@phoenixwarbird I think the point of Law 10 is to prevent the trivial "I break the mirror with a foo" arguments - which, incidentally, is not confined to glass with a reflective coating adhered to one side; Law 10 also precludes "I drop a knife from 6 feel point downward into a highly polished, perfectly reflecting silver platter" which should be a "mirror" boundary with no glass to impede the knife.

In either case the mirror/boundary has a physical form that must remain intact as a flat rigid plane (Law 8) for the boundary interactions to function, and that per Law 10, the surface integrity being violated by an object or a force moving against it will break the Law 8 constraint before the moving object or force could pass through the boundary.