fix(llm): send MiniMax reasoning_split via extra_body so the openai SDK accepts it (#826)

tests/test_minimax.py

@@ -25,34 +25,22 @@ def _client(model: str = "MiniMax-M2.7"):
 
 @pytest.mark.unit
 class TestMinimaxReasoningSplit:
-    def test_request_payload_sets_reasoning_split(self):
+    def test_reasoning_split_sent_via_extra_body_not_top_level(self):
+        # Must be in extra_body, not top-level: the openai SDK validates
+        # top-level params and rejects unknown ones like reasoning_split (#826).
         payload = _client()._get_request_payload([HumanMessage(content="hi")])
-        assert payload.get("reasoning_split") is True
-
-    def test_caller_supplied_reasoning_split_is_preserved(self):
-        """If the user explicitly sets reasoning_split, don't override it
-        (setdefault semantics — caller wins)."""
-        client = _client()
-        payload = client._get_request_payload(
-            [HumanMessage(content="hi")],
-            reasoning_split=False,
-        )
-        # langchain may or may not surface that kwarg into the payload;
-        # what matters is we don't blindly overwrite a non-default value
-        # the caller passed. setdefault leaves an existing value alone.
-        assert payload.get("reasoning_split") in (False, True)
+        assert payload.get("extra_body", {}).get("reasoning_split") is True
+        assert "reasoning_split" not in payload  # never top-level
 
     def test_non_reasoning_minimax_does_not_inject_reasoning_split(self):
         """Coding Plan / MiniMax-Text-01 / any non-M2-prefixed model must NOT
-        receive reasoning_split — the openai SDK rejects unknown kwargs with
-        TypeError (#826)."""
+        receive reasoning_split at all (top-level or extra_body) (#826)."""
         for model in ("minimax-text-01", "MiniMax-Coding-Plan"):
             payload = _client(model)._get_request_payload(
                 [HumanMessage(content="hi")]
             )
-            assert "reasoning_split" not in payload, (
-                f"{model!r} payload unexpectedly contains reasoning_split"
-            )
+            assert "reasoning_split" not in payload
+            assert "reasoning_split" not in payload.get("extra_body", {})
 
 
 @pytest.mark.unit