When a new major release of a non-rolling distro (e.g. Debian) is out, I make a new stratum for the corresponding release. I slowly migrate things over, a few packages at a time. If anything doesn't just-work with the new release, I can easily revert to getting the given functionality from the old one until I've made the necessary adjustments. Once I have everything working confidently with the new release, I can remove the old one.
Bedrock offers a configuration file that declares which packages should come from which stratum [0]. A section of it might look something like this:
# e-mail
arch:pacman isync # mbsync
buster:apt msmtp
buster:apt mutt
buster:apt urlview
# e-mail
arch:pacman isync # mbsync
bullseye:apt msmtp
bullseye:apt mutt
bullseye:apt urlview
That having been said, I don't think this compares favorably to NixOS's much stronger rollback system here. It's a nice bonus for people who otherwise are interested in Bedrock.
[0] https://bedrocklinux.org/0.7/commands.html#pmm-world-file
The general pattern, in case it covers what you are looking for:
- By default, files/filepaths are isolated, similar to chroots/containers. Features the Bedrock Linux development team haven't taken time to work on yet usually work as they would in their native distro, but are not integrated with the rest of the system. This notably includes most things that package managers touch to keep them from fighting each other.
- Bedrock actively integrates a supported list of files/filepaths which are needed to ensure features from different distros interact transparently. The specifics here vary depending on the given feature. Over time, the Bedrock team expands the list of files/filepaths that do something to integrate across strata as solutions are found to do so without introducing conflicts.
- Bedrock purposefully eschews isolating things like processes and network namespaces. Running `htop` shows all processes from all distros. In the worst case scenario, the user can only get the given feature from one distro at a time. The most notable example here is systemd, which requires being run as PID 1; the lack of PID namespacing means a Bedrock system only has one PID 1 at a time. Switching between different distro inits usually requires a reboot.
- A stratum can be "disabled," which both kills all of the associated process and removes the runtime integration with other strata. Once this is done, it can be copied (backed up) or removed safely. The stratum providing PID 1 cannot be disabled, as Linux is not designed to run without a PID 1; to remove the PID 1-providing stratum, a user must first reboot and select another init. The `bedrock` stratum cannot be disabled, mostly because the Bedrock developers didn't put time and effort into supporting that workflow.