I have. I thought it was okay, but it wasn't really the radical departure from other coding harnesses that I was looking for. Perhaps I could have made it that with more customization, I'm not sure.

My own harness doesn't provide the agent with shell access, so everything has to go through focused tools with limited functionality. There's also a navigator mode where the agent has no writable tools at all, instead it monitors the project for changes you make in your regular editor and comments on them in real-time. That stuff seemed easier to implement from the ground up.