Copy-paste fix pattern
library CB-Math
fn main() {
u256 coins = 10
u256 cost = 20
u256 safe = CB-Math.max(coins, cost) - cost
save safe
}Why it happens
A checked unsigned 256-bit subtraction or operation produced a negative result.
How to fix it
Compare before subtracting, clamp to zero, or use a signed type when negative values are intentional.
If the IDE reports a line number, fix that line first, then scan the previous line for an unclosed string, bracket, or block.