Leftover of whatever baseCoin/quoteCoin you supplied as the input
side (same coin type you passed in as input). This is NOT guaranteed
to be zero-value — a partial fill on a real order book leaves genuine
change here. Coin<T> has no drop ability, so this result MUST be
consumed downstream (merged, transferred, or destroy_zero'd) or the
transaction aborts with an unused-value error. If you didn't supply
an explicit input coin, this is a freshly zero-funded coin and is
safe to transfer/destroy unconditionally.
The coin actually produced by the swap (quote if isBaseToCoin, base otherwise) — pipe this into the next call.
Unused DEEP fee change — refund or reuse it, don't let it silently vanish from the PTB's result set.