diff --git a/tests/ScadaLink.Communication.Tests/Grpc/CleanupVerificationTests.cs b/tests/ScadaLink.Communication.Tests/Grpc/CleanupVerificationTests.cs
new file mode 100644
index 0000000..c665238
--- /dev/null
+++ b/tests/ScadaLink.Communication.Tests/Grpc/CleanupVerificationTests.cs
@@ -0,0 +1,129 @@
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Grpc.Core;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using ScadaLink.Communication.Grpc;
+
+namespace ScadaLink.Communication.Tests.Grpc;
+
+/// <summary>
+/// Verifies that after a gRPC stream is cancelled, the SiteStreamManager
+/// subscription is properly cleaned up with no leaked subscriptions.
+/// </summary>
+public class CleanupVerificationTests : TestKit
+{
+    [Fact]
+    public async Task Stream_Cancellation_CleansUp_SiteStreamManager_Subscription()
+    {
+        // Arrange: create server with mock subscriber that tracks subscribe/remove calls
+        var subscriber = Substitute.For<ISiteStreamSubscriber>();
+        var subscribeCalled = false;
+        var removeCalled = false;
+        IActorRef? subscribedActor = null;
+
+        subscriber.Subscribe(Arg.Any<string>(), Arg.Any<IActorRef>())
+            .Returns(ci =>
+            {
+                subscribeCalled = true;
+                subscribedActor = ci.Arg<IActorRef>();
+                return "sub-cleanup-test";
+            });
+
+        subscriber.When(x => x.RemoveSubscriber(Arg.Any<IActorRef>()))
+            .Do(_ => removeCalled = true);
+
+        var logger = NullLogger<SiteStreamGrpcServer>.Instance;
+        var server = new SiteStreamGrpcServer(subscriber, logger);
+        server.SetReady(Sys);
+
+        var cts = new CancellationTokenSource();
+        var context = Substitute.For<ServerCallContext>();
+        context.CancellationToken.Returns(cts.Token);
+
+        var writer = Substitute.For<IServerStreamWriter<SiteStreamEvent>>();
+
+        var request = new InstanceStreamRequest
+        {
+            CorrelationId = "corr-cleanup-verify",
+            InstanceUniqueName = "Site1.TestInst"
+        };
+
+        // Act: start a stream, wait for it to register, then cancel
+        var streamTask = Task.Run(() => server.SubscribeInstance(request, writer, context));
+
+        await WaitForConditionAsync(() => subscribeCalled);
+        Assert.True(subscribeCalled, "Subscribe should have been called");
+        Assert.Equal(1, server.ActiveStreamCount);
+
+        cts.Cancel();
+        await streamTask;
+
+        // Assert: verify cleanup
+        Assert.True(removeCalled, "RemoveSubscriber should have been called after cancellation");
+        Assert.Equal(0, server.ActiveStreamCount);
+
+        // Verify the same actor that was subscribed is the one that was removed
+        subscriber.Received(1).RemoveSubscriber(subscribedActor!);
+    }
+
+    [Fact]
+    public async Task Multiple_Streams_Cancelled_AllCleanedUp()
+    {
+        var subscriber = Substitute.For<ISiteStreamSubscriber>();
+        var removeCount = 0;
+
+        subscriber.Subscribe(Arg.Any<string>(), Arg.Any<IActorRef>())
+            .Returns("sub-multi");
+
+        subscriber.When(x => x.RemoveSubscriber(Arg.Any<IActorRef>()))
+            .Do(_ => Interlocked.Increment(ref removeCount));
+
+        var logger = NullLogger<SiteStreamGrpcServer>.Instance;
+        var server = new SiteStreamGrpcServer(subscriber, logger);
+        server.SetReady(Sys);
+
+        // Start 3 streams
+        var ctsList = new List<CancellationTokenSource>();
+        var tasks = new List<Task>();
+
+        for (var i = 0; i < 3; i++)
+        {
+            var cts = new CancellationTokenSource();
+            ctsList.Add(cts);
+            var ctx = Substitute.For<ServerCallContext>();
+            ctx.CancellationToken.Returns(cts.Token);
+            var w = Substitute.For<IServerStreamWriter<SiteStreamEvent>>();
+
+            var req = new InstanceStreamRequest
+            {
+                CorrelationId = $"corr-multi-{i}",
+                InstanceUniqueName = $"Site1.Inst{i}"
+            };
+
+            tasks.Add(Task.Run(() => server.SubscribeInstance(req, w, ctx)));
+        }
+
+        await WaitForConditionAsync(() => server.ActiveStreamCount == 3);
+
+        // Cancel all
+        foreach (var cts in ctsList)
+            cts.Cancel();
+
+        await Task.WhenAll(tasks);
+
+        Assert.Equal(0, server.ActiveStreamCount);
+        Assert.Equal(3, removeCount);
+    }
+
+    private static async Task WaitForConditionAsync(Func<bool> condition, int timeoutMs = 5000)
+    {
+        var deadline = DateTime.UtcNow.AddMilliseconds(timeoutMs);
+        while (!condition() && DateTime.UtcNow < deadline)
+        {
+            await Task.Delay(25);
+        }
+
+        Assert.True(condition(), $"Condition not met within {timeoutMs}ms");
+    }
+}
diff --git a/tests/ScadaLink.Communication.Tests/Grpc/NoClusterClientStreamingRegressionTests.cs b/tests/ScadaLink.Communication.Tests/Grpc/NoClusterClientStreamingRegressionTests.cs
new file mode 100644
index 0000000..28dcf33
--- /dev/null
+++ b/tests/ScadaLink.Communication.Tests/Grpc/NoClusterClientStreamingRegressionTests.cs
@@ -0,0 +1,51 @@
+using System.Reflection;
+using ScadaLink.Communication.Actors;
+
+namespace ScadaLink.Communication.Tests.Grpc;
+
+/// <summary>
+/// Regression tests ensuring that the old ClusterClient-based debug streaming
+/// path is not reintroduced. Debug streaming now flows through gRPC.
