duplicate_chess/CLAUDE.md

Duplicate Chess

Local browser sandbox for "duplicate chess" — a four-player coupled-board chess variant.

Start Here

Read the latest handoff first: .claude/handoffs/ (most recent file). It has session state, in-progress work, and ordered next steps.

Then check IDEA.md for the project brief, DECISIONS.md for settled choices, and docs/superpowers/specs/2026-05-19-duplicate-chess-design.md for the full design.

Project Identity

A digitization of "duplicate chess," a four-player chess variant invented by Andrew Freiberg (Seth's father — also the inventor of the blind-chess variant behind the sibling blind_chess project). 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 algebraic move on both. A captured piece leaves a frozen, capturable "ghost" twin on the player's other board. Every individual board always remains a legal game of orthodox chess.

This project is a local, single-operator sandbox/visualizer: one screen, all four boards, an engine that enforces the synchronized-move coupling, renders ghosts, and detects the endgame. Its purpose is to let the variant be seen and studied — the inventor's own point is that it cannot be understood from prose alone.

Current State

• Phase: v1 implemented and merged to main — the engine and the compass UI are complete. Not yet manually browser-tested.
• Repo: git.sethpc.xyz/Seth/duplicate_chess (main).
• Deploy target: n/a — runs locally (pnpm install && pnpm dev).
• Stack: Vite + Svelte 5 + TypeScript, chess.js. Single package; engine in src/engine/ (pure, DOM-free; 27 vitest tests passing), UI in src/lib/.
• Commands: pnpm dev (run) · pnpm build · pnpm test (engine) · pnpm exec svelte-check --tsconfig ./tsconfig.json (typecheck).
• Known follow-ups (not blocking): interactive browser test still pending (a human task — svelte-check + manual is the design, see spec §8); history scrubbing is view-only whereas spec §4.3 says truncate-on-move (deviation — confirm which to keep); deserialize trusts the player field on replay; move log has no round numbers. See the latest handoff in .claude/handoffs/.

Conventions

• Inherits homelab conventions from ~/bin/CLAUDE.md (gitea CLI, conventional commits, .claude/handoffs/ for session state).
• The engine (src/engine/) is DOM-free and the single source of truth for game state. The UI never computes legality itself.
• Provisional endgame rules are marked PROVISIONAL in the spec — they are Claude's chosen defaults, not Andrew's rulings. Flag them if revisited.