I did a similar system myself, then I run evals on it and found that the planning ceremony is mostly useless, claude can deal with simple prose, item lists, checkbox todos, anything works. The agent won't be a better coder for how you deliver your intent.

But what makes a difference is running plan review and work review agent, they fix issues before and after work. Both pull their weight but the most surprising is the plan-review one. The work review judge reliably finds bugs to fix, but not as surprising in its insights. But they should run from separate subagents not main one because they need a fresh perspective.

Other things that matter are 1. testing enforcement, 2. cross task project memory. My implementation for memory is a combination of capturing user messages with a hook, append only log, and keeping a compressed memory state of the project, which gets read before work and updated after each task.