diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
index d87de52f..491ba568 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ScriptedAlarms/ScriptedAlarmHostActor.cs
@@ -310,6 +310,8 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
     {
         // Ownership filter FIRST: ignore commands for alarms this engine doesn't own. The topic is a
         // cluster-wide broadcast, so the same command lands on every host — only the owner acts.
+        // Note: a concurrent LoadAsync can momentarily clear the loaded set, so a racing command may
+        // surface a spurious ArgumentException from the engine below — the outer catch absorbs it (benign).
         if (!_engine.LoadedAlarmIds.Contains(cmd.AlarmId))
         {
             _log.Debug("ScriptedAlarmHost: ignoring AlarmCommand {Op} for unowned alarm {AlarmId}",
@@ -333,7 +335,7 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
                 case "TimedShelve":
                     // A timed shelve needs the absolute unshelve instant. T18 derives it from the OPC UA
                     // Duration (UtcNow + shelvingTime); a command missing it is malformed — log + reject
-                    // rather than throw (a throw out of this async void would crash the actor).
+                    // rather than throw (a fault escaping the async Task would trigger a supervision restart).
                     if (cmd.UnshelveAtUtc is not { } unshelveAt)
                     {
                         _log.Warning("ScriptedAlarmHost: rejecting TimedShelve for {AlarmId} — missing UnshelveAtUtc",
@@ -352,10 +354,12 @@ public sealed class ScriptedAlarmHostActor : ReceiveActor
                     await _engine.DisableAsync(cmd.AlarmId, cmd.User, CancellationToken.None);
                     break;
                 case "AddComment":
-                    // AddComment's text is required by the engine (ApplyAddComment takes a non-null text);
-                    // coalesce a null comment to empty so a comment-less AddComment is still a valid no-op
-                    // rather than an NRE.
-                    await _engine.AddCommentAsync(cmd.AlarmId, cmd.User, cmd.Comment ?? string.Empty, CancellationToken.None);
+                    if (string.IsNullOrWhiteSpace(cmd.Comment))
+                    {
+                        _log.Warning("ScriptedAlarmHost: rejecting AddComment for {AlarmId} — empty comment text", cmd.AlarmId);
+                        return;
+                    }
+                    await _engine.AddCommentAsync(cmd.AlarmId, cmd.User, cmd.Comment, CancellationToken.None);
                     break;
                 default:
                     _log.Warning("ScriptedAlarmHost: ignoring AlarmCommand with unknown operation {Op} for {AlarmId}",
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
index 3b6db3f2..983df7f2 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/ScriptedAlarms/ScriptedAlarmHostActorTests.cs
@@ -305,6 +305,58 @@ public sealed class ScriptedAlarmHostActorTests : RuntimeActorTestBase
         alerts.ExpectNoMsg(TimeSpan.FromMilliseconds(500)); // no engine op → no transition
     }
 
+    /// <summary>Validation: an AddComment command with empty or whitespace comment text is rejected (logged),
+    /// NOT propagated to the engine — the actor stays alive and still processes a subsequent valid command,
+    /// proving it didn't fault and the engine's AddCommentAsync was never driven.</summary>
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void AlarmCommand_add_comment_empty_text_is_rejected_not_driven(string emptyComment)
+    {
+        var publish = CreateTestProbe();
+        var mux = CreateTestProbe();
+        var alerts = CreateTestProbe();
+        SubscribeToAlerts(alerts);
+
+        var (host, _) = Spawn(publish, mux);
+        host.Tell(new ScriptedAlarmHostActor.ApplyScriptedAlarms(new[] { Plan(id: "alm-1", depRef: "M.T") }));
+        mux.ExpectMsg<DependencyMuxActor.RegisterInterest>(Timeout); // load completed
+
+        // AddComment with empty/whitespace text is rejected before reaching the engine.
+        host.Tell(new AlarmCommand(
+            AlarmId: "alm-1", Operation: "AddComment", User: "alice", Comment: emptyComment, UnshelveAtUtc: null));
+        publish.ExpectNoMsg(TimeSpan.FromMilliseconds(500)); // rejected → no engine op → no OPC UA projection
+        alerts.ExpectNoMsg(TimeSpan.FromMilliseconds(200));  // rejected → no alerts event
+
+        // Prove the actor survived: activate the alarm and observe the normal projection flow.
+        host.Tell(new VirtualTagActor.DependencyValueChanged("M.T", 99, DateTime.UtcNow));
+        var state = publish.FishForMessage<OpcUaPublishActor.AlarmStateUpdate>(m => m.State.Active, Timeout);
+        state.AlarmNodeId.ShouldBe("alm-1");
+    }
+
+    /// <summary>Positive AddComment path: a non-empty AddComment for a loaded alarm drives the engine's
+    /// AddCommentAsync — observed via an AlarmTransitionEvent("CommentAdded") on the alerts topic carrying
+    /// the acting user (proves the op ran end-to-end through the host dispatch).</summary>
+    [Fact]
+    public void AlarmCommand_add_comment_nonempty_drives_engine()
+    {
+        var publish = CreateTestProbe();
+        var mux = CreateTestProbe();
+        var alerts = CreateTestProbe();
+        SubscribeToAlerts(alerts);
+
+        var (host, _) = Spawn(publish, mux);
+        host.Tell(new ScriptedAlarmHostActor.ApplyScriptedAlarms(new[] { Plan(id: "alm-1", depRef: "M.T") }));
+        mux.ExpectMsg<DependencyMuxActor.RegisterInterest>(Timeout); // load completed
+
+        // AddComment with a non-empty comment drives the engine — CommentAdded transition emitted.
+        host.Tell(new AlarmCommand(
+            AlarmId: "alm-1", Operation: "AddComment", User: "bob", Comment: "note from operator", UnshelveAtUtc: null));
+
+        var evt = alerts.FishForMessage<AlarmTransitionEvent>(e => e.TransitionKind == "CommentAdded", Timeout);
+        evt.AlarmId.ShouldBe("alm-1");
+    }
+
     /// <summary>Validation: a TimedShelve command missing UnshelveAtUtc is rejected (logged), NOT thrown —
     /// the actor stays alive and still processes a subsequent valid command, proving it didn't fault.</summary>
     [Fact]