fix(deepseek): deepseek-reasoner model cannot return reasoning_content with tools

libs/core/langchain_core/output_parsers/openai_tools.py

@@ -242,6 +242,18 @@ def parse_result(self, result: list[Generation], *, partial: bool = False) -> An
             msg = "This output parser can only be used with a chat generation."
             raise OutputParserException(msg)
         message = generation.message
+
+        # Preserve DeepSeek reasoning during OpenAI-tool parsing
+        if (
+            hasattr(message, "additional_kwargs")
+            and "reasoning_content" in message.additional_kwargs
+            and isinstance(message, AIMessage)
+            and message.tool_calls
+        ):
+            message.additional_kwargs["_deepseek_reasoning"] = (
+                message.additional_kwargs["reasoning_content"]
+            )
+
         if isinstance(message, AIMessage) and message.tool_calls:
             parsed_tool_calls = [dict(tc) for tc in message.tool_calls]
             for tool_call in parsed_tool_calls:

libs/partners/deepseek/langchain_deepseek/chat_models.py

@@ -288,25 +288,36 @@ def _create_chat_result(
         if not isinstance(response, openai.BaseModel):
             return rtn
 
-        for generation in rtn.generations:
-            if generation.message.response_metadata is None:
-                generation.message.response_metadata = {}
-            generation.message.response_metadata["model_provider"] = "deepseek"
-
         choices = getattr(response, "choices", None)
-        if choices and hasattr(choices[0].message, "reasoning_content"):
-            rtn.generations[0].message.additional_kwargs["reasoning_content"] = choices[
-                0
-            ].message.reasoning_content
-        # Handle use via OpenRouter
-        elif choices and hasattr(choices[0].message, "model_extra"):
-            model_extra = choices[0].message.model_extra
-            if isinstance(model_extra, dict) and (
-                reasoning := model_extra.get("reasoning")
-            ):
-                rtn.generations[0].message.additional_kwargs["reasoning_content"] = (
-                    reasoning
-                )
+
+        for generation in rtn.generations:
+            msg = generation.message
+
+            if msg.response_metadata is None:
+                msg.response_metadata = {}
+            msg.response_metadata["model_provider"] = "deepseek"
+
+            # native reasoning_content
+            if choices and hasattr(choices[0].message, "reasoning_content"):
+                msg.additional_kwargs["reasoning_content"] = choices[
+                    0
+                ].message.reasoning_content
+                continue
+
+            # recovered reasoning from parser patch
+            if "_deepseek_reasoning" in msg.additional_kwargs:
+                msg.additional_kwargs["reasoning_content"] = msg.additional_kwargs[
+                    "_deepseek_reasoning"
+                ]
+                continue
+
+            # Handle use via OpenRouter
+            if choices and hasattr(choices[0].message, "model_extra"):
+                model_extra = choices[0].message.model_extra
+                if isinstance(model_extra, dict):
+                    reasoning = model_extra.get("reasoning")
+                    if reasoning:
+                        msg.additional_kwargs["reasoning_content"] = reasoning
 
         return rtn