Auto-detect host architecture for downloaded images

Debian/AlmaLinux/Fedora image filenames, URLs, and checksums were
hardcoded to arm64/aarch64 (for Apple Silicon macOS), which would
silently download the wrong-architecture image on an Intel/amd64
host. Detect the architecture from the host (uname -m), normalized
to arm64/amd64, with VM_IMAGE_ARCH as an override; the run-*.sh
scripts in the parent repo use the same override so both stay in
sync. amd64 keeps the previously pinned checksums; arm64 checksums
are still unpinned pending upstream publication.

windows11 is unaffected: it stays x86_64-only, matching run-windows11.sh.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

download-images.sh

@@ -5,20 +5,53 @@ images_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 base_qcow2_dir="${images_dir}/base-qcow2"
 install_iso_dir="${images_dir}/install-iso"
 tools_iso_dir="${images_dir}/tools-iso"
-debian_image="${base_qcow2_dir}/debian-13-generic-amd64-20260810-2566.qcow2"
+
-alma_image="${base_qcow2_dir}/AlmaLinux-10-GenericCloud-10.2-20260526.0.x86_64.qcow2"
+normalize_arch() {
-fedora_image="${base_qcow2_dir}/Fedora-Cloud-Base-Generic-44-1.7.x86_64.qcow2"
+  case "$1" in
+    arm64|aarch64) printf 'arm64\n' ;;
+    x86_64|amd64) printf 'amd64\n' ;;
+    *) printf 'Error: unsupported architecture: %s\n' "$1" >&2; exit 1 ;;
+  esac
+}
+image_arch="$(normalize_arch "${VM_IMAGE_ARCH:-$(uname -m)}")"
+
+if [[ "$image_arch" == arm64 ]]; then
+  debian_image="${base_qcow2_dir}/debian-13-generic-arm64-20260810-2566.qcow2"
+  alma_image="${base_qcow2_dir}/AlmaLinux-10-GenericCloud-10.2-20260526.0.aarch64.qcow2"
+  fedora_image="${base_qcow2_dir}/Fedora-Cloud-Base-Generic-44-1.7.aarch64.qcow2"
+  debian_url_default="https://cloud.debian.org/images/cloud/trixie/20260810-2566/debian-13-generic-arm64-20260810-2566.qcow2"
+  alma_url_default="https://repo.almalinux.org/almalinux/10/cloud/aarch64/images/AlmaLinux-10-GenericCloud-10.2-20260526.0.aarch64.qcow2"
+  fedora_url_default="https://download.fedoraproject.org/pub/fedora/linux/releases/44/Cloud/aarch64/images/Fedora-Cloud-Base-Generic-44-1.7.aarch64.qcow2"
+  # TODO: these were pinned for the amd64/x86_64 builds; verification is
+  # skipped (empty default) for the arm64/aarch64 builds until their
+  # checksums are fetched and pinned via DEBIAN_IMAGE_SHA512 /
+  # ALMA_IMAGE_SHA256 / FEDORA_IMAGE_SHA256.
+  debian_sha512_default=""
+  alma_sha256_default=""
+  fedora_sha256_default=""
+else
+  debian_image="${base_qcow2_dir}/debian-13-generic-amd64-20260810-2566.qcow2"
+  alma_image="${base_qcow2_dir}/AlmaLinux-10-GenericCloud-10.2-20260526.0.x86_64.qcow2"
+  fedora_image="${base_qcow2_dir}/Fedora-Cloud-Base-Generic-44-1.7.x86_64.qcow2"
+  debian_url_default="https://cloud.debian.org/images/cloud/trixie/20260810-2566/debian-13-generic-amd64-20260810-2566.qcow2"
+  alma_url_default="https://repo.almalinux.org/almalinux/10/cloud/x86_64/images/AlmaLinux-10-GenericCloud-10.2-20260526.0.x86_64.qcow2"
+  fedora_url_default="https://download.fedoraproject.org/pub/fedora/linux/releases/44/Cloud/x86_64/images/Fedora-Cloud-Base-Generic-44-1.7.x86_64.qcow2"
+  debian_sha512_default="f6978100d8031c266d55d7815ceea7fcdeacf28e1e5834fdb9c94ac96880a054a6e6f8681c2d3b0584e0057eaf3ef7353856b85212d04134744faa9b3bb1f24f"
+  alma_sha256_default="47f2218668dd4776be140dd92fa3bea700be1766e2c7d88bdfd6a4b50f477b4d"
+  fedora_sha256_default="28680fe5b371a5a82ebf43a31926e086a168e59949d03969c5093e7071f90b7f"
+fi
+
 virtio_image="${tools_iso_dir}/virtio-win.iso"
 windows_qcow2_image="${base_qcow2_dir}/Win11_25H2_English_x64_v2.qcow2"
 windows_iso_image="${install_iso_dir}/Win11_25H2_English_x64_v2.iso"
 
-debian_url="${DEBIAN_IMAGE_URL:-https://cloud.debian.org/images/cloud/trixie/20260810-2566/debian-13-generic-amd64-20260810-2566.qcow2}"
+debian_url="${DEBIAN_IMAGE_URL:-$debian_url_default}"
-alma_url="${ALMA_IMAGE_URL:-https://repo.almalinux.org/almalinux/10/cloud/x86_64/images/AlmaLinux-10-GenericCloud-10.2-20260526.0.x86_64.qcow2}"
+alma_url="${ALMA_IMAGE_URL:-$alma_url_default}"
-fedora_url="${FEDORA_IMAGE_URL:-https://download.fedoraproject.org/pub/fedora/linux/releases/44/Cloud/x86_64/images/Fedora-Cloud-Base-Generic-44-1.7.x86_64.qcow2}"
+fedora_url="${FEDORA_IMAGE_URL:-$fedora_url_default}"
 virtio_url="${VIRTIO_WIN_ISO_URL:-https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win.iso}"
-debian_sha512="${DEBIAN_IMAGE_SHA512:-f6978100d8031c266d55d7815ceea7fcdeacf28e1e5834fdb9c94ac96880a054a6e6f8681c2d3b0584e0057eaf3ef7353856b85212d04134744faa9b3bb1f24f}"
+debian_sha512="${DEBIAN_IMAGE_SHA512:-$debian_sha512_default}"
-alma_sha256="${ALMA_IMAGE_SHA256:-47f2218668dd4776be140dd92fa3bea700be1766e2c7d88bdfd6a4b50f477b4d}"
+alma_sha256="${ALMA_IMAGE_SHA256:-$alma_sha256_default}"
-fedora_sha256="${FEDORA_IMAGE_SHA256:-28680fe5b371a5a82ebf43a31926e086a168e59949d03969c5093e7071f90b7f}"
+fedora_sha256="${FEDORA_IMAGE_SHA256:-$fedora_sha256_default}"
 force_download=false
 
 usage() {
@@ -27,7 +60,8 @@ Usage: $(basename "$0") [--force] [all|debian13|almalinux10|fedora44|virtio-win]
        $(basename "$0") --print-path TARGET [--iso]
 
 Download one or more shared VM images. With no arguments, all targets are
-processed.
+processed. The Debian/AlmaLinux/Fedora image architecture (arm64 or amd64)
+is auto-detected from the host; override it with VM_IMAGE_ARCH.
 
 --force removes existing files and partial downloads for the selected targets,
 then downloads them again from the beginning.