I am about to start a bigger project with several subprojects and want to be a human in the loop of otherwise fairly automated loop, which should ideally use different agents for different roles (coding, design, testing, supervision, etc). I know this approach is becoming increasingly common and I wonder if there's already some tooling that facilitates that? Or do you simply use some specific model as a coordinator?

https://googlecloudplatform.github.io/scion/overview/

OpenCode subagents

In my experience, I've gone back to basics and want to make them really good before going back up to multi-agent. This is why I'm using opencode now, one top-level agent, no message passing. Scion can then run these OC agent trees and they can send messages to each other. If you don't have the basics in a good place, they will go off the rails and you will burn more tokens.

There are some opencode plugins that take things further. Keeps things simple and understandable first, then move up the stack. (imo)

try AG2