Merge pull request #504 from open-pencil/fig-export-memory

perf(fig): reduce export graph cloning

CHANGELOG.md

@@ -8,6 +8,10 @@
 - Allow supported AI model profiles to set a provider-specific reasoning effort. (#454)
 - Show unavailable or substituted document fonts with affected-layer selection and retry actions, and expose font fidelity through the Figma API and MCP tooling. (#503)
 
+### Performance
+
+- Reduce peak memory during `.fig` export by sharing immutable binary resources with the isolated export graph.
+
 ### Fixed
 
 - Report exhausted provider credit, request failures, and output-token limits through localized chat toasts and copied diagnostics. (#451, #454)

packages/core/src/io/formats/fig/export.ts

@@ -23,7 +23,7 @@ import {
   makeDocumentNodeChange,
   makeCanvasNodeChange
 } from '#core/kiwi/fig/node-change/serialize'
-import { deserializeSceneGraph, serializeSceneGraph } from '#core/kiwi/fig/parse/transfer'
+import { cloneSceneGraphForFigExport } from '#core/kiwi/fig/parse/transfer'
 
 const THUMBNAIL_1X1 = decodeBase64(
   'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg=='
@@ -388,7 +388,7 @@ export async function exportFigFile(
 ): Promise<Uint8Array> {
   // Lazy population synchronizes component trees and therefore mutates its graph. Saving must not
   // rewrite the live editor document or restore component values over edits made by the user.
-  const graph = deserializeSceneGraph(structuredClone(serializeSceneGraph(sourceGraph)))
+  const graph = cloneSceneGraphForFigExport(sourceGraph)
   populateAllLazyFigImportRoots(graph)
   await initCodec()
 

packages/core/src/kiwi/fig/parse/transfer.ts

@@ -86,6 +86,40 @@ export function serializedSceneGraphTransferList(data: SerializedSceneGraph): Tr
   return [...buffers]
 }
 
+/**
+ * Clone the graph state that lazy FIG population may mutate while retaining immutable imported
+ * resources by reference. Population replaces node fields and mutates child ID arrays, but only
+ * reads image bytes, variables, source changes, GUID mappings, blobs, and schema bytes.
+ */
+export function cloneSceneGraphForFigExport(graph: SceneGraph): SceneGraph {
+  const cloned = new SceneGraph()
+  cloned.rootId = graph.rootId
+  cloned.nodes = new Map(
+    [...graph.nodes].map(([id, node]) => [id, { ...node, childIds: [...node.childIds] }])
+  )
+  cloned.images = new Map(graph.images)
+  cloned.variables = new Map(graph.variables)
+  cloned.variableCollections = new Map(graph.variableCollections)
+  cloned.activeMode = new Map(graph.activeMode)
+  cloned.instanceIndex = new Map(
+    [...graph.instanceIndex].map(([id, nodeIds]) => [id, new Set(nodeIds)])
+  )
+  cloned.figKiwiVersion = graph.figKiwiVersion
+  cloned.figSchemaDeflated = graph.figSchemaDeflated
+  cloned.documentColorSpace = graph.documentColorSpace
+
+  const lazyFigImport = getLazyFigImportContext(graph)
+  if (lazyFigImport) {
+    setLazyFigImportContext(cloned, {
+      changeMap: lazyFigImport.changeMap,
+      guidToNodeId: lazyFigImport.guidToNodeId,
+      blobs: lazyFigImport.blobs,
+      populatedRootIds: new Set(lazyFigImport.populatedRootIds)
+    })
+  }
+  return cloned
+}
+
 export function deserializeSceneGraph(data: SerializedSceneGraph): SceneGraph {
   const graph = new SceneGraph()
   graph.rootId = data.rootId

tests/engine/io/fig/export/lazy-population.test.ts

@@ -1,7 +1,11 @@
 import { describe, expect, test } from 'bun:test'
 
 import { exportFigFile, initCodec, parseFigFile } from '@open-pencil/core'
-import { setLazyFigImportContext } from '@open-pencil/core/kiwi/fig/lazy-import'
+import {
+  getLazyFigImportContext,
+  setLazyFigImportContext
+} from '@open-pencil/core/kiwi/fig/lazy-import'
+import { cloneSceneGraphForFigExport } from '@open-pencil/core/kiwi/fig/parse/transfer'
 import { SceneGraph } from '@open-pencil/scene-graph'
 
 function lazyExportGraph() {
@@ -39,6 +43,27 @@ function createEditedInstance(
 }
 
 describe('FIG population export lifecycle', () => {
+  test('isolates mutable graph state while sharing immutable binary resources', () => {
+    const { graph } = lazyExportGraph()
+    const image = new Uint8Array([1, 2, 3])
+    graph.images.set('image', image)
+    const context = getLazyFigImportContext(graph)
+    expect(context).toBeDefined()
+
+    const clone = cloneSceneGraphForFigExport(graph)
+    const cloneContext = getLazyFigImportContext(clone)
+    const firstPage = graph.getPages()[0]
+    clone.getNode(firstPage.id)?.childIds.push('export-only')
+    cloneContext?.populatedRootIds.add('export-only')
+
+    expect(graph.getNode(firstPage.id)?.childIds).not.toContain('export-only')
+    expect(context?.populatedRootIds).not.toContain('export-only')
+    expect(clone.images.get('image')).toBe(image)
+    expect(cloneContext?.changeMap).toBe(context?.changeMap)
+    expect(cloneContext?.guidToNodeId).toBe(context?.guidToNodeId)
+    expect(cloneContext?.blobs).toBe(context?.blobs)
+  })
+
   test('exports all remaining lazy pages after a partial visit', async () => {
     await initCodec()
     const { graph, instance } = lazyExportGraph()