fix(base): Load udev initramfs hook (#28)

This replaces the modern Arch Linux default hook of 'systemd' with
'udev' which allows a clean boot of a boot environment via ZFSBootMenu.

setup.sh

@@ -936,8 +936,49 @@ function add_zfs_hook_to_initramfs () {
         '/mnt/etc/mkinitcpio.conf'
 }
 
-function set_initramfs_build_list () {
+function replace_systemd_initramfs_with_udev () {
     #1.17
+    # Replace systemd-boot hooks with udev hooks in initramfs. For some odd
+    # reason we have not yet understood the modern default on a fresh Arch
+    # Linux installation ('systemd' and 'sd-vconsole' hooks) doesn't cleanly
+    # boot into a boot environment via ZFSBootMenu.
+    #
+    # 1. If we left both hooks in place we'd see an error related
+    # to '/dev/gpt-auto-root'; that can be worked around by loading the 'vfat'
+    # module via the 'MODULES=(...)' array in '/etc/mkinitcpio.conf'.
+    #
+    # 2. On next try we see the system failing into an emergency shell at a
+    # later point in initramfs execution due to a failure with
+    # 'initrd-switch-root.service'. Since the 'systemd' hook disables the
+    # 'root' account we enter a non-functional emergency shell. See
+    # https://wiki.archlinux.org/title/Mkinitcpio section 6.7 "Cannot open
+    # access to console, the root account is locked" where we learn that we can
+    # install AUR package initcpio-hook-shadowcopy and load the 'shadowcopy'
+    # hook right after the 'systemd' hook in order to get a fully functional
+    # emergency shell.
+    #
+    # 3. On next try 'initrd-switch-root.service' fails into a functional
+    # emergency shell which allows us to check systemd status of
+    # 'initrd-switch-root.service'. This seems to tell us that '/sysroot' is
+    # wanted but missing which appears to be true.
+    #
+    # At this point in December 2025 we stopped investigating how to properly
+    # pair 'systemd' and 'sd-vconsole' hooks with ZFSBootMenu. We're instead
+    # replacing both as follows:
+    #
+    #     systemd <--> udev
+    # sd-vconsole <--> consolefont
+    #
+    # This cleanly boots a boot environment. Further investigation may be
+    # warranted at a later date. For now this workaround is good enough.
+    in_file_in_array_insert_n_before_m '/mnt/etc/mkinitcpio.conf' 'HOOKS' 'udev' 'systemd'
+    in_file_in_array_remove_n '/mnt/etc/mkinitcpio.conf' 'HOOKS' 'systemd'
+    in_file_in_array_insert_n_before_m '/mnt/etc/mkinitcpio.conf' 'HOOKS' 'consolefont' 'sd-vconsole'
+    in_file_in_array_remove_n '/mnt/etc/mkinitcpio.conf' 'HOOKS' 'sd-vconsole'
+}
+
+function set_initramfs_build_list () {
+    #1.18
     # No need to build fallback initramfs, our new fallback is ZFS snapshots
     sed -ri \
         -e '/^#/d' \
@@ -951,7 +992,7 @@ function set_initramfs_build_list () {
 }
 
 function add_zfs_files_to_new_os () {
-    #1.18
+    #1.19
     for zfs_file in '/etc/hostid' '/etc/zfs/zpool.cache' $([[ ! "${ARCHZBM_ZFSPROPS_NO_ENCRYPTION}" ]] && printf -- '%s' '/etc/zfs/'"${zpool_name}"'.key'); do
         rsync -av --itemize-changes {'','/mnt'}"${zfs_file}"
     done
@@ -1579,8 +1620,9 @@ function main () {
         set_hostname                                #1.14
         set_locale                                  #1.15
         add_zfs_hook_to_initramfs                   #1.16
-        set_initramfs_build_list                    #1.17
+        replace_systemd_initramfs_with_udev         #1.17
-        add_zfs_files_to_new_os                     #1.18
+        set_initramfs_build_list                    #1.18
+        add_zfs_files_to_new_os                     #1.19
         enter_chroot                                #2.1
         # We're done in chroot
         finalize_os_setup                           #3.1