Interesting project. I am working on a similar solution. Eventually you will run into the following with harnesses, so I wonder how these questions work with your project;

1) Can you define a process other than build -> review -> .. etc. And more importantly, can you define a process that is more complex? For example for each review finding, do X. Or go from end-to-end test, back to build.

2) In your setup, how does a sub-agent prove undeniably, that it's work is complete? Does the "lead" agent just look at the output? If so, it would effectively make the lead an implicit reviewer for all agents, so I don't follow why you would need a review step.

3) Can you have steps in between these agentic processes that do not involve agents?