Getting Snowpack to work with the Skypin Rollup plugin

I'm trying to get rollup-plugin-skypin to work with snowpack through snowpack-plugin-rollup-bundle. I have a small project set up like so:

snowpack.config.mjs

// Snowpack Configuration File
// See all supported options: https://www.snowpack.dev/reference/configuration
import { skypin } from 'rollup-plugin-skypin';

/** @type {import("snowpack").SnowpackUserConfig } */
export default {
  mount: {
    src: '/src/'
  },
  plugins: [
    [
      "snowpack-plugin-rollup-bundle",
      {
        extendConfig: (config) => {
          config.inputOptions.plugins.push(skypin())
          config.inputOptions.input = 'index.js'
          config.outputOptions.file = 'dist/index.js'
          config.outputOptions.format = 'esm'
          return config
        }
      }
    ]
  ],
  packageOptions: {
    /* rollup: {
      options: {
        input: 'src/index.js',
        output: {
          file: 'dist/index.js',
          format: 'esm'
        }
      }
    } */
  },
  devOptions: {
    /* ... */
  },
  buildOptions: {
    clean: true
  },
};

package.json

{
  "name": "test",
  "version": "1.0.0",
  "license": "MIT",
  "type": "module",
  "devDependencies": {
    "hueman": "^2.1.3",
    "rollup": "^2.56.3",
    "rollup-plugin-skypin": "^1.1.2",
    "skypin": "^2.0.10",
    "snowpack": "^3.8.8",
    "snowpack-plugin-rollup-bundle": "^0.4.4"
  },
  "scripts": {
    "start": "snowpack dev",
    "build": "snowpack build"
  }
}

index.js

// src/index.js
import { hueman } from 'hueman';

console.log(hueman(100,1.0,0.5));

And then get this error when running yarn build:

[17:48:10] [snowpack] ! optimizing build...
Error fetching module from skypack. Returning empty strings
ReferenceError: fetch is not defined
    at fetchSkypack (file:///C:/test/node_modules/skypin/dist/browser.mjs:52:22)
    at lookup (file:///C:/test/node_modules/skypin/dist/browser.mjs:47:61)
    at skypin (file:///C:/test/node_modules/skypin/dist/browser.mjs:40:18)
    at Object.resolveId (file:///C:/test/node_modules/rollup-plugin-skypin/dist/index.mjs:27:31)
    at C:\test\node_modules\rollup\dist\shared\rollup.js:20218:25
[17:48:10] [snowpack-plugin-rollup-bundle] Error: Entry module cannot be external (index.js).
error Command failed with exit code 1.

What does this error mean? Is it possible to get everything to work together?

Turns out this functionality is built into Snowpack, but took some digging to find it.

https://github.com/TropicalRaisel/avalanche