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tests/TC136-metabox-truncated-super-extension.md

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+# Test Case: Truncated metabox super extension
+
+**Test ID**: TC136-metabox-truncated-super-extension
+**Fixtures**: `bad-metabox-truncated-extension.erofs`, `bad-ishare-prefix-id.erofs`
+
+## Objective
+
+Reject `METABOX` when `sb_extslots=0` leaves `metabox_nid` undeclared, and
+reject `ISHARE_XATTRS` when its prefix ID equals `xattr_prefix_count`.
+
+## Manual steps
+
+For each image, attach it and trace the read-only mount:
+
+```sh
+truss -f -o /tmp/tc136.truss mount -t erofs -o ro \
+  /dev/${unit} /mnt/repo22-g4
+grep nmount /tmp/tc136.truss
+mount | grep repo22-g4 || true
+mdconfig -d -u "${unit#md}"
+```
+
+## Expected results
+
+Both `nmount` calls return `EINTEGRITY` (97). The extension bytes are not
+consumed, no mount appears, and detach succeeds without a vnode/md leak.