fix(dashboard): guard stale-session batches inside the renderer dispatch; register IDashboardSessionEventSubscriber

src/ZB.MOM.WW.MxGateway.Tests/Gateway/Dashboard/DashboardHubsRegistrationTests.cs

@@ -45,4 +45,23 @@ public sealed class DashboardHubsRegistrationTests
             .GetRequiredService<DashboardHubConnectionFactory>();
         Assert.NotNull(factory);
     }
+
+    /// <summary>
+    /// The publish and in-process subscribe faces of the event mirror must resolve to
+    /// one instance: two would leave the session-details page reading a mirror the
+    /// session pipeline never publishes to, and the viewer gate would never open.
+    /// </summary>
+    /// <returns>A task that represents the asynchronous operation.</returns>
+    [Fact]
+    public async Task Build_WhenDashboardEnabled_ResolvesBothEventMirrorInterfacesToOneInstance()
+    {
+        await using WebApplication app = GatewayApplication.Build([]);
+
+        IDashboardEventBroadcaster broadcaster = app.Services.GetRequiredService<IDashboardEventBroadcaster>();
+        IDashboardSessionEventSubscriber subscriber = app.Services
+            .GetRequiredService<IDashboardSessionEventSubscriber>();
+
+        Assert.Same(broadcaster, subscriber);
+        Assert.Same(app.Services.GetRequiredService<DashboardEventBroadcaster>(), broadcaster);
+    }
 }