I think that’s almost it. My bet is that the invisibility cloak detector is the missing charm. Harry and Quirrell are already in the room when they arrive for the first time, and as soon as they see themselves leave via Time-Turner, they take the cloak off and finish their meal before leaving. But yeah, they have to be in the room at the same time that a bunch of charms are on it, so they can’t seal it off completely.
I’m pretty sure you (and VN) have it right. EY commented (to VN) that someone had already figured it out, and your theory had already appeared in a comment at the main fanfic review site.
I think that’s almost it. My bet is that the invisibility cloak detector is the missing charm. Harry and Quirrell are already in the room when they arrive for the first time, and as soon as they see themselves leave via Time-Turner, they take the cloak off and finish their meal before leaving. But yeah, they have to be in the room at the same time that a bunch of charms are on it, so they can’t seal it off completely.
I’m pretty sure you (and VN) have it right. EY commented (to VN) that someone had already figured it out, and your theory had already appeared in a comment at the main fanfic review site.