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FA-82371 / Chess move legality / Open access

Rays run onto a ninth file and rank · case 01

A rook on a1 is offered "i1" and "a9".

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The edge test uses inclusive upper bounds of 8 for zero-based coordinates.

THE FAILURE

The edge test uses inclusive upper bounds of 8 for zero-based coordinates.

Unsuccessful approach: A strict lower bound on the rank drops every first-rank square.

Case contract

Input: {"board", "from": square of a rook, bishop or queen}. Return the sorted pseudo-legal destinations: walk each ray until the edge; an empty square is added, an enemy piece is added and ends the ray, a friendly piece ends the ray without being added.

Why this case matters

Move validators gate every move in engines, servers and arbiters; accepting an illegal move or rejecting a legal one corrupts the game record.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    b=x['board']; sq=x['from']; p=b[sq]
    f,r=ord(sq[0])-97,int(sq[1])-1
    dirs={'r':[(1,0),(-1,0),(0,1),(0,-1)],'b':[(1,1),(1,-1),(-1,1),(-1,-1)]}
    dirs['q']=dirs['r']+dirs['b']
    out=[]
    for df,dr in dirs[p.lower()]:
        cf,cr=f+df,r+dr
        while 0<=cf<=8 and 0<=cr<=8:
            t=chr(97+cf)+str(cr+1)
            occ=b.get(t)
            if occ is None:
                out.append(t)
            else:
                if occ.isupper()!=p.isupper(): out.append(t)
                break
            cf+=df; cr+=dr
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6'])],
 [('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'error:' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
rook blocked by enemy['a2', 'a3', 'b1']['a2', 'a3', 'b1']Passed
rook behind enemy['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']Passed
bishop corner['e4', 'f3', 'g2', 'i2']['e4', 'f3', 'g2']Failed
bishop centre['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']Passed
queen boxed[][]Passed
queen open['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5', 'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5', 'i5']['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5', 'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']Failed
black rook top edge['f8', 'g8', 'h5', 'h6', 'h7', 'h9', 'i8']['f8', 'g8', 'h5', 'h6', 'h7']Failed
queen along diagonal capture['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6', 'i1']['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']Failed

SHA-256 / 8c76d43a5ce4923e1152ebea09c3c94ad899a3eeb9b34c394f360e2b8ee1a255

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    b=x['board']; sq=x['from']; p=b[sq]
    f,r=ord(sq[0])-97,int(sq[1])-1
    dirs={'r':[(1,0),(-1,0),(0,1),(0,-1)],'b':[(1,1),(1,-1),(-1,1),(-1,-1)]}
    dirs['q']=dirs['r']+dirs['b']
    out=[]
    for df,dr in dirs[p.lower()]:
        cf,cr=f+df,r+dr
        while 0<=cf<8 and 0<cr<8:
            t=chr(97+cf)+str(cr+1)
            occ=b.get(t)
            if occ is None:
                out.append(t)
            else:
                if occ.isupper()!=p.isupper(): out.append(t)
                break
            cf+=df; cr+=dr
    return sorted(out)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6'])],
 [('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('rook behind enemy',
   {'board': {'b4': 'b', 'd4': 'R', 'd6': 'p', 'd8': 'k', 'f4': 'P'}, 'from': 'd4'},
   ['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])],
 [('rook blocked by enemy', {'board': {'a1': 'R', 'a3': 'p', 'c1': 'N'}, 'from': 'a1'},
   ['a2', 'a3', 'b1']),
  ('bishop corner', {'board': {'e4': 'P', 'h1': 'b'}, 'from': 'h1'}, ['e4', 'f3', 'g2']),
  ('bishop centre',
   {'board': {'b2': 'P', 'b6': 'P', 'd4': 'B', 'f6': 'n', 'g1': 'q'}, 'from': 'd4'},
   ['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']),
  ('queen boxed',
   {'board': {'d1': 'K', 'd2': 'P', 'e1': 'Q', 'e2': 'P', 'f1': 'B', 'f2': 'P'}, 'from': 'e1'},
   []),
  ('queen open', {'board': {'a5': 'R', 'd5': 'q', 'd7': 'p', 'g8': 'P'}, 'from': 'd5'},
   ['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5',
    'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']),
  ('black rook top edge', {'board': {'e8': 'k', 'h5': 'P', 'h8': 'r'}, 'from': 'h8'},
   ['f8', 'g8', 'h5', 'h6', 'h7']),
  ('queen along diagonal capture',
   {'board': {'a3': 'n', 'c1': 'Q', 'c3': 'P', 'h6': 'r'}, 'from': 'c1'},
   ['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']),
  ('bishop sw ray', {'board': {'c2': 'r', 'f5': 'B', 'h7': 'p'}, 'from': 'f5'},
   ['c2', 'c8', 'd3', 'd7', 'e4', 'e6', 'g4', 'g6', 'h3', 'h7'])]]
for label, args, expected in fixtures[N-1]:
    try:
        actual = solve(args)
    except Exception as exc:
        actual = 'error:' + type(exc).__name__
    check(label, actual, expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
rook blocked by enemy['a2', 'a3']['a2', 'a3', 'b1']Failed
rook behind enemy['b4', 'c4', 'd2', 'd3', 'd5', 'd6', 'e4']['b4', 'c4', 'd1', 'd2', 'd3', 'd5', 'd6', 'e4']Failed
bishop corner['e4', 'f3', 'g2']['e4', 'f3', 'g2']Passed
bishop centre['c3', 'c5', 'e3', 'e5', 'f2', 'f6']['c3', 'c5', 'e3', 'e5', 'f2', 'f6', 'g1']Failed
queen boxed[][]Passed
queen open['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5', 'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h5']['a2', 'a5', 'a8', 'b3', 'b5', 'b7', 'c4', 'c5', 'c6', 'd1', 'd2', 'd3', 'd4', 'd6', 'e4', 'e5', 'e6', 'f3', 'f5', 'f7', 'g2', 'g5', 'g8', 'h1', 'h5']Failed
black rook top edge['f8', 'g8', 'h5', 'h6', 'h7']['f8', 'g8', 'h5', 'h6', 'h7']Passed
queen along diagonal capture['a3', 'b2', 'c2', 'd2', 'e3', 'f4', 'g5', 'h6']['a1', 'a3', 'b1', 'b2', 'c2', 'd1', 'd2', 'e1', 'e3', 'f1', 'f4', 'g1', 'g5', 'h1', 'h6']Failed

SHA-256 / bd063c35e76000917d69fd04e0f0f0166d5dde0763ee9d05281b61aa23f8e7cd

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic toy model with an explicitly stated contract; boards are {square: piece} with white upper-case and black lower-case pieces; no claim of full FIDE Laws conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:11.467056+00:00.

Case digest / 9ed124341739bb372a2727aca150e5abfa86f6250233c9093a324dac610411d5