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 d3eccd8a..8d12249f 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/Phase7ApplierTests.cs
@@ -1277,6 +1277,102 @@ public sealed class Phase7ApplierTests
         sink.SurgicalCalls.ShouldBeEmpty();
     }
 
+    /// <summary>F10b guard — a tag that ALREADY carries an alarm (<c>Alarm is not null</c> on BOTH previous
+    /// and current, identical alarm info) is NOT surgical-eligible even when only <c>Writable</c> changes.
+    /// The explicit <c>Alarm is null</c> guard in <c>TagDeltaIsSurgicalEligible</c> prevents a false
+    /// positive: without it the <c>with { Writable = … }</c> override (which does NOT touch <c>Alarm</c>)
+    /// would leave both sides with equal <c>Alarm</c> values and the delta would WRONGLY look surgical.
+    /// An alarm-bearing tag is a Part 9 condition node, not a plain value variable, so any change to it
+    /// must go through a full rebuild.</summary>
+    [Fact]
+    public void Changed_alarm_bearing_tag_writable_only_still_rebuilds()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        // Both previous and current carry an identical, non-null alarm — the tag is an alarm-bearing node.
+        var alarm = new EquipmentTagAlarmInfo("OffNormalAlarm", 700);
+        var previous = CompositionWithTags(
+            new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "OverTemp", DataType: "Boolean",
+                FullName: "00001", Writable: false, Alarm: alarm));
+        // Only Writable flips; alarm is unchanged (and still non-null on both sides).
+        var next = CompositionWithTags(
+            new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "OverTemp", DataType: "Boolean",
+                FullName: "00001", Writable: true, Alarm: alarm));
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: the planner sees a changed tag (Writable differs) and nothing else.
+        plan.ChangedEquipmentTags.Count.ShouldBe(1);
+        plan.AddedEquipmentTags.ShouldBeEmpty();
+        plan.RemovedEquipmentTags.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        // The alarm-bearing tag is NOT surgical-eligible — it must rebuild and make NO surgical call.
+        outcome.RebuildCalled.ShouldBeTrue();
+        sink.RebuildCalls.ShouldBe(1);
+        sink.SurgicalCalls.ShouldBeEmpty();  // NO surgical write on an alarm-bearing tag
+    }
+
+    /// <summary>F10b multi-delta — when a plan contains TWO distinct surgical-eligible tag deltas (plain
+    /// value variables, no alarm, both changing only <c>Writable</c>), the applier must apply BOTH in
+    /// place (two <c>UpdateTagAttributes</c> calls) without triggering any rebuild. Proves the surgical
+    /// path iterates all eligible deltas rather than stopping after the first.</summary>
+    [Fact]
+    public void Two_surgical_eligible_tag_deltas_both_apply_in_place_no_rebuild()
+    {
+        var sink = new RecordingSink();
+        var applier = new Phase7Applier(sink, NullLogger<Phase7Applier>.Instance);
+
+        // Two distinct plain (no-alarm) tags, both will flip Writable — both are surgical-eligible.
+        var previous = new Phase7CompositionResult(
+            Array.Empty<EquipmentNode>(), Array.Empty<DriverInstancePlan>(), Array.Empty<ScriptedAlarmPlan>())
+        {
+            EquipmentTags = new[]
+            {
+                new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "Speed",    DataType: "Float",   FullName: "40001", Writable: false, Alarm: null),
+                new EquipmentTagPlan("tag-2", "eq-1", "drv", FolderPath: "", Name: "Pressure", DataType: "Float",   FullName: "40002", Writable: false, Alarm: null),
+            },
+        };
+        // Only Writable flips on both tags; everything else is identical.
+        var next = new Phase7CompositionResult(
+            Array.Empty<EquipmentNode>(), Array.Empty<DriverInstancePlan>(), Array.Empty<ScriptedAlarmPlan>())
+        {
+            EquipmentTags = new[]
+            {
+                new EquipmentTagPlan("tag-1", "eq-1", "drv", FolderPath: "", Name: "Speed",    DataType: "Float",   FullName: "40001", Writable: true,  Alarm: null),
+                new EquipmentTagPlan("tag-2", "eq-1", "drv", FolderPath: "", Name: "Pressure", DataType: "Float",   FullName: "40002", Writable: true,  Alarm: null),
+            },
+        };
+
+        var plan = Phase7Planner.Compute(previous, next);
+
+        // Guard the arrange: exactly two changed tags, nothing else.
+        plan.ChangedEquipmentTags.Count.ShouldBe(2);
+        plan.AddedEquipmentTags.ShouldBeEmpty();
+        plan.RemovedEquipmentTags.ShouldBeEmpty();
+        plan.AddedEquipment.ShouldBeEmpty();
+        plan.RemovedEquipment.ShouldBeEmpty();
+
+        var outcome = applier.Apply(plan);
+
+        // No rebuild — both deltas are surgical-eligible.
+        outcome.RebuildCalled.ShouldBeFalse();
+        sink.RebuildCalls.ShouldBe(0);
+
+        // Exactly two surgical calls — one per eligible delta.
+        sink.SurgicalCalls.Count.ShouldBe(2);
+
+        // Both expected node ids must appear (order is not guaranteed).
+        var nodeId1 = EquipmentNodeIds.Variable("eq-1", "", "Speed");
+        var nodeId2 = EquipmentNodeIds.Variable("eq-1", "", "Pressure");
+        sink.SurgicalCalls.ShouldContain(c => c.NodeId == nodeId1 && c.Writable);
+        sink.SurgicalCalls.ShouldContain(c => c.NodeId == nodeId2 && c.Writable);
+
+        outcome.ChangedNodes.ShouldBe(2);
+    }
+
     /// <summary>F10b — a surgical-eligible tag delta MIXED with another change (here an added equipment)
     /// must still rebuild: the rebuild is forced by the OTHER change. The surgical path is taken ONLY when
     /// the tag deltas are the sole change. No surgical call is made (the rebuild materialises everything).</summary>