diff --git a/CHANGELOG.md b/CHANGELOG.md
index 02c5c0ad1..fbd2665c5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Breaking changes
 
+- `SceneNode.booleanOperation` is a required key whose value may be `undefined`, like every other scene node field, so code that builds `SceneNode` objects itself must include it.
 - `sceneNodeToDesignDocument` from `@open-pencil/dom-css` takes an options object, `{ includeSourceIds, tokens }`, instead of a boolean third argument; `tokens: false` writes literal values instead of variable references.
 - `randomHex`, `randomInt`, and `randomIndex` moved from `@open-pencil/core/random` and the `@open-pencil/core` barrel to `@open-pencil/scene-graph/random`.
 - `Stroke` from `@open-pencil/scene-graph` extends `Fill`, so every stroke states a paint `type` that code constructing one must set to `'SOLID'`, and `copyStroke` deep-copies the paint fields a fill already copied.
@@ -144,6 +145,7 @@
 
 ### Performance
 
+- Open large `.fig` files with less memory in the macOS desktop app and Safari: imported layers now share one object layout in JavaScriptCore instead of each being stored as a slower, larger dictionary.
 - Open multi-page `.fig` documents faster: the archive is indexed once rather than once for every page, each page resolves only the layers it adds instead of rescanning the whole document, placing an instance no longer re-synchronises every other instance of its component, and archive records are copied directly rather than through `structuredClone`. A 33-page file loads about a fifth quicker, and a page of repeated components opens three to four times faster once a document is already open.
 
 ### Security
diff --git a/packages/fig/tests/document/node-shape.test.ts b/packages/fig/tests/document/node-shape.test.ts
new file mode 100644
index 000000000..50743dfee
--- /dev/null
+++ b/packages/fig/tests/document/node-shape.test.ts
@@ -0,0 +1,23 @@
+import { expect, test } from 'bun:test'
+
+import { readFixtureArrayBuffer } from '#fig-tests/helpers/fig-fixtures'
+
+import { createFigDocumentSession } from '@open-pencil/fig'
+import { createDefaultNode } from '@open-pencil/scene-graph/node-defaults'
+
+// Imported nodes must keep the shape every node is created with: a key outside it turns each
+// node into a JavaScriptCore dictionary, which made opening large files in WebKit take about a
+// fifth more memory.
+test('imported nodes carry exactly the default scene node fields', () => {
+  const session = createFigDocumentSession(readFixtureArrayBuffer('gold-preview.fig'))
+  for (const page of session.pages) if (!page.internalOnly) session.loadPage(page.id)
+  // Insertion order matters too: JavaScriptCore lays out the same keys added in another order
+  // as a different shape.
+  const fields = Object.keys(createDefaultNode(() => 'node', 'FRAME'))
+  const shapes = new Map<string, string>()
+  for (const node of session.graph.nodes.values()) {
+    const keys = Object.keys(node).join(',')
+    if (!shapes.has(keys)) shapes.set(keys, node.id)
+  }
+  expect([...shapes.keys()].map((keys) => keys.split(','))).toEqual([fields])
+})
diff --git a/packages/scene-graph/src/node-defaults.ts b/packages/scene-graph/src/node-defaults.ts
index f7abe2bd3..dad744306 100644
--- a/packages/scene-graph/src/node-defaults.ts
+++ b/packages/scene-graph/src/node-defaults.ts
@@ -22,6 +22,13 @@ export function createDefaultSourceMetadata(): SourceMetadata {
   }
 }
 
+/**
+ * Every SceneNode field. Nodes start with all of them, so setting any field later keeps the
+ * shape every node shares; a key added after creation turns a JavaScriptCore object into a
+ * slower, larger dictionary.
+ */
+type CompleteNodeFields = SceneNode & Record<keyof SceneNode, unknown>
+
 export function createDefaultNode(
   generateId: () => string,
   type: NodeType,
@@ -173,8 +180,9 @@ export function createDefaultNode(
     derivedTextGlyphs: null,
     textPathData: null,
     textPathBox: null,
+    booleanOperation: undefined,
     ...overrides
-  }
+  } satisfies CompleteNodeFields
 }
 
 export const CONTAINER_TYPES = new Set<NodeType>([
diff --git a/packages/scene-graph/src/types.ts b/packages/scene-graph/src/types.ts
index 35c8150cb..4dd4dacf4 100644
--- a/packages/scene-graph/src/types.ts
+++ b/packages/scene-graph/src/types.ts
@@ -504,7 +504,7 @@ export interface SceneNode {
 
   vectorNetwork: VectorNetwork | null
   handleMirroring: HandleMirroring
-  booleanOperation?: 'UNION' | 'SUBTRACT' | 'INTERSECT' | 'EXCLUDE'
+  booleanOperation: 'UNION' | 'SUBTRACT' | 'INTERSECT' | 'EXCLUDE' | undefined
   fillGeometry: GeometryPath[]
   strokeGeometry: GeometryPath[]