During bootc installation as of current implementations, files written to `/var` in `%post` scripts are not accessible after reboot. The files end up in the deployment directory's `/var` (`/ostree/deploy/<stateroot>/deploy/<commit>/var/...`) instead of the physical root's `/var` (`/ostree/deploy/<stateroot>/var`), which is where `/var` is bind-mounted in the running system.

Current Behavior

• When `%post` scripts write to `/var/lib/extensions/kickstart-tests`, files are written to the deployment directory's `/var`
• After reboot, `/var` is bind-mounted from `/ostree/deploy/<stateroot>/var`
• Files written during `%post` are not accessible at `/var` in the running system

Expected Behavior

Files written to `/var` during `%post` should be accessible after reboot at the same path, as `/var` should be writable and persist across deployments.

Impact

• Blocks `%post` scripts that need to write files to `/var` for use after reboot
• Affects kickstart tests that rely on files in `/var` being accessible after first boot

Related to: https://issues.redhat.com/browse/INSTALLER-4026
Related to: https://issues.redhat.com/browse/INSTALLER-4273