bug#40386: guix system init can't find file system by UUID, workaround results in broken boot

[raingloom]

Trying to install Guix System onto an SSD using an UltraBay dock.
Config is the attached file (with slight variations in the obvious
places)

`readlink /dev/disk/by-uuid/643a215d-a30e-473b-826e-5c35de29e38f` gives
me /dev/sdb1

Yet using (uuid "643a215d-a30e-473b-826e-5c35de29e38f") results in:

```
sudo -E guix system init --no-bootloader
Configs/Guix/desktop-parametric.scm /mnt
 :( /home/raingloom/Configs/Guix/desktop-parametric.scm:50:26: error:
file system with UUID '643a215d-a30e-473b-826e-5c35de29e38f' not found
```

Switching the UUID to uppercase as in the example (thankfully) doesn't
change anything, not even the error message.

I tried using a label, same result.

I ended up using the /dev/disk/by-uuid and /dev/disk/by-id paths for
the root file system and the bootloader respectively, and that resulted
in a succesful system init, but upon trying to boot the SSD with the
other machine, I got thrown into a rescue shell, because it couldn't
find the root using that path.

**(Quick aside: there really should be a guide for using that rescue
shell. I can get around in a /bin/sh one, but this is nearly unusable.
At least autocompletion should be supported.)**

I tried modifying the --root kernel parameter from Grub, so that it
would point to /dev/sda1 directly (which is the device's name on the
other machine), but I was thrown into the rescue shell again, with the
same backtrace (with the old path replaced with /dev/sda1 of course).

Sooo, I have no idea what to do. Any tips on debugging this?

Or on reconfiguring a Guix System install that is on an external file
system? On Arch I'd just arch-chroot into it and fix it from there, but
I don't know of anything similar for Guix.

desktop-parametric.scm
Description: Text Data