This actually bumps the lower bound for optparse-applicative, which allows us to rely on its export of (<>).
extopenscad: Compatibility with optparse-applicative-0.5
extopenscad.hs:57:54: Not in scope: `<>'
extopenscad.hs:67:17: Not in scope: `<>'
I'm not sure what is going on with later versions. I suspect that this is it, though:
I think my solution (hiding (<>) and reimplementing it) is probably the most widely compatible approach.