test code v1

tests/TC013-vget-invalid.md

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+# Test Case: Vget with Invalid NID
+
+**Test ID**: TC013-vget-invalid
+
+## Objective
+
+Verify a checksum-valid directory entry that points outside the image reaches
+the cold lookup/vget path and fails consistently with `EINTEGRITY`.
+
+## Fixture
+
+Use `images/invalid-dirent-nid.erofs`. `fixture-evidence.txt` records the exact
+dirent offset, old NID, out-of-range NID, and valid recomputed CRC. Compile
+`tests/read_probe.c` in the guest.
+
+## Procedure
+
+Mount the image without first listing the root, then run:
+
+```sh
+./read_probe expect-error "$mnt/invalid-target.txt" 97
+./read_probe expect-error "$mnt/invalid-target.txt" 97
+set +e
+truss -o /tmp/tc013.truss stat "$mnt/invalid-target.txt"
+rc=$?
+set -e
+printf 'stat_rc=%d\n' "$rc"
+tail -20 /tmp/tc013.truss
+```
+
+Record dmesg before/after, remove the trace, then unmount and detach.
+
+## Expected Results
+
+- Mount succeeds because only the child dirent is malformed.
+- Both cold/repeated opens fail at pathname acquisition with FreeBSD errno 97
+  (`EINTEGRITY`); `truss` shows the same syscall errno.
+- The second failure is not converted to `ENOENT`; no panic or stale vnode
+  appears, and cleanup succeeds.