Fix findUsages/undo/node-lookup bugs, split Viewport and Editor, share command and inspector helpers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/store/serialize.ts

@@ -5,6 +5,7 @@ import { isAssetType } from '../model/AssetTypes';
 import type { PropertyBag, PropertyValue } from '../model/Properties';
 import { PROJECT_FORMAT_VERSION, type Project } from '../model/Project';
 import type { SceneObject } from '../model/SceneObject';
+import { hasParentCycle } from '../model/walk';
 import { coerceValue, COMMON_PROPS, isCommonProp, type PropertyDef, type PropertySchema, schemaFor, VARIABLE_KINDS, variableDef, type VariableKind } from '../properties/PropertySchema';
 
 /**
@@ -94,18 +95,9 @@ function normalizeObjects(raw: unknown, schemas: Map<string, PropertySchema>): S
   // Parents must exist in the same scene, differ from the object itself and not form cycles.
   const byId = new Map(objects.map((o) => [o.id, o]));
   for (const o of objects) if (o.parentId && (o.parentId === o.id || !byId.has(o.parentId))) o.parentId = '';
-  for (const o of objects) {
-    const seen = new Set<string>([o.id]);
-    let current = o.parentId ? byId.get(o.parentId) : undefined;
-    while (current) {
-      if (seen.has(current.id)) {
-        o.parentId = '';
-        break;
-      }
-      seen.add(current.id);
-      current = current.parentId ? byId.get(current.parentId) : undefined;
-    }
-  }
+  // Cut one link per cycle: an object already unlinked here is a root for the objects checked after it.
+  const parentOf = (o: SceneObject) => (o.parentId ? byId.get(o.parentId) : undefined);
+  for (const o of objects) if (hasParentCycle(o, parentOf)) o.parentId = '';
   return objects;
 }