fix: 'HandoffTool' object has no attribute 'agent' (#5005)

* fix: 移动agent的位置到super().__init__之后

* add: 添加一行注释

astrbot/core/agent/handoff.py

@@ -15,7 +15,6 @@ class HandoffTool(FunctionTool, Generic[TContext]):
         tool_description: str | None = None,
         **kwargs,
     ) -> None:
-        self.agent = agent
 
         # Avoid passing duplicate `description` to the FunctionTool dataclass.
         # Some call sites (e.g. SubAgentOrchestrator) pass `description` via kwargs
@@ -34,6 +33,8 @@ class HandoffTool(FunctionTool, Generic[TContext]):
         # Optional provider override for this subagent. When set, the handoff
         # execution will use this chat provider id instead of the global/default.
         self.provider_id: str | None = None
+        # Note: Must assign after super().__init__() to prevent parent class from overriding this attribute
+        self.agent = agent
 
     def default_parameters(self) -> dict:
         return {