Canon PR Review — Top 20 Tier 2 Practices

Scores a PR against 20 LLM-enforceable practices from seminal engineering books, across four dimensions. Each dimension scored 0-5. Decision: APPROVE (all ≥ 3), REQUEST_CHANGES (any < 3 but none < 1), BLOCK (any < 1 or security violation).

Phase 0: Fetch PR diff and context

# Auto-detect repo from cwd if not specified
git remote get-url origin 2>/dev/null

# Fetch PR diff (GitHub.com)
gh pr view <NUMBER> --json title,body,additions,deletions,changedFiles,baseRefName,headRefName
gh pr diff <NUMBER>