We don't, and legally we can't. Once they accept the ticket to SF and choose to make their home on the sidewalk, they become our problem, legally. And SF (even now) is so much nicer than Texas that few of the homeless are willing to go back.
Disputes between states are always political and only occasionally legal.
But yeah I can see it being difficult to prove, and harder to action. If one state wanted to sue the other, what is the process? Congress? Supreme court?
