fix(communication): debug-stream teardown/failover unsubscribes via TryGet, never creates or disposes shared channels

tests/ZB.MOM.WW.ScadaBridge.Communication.Tests/Grpc/DebugStreamBridgeActorTests.cs

@@ -400,6 +400,60 @@ public class DebugStreamBridgeActorTests : TestKit
         Assert.Equal("corr-1", factory.ClientFor(GrpcNodeB).SubscribeCalls[0].CorrelationId);
     }
 
+    // ── Task 6 (arch review 02, High): teardown/failover unsubscribe is endpoint-safe ──
+    // Both paths use TryGet, never GetOrCreate, so cleanup can never open a fresh
+    // channel or (with (site,endpoint) keying) touch another session's channel.
+
+    private (IActorRef Actor, EndpointTrackingGrpcClientFactory Factory) CreateBridgeWithTrackingFactory()
+    {
+        var commProbe = CreateTestProbe();
+        var factory = new EndpointTrackingGrpcClientFactory();
+        var props = Props.Create(typeof(DebugStreamBridgeActor),
+            SiteId, InstanceName, "corr-1", commProbe.Ref,
+            (Action<object>)(_ => { }), (Action)(() => { }),
+            factory, GrpcNodeA, GrpcNodeB);
+        var actor = Sys.ActorOf(props);
+        commProbe.ExpectMsg<SiteEnvelope>(); // PreStart subscribe handshake
+        return (actor, factory);
+    }
+
+    [Fact]
+    public void CleanupGrpc_UnsubscribesViaTryGet_WithoutOpeningAChannel()
+    {
+        var (actor, factory) = CreateBridgeWithTrackingFactory();
+        AwaitCondition(() => factory.ClientFor(GrpcNodeA).SubscribeCalls.Count == 1,
+            TimeSpan.FromSeconds(3));
+        var createdBefore = factory.CreatedCount; // node-a only
+
+        actor.Tell(new StopDebugStream());
+
+        AwaitCondition(() => factory.ClientFor(GrpcNodeA).UnsubscribedCorrelationIds.Contains("corr-1"),
+            TimeSpan.FromSeconds(3));
+        // Pre-fix CleanupGrpc called GetOrCreate → could open a fresh channel here.
+        Assert.Equal(createdBefore, factory.CreatedCount);
+    }
+
+    [Fact]
+    public void SessionFailover_UnsubscribesFailedEndpointViaTryGet_OpensOnlyTheReconnectChannel()
+    {
+        var (_, factory) = CreateBridgeWithTrackingFactory();
+        AwaitCondition(() => factory.ClientFor(GrpcNodeA).SubscribeCalls.Count == 1,
+            TimeSpan.FromSeconds(3));
+
+        // Fail NodeA: the bridge unsubscribes the failed NodeA stream via TryGet
+        // (if that path had used GetOrCreate on the post-flip cache it could have
+        // disposed/created the wrong client), then reconnects to NodeB.
+        factory.ClientFor(GrpcNodeA).SubscribeCalls[0].OnError(new Exception("NodeA down"));
+
+        AwaitCondition(() => factory.ClientFor(GrpcNodeA).UnsubscribedCorrelationIds.Contains("corr-1"),
+            TimeSpan.FromSeconds(5));
+        AwaitCondition(() => factory.ClientFor(GrpcNodeB).SubscribeCalls.Count == 1,
+            TimeSpan.FromSeconds(5));
+        // Only the two real node endpoints were ever opened — the unsubscribe
+        // itself created nothing.
+        Assert.Equal(2, factory.CreatedCount);
+    }
+
     // ---------------------------------------------------------------------
     // M2.18 (#26) — stream-first + replay/dedup
     // ---------------------------------------------------------------------
@@ -883,6 +937,12 @@ internal class MockSiteStreamGrpcClientFactory : SiteStreamGrpcClientFactory
         RequestedEndpoints.Add(grpcEndpoint);
         return _mockClient;
     }
+
+    // Mirrors the real factory's TryGet: returns the client only for an endpoint
+    // already opened via GetOrCreate, never creating one. Lets teardown/failover
+    // unsubscribe paths (now TryGet-based, Task 6) resolve the mock client.
+    public override SiteStreamGrpcClient? TryGet(string siteIdentifier, string grpcEndpoint)
+        => RequestedEndpoints.Contains(grpcEndpoint) ? _mockClient : null;
 }
 
 /// <summary>
@@ -902,6 +962,13 @@ internal class EndpointTrackingGrpcClientFactory : SiteStreamGrpcClientFactory
     public MockSiteStreamGrpcClient ClientFor(string endpoint) =>
         _byEndpoint.GetOrAdd(endpoint, _ => new MockSiteStreamGrpcClient());
 
+    /// <summary>Number of distinct endpoint clients created so far (channels opened).</summary>
+    public int CreatedCount => _byEndpoint.Count;
+
     public override SiteStreamGrpcClient GetOrCreate(string siteIdentifier, string grpcEndpoint)
         => ClientFor(grpcEndpoint);
+
+    // TryGet never creates: returns the client only for an already-opened endpoint.
+    public override SiteStreamGrpcClient? TryGet(string siteIdentifier, string grpcEndpoint)
+        => _byEndpoint.TryGetValue(grpcEndpoint, out var client) ? client : null;
 }