• ✓The whole rule is lib/duel.ts, pure — the screen only decides how big a digit is
• ✓verify:duel makes 339,263 checks over 3,000 duels: a wrong press costs nothing, a question goes to one side at most, and the two scores always add up to the questions taken
• ✓The sums are numbers only, from lib/versus.ts (two Quick Maths sets) — readable from the back of the queue, no new art
• ✓No phones: walk up and press the same screen, or use the keyboard — A S D F and H J K L
• ✓Three wrong in a row on either side is a breath for both, naming nobody
• ✓The booth board always holds both people who just played (boothBoard takes two names)
• ✓Played on 390×844 and 1440×900 by playtest:one-vs-one — every button on both halves is at least 46px
• ✓Two painted buzzers, one a side (today they are BRAND-edged boxes), and two name boardsplanned

✓ = done · ☐ = planned. Every game is built one step at a time like this.