convertOrNullStrict
inline fun <S : Any, T : Any> S?.convertOrNullStrict(path: String, from: String, to: String, convert: (S) -> T?): T?
Nullable target, OnFail.Throw: broken → rethrow typed via toMappingException (hard); absent and sanctioned null stay type-driven → null, silent. CancellationException rethrows untouched.