How do you handle students who cancel last-minute?

Genuinely curious how other tutors deal with this. I keep getting "can I still cancel?" texts an hour or two before a session — I lose the prep time and the slot either way, but it always feels awkward to actually charge for it.

Right now the fixes I've seen people use: a flat cancellation policy in writing, a deposit up front, or software that just applies pricing automatically inside a set window so you don't have to be the bad guy about it (that's actually the route I went — set a threshold and it handles it without a conversation).

What's worked for you? Flat rule, deposit, something else?