code: func (sm *StateMachine) setEntered(in *Msg) {
  	sm.stateEntered = true
  	sm.plugin.SetMemory(in, stateEnteredKey, true)
  }
docs: // setEntered is used internally to set a state as having been entered both in
  // memory and persisted to the database. This ensures that a stateMachine does
  // not run a state's OnEntry function twice.