The actual API isn’t complete yet, so I can’t point you to an example (If you really want you can look at Arsenic.jl to see the C/C++ version, but it’s still a bit of a mess at the moment).
Remote debugging should be fairly simple. You’d just need an extra process:
VS Code <— VS Code protocol —> Debug Adapter ← Regular Julia RPC → Gallium.jl debugger ← ptrace, etc. → debuggee