Function ensure_alias 

pub fn ensure_alias() -> Outcome

Keep dev-prune and devp beside each other, whichever of the two is running.

The pair is one binary under two names, and either one can be the survivor. An upgrade that could not replace a running devp leaves a stale alias; an antivirus quarantine, a half-finished uninstall or a Remove-Item aimed at the wrong name leaves only devp. So this restores the other name in whichever direction is missing, rather than only ever creating devp — running either one puts the pair back.