[mikepurvis]

Interestingly, the legacy debian-installer is based on a package manager called anna (Anna's not nearly Apt), where most of the installation steps are implemented as postinst bash scripts of various udeb packages: https://salsa.debian.org/installer-team/anna#README

However, there's little documentation for any of this, and it's clearly not intended to be used for anything outside of the installer context— I couldn't even figure out how to do the equivalent of a debootstrap for an anna environment. For my own custom installer needs it turned out to be easier to use a conventional deb/apt environment and implement most of the logic in Python.