diff --git a/src/autosave/package.ts b/src/autosave/package.ts
index 64fb4436..3e971ae4 100644
--- a/src/autosave/package.ts
+++ b/src/autosave/package.ts
@@ -240,9 +240,11 @@ function createInvalidQueueOptionsError(): InternalDocumentAutosaveQueueError {
 /**
  * Read exact queue option values without invoking accessors or retaining extras.
  *
- * The optional observer must be an enumerable data property when present.
- * Unknown keys, symbols, accessors, non-enumerable fields, and reflection
- * failures are rejected before any host callback can execute.
+ * The required save callback is validated before global key enumeration so an
+ * already-invalid capability cannot trigger unrelated caller-controlled Proxy
+ * key reflection. The optional observer must be an enumerable data property
+ * when present. Unknown keys, symbols, accessors, non-enumerable fields, and
+ * reflection failures are rejected before any host callback can execute.
  */
 function readDocumentAutosaveQueueOptions(
   options: DocumentAutosaveQueueOptions,
@@ -254,6 +256,15 @@ function readDocumentAutosaveQueueOptions(
     if (typeof options !== 'object' || options === null) {
       throw createInvalidQueueOptionsError();
     }
+    const saveDescriptor = Object.getOwnPropertyDescriptor(options, 'save');
+    if (
+      saveDescriptor === undefined ||
+      !saveDescriptor.enumerable ||
+      !Object.prototype.hasOwnProperty.call(saveDescriptor, 'value') ||
+      typeof saveDescriptor.value !== 'function'
+    ) {
+      throw createInvalidQueueOptionsError();
+    }
     const optionKeys = Reflect.ownKeys(options);
     if (
       optionKeys.length < 1 ||
@@ -268,20 +279,15 @@ function readDocumentAutosaveQueueOptions(
     ) {
       throw createInvalidQueueOptionsError();
     }
-    const saveDescriptor = Object.getOwnPropertyDescriptor(options, 'save');
     const observerDescriptor = Object.getOwnPropertyDescriptor(
       options,
       'onSnapshotChange',
     );
     if (
-      saveDescriptor === undefined ||
-      !saveDescriptor.enumerable ||
-      !Object.prototype.hasOwnProperty.call(saveDescriptor, 'value') ||
-      typeof saveDescriptor.value !== 'function' ||
-      (observerDescriptor !== undefined &&
-        (!observerDescriptor.enumerable ||
-          !Object.prototype.hasOwnProperty.call(observerDescriptor, 'value') ||
-          typeof observerDescriptor.value !== 'function'))
+      observerDescriptor !== undefined &&
+      (!observerDescriptor.enumerable ||
+        !Object.prototype.hasOwnProperty.call(observerDescriptor, 'value') ||
+        typeof observerDescriptor.value !== 'function')
     ) {
       throw createInvalidQueueOptionsError();
     }
diff --git a/src/autosave/packageOptionPreflight.test.ts b/src/autosave/packageOptionPreflight.test.ts
new file mode 100644
index 00000000..02b66eb7
--- /dev/null
+++ b/src/autosave/packageOptionPreflight.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest';
+import { createDocumentAutosaveQueue } from './package.js';
+
+describe('framework-free autosave option preflight', () => {
+  it('rejects an invalid required save descriptor before key enumeration', () => {
+    let ownKeysCalls = 0;
+    const options = new Proxy(
+      { save: 1 },
+      {
+        ownKeys() {
+          ownKeysCalls += 1;
+          throw new Error('private option keys');
+        },
+      },
+    );
+
+    expect(() => createDocumentAutosaveQueue(options as never)).toThrowError(
+      expect.objectContaining({
+        code: 'invalid_options',
+        message: 'Document autosave queue options are invalid.',
+      }),
+    );
+    expect(ownKeysCalls).toBe(0);
+  });
+});