As an administrator, I want to be able to keep track of which blueprint version (at least) has been used to create which ostree commit so that I can validate down to each individual edge device which commit I have and where it did come from, without having to document and compare commit IDs.

As we discussed in Slack, the basic idea would be for composer-cli compose start-ostree to understand some metadata options and pass them to the underlying ostree or rpm-ostree command, like rpm-ostree compose commit --add-metadata-string=KEY=VALUE or ostree commit --add-metadata-string=KEY=VALUE --subject=SUBJECT --body=BODY --body-file=FILE...

I have a preference for the -subject because it is easy to retrieve using rpm-ostree log, but -add-metadata-string is also covering the requirement (using ostree show), long term more powerful, and apparently easier to implement.