How to write commits and open pull requests in the sb repository — commit message structure (previous behavior, why it was a problem, what changed, how it's tested), branching, and PR conventions. Use whenever you are about to commit changes or open a PR.
How to tackle any implementation task in the sb repository — workflow, design-first discipline, commit/PR scoping, testing, and code-quality bar. Use whenever the user asks you to start working on a task, whether it comes from MODERNIZATION.md or any other scoping document. Invoke at the very start, BEFORE writing any implementation code.