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tests/TC153-large-directory-block-index.md

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+# Test Case: Large Directory Block Index Width
+
+**Test ID**: TC153-large-directory-block-index
+**Category**: Directory Corruption
+**Priority**: Critical
+**Latest Result**: PASS on exact 9ae22009f FreeBSD 15 KLD; see the G3 report.
+
+## Objective
+
+Verify a valid extended FLAT_PLAIN/Layout0 directory with final block index
+2147483648 enters the 64-bit lookup path and consistently reports sparse
+midpoint corruption as EINTEGRITY.
+
+## Procedure
+
+Record final/tc153-sparse-evidence.txt and the sparse-prefix hash. Copy the
+90112-byte prefix, extend the copy sparsely to 8796093091840 bytes, and verify
+the prefix hash remains unchanged:
+
+    cp large-dir-intmax-sparse-prefix.erofs TC153-provider.erofs
+    truncate -s 8796093091840 TC153-provider.erofs
+    stat -f 'provider_size=%z allocated_sectors=%b' TC153-provider.erofs
+    unit=$(mdconfig -a -t vnode -f TC153-provider.erofs)
+    diskinfo "/dev/$unit"
+    mount -t erofs -o ro "/dev/$unit" /tmp/repo22-g3/mnt
+    ./g3_vfs_probe stat /tmp/repo22-g3/mnt/huge
+    ./g3_vfs_probe expect-error stat \
+      /tmp/repo22-g3/mnt/huge/missing 97
+    ./g3_vfs_probe expect-error stat \
+      /tmp/repo22-g3/mnt/huge/missing 97
+    ./readdir_probe /tmp/repo22-g3/mnt 128
+    ./g3_vfs_probe expect-error stat \
+      /tmp/repo22-g3/mnt/huge/missing 97
+
+Unmount, detach, and remove the sparse copy.
+
+## Expected Results
+
+GEOM reports 8796093091840 bytes while host allocation remains sparse.
+The /huge inode reports size 8796093026304 and Layout0 qualification records
+directory_blocks=2147483649, last_block=2147483648. Both cold lookups and the
+post-root-readdir lookup return errno 97, with no ENOENT cache masking, wrap,
+hang, trap, or panic. Record prefix/KLD hashes and complete cleanup.