convertEachOrFailToSet
inline fun <S : Any, T : Any> Iterable<S?>.convertEachOrFailToSet(path: String, from: String, to: String, convert: (S) -> T): Set<T>
OnFail.Throw to Set<T>: broken element → HARD typed MappingException at the indexed path; null element skips with report; post-conversion convergence is reported. CancellationException rethrows untouched.