fix(vtags): prune _planByVtag on child termination + crash-then-change test (H1b review follow-up)

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/VirtualTags/VirtualTagHostActor.cs

@@ -39,8 +39,9 @@ public sealed class VirtualTagHostActor : ReceiveActor
     private readonly Dictionary<string, IActorRef> _children = new(StringComparer.Ordinal);
     // vtagId -> folder-scoped OPC UA NodeId the materialiser placed the variable at.
     private readonly Dictionary<string, string> _nodeIdByVtag = new(StringComparer.Ordinal);
-    // vtagId -> the plan its currently-spawned child was built from, so we can detect an in-place
-    // change (edited Expression/DependencyRefs) and stop+respawn the child to adopt it.
+    // vtagId -> the plan its live child was built from, so we can detect an in-place change (edited
+    // Expression/DependencyRefs) and stop+respawn the child to adopt it. Kept in lock-step with
+    // _children: rebuilt to the desired set at the end of every apply, and pruned in OnChildTerminated.
     private readonly Dictionary<string, EquipmentVirtualTagPlan> _planByVtag = new(StringComparer.Ordinal);
 
     /// <summary>Factory method to create Props for a VirtualTagHostActor.</summary>
@@ -161,8 +162,11 @@ public sealed class VirtualTagHostActor : ReceiveActor
         foreach (var id in stale)
         {
             _children.Remove(id);
-            // NodeId map is rebuilt on the next ApplyVirtualTags; leaving the mapping is harmless
-            // (no child will publish for it until respawned). A dead child is respawned on next apply.
+            // Keep _planByVtag in lock-step with _children so it never holds a plan for a dead child.
+            // (The next apply also resets it, and the change-detect guard short-circuits on the missing
+            // _children entry — so this is defensive consistency, not a live-bug fix.) NodeId map is
+            // rebuilt on the next ApplyVirtualTags; leaving that mapping is harmless. Dead child respawns.
+            _planByVtag.Remove(id);
             _log.Warning("VirtualTagHost: child for vtag {VirtualTagId} terminated; will respawn on next apply", id);
         }
     }