fix(twincat): retract the fresh ADS notification when unsubscribe raced the replay (05/STAB-17)

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests/FakeTwinCATClient.cs

@@ -118,6 +118,9 @@ internal class FakeTwinCATClient : ITwinCATClient
     public bool ThrowOnAddNotification { get; set; }
     /// <summary>Records the most recently-supplied <c>maxDelayMs</c> for Driver.TwinCAT-014 tests.</summary>
     public int LastMaxDelayMs { get; private set; }
+    /// <summary>When set, <see cref="AddNotificationAsync"/> awaits this gate before creating the handle —
+    ///     lets a test wedge a replay/register mid-flight (STAB-17 orphan race).</summary>
+    public TaskCompletionSource? AddNotificationGate { get; set; }
 
     /// <summary>Simulates adding a notification for value changes.</summary>
     /// <param name="symbolPath">The path to the symbol to watch.</param>
@@ -128,17 +131,20 @@ internal class FakeTwinCATClient : ITwinCATClient
     /// <param name="onChange">The callback to invoke on value change.</param>
     /// <param name="cancellationToken">The cancellation token.</param>
     /// <returns>A task that returns a notification handle.</returns>
-    public virtual Task<ITwinCATNotificationHandle> AddNotificationAsync(
+    public virtual async Task<ITwinCATNotificationHandle> AddNotificationAsync(
         string symbolPath, TwinCATDataType type, int? bitIndex, TimeSpan cycleTime,
         int maxDelayMs, Action<string, object?> onChange, CancellationToken cancellationToken)
     {
         if (ThrowOnAddNotification)
             throw Exception ?? new InvalidOperationException("fake AddNotification failure");
 
+        if (AddNotificationGate is { } gate)
+            await gate.Task.ConfigureAwait(false);
+
         LastMaxDelayMs = maxDelayMs;
         var reg = new FakeNotification(symbolPath, type, bitIndex, onChange, this);
         Notifications.Add(reg);
-        return Task.FromResult<ITwinCATNotificationHandle>(reg);
+        return reg;
     }
 
     /// <summary>Fire a change event through the registered callback for <paramref name="symbolPath"/>.</summary>