I'm trying to use worker threads in my API route using the app router. Specifically, I have a piece of code that uses threads (https://www.npmjs.com/package/threads) to run some CPU intensive operations in a worker thread. Originally, my code looked like this:

import { Pool, spawn, Worker } from "threads";
const pool = Pool(() => spawn(new Worker("./cryptWorker.js"), { timeout: 10 * MINUTES }), 8);

This resulted in the following error:

Error: Cannot find module '<path>/.next/server/app/schema/cryptWorker.js'

I understood this to mean that Webpack never bundled/copied the worker code anywhere, which would make sense since it's not directly imported or referenced other than by a string.
Looking up how workers should be used in Webpack 5, I refactored the code to this:

import { Pool, spawn } from "threads";
import { Worker } from "node:worker_threads";
const pool = Pool(() => spawn(new Worker(new URL("./cryptWorker.js", import.meta.url)), { timeout: 10 * MINUTES }), 8);

The error I got now was slightly different:

Error: Cannot find module '/_next/_rsc_backend_dist_out_utils_cryptWorker_js.js'

This is promising, it's definitely being picked up by Webpack now. I can also see the file in .next/server. However, I'm not sure where to go from here. What is the /_next directory it's looking it up in? Is this an alias for .next/server or something different? Any help would be appreciated!