Usernames can have underscores in them, but domains can't, breaking username-valname.val.run.

[CarlQLange]

Eg my username is csl_, so my val csl_-whatever.val.run is technically an invalid domain. Probably you need to disallow usernames with underscores, or rewrite the underscores to dashes, or both :)

[singpolyma]

I noticed the same problem in that vals can have underscores in the name