(NormalizedChatOpenAI):
     def _get_request_payload(self, input_, *, stop=None, **kwargs):
         payload = super()._get_request_payload(input_, stop=stop, **kwargs)
         outgoing = payload.get("messages", [])
-        for message_dict, message in zip(outgoing, _input_to_messages(input_)):
+        for message_dict, message in zip(outgoing, _input_to_messages(input_), strict=False):
             if not isinstance(message, AIMessage):
                 continue
             reasoning = message.additional_kwargs.get("reasoning_content")
@@ -102,7 +103,7 @@ class DeepSeekChatOpenAI(NormalizedChatOpenAI):
             )
         )
         for generation, choice in zip(
-            chat_result.generations, response_dict.get("choices", [])
+            chat_result.generations, response_dict.get("choices", []), strict=False
         ):
             reasoning = choice.get("message", {}).get("reasoning_content")
             if reasoning is not None:
@@ -167,8 +168,8 @@ class ProviderSpec:
     """
 
     chat_class: type = NormalizedChatOpenAI   # provider quirks live in the subclass
-    base_url: Optional[str] = None            # default endpoint (None -> SDK default)
-    base_url_env: Optional[str] = None        # env var that overrides base_url (e.g. OLLAMA_BASE_URL)
+    base_url: str | None = None            # default endpoint (None -> SDK default)
+    base_url_env: str | None = None        # env var that overrides base_url (e.g. OLLAMA_BASE_URL)
     key_optional: bool = False                # don't require/prompt; send a placeholder if unset
     placeholder_key: str = "EMPTY"            # sent when no key is available (keyless local servers)
     require_base_url: bool = False            # error if no base_url is resolved (generic endpoint)
@@ -205,6 +206,22 @@ def is_openai_compatible(provider: str) -> bool:
     return provider.lower() in OPENAI_COMPATIBLE_PROVIDERS
 
 
+def _is_native_openai_base_url(base_url: str | None) -> bool:
+    """True when ``base_url`` is unset or points at api.openai.com.
+
+    The Responses API (/v1/responses) only exists on native OpenAI. A custom
+    base_url on the ``openai`` provider (a proxy, gateway, or local server)
+    speaks only Chat Completions, so the Responses API must stay off there even
+    though the provider spec enables it (#1024).
+    """
+    if not base_url:
+        return True
+    if "://" not in base_url:
+        base_url = "https://" + base_url
+    host = urlparse(base_url).hostname or ""
+    return host == "api.openai.com" or host.endswith(".openai.com")
+
+
 class OpenAIClient(BaseLLMClient):
     """Client for OpenAI, Ollama, OpenRouter, and xAI providers.
 
@@ -217,7 +234,7 @@ class OpenAIClient(BaseLLMClient):
     def __init__(
         self,
         model: str,
-        base_url: Optional[str] = None,
+        base_url: str | None = None,
         provider: str = "openai",
         **kwargs,
     ):
@@ -264,7 +281,10 @@ class OpenAIClient(BaseLLMClient):
                     f"(e.g. add {api_key_env}=your_key to your .env file)."
                 )
 
-            if spec.use_responses_api:
+            # The Responses API only exists on native OpenAI; if the user points
+            # the openai provider at a custom base_url (proxy/gateway/local), it
+            # only speaks Chat Completions, so keep Responses off there (#1024).
+            if spec.use_responses_api and _is_native_openai_base_url(base_url):
                 llm_kwargs["use_responses_api"] = True
         elif self.base_url:
             llm_kwargs["base_url"] = self.base_url