Tests 17-20: catch-up ACK exclusion vs pending waiter, membership-change
wake of covered waiter, removal-below-majority fails at own deadline
(no forced early-fail), non-blocking bound. Landed GREEN: task 1.2's
commit_on_membership_change already implements the full 3.2 contract,
so RED was unachievable; reviewer confirmed mutation-killing power and
zero production changes. 20/20 group tests; suite at baseline.
Rongsong Shen
631a08939b