fix(cluster): enable SBR downing provider — automatic failover was inert for crashes/partitions

src/ZB.MOM.WW.ScadaBridge.Host/Actors/AkkaHostedService.cs

@@ -201,6 +201,11 @@ public class AkkaHostedService : IHostedService
     /// <see cref="ClusterOptions.DownIfAlone"/> rather than hard-coded, so the bound
     /// configuration value is actually consumed.
     ///
+    /// The split-brain-resolver <c>downing-provider-class</c> is installed
+    /// explicitly: Akka defaults to <c>NoDowning</c>, under which the entire
+    /// split-brain-resolver section is inert and singletons never migrate on a hard
+    /// crash or partition. Naming the SBR provider is what activates automatic downing.
+    ///
     /// Every duration is rendered via <see cref="DurationHocon"/> in
     /// milliseconds, so sub-second cluster timing values (e.g. a 750ms heartbeat) are
     /// preserved exactly instead of being rounded to whole seconds.
@@ -251,6 +256,7 @@ akka {{
         seed-nodes = [{seedNodesStr}]
         roles = [{rolesStr}]
         min-nr-of-members = {clusterOptions.MinNrOfMembers}
+        downing-provider-class = ""Akka.Cluster.SBR.SplitBrainResolverProvider, Akka.Cluster""
         split-brain-resolver {{
             active-strategy = {QuoteHocon(clusterOptions.SplitBrainResolverStrategy)}
             stable-after = {DurationHocon(clusterOptions.StableAfter)}

tests/ZB.MOM.WW.ScadaBridge.Host.Tests/HoconBuilderTests.cs

@@ -160,4 +160,22 @@ public class HoconBuilderTests
             TimeSpan.FromMilliseconds(7500),
             config.GetTimeSpan("akka.remote.transport-failure-detector.acceptable-heartbeat-pause"));
     }
+
+    [Fact]
+    public void BuildHocon_EnablesSplitBrainResolverDowningProvider()
+    {
+        // Review 01 [Critical]: without downing-provider-class the entire
+        // split-brain-resolver section is inert (Akka default = NoDowning) and
+        // singletons never migrate on a hard crash.
+        var node = new NodeOptions { Role = "Central", NodeHostname = "node1", RemotingPort = 8081 };
+
+        var hocon = AkkaHostedService.BuildHocon(
+            node, DefaultCluster(), new[] { "Central" },
+            TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(15));
+
+        var config = ConfigurationFactory.ParseString(hocon);
+        Assert.Equal(
+            "Akka.Cluster.SBR.SplitBrainResolverProvider, Akka.Cluster",
+            config.GetString("akka.cluster.downing-provider-class"));
+    }
 }