fix(cohere): address review suggestions

- Guard data["messages"] write with 'if messages in data' to avoid
  injecting an empty list when parent transform omits the key
- Add hasattr(tc, "model_dump") guard before calling model_dump on
  non-dict tool calls to avoid AttributeError on unknown types
- Assert type and function fields are preserved after Pydantic model_dump

litellm/llms/cohere/chat/v2_transformation.py

@@ -179,8 +179,10 @@ class CohereV2ChatConfig(OpenAIGPTConfig):
         # Cohere v2 rejects fields that are valid in OpenAI but not in Cohere:
         # 1. 'index' in assistant tool_calls
         # 2. 'name' in tool result messages
+        if "messages" not in data:
+            return data
         sanitized: List[AllMessageValues] = []
-        for message in data.get("messages", []):
+        for message in data["messages"]:
             if hasattr(message, "model_dump"):
                 message = message.model_dump(exclude_unset=True)
             if isinstance(message, dict):
@@ -190,6 +192,8 @@ class CohereV2ChatConfig(OpenAIGPTConfig):
                         {k: v for k, v in tc.items() if k != "index"}
                         if isinstance(tc, dict)
                         else {k: v for k, v in tc.model_dump(exclude_unset=True).items() if k != "index"}
+                        if hasattr(tc, "model_dump")
+                        else tc
                         for tc in message["tool_calls"]
                     ]
                     message = {**message, "tool_calls": cleaned_tool_calls}

tests/test_litellm/llms/cohere/chat/test_cohere_transformation.py

@@ -133,6 +133,8 @@ class TestCohereV2Transform:
         assistant_msg = result["messages"][1]
         assert "index" not in assistant_msg["tool_calls"][0]
         assert assistant_msg["tool_calls"][0]["id"] == "call_abc"
+        assert assistant_msg["tool_calls"][0]["type"] == "function"
+        assert assistant_msg["tool_calls"][0]["function"]["name"] == "get_time"
 
     def test_preserves_messages_without_offending_fields(self):
         """Messages that don't have index or name are passed through unchanged."""