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) ─────────────────────────────────

tests/ZB.MOM.WW.ScadaBridge.Communication.Tests/SiteAlarmLiveCacheServiceTests.cs

@@ -258,4 +258,48 @@ public class SiteAlarmLiveCacheServiceTests : TestKit
         Assert.False(service.IsLive(999));
         Assert.Empty(service.GetCurrentAlarms(999));
     }
+
+    // ── R2 T15: single-endpoint sites can go live (N9) ──
+
+    [Fact]
+    public void SiteWithOnlyNodeAEndpoint_StartsAnAggregator_AgainstThatEndpoint()
+    {
+        var site = new Site("Three", "site-3")
+        {
+            Id = 3,
+            GrpcNodeAAddress = "http://only-node:8083",
+            GrpcNodeBAddress = null, // single-endpoint site — pre-fix: never goes live
+        };
+
+        var siteRepo = Substitute.For<ISiteRepository>();
+        siteRepo.GetSiteByIdAsync(3, Arg.Any<CancellationToken>()).Returns(site);
+
+        var instanceRepo = Substitute.For<ITemplateEngineRepository>();
+        instanceRepo.GetInstancesBySiteIdAsync(3, Arg.Any<CancellationToken>())
+            .Returns(new List<Instance>());
+
+        var services = new ServiceCollection();
+        services.AddScoped(_ => siteRepo);
+        services.AddScoped(_ => instanceRepo);
+        var provider = services.BuildServiceProvider();
+
+        var options = Options.Create(new CommunicationOptions
+        {
+            LiveAlarmCacheLinger = TimeSpan.FromSeconds(30),
+            LiveAlarmCacheReconcileInterval = TimeSpan.FromMinutes(10),
+        });
+        var comm = new CommunicationService(Options.Create(new CommunicationOptions()),
+            NullLogger<CommunicationService>.Instance);
+        var factory = new CountingFactory();
+
+        var service = new SiteAlarmLiveCacheService(
+            provider, comm, factory, options, NullLogger<SiteAlarmLiveCacheService>.Instance);
+        service.SetActorSystem(Sys);
+
+        using var sub = service.Subscribe(3, () => { });
+
+        // Pre-fix: ResolveSiteAsync required BOTH endpoints and bailed → never live, no client.
+        AwaitCondition(() => service.IsLive(3), TimeSpan.FromSeconds(5));
+        Assert.True(factory.GetOrCreateCount >= 1); // a client was created for the single endpoint
+    }
 }