code: func (s *SeesawEngine) OverrideBackend(args *ipc.Override, reply *int) error {
  	if args == nil {
  		return errors.New("args is nil")
  	}
  	ctx := args.Ctx
  	s.trace("OverrideBackend", ctx)
  	if ctx == nil {
  		return errors.New("context is nil")
  	}
  
  	if !ctx.IsTrusted() {
  		return errors.New("insufficient access")
  	}
  
  	if args.Backend == nil {
  		return errors.New("backend is nil")
  	}
  	s.engine.queueOverride(args.Backend)
  	return nil
  }
docs: // OverrideBackend passes a BackendOverride to the engine.