fix(communication): cancel-only CTS replacement, deferred channel disposal, single-endpoint debug stream (arch-review 2026-08-19 P3-1 + P3-2 + P3-3)

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

@@ -66,6 +66,74 @@ public class SiteStreamGrpcClientFactoryDisposeTests
         });
     }
 
+    /// <summary>
+    /// Test client whose disposal always throws — stands in for a client whose
+    /// <c>ReleaseResources</c> hit an <see cref="ObjectDisposedException"/> on a subscription
+    /// token source (arch-review 2026-08-19 P3-1).
+    /// </summary>
+    private sealed class ThrowingClient : SiteStreamGrpcClient
+    {
+        public override void Dispose() => throw new ObjectDisposedException(nameof(CancellationTokenSource));
+
+        public override ValueTask DisposeAsync() =>
+            throw new ObjectDisposedException(nameof(CancellationTokenSource));
+    }
+
+    /// <summary>Hands out one throwing client followed by tracking clients.</summary>
+    private sealed class OneThrowingClientFactory : SiteStreamGrpcClientFactory
+    {
+        private readonly ConcurrentBag<TrackingClient> _created = new();
+        private int _next;
+
+        public OneThrowingClientFactory() : base(NullLoggerFactory.Instance) { }
+
+        public IReadOnlyCollection<TrackingClient> Created => _created.ToList();
+
+        protected override SiteStreamGrpcClient CreateClient(string siteIdentifier, string grpcEndpoint)
+        {
+            if (Interlocked.Increment(ref _next) == 1)
+            {
+                return new ThrowingClient();
+            }
+
+            var client = new TrackingClient();
+            _created.Add(client);
+            return client;
+        }
+    }
+
+    [Fact]
+    public async Task DisposeAsync_OneClientThrowing_StillDisposesEveryOtherClient()
+    {
+        // The disposal loop used to abort on the first throwing client, leaving every LATER
+        // client — and its gRPC channel — undisposed for the life of the process.
+        var factory = new OneThrowingClientFactory();
+        factory.GetOrCreate("site-a", "http://localhost:5100"); // throwing
+        factory.GetOrCreate("site-b", "http://localhost:5200");
+        factory.GetOrCreate("site-c", "http://localhost:5300");
+
+        await factory.DisposeAsync();
+
+        Assert.Equal(2, factory.Created.Count);
+        Assert.All(factory.Created, c =>
+            Assert.True(c.AsyncDisposeCalled, "a throwing client must not strand its peers undisposed"));
+    }
+
+    [Fact]
+    public void Dispose_OneClientThrowing_StillDisposesEveryOtherClient()
+    {
+        var factory = new OneThrowingClientFactory();
+        factory.GetOrCreate("site-a", "http://localhost:5100"); // throwing
+        factory.GetOrCreate("site-b", "http://localhost:5200");
+        factory.GetOrCreate("site-c", "http://localhost:5300");
+
+        factory.Dispose();
+
+        Assert.Equal(2, factory.Created.Count);
+        Assert.All(factory.Created, c =>
+            Assert.True(c.SyncDisposeCalled, "a throwing client must not strand its peers undisposed"));
+    }
+
     [Fact]
     public void Dispose_DoesNotDeadlock_UnderSingleThreadedSynchronizationContext()
     {