Resolve Tests-025..026

Tests-025 (Conventions): Extracted the previously-duplicated
NullDashboardEventBroadcaster into TestSupport/NullDashboardEventBroadcaster.cs
(singleton Instance, private ctor). The two nested copies in
EventStreamServiceTests and GatewayEndToEndFakeWorkerSmokeTests were
removed; both files now use the shared type via
'using ZB.MOM.WW.MxGateway.Tests.TestSupport;'. The Server-041 regression
test's ThrowingDashboardEventBroadcaster is intentionally left nested —
single-file usage doesn't warrant promotion to TestSupport. The third
copy in IntegrationTests/WorkerLiveMxAccessSmokeTests was handled by
IntegrationTests-024 in its own commit.

Tests-026 (Testing coverage): Added a new RecordingDashboardEventBroadcaster
test double in TestSupport — a thread-safe (ConcurrentQueue<DashboardEventCapture>)
recorder. New fixture
StreamEventsAsync_PublishesEachEventToDashboardBroadcaster in
EventStreamServiceTests pushes two events through the fake session and
asserts the broadcaster received both with the correct sessionId and
WorkerSequence. TDD red→green confirmed: the deliberately-wrong
"Expected 3, Actual 2" red phase proved the recording fake was actually
invoked by the production code path.

Verification: 486/486 server tests passing (485 previous + 1 new).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.MxGateway.Tests/Gateway/GatewayEndToEndFakeWorkerSmokeTests.cs

@@ -414,9 +414,4 @@ public sealed class GatewayEndToEndFakeWorkerSmokeTests
         }
     }
 
-    private sealed class NullDashboardEventBroadcaster : ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs.IDashboardEventBroadcaster
-    {
-        public static readonly NullDashboardEventBroadcaster Instance = new();
-        public void Publish(string sessionId, ZB.MOM.WW.MxGateway.Contracts.Proto.MxEvent mxEvent) { }
-    }
 }

src/ZB.MOM.WW.MxGateway.Tests/TestSupport/NullDashboardEventBroadcaster.cs

@@ -0,0 +1,26 @@
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+using ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;
+
+namespace ZB.MOM.WW.MxGateway.Tests.TestSupport;
+
+/// <summary>
+/// <see cref="IDashboardEventBroadcaster"/> that drops every event on the floor.
+/// Used by tests that need to wire up <c>EventStreamService</c> but do not care
+/// about the dashboard fan-out side-channel. The singleton <see cref="Instance"/>
+/// mirrors the Tests-007 / Tests-021 shared-fake pattern under
+/// <c>src/ZB.MOM.WW.MxGateway.Tests/TestSupport/</c>.
+/// </summary>
+public sealed class NullDashboardEventBroadcaster : IDashboardEventBroadcaster
+{
+    /// <summary>Shared instance for tests that do not need to inspect broadcaster state.</summary>
+    public static readonly NullDashboardEventBroadcaster Instance = new();
+
+    private NullDashboardEventBroadcaster()
+    {
+    }
+
+    /// <inheritdoc />
+    public void Publish(string sessionId, MxEvent mxEvent)
+    {
+    }
+}

src/ZB.MOM.WW.MxGateway.Tests/TestSupport/RecordingDashboardEventBroadcaster.cs

@@ -0,0 +1,30 @@
+using System.Collections.Concurrent;
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+using ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;
+
+namespace ZB.MOM.WW.MxGateway.Tests.TestSupport;
+
+/// <summary>
+/// <see cref="IDashboardEventBroadcaster"/> test double that captures every
+/// <c>Publish(sessionId, mxEvent)</c> call into a thread-safe list, so tests
+/// can prove the gRPC producer loop actually mirrors events to the dashboard
+/// fan-out seam. Tests-026.
+/// </summary>
+public sealed class RecordingDashboardEventBroadcaster : IDashboardEventBroadcaster
+{
+    private readonly ConcurrentQueue<DashboardEventCapture> _captures = new();
+
+    /// <summary>Gets a snapshot of every <c>Publish</c> call in arrival order.</summary>
+    public IReadOnlyList<DashboardEventCapture> Captures => _captures.ToArray();
+
+    /// <inheritdoc />
+    public void Publish(string sessionId, MxEvent mxEvent)
+    {
+        _captures.Enqueue(new DashboardEventCapture(sessionId, mxEvent));
+    }
+}
+
+/// <summary>Captured <c>(sessionId, mxEvent)</c> pair from a Publish invocation.</summary>
+/// <param name="SessionId">The session id passed to Publish.</param>
+/// <param name="MxEvent">The MxEvent passed to Publish.</param>
+public sealed record DashboardEventCapture(string SessionId, MxEvent MxEvent);