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 67d9ef55..ab7d208c 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/OpcUa/DeferredAddressSpaceSink.cs
@@ -12,7 +12,7 @@ namespace ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
 ///     no-op against <see cref="NullOpcUaAddressSpaceSink"/>, so the actor stays safe to
 ///     receive messages from the moment it boots.
 /// </summary>
-public sealed class DeferredAddressSpaceSink : IOpcUaAddressSpaceSink
+public sealed class DeferredAddressSpaceSink : IOpcUaAddressSpaceSink, ISurgicalAddressSpaceSink
 {
     private volatile IOpcUaAddressSpaceSink _inner = NullOpcUaAddressSpaceSink.Instance;
 
@@ -69,4 +69,17 @@ public sealed class DeferredAddressSpaceSink : IOpcUaAddressSpaceSink
 
     /// <summary>Rebuilds the address space through the inner sink.</summary>
     public void RebuildAddressSpace() => _inner.RebuildAddressSpace();
+
+    /// <summary>Forwards an in-place tag-attribute update (F10b) to the inner sink when it supports the
+    /// surgical capability. Returns false otherwise — before the real <c>SdkAddressSpaceSink</c> is
+    /// swapped in (inner is still the null sink), or any inner sink that isn't surgical — so the caller
+    /// (Phase7Applier) falls back to a full rebuild. Without this forward the surgical optimization is
+    /// inert on every driver-role host, because actors inject THIS wrapper, not the inner sink.</summary>
+    /// <param name="variableNodeId">The node ID of the variable to update in place.</param>
+    /// <param name="writable">Whether the node should be read/write.</param>
+    /// <param name="historianTagname">null ⇒ not historized; non-null ⇒ Historizing + historian binding.</param>
+    /// <returns>True when the inner sink applied the update; false when it lacks the capability or the node is missing.</returns>
+    public bool UpdateTagAttributes(string variableNodeId, bool writable, string? historianTagname)
+        => _inner is ISurgicalAddressSpaceSink surgical
+           && surgical.UpdateTagAttributes(variableNodeId, writable, historianTagname);
 }
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 d4df9737..2fdae40e 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/DeferredAddressSpaceSinkTests.cs
@@ -83,6 +83,53 @@ public sealed class DeferredAddressSpaceSinkTests
         call.HistorianTagname.ShouldBe("MyTag.PV");
     }
 
+    /// <summary>F10b regression: the deferred wrapper MUST forward the surgical capability to a
+    /// surgical inner sink — otherwise <c>Phase7Applier</c> (which injects THIS wrapper on every
+    /// driver-role host, not the inner <c>SdkAddressSpaceSink</c>) never sees the capability and the
+    /// in-place tag-attribute optimization is inert in production (it silently falls back to rebuild).</summary>
+    [Fact]
+    public void UpdateTagAttributes_forwards_to_a_surgical_inner_sink()
+    {
+        var deferred = new DeferredAddressSpaceSink();
+        var inner = new SurgicalRecordingSink { Result = true };
+        deferred.SetSink(inner);
+
+        ((ISurgicalAddressSpaceSink)deferred).UpdateTagAttributes("v-1", writable: true, historianTagname: "MyTag.PV")
+            .ShouldBeTrue();
+
+        var call = inner.SurgicalCalls.ShouldHaveSingleItem();
+        call.NodeId.ShouldBe("v-1");
+        call.Writable.ShouldBeTrue();
+        call.Historian.ShouldBe("MyTag.PV");
+    }
+
+    /// <summary>The surgical forward returns the inner's own result (false ⇒ node missing) so the caller
+    /// falls back to a full rebuild.</summary>
+    [Fact]
+    public void UpdateTagAttributes_returns_inner_result_when_node_missing()
+    {
+        var deferred = new DeferredAddressSpaceSink();
+        deferred.SetSink(new SurgicalRecordingSink { Result = false });
+
+        ((ISurgicalAddressSpaceSink)deferred).UpdateTagAttributes("v-1", writable: false, historianTagname: null)
+            .ShouldBeFalse();
+    }
+
+    /// <summary>When the inner sink does NOT implement <see cref="ISurgicalAddressSpaceSink"/> (e.g. the
+    /// null sink before the real one is swapped in, or any non-surgical sink) the wrapper returns false
+    /// so the caller rebuilds.</summary>
+    [Fact]
+    public void UpdateTagAttributes_returns_false_when_inner_is_not_surgical()
+    {
+        var deferred = new DeferredAddressSpaceSink();   // default inner = null sink (not surgical)
+        ((ISurgicalAddressSpaceSink)deferred).UpdateTagAttributes("v-1", writable: true, historianTagname: null)
+            .ShouldBeFalse();
+
+        deferred.SetSink(new RecordingSink());           // a non-surgical inner
+        ((ISurgicalAddressSpaceSink)deferred).UpdateTagAttributes("v-1", writable: true, historianTagname: null)
+            .ShouldBeFalse();
+    }
+
     /// <summary>Builds a minimal <see cref="AlarmConditionSnapshot"/> for the forwarding tests (the
     /// inner sink only records the node id, so the exact state values don't matter here).</summary>
     private static AlarmConditionSnapshot Snapshot(bool active = false) =>
@@ -123,4 +170,32 @@ public sealed class DeferredAddressSpaceSinkTests
         /// <inheritdoc />
         public void RebuildAddressSpace() => CallQueue.Enqueue("RB");
     }
+
+    private sealed class SurgicalRecordingSink : IOpcUaAddressSpaceSink, ISurgicalAddressSpaceSink
+    {
+        /// <summary>Gets or sets the value <see cref="UpdateTagAttributes"/> returns.</summary>
+        public bool Result { get; set; } = true;
+        /// <summary>Gets the recorded surgical calls.</summary>
+        public List<(string NodeId, bool Writable, string? Historian)> SurgicalCalls { get; } = new();
+
+        /// <inheritdoc />
+        public bool UpdateTagAttributes(string variableNodeId, bool writable, string? historianTagname)
+        {
+            SurgicalCalls.Add((variableNodeId, writable, historianTagname));
+            return Result;
+        }
+
+        /// <inheritdoc />
+        public void WriteValue(string nodeId, object? value, OpcUaQuality quality, DateTime sourceTimestampUtc) { }
+        /// <inheritdoc />
+        public void WriteAlarmCondition(string alarmNodeId, AlarmConditionSnapshot state, DateTime sourceTimestampUtc) { }
+        /// <inheritdoc />
+        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) { }
+        /// <inheritdoc />
+        public void EnsureVariable(string variableNodeId, string? parentFolderNodeId, string displayName, string dataType, bool writable, string? historianTagname = null, bool isArray = false, uint? arrayLength = null) { }
+        /// <inheritdoc />
+        public void RebuildAddressSpace() { }
+    }
 }