1st of all, I'd like to thank stupot (see reply below) because of my crazy question... Please, let me submit my question again:
Why magneto-gtk3 doesn't depend on rigo?
Indeed, when installing magneto-gtk3 following packages are also installed because of their dependency:
magneto-loader => magneto-core => rigo-daemon
But rigo isn't installed implicitly
So, without rigo installed, how using magneto for updating our OS? Option which launch frontend (rigo I guess) doesn't work because there is no frontend installed yet.
Installing rigo explicitly indeed solve this issue but I wonder if there is another solution (fixing dependency issue if lxnay thinks there is a dependency issue)

