Three fixes for the 'vmlinuz-* not found' failure:
1. Override releng profile's pacman.conf to add [alarm] and [aur] repos.
linux-aarch64 lives in [alarm] — without this the kernel package was
silently missing from the airootfs and /boot was empty.
2. Remove linux.preset from releng airootfs (references vmlinuz-linux,
the x86_64 kernel name that doesn't exist on ALARM).
3. Add linux-aarch64.preset to the airootfs with an 'archiso' preset entry
(ALL_kver=/boot/vmlinuz-linux-aarch64, archiso_image=initramfs-linux-aarch64.img).
mkarchiso looks for this 'archiso' preset to build the live initramfs.
4. Switch customize_airootfs.sh from mkinitcpio -P to mkinitcpio -p linux-aarch64
so only the aarch64 preset runs (not the stale x86_64 linux preset).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
nmemmertandClaude Sonnet 4.6
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