Is there a way to get a OsChar literal more conveniently than osp + head

I can certainly add such a quasiquoter if you find it useful.

Feel free to create a PR. The osstr quasiquoter is here for an example: os-string/System/OsString/Internal.hs at 0cc9aded7e582c508fb4246700aaecf7956d9877 · haskell/os-string · GitHub