Never add "Co-Authored-By" lines to commits
Comment sparingly. A comment earns its place only by stating something the code cannot: an invariant, a security-relevant ordering, a compatibility trap, or a non-obvious "why". Do not narrate what the code does, restate the function name, tag lines with version or PR numbers, or add banners over self-evident blocks. When in doubt, delete it. Match the comment density of the surrounding file.