@tdd_issue @tdd_issue_9994
Feature: TDD Issue #9994 — LangGraph.execute() bypasses is_closed guard
  As a developer using LangGraph
  I want execute() to raise RuntimeError when StateManager is closed
  So that state corruption after close() is prevented

  Background:
    Given the state management system is available

  Scenario: execute() raises RuntimeError after StateManager.close()
    Given a LangGraph instance in running state with a closed StateManager
    When I attempt to execute the graph after close
    Then a RuntimeError should be raised with message "StateManager is closed"

  Scenario: execute() succeeds when StateManager is open
    Given a LangGraph instance in running state with an open StateManager
    When I execute the graph with valid input
    Then the execution should succeed and return a GraphState
