create-recore-config fails to provision config on eMMC boot partition

[eliasbakken]

On a fresh Recore A8, sudo get-recore-serial-number prints nothing (exits 1) because
create-recore-config never creates the ext4 config image, so mount-config has nothing
to mount and set -e aborts before the cat.

Env: Recore A8, kernel 6.12.69-current-sunxi64, e2fsprogs 1.47.2.

Two bugs in create-recore-config

1. Formats a nonexistent partition node. It runs mkfs.ext4 /dev/${DEV}boot0p1, but
   the kernel doesn't create child partition nodes for eMMC boot partitions —
   /dev/mmcblk2boot0p1 never exists, so mkfs is skipped:

   mke2fs ... The file /dev/mmcblk2boot0p1 does not exist and no size was specified.
   

   mount-config doesn't use a partition node anyway — it loop-mounts the raw device at
   offset=17408. The fs must be created at that offset, not on a ...p1 partition.

2. metadata_csum breaks reads. Once the fs is created at offset 17408, reads fail:

   cat: serial_number: Bad message
   EXT4-fs: ext4_dirblock_csum_verify: No space for directory leaf checksum
   

   The fs is tiny → 1K block size, and metadata_csum (default-on in e2fsprogs 1.47)
   leaves no room for the dir-leaf checksum at 1K blocks on this kernel.

Also: the create path writes via mount-config, which mounts read-only, so the
echo > serial_number would fail even with a valid fs.

Workaround (works)

  echo 0 | sudo tee /sys/block/mmcblk2boot0/force_ro
  LOOP=$(sudo losetup -f --show -o 17408 /dev/mmcblk2boot0)
  sudo mkfs.ext4 -F -q -O ^metadata_csum,^64bit -E nodiscard "$LOOP"
  sudo mount "$LOOP" /mnt/config
  printf '0481\n' | sudo tee /mnt/config/serial_number
  sudo wget -O /mnt/config/calibration.json \
    https://raw.githubusercontent.com/intelligent-agent/Recore/master/Calibrations/Recore_A8_0481/calibration.json
  sync; sudo umount /mnt/config; sudo losetup -d "$LOOP"
  echo 1 | sudo tee /sys/block/mmcblk2boot0/force_ro

Suggested fix

Create the fs directly at offset 17408 via a loop device (drop fdisk/...boot0p1), pass
-O ^metadata_csum, and use a read-write mount in the create path.