+///
+/// Note: The DebugStreamEvent type-does-not-exist check lives in
+/// ScadaLink.Commons.Tests/ArchitecturalConstraintTests.cs and is not
+/// duplicated here.
+/// </summary>
+public class NoClusterClientStreamingRegressionTests
+{
+    [Fact]
+    public void CentralCommunicationActor_DoesNotHave_HandleDebugStreamEvent()
+    {
+        var type = typeof(CentralCommunicationActor);
+        var method = type.GetMethod("HandleDebugStreamEvent",
+            BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
+        Assert.Null(method);
+    }
+
+    [Fact]
+    public void SiteCommunicationActor_DoesNotHave_HandleDebugStreamEvent()
+    {
+        var type = typeof(SiteCommunicationActor);
+        var method = type.GetMethod("HandleDebugStreamEvent",
+            BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
+        Assert.Null(method);
+    }
+
+    [Fact]
+    public void CentralCommunicationActor_DoesNotHave_ForwardDebugStreamEvent()
+    {
+        var type = typeof(CentralCommunicationActor);
+        var method = type.GetMethod("ForwardDebugStreamEvent",
+            BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);
+        Assert.Null(method);
+    }
+
+    [Fact]
+    public void Communication_Assembly_DoesNotContain_DebugStreamEvent_Type()
+    {
+        // DebugStreamEvent should not exist in the Communication assembly either
+        var assembly = typeof(CentralCommunicationActor).Assembly;
+        var type = assembly.GetTypes().FirstOrDefault(t => t.Name == "DebugStreamEvent");
+        Assert.Null(type);
+    }
+}
diff --git a/tests/ScadaLink.Communication.Tests/Grpc/ProtoContractTests.cs b/tests/ScadaLink.Communication.Tests/Grpc/ProtoContractTests.cs
new file mode 100644
index 0000000..26bc7eb
--- /dev/null
+++ b/tests/ScadaLink.Communication.Tests/Grpc/ProtoContractTests.cs
@@ -0,0 +1,79 @@
+using Google.Protobuf.WellKnownTypes;
+using ScadaLink.Communication.Grpc;
+
+namespace ScadaLink.Communication.Tests.Grpc;
+
+/// <summary>
+/// Guardrail tests that verify all oneof variants in SiteStreamEvent have
+/// corresponding conversion handlers. Adding a new proto field without
+/// implementing the conversion will cause these tests to fail.
+/// </summary>
+public class ProtoContractTests
+{
+    /// <summary>
+    /// The set of EventOneofCase values we handle in ConvertToDomainEvent.
+    /// Update this array when adding a new oneof variant.
+    /// </summary>
+    private static readonly SiteStreamEvent.EventOneofCase[] HandledCases =
+    [
+        SiteStreamEvent.EventOneofCase.AttributeChanged,
+        SiteStreamEvent.EventOneofCase.AlarmChanged
+    ];
+
+    [Fact]
+    public void AllOneofVariants_HaveConversionHandlers()
+    {
+        var allCases = System.Enum.GetValues<SiteStreamEvent.EventOneofCase>()
+            .Where(c => c != SiteStreamEvent.EventOneofCase.None)
+            .ToArray();
+
+        Assert.Equal(allCases.Length, HandledCases.Length);
+        foreach (var c in allCases)
+            Assert.Contains(c, HandledCases);
+    }
+
+    [Theory]
+    [InlineData(SiteStreamEvent.EventOneofCase.AttributeChanged)]
+    [InlineData(SiteStreamEvent.EventOneofCase.AlarmChanged)]
+    public void ConvertToDomainEvent_HandlesAllOneofVariants(SiteStreamEvent.EventOneofCase eventCase)
+    {
+        var evt = CreateTestEvent(eventCase);
+        var result = SiteStreamGrpcClient.ConvertToDomainEvent(evt);
+        Assert.NotNull(result);
+    }
+
+    private static SiteStreamEvent CreateTestEvent(SiteStreamEvent.EventOneofCase eventCase)
+    {
+        var ts = Timestamp.FromDateTimeOffset(DateTimeOffset.UtcNow);
+
+        return eventCase switch
+        {
+            SiteStreamEvent.EventOneofCase.AttributeChanged => new SiteStreamEvent
+            {
+                CorrelationId = "test",
+                AttributeChanged = new AttributeValueUpdate
+                {
+                    InstanceUniqueName = "Site1.Inst1",
+                    AttributePath = "Path",
+                    AttributeName = "Attr",
+                    Value = "42",
+                    Quality = Quality.Good,
+                    Timestamp = ts
+                }
+            },
+            SiteStreamEvent.EventOneofCase.AlarmChanged => new SiteStreamEvent
+            {
+                CorrelationId = "test",
+                AlarmChanged = new AlarmStateUpdate
+                {
+                    InstanceUniqueName = "Site1.Inst1",
+                    AlarmName = "HighTemp",
+                    State = AlarmStateEnum.AlarmStateActive,
+                    Priority = 1,
+                    Timestamp = ts
+                }
+            },
+            _ => throw new ArgumentOutOfRangeException(nameof(eventCase), eventCase, "Unhandled event case")
+        };
+    }
+}