I once tried to build something similar to your product on top of Codex, and I failed.

But my conclusion on plan mode is slightly different. I agree that plan mode itself may be a dead end, but I still believe there might be another way to achieve the same goal.

When I was building my product, I found that the biggest issue wasn't capability, but taste. The agent could build something that worked, but it often wasn't what I actually wanted. And behind that "taste" is a huge amount of implicit context — preferences, past decisions, product intuition, and trade-offs that live in my head. Distilling all of that into context takes a lot of effort, and I suspect giving it all to a single agent may eventually become overwhelming.

I've been wondering whether a better approach is to have multiple agents with different roles, prompts, and perspectives, and find a way for them to work together efficiently.

It's still just a hypothesis though. There are a lot of complicated coordination problems to figure out, and I don't have the answer yet.