Let my canister C has an XDR subaccount for every user. Users send cycles to the subaccount before they can act.
How can I enforce that a user does not use more (or, to say, “much more”, a strict warranty is not necessary) cycles than he/she paid?
Should I to do this estimate (approximate) cost of every operation to count it?
Especially, how to do with “heavy” operations (like canister creation)? I need to know how much it will use, don’t I?