Push rejected after user edited README on GitHub web UI

When a user edits files directly on github.com while you prepare local commits, git push is rejected even though git status only says 'ahead 1' (the remote ref is stale until you fetch). Run git fetch first, inspect git log main..origin/main to see the web commits, then git rebase origin/main and push normally; never force-push over them. Also: GitHub renders ```mermaid fenced blocks natively, so they beat hand-drawn ASCII box diagrams in a README, where box-drawing characters easily come out misaligned.