I think you underestimate how good cleaning spells are. You think some wizard is going to clean that pizza stone with their hands like some sort of peasant? They didn’t go to Hogwarts to learn some substandard spell that requires you to preclean like some bargain bin dish soap would.
You think they wouldnt clean the trap after every activation? Leaving scorch marks wouldnt make for a very good trap would it?
Ever tried to clean a pizza stone? Pretty sure that magical fire is supposed to be hotter than the 400 something degrees my oven gets to in using one.
I think you underestimate how good cleaning spells are. You think some wizard is going to clean that pizza stone with their hands like some sort of peasant? They didn’t go to Hogwarts to learn some substandard spell that requires you to preclean like some bargain bin dish soap would.
The trap has a timer that uses prestidigitation to clean the area shortly there after.