Prototype: implement <T> Optional<T> first(List<T> values). Return empty only for an empty list, otherwise the first element. Null elements are outside the domain; do not mutate input.
Final: implement <T,R> List<R> map(List<? extends T> values, Function<? super T,? extends R> transform). Apply transform exactly once per element in encounter order, return a fresh list, preserve input, and propagate a transform's exception unchanged. Results may be null. Empty input invokes no transform. Keep the generic signatures: tests compile a Number consumer against Integer inputs.
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