diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/HistorianAdapterActor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/HistorianAdapterActor.cs
index 6dd62c3c..253c3c82 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/HistorianAdapterActor.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Historian/HistorianAdapterActor.cs
@@ -60,15 +60,18 @@ public sealed class HistorianAdapterActor : ReceiveActor
         _sink = sink;
         _localNode = localNode;
 
-        // A direct AlarmHistorianEvent source (kept for a future engine→historian path) goes through the
-        // same Primary gate as the alerts-topic feed below.
-        Receive<AlarmHistorianEvent>(Historize);
+        // A direct AlarmHistorianEvent source is kept for a future engine→historian path; it goes through the
+        // SAME ShouldHistorize gate. WARNING: do NOT Tell an AlarmHistorianEvent for a transition that is ALSO
+        // published on the `alerts` topic — the sink would then double-write (both handlers enqueue it).
+        Receive<AlarmHistorianEvent>(evt => { if (ShouldHistorize()) _ = EnqueueAsync(evt); });
 
         // Live alarm transitions arrive off the cluster `alerts` DPS topic (subscribed in PreStart). The
         // Primary ScriptedAlarmHostActor publishes each transition ONCE, but DistributedPubSub fans that
         // single message to EVERY node's subscriber — including BOTH central nodes' historian adapters. The
-        // Primary gate in Historize keeps only the Primary writing ⇒ exactly-once across the warm pair.
-        Receive<AlarmTransitionEvent>(t => Historize(Translate(t)));
+        // ShouldHistorize gate keeps only the Primary writing ⇒ exactly-once across the warm pair.
+        // NOTE: Translate is intentionally inside the gate so Secondary/Detached nodes never allocate a
+        // discarded AlarmHistorianEvent.
+        Receive<AlarmTransitionEvent>(t => { if (ShouldHistorize()) _ = EnqueueAsync(Translate(t)); });
 
         Receive<GetStatus>(_ => Sender.Tell(_sink.GetStatus()));
 
@@ -79,22 +82,11 @@ public sealed class HistorianAdapterActor : ReceiveActor
         Receive<SubscribeAck>(_ => { });
     }
 
-    /// <summary>Gates a historian event to the Primary then enqueues it fire-and-forget. Warm-standby
-    /// dedup: only the Primary historizes to the durable sink so the per-node alerts feed writes exactly
-    /// once. Default-write until told Secondary/Detached so single-node deploys + the boot window never
-    /// drop historization. Fire-and-forget because <see cref="SqliteStoreAndForwardSink"/> persists to
-    /// local SQLite synchronously inside <see cref="EnqueueAsync"/> (it returns once the row is committed),
-    /// so we don't block the mailbox on network/pipe latency; failures surface via <see cref="GetStatus"/>.</summary>
-    /// <param name="evt">The historian event to gate + enqueue.</param>
-    private void Historize(AlarmHistorianEvent evt)
-    {
-        if (_localRole is RedundancyRole.Secondary or RedundancyRole.Detached)
-        {
-            return;
-        }
-
-        _ = EnqueueAsync(evt);
-    }
+    /// <summary>True iff this node should write to the durable sink: only the Primary historizes
+    /// (default-write while the role is unknown so single-node deploys + the boot window never drop
+    /// historization). DPS fans the Primary's single alerts publish to BOTH nodes' historians, so this
+    /// gate is what keeps the durable write exactly-once across the warm-redundant pair.</summary>
+    private bool ShouldHistorize() => _localRole is not (RedundancyRole.Secondary or RedundancyRole.Detached);
 
     /// <summary>Translates a live <see cref="AlarmTransitionEvent"/> (the alerts-topic shape) into the
     /// historian's <see cref="AlarmHistorianEvent"/>. <c>AlarmTypeName</c> is null-coalesced to
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/HistorianAdapterActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/HistorianAdapterActorTests.cs
index 34387e4f..2dff60f4 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/HistorianAdapterActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Historian/HistorianAdapterActorTests.cs
@@ -29,12 +29,11 @@ public sealed class HistorianAdapterActorTests : RuntimeActorTestBase
     /// <summary>Thread-safe fake sink that records every <see cref="EnqueueAsync"/> call.</summary>
     private sealed class RecordingSink : IAlarmHistorianSink
     {
-        private int _count;
         private readonly object _lock = new();
         private readonly List<AlarmHistorianEvent> _events = new();
 
         /// <summary>The number of <see cref="EnqueueAsync"/> calls observed so far.</summary>
-        public int EnqueueCount => Volatile.Read(ref _count);
+        public int EnqueueCount { get { lock (_lock) { return _events.Count; } } }
 
         /// <summary>A snapshot of every event enqueued so far (in arrival order).</summary>
         public IReadOnlyList<AlarmHistorianEvent> Events
@@ -50,7 +49,6 @@ public sealed class HistorianAdapterActorTests : RuntimeActorTestBase
                 _events.Add(evt);
             }
 
-            Interlocked.Increment(ref _count);
             return Task.CompletedTask;
         }