explain-why

Find out why code or infrastructure is the way it is (a design choice, a threshold, a workaround, or a regression) from git history, GitHub PRs and issues, ADRs, phase docs, CHANGELOG, CLAUDE.md/AGENTS.md, and memory, and report each claim at a stated confidence (found, inferred, unknown) with a citation. Read-only. A Sonnet digger works the git and PR history. Before a change, it ends with a Preserve / Change / Avoid / Risk set. Triggers on "/explain-why", "why does X work this way", "why did we pick Y", "where did this number come from", or "is it safe to remove this". Optional leading level. Use explain-how for runtime behavior.