Im nor arguing exactly since I dont know the halachah but you say it has to have no effect in addition to being not visible. Flicking a switch does build a circuit that wasn’t there before. It certainly DOES have an effect, just not the effect of turning on a light This idea of not seeing an effect also puzzles me.
So if I build something inside a hollow wall, say by using magnets to move metal parts that are behind the wall, to build a complete vessel, that is not a melacha?