ruff check --select F,E9 tools/ -> 3 errors at 960b852:
checkin_check.py:421 F541 f-string with no placeholder
checkin_check.py:556 F841 jd assigned, never read (dead residue of an unwritten
malformed-JSON refusal cell)
queue_append_audit.py:73 F401 re imported, never used (no 're.' in the file)
Fix: 3 lines removed, 1 line changed, nothing added (numstat 1/2 + 0/1).
Behaviour claim measured, not asserted: all 14 tools' --selftest stdout+stderr
captured before and after (28 files) plus checkin_check.py --dir checkins and
queue_append_audit.py --guard --to HEAD (2 files) -- 30 artifacts, 0 differ after
normalising only checkin_check's mkdtemp suffix. 14 tools / 429 cells / 429 pass
on both sides; verify.py 3/3 PASS rc 0.
Not enforced by the gate: verify.py has no static-check leg, so this property is
observed here only. Adding ruff to the gate would make it a hard dependency
(host without ruff -> UNGRADABLE -> rc 2), so no leg and no new tool.