> I am not sure we are talking about the same channels.scm file.  I guess,
> you have in mind ~/.config/guix/channels.scm but it is not the one of
> interest for reproducing.  You need the real one, i.e., "guix describe
> -f channels".
> 
> AFAIU, manifest.scm+$(guix describe -f channel) is enough to have
> "deterministic profile (re)generation".  If not, it means there is a
> "bug" in Inferiors or I miss something.

Bingo! This is exactly what I was missing. Thank you for sifting this out.

Given the stated "goal of ... [allowing] users to move towards declarative
'manifest.scm' style..." I completely mis-interpreted the sense in which you
were using "channels.scm".