fix(comm): single-gRPC-endpoint sites can go live (flip degenerates to same-node reconnect) (plan R2-02 T15)

src/ZB.MOM.WW.ScadaBridge.Communication/SiteAlarmLiveCacheService.cs

@@ -294,7 +294,9 @@ public sealed class SiteAlarmLiveCacheService : ISiteAlarmLiveCache
             return null;
         }
 
-        if (string.IsNullOrWhiteSpace(site.GrpcNodeAAddress) || string.IsNullOrWhiteSpace(site.GrpcNodeBAddress))
+        var nodeA = site.GrpcNodeAAddress;
+        var nodeB = site.GrpcNodeBAddress;
+        if (string.IsNullOrWhiteSpace(nodeA) && string.IsNullOrWhiteSpace(nodeB))
         {
             _logger.LogWarning(
                 "Live alarm cache: site {SiteId} ({SiteIdentifier}) has no gRPC node addresses; " +
@@ -302,7 +304,13 @@ public sealed class SiteAlarmLiveCacheService : ISiteAlarmLiveCache
             return null;
         }
 
-        return (site.SiteIdentifier, site.GrpcNodeAAddress!, site.GrpcNodeBAddress!);
+        // Single-endpoint site (review 02 round 2, N9): reuse the sole configured
+        // endpoint for both slots — the aggregator's NodeA↔NodeB failover flip
+        // degenerates to a reconnect against the same node, which is exactly the
+        // right behavior for a one-node site.
+        var grpcA = !string.IsNullOrWhiteSpace(nodeA) ? nodeA! : nodeB!;
+        var grpcB = !string.IsNullOrWhiteSpace(nodeB) ? nodeB! : nodeA!;
+        return (site.SiteIdentifier, grpcA, grpcB);
     }
 
     // ── Snapshot fan-out (the seed / reconcile) ─────────────────────────────────