diff --git a/packages/code-runtime/code-runtime-worker/README.md b/packages/code-runtime/code-runtime-worker/README.md
index cc49c2f723..bfa19b1189 100644
--- a/packages/code-runtime/code-runtime-worker/README.md
+++ b/packages/code-runtime/code-runtime-worker/README.md
@@ -29,7 +29,7 @@ Every field is validated and defaulted; `maxOutputBytes` is a safe integer of at
 
 ## The worker entry, unbuilt and built
 
-Source mode loads erasable-only `src/worker.ts` through Node's native type stripping. Built mode passes the sibling `lib/worker.cjs` as a filesystem path because pkg's VFS Worker hook expects CommonJS; the same path works under ordinary Node. `tests/built-lib.e2e.ts` pins the real load path required by [docs/testing.md](../../../docs/testing.md).
+Source mode loads erasable-only `src/worker.ts` through Node's native type stripping. Its transitive runtime closure contains only Node built-ins and relative source modules, so a fresh checkout never requires a sibling workspace package's unbuilt `lib/` export. The worker-local JSON snapshotter is parity-tested against the session-owned canonical boundary; the host repeats canonical validation after structured clone. Built mode passes the sibling `lib/worker.cjs` as a filesystem path because pkg's VFS Worker hook expects CommonJS; the same path works under ordinary Node. `tests/built-lib.e2e.ts` pins the real load path required by [docs/testing.md](../../../docs/testing.md).
 
 The SDK surface is the default/named `WorkerCodeRuntime` class plus `Config`. The operational `./worker` subpath exists only as the packaged spawn entry; the wire protocol and bootstrap helpers are source-private implementation details.
 
diff --git a/packages/code-runtime/code-runtime-worker/src/bootstrap.ts b/packages/code-runtime/code-runtime-worker/src/bootstrap.ts
index e62ddd405e..45c8a4d2d2 100644
--- a/packages/code-runtime/code-runtime-worker/src/bootstrap.ts
+++ b/packages/code-runtime/code-runtime-worker/src/bootstrap.ts
@@ -6,8 +6,8 @@
  */
 
 import { inspect } from 'node:util'
-import { snapshotJsonValue } from '@deepseek-ai/dsh-session'
 import type { DoneMessage, ReplyMessage, WorkerBootData, WorkerToHost } from './protocol.ts'
+import { snapshotCodeJsonValue } from './worker-json.ts'
 
