Adds wizard-work/cassian/q84_mutants.py (harness, rc 0). Written as
'**Q<n> addendum' lines (the Q129/Q156 addendum form), so open_set.py's pin
does not move: --check -> counts match the pin. docs/queue-index.md
re-rendered with tools/queue_index.py --write in this commit.
Supersedes the 330 figure at d843ce2. Query + read window in
checkins/2026-10-07-cassian-02.md; slim table in
checkins/2026-10-07-cassian-q5-recount.md. Aligns with Timmy's 314
(nine public, excl. PRs) after #1 and talking-turd#12 closed.