feat(dashboard): mirror events via SessionEventDistributor subscriber (fixes dark feed without gRPC client)

src/ZB.MOM.WW.MxGateway.Server/Sessions/SessionEventStreaming.cs

@@ -1,5 +1,6 @@
 using Microsoft.Extensions.Logging.Abstractions;
 using ZB.MOM.WW.MxGateway.Server.Configuration;
+using ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;
 using ZB.MOM.WW.MxGateway.Server.Grpc;
 using ZB.MOM.WW.MxGateway.Server.Metrics;
 
@@ -30,17 +31,25 @@ namespace ZB.MOM.WW.MxGateway.Server.Sessions;
 ///     fault. Carrying it here keeps the distributor decoupled from the metrics type while
 ///     preserving the observability the pre-epic per-RPC overflow path emitted.
 /// </param>
+/// <param name="DashboardBroadcaster">
+///     Sink the session's internal dashboard mirror loop (Task 6) publishes raw session
+///     <c>MxEvent</c>s to. When non-null the session registers an internal distributor
+///     subscriber on becoming Ready and mirrors every fanned event to the dashboard
+///     EventsHub group regardless of whether a gRPC client is streaming. When null
+///     (unit tests that don't exercise the dashboard mirror) no mirror is started.
+/// </param>
 public sealed record SessionEventStreaming(
     MxAccessGrpcMapper Mapper,
     EventOptions EventOptions,
     ILogger<SessionEventDistributor> DistributorLogger,
     TimeProvider TimeProvider,
-    GatewayMetrics Metrics)
+    GatewayMetrics Metrics,
+    IDashboardEventBroadcaster? DashboardBroadcaster = null)
 {
     /// <summary>
     ///     Defaults used when a session is constructed without explicit streaming
     ///     dependencies (unit tests). Uses a fresh mapper, default event options, a no-op
-    ///     logger, the system clock, and a fresh metrics sink.
+    ///     logger, the system clock, a fresh metrics sink, and no dashboard mirror.
     /// </summary>
     public static SessionEventStreaming Default { get; } = new(
         new MxAccessGrpcMapper(),