I'm telling you explicitly that the idea that you need a policy is the whole problem with how you are thinking about this. "We" will do literally nothing. I might do something. You might do something. But no centrally planned collective action whatsoever.
At the scale we're talking about here, the problem described in the subject of this thread is already solved.
One more time, for these people what are your options except giving them free housing, jailing them, or letting them live unhoused?
Reducing the problem is nice but you still have to a policy at the bottom when all else still fails.