Extend the salvaged regression test so it asserts the exact invariant from
#114048 rather than only "a replay happens": socket 3 asks for
last_seen=1, a live seq=3 racing that replay is parked by the NEW hold
(watermark stays at 1 until the gap is recovered), and the final order is
[1, 2, 3] with the watermark at 3. On origin/main this fails at the first
assertion (no replay is sent on socket 3 because the stale flag is still
set), which is the reporter's observed `replayOnThird: []`.
fff7c83113