Generated Dockerfile can't build assets installed with `npm --save`

[mrkurt]

Environment

• Elixir version (elixir -v): Elixir 1.17.3 (compiled with Erlang/OTP 27)
• Phoenix version (mix deps): 1.7.14
• Operating system: MacOS, Docker, and Linux

Actual behavior

I've installed xterm.js with npm i @xterm/xterm --save (straight from the phoenix docs), which placed it in assets/node_modules as expected. When I import this in either my app.css or app.js it works as expected when running in development:

@import "@xterm/xterm";

import { Terminal } from '@xterm/xterm';

When I attempt to build this with Docker, however, it fails because .dockerignore includes this:

# Static artifacts - These should be fetched and built inside the Docker image
/assets/node_modules/

Expected behavior

I'd like my Dockerfile to build my assets properly when I follow the docs for adding using an npm.