//
// If the script runs to completion or ends by a 'stop' command,
// Execute returns nil.
//
// Execute does not stop background commands started by the script
// before returning. To stop those, use [State.CloseAndWait] or the
// [Wait] command.
func (e *Engine) Execute(s *State, file string, script *bufio.Reader, log io.Writer) (err error) {
	defer func(prev *Engine) { s.engine = prev }(s.engine)
	s.engine = e