 /** The port surface the bootstrap needs — satisfied by `parentPort` and by the tests' fake. */
 export interface BootstrapPort {
@@ -157,7 +157,7 @@ export function prepareCompletion(value: unknown, maxOutputBytes: number): Omit<
   if (value === undefined) return {}
   let snapshot: unknown
   try {
-    snapshot = snapshotJsonValue(value)
+    snapshot = snapshotCodeJsonValue(value)
   } catch {
     snapshot = undefined
   }
diff --git a/packages/code-runtime/code-runtime-worker/src/worker-json.ts b/packages/code-runtime/code-runtime-worker/src/worker-json.ts
new file mode 100644
index 0000000000..eec80184f6
--- /dev/null
+++ b/packages/code-runtime/code-runtime-worker/src/worker-json.ts
@@ -0,0 +1,67 @@
+/** Lossless-JSON snapshots for the dependency-free source worker closure. @module @deepseek-ai/dsh-code-runtime-worker/worker-json */
+
+import type { CodeJsonValue } from '@deepseek-ai/dsh-code-runtime'
+
+/**
+ * Validate and detach one worker-boundary value without loading another
+ * workspace package at runtime. This mirrors the session-owned canonical
+ * JSON boundary while remaining safe to import from the unbuilt worker.
+ *
+ * @param value - the candidate completion value.
+ * @returns a detached lossless-JSON snapshot, or `undefined` when invalid.
+ */
+export function snapshotCodeJsonValue(value: unknown): CodeJsonValue | undefined {
+  const active = new Set<object>()
+
+  const within = <T extends CodeJsonValue>(source: object, build: () => T | undefined): T | undefined => {
+    if (active.has(source)) return undefined
+    active.add(source)
+    try {
+      return build()
+    } finally {
+      active.delete(source)
+    }
+  }
+
+  const copy = (candidate: unknown): CodeJsonValue | undefined => {
+    if (candidate === null) return null
+    if (typeof candidate === 'boolean' || typeof candidate === 'string') return candidate
+    if (typeof candidate === 'number') {
+      return Number.isFinite(candidate) && !Object.is(candidate, -0) ? candidate : undefined
+    }
+    if (typeof candidate !== 'object') return undefined
+
+    if (Array.isArray(candidate)) {
+      if (Object.getPrototypeOf(candidate) !== Array.prototype) return undefined
+      return within(candidate, () => {
+        const result: CodeJsonValue[] = []
+        for (let index = 0; index < candidate.length; index++) {
+          if (!Object.hasOwn(candidate, index)) return undefined
+          const item = copy(candidate[index])
+          if (item === undefined) return undefined
+          result.push(item)
+        }
+        return result
+      })
+    }
+
+    const prototype = Object.getPrototypeOf(candidate) as unknown
+    if (prototype !== Object.prototype && prototype !== null) return undefined
+    return within(candidate, () => {
+      const result: Record<string, CodeJsonValue> = {}
+      for (const key of Object.keys(candidate)) {
+        const item = copy((candidate as Record<string, unknown>)[key])
+        if (item === undefined) return undefined
+        Object.defineProperty(result, key, {
+          value: item,
+          enumerable: true,
+          configurable: true,
+          writable: true,
+        })
+      }
+      return result
+    })
+  }
+
+  return copy(value)
+}
diff --git a/packages/code-runtime/code-runtime-worker/tests/source-worker.compat.spec.ts b/packages/code-runtime/code-runtime-worker/tests/source-worker.compat.spec.ts
new file mode 100644
index 0000000000..5b71a9a94a
--- /dev/null
+++ b/packages/code-runtime/code-runtime-worker/tests/source-worker.compat.spec.ts
@@ -0,0 +1,36 @@
+import { copyFile, mkdtemp, rm } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+import { Worker } from 'node:worker_threads'
+import { expect, it } from 'vitest'
+
+/**
+ * Prove the unbuilt worker is a self-contained source closure. Copying it out
+ * of the workspace makes any package runtime import fail even when local
+ * `lib/` artifacts happen to exist.
+ */
+it('boots the source worker without workspace package outputs', async () => {
+  const directory = await mkdtemp(join(tmpdir(), 'dsh-code-source-worker-'))
+  let worker: Worker | undefined
+  try {
+    const files = ['worker.ts', 'bootstrap.ts', 'protocol.ts', 'worker-json.ts']
+    await Promise.all(files.map(async (file) => {
+      await copyFile(new URL(`../src/${file}`, import.meta.url), join(directory, file))
+    }))
+
+    worker = new Worker(join(directory, 'worker.ts'), {
+      workerData: { code: 'return { answer: 42 }', namespaces: [], maxOutputBytes: 65_536 },
+      env: {},
+      execArgv: [],
+    })
+    const message = await new Promise<unknown>((resolve, reject) => {
+      worker?.once('message', resolve)
+      worker?.once('error', reject)
+    })
+
+    expect(message).toEqual({ type: 'done', value: { answer: 42 } })
+  } finally {
+    if (worker) await worker.terminate()
+    await rm(directory, { recursive: true, force: true })
+  }
+})
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
new file mode 100644
index 0000000000..3f717599b7
--- /dev/null
+++ b/packages/code-runtime/code-runtime-worker/tests/worker-json.spec.ts
@@ -0,0 +1,87 @@
+import { describe, expect, it } from 'vitest'
+import { snapshotJsonValue } from '@deepseek-ai/dsh-session'
+import { snapshotCodeJsonValue } from '../src/worker-json.ts'
+
+describe('snapshotCodeJsonValue', () => {
+  it('matches the canonical scalar boundary', () => {
+    const unsupported = [undefined, 1n, Symbol('value'), () => 1]
+    for (const value of [null, false, 'text', 1.25, -0, Number.NaN, Number.POSITIVE_INFINITY, ...unsupported]) {
+      expect(snapshotCodeJsonValue(value)).toEqual(snapshotJsonValue(value))
+    }
+  })
+
+  it('detaches dense arrays and plain or null-prototype records', () => {
+    const shared = { value: 1 }
+    const nullPrototype = Object.assign(Object.create(null) as Record<string, unknown>, { shared })
+    const source = { list: [nullPrototype, shared], alias: shared }
+
+    const snapshot = snapshotCodeJsonValue(source) as Record<string, unknown>
+    shared.value = 2
+
+    expect(snapshot).toEqual({ list: [{ shared: { value: 1 } }, { value: 1 }], alias: { value: 1 } })
+    expect(snapshot).not.toBe(source)
+    expect((snapshot.list as unknown[])[0]).not.toBe(nullPrototype)
+    expect(snapshot.alias).not.toBe(shared)
+  })
+
+  it('reads each accepted slot once and preserves a literal __proto__ key', () => {
+    let objectReads = 0
+    let arrayReads = 0
+    const source = Object.create(null) as Record<string, unknown>
+    Object.defineProperty(source, '__proto__', {
+      enumerable: true,
+      get: () => {
+        objectReads += 1
+        return { safe: true }
+      },
+    })
+    const array = new Array<unknown>(1)
+    Object.defineProperty(array, 0, {
+      enumerable: true,
+      get: () => {
+        arrayReads += 1
+        return arrayReads === 1 ? source : undefined
+      },
+    })
+
+    const snapshot = snapshotCodeJsonValue(array) as Record<string, unknown>[]
+
+    expect(objectReads).toBe(1)
+    expect(arrayReads).toBe(1)
+    expect(Object.getPrototypeOf(snapshot[0])).toBe(Object.prototype)
+    expect(Object.hasOwn(snapshot[0]!, '__proto__')).toBe(true)
+    expect(snapshot[0]?.['__proto__']).toEqual({ safe: true })
+  })
+
+  it('rejects exotic containers, sparse arrays, cycles, and invalid children', () => {
+    class ExoticObject {
+      readonly value = 1
+    }
+    class ExoticArray extends Array<number> {}
+    const cyclic: Record<string, unknown> = {}
+    cyclic.self = cyclic
+
+    for (const value of [
+      new ExoticObject(),
+      new Map([['value', 1]]),
+      new ExoticArray(1),
+      new Array(1),
+      cyclic,
+      [undefined],
+      { value: undefined },
+    ]) {
+      expect(snapshotCodeJsonValue(value)).toBeUndefined()
+    }
+  })
+
+  it('propagates a throwing getter and releases its recursion guard', () => {
+    const failure = new Error('getter failed')
+    const source = Object.defineProperty({}, 'value', {
+      enumerable: true,
+      get: () => { throw failure },
+    })
+
+    expect(() => snapshotCodeJsonValue(source)).toThrow(failure)
+    expect(snapshotCodeJsonValue({ after: true })).toEqual({ after: true })
+  })
+})