Great post and paclet! Glad someone else found my code useful! I know how to make the function that will not block the kernel.

1. To do this you would have to create an asynchronous task directly on the C side, but then the very idea of writing a server only in a top-level language is already broken.
2. You could just make the server run by default on a parallel kernel with ParallelSubmit/LinkCreate and return a task that can be stop the server if it necessary.

I think you can use LinkCreate to

1. Exchange data with the parallel kernel via WSTP
2. To have a possibility to stop the process completely

But then in this case there will be a big overhead related to work via WSTP, so there are some disadvantages here too. In fact, I thought over many variants when I was writing my implementation and came to the conclusion that minimalistic C implementation will be the most efficient.