It's a good question. It's hard to understand what all is involved in building something like that until you have to get into the details. You can think of Extism as a layer around wasmtime. There is an ABI of sorts that helps you communicate with the plugin: Send data to it, invoke functions, and get data out. With our system, you don't need to enable WASI to use a plugin. You can invoke functions directly. However, you can use WASI for other purposes. And we are working on a way to do POSIX-like stuff (e.g. programs with a main function that use stdin and stdout).

Because we wrap wasmtime, we can also switch it out. That's how we are able to run the same plugins in the browser. There we use the browsers' implementation.

I think one day we will replace some internal pieces of Extism with pieces of the Component Model spec. As of today it's not in a state where we can do all of this in this many languages.

edit: rewording, grammar