That’s what every Cashu wallet does. If the proofs in store don’t fit the required amount the wallet will do a swap first. Only in offline environments wallets will tolerate an overspend if instru...
Even if it's possible to make the exact amount with the current token combinations, it still ends up using just the tokens I have on hand, which can result in multiple inputs—like sending 256 using two 128s, for example. Swapping to send a single 256 token looks cleaner. But would making that the default behavior be wasteful due to the extra network round trip?