That's pretty right, with the addition that other things can target Browsix (like the gopherjs toolchain). Emscripten provides default implementations of a bun

That's pretty right, with the addition that other things can target Browsix (like the gopherjs toolchain). Emscripten provides default implementations of a bunch of syscalls (and even a way to embed a file system), and we override those to instead do actual syscalls to a shared kernel (running in JS)