[margani]

Closes #357

The owner said yes in chat (2026-10-19). Thanks to @unmashedpotatoes for the suggestion and for the link to the Spanish draughts rules.

What it is. Draughts on the 32 dark squares of an 8×8 board, against the AI at three levels or two players on one phone. The daily challenge is a classic game from a seeded four-ply opening against the hard AI, like Reversi's.

Two rule sets, chosen with a picker:

• Classic checkers (English draughts):
  • men step diagonally forward;
  • jumps are compulsory and must run to the end;
  • a jump that crowns a man ends the move;
  • kings step one square, backwards too.
• Spanish draughts, from the rules the issue linked (ludoteka.com, read for this PR):
  • kings fly along the whole diagonal and capture from a distance, landing on any empty square beyond;
  • a capture must take the most pieces (quantity rule), then the most kings (quality rule).
• Draws: after 80 plies (classic) or 40 king moves (Spanish) without a capture or a man moving.
• Not implemented from the Spanish rules: draw by agreement, threefold repetition, and the "three kings against one in 13 moves" rule.

The AI. Negamax with alpha-beta, extending forced captures. Easy looks 1 ply ahead with a lot of noise, medium 3, hard 7. I measured it before writing the test bands, 8–10 games per pairing:

	classic	Spanish
hard vs easy	8–0	8–0
hard vs medium	8–0	7–0, 1 draw
medium vs easy	7–0, 1 draw	8–0

The slowest hard move took 367 ms on this laptop.

Page

• Canvas board in the core's .ch-fit / .ch-split layout (Games use only part of larger screens (7-inch phones, tablets, laptops) #359) from the start, and the canvas checks both sides before reusing its backing.
• Tap a piece, then its landing square. On a multiple jump, tap each landing in turn. Pieces that can move are ringed, and "You must jump" shows when a capture is compulsory.
• Keyboard: arrows, Space/Enter, Esc to drop a pick (before Esc would leave the game), U/Ctrl+Z to undo.
• Three awards: ck-win, ck-hard, ck-clean (win without losing a piece).
• Accent #B82066: ΔE 22 from the nearest game, white text 6.1:1.
• games.json, README (en and fa), and the five store descriptions (35 games). I trimmed the German and Spanish texts elsewhere, so they stay under Play's 4000 characters: 3987 and 3975.

Proof

• 37 checks in testCheckers(). Rules: start position, men forward only, compulsory and complete jumps, crowning ends a jump, win by blocking or capture, both draw counts, undo back to the start. Spanish: flying moves and distant captures, the quantity and quality rules, a whole Spanish AI game. Plus AI bands, the daily seed and the page wiring.
• Mutations, each caught by its own check:
  • captures made optional;
  • jumps that stop after one;
  • a crowning that doesn't end the jump;
  • no quantity rule;
  • no quality rule;
  • kings that never fly.
    The first mutation went uncaught at first, because the test position put the jumping piece first in board order. I moved the free man before it, and that version is in the test.
• node tools/test.js: همه‌ی 4186 بررسی سبز; MIN_CHECKS is now 4185. tools/browser-check.sh: 36 of 36 pages.
• Clicks in Playwright:
  • a move against the AI: the AI replied, at 390×844 and 1280×800;
  • a double jump tapped landing by landing: rival men 3 → 3 → 1, the turn passes;
  • a Spanish king flying from d5 to b2.
    No page errors.
• Visual check: 390×844, 844×390, 600×960 and 1280×800, light Persian and dark English. Nothing clips or scrolls.

Not tested: a real phone. The bot's speed on a slow phone is estimated from this laptop.

🤖 Generated with Claude Code

https://claude.ai/code/session_01VoRrYWfb9CHLaEtJPXc4HH

[margani]

Diff review

• Engine: pure, between the ENGINE markers. moves() lifts the moving piece off its square while searching for jumps, so a king can pass back over its own starting square. Captured pieces stay on the board until the move ends, so none is jumped twice and they block a flying king, as in both rule sets.
• Spanish quantity rule: it applies across all pieces, not per piece. moves() collects every capture first, then filters.
• The page's pick flow: candidates are the legal moves whose path starts with the landings tapped so far. A move is played when one of them is fully matched. A path pins down its captures, so the match is unique.
• Daily: always classic, so every player plays the same rules. The rules picker isn't shown in the daily game.
• Core: only the three awards are added. whoosh/thud and the layout classes are untouched.
• Risk: a flying-king position deep in the middlegame makes the hard search wider. The worst move I measured was 367 ms, from simulated games, not every position.