Fix archiso initcpio hook: use run_hook+mount_handler override

run_latehook fires after mkinitcpio already attempts to mount root= (empty),
which fails. Switch to run_hook() setting mount_handler=archiso_mount_handler
so mkinitcpio calls our handler instead of the default block-device mount.

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

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

@@ -1,7 +1,7 @@
 #!/usr/bin/ash
-# Live-boot hook: find ISO by UUID, mount squashfs, set up overlay on /new_root.
 
-run_latehook() {
+archiso_mount_handler() {
+    local _new_root="$1"
     local _uuid _basedir _dev _img
 
     _uuid="$(getarg archisosearchuuid=)"
@@ -13,7 +13,6 @@ run_latehook() {
         return 1
     fi
 
-    # Wait up to 30 s for a block device with the ISO UUID to appear
     local _waited=0
     while [ "${_waited}" -lt 30 ]; do
         _dev="$(blkid -l -o device -t UUID="${_uuid}" 2>/dev/null)"
@@ -41,15 +40,17 @@ run_latehook() {
     mkdir -p /run/archiso/airootfs
     mount -r -t squashfs "${_img}" /run/archiso/airootfs || { echo "archiso: squashfs mount failed"; return 1; }
 
-    # RAM-backed writable overlay layer
     mkdir -p /run/archiso/overlay
     mount -t tmpfs tmpfs -o mode=0755 /run/archiso/overlay
     mkdir -p /run/archiso/overlay/upper /run/archiso/overlay/work
 
-    mkdir -p /new_root
     mount -t overlay overlay \
         -o lowerdir=/run/archiso/airootfs,upperdir=/run/archiso/overlay/upper,workdir=/run/archiso/overlay/work \
-        /new_root || { echo "archiso: overlay mount failed"; return 1; }
+        "${_new_root}" || { echo "archiso: overlay mount failed"; return 1; }
 
-    echo "archiso: live root mounted on /new_root"
+    echo "archiso: live root mounted on ${_new_root}"
+}
+
+run_hook() {
+    mount_handler="archiso_mount_handler"
 }