It seems impossible to run snap_1 from snap_2 where snap_2 is classic. This seems significant.
alan@hal:~$ snap version
alan@hal:~$ snap run zzt
cannot execute snap-update-ns: Permission denied
snap-update-ns failed with code 1: No such file or directory
Steps to reproduce.
snap install cool-retro-term --classic
snap install zzt
snap run cool-retro-term
Then, inside cool-retro-term (which, is very cool).
snap run zzt
Here’s a pretty picture.