feat(opcua): materialise SystemPlatform tags (Galaxy) as OPC UA variables

Closes the gap where Tag rows with EquipmentId=NULL + Namespace.Kind=SystemPlatform
(Galaxy hierarchy) existed in ConfigDb but were never surfaced in the OPC UA
address space. Now they materialise as Variable nodes under a folder named for
their FolderPath, browseable through any OPC UA client.

Layers touched:

- IOpcUaAddressSpaceSink: new EnsureVariable(nodeId, parentFolderId, displayName,
  dataType) signature on the sink interface, NullSink, DeferredSink, SdkSink.
- OtOpcUaNodeManager.EnsureVariable: creates a BaseDataVariableState parented
  under the named folder (or root), initial Value=null +
  StatusCode=BadWaitingForInitialData; resolves Tag.DataType strings to the
  matching OPC UA built-in NodeId. Idempotent.
- Phase7CompositionResult: new GalaxyTags collection of GalaxyTagPlan records
  carrying (TagId, DriverInstanceId, FolderPath, DisplayName, DataType,
  MxAccessRef). Constructor overloads keep existing call sites compiling.
- Phase7Composer.Compose: now takes Tag + Namespace inputs, filters for
  SystemPlatform-namespace tags with EquipmentId=NULL, emits GalaxyTagPlan
  rows with MXAccess ref "FolderPath.Name".
- Phase7Plan: new AddedGalaxyTags / RemovedGalaxyTags / ChangedGalaxyTags
  collections + GalaxyTagDelta record; IsEmpty + needsRebuild updated.
- Phase7Planner.Compute: diffs GalaxyTags by TagId via existing DiffById helper.
- DeploymentArtifact.ParseComposition: reads the Tags + Namespaces +
  DriverInstances arrays the ConfigComposer already emits, applies the same
  SystemPlatform filter, returns the same GalaxyTagPlan list as the composer
  so artifact-side and compose-side plans agree.
- Phase7Applier: new MaterialiseGalaxyTags pass that ensures one folder per
  distinct FolderPath then one Variable per tag. NodeId for the variable is
  "<FolderPath>.<Name>" matching the MXAccess ref so the future Galaxy
  SubscribeBulk wiring can address them directly.
- OpcUaPublishActor.RebuildAddressSpace: invokes MaterialiseGalaxyTags after
  MaterialiseHierarchy. _lastApplied initialiser updated for the new ctor.
- seed-clusters.sql: pre-existing TestMachine_001.TestAlarm001..003 rows
  needed no change — the composer/applier now picks them up automatically.

Verified end-to-end via docker-dev: deploy click → driver-a logs
"Phase7Applier: Galaxy tags materialised (tags=3, folders=1)" → OPC UA Client
CLI browses the three Variable nodes under TestMachine_001 folder. Reads
return BadWaitingForInitialData status (expected — Galaxy driver's
SubscribeBulk wiring to push values into the nodes is the remaining
follow-up).

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

@@ -101,8 +101,9 @@ public static class DeploymentArtifact
             var equipment = ReadArray(root, "Equipment", ReadEquipmentNode);
             var drivers = ReadArray(root, "DriverInstances", ReadDriverPlan);
             var alarms = ReadArray(root, "ScriptedAlarms", ReadAlarmPlan);
+            var galaxyTags = BuildGalaxyTagPlans(root, drivers);
 
