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tests/TC142-fragment-backed-compressed-metabox.md

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+# Test Case: Fragment-backed compressed metabox
+
+**Test ID**: TC142-fragment-backed-compressed-metabox
+**Fixture**: `metabox-fragment.erofs` and its four negative variants
+
+## Objective
+
+Independently regress packed-carrier initialization before a fragment-backed
+metabox read and recursion/range rejection. Do not reuse TC140 guest results.
+
+## Layout qualification
+
+`g4_fixtures.py verify` must prove a compressed metabox carrier, whole-file
+fragment header with bit 63 set, `fragment_offset + carrier_size <= packed_size`,
+ordinary metabox/packed NIDs, bit-63 synthetic inode NIDs, CRC-valid images,
+and one-field mutations for self-loop, range, metabox recursion, and packed
+recursion. Record source and all image SHA256 values.
+
+## Positive steps
+
+```sh
+unit=$(mdconfig -a -t vnode -f /tmp/repo22-g4/images/metabox-fragment.erofs)
+mount -t erofs -o ro /dev/${unit} /mnt/repo22-g4
+stat -f 'mode=%Sp size=%z inode=%i' /mnt/repo22-g4/metabox-a
+sha256 -q /mnt/repo22-g4/metabox-a
+lsextattr user /mnt/repo22-g4/metabox-a
+getextattr -qq -x user shared-prefix-key /mnt/repo22-g4/metabox-a
+getextattr -qq -x user item /mnt/repo22-g4/metabox-a
+umount /mnt/repo22-g4
+mdconfig -d -u "${unit#md}"
+```
+
+## Negative steps
+
+Trace-mount each of the four negative images in a fresh md cycle. Capture the
+exact `nmount` errno/text, pre/post dmesg, `vmstat -m`, guest responsiveness,
+and zero mount/md cleanup.
+
+## Expected results
+
+Positive file SHA256 and values `shared-value`/`value-000` match source. Every
+negative returns `EINTEGRITY` (97), with no leak, hang, panic, trap, or residue.