vm2 is a sandbox library for running untrusted JavaScript in Node.js. In versions >= 3.10.0 and <= 3.11.7, Promises returned from the host realm into the sandbox are not marked as handled at the bridge boundary; only Promises created inside the sandbox are wrapped with a rejection-swallowing handler (lib/setup-sandbox.js), and the bridge only installs host-side rejection sanitizers when sandbox code calls .then/.catch/.finally. As a result, code running in the sandbox can invoke a host function that returns a rejected Promise (for example events.once() exposed via the NodeVM events builtin, or any embedder-provided Promise-returning API) and simply ignore the return value, leaving the host Promise unhandled so that Node.js's default unhandled-rejection behavior terminates the host process. This is an incomplete fix of GHSA-hw58-p9xv-2mjh. The issue is fixed in version 3.11.8.

Affected: npm: vm2

## Summary

vm2 current head (`v3.11.5`, commit `7a1f5100b96f48d34e0fe104ab37c0acc5944f92`) can still be used to terminate the host Node.js process when sandbox code calls a host-realm function that returns a rejected host Promise and then ignores the returned value.

This is an incomplete-fix variant of the `GHSA-hw58-p9xv-2mjh` unhandled rejection hardening. The `localPromise` constructor now catches and consumes sandbox-created unhandled rejections, but host Promises returned across the bridge are not marked handled at the bridge boundary. If the sandbox does not attach `.catch()` or `.then(..., onRejected)`, Node's default unhandled rejection behavior terminates the host process.

## Technical Details

`lib/setup-sandbox.js` hardens sandbox-created Promises by wrapping the executor and attaching a benign swallow tail:

```js apply(globalPromisePrototypeThen, this, [undefined, localPromiseSwallow]); ```

That only applies to `localPromise` instances created inside the sandbox.

Host-returned Promises cross the membrane through the bridge apply path. The bridge wraps callbacks when sandbox code later calls `.then`, `.catch`, or `.finally` on a host Promise:

```js bridge.setHostPromiseSanitizers(e => handleException(from(e)), from); ```

However, if sandbox code ignores the returned host Promise, no host-side rejection handler is attached. The original host Promise remains unhandled and Node terminates the host process under the default unhandled-rejection behavior.

`Node…