{"abstract":"LZ history keeps references beyond its window.","category":"Compression format semantics","checks":6,"contract":"Return the byte distance behind output only if 1 <= distance <= min(width,len(history)); otherwise return None. Width is positive.","evaluation_group":"model-6b2225096f491b30","failed_approach":"A strict less-than boundary rejects the oldest still-valid byte.","family":"z-compression-window-expiration","id":"FA-11596","implementations":{"attempt":{"sha256":"26d59651df9951d7376dd282720285f9d5c577a6997dd24c6f420b82ce8aeec9","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(history, width, distance):\n    return history[-distance] if 1 <= distance < min(width,len(history)) else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('expired',solve('a'*(N+3),N,N+1),None)\ncheck('oldest valid',solve('abcdef',3,3),'d')\ncheck('nearest',solve('abc',2,1),'c')\ncheck('before stream',solve('a',5,2),None)\ncheck('zero',solve('abc',2,0),None)\ncheck('empty history',solve('',4,1),None)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"6d505a172a4c31ab6a852d2824f9ca4377c342ceb8a9da43510bbcd7dad36de1","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(history, width, distance):\n    return history[-distance] if 1 <= distance <= len(history) else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('expired',solve('a'*(N+3),N,N+1),None)\ncheck('oldest valid',solve('abcdef',3,3),'d')\ncheck('nearest',solve('abc',2,1),'c')\ncheck('before stream',solve('a',5,2),None)\ncheck('zero',solve('abc',2,0),None)\ncheck('empty history',solve('',4,1),None)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"aa5596f5a2421fdd599c3688f57469ba0bf2ef887c2cdd3759c5