perf(opcua): skip address-space rebuild for vtag expression/deps/historize-only edits (F10b)

src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs

@@ -84,16 +84,23 @@ public sealed class Phase7Applier
         // Any add / remove / in-place CHANGE of Equipment, ScriptedAlarm, Equipment tag, or Equipment
         // VirtualTag topology requires a real address-space rebuild — the materialise passes re-derive
         // every node from the composition, so a changed-only deploy (e.g. a renamed equipment, a
-        // re-severitied alarm, a flipped tag dataType/Writable, or an edited VirtualTag expression) must
-        // still rebuild or the running server keeps the stale node.
+        // re-severitied alarm, a flipped tag dataType/Writable) must still rebuild or the running server
+        // keeps the stale node.
         // ChangedDrivers is deliberately EXCLUDED: a driver-instance config change doesn't touch the
         // address-space topology — it routes through DriverHostActor's spawn-plan in Runtime, which
         // re-spawns the affected driver actor without re-materialising any nodes.
+        // F10b: a CHANGED VirtualTag whose ONLY differences are Expression/DependencyRefs/Historize is
+        // node-IRRELEVANT (see VtagDeltaIsNodeIrrelevant) — its materialised node is byte-identical and
+        // the vtag engine adopts those edits via VirtualTagHostActor's INDEPENDENT respawn
+        // (DriverHostActor → ApplyVirtualTags), so it skips the rebuild and PRESERVES every client's
+        // server-wide subscriptions. Any structural / node-affecting vtag change (Name/FolderPath/
+        // DataType) — or any non-vtag change anywhere — still forces a full rebuild (safe default).
         var needsRebuild =
             plan.AddedEquipment.Count > 0 || plan.RemovedEquipment.Count > 0 || plan.ChangedEquipment.Count > 0 ||
             plan.AddedAlarms.Count > 0 || plan.RemovedAlarms.Count > 0 || plan.ChangedAlarms.Count > 0 ||
             plan.AddedEquipmentTags.Count > 0 || plan.RemovedEquipmentTags.Count > 0 || plan.ChangedEquipmentTags.Count > 0 ||
-            plan.AddedEquipmentVirtualTags.Count > 0 || plan.RemovedEquipmentVirtualTags.Count > 0 || plan.ChangedEquipmentVirtualTags.Count > 0;
+            plan.AddedEquipmentVirtualTags.Count > 0 || plan.RemovedEquipmentVirtualTags.Count > 0 ||
+            plan.ChangedEquipmentVirtualTags.Any(d => !VtagDeltaIsNodeIrrelevant(d));
 
         if (needsRebuild)
         {
@@ -319,6 +326,20 @@ public sealed class Phase7Applier
         catch (Exception ex) { _logger.LogWarning(ex, "Phase7Applier: EnsureVariable threw for {Node}", nodeId); }
     }
 
+    // A VirtualTag's materialised OPC UA node (MaterialiseEquipmentVirtualTags) is derived ONLY from
+    // {EquipmentId, FolderPath, Name, DataType}. Expression/DependencyRefs/Historize are engine/write-side
+    // only and are adopted by VirtualTagHostActor's INDEPENDENT respawn (DriverHostActor → ApplyVirtualTags),
+    // so a delta changing ONLY those three leaves a byte-identical node and needs no address-space rebuild.
+    // Whitelist-of-may-differ via `with` + the record's custom Equals: any OTHER field difference (current
+    // or future) makes the override unequal → falls back to a full rebuild (safe default).
+    private static bool VtagDeltaIsNodeIrrelevant(Phase7Plan.EquipmentVirtualTagDelta d) =>
+        (d.Previous with
+        {
+            Expression = d.Current.Expression,
+            DependencyRefs = d.Current.DependencyRefs,
+            Historize = d.Current.Historize,
+        }).Equals(d.Current);
+
     /// <summary>The "no-event" condition state written to a removed equipment / alarm node before the
     /// rebuild tears it down: inactive, acked, confirmed, enabled, unshelved, severity 0, empty message.
     /// Drives Retain to false so a removed condition stops replaying on ConditionRefresh.</summary>