fix(comm): shared oldest-Up ActiveNodeEvaluator in Communication; Host evaluator delegates (plan R2-02 T1)

src/ZB.MOM.WW.ScadaBridge.Communication/ClusterState/ActiveNodeEvaluator.cs

@@ -0,0 +1,39 @@
+using Akka.Cluster;
+
+namespace ZB.MOM.WW.ScadaBridge.Communication.ClusterState;
+
+/// <summary>
+/// THE single definition of "active node" (review 01 [High]; review 02 round 2 [Critical] N1):
+/// a node is active when it is the OLDEST Up member (optionally within a role scope) — i.e.
+/// the member the ClusterSingletonManager places singletons on. Cluster LEADERSHIP (lowest
+/// address) is an Akka-internal concept that diverges from singleton placement permanently
+/// once the original first node restarts and rejoins; every product-level active/standby
+/// decision must use this evaluator, never <c>cluster.State.Leader</c>.
+/// <para>
+/// Lives in Communication (not Host) so BOTH <c>SiteCommunicationActor</c> and
+/// <c>SiteReplicationActor</c> can default to it — Host cannot be referenced from either.
+/// The Host's <c>ClusterActivityEvaluator.SelfIsOldest</c> delegates here, so the S&amp;F
+/// delivery gate (<c>IClusterNodeProvider.SelfIsPrimary</c>), the resync authority checks,
+/// and the heartbeat IsActive stamp all share one implementation.
+/// </para>
+/// </summary>
+public static class ActiveNodeEvaluator
+{
+    /// <summary>True when self is Up and no other Up member (in the role scope) is older.</summary>
+    /// <param name="cluster">The Akka cluster to evaluate.</param>
+    /// <param name="role">Optional role scope; when set, only members with this role are considered.</param>
+    /// <returns><c>true</c> when self is Up and the oldest Up member in the role scope.</returns>
+    public static bool SelfIsOldestUp(Cluster cluster, string? role = null)
+    {
+        var self = cluster.SelfMember;
+        if (self.Status != MemberStatus.Up)
+            return false;
+        if (role != null && !self.HasRole(role))
+            return false;
+
+        return cluster.State.Members
+            .Where(m => m.Status == MemberStatus.Up)
+            .Where(m => role == null || m.HasRole(role))
+            .All(m => m.UniqueAddress.Equals(self.UniqueAddress) || self.IsOlderThan(m));
+    }
+}

src/ZB.MOM.WW.ScadaBridge.Host/Health/ClusterActivityEvaluator.cs

@@ -13,23 +13,15 @@ namespace ZB.MOM.WW.ScadaBridge.Host.Health;
 /// </summary>
 public static class ClusterActivityEvaluator
 {
-    /// <summary>True when self is Up and no other Up member (in the role scope) is older.</summary>
+    /// <summary>True when self is Up and no other Up member (in the role scope) is older.
+    /// Delegates to the shared <see cref="Communication.ClusterState.ActiveNodeEvaluator"/> —
+    /// one implementation for the delivery gate, the resync authority checks, and the
+    /// heartbeat IsActive stamp (review 02 round 2, N1).</summary>
     /// <param name="cluster">The Akka cluster to evaluate.</param>
     /// <param name="role">Optional role scope; when set, only members with this role are considered.</param>
     /// <returns><c>true</c> when self is Up and the oldest Up member in the role scope.</returns>
-    public static bool SelfIsOldest(Cluster cluster, string? role = null)
-    {
-        var self = cluster.SelfMember;
-        if (self.Status != MemberStatus.Up)
-            return false;
-        if (role != null && !self.HasRole(role))
-            return false;
-
-        return cluster.State.Members
-            .Where(m => m.Status == MemberStatus.Up)
-            .Where(m => role == null || m.HasRole(role))
-            .All(m => m.UniqueAddress.Equals(self.UniqueAddress) || self.IsOlderThan(m));
-    }
+    public static bool SelfIsOldest(Cluster cluster, string? role = null) =>
+        Communication.ClusterState.ActiveNodeEvaluator.SelfIsOldestUp(cluster, role);
 
     /// <summary>The oldest Up member in the role scope, or null while none is Up. Used for Primary/Standby labelling.</summary>
     /// <param name="cluster">The Akka cluster to evaluate.</param>