diff --git a/packages/code-runtime/code-runtime-worker/src/worker-json.ts b/packages/code-runtime/code-runtime-worker/src/worker-json.ts
index 9151d07e7e..d49c26d7d1 100644
--- a/packages/code-runtime/code-runtime-worker/src/worker-json.ts
+++ b/packages/code-runtime/code-runtime-worker/src/worker-json.ts
@@ -2,6 +2,31 @@
 
 import type { CodeJsonValue } from '@deepseek-ai/dsh-code-runtime'
 
+/* jscpd:ignore-start -- the source worker mirrors session JSON helpers without workspace runtime imports */
+/** Whether an array uses one realm's intrinsic `Array.prototype`, not a subclass or forged prototype. */
+function hasPlainArrayPrototype(value: unknown[]): boolean {
+  const prototype: unknown = Object.getPrototypeOf(value)
+  if (!Array.isArray(prototype)) return false
+  const objectPrototype: unknown = Object.getPrototypeOf(prototype)
+  return objectPrototype !== null
+    && !Array.isArray(objectPrototype)
+    && Object.getPrototypeOf(objectPrototype) === null
+}
+
+/** Whether an object is a plain or null-prototype record from any JavaScript realm. */
+function hasPlainObjectPrototype(value: object): boolean {
+  const prototype: unknown = Object.getPrototypeOf(value)
+  return prototype === null || Object.getPrototypeOf(prototype) === null
+}
+
+/** Return every JSON-visible object key, or reject own data JSON would discard. */
+function enumerableStringKeys(value: object): string[] | undefined {
+  const keys = Reflect.ownKeys(value)
+  if (keys.some(key => typeof key !== 'string' || !Object.prototype.propertyIsEnumerable.call(value, key))) return undefined
+  return keys as string[]
+}
+/* jscpd:ignore-end */
+
 /**
  * Validate and detach one worker-boundary value without loading another
  * workspace package at runtime. This mirrors the session-owned canonical
@@ -32,11 +57,12 @@ export function snapshotCodeJsonValue(value: unknown): CodeJsonValue | undefined
     if (typeof candidate !== 'object') return undefined
 
     if (Array.isArray(candidate)) {
-      if (Object.getPrototypeOf(candidate) !== Array.prototype) return undefined
-      if (Reflect.ownKeys(candidate).length !== candidate.length + 1) return undefined
+      if (!hasPlainArrayPrototype(candidate)) return undefined
+      const length = candidate.length
+      if (Reflect.ownKeys(candidate).length !== length + 1) return undefined
       return within(candidate, () => {
         const result: CodeJsonValue[] = []
-        for (let index = 0; index < candidate.length; index++) {
+        for (let index = 0; index < length; index++) {
           if (!Object.hasOwn(candidate, index)) return undefined
           const item = copy(candidate[index])
           if (item === undefined) return undefined
@@ -46,11 +72,12 @@ export function snapshotCodeJsonValue(value: unknown): CodeJsonValue | undefined
       })
     }
 
-    const prototype = Object.getPrototypeOf(candidate) as unknown
-    if (prototype !== Object.prototype && prototype !== null) return undefined
+    if (!hasPlainObjectPrototype(candidate)) return undefined
+    const keys = enumerableStringKeys(candidate)
+    if (keys === undefined) return undefined
     return within(candidate, () => {
       const result: Record<string, CodeJsonValue> = {}
-      for (const key of Object.keys(candidate)) {
+      for (const key of keys) {
         const item = copy((candidate as Record<string, unknown>)[key])
         if (item === undefined) return undefined
         Object.defineProperty(result, key, {
diff --git a/packages/code-runtime/code-runtime-worker/tests/worker-json.spec.ts b/packages/code-runtime/code-runtime-worker/tests/worker-json.spec.ts
index b574e80aff..029b5789ac 100644
--- a/packages/code-runtime/code-runtime-worker/tests/worker-json.spec.ts
+++ b/packages/code-runtime/code-runtime-worker/tests/worker-json.spec.ts
@@ -1,3 +1,4 @@
+import { runInNewContext } from 'node:vm'
 import { describe, expect, it } from 'vitest'
 import { snapshotJsonValue } from '@deepseek-ai/dsh-session'
 import { snapshotCodeJsonValue } from '../src/worker-json.ts'
@@ -24,6 +25,16 @@ describe('snapshotCodeJsonValue', () => {
     expect(snapshot.alias).not.toBe(shared)
   })
 
+  it('accepts intrinsic plain containers from another JavaScript realm', () => {
+    const foreign = runInNewContext('({ object: { nested: [1] }, array: [2, { ok: true }] })') as {
+      object: unknown
+      array: unknown
+    }
+
+    expect(snapshotCodeJsonValue(foreign.object)).toEqual({ nested: [1] })
+    expect(snapshotCodeJsonValue(foreign.array)).toEqual([2, { ok: true }])
+  })
+
   it('reads each accepted slot once and preserves a literal __proto__ key', () => {
     let objectReads = 0
     let arrayReads = 0
@@ -66,6 +77,12 @@ describe('snapshotCodeJsonValue', () => {
     Object.defineProperty(compensatedSparse, 'extra', { value: true })
     const symbolDecorated = [1]
     Object.defineProperty(symbolDecorated, Symbol('extra'), { value: true })
+    const hiddenObject = Object.defineProperty({}, 'hidden', { value: true })
+    const symbolObject = { [Symbol('extra')]: true }
+    const forgedPrototype: unknown[] = []
+    Object.setPrototypeOf(forgedPrototype, null)
+    const forgedArray = [1]
+    Object.setPrototypeOf(forgedArray, forgedPrototype)
 
     for (const value of [
       new ExoticObject(),
@@ -75,6 +92,9 @@ describe('snapshotCodeJsonValue', () => {
       decorated,
       compensatedSparse,
       symbolDecorated,
+      hiddenObject,
+      symbolObject,
+      forgedArray,
       cyclic,
       [undefined],
       { value: undefined },
@@ -83,6 +103,19 @@ describe('snapshotCodeJsonValue', () => {
     }
   })
 
+  it('rejects an array whose getter mutates the validated length', () => {
+    const array = [0, 2]
+    Object.defineProperty(array, 0, {
+      enumerable: true,
+      get: () => {
+        array.length = 1
+        return 1
+      },
+    })
+
+    expect(snapshotCodeJsonValue(array)).toBeUndefined()
+  })
+
   it('propagates a throwing getter and releases its recursion guard', () => {
     const failure = new Error('getter failed')
     const source = Object.defineProperty({}, 'value', {