test(groq): add test_litellm regression for assistant metadata strip

tests/test_litellm/llms/groq/chat/test_groq_chat_transformation.py

@@ -0,0 +1,31 @@
+from typing import List, cast
+
+from litellm.llms.groq.chat.transformation import GroqChatConfig
+from litellm.types.llms.openai import AllMessageValues
+
+
+def test_transform_messages_strips_assistant_provider_specific_fields() -> None:
+    """Groq payloads should not include LiteLLM internal assistant metadata."""
+    config = GroqChatConfig()
+    messages = cast(
+        List[AllMessageValues],
+        [
+            {
+                "role": "assistant",
+                "content": "Tool metadata",
+                "provider_specific_fields": {
+                    "mcp_list_tools": [{"name": "weather"}],
+                    "mcp_tool_calls": [{"id": "call_123"}],
+                },
+            }
+        ],
+    )
+
+    transformed = cast(
+        List[AllMessageValues],
+        config._transform_messages(messages=messages, model="qwen/qwen3-32b"),
+    )
+
+    assert transformed[0]["role"] == "assistant"
+    assert transformed[0].get("content") == "Tool metadata"
+    assert "provider_specific_fields" not in transformed[0]