DNF5 has a transaction serialize method: https://dnf5.readthedocs.io/en/latest/api/python/libdnf5_transaction.html#libdnf5.transaction.Transaction.serialize (experimental) and the ability to replay transactions from that JSON where the RPMs and comps are sourced from the local filesystem: https://dnf5.readthedocs.io/en/latest/commands/replay.8.html

We should see if we can whip up an experimental depsolver that dumps transaction jsons + comps + rpms and then have a org.osbuild.dnf5.replay stage that can run dnf5 on those.