archiso hook: support archisolabel= fallback for syslinux boots

Syslinux passes archisolabel= not archisosearchuuid= (UUID is only in
systemd-boot entries). Add blkid label lookup as fallback so both boot
paths work.

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

iso/profile/airootfs/usr/lib/initcpio/hooks/archiso

@@ -2,27 +2,32 @@
 
 archiso_mount_handler() {
     local _new_root="$1"
-    local _uuid _basedir _dev _img
+    local _uuid _label _basedir _dev _img
 
     _uuid="$(getarg archisosearchuuid=)"
+    _label="$(getarg archisolabel=)"
     _basedir="$(getarg archisobasedir=)"
     : "${_basedir:=arch}"
 
-    if [ -z "${_uuid}" ]; then
+    if [ -z "${_uuid}" ] && [ -z "${_label}" ]; then
-        echo "archiso: archisosearchuuid not set in kernel cmdline"
+        echo "archiso: neither archisosearchuuid nor archisolabel set in kernel cmdline"
         return 1
     fi
 
     local _waited=0
     while [ "${_waited}" -lt 30 ]; do
-        _dev="$(blkid -l -o device -t UUID="${_uuid}" 2>/dev/null)"
+        if [ -n "${_uuid}" ]; then
+            _dev="$(blkid -l -o device -t UUID="${_uuid}" 2>/dev/null)"
+        else
+            _dev="$(blkid -l -o device -t LABEL="${_label}" 2>/dev/null)"
+        fi
         [ -n "${_dev}" ] && break
         sleep 1
         _waited=$(( _waited + 1 ))
     done
 
     if [ -z "${_dev}" ]; then
-        echo "archiso: could not find boot medium with UUID=${_uuid}"
+        echo "archiso: could not find boot medium (uuid=${_uuid} label=${_label})"
         return 1
     fi