The ARM64 kernel Image is ~50 MB. mkarchiso calculates the EFI FAT image size as int(total_bytes/MiB)+2, which leaves no room for FAT filesystem overhead → "Disk full" when copying the kernel in. Patch mkarchiso at container startup (before mkarchiso runs) to use +128 MiB buffer instead, giving plenty of headroom. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>