explain-diff

Explains a code diff, commit, branch, or PR at three depths — summary (quick triage for humans or AI agents), teach-me (teaching walkthrough for novice coders), or expert (dense expert analysis with a review-focus map highlighting likely bugs, regressions, and design problems). Use when the user asks to "explain this diff", "explain this PR", "what does this change do", "walk me through these changes", or wants to understand a code change before reviewing or merging it. Supports --html for a rich interactive page and "help" for usage. Do NOT use for verified bug-hunting or posting review verdicts — hand off to a dedicated code-review pass for that (e.g. /code-review in Claude Code).