I just use /brainstorming from https://github.com/obra/superpowers/tree/main

Then I tell it to write a high level plan. And then rum subagents to create detailed plans from each of the steps in the high-level one. All olans must include the what, the why, and the how.

Works surprisingly well, especially for greenfield projects.

You have to manually revie the code though. No amount of agentic code review will fix the idiocy LLMs routinely produce.