feat(backend): tool support in send agent prompt, regularize inference messages (wip)

backend/src/tool.py

@@ -218,24 +218,17 @@ class ToolCall:
         is_error: Whether the result represents an error.
     """
 
-    def __init__(self, tool_name, arguments={}, id=None):
+    def __init__(self, tool_name, arguments={}, id=None, result=None):
         self.id = id or ""
         self.tool_name = tool_name
         self.arguments = arguments
 
-        self.result = None
+        self.result = result
 
     def __repr__(self):
         id_prefix = self.id + ', ' if self.id else ''
         return f"ToolCall({id_prefix}tool={self.tool_name!r}, args={self.arguments!r})"
 
-    def call_message(self):
-        raise Exception("TODO: Llama message for tool call")
-
-    def result_message(self):
-        from inference import LlamaMessage
-        return LlamaMessage("tool", self.result)
-
 
 # ---------------------------------------------------------------------------
 # Helpers to format tool specs per engine