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Implement Check Detection System#79

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walshb421 wants to merge 6 commits into
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issue-76-check-detection
Open

Implement Check Detection System#79
walshb421 wants to merge 6 commits into
mainfrom
issue-76-check-detection

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@walshb421 walshb421 commented Jan 12, 2026

Summary

This PR implements a comprehensive check detection system for the chess engine, addressing issue #76.

New Methods Added to ChessBoard

  • get_king_position(color): Returns the (row, col) tuple of the specified color king
  • is_square_attacked(square, by_color): Returns True if any piece of the attacking color can reach the given square
  • is_in_check(color): Returns True if the king of the specified color is currently in check
  • would_be_in_check(move, color): Simulates a move and checks if it would leave the king in check

Updated Move Validation

  • can_move_piece(): Now filters out any move that would leave the king in check
  • castling_check(): Updated to enforce all castling rules (cannot castle out of, through, or into check)

Game State

  • Added in_check boolean to the game state JSON

How to Test

  1. Basic Check Detection

    • Load FEN: rnbqkbnr/pppp1ppp/8/4p3/6P1/5P2/PPPPP2P/RNBQKBNR b KQkq - 0 2
    • Move black queen to h4 (Qh4+) - white king should be in check
    • White should only be able to make moves that escape check

  2. Pinned Piece

    • Load FEN: rnb1kbnr/pppp1ppp/8/4p3/7q/5NP1/PPPPP2P/RNBQKB1R w KQkq - 0 3
    • The g3 pawn is pinned - try moving it (should be blocked)

  3. Castling Through Check

    • Load FEN: r3k2r/pppp1ppp/8/4p3/1b6/8/PPPPPPPP/R3K2R w KQkq - 0 1
    • White cannot castle queenside (d1 is attacked by bishop)

Closes #76

MCP Agent added 6 commits January 11, 2026 01:28
Add FEN test fixtures module
47b58d6 
Add engine/fixtures.py with predefined chess positions for testing:
- Basic positions (starting, empty)
- Checkmate scenarios
- Special moves (en passant, castling)
- Check scenarios
- Pawn promotion positions
- Stalemate and endgame positions
Add FEN support to ChessBoard
7d47f42 
- Add load_fen() method to parse FEN strings and set board state
- Add to_fen() method to export current position as FEN
- Add WebSocket callbacks for load_fen, load_fixture, get_fixtures
- Track en_passant_target for FEN compatibility
- Include turn and FEN in game state JSON
- Update en passant logic to work with FEN-loaded positions
- Convert indentation from tabs to spaces
Add FEN support to chess.js composable
5c07db6 
- Add loadFen() to load arbitrary FEN positions
- Add loadFixture() to load named test fixtures
- Add getFixtures() to request fixture list from server
- Add reactive refs for turn, currentFen, and fixtures
- Update data watcher to handle new state fields
Add DebugPanel component for testing
4ba06c3 
- Display current game state (turn, player, move number)
- Show current FEN with copy-to-clipboard button
- FEN input field to load arbitrary positions
- Dropdown with categorized test fixtures
- Reset board button
- Dark theme styling to match app
Integrate DebugPanel into App.vue
c4c9b85 
- Add DebugPanel component with toggle visibility
- Press D key to show/hide debug panel
- Add sidebar layout for debug panel
- Ignore keypress when typing in input fields
Implement check detection system (closes #76)
85be22b
@walshb421 walshb421 mentioned this pull request Jan 23, 2026
Open
Base automatically changed from add-fen-support to main March 23, 2026 02:24
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