DXN sorted-set (@sorted-set @{ ... }). Wraps a list kept sorted (and deduplicated) as a hard invariant at every construction site — new/1 is the only way to build one, precisely so that structural == between two Dextrin.SortedSets is valid set-equality rather than something that happens to work only when both were built the same way — every construction site (decode, encode, public API) goes through new/1, so the sorted/deduplicated invariant can never be bypassed.