lb binary_grub-efi and lb binary_syslinux create these files from templates that already have memtest entries hardcoded. The hook should not fail when the files don't exist yet — validate_iso_memtest() checks the final ISO. Only the binary files (x64.bin, x64.efi) are required here. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>