worker(alarms): advise ack-comment subtag so the ack write targets an active MXAccess item

src/ZB.MOM.WW.MxGateway.Worker.Tests/MxAccess/SubtagAlarmConsumerTests.cs

@@ -40,9 +40,9 @@ public sealed class SubtagAlarmConsumerTests
         return new SubtagAlarmConsumer(source, new[] { BuildTarget() });
     }
 
-    /// <summary>Verifies Subscribe advises the active, acked, and priority subtags but not the ack-comment subtag.</summary>
+    /// <summary>Verifies Subscribe advises the active, acked, priority, and ack-comment subtags (the ack-comment is advised so it is an active, writable MXAccess item).</summary>
     [Fact]
-    public void Subscribe_AdvisesActiveAndAckedSubtags()
+    public void Subscribe_AdvisesAllSubtagsIncludingAckComment()
     {
         FakeSource source = new FakeSource();
         using SubtagAlarmConsumer consumer = BuildConsumer(source);
@@ -52,7 +52,7 @@ public sealed class SubtagAlarmConsumerTests
         Assert.Contains(ActiveSubtag, source.Advised);
         Assert.Contains(AckedSubtag, source.Advised);
         Assert.Contains(PrioritySubtag, source.Advised);
-        Assert.DoesNotContain(AckCommentSubtag, source.Advised);
+        Assert.Contains(AckCommentSubtag, source.Advised);
     }
 
     /// <summary>Verifies an active=true value change raises a degraded, GUID-stamped UNACK_ALM transition.</summary>

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

@@ -78,10 +78,15 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
     }
 
     /// <summary>
-    ///     Advises every observable alarm subtag (active / acked / priority —
+    ///     Advises every alarm subtag (active / acked / priority, plus the
-    ///     the ack-comment subtag is a write-only target and is not advised)
+    ///     ack-comment subtag) and begins listening for value changes. The
-    ///     and begins listening for value changes. The <paramref name="subscription"/>
+    ///     ack-comment subtag is advised so it is an active MXAccess item by the
-    ///     expression is ignored: the subtag set is fixed by the watch list.
+    ///     time <see cref="AcknowledgeByName"/> writes it — MXAccess rejects a
+    ///     write to an added-but-not-advised item with E_INVALIDARG (confirmed
+    ///     against live MXAccess). Its value changes carry no transition (the
+    ///     state machine ignores addresses it does not map to active/acked).
+    ///     The <paramref name="subscription"/> expression is ignored: the subtag
+    ///     set is fixed by the watch list.
     /// </summary>
     /// <param name="subscription">The subscription expression (unused in subtag mode).</param>
     public void Subscribe(string subscription)
@@ -97,6 +102,7 @@ public sealed class SubtagAlarmConsumer : IMxAccessAlarmConsumer
             AddIfNotEmpty(addresses, target.ActiveSubtag);
             AddIfNotEmpty(addresses, target.AckedSubtag);
             AddIfNotEmpty(addresses, target.PrioritySubtag);
+            AddIfNotEmpty(addresses, target.AckCommentSubtag);
         }
 
         source.Advise(addresses);