diff --git a/libs/core/src/__tests__/enclave.result-sanitization.spec.ts b/libs/core/src/__tests__/enclave.result-sanitization.spec.ts
index ddaf693..8f826a9 100644
--- a/libs/core/src/__tests__/enclave.result-sanitization.spec.ts
+++ b/libs/core/src/__tests__/enclave.result-sanitization.spec.ts
@@ -3,13 +3,16 @@
  *
  * The sanitizer used to recognize Dates, Maps, Sets and RegExps with `instanceof`, which is false
  * for values built in the sandbox realm, so a script's `new Date(0)` came back as `{}`. It now
- * checks the builtin's internal slot, as `@enclave-vm/browser` does inside its iframe. (The single
- * VM still returns `{}`: its membrane hands the sanitizer a proxy, which the check refuses.)
+ * checks the builtin's internal slot, as `@enclave-vm/browser` does inside its iframe. The single
+ * VM's membrane wraps the script's Dates in a proxy, which has no slot, so that adapter hands the
+ * sanitizer `unwrapSecureProxy` to reach the Date behind it.
  */
 
 import * as vm from 'vm';
 import { Enclave } from '../enclave';
+import { createSecureProxy, unwrapSecureProxy } from '../secure-proxy';
 import { sanitizeValue } from '../value-sanitizer';
+import type { CreateEnclaveOptions } from '../types';
 
 describe('sanitizeValue with values from another realm', () => {
   const foreign = vm.runInNewContext(`({
@@ -52,11 +55,47 @@ describe('sanitizeValue with values from another realm', () => {
   });
 });
 
-describe('script results on the double VM', () => {
+describe('unwrapSecureProxy', () => {
+  it('returns the object a secure proxy wraps', () => {
+    const date = new Date(0);
+
+    expect(unwrapSecureProxy(createSecureProxy(date))).toBe(date);
+  });
+
+  it('returns any other value unchanged', () => {
+    const plain = { a: 1 };
+    const foreignProxy = new Proxy(new Date(0), {});
+
+    expect(unwrapSecureProxy(plain)).toBe(plain);
+    expect(unwrapSecureProxy(foreignProxy)).toBe(foreignProxy);
+    expect(unwrapSecureProxy(null)).toBeNull();
+    expect(unwrapSecureProxy(1)).toBe(1);
+  });
+
+  it('lets sanitizeValue read a wrapped Date', () => {
+    const wrapped = { date: createSecureProxy(new Date(0)) };
+
+    expect(sanitizeValue(wrapped)).toEqual({ date: {} });
+    expect(sanitizeValue(wrapped, { unwrap: unwrapSecureProxy })).toEqual({ date: new Date(0) });
+  });
+});
+
+describe.each<[string, CreateEnclaveOptions]>([
+  ['double VM', {}],
+  ['single VM', { doubleVm: { enabled: false } }],
+])('script results on the %s', (_name, adapterOptions) => {
   let enclave: Enclave;
 
+  beforeAll(() => {
+    jest.spyOn(console, 'warn').mockImplementation(() => undefined);
+  });
+
+  afterAll(() => {
+    jest.restoreAllMocks();
+  });
+
   beforeEach(() => {
-    enclave = new Enclave({ timeout: 5000 });
+    enclave = new Enclave({ timeout: 5000, ...adapterOptions });
   });
 
   afterEach(() => {
@@ -64,11 +103,14 @@ describe('script results on the double VM', () => {
   });
 
   it('returns a Date as a Date', async () => {
-    const result = await enclave.run<{ date: Date }>('return { date: new Date(0) };');
+    const result = await enclave.run<{ date: Date; nested: Date[] }>(
+      'return { date: new Date(0), nested: [new Date(1)] };',
+    );
 
     expect(result.error).toBeUndefined();
     expect(result.value?.date).toBeInstanceOf(Date);
     expect(result.value?.date.getTime()).toBe(0);
+    expect(result.value?.nested[0].getTime()).toBe(1);
   });
 
   it('keeps the other conversions', async () => {
diff --git a/libs/core/src/adapters/vm-adapter.ts b/libs/core/src/adapters/vm-adapter.ts
index 5c3022b..73040bf 100644
--- a/libs/core/src/adapters/vm-adapter.ts
+++ b/libs/core/src/adapters/vm-adapter.ts
@@ -10,7 +10,7 @@
 import * as vm from 'vm';
 import type { SandboxAdapter, ExecutionContext, ExecutionResult, SecurityLevel } from '../types';
 import { createSafeRuntime } from '../safe-runtime';
-import { createSafeReflect, createSecureProxy } from '../secure-proxy';
+import { createSafeReflect, createSecureProxy, unwrapSecureProxy } from '../secure-proxy';
 import { createSafeError } from '../safe-error';
 import { MemoryTracker, MemoryLimitError } from '../memory-tracker';
 import { createHostToolBridge } from '../tool-bridge';
@@ -1186,6 +1186,8 @@ export class VmAdapter implements SandboxAdapter {
         maxProperties: clampedProperties,
         allowDates: true,
         allowErrors: true,
+        // The membrane wraps the script's Dates; read them through their targets.
+        unwrap: unwrapSecureProxy,
       });
 
       return {
diff --git a/libs/core/src/secure-proxy.ts b/libs/core/src/secure-proxy.ts
index 9bf2e15..2e59d34 100644
--- a/libs/core/src/secure-proxy.ts
+++ b/libs/core/src/secure-proxy.ts
@@ -1028,6 +1028,22 @@ export function isSecureProxy(obj: unknown): boolean {
   return proxySet.has(obj as object);
 }
 
