test(communication): M2.11 review nits — bridge-actor not-found test + dead-letter comment + toast wording (#24)

- Add DebugStreamBridgeActorTests: On_InstanceNotFound_Snapshot_Forwards_To_OnEvent_Does_Not_Open_Stream_And_Terminates — asserts _onEvent receives the not-found snapshot, SubscribeCalls remains empty, and the actor terminates cleanly via Watch/ExpectTerminated.
- Add comment in DebugStreamBridgeActor near Context.Stop(Self) explaining that the subsequent StopDebugStream Tell from DebugStreamService.StopStream produces a benign expected dead-letter.
- Reword not-found toast in DebugView.razor to "Instance not found on the selected site — check the deployment target." (accurate when the instance may be deployed to a different site).

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

@@ -60,6 +60,44 @@ public class DebugStreamBridgeActorTests : TestKit
         return new TestContext(actor, commProbe, mockClient, events, terminated);
     }
 
+    [Fact]
+    public void On_InstanceNotFound_Snapshot_Forwards_To_OnEvent_Does_Not_Open_Stream_And_Terminates()
+    {
+        // M2.11: when the site reports InstanceNotFound=true the bridge actor must
+        // (a) forward the not-found snapshot to _onEvent so DebugStreamService's TCS
+        //     resolves and the caller can inspect the flag,
+        // (b) NOT open a gRPC stream (SubscribeCalls must remain empty), and
+        // (c) stop itself cleanly.
+        var ctx = CreateBridgeActor();
+        ctx.CommProbe.ExpectMsg<SiteEnvelope>(); // initial subscribe envelope
+
+        var notFoundSnapshot = new DebugViewSnapshot(
+            InstanceName,
+            new List<AttributeValueChanged>(),
+            new List<AlarmStateChanged>(),
+            DateTimeOffset.UtcNow,
+            InstanceNotFound: true);
+
+        Watch(ctx.BridgeActor);
+        ctx.BridgeActor.Tell(notFoundSnapshot);
+
+        // (a) _onEvent must receive the not-found snapshot
+        AwaitCondition(() => { lock (ctx.ReceivedEvents) { return ctx.ReceivedEvents.Count == 1; } },
+            TimeSpan.FromSeconds(3));
+        lock (ctx.ReceivedEvents)
+        {
+            var received = Assert.IsType<DebugViewSnapshot>(ctx.ReceivedEvents[0]);
+            Assert.True(received.InstanceNotFound);
+        }
+
+        // (b) no gRPC stream opened
+        ExpectTerminated(ctx.BridgeActor, TimeSpan.FromSeconds(3));
+        Assert.Empty(ctx.MockGrpcClient.SubscribeCalls);
+
+        // (c) actor terminates cleanly
+        // ExpectTerminated above already verified termination
+    }
+
     [Fact]
     public void PreStart_Sends_SubscribeDebugViewRequest_Via_ClusterClient()
     {