Using PLANS.md for multi-hour problem solving

# Using PLANS.md for multi-hour problem solving Codex and the `gpt-5.2-codex` model (recommended) can be used to implement complex tasks that take significant time to research, design, and implement. The approach described here is one way to prompt the model to implement these tasks and to steer it towards successful completion of a project. These plans are thorough design documents, and "living documents". As a user of Codex, you can use these documents to verify the approach that Codex will take before it begins a long implementation process. The particular `PLANS.md` included below is very similar to one that has enabled Codex to work for more than seven hours from a single prompt. We enable Codex to use these documents by first updating `AGENTS.md` to describe when to use `PLANS.md`, and then of course, to add the `PLANS.md` file to our repository.