> Really got me pissed, the fact that library mobs even attack him in the first place is annoying and unintuitive, but the fact he's weak enough to die to a random fire giant only adds up to the jarringness
see, this isn't a bug in adom, it is a feature. It will teach you, like a twitchy sadist with a cattle prod, it will teach you to never trust anything. You will soon be looking 4 ways before crossing the street. Things could come dropping from the sky or crashing up from the underground at any time, it is best to be prepared.
If it were me, I would not suffice at walling off the librarian with simple locked doors, as too many mobs can smash through those. It would be much better to fill a large portion of the level with breeders, then wall them off and kill all other mobs on the level. (don't forget to check every tile on the map for tp and corruption traps though, else you are asking for breeder problems )
The uncooperative librarian problem is a well-known one. Don't look for a bugfix anytime soon, as we were asking for that for half a dozen years before the resurrection.
"Whip me!" pleads the adom player. The rng replies... "No."