Generate pull request description

Generate PR description markdown summarizing branch changes vs main

Pre-PR documentation when commit messages are thin and reviewers need executive summary of what changed, why, and what breaks.

• · Current git branch with commits vs main
• · Optional user hint ($ARGUMENTS for custom context)

• · Markdown file: pr-descriptions/branch-name-YYYY-MM-DD.md
• · PR title, what it does, files changed, breaking changes, testing checklist

• · git (log, diff, merge-base, branch commands)

• · Git repo with main branch
• · Current branch has commits ahead of main
• · pr-descriptions/ directory created (mkdir -p)

• · No commits on branch = PR description empty
• · Branch not tracking main = merge-base fails, use HEAD vs main explicitly
• · pr-descriptions/ doesn't exist = mkdir -p must run first
• · Breaking changes not documented = reviewers miss migration guidance

• · Analyzes full diff, not just commit messages
• · Explicitly flags breaking changes with migration guidance
• · Provides testing checklist and folder organization