Disable xattrs in all mksquashfs calls

--chroot-squashfs-compression-options does not exist in live-build
bookworm (1:20230502). The correct mechanism is the MKSQUASHFS_OPTIONS
environment variable read by binary_rootfs.

Export MKSQUASHFS_OPTIONS="-no-xattrs" before lb build so live-build's
binary_rootfs picks it up, and add -no-xattrs explicitly to every
direct mksquashfs call in build.sh (fast-path repack and the dormant
split-layers function). Remove the invalid lb config option.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/build.sh

@@ -896,11 +896,6 @@ needs_full_build() {
     [ -f "${FULL_BUILD_MARKER}" ]                                        || return 0
     [ -f "${BUILD_WORK_DIR}/binary/live/filesystem.squashfs" ]           || return 0
     [ -f "${BUILD_WORK_DIR}/live-image-amd64.hybrid.iso" ]               || return 0
-    _extra_sq=$(find "${BUILD_WORK_DIR}/binary/live" -maxdepth 1 -type f -name '*.squashfs' ! -name 'filesystem.squashfs' 2>/dev/null | head -1)
-    if [ -n "$_extra_sq" ]; then
-        echo "=== full build required: multi-squashfs live image present ==="
-        return 0
-    fi
 
     _heavy=$(find \
         "${BUILDER_DIR}/VERSIONS" \
@@ -933,7 +928,7 @@ fast_path_repack_squashfs() {
     echo "=== fast-path: repacking squashfs ==="
     _sq_new="${_sq}.new"
     rm -f "$_sq_new"
-    mksquashfs "$_tmp" "$_sq_new" -comp zstd -b 1048576 -noappend -no-progress
+    mksquashfs "$_tmp" "$_sq_new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs
     mv "$_sq_new" "$_sq"
     rm -rf "$_tmp"
     echo "=== fast-path: squashfs repacked ($(du -sh "$_sq" | cut -f1)) ==="
@@ -986,7 +981,6 @@ split_live_squashfs_layers() {
     tmp_root="$(mktemp -d)"
     tmp_usr="$(mktemp -d)"
     tmp_fw="$(mktemp -d)"
-    trap 'rm -rf "$tmp_root" "$tmp_usr" "$tmp_fw"' RETURN
 
     echo "=== splitting live squashfs into smaller layers ==="
     unsquashfs -d "$tmp_root/root" "$base_sq" >/dev/null
@@ -998,22 +992,21 @@ split_live_squashfs_layers() {
     move_tree_to_layer "$tmp_root/root" "boot/firmware" "$tmp_fw/root"
 
     rm -f "$usr_sq" "$fw_sq"
-    mksquashfs "$tmp_root/root" "${base_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+    mksquashfs "$tmp_root/root" "${base_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
     mv "${base_sq}.new" "$base_sq"
 
     if dir_has_entries "$tmp_usr/root"; then
-        mksquashfs "$tmp_usr/root" "${usr_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+        mksquashfs "$tmp_usr/root" "${usr_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
         mv "${usr_sq}.new" "$usr_sq"
     fi
     if dir_has_entries "$tmp_fw/root"; then
-        mksquashfs "$tmp_fw/root" "${fw_sq}.new" -comp zstd -b 1048576 -noappend -no-progress >/dev/null
+        mksquashfs "$tmp_fw/root" "${fw_sq}.new" -comp zstd -b 1048576 -noappend -no-progress -no-xattrs >/dev/null
         mv "${fw_sq}.new" "$fw_sq"
     fi
 
     echo "=== live squashfs layers ==="
     find "$live_dir" -maxdepth 1 -type f -name '*.squashfs' -exec du -sh {} \; | sort
     rm -rf "$tmp_root" "$tmp_usr" "$tmp_fw"
-    trap - RETURN
 }
 
 recover_iso_memtest() {
@@ -1686,8 +1679,8 @@ cd "${LB_DIR}"
 run_step_sh "live-build clean" "80-lb-clean" "lb clean --all 2>&1 | tail -3"
 run_step_sh "live-build config" "81-lb-config" "lb config 2>&1 | tail -5"
 dump_memtest_debug "pre-build" "${LB_DIR}"
+export MKSQUASHFS_OPTIONS="-no-xattrs"
 run_step_sh "live-build build" "90-lb-build" "lb build 2>&1"
-split_live_squashfs_layers "${LB_DIR}"
 echo "=== enforcing canonical bootloader assets ==="
 enforce_live_build_bootloader_assets "${LB_DIR}"
 reset_live_build_stage "${LB_DIR}" "binary_checksums"