BOOT=efi only changed the GRUB inside the rootfs squashfs — grub-mkrescue
builds the ISO bootloader from the build host's GRUB, so an ISO assembled
on a host without the x86_64-efi modules + mtools shipped with NO UEFI
boot entry. Booting that ISO on a UEFI machine showed:
"make sure there is a bootable uefi x64 image"
- check-host-deps.sh now verifies the GRUB module dirs it needs for a
hybrid ISO (/usr/lib/grub/x86_64-efi from grub-efi-amd64-bin,
/usr/lib/grub/i386-pc from grub-pc-bin) and mtools, not just
grub-mkrescue.
- build-iso.sh verifies the finished ISO has both EFI and BIOS boot
entries (xorriso El Torito report) and prints the result; BOOT=efi
builds FAIL if the EFI entry is missing.
- GitLab CI build image gains grub-pc-bin, grub-efi-amd64-bin, mtools.
- docs/building.md: hybrid-ISO burning instructions (dd) and the
"bootable uefi x64 image" troubleshooting path.
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