> And what's the public API/stdlib/bindings inside the WASM workers?
Wazero (via Extism) carries the load here. As it stands, the runtime lifts three basic host functions into guest code which enable the RPC-like behaviour, injection of caller-context and basic logging[1], which are in turn referenced in the guest code like in the example[2].
In the reverse direction, guest code exposes it's public APIs via build directives[3], which are handled by the runtime code[4].
Figured that concrete examples might be more helpful here (I hope the formatting works).