Fully consistent fall warnings. There are at least three kinds:
(1) By naming convention:
> look s
South of here is Over the Edge.
[Near]
Nothing.
(2) When you look <direction>; e.g.:
> s
Some Place [N, E, S, W]
Sand. Scrub. Rocks. It smells like dust and sweat.
> lo s
To the south, the dessert plunges into a vast crevasse. Do you feel lucky?
[Near]
Nothing.
(3) When you enter a room with fall-danger exits; e.g.:
> s
The ground crumbles and falls away treacherously to the south!
Some Place [N, E, S, W]
Sand. Scrub. Rocks. It smells like dust and sweat.
> lo s
South of here is A Crumbly Edge.
[Near]
Nothing.
My choice would be "everything follows method #1 + method #2" (consistent naming of fall rooms; consistent warning when you look). I find #3 easy to miss. But making everything consistent, one way or another, would help this player's cognition.
For triple bonus points: a mode-toggle that can prevent you from attempting to enter climb rooms (similar to how follow currently stops you when the leader enters a climb room).
Obviously there's a game design aspect here...some people find this kind of random danger fun. So that's a decision to be made. (If we wanted to play up the danger, making everything less consistent would be more to the point.)