test code v1

tests/TC063-setattr-write-reject.md

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+# Test Case: Write, Truncate, and Create Rejection
+
+**Test ID**: TC063-setattr-write-reject
+**Category**: Read-Only Enforcement
+**Priority**: Critical
+
+## Objective
+
+Verify direct open-for-write, truncate, and create requests return EROFS and
+leave the mounted tree unchanged.
+
+## Procedure
+
+Mount vfs/vfs-plain.erofs and run:
+
+    sha256 /tmp/repo22-g3/mnt/testdir/file.txt > TC063-before.txt
+    ./g3_vfs_probe expect-error open-rdwr \
+      /tmp/repo22-g3/mnt/testdir/file.txt 30
+    ./g3_vfs_probe expect-error truncate \
+      /tmp/repo22-g3/mnt/testdir/file.txt 30
+    ./g3_vfs_probe expect-error create \
+      /tmp/repo22-g3/mnt/testdir/newfile.txt 30
+    sha256 /tmp/repo22-g3/mnt/testdir/file.txt > TC063-after.txt
+    cmp TC063-before.txt TC063-after.txt
+    test ! -e /tmp/repo22-g3/mnt/testdir/newfile.txt
+
+## Expected Results
+
+All mutation syscalls report errno 30, the file hash is unchanged, and no new
+entry exists. Record output and cleanup.