Wasmtime implements a remote debugging server, so that you can debug guest programs with a recent build of LLDB. Set breakpoints based on the source language symbols, single-step through wasm opcodes, anything you'd expect: https://docs.wasmtime.dev/examples-debugging-guest.html

Why can’t you?

This! The only way to get to a stable system at least with c/c++ source, where you can hunt bugs, is to have a fairly large unit test coverage. When something fails - add that as test case; run ctest - pray that this is discoverable with tests.

So wasm is a really strange compilation target for systems programming languages.

I mean there _are_ ways to debug it in a browser but they sort of suck.