In case this is of interest to someone: I've created a fork of the
Devuan unstable mdadm package which can be built on daedalus. This has
mdadm version 4.5 which is required for creating persistent
superblocks which work with newer kernels (at least 6.18 and 6.19, I'm
presently running 6.19.1). I've also done some cleanup work on this
(refreshed patches), made working with the package a little easier
and removed all traces of systemd support from the generated package
(this is not a meaningul technical improvement for any definition of
that, I just wanted it gone for spiritual reasons).

I'm planning to do some more work on this but - so far - have no idea
what exactly. Probably go over the bug list and fix whatever I can.

This is available from GitHub:

https://github.com/rweikusat/mdadm-devuan