fix(siteruntime): M2.11 — unknown-instance debug snapshot returns InstanceNotFound=true (#24)

RouteDebugSnapshot and RouteDebugViewSubscribe on DeploymentManagerActor
previously returned an empty DebugViewSnapshot for unknown instances,
indistinguishable from a deployed-but-empty instance. Callers had no way
to differentiate "not deployed here" from "deployed, no data yet."

Approach — additive field on existing message contract:
  Added `bool InstanceNotFound = false` as an optional trailing parameter
  to DebugViewSnapshot (Commons). All existing positional constructor calls
  and serialized wire frames are unaffected (default = false). A dedicated
  new message type was considered but rejected: the ClusterClient channel
  and DebugStreamService TCS are already typed on DebugViewSnapshot, and a
  second reply union would require wider changes for zero additive-safety
  gain.

Changes:
  - Commons/DebugViewSnapshot: add InstanceNotFound = false (additive)
  - DeploymentManagerActor: set InstanceNotFound=true in both unknown-
    instance branches (RouteDebugViewSubscribe, RouteDebugSnapshot)
  - DebugStreamBridgeActor: when snapshot.InstanceNotFound, forward it to
    _onEvent (resolves the TCS) then stop cleanly; no gRPC stream opened
  - DebugView.razor: check session.InitialSnapshot.InstanceNotFound after
    connect and show a clear "not deployed on this site" error toast
  - 3 new tests in DeploymentManagerActorTests covering: unknown→snapshot,
    unknown→subscribe, known-empty→InstanceNotFound stays false

tests/ZB.MOM.WW.ScadaBridge.SiteRuntime.Tests/Actors/DeploymentManagerActorTests.cs

@@ -3,6 +3,7 @@ using Akka.TestKit.Xunit2;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Deployment;
+using ZB.MOM.WW.ScadaBridge.Commons.Messages.DebugView;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.InboundApi;
 using ZB.MOM.WW.ScadaBridge.Commons.Messages.Lifecycle;
 using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
@@ -387,4 +388,64 @@ public class DeploymentManagerActorTests : TestKit, IDisposable
         Assert.Equal("route-corr-2", response.CorrelationId);
         Assert.True(response.Success, $"Routed call failed: {response.ErrorMessage}");
     }
+
+    // ── M2.11: Debug-view routing — unknown-instance not-found signal ──
+
+    [Fact]
+    public async Task RouteDebugSnapshot_UnknownInstance_SetsInstanceNotFound()
+    {
+        // An instance that was never deployed to this site must return a
+        // DebugViewSnapshot with InstanceNotFound=true so the caller can
+        // distinguish "not deployed here" from a deployed-but-empty instance.
+        var actor = CreateDeploymentManager();
+        await Task.Delay(500);
+
+        actor.Tell(new DebugSnapshotRequest("NeverDeployed", "snap-corr-1"));
+
+        var snapshot = ExpectMsg<DebugViewSnapshot>(TimeSpan.FromSeconds(5));
+        Assert.Equal("NeverDeployed", snapshot.InstanceUniqueName);
+        Assert.True(snapshot.InstanceNotFound,
+            "Expected InstanceNotFound=true for an instance not registered on this site.");
+        Assert.Empty(snapshot.AttributeValues);
+        Assert.Empty(snapshot.AlarmStates);
+    }
+
+    [Fact]
+    public async Task RouteDebugViewSubscribe_UnknownInstance_SetsInstanceNotFound()
+    {
+        // Same contract for the subscribe path: unknown instance → InstanceNotFound=true.
+        var actor = CreateDeploymentManager();
+        await Task.Delay(500);
+
+        actor.Tell(new SubscribeDebugViewRequest("NeverDeployed2", "sub-corr-1"));
+
+        var snapshot = ExpectMsg<DebugViewSnapshot>(TimeSpan.FromSeconds(5));
+        Assert.Equal("NeverDeployed2", snapshot.InstanceUniqueName);
+        Assert.True(snapshot.InstanceNotFound,
+            "Expected InstanceNotFound=true for an instance not registered on this site.");
+        Assert.Empty(snapshot.AttributeValues);
+        Assert.Empty(snapshot.AlarmStates);
+    }
+
+    [Fact]
+    public async Task RouteDebugSnapshot_KnownButEmptyInstance_DoesNotSetInstanceNotFound()
+    {
+        // A deployed instance with no runtime data yet must return an empty
+        // snapshot with InstanceNotFound=false — the known-empty path is unchanged.
+        var actor = CreateDeploymentManager();
+        await Task.Delay(500);
+
+        actor.Tell(new DeployInstanceCommand(
+            "dep-dbg", "EmptyPump", "sha256:dbg",
+            MakeConfigJson("EmptyPump"), "admin", DateTimeOffset.UtcNow));
+        ExpectMsg<DeploymentStatusResponse>(TimeSpan.FromSeconds(5));
+        await Task.Delay(800); // let InstanceActor spin up
+
+        actor.Tell(new DebugSnapshotRequest("EmptyPump", "snap-corr-2"));
+
+        var snapshot = ExpectMsg<DebugViewSnapshot>(TimeSpan.FromSeconds(5));
+        Assert.Equal("EmptyPump", snapshot.InstanceUniqueName);
+        Assert.False(snapshot.InstanceNotFound,
+            "A deployed (but empty) instance must NOT set InstanceNotFound.");
+    }
 }