How to communicate between the host and a WebContainer?

Question

I have a use case where I would like my main application to call API endpoints exposed by the application running within the WebContainer (https://webcontainers.io/) and vice versa. When my host server is running locally at localhost:3000 and I call fetch("http://localhost:3000/api/...") from within the WebContainer, obviously it doesn't work, because that API endpoint does not exist within the container.

I already thought of a few rather "hacky" solutions, such as:

• Writing a file to the WebContainer's file system whenever I want to communicate with it, and polling for changes within the WebContainer.
• Using some sort of reverse proxy (e.g. ngrok), so that e.g. "myapp.example.com" is forwarded to my host application running on localhost, and then I could just fetch "myapp.example.com" from within the WebContainer. I already tried it out and this does actually work using ngrok, but it feels much more complicated than necessary.

But there must be a better solution for this kind of basic HTTP communication between host and container. How do I do this?