The semi-permeable barrier is in place.
Permeability to Kitty / Paws / Shadow / Мало, or whatever her actual name might be, is confirmed:
It seems to be a snuggish fit for the little critter, so it should probably provide some fair bit of discouragement for the three monsters. Hm. Probably merging households next week, so I ought to figure out what to do about extending the height of the kitty filter, so's Huckleberry won't just jump over it.