Sum Duel

Quick maths, head to head: https://sumduel.app

Play Online: seven live two-player games, on two devices (both players signed in), server-timed, public or private (password) games, and "Find an opponent" for one-tap matches:

• Duel: the same sums for both of you, separate clocks, +3 s per wrong answer. Fastest time wins.
• The Climb: race up a cliff of 12 ledges that gets harder as you go. A wrong answer slips you down a ledge. First to the top wins.
• Truth or Lie: call each sum true or a lie; the quickest right call scores. First to 7.
• Sprint: 60 seconds of sums. Most right answers wins.
• Missing Number: find the hidden number, like 7 × ? = 42.
• Target: combine the number tiles with + − × ÷ to hit the target. Five puzzles; a skip costs 10 s.
• Bigger: two sums side by side; tap the bigger one. Fifteen pairs, +3 s per wrong tap.

On This Device:

• Climb the Coast: a seaside trail of levels, 12 per area, with stars, coins and a treasure chest at the end of every area.
• The Daily: 20 questions, the same for everyone that day; the first attempt counts.
• Daily VS: race the ghost of anyone who's already played today, or one of three bots. The first race of the day pays a prize.
• Sprint (solo, with a global leaderboard), Pass the Phone (a take-turns Duel on one device) and Little Ones (counting with pictures and a voice, for ages 4 to 6).

Also:

• Coins, hearts and the daily gift: every game pays coins; a Climb the Coast level costs a heart only if you don't make it; hearts refill every 10 minutes or cost a few coins; a 7-day gift calendar.
• Home leaderboard: today's Daily and Sprint top 5, with podiums, on the Arena.
• Players dashboard: once signed in, everyone's game report (games, wins, best scores, activity chart), by display name only.
• Your Colours: four palettes on the Arena and in Preferences (Seaside, Shades of Blue, Shades of Pink and ASCII Mode), each with day and night.
• Accounts: email + password, no confirmation. Every battle goes on your record, with head-to-head stats against each rival.

Static frontend (no build) + Vercel functions + Neon Postgres. Works offline as a PWA. Chat exists in the code but is switched off (api/_features.js).

npm install
vercel env pull .env.local   # DATABASE_URL from the Neon integration
npm run migrate              # idempotent schema (on the live database: check first, apply by hand, before deploying)
vercel dev

Architecture, data flow, design system and deploy notes: see master-ref.md.