fix: keep source Code Mode worker self-contained

A direct runtime import of the session package made the unbuilt worker depend on sibling lib output. Use a parity-tested local JSON snapshotter and pin the isolated source closure with a real-worker test.

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 })
+  }
+})