fix(otopcua): guard root-level discovered var parent + tighten mapper

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/Drivers/DiscoveredNodeMapper.cs

@@ -5,6 +5,13 @@ using ZB.MOM.WW.OtOpcUa.OpcUaServer;
 namespace ZB.MOM.WW.OtOpcUa.Runtime.Drivers;
 
 /// <summary>The mapped result of grafting discovered nodes under an equipment node.</summary>
+/// <param name="Folders">
+///     Folders to ensure, in insertion order (parent-before-child within each node's prefix chain) — NOT
+///     globally depth-sorted. The applier sorts by depth before ensuring, so consumers must not assume a
+///     global parent-before-child ordering across the whole list.
+/// </param>
+/// <param name="Variables">Variables to ensure under the (post-collapse) folders.</param>
+/// <param name="RoutingByRef">Driver FullReference -> equipment NodeId, for live-value routing.</param>
 public sealed record DiscoveredInjectionPlan(
     IReadOnlyList<DiscoveredFolder> Folders,
     IReadOnlyList<DiscoveredVariable> Variables,
@@ -29,7 +36,7 @@ public static class DiscoveredNodeMapper
     /// </param>
     /// <returns>The folders, variables, and routing map to apply against the OPC UA address space.</returns>
     public static DiscoveredInjectionPlan Map(
-        string equipmentId, IReadOnlyList<DiscoveredNode> nodes, ISet<string> authoredRefs)
+        string equipmentId, IReadOnlyList<DiscoveredNode> nodes, IReadOnlySet<string> authoredRefs)
     {
         var kept = nodes.Where(n => !authoredRefs.Contains(n.FullReference)).ToList();
 
@@ -65,7 +72,12 @@ public static class DiscoveredNodeMapper
 
             var varFolderPath = string.Join('/', segs);
             var varNodeId = EquipmentNodeIds.Variable(equipmentId, varFolderPath, n.BrowseName);
-            var varParent = EquipmentNodeIds.SubFolder(equipmentId, varFolderPath);
+            // Mirror AddressSpaceApplier.MaterialiseEquipmentTags: a folder-less variable parents directly
+            // at the equipment (SubFolder("", ...) would yield a trailing-slash "EQ-1/" that mismatches the
+            // EquipmentNodeIds.Variable NodeId, which guards IsNullOrWhiteSpace).
+            var varParent = string.IsNullOrEmpty(varFolderPath)
+                ? equipmentId
+                : EquipmentNodeIds.SubFolder(equipmentId, varFolderPath);
             variables.Add(new DiscoveredVariable(
                 varNodeId, varParent, n.DisplayName, ToBuiltinTypeString(n.DataType), n.Writable, n.IsArray, n.ArrayDim));
             routing[n.FullReference] = varNodeId;