feat(rootfs): native armhf on aarch64 host via runtime-disable of qemu-arm

lib/functions/logging/traps.sh

@@ -140,6 +140,25 @@ function add_cleanup_handler() {
 	trap_manager_cleanup_handlers=("${callback}" "${trap_manager_cleanup_handlers[@]}")
 }
 
+# Like add_cleanup_handler but appends to the tail of the list, so the
+# registered callback runs AFTER everything added with add_cleanup_handler
+# at the time run_cleanup_handlers fires. Use this when a handler needs to
+# observe a fully-torn-down state — e.g. it can't safely re-mutate a
+# kernel-global resource while subshells of the build are still alive and
+# may have inherited the resource's fd.
+function add_cleanup_handler_last() {
+	if [[ $# -gt 1 ]]; then
+		exit_with_error "add_cleanup_handler_last: too many params"
+	fi
+	local callback="$1"
+	if [[ -z "${callback}" ]]; then
+		exit_with_error "add_cleanup_handler_last: no callback specified"
+	fi
+
+	display_alert "Add callback as last cleanup handler" "${callback}" "cleanup"
+	trap_manager_cleanup_handlers+=("${callback}")
+}
+
 function execute_and_remove_cleanup_handler() {
 	local callback="$1"
 	display_alert "Execute and remove cleanup handler" "${callback}" "cleanup"

lib/functions/main/rootfs-image.sh

@@ -13,6 +13,11 @@ function build_rootfs_and_image() {
 	# get a basic rootfs, either from cache or from scratch
 	get_or_create_rootfs_cache_chroot_sdcard # only occurrence of this; has its own logging sections
 
+	# Cache-hit path also benefits — the extracted rootfs has libc/ld-linux, so kernel
+	# binfmt_elf can run 32-bit ARM ELF natively. Idempotent on cache-miss path where
+	# create_new_rootfs_cache_via_debootstrap already activated this.
+	_native_armhf_setup_binfmt_elf || true
+
 	# deploy the qemu binary, no matter where the rootfs came from (built or cached)
 	LOG_SECTION="deploy_qemu_binary_to_chroot_image" do_with_logging deploy_qemu_binary_to_chroot "${SDCARD}" "image" # undeployed at end of this function