docs(code): close-out comment fixes from the follow-ups review round

src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmEngine.cs

@@ -1036,6 +1036,9 @@ public sealed class ScriptedAlarmEngine : IDisposable
         Task work;
         try
         {
+            // The null coalesce is defensive only: no current caller can return a null Task
+            // (every factory is an async lambda or returns a started Task). It costs nothing and
+            // keeps a future non-async factory from NREing the continuation wiring below.
             work = factory() ?? Task.CompletedTask;
         }
         catch (Exception ex)
@@ -1057,6 +1060,9 @@ public sealed class ScriptedAlarmEngine : IDisposable
         // so Dispose's WhenAll still observes (and logs) a background failure.
         work.ContinueWith(t =>
         {
+            // Removing BEFORE completing the placeholder is safe (not a window where Dispose could
+            // miss still-running work): this continuation only runs once the REAL task has already
+            // finished, so anything a concurrent Dispose could still be waiting for is done.
             lock (_inFlightLock) { _inFlight.Remove(placeholder.Task); }
             if (t.IsFaulted)
             {