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+# Test Case: NFS Per-Inode Generation on Same-Superblock Replacement
+
+**Test ID**: TC154-nfs-per-inode-generation
+**Category**: NFS Export
+**Priority**: Critical
+**Regression**: A mount-wide superblock hash aliases a replacement inode at the same NID
+
+## Objective
+
+Verify that an EROFS file handle keeps the existing 16-byte FreeBSD FID ABI but
+uses a stable per-inode generation. Remounting an unchanged image must preserve
+the complete handle. Replacing it with an image whose superblock block, UUID,
+NID, and file content are identical but whose raw inode metadata differs must
+make the old handle return `ESTALE`.
+
+Also verify that a valid-NID handle resolving to a malformed replacement inode
+returns the positive inode-read errno instead of a negative Linux errno or a
+successful alias.
+
+## Fixture
+
+Generate all review fixtures on the host:
+
+```sh
+python3 tests/review_fixtures.py make \
+  --output /work/build/repo22-review-fixes-fixtures
+```
+
+For `nfs-inode-a.erofs`, `nfs-inode-b.erofs`, and
+`nfs-inode-corrupt.erofs`, require the helper evidence to prove:
+
+- target `/zz-identity.txt` has the same NID and inode offset;
+- the inode lies after the complete superblock checksum block;
+- the complete checksum block and declared superblock are byte-identical;
+- A and B differ only in the compact inode `i_mtime` field;
+- the helper's superblock-seeded raw-inode FNV generations are nonzero and
+  different;
+- all three images retain a valid superblock checksum.
+
+## Procedure
+
+1. Compile `tests/nfs_fh_tool.c` natively on FreeBSD 15.
+2. Attach image A to an explicit md unit, mount it, capture `a.fh`, and compare
+   `nfs_fh_tool describe`, `nfs_fh_tool stat`, and `stat -f '%v'`. The FID and
+   `st_gen` values must equal `generation_a` in `fixture-manifest.json`.
+3. Unmount and detach image A, then reattach the unchanged image to the same md
+   unit. Capture `a-remount.fh`, require a byte-for-byte handle match, and read
+   through `a.fh`.
+4. Replace A with image B on the same md unit. Capture `b.fh`, require the same
+   fsid and NID but `generation_b`, then run:
+
+   ```sh
+   nfs_fh_tool expect-stat a.fh ESTALE
+   nfs_fh_tool expect-open a.fh ESTALE
+   nfs_fh_tool stat b.fh
+   ```
+
+5. Replace B with `nfs-inode-corrupt.erofs` on the same md unit. Resolving
+   `a.fh` must return positive FreeBSD `EOPNOTSUPP` (45) from inode decoding:
+
+   ```sh
+   nfs_fh_tool expect-stat a.fh 45
+   nfs_fh_tool expect-open a.fh 45
+   ```
+
+6. Compare pre/post dmesg, unmount, detach the md unit, and unload the exact
+   module under test.
+
+## Expected Results
+
+- Image A has an identical handle and generation across remounts.
+- Image B's same-NID replacement has a different generation and both old-handle
+  operations return `ESTALE`.
+- The new handle resolves successfully and `va_gen == FID.gen`.
+- The malformed inode propagates errno 45 as a positive error and never returns
+  a vnode.
+- The FID remains exactly 16 bytes with unchanged field offsets.