Replaces binary degraded flag with ReplicaState type:
Disconnected, Connecting, CatchingUp, InSync, Degraded, NeedsRebuild.
Ship() allowed from Disconnected (bootstrap: data must flow before
first barrier) and InSync (steady state). Ship does NOT change state.
Barrier() gating:
- InSync: proceed normally
- Disconnected: bootstrap path (connect + barrier)
- Degraded: reconnect both data+ctrl connections, then barrier
- Connecting/CatchingUp/NeedsRebuild: rejected immediately
Only barrier success grants InSync. Reconnect alone does not.
IsDegraded() now means "not sync-eligible" (any non-InSync state).
InSyncCount() added to ShipperGroup.
dist_group_commit.go: removed AllDegraded short-circuit that
prevented bootstrap. Barrier attempts always run — individual
shippers handle their own state-based gating.
8 CP13-4 tests + TestBarrier_RejectsReplicaNotInSync flips FAIL→PASS.
All previously-passing baseline tests remain green.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
