I'm sure that I can figure out either some `defcustom' goop or worse to
sort it out so that the initialisation happens correctly.

> > `notmuch-crypto-process-mime' is used only in notmuch-show.el, so the
> > setting really belongs there with an appropriate name.
> 
> I intentionally put this in a separate section in case there were
> eventually other needs for this setting beyond just show mode.  I
> personally think we should just leave it where it is, particularly
> since it's been there for a while.

Okay.