diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IEffectiveNameGuard.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IEffectiveNameGuard.cs
new file mode 100644
index 00000000..959d8acd
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IEffectiveNameGuard.cs
@@ -0,0 +1,61 @@
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Uns;
+
+/// <summary>
+///     Which authoring surface a proposed effective name comes from. Used to word the collision
+///     error and to exclude the correct same-kind self-row on an edit (rename / override change).
+/// </summary>
+public enum EffectiveNameSourceKind
+{
+    /// <summary>A <see cref="Configuration.Entities.UnsTagReference"/> (effective name =
+    /// <c>DisplayNameOverride</c> else the backing raw tag's <c>Name</c>).</summary>
+    Reference,
+
+    /// <summary>An equipment-bound <see cref="Configuration.Entities.VirtualTag"/> (effective name = <c>Name</c>).</summary>
+    VirtualTag,
+
+    /// <summary>An equipment-bound <see cref="Configuration.Entities.ScriptedAlarm"/> (effective name = <c>Name</c>).</summary>
+    ScriptedAlarm,
+}
+
+/// <summary>
+///     v3 Batch 3 authoring-time guard for the UNS effective-name uniqueness rule. Within an
+///     equipment the EFFECTIVE leaf name must be unique across its <c>UnsTagReferences</c>
+///     (<c>DisplayNameOverride</c> else the backing raw tag's <c>Name</c>), its <c>VirtualTags</c>
+///     (<c>Name</c>), and its <c>ScriptedAlarms</c> (<c>Name</c>) — the three share the equipment's
+///     UNS NodeId space (<c>{EquipmentId}/{EffectiveName}</c>). This is the authoring mirror of the
+///     deploy-time <c>DraftValidator</c> <c>UnsEffectiveNameCollision</c> rule; comparison is
+///     <see cref="StringComparer.Ordinal"/> to match NodeId semantics and the validator.
+/// </summary>
+/// <remarks>
+///     Injectable (registered <c>Scoped</c>, its own pooled context per call — the same pattern
+///     <c>UnsTreeService</c> uses). Consumed by <c>UnsTreeService</c>'s reference / virtual-tag /
+///     scripted-alarm mutations, which call <see cref="CheckAsync"/> before persisting and surface a
+///     non-null result as the mutation's readable failure. The deploy gate remains the backstop for
+///     rename-induced collisions the authoring check never saw.
+/// </remarks>
+public interface IEffectiveNameGuard
+{
+    /// <summary>
+    ///     Tests whether <paramref name="proposedEffectiveName"/> would collide with an existing
+    ///     effective name within <paramref name="equipmentId"/>.
+    /// </summary>
+    /// <param name="equipmentId">The owning equipment's logical id.</param>
+    /// <param name="proposedEffectiveName">The effective name to be authored (override else raw name for a reference; Name for a VT/alarm).</param>
+    /// <param name="kind">Which surface the proposed name is for (words the error; identifies the self-row kind to exclude).</param>
+    /// <param name="excludeSourceId">
+    ///     On an edit, the logical id of the row being changed (its <c>UnsTagReferenceId</c> /
+    ///     <c>VirtualTagId</c> / <c>ScriptedAlarmId</c>) so it is excluded from the collision set;
+    ///     <see langword="null"/> on a create.
+    /// </param>
+    /// <param name="ct">Cancellation token.</param>
+    /// <returns>
+    ///     <see langword="null"/> when the name is free; otherwise a readable error naming the
+    ///     colliding existing source and the equipment.
+    /// </returns>
+    Task<string?> CheckAsync(
+        string equipmentId,
+        string proposedEffectiveName,
+        EffectiveNameSourceKind kind,
+        string? excludeSourceId,
+        CancellationToken ct = default);
+}