Pay for their lodging and food, as long as they never leave the building, and force them to be very close roommates with gang members?

Basically the question is: what do you do with a crazy person, or someone who has relegated themselves to squalor?

The answer for both is that we continue to try to rehabilitate. That means not just throwing them in a hole. A simple example would be to take the money we spend on incarcerating them and spend it on multifaceted programs.

Prison should not be a panacea. Reminder: the US incarcerates more people than the next two biggest encarcerating countries combined, even though our population is 1/5th the size. Either our people are the scum of the earth, or we just find locking people up an acceptable solution to most problems.

Not being interested in rehabilitation isn't an excuse to let folks starve on the streets. Go ahead and make sure folks have a room with a lockable door and food available to them. Keep folks as safe and healthy as possible. Keep offering ways to improve life.