-            return new Phase7CompositionResult(areas, lines, equipment, drivers, alarms);
+            return new Phase7CompositionResult(areas, lines, equipment, drivers, alarms, galaxyTags);
         }
         catch (JsonException)
         {
@@ -115,7 +116,87 @@ public static class DeploymentArtifact
         Array.Empty<UnsLineProjection>(),
         Array.Empty<EquipmentNode>(),
         Array.Empty<DriverInstancePlan>(),
-        Array.Empty<ScriptedAlarmPlan>());
+        Array.Empty<ScriptedAlarmPlan>(),
+        Array.Empty<GalaxyTagPlan>());
+
+    /// <summary>
+    ///     Cross-reference the artifact's Tags + Namespaces + DriverInstances arrays to find
+    ///     SystemPlatform-namespace tags (Galaxy hierarchy), then emit one <see cref="GalaxyTagPlan"/>
+    ///     per qualifying tag. Mirrors <c>Phase7Composer.Compose</c>'s filter so a compose-side
+    ///     plan and an artifact-decode plan agree on the same set of tags.
+    /// </summary>
+    private static IReadOnlyList<GalaxyTagPlan> BuildGalaxyTagPlans(JsonElement root, IReadOnlyList<DriverInstancePlan> drivers)
+    {
+        if (!root.TryGetProperty("Tags", out var tagsArr) || tagsArr.ValueKind != JsonValueKind.Array)
+            return Array.Empty<GalaxyTagPlan>();
+        if (!root.TryGetProperty("Namespaces", out var nsArr) || nsArr.ValueKind != JsonValueKind.Array)
+            return Array.Empty<GalaxyTagPlan>();
+        if (!root.TryGetProperty("DriverInstances", out var diArr) || diArr.ValueKind != JsonValueKind.Array)
+            return Array.Empty<GalaxyTagPlan>();
+
+        // namespaceId → Kind ("SystemPlatform"/"Equipment"/"Simulated") — enum serialises as int by default,
+        // but ConfigComposer's snapshot uses default JsonSerializer which writes numbers. Tolerate both.
+        var systemPlatformNamespaces = new HashSet<string>(StringComparer.Ordinal);
+        foreach (var el in nsArr.EnumerateArray())
+        {
+            if (el.ValueKind != JsonValueKind.Object) continue;
+            var id = el.TryGetProperty("NamespaceId", out var idEl) ? idEl.GetString() : null;
+            if (string.IsNullOrWhiteSpace(id)) continue;
+            if (!el.TryGetProperty("Kind", out var kindEl)) continue;
+            var isSystemPlatform = kindEl.ValueKind switch
+            {
+                JsonValueKind.Number => kindEl.GetInt32() == 1, // NamespaceKind.SystemPlatform = 1
+                JsonValueKind.String => string.Equals(kindEl.GetString(), "SystemPlatform", StringComparison.Ordinal),
+                _ => false,
+            };
+            if (isSystemPlatform) systemPlatformNamespaces.Add(id!);
+        }
+
+        // driverInstanceId → namespaceId
+        var driverToNamespace = new Dictionary<string, string>(StringComparer.Ordinal);
+        foreach (var el in diArr.EnumerateArray())
+        {
+            if (el.ValueKind != JsonValueKind.Object) continue;
+            var id = el.TryGetProperty("DriverInstanceId", out var idEl) ? idEl.GetString() : null;
+            var ns = el.TryGetProperty("NamespaceId", out var nsEl) ? nsEl.GetString() : null;
+            if (!string.IsNullOrWhiteSpace(id) && !string.IsNullOrWhiteSpace(ns))
+                driverToNamespace[id!] = ns!;
+        }
+
+        var result = new List<GalaxyTagPlan>(tagsArr.GetArrayLength());
+        foreach (var el in tagsArr.EnumerateArray())
+        {
+            if (el.ValueKind != JsonValueKind.Object) continue;
+            // Skip tags with non-null EquipmentId (Equipment-namespace tags belong to a different path).
+            if (el.TryGetProperty("EquipmentId", out var eqEl) && eqEl.ValueKind != JsonValueKind.Null) continue;
+
+            var tagId = el.TryGetProperty("TagId", out var tEl) ? tEl.GetString() : null;
+            var di = el.TryGetProperty("DriverInstanceId", out var diEl) ? diEl.GetString() : null;
+            var name = el.TryGetProperty("Name", out var nmEl) ? nmEl.GetString() : null;
+            var folder = el.TryGetProperty("FolderPath", out var fpEl) && fpEl.ValueKind != JsonValueKind.Null
+                ? fpEl.GetString() : null;
+            var dataType = el.TryGetProperty("DataType", out var dtEl) ? dtEl.GetString() : null;
+
+            if (string.IsNullOrWhiteSpace(tagId) || string.IsNullOrWhiteSpace(di) || string.IsNullOrWhiteSpace(name))
+                continue;
+            if (!driverToNamespace.TryGetValue(di!, out var nsId)) continue;
+            if (!systemPlatformNamespaces.Contains(nsId)) continue;
+
+            var folderPath = folder ?? string.Empty;
+            var mxRef = string.IsNullOrWhiteSpace(folderPath) ? name! : $"{folderPath}.{name}";
+            result.Add(new GalaxyTagPlan(tagId!, di!, folderPath, name!, dataType ?? "BaseDataType", mxRef));
+        }
+
+        result.Sort((a, b) =>
+        {
+            var byDriver = string.CompareOrdinal(a.DriverInstanceId, b.DriverInstanceId);
+            if (byDriver != 0) return byDriver;
+            var byFolder = string.CompareOrdinal(a.FolderPath, b.FolderPath);
+            if (byFolder != 0) return byFolder;
+            return string.CompareOrdinal(a.DisplayName, b.DisplayName);
+        });
+        return result;
+    }
 
     private static IReadOnlyList<T> ReadArray<T>(JsonElement root, string propertyName, Func<JsonElement, T?> reader)
         where T : class

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/OpcUa/OpcUaPublishActor.cs

@@ -45,9 +45,12 @@ public sealed class OpcUaPublishActor : ReceiveActor
     private int _writes;
     private byte _lastServiceLevel;
     private Phase7CompositionResult _lastApplied = new(
+        Array.Empty<UnsAreaProjection>(),
+        Array.Empty<UnsLineProjection>(),
         Array.Empty<EquipmentNode>(),
         Array.Empty<DriverInstancePlan>(),
-        Array.Empty<ScriptedAlarmPlan>());
+        Array.Empty<ScriptedAlarmPlan>(),
+        Array.Empty<GalaxyTagPlan>());
 
     public int WriteCount => _writes;
     public byte LastServiceLevel => _lastServiceLevel;
@@ -190,6 +193,10 @@ public sealed class OpcUaPublishActor : ReceiveActor
             // clients see Area/Line/Equipment as proper folders. Idempotent; Phase7Applier
             // skips folders that already exist with the same node id.
             _applier.MaterialiseHierarchy(composition);
+            // Galaxy / SystemPlatform tags get their own pass: ensures their FolderPath folder
+            // + Variable node exist so clients can browse them. The Galaxy driver fills values
+            // on a future SubscribeBulk pass; until then variables show BadWaitingForInitialData.
+            _applier.MaterialiseGalaxyTags(composition);
 
             OtOpcUaTelemetry.OpcUaSinkWrite.Add(1, new KeyValuePair<string, object?>("kind", "rebuild"));
             _log.Info("OpcUaPublish: applied rebuild (correlation={Correlation}, added={Added}, removed={Removed}, changed={Changed}, rebuild={Rebuild})",