While the debian repository delivers Contents files (see e.g. http://cdn-fastly.deb.debian.org/debian/dists/testing/main/), the Purism repository does not. There *are* Contents* files, but they are outdated (March 2017) and are not delivered to apt (see https://repo.puri.sm/pureos/dists/green/main/).
Whithout Contents files, e.g. command-not-found is useless (see T637).
[Update: I now see that this is T155. Possibly this should be marked as a duplicate of that? I don't yet know how to do that.]
The terminology on the user interface of this bug system is a bit confusing to me. What I'm trying to do with this is “add a comment to a bug report”. If I'm doing the wrong thing here, please explain the correct way to do what I want.
My comment is that there are “Contents” files in the repo, but they are all gzip-compressed empty files. For example, if you run the command “wget http://repo.pureos.net/pureos/dists/byzantium/main/Contents-amd64.gz”, you will get back a 20-byte file that decompresses to the 0-byte file. This is, of course, not the way it should be. This breaks not only command-not-found, but also apt-file. Can someone please investigate why the repo-generation procedure is making empty Contents indices and fix it so that these files obey the Debian repository rules? This would be a huge help to many people. apt-file is one of the most useful Debian tools. It is much easier to use a Debian-based system when apt-file is working. You can figure out which package you need much more quickly.