Add State property

libs/langgraph/langgraph/agent/__init__.py

@@ -81,9 +81,17 @@ def create_agent(
     graph.add_node("tools", tool_node)
     for m in middleware:
         if m.__class__.before_model is not AgentMiddleware.before_model:
-            graph.add_node(f"{m.__class__.__name__}.before_model", m.before_model)
+            graph.add_node(
+                f"{m.__class__.__name__}.before_model",
+                m.before_model,
+                input_schema=m.State,
+            )
         if m.__class__.after_model is not AgentMiddleware.after_model:
-            graph.add_node(f"{m.__class__.__name__}.after_model", m.after_model)
+            graph.add_node(
+                f"{m.__class__.__name__}.after_model",
+                m.after_model,
+                input_schema=m.State,
+            )
 
     # add start edge
     first_node = (

libs/langgraph/langgraph/agent/types.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from collections.abc import Sequence
 from dataclasses import dataclass
-from typing import Annotated, Any, Literal, Self
+from typing import Annotated, Any, Literal
 
 from langchain_core.language_models.chat_models import BaseChatModel
 from langchain_core.messages import AnyMessage
@@ -27,22 +27,24 @@ class ModelRequest:
     response_format: ResponseFormat | None
 
 
+@dataclass
+class AgentState:
+    messages: Annotated[list[AnyMessage], add_messages]
+    jump_to: Annotated[JumpTo | None, EphemeralValue] = None
+    response: dict | None = None
+
+
 class AgentMiddleware:
-    def __init__(self) -> None:
+    class State(AgentState):
         pass
 
-    def __copy__(self) -> Self:
-        return self.__class__(**self.__dict__)
-
-    def before_model(self, state: AgentState) -> AgentUpdate | AgentJump | None:
+    def before_model(self, state: State) -> AgentUpdate | AgentJump | None:
         pass
 
-    def modify_model_request(
-        self, request: ModelRequest, state: AgentState
-    ) -> ModelRequest:
+    def modify_model_request(self, request: ModelRequest, state: State) -> ModelRequest:
         return request
 
-    def after_model(self, state: AgentState) -> AgentUpdate | AgentJump | None:
+    def after_model(self, state: State) -> AgentUpdate | AgentJump | None:
         pass
 
 
@@ -54,10 +56,3 @@ class AgentUpdate(TypedDict, total=False):
 class AgentJump(TypedDict, total=False):
     messages: Messages
     jump_to: JumpTo
-
-
-@dataclass
-class AgentState:
-    messages: Annotated[list[AnyMessage], add_messages]
-    jump_to: Annotated[JumpTo | None, EphemeralValue] = None
-    response: dict | None = None