Thanks for coming back to this!

The case should be testable, right?

@ianna UnmaskedArray behaves as an option, and so we will be taking slow paths if we're only testing is_option. My feeling with Awkward is that we're dealing with a closed set of node types (or at least, closed set of families), so adding a new flag that's helpful to identify a member of that set is fine!

I don't entirely follow your question about dropping recursively; we can repeatedly simplify UnmaskedArray(UnmaskedArray(...)), but we can't simplify through type boundaries like lists.