sources is up and I can mount it from inside and outside, with and
without authentication, though we do get occasional console messages
like these:

Mon Nov 27 15:16:53: attach main as forsyth: not enough data in auth read
Mon Nov 27 16:16:12: attach main as forsyth: not enough data in auth read
Tue Nov 28 09:30:11: attach main as geoff: phase error protocol phase error: read in state SNeedProto
Tue Nov 28 09:30:13: attach main as geoff: phase error protocol phase error: read in state SNeedProto
Wed Nov 29 09:30:11: attach main as geoff: phase error protocol phase error: read in state SNeedProto
Wed Nov 29 09:30:13: attach main as geoff: phase error protocol phase error: read in state SNeedProto

In this case, your connection to sources has dropped, so you need to
remove /srv/sources, and you'll need to be hostowner to do that if you
don't own /srv/sources, then execute `9fs sources' again.