RED CRITICAL: the frontier caught-up shortcut gated on CONNECTIVITY
(fullyConnectedBeacons) while the tally keyed on REPLIES (CaughtUp over
withSelfVote). The two diverge for a beacon that is CONNECTED but SILENT
(TCP up, frontier reply delayed/withheld) — a capability strictly weaker
than a full eclipse, and one that occurs naturally when an ahead beacon
replays state on a mass co-restart. Such a beacon counts as fully
connected yet is absent from the tally, so self's heavy weight backfills
the naming floor and the node goes live at a forged STALE height.
Add repliedCovers() set-containment guard: every connected beacon must
have answered THIS frontier round before the self-vote shortcut can fire.
A silent ahead-beacon now blocks caught-up -> node fails safe to
FrontierConnecting (keeps waiting); a genuine fresh net (every connected
beacon answers genesis) still completes.
Keep RED's zz_red_probe_test.go as a permanent regression guard:
connected-but-silent ahead beacon -> status=FrontierConnecting (was
FrontierCaughtUp). Fresh-net + equal-stake self-vote tests still pass.
