Fix ARM64 boot: use official archiso mkinitcpio hooks from releng profile

The custom simplified hooks we were writing to the airootfs overlay
overwrote the official hooks shipped in the releng profile. The official
hooks handle uname -m for the aarch64 squashfs path, include all required
modules (squashfs, overlay, iso9660, loop, dm-snapshot, nls_*) and
binaries (blkid, findfs, losetup, switch_root), and wire up mount_handler
correctly. Our stripped-down hooks caused the overlay to mount empty,
producing the "Root device mounted successfully, but /sbin/init does not
exist" panic at boot.

Fix: stop overwriting the official hooks; keep only the mkinitcpio.conf
(which lists the hook names, not their implementation). Also remove
plymouth from initramfs HOOKS to reduce boot complexity.

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

iso/docker/entrypoint-arm64.sh

@@ -146,79 +146,18 @@ rm -f "$PROFILE/packages.x86_64"
 # ── 3. airootfs overlay — files that land in the live system ─────────
 AIROOTFS="$PROFILE/airootfs"
 
-# ── Ship our own archiso mkinitcpio hooks ────────────────────────────
-mkdir -p "$AIROOTFS/usr/lib/initcpio/hooks"
-mkdir -p "$AIROOTFS/usr/lib/initcpio/install"
-
-cat > "$AIROOTFS/usr/lib/initcpio/hooks/archiso" <<'HOOK'
-run_hook() {
-    export mount_handler="archiso_mount_handler"
-}
-
-archiso_mount_handler() {
-    local _newroot="${1}"
-    local _dev _sfs _i
-
-    [ -z "${archisobasedir}" ] && archisobasedir="arch"
-    if [ -z "${archisolabel}" ]; then
-        echo "ERROR: archisolabel not set"
-        return 1
-    fi
-
-    _i=0
-    while [ "${_i}" -lt 30 ]; do
-        _dev=$(blkid --match-token LABEL="${archisolabel}" --output device 2>/dev/null | head -1)
-        [ -n "${_dev}" ] && break
-        sleep 1
-        _i=$((_i + 1))
-    done
-    if [ -z "${_dev}" ]; then
-        echo "ERROR: archiso: cannot find device with label '${archisolabel}'"
-        return 1
-    fi
-
-    mkdir -p /run/archiso/bootmnt
-    mount -r "${_dev}" /run/archiso/bootmnt
-
-    # aarch64 squashfs path
-    _sfs="/run/archiso/bootmnt/${archisobasedir}/aarch64/airootfs.sfs"
-    mkdir -p /run/archiso/airootfs
-    mount -r -t squashfs "${_sfs}" /run/archiso/airootfs
-
-    mkdir -p /run/archiso/cowspace
-    mount -t tmpfs -o "size=75%,mode=0755" tmpfs /run/archiso/cowspace
-    mkdir -p /run/archiso/cowspace/upper /run/archiso/cowspace/work
-
-    mount -t overlay overlay \
-        -o "lowerdir=/run/archiso/airootfs,upperdir=/run/archiso/cowspace/upper,workdir=/run/archiso/cowspace/work" \
-        "${_newroot}"
-}
-HOOK
-
-cat > "$AIROOTFS/usr/lib/initcpio/install/archiso" <<'INSTALL'
-build() {
-    add_runscript
-    add_binary blkid
-    add_binary sleep
-    add_module squashfs
-    add_module overlay
-    add_module iso9660
-    add_module vfat
-    add_dir /run/archiso/bootmnt
-    add_dir /run/archiso/airootfs
-    add_dir /run/archiso/cowspace
-}
-help() {
-    echo "Mounts the archiso squashfs for live boot."
-}
-INSTALL
+# The releng profile already ships official archiso mkinitcpio hooks at
+# $PROFILE/airootfs/usr/lib/initcpio/{hooks,install}/archiso.
+# Do NOT overwrite them — the official hooks handle uname -m arch detection,
+# correct squashfs paths, all required modules/binaries, and mount_handler
+# wiring. Our simplified custom hooks were causing "sbin/init not found".
 
 mkdir -p "$AIROOTFS/etc/mkinitcpio.conf.d"
 cat > "$AIROOTFS/etc/mkinitcpio.conf.d/archiso.conf" <<'MKCONF'
 MODULES=()
 BINARIES=()
 FILES=()
-HOOKS=(base udev plymouth archiso block filesystems keyboard)
+HOOKS=(base udev archiso block filesystems keyboard)
 MKCONF
 
 cat > "$AIROOTFS/etc/hostname" <<'EOF'