Surprising results when using pydantic for state schema

[eyurtsev]

Privileged issue

• I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here.

Issue Content

Run time validation with pydantic schema does not work with output schema.

from langgraph.graph import StateGraph, START, END
from typing_extensions import TypedDict

from pydantic import BaseModel

# The overall state of the graph (this is the public state shared across nodes)
class OverallState(BaseModel):
    a: float

def node_1(state: OverallState) -> OverallState:
    return {
        "a": "foo"
    }

# Build the state graph
builder = StateGraph(OverallState, output=OverallState)
builder.add_node(node_1)  # node_1 is the first node
builder.add_edge(START, "node_1")  # Start the graph with node_1
builder.add_edge("node_1", END)  # End the graph after node_1
graph = builder.compile()

graph.invoke(
    {
        "a": 2.3
    }
)

Result

{'a': 'foo'}

This result does not match the output schema!

Expected

Expected a validation error