Cannot find module 'socket.io'

I am aware of the other questions about this issue. The answers on them are of no help, however. I've been dealing with Node and npm for a few years and I've never come across something so confusing. This is my first time dealing with socket.io, however.

I've installed socket.io as a dependency on a git submodule of my project:

npm install --save socket.io

Then I require it:

const io = require("socket.io")(8099);

However, when I attempt to run the app, I get an error:

[error:app 10:31:32.339 C:\Users\<username>\dev\projects\js-ps-app\generator\generator-core\app.js:336:37] Unable to load plugin at 'C:\Users\<username>\dev\projects\js-ps-app\generator\plugins\generator-starter': Could not load plugin at path 'C:\Users\<username>\dev\projects\js-ps-app\generator\plugins\generator-starter': Cannot find module 'socket.io'

When attempting to reference the module relatively:

const io = require(".\\node_modules\\socket.io")(8099);

The error seems to shift to engine.io, which isn't even referenced in my project:

[error:app 10:38:40.630 C:\Users\<username>\dev\projects\js-ps-app\generator\generator-core\app.js:336:37] Unable to load plugin at 'C:\Users\<username>\dev\projects\js-ps-app\generator\plugins\generator-starter': Could not load plugin at path 'C:\Users\<username>\dev\projects\js-ps-app\generator\plugins\generator-starter': Cannot find module 'engine.io'

I am at a loss to know what to do.

For context: This is in the middle of working on Davide Barranca's Native Photoshop Apps video course—Lesson #15, specifically. Adobe Generator is working and connecting to Adobe Photoshop just fine. You can see where this project stands currently at its repo.

For example, here's the main repo's package.json:

{
  "name": "js-ps-app",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "serve": "vue-cli-service serve",
    "build": "vue-cli-service build",
    "lint": "vue-cli-service lint",
    "nwdev": "concurrently --kill-others --raw \"npm:serve\" \".\\node_modules\\.bin\\run .\\nwdev\" --success 'first'",
    "generator": "node --inspect .\\generator\\generator-core\\app -f .\\generator\\plugins -v"
  },
  "dependencies": {
    "@mdi/font": "^3.6.95",
    "core-js": "^3.6.5",
    "roboto-fontface": "*",
    "vue": "^2.6.11",
    "vue-router": "^3.2.0",
    "vue-the-mask": "^0.11.1",
    "vuetify": "^2.2.11",
    "vuex": "^3.4.0"
  },
  "devDependencies": {
    "7zip-bin-win": "^2.2.0",
    "@vue/cli-plugin-babel": "~4.5.0",
    "@vue/cli-plugin-eslint": "~4.5.0",
    "@vue/cli-plugin-router": "~4.5.0",
    "@vue/cli-plugin-vuex": "~4.5.0",
    "@vue/cli-service": "~4.5.0",
    "babel-eslint": "^10.1.0",
    "concurrently": "^5.3.0",
    "eslint": "^6.7.2",
    "eslint-plugin-vue": "^7.1.0",
    "node-sass": "^4.12.0",
    "nw-vue-devtools-prebuilt": "0.0.10",
    "nwjs-builder-phoenix": "^1.15.0",
    "sass": "^1.19.0",
    "sass-loader": "^8.0.2",
    "vue-cli-plugin-vuetify": "~2.0.7",
    "vue-template-compiler": "^2.6.11",
    "vuetify-loader": "^1.3.0"
  }
}

And here's generator-starter's package.json, which is what needs socket.io:

{
  "name": "generator-starter",
  "version": "1.0.0",
  "description": "Blank Adobe Generator Plugin",
  "main": "main.js",
  "generator-core-version": "~3",
  "menu": {
    "id": "generator-starter",
    "label": "Generator Plugin"
  },
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "Davide Barranca",
  "license": "ISC",
  "dependencies": {
    "engine.io": "^4.0.1",
    "socket.io": "^2.3.0"
  }
}

"Running the app" means running npm run generator from the root of the project. It uses node to run app.js inside generator\generator-core, which takes the sibling directory generator\plugins as an argument.

from Cannot find module 'socket.io'