composefs: install --bootloader systemd creates no firmware boot entry (bootctl --root skips EFI variables) #2557

Environment: bootc 1.17.1 (built from source, no selinux feature) in an Arch Linux based image (systemd 262), composefs backend, btrfs root, UEFI. Installed from a live ISO with podman run --privileged --pid=host -v /dev:/dev -v /var/lib/containers:/var/lib/containers -v <target>:/target <image> bootc install to-filesystem --composefs-backend --bootloader systemd --skip-finalize /target, reproduced in QEMU/OVMF and used on a ThinkPad T480.

What happens: systemd-boot is installed to EFI/systemd/systemd-bootx64.efi and EFI/BOOT/BOOTX64.EFI, but no firmware boot entry ("Linux Boot Manager") is created and BootOrder is not touched. On a machine whose NVRAM still lists the previous OS (here its GRUB entry, whose root partition was just reformatted), the firmware keeps booting that entry instead of the new system. We work around it with efibootmgr --create ... --loader '\EFI\systemd\systemd-bootx64.efi' after the install.

Why: install_systemd_boot runs bootctl install --root <target> --esp-path ... and passes --no-variables only for generic_image

so for a non-generic install the intent is to update the EFI variables, like the bootupd path does with --update-firmware --auto.

But bootctl skips EFI variable changes whenever --root is given, unless --variables=yes is passed explicitly: touch_variables() in systemd's src/bootctl/bootctl-util.c logs "Operating on root directory, skipping EFI variable modifications."

Suggestion: pass --variables=yes when !configopts.generic_image. (#2512 would cover installs where bootupd handles systemd-boot, but not plain bootctl installs.)