feat(GWC-37,WRK-32): refresh live alarm watch lists

src/ZB.MOM.WW.MxGateway.Worker/MxAccess/AlarmCommandHandler.cs

@@ -45,6 +45,7 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
     private FailoverAlarmConsumer? failoverConsumer;
     private EventHandler<AlarmProviderModeChange>? providerModeChangedHandler;
     private string subscribeSessionId = string.Empty;
+    private string subscriptionExpression = string.Empty;
     private bool disposed;
 
     /// <summary>Initializes a new alarm command handler with the given event queue.</summary>
@@ -153,6 +154,7 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             }
 
             subscribeSessionId = sessionId ?? string.Empty;
+            subscriptionExpression = command.SubscriptionExpression ?? string.Empty;
             IMxAccessAlarmConsumer consumer = BuildConsumer(command)
                 ?? throw new InvalidOperationException("Alarm consumer factory returned null.");
 
@@ -171,7 +173,7 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             dispatcher = new AlarmDispatcher(consumer, sink, subscribeSessionId);
             try
             {
-                dispatcher.Subscribe(command.SubscriptionExpression ?? string.Empty);
+                dispatcher.Subscribe(subscriptionExpression);
             }
             catch
             {
@@ -212,7 +214,8 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             return BuildStandby(watchList);
         }
 
-        if (command.ForcedMode == AlarmProviderMode.Unspecified && watchList.Count > 0)
+        if (command.ForcedMode == AlarmProviderMode.Unspecified
+            && (command.FallbackEnabled || watchList.Count > 0))
         {
             IMxAccessAlarmConsumer primary = consumerFactory()
                 ?? throw new InvalidOperationException("Alarm consumer factory returned null.");
@@ -230,6 +233,26 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             ?? throw new InvalidOperationException("Alarm consumer factory returned null.");
     }
 
+    /// <inheritdoc />
+    public void UpdateWatchList(IReadOnlyList<AlarmSubtagTarget> watchList)
+    {
+        if (disposed) throw new ObjectDisposedException(nameof(AlarmCommandHandler));
+        if (watchList is null) throw new ArgumentNullException(nameof(watchList));
+        threadAffinityCheck?.Invoke();
+
+        lock (syncRoot)
+        {
+            if (dispatcher is null || failoverConsumer is null)
+            {
+                throw new InvalidOperationException(
+                    "UpdateAlarmWatchList requires an active fallback-capable alarm subscription.");
+            }
+
+            IMxAccessAlarmConsumer replacement = BuildStandby(watchList);
+            failoverConsumer.ReplaceStandby(replacement, subscriptionExpression);
+        }
+    }
+
     private IMxAccessAlarmConsumer BuildStandby(IReadOnlyList<AlarmSubtagTarget> watchList)
     {
         if (standbyFactory is not null)
@@ -276,6 +299,7 @@ public sealed class AlarmCommandHandler : IAlarmCommandHandler
             DetachProviderModeChanged();
             toDispose = dispatcher;
             dispatcher = null;
+            subscriptionExpression = string.Empty;
         }
         toDispose?.Dispose();
     }