Write the PR description

Opening a pull request someone else has to review.

Write a pull request description for this change, aimed at a reviewer who has not seen the work.

Sections:
- **What changed** — two or three sentences
- **Why** — the problem this solves, including what happens if we don't
- **How to review** — where to start, which files matter most, which are mechanical
- **How it was tested** — what I verified and how
- **Risks** — what could break, what I am unsure about

Be honest about the risks section. A reviewer who trusts it reviews better.

Diff:

Writing the change up. Commit messages, PR descriptions, and review feedback that lands the way you meant it.