Followers lack reshare history but still participate in Simplex. Let the
inner application verify boundary proposals instead of forcing a nullify
or leaving verification pending.

enter_epoch unwrapped every mux registration, so a vote/resolver muxer
exiting on the stop signal (or the externally owned certificate mux
stopping) mid-transition panicked the orchestrator instead of stopping
it. The gate wait also polled the marked gate before the shutdown
signal, making the race deterministic once the fence advanced. Treat a
closed mux as a clean stop and poll shutdown first.

FailedCeremonyCarryOver read both boundaries from one reference node,
failing correct runs when that node state-synced past the previous
boundary (its floor excludes height 31 while the property needs it).
Read the pre-floor boundary from whichever node retains it, and demand
the carry-over boundary from the state-synced node itself whenever its
floor covers that height. Apply the retaining-node read to
BoundaryOutputMode, which sampled a single node the same way.