fix(tests,cli): implement IOpcUaAddressSpaceSink.EnsureVariable in test fakes; fix CLI CS1587

Resolves the 12 reported build errors (7 CS0535 sink fakes + 5 CLI CS1587).
Runtime.Tests green (74). NOTE: OpcUaServer.Tests still has pre-existing CS7036
errors from the in-progress Galaxy-tag workstream (Phase7Plan/Phase7CompositionResult
new required params) — separate, test-only, not addressed here.

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/Observability/OtOpcUaTelemetryHookTests.cs

@@ -206,6 +206,12 @@ public sealed class OtOpcUaTelemetryHookTests : RuntimeActorTestBase
         /// <param name="parentNodeId">The parent folder node identifier.</param>
         /// <param name="displayName">The display name for the folder.</param>
         public void EnsureFolder(string folderNodeId, string? parentNodeId, string displayName) { }
+        /// <summary>Ensures variable exists (stub implementation).</summary>
+        /// <param name="variableNodeId">The variable node identifier.</param>
+        /// <param name="parentFolderNodeId">The parent folder node identifier.</param>
+        /// <param name="displayName">The display name for the variable.</param>
+        /// <param name="dataType">The OPC UA built-in type name.</param>
+        public void EnsureVariable(string variableNodeId, string? parentFolderNodeId, string displayName, string dataType) { }
         /// <summary>Rebuilds address space (recorded via span).</summary>
         public void RebuildAddressSpace() { /* recorded via span */ }
     }

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorRebuildTests.cs

@@ -161,6 +161,13 @@ public sealed class OpcUaPublishActorRebuildTests : RuntimeActorTestBase
         /// <param name="displayName">The display name of the folder.</param>
         public void EnsureFolder(string folderNodeId, string? parentNodeId, string displayName)
             => Calls.Enqueue($"EF:{folderNodeId}");
+        /// <summary>Records a variable ensure call.</summary>
+        /// <param name="variableNodeId">The variable node ID.</param>
+        /// <param name="parentFolderNodeId">The parent folder node ID, or null if this is a root variable.</param>
+        /// <param name="displayName">The display name of the variable.</param>
+        /// <param name="dataType">The OPC UA built-in type name.</param>
+        public void EnsureVariable(string variableNodeId, string? parentFolderNodeId, string displayName, string dataType)
+            => Calls.Enqueue($"EV:{variableNodeId}");
         /// <summary>Records a rebuild address space call.</summary>
         public void RebuildAddressSpace() => Interlocked.Increment(ref RebuildCalls);
     }

tests/Server/ZB.MOM.WW.OtOpcUa.Runtime.Tests/OpcUa/OpcUaPublishActorTests.cs

@@ -182,6 +182,13 @@ public sealed class OpcUaPublishActorTests : RuntimeActorTestBase
         /// <param name="displayName">The display name of the folder.</param>
         public void EnsureFolder(string folderNodeId, string? parentNodeId, string displayName) { }
 
+        /// <summary>Ensures a variable exists (no-op in test).</summary>
+        /// <param name="variableNodeId">The OPC UA variable node identifier.</param>
+        /// <param name="parentFolderNodeId">The parent folder node identifier, or null for root.</param>
+        /// <param name="displayName">The display name of the variable.</param>
+        /// <param name="dataType">The OPC UA built-in type name.</param>
+        public void EnsureVariable(string variableNodeId, string? parentFolderNodeId, string displayName, string dataType) { }
+
         /// <summary>Records a rebuild call.</summary>
         public void RebuildAddressSpace() => Interlocked.Increment(ref RebuildCalls);
     }