# Test Case: Long-prefix backing selection

**Test ID**: TC135-prefix-metabox-and-primary-fallback
**Fixtures**: `metabox-plain.erofs`, `basic.erofs`, `prefix-primary.erofs`

## Objective

Verify prefix table selection in order: metabox, packed inode, then primary
metadata. The manifest must prove each backing and record all changed super
fields and image hashes.

## Manual steps

Use a separate attach/mount/cleanup cycle for each image:

```sh
# metabox-plain.erofs
lsextattr user /mnt/repo22-g4/metabox-a
getextattr -qq -x user repo22.application.component.setting \
  /mnt/repo22-g4/metabox-a

# basic.erofs (packed backing)
lsextattr user /mnt/repo22-g4/prefix-user-0
getextattr -qq -x user repo22.application.component.setting \
  /mnt/repo22-g4/prefix-user-0

# prefix-primary.erofs (PLAIN_XATTR_PFX)
lsextattr user /mnt/repo22-g4/prefix-user-0
getextattr -qq -x user repo22.application.component.setting \
  /mnt/repo22-g4/prefix-user-0
```

## Expected results

Values are `long-prefix-value`, `prefix-value-0`, and `prefix-value-0`.
Every cycle cleans its mount and md provider.
