So... more on this. Appears to just be a problem getting rvm in place when using xsh to execute something.
(experienced the same thing when trying to execute these tasks directly from vim, and the solution there was to add
set shell=/bin/sh in .vimrc, but clearly that doesn't work for xsh)
I have this line in .bash_profile, .bashrc, and now in .profile
[[ -s "$HOME/.rvm/scripts/rvm" ]] && source "$HOME/.rvm/scripts/rvm"
Still, can't get xiki to execute a rake task.