The split-brain-resolver HOCON block in akka.conf was inert — nothing
registered a downing provider, so the cluster ran Akka's default NoDowning:
a hard-crashed node was never downed, cluster singletons + the driver
role-leader never failed over, and a partition left both redundancy sides
at ServiceLevel 240 indefinitely.
Activate the resolver via the typed ClusterOptions.SplitBrainResolver
(KeepOldestOption { DownIfAlone = true }) in a new testable
BuildClusterOptions helper. keep-oldest + down-if-alone is correct for a
2-node warm-redundancy pair. HOCON keeps stable-after (typed option can't
express it) + a cross-reference comment. Deterministic unit guard added;
end-to-end verified the resolved ActorSystem config carries the provider
and stable-after survives the HOCON/Hosting merge. Redundancy.md corrected.
Hard-kill failover integration test tracked as a follow-up (effort-M harness).
Joseph Doherty
a81dea102c