Building a foreign-arch image (e.g. arm64 Raspberry Pi OS on an x86 host) needs
a qemu binfmt handler, or the chroot fails with "Exec format error". crossarch
detects this before the target is erased and, on confirmation, installs
qemu-user-static via the host package manager (apt-get/dnf/zypper/pacman) and
registers binfmt; otherwise it aborts with per-distro instructions.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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