PR description

Print a markdown PR description for the current branch. Make no GitHub writes, no commits, and no edits to tracked files.

The diff is the source of truth for what changed, and the reviewer can already read it. The description earns its place by carrying why: the problem, the approach, and what no diff reveals. Length tracks the change, and most changes are small.

1. Gather evidence

Establish the base as the merge-base between the current branch and the repository's default branch. Read the commit subjects and bodies on the branch, and the diff against that base.

Collect, where each exists:

• an issue or ticket reference in the branch name, the commit messages, or a PR already open on the branch;
• a template at .github/PULL_REQUEST_TEMPLATE.md, .github/pull_request_template.md, or under .github/PULL_REQUEST_TEMPLATE/;
• contributing guidance covering what a PR description must contain.

Completion criterion: every commit on the branch is accounted for in your understanding of the change, and you know whether a template governs the output.

2. Choose the shape