FAILURE MAP
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FA-54201 / Accessibility interaction semantics / Open access

Negative braille pan offsets index from the document end · case 01

Negative braille pan offsets index from the document end.

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

ROOT CAUSE

The pan origin decision in the braille routing adapter violates its declared contract.

THE FAILURE

The pan origin decision in the braille routing adapter violates its declared contract.

Unsuccessful approach: The local repair substitutes max(-1,offset) but still mishandles the regression fixtures.

Case contract

Input [cells,offset,width,route] where cells [source_start,source_end,content,editable]. Clip display window by nonnegative offset and width. Each cell has one display position regardless of content length. Routing uses a zero-based position inside displayed cells; return None if outside window or cell not editable, otherwise [source_start,source_end]. Display contents replace empty cell content with a space; protected content (exact token SECRET) displays a bullet. Return [display,source_ranges,route_result,has_previous,has_next]. Source ranges preserve zero-width insertion cells.

Why this case matters

Offline accessibility bridge model with explicit policy; useful for testing semantic API adapters independently of browser implementations.

1 / The failure

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

N = 1
observations = []
def solve(data):
    cells,offset,width,route = data
    offset,width = offset,max(0,width)
    window = cells[offset:offset+width]
    contents = [('•' if c == 'SECRET' else (c if c else ' ')) for s,e,c,editable in window]
    ranges = [[s,e] for s,e,c,editable in window]
    routed = None
    if 0 <= route < len(window):
        s,e,c,editable = window[route]
        if editable: routed = [s,e]
    return [contents,ranges,routed,offset>0,offset+len(window)<len(cells)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve([[[0,N,'ab',True],[N,N+2,'SECRET',False],[N+2,N+2,'',True]],1,2,1],), [['•',' '],[[N,N+2],[N+2,N+2]],[N+2,N+2],True,False])
check('contract fixture 2', solve([[[0,2,'ab',True],[2,3,'c',True],[3,4,'d',True]],0,2,0],), [['ab','c'],[[0,2],[2,3]],[0,2],False,True])
check('contract fixture 3', solve([[[0,1,'x',False]],0,1,0],), [['x'],[[0,1]],None,False,False])
check('contract fixture 4', solve([[[0,1,'x',True]],0,1,-1],), [['x'],[[0,1]],None,False,False])
check('contract fixture 5', solve([[[0,1,'x',True]],0,1,1],), [['x'],[[0,1]],None,False,False])
check('contract fixture 6', solve([[[0,1,'x',True]],-2,0,0],), [[],[],None,False,True])
check('contract fixture 7', solve([[[0,1,'a',True],[1,2,'b',True]],-1,1,0],), [['a'],[[0,1]],[0,1],False,True])
check('contract fixture 8', solve([[],0,4,0],), [[],[],None,False,False])
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
contract fixture 1[['•', ' '], [[1, 3], [3, 3]], [3, 3], True, False][['•', ' '], [[1, 3], [3, 3]], [3, 3], True, False]Passed
contract fixture 2[['ab', 'c'], [[0, 2], [2, 3]], [0, 2], False, True][['ab', 'c'], [[0, 2], [2, 3]], [0, 2], False, True]Passed
contract fixture 3[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 4[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 5[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 6[[], [], None, False, True][[], [], None, False, True]Passed
contract fixture 7[[], [], None, False, True][['a'], [[0, 1]], [0, 1], False, True]Failed
contract fixture 8[[], [], None, False, False][[], [], None, False, False]Passed

SHA-256 / 4df1f1125c1899790916154184ddc1919463ee96046b2d798459e782e8eb4b70

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(data):
    cells,offset,width,route = data
    offset,width = max(-1,offset),max(0,width)
    window = cells[offset:offset+width]
    contents = [('•' if c == 'SECRET' else (c if c else ' ')) for s,e,c,editable in window]
    ranges = [[s,e] for s,e,c,editable in window]
    routed = None
    if 0 <= route < len(window):
        s,e,c,editable = window[route]
        if editable: routed = [s,e]
    return [contents,ranges,routed,offset>0,offset+len(window)<len(cells)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve([[[0,N,'ab',True],[N,N+2,'SECRET',False],[N+2,N+2,'',True]],1,2,1],), [['•',' '],[[N,N+2],[N+2,N+2]],[N+2,N+2],True,False])
check('contract fixture 2', solve([[[0,2,'ab',True],[2,3,'c',True],[3,4,'d',True]],0,2,0],), [['ab','c'],[[0,2],[2,3]],[0,2],False,True])
check('contract fixture 3', solve([[[0,1,'x',False]],0,1,0],), [['x'],[[0,1]],None,False,False])
check('contract fixture 4', solve([[[0,1,'x',True]],0,1,-1],), [['x'],[[0,1]],None,False,False])
check('contract fixture 5', solve([[[0,1,'x',True]],0,1,1],), [['x'],[[0,1]],None,False,False])
check('contract fixture 6', solve([[[0,1,'x',True]],-2,0,0],), [[],[],None,False,True])
check('contract fixture 7', solve([[[0,1,'a',True],[1,2,'b',True]],-1,1,0],), [['a'],[[0,1]],[0,1],False,True])
check('contract fixture 8', solve([[],0,4,0],), [[],[],None,False,False])
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
contract fixture 1[['•', ' '], [[1, 3], [3, 3]], [3, 3], True, False][['•', ' '], [[1, 3], [3, 3]], [3, 3], True, False]Passed
contract fixture 2[['ab', 'c'], [[0, 2], [2, 3]], [0, 2], False, True][['ab', 'c'], [[0, 2], [2, 3]], [0, 2], False, True]Passed
contract fixture 3[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 4[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 5[['x'], [[0, 1]], None, False, False][['x'], [[0, 1]], None, False, False]Passed
contract fixture 6[[], [], None, False, True][[], [], None, False, True]Passed
contract fixture 7[[], [], None, False, True][['a'], [[0, 1]], [0, 1], False, True]Failed
contract fixture 8[[], [], None, False, False][[], [], None, False, False]Passed

SHA-256 / 6d3ee69343cb7d85583635e2a09a47e29cd9c3e2c13b9a0a2c86d7e0dab98d3a

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

Stipulated finite adapter contract, not a claim of platform accessibility or ARIA 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 2026-09-29T14:45:46.554659+00:00.

Case digest / 33c61352831ce8e0f954f2edbadf10db16904f1a26f50ed5bafb53b7f57d7d9d