Implement systemd soft-reboot for seamless post-installation transitions

[leandromqrs]

Requiring a hardware reboot after installation adds unnecessary friction for image-based OSes. I propose using systemd soft-reboot to transition directly from the Live USB into the installed system, skipping the BIOS/UEFI boot entirely.

The flow is straightforward: mount the new root to /run/nextroot/, verify if the Live USB kernel matches the installed one, and trigger systemctl soft-reboot. If they mismatch, it falls back to a standard hardware reboot.

Let me know if you're open to a PR implementing this seamless transition.

[nothingneko]

a real reboot makes it absolutely clear that the USB is no longer in use. also does this require the USB to remain plugged in until the next real reboot?

[Owen-sz]

We could have a prompt pop up telling the user it's ok to remove?

[leandromqrs]

We can eject the device too and show a message that is safe to remove it

[korewaChino]

this might not work well with bootc since the root backend is kind of different now that you mount OSTree or composefs as root, so yeah...

[nothingneko]

i'm also questioning how this would work with traditional installs and bootc combo images

[madonuko]

I suppose bootc also uses switchroot during boot anyway since it's RH?