diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs
index a52f8fe0..7184bc58 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs
@@ -43,8 +43,9 @@ public sealed class DeferredAddressSpaceSink : IOpcUaAddressSpaceSink
     /// <param name="displayName">The human-readable condition name.</param>
     /// <param name="alarmType">The domain alarm type.</param>
     /// <param name="severity">The domain severity.</param>
-    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
-        => _inner.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity);
+    /// <param name="isNative">True for a driver-fed (native) equipment-tag alarm; false (default) for a scripted alarm.</param>
+    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
+        => _inner.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity, isNative);
 
     /// <summary>Ensures a folder exists in the address space through the inner sink.</summary>
     /// <param name="folderNodeId">The node ID of the folder.</param>
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/IOpcUaAddressSpaceSink.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/IOpcUaAddressSpaceSink.cs
index 2b45fd8a..62469be8 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/IOpcUaAddressSpaceSink.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/IOpcUaAddressSpaceSink.cs
@@ -38,7 +38,10 @@ public interface IOpcUaAddressSpaceSink
     /// <param name="displayName">Human-readable condition name (BrowseName / DisplayName / Message).</param>
     /// <param name="alarmType">Domain alarm type — mapped to the SDK condition subtype by the sink.</param>
     /// <param name="severity">Domain severity (OPC UA 1..1000 scale); mapped to the SDK severity buckets.</param>
-    void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity);
+    /// <param name="isNative">When true this is a driver-fed (native, e.g. Galaxy) equipment-tag alarm; when
+    /// false (default) it is a scripted alarm. The node manager tracks native condition node ids so a later
+    /// task can route a native condition's inbound Acknowledge to the driver instead of the scripted engine.</param>
+    void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false);
 
     /// <summary>
     ///     Ensure a folder node exists under the given parent. Used by <c>Phase7Applier</c> to
@@ -95,7 +98,7 @@ public sealed class NullOpcUaAddressSpaceSink : IOpcUaAddressSpaceSink
     public void WriteAlarmCondition(string alarmNodeId, AlarmConditionSnapshot state, DateTime sourceTimestampUtc) { }
 
     /// <inheritdoc />
-    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity) { }
+    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false) { }
 
     /// <inheritdoc />
     public void EnsureFolder(string folderNodeId, string? parentNodeId, string displayName) { }
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
index 457b2331..3327bf40 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs
@@ -36,6 +36,13 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
     private readonly ConcurrentDictionary<string, BaseDataVariableState> _variables = new(StringComparer.Ordinal);
     private readonly ConcurrentDictionary<string, FolderState> _folders = new(StringComparer.Ordinal);
     private readonly ConcurrentDictionary<string, AlarmConditionState> _alarmConditions = new(StringComparer.Ordinal);
+    /// <summary>H6a: the subset of <see cref="_alarmConditions"/> node ids materialised as NATIVE
+    /// (driver-fed, e.g. Galaxy equipment-tag alarms) rather than scripted. A later task routes a native
+    /// condition's inbound Acknowledge to the driver instead of the scripted engine, so the node manager
+    /// must know which conditions are native. Maintained in lock-step with <see cref="_alarmConditions"/>:
+    /// a native re-materialise adds, and <see cref="RebuildAddressSpace"/> clears it alongside
+    /// <see cref="_alarmConditions"/> so a re-materialise as the other kind is correct.</summary>
+    private readonly HashSet<string> _nativeAlarmNodeIds = new(StringComparer.Ordinal);
     /// <summary>Phase C: NodeId → resolved historian tagname for every variable materialised
     /// Historizing. Populated by <see cref="EnsureVariable"/> when a historian tagname is supplied; the
     /// (later) HistoryRead override resolves a HistoryRead request's NodeId against this map. Cleared on
@@ -535,7 +542,7 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
     ///     <see cref="AlarmConditionState"/>. LimitAlarm deliberately falls back to base per the T13
     ///     notes — a script alarm carries no High/Low limits to populate.</para>
     /// </remarks>
-    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
+    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
     {
         ArgumentException.ThrowIfNullOrEmpty(alarmNodeId);
         ArgumentException.ThrowIfNullOrEmpty(displayName);
@@ -550,6 +557,10 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
                 PredefinedNodes?.Remove(existing.NodeId);
             }
 
+            // H6a: re-materialising the same id as the OTHER kind (native↔scripted) must reflect the new
+            // kind, so always drop the stale native flag first and only re-add it below when isNative.
+            _nativeAlarmNodeIds.Remove(alarmNodeId);
+
             var parent = ResolveParentFolder(equipmentNodeId);
 
             AlarmConditionState alarm = CreateAlarmConditionOfType(alarmType, parent);
@@ -632,9 +643,23 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
 
             AddPredefinedNode(SystemContext, alarm);
             _alarmConditions[alarmNodeId] = alarm;
+            // H6a: record native (driver-fed) conditions so a later task can route their inbound
+            // Acknowledge to the driver rather than the scripted engine.
+            if (isNative) _nativeAlarmNodeIds.Add(alarmNodeId);
         }
     }
 
+    /// <summary>H6a — true if the condition materialised at <paramref name="alarmNodeId"/> is a NATIVE
+    /// (driver-fed) alarm rather than a scripted one. A later task uses this to route a native condition's
+    /// inbound Acknowledge to the driver instead of the scripted engine.</summary>
+    /// <param name="alarmNodeId">The alarm condition node id.</param>
+    internal bool IsNativeAlarmNode(string alarmNodeId)
+    {
+        // _nativeAlarmNodeIds is a plain HashSet mutated only under Lock (in MaterialiseAlarmCondition /
+        // RebuildAddressSpace), so guard the read with the same Lock rather than risk a torn concurrent read.
+        lock (Lock) return _nativeAlarmNodeIds.Contains(alarmNodeId);
+    }
+
     /// <summary>
     ///     Shared body for every inbound Part 9 alarm method handler (T18). Resolves the calling
     ///     principal off the SDK <paramref name="context"/>, applies the <c>AlarmAck</c> role gate
@@ -1289,6 +1314,9 @@ public sealed class OtOpcUaNodeManager : CustomNodeManager2
                 PredefinedNodes?.Remove(alarm.NodeId);
             }
             _alarmConditions.Clear();
+            // H6a: drop the native-alarm flags in lock-step with the conditions they classify, so a
+            // re-materialise on the next apply (possibly as the other kind) starts from a clean slate.
+            _nativeAlarmNodeIds.Clear();
 
             foreach (var f in _folders.Values)
             {
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
index 72b9d1c4..8dba58f4 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs
@@ -201,7 +201,7 @@ public sealed class Phase7Applier
             {
                 // Native alarm tag → a real Part 9 condition node (reuses the scripted-alarm path),
                 // NOT a value variable. Parent is the sub-folder when set, else the equipment folder.
-                SafeMaterialiseAlarmCondition(nodeId, parent, tag.Name, tag.Alarm.AlarmType, tag.Alarm.Severity);
+                SafeMaterialiseAlarmCondition(nodeId, parent, tag.Name, tag.Alarm.AlarmType, tag.Alarm.Severity, isNative: true);
             }
             else
             {
@@ -292,7 +292,7 @@ public sealed class Phase7Applier
         foreach (var alarm in composition.EquipmentScriptedAlarms)
         {
             if (!alarm.Enabled) continue;
-            SafeMaterialiseAlarmCondition(alarm.ScriptedAlarmId, alarm.EquipmentId, alarm.Name, alarm.AlarmType, alarm.Severity);
+            SafeMaterialiseAlarmCondition(alarm.ScriptedAlarmId, alarm.EquipmentId, alarm.Name, alarm.AlarmType, alarm.Severity, isNative: false);
             materialised++;
         }
 
@@ -333,9 +333,9 @@ public sealed class Phase7Applier
         catch (Exception ex) { _logger.LogWarning(ex, "Phase7Applier: WriteAlarmCondition threw for {Node}", nodeId); }
     }
 
-    private void SafeMaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
+    private void SafeMaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative)
     {
-        try { _sink.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity); }
+        try { _sink.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity, isNative); }
         catch (Exception ex) { _logger.LogWarning(ex, "Phase7Applier: MaterialiseAlarmCondition threw for {Node}", alarmNodeId); }
     }
 }
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs
index 474155cf..6357f31c 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs
@@ -41,8 +41,9 @@ public sealed class SdkAddressSpaceSink : IOpcUaAddressSpaceSink
     /// <param name="displayName">The human-readable condition name.</param>
     /// <param name="alarmType">The domain alarm type.</param>
     /// <param name="severity">The domain severity.</param>
-    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
-        => _nodeManager.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity);
+    /// <param name="isNative">True for a driver-fed (native) equipment-tag alarm; false (default) for a scripted alarm.</param>
+    public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
+        => _nodeManager.MaterialiseAlarmCondition(alarmNodeId, equipmentNodeId, displayName, alarmType, severity, isNative);
 
     /// <summary>Ensures a folder node exists in the address space.</summary>
     /// <param name="folderNodeId">The folder node identifier.</param>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/AlarmCommandRouterTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/AlarmCommandRouterTests.cs
index 1594c2c1..b629a79f 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/AlarmCommandRouterTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/AlarmCommandRouterTests.cs
@@ -323,6 +323,37 @@ public sealed class AlarmCommandRouterTests : IDisposable
         await host.DisposeAsync();
     }
 
+    /// <summary>H6a — a condition materialised with <c>isNative:true</c> is tracked so later inbound-ack
+    /// routing can dispatch its Acknowledge to the driver rather than the scripted engine.</summary>
+    [Fact]
+    public async Task Native_materialise_is_tracked_as_native()
+    {
+        var (host, server) = await BootAsync();
+        var nm = server.NodeManager!;
+
+        nm.EnsureFolder("eq", parentNodeId: null, displayName: "Equipment");
+        nm.MaterialiseAlarmCondition("a1", "eq", "d", "OffNormalAlarm", 700, isNative: true);
+
+        nm.IsNativeAlarmNode("a1").ShouldBeTrue();
+
+        await host.DisposeAsync();
+    }
+
+    /// <summary>H6a — a scripted condition (the default, <c>isNative:false</c>) is NOT tracked as native.</summary>
+    [Fact]
+    public async Task Scripted_materialise_is_not_native()
+    {
+        var (host, server) = await BootAsync();
+        var nm = server.NodeManager!;
+
+        nm.EnsureFolder("eq", parentNodeId: null, displayName: "Equipment");
+        nm.MaterialiseAlarmCondition("a2", "eq", "d", "OffNormalAlarm", 700, isNative: false);
+
+        nm.IsNativeAlarmNode("a2").ShouldBeFalse();
+
+        await host.DisposeAsync();
+    }
+
     /// <summary>Builds a <see cref="ServerSystemContext"/> (an <see cref="ISessionOperationContext"/>)
     /// carrying a <see cref="RoleCarryingUserIdentity"/> with the given name + roles — the exact seam the
     /// gate reads via <c>(context as ISessionOperationContext)?.UserIdentity as RoleCarryingUserIdentity</c>.</summary>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs
index cd6793ab..644ac4c4 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs
@@ -109,7 +109,7 @@ public sealed class DeferredAddressSpaceSinkTests
         public void WriteAlarmCondition(string alarmNodeId, AlarmConditionSnapshot state, DateTime sourceTimestampUtc)
             => CallQueue.Enqueue($"WA:{alarmNodeId}");
         /// <inheritdoc />
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
             => CallQueue.Enqueue($"MA:{alarmNodeId}");
         /// <inheritdoc />
         public void EnsureFolder(string folderNodeId, string? parentNodeId, string displayName)
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierHierarchyTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierHierarchyTests.cs
index 15a12123..1d8affdb 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierHierarchyTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierHierarchyTests.cs
@@ -252,7 +252,7 @@ public sealed class Phase7ApplierHierarchyTests : IDisposable
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity) { }
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false) { }
         /// <summary>Records a folder creation request.</summary>
         /// <param name="folderNodeId">The node ID of the folder.</param>
         /// <param name="parentNodeId">The node ID of the parent folder, or null for root.</param>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
index 6bdc71b3..074b99d3 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
@@ -750,7 +750,7 @@ public sealed class Phase7ApplierTests
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
             => AlarmConditionQueue.Enqueue((alarmNodeId, equipmentNodeId, displayName, alarmType, severity));
         /// <summary>Records a folder creation call.</summary>
         /// <param name="folderNodeId">The folder node ID.</param>
@@ -802,7 +802,7 @@ public sealed class Phase7ApplierTests
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity) { }
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false) { }
         /// <summary>No-op folder creation call.</summary>
         /// <param name="folderNodeId">The folder node ID.</param>
         /// <param name="parentNodeId">The parent folder node ID, if any.</param>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Observability/OtOpcUaTelemetryHookTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Observability/OtOpcUaTelemetryHookTests.cs
index 74ca4a5a..44432435 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Observability/OtOpcUaTelemetryHookTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Observability/OtOpcUaTelemetryHookTests.cs
@@ -206,7 +206,7 @@ public sealed class OtOpcUaTelemetryHookTests : RuntimeActorTestBase
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity) { }
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false) { }
         /// <summary>Ensures folder exists (stub implementation).</summary>
         /// <param name="folderNodeId">The folder node identifier.</param>
         /// <param name="parentNodeId">The parent folder node identifier.</param>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorRebuildTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorRebuildTests.cs
index 6329d183..eeb45342 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorRebuildTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorRebuildTests.cs
@@ -274,7 +274,7 @@ public sealed class OpcUaPublishActorRebuildTests : RuntimeActorTestBase
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity)
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false)
             => Calls.Enqueue($"MA:{alarmNodeId}");
         /// <summary>Records a folder ensure call.</summary>
         /// <param name="folderNodeId">The folder node ID.</param>
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs
index 7d829ec3..e0368ba3 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs
@@ -577,7 +577,7 @@ public sealed class OpcUaPublishActorTests : RuntimeActorTestBase
         /// <param name="displayName">The condition display name.</param>
         /// <param name="alarmType">The domain alarm type.</param>
         /// <param name="severity">The domain severity.</param>
-        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity) { }
+        public void MaterialiseAlarmCondition(string alarmNodeId, string equipmentNodeId, string displayName, string alarmType, int severity, bool isNative = false) { }
 
         /// <summary>Ensures a folder exists (no-op in test).</summary>
         /// <param name="folderNodeId">The OPC UA folder node identifier.</param>