(feat:attach) handle unsupported attachments

application/llm/base.py

@@ -55,3 +55,12 @@ class BaseLLM(ABC):
 
     def _supports_tools(self):
         raise NotImplementedError("Subclass must implement _supports_tools method")
+        
+    def get_supported_attachment_types(self):
+        """
+        Return a list of MIME types supported by this LLM for file uploads.
+        
+        Returns:
+            list: List of supported MIME types
+        """
+        return []  # Default: no attachments supported