You can do this in opencode and pi (haven't used), by defining your own agents or overriding the built-in ones, so in your primary agent you can disable all tools and give it good instructions for how to delegate

I imagine most harnesses should have a way to do this today, if they don't, get a new one. OpenCode i.e. is highly customizable, Claude and VS Code both support a ton as well including custom agents (though unclear if you can create custom top-level in claude-code)

https://opencode.ai/docs/agents/

https://code.claude.com/docs/en/sub-agents

https://code.visualstudio.com/docs/agent-customization/custo...