+/**
+ * The object a secure proxy wraps, or `value` itself when it is not one.
+ *
+ * For host code that must read a sandbox value's internal slots, which a proxy does not carry
+ * (a proxied Date fails `Date.prototype.getTime`). Never hand the result back to the sandbox.
+ */
+export function unwrapSecureProxy<T>(value: T): T {
+  let current: unknown = value;
+  while (current !== null && (typeof current === 'object' || typeof current === 'function')) {
+    const target = proxyToTarget.get(current as object);
+    if (target === undefined) break;
+    current = target;
+  }
+  return current as T;
+}
+
 /**
  * Clear the proxy cache
  *
diff --git a/libs/core/src/value-sanitizer.ts b/libs/core/src/value-sanitizer.ts
index 0d1e971..a762a8c 100644
--- a/libs/core/src/value-sanitizer.ts
+++ b/libs/core/src/value-sanitizer.ts
@@ -38,6 +38,13 @@ export interface SanitizeOptions {
    * @default true
    */
   allowErrors?: boolean;
+
+  /**
+   * Returns the object to check for a Date, Map, Set or RegExp in place of a wrapper around it
+   * (the single VM's secure proxy, which has no internal slots). Only builtins are read from the
+   * unwrapped object; everything else is still read through `value`.
+   */
+  unwrap?: (value: object) => object;
 }
 
 /**
@@ -270,19 +277,20 @@ export function sanitizeValue(
     return result;
   }
 
-  const isPlain = isPlainObject(value as object);
+  const inspected = options.unwrap ? options.unwrap(value as object) : (value as object);
+  const isPlain = isPlainObject(inspected);
 
   // Handle Date objects, including the sandbox realm's.
   // SECURITY: read the timestamp via the captured Date.prototype.getTime (Reflect.apply),
   // never `value.getTime()`, so the value cannot supply its own method.
-  if (!isPlain && hasBrand(DateProtoGetTime, value as object)) {
-    const time = ReflectApply(DateProtoGetTime, value, []) as number;
+  if (!isPlain && hasBrand(DateProtoGetTime, inspected)) {
+    const time = ReflectApply(DateProtoGetTime, inspected, []) as number;
     if (allowDates) {
       // Return a new Date to prevent reference sharing
       return new Date(time);
     }
     // Convert to ISO string if dates not allowed
-    return ReflectApply(DateProtoToISOString, value, []) as string;
+    return ReflectApply(DateProtoToISOString, inspected, []) as string;
   }
 
   // Handle Error objects
@@ -305,17 +313,17 @@ export function sanitizeValue(
   }
 
   // Handle RegExp objects (convert to their /source/flags string)
-  if (!isPlain && hasBrand(RegExpProtoSourceGetter, value as object)) {
-    return regExpToString(value as object);
+  if (!isPlain && hasBrand(RegExpProtoSourceGetter, inspected)) {
+    return regExpToString(inspected);
   }
 
   // Handle Map objects, including the sandbox realm's.
   // SECURITY: enumerate with the captured Map.prototype.entries (Reflect.apply) rather than
   // `value.entries()`, so the value cannot hijack the iteration. The returned iterator is a
   // genuine host Map Iterator, safe to `for..of`.
-  if (!isPlain && hasBrand(MapProtoSizeGetter, value as object)) {
+  if (!isPlain && hasBrand(MapProtoSizeGetter, inspected)) {
     const sanitizedMap: Record<string, unknown> = ObjectCreate(null);
-    const entries = ReflectApply(MapProtoEntries, value, []) as IterableIterator<[unknown, unknown]>;
+    const entries = ReflectApply(MapProtoEntries, inspected, []) as IterableIterator<[unknown, unknown]>;
     for (const [key, val] of entries) {
       if (typeof key !== 'string') continue; // Only string keys
       if (DANGEROUS_KEYS.has(key)) continue; // Skip dangerous keys
@@ -328,8 +336,8 @@ export function sanitizeValue(
   // Handle Set objects (convert to array), including the sandbox realm's.
   // SECURITY: enumerate with the captured Set.prototype.values (Reflect.apply), not
   // `Array.from(value)` / the value's own iterator, so the value cannot hijack it.
-  if (!isPlain && hasBrand(SetProtoSizeGetter, value as object)) {
-    const iter = ReflectApply(SetProtoValues, value, []) as IterableIterator<unknown>;
+  if (!isPlain && hasBrand(SetProtoSizeGetter, inspected)) {
+    const iter = ReflectApply(SetProtoValues, inspected, []) as IterableIterator<unknown>;
     const result: unknown[] = [];
     for (const item of iter) {
       context.propCount.count++;