> Alas, I'm not a Linux wizard.
We got a volunteer from Guix.
> But could we just move the cron entry back to /etc/cron.daily/?
Yes, we should do that if cron.d does not work. In any case, I ran the
updater manually and new posts showed up.
> I spent a long time yesterday looking for suitable software to replace
> Planet Venus, but in vain.  All the software I found was designed for
> individual use, or was otherwise unsuitable.  I would love to have
> something written in Scheme, of course,

I came to the same conclusion. Indeed, a Scheme aggregator would be just
the ticket.

> but all the corner cases and error handling make it look like a big
> job to write something new.  I'm not sure what to do.  I'd even be
> willing to contribute to paying a small annual fee if there were a
> company out there that would do this for us.

IMHO the best approach is to ship Scheme libraries from which a
tailor-made aggregator can be easily built.

For example, if you look at Planet Venus' configuration files
(https://github.com/schemeorg-community/planet.scheme.org/tree/master/planet),
they're trying to shoehorn an entire web framework into some .ini files
and HTML/XML templates. One can predict that all Planet software will
eventually turn out this way, as there are so many peculiar
customizations that users will want to do.

The problem is best solved by inverting that appoach. Let users build a
web app using the web framework they want, using the templates and
customizations they want, and then call out to a Planet library to fill
in content from the feed and to update the feed. It might make sense to
use Racket or Chicken.