# Duplicate Chess

A local, single-operator browser sandbox for **duplicate chess** — a four-player
chess variant invented by Andrew Freiberg. Four players (North, South, East, West)
and four boards (NW, NE, SW, SE); each player controls one colour on two boards and
must play the identical move on both. A captured piece leaves a frozen "ghost" twin
on the player's other board.

This tool puts all four boards on one screen as a rotated "compass", enforces the
synchronized-move coupling, renders ghosts, shows the move-legality intersection,
and detects the endgame.

## Develop

```
pnpm install
pnpm dev      # run the dev server
pnpm build    # production build
pnpm test     # run the engine test suite (vitest)
```

`pnpm exec svelte-check --tsconfig ./tsconfig.json` typechecks the Svelte/TS code.

## Design

See `docs/superpowers/specs/2026-05-19-duplicate-chess-design.md` for the full design,
and `docs/superpowers/plans/2026-05-19-duplicate-chess-sandbox.md` for the build plan.

This is v1 — a local sandbox. Networked multiplayer, AI opponents, and a free
position editor are explicitly out of scope (see the spec, §7).