diff --git a/packages/core/src/lib/asset-storage.test.ts b/packages/core/src/lib/asset-storage.test.ts
index 432b79f900..30f7733921 100644
--- a/packages/core/src/lib/asset-storage.test.ts
+++ b/packages/core/src/lib/asset-storage.test.ts
@@ -1,6 +1,7 @@
 import 'fake-indexeddb/auto'
 import { afterEach, describe, expect, test } from 'bun:test'
-import { loadAssetUrl, saveAsset } from './asset-storage'
+import { get, set } from 'idb-keyval'
+import { ASSET_PREFIX, loadAssetUrl, saveAsset } from './asset-storage'
 
 function file(contents: string, name = 'test.txt'): File {
   return new File([contents], name, { type: 'text/plain' })
@@ -46,6 +47,32 @@ describe('loadAssetUrl', () => {
     expect(objectUrl?.startsWith('blob:')).toBe(true)
   })
 
+  // Regression test: saveAsset used to put the File object itself into
+  // IndexedDB. Not every engine accepts File/Blob records (WebKit rejects
+  // them), so the record is now plain bytes plus the content type.
+  test('stores raw bytes and the content type, not a File object', async () => {
+    const url = await saveAsset(new File(['png-bytes'], 'a.png', { type: 'image/png' }))
+    const stored = await get<{ assetVersion: number; bytes: ArrayBuffer; type: string }>(
+      `${ASSET_PREFIX}${url.replace('asset://', '')}`,
+    )
+    expect(stored).not.toBeInstanceOf(Blob)
+    expect(stored?.assetVersion).toBe(1)
+    expect(stored?.bytes).toBeInstanceOf(ArrayBuffer)
+    expect(new TextDecoder().decode(stored?.bytes)).toBe('png-bytes')
+    expect(stored?.type).toBe('image/png')
+  })
+
+  test('still reads File/Blob records written before the byte format', async () => {
+    await set(`${ASSET_PREFIX}legacy`, new Blob(['old'], { type: 'text/plain' }))
+    const objectUrl = await loadAssetUrl('asset://legacy')
+    expect(objectUrl?.startsWith('blob:')).toBe(true)
+  })
+
+  test('returns null instead of throwing for an unreadable record', async () => {
+    await set(`${ASSET_PREFIX}broken`, { unexpected: true })
+    expect(await loadAssetUrl('asset://broken')).toBeNull()
+  })
+
   test('passes through blob: and http(s) URLs unchanged', async () => {
     expect(await loadAssetUrl('blob:http://example.com/1234')).toBe('blob:http://example.com/1234')
     expect(await loadAssetUrl('https://cdn.example.com/a.glb')).toBe(
diff --git a/packages/core/src/lib/asset-storage.ts b/packages/core/src/lib/asset-storage.ts
index 7f2213f445..9ad614e71a 100644
--- a/packages/core/src/lib/asset-storage.ts
+++ b/packages/core/src/lib/asset-storage.ts
@@ -9,12 +9,52 @@ const urlCache = new Map<string, string>()
 // Unlike crypto.randomUUID(), nanoid works outside secure contexts.
 const nanoAssetId = customAlphabet('0123456789abcdefghijklmnopqrstuvwxyz', 16)
 
+/**
+ * Save a file to IndexedDB and return a custom protocol URL
+ */
+/**
+ * Stored shape for assets. Raw bytes go through the portable structured-clone
+ * path, which every IndexedDB implementation supports; File/Blob records do
+ * not (WebKit has rejected them). The content type is kept so the object URL
+ * served later still carries the original MIME type.
+ */
+export interface StoredAssetRecord {
+  assetVersion: 1
+  bytes: ArrayBuffer
+  type: string
+}
+
+function isStoredAssetRecord(value: unknown): value is StoredAssetRecord {
+  return (
+    typeof value === 'object' &&
+    value !== null &&
+    (value as StoredAssetRecord).assetVersion === 1 &&
+    (value as StoredAssetRecord).bytes instanceof ArrayBuffer &&
+    typeof (value as StoredAssetRecord).type === 'string'
+  )
+}
+
+/**
+ * Turn whatever is in IndexedDB back into a Blob. Records written before the
+ * byte format existed are plain File/Blob objects and stay readable.
+ */
+function toBlob(value: unknown): Blob | null {
+  if (value instanceof Blob) return value
+  if (isStoredAssetRecord(value)) return new Blob([value.bytes], { type: value.type })
+  return null
+}
+
 /**
  * Save a file to IndexedDB and return a custom protocol URL
  */
 export async function saveAsset(file: File): Promise<string> {
   const id = nanoAssetId()
-  await set(`${ASSET_PREFIX}${id}`, file)
+  const record: StoredAssetRecord = {
+    assetVersion: 1,
+    bytes: await file.arrayBuffer(),
+    type: file.type,
+  }
+  await set(`${ASSET_PREFIX}${id}`, record)
   return `asset://${id}`
 }
 
@@ -40,12 +80,17 @@ export async function loadAssetUrl(url: string): Promise<string | null> {
     }
 
     try {
-      const file = await get<File | Blob>(`${ASSET_PREFIX}${id}`)
-      if (!file) {
+      const stored = await get<unknown>(`${ASSET_PREFIX}${id}`)
+      if (!stored) {
         console.warn(`Asset not found: ${id}`)
         return null
       }
-      const objectUrl = URL.createObjectURL(file)
+      const blob = toBlob(stored)
+      if (!blob) {
+        console.warn(`Asset ${id} has an unreadable record`)
+        return null
+      }
+      const objectUrl = URL.createObjectURL(blob)
       urlCache.set(id, objectUrl)
       return objectUrl
     } catch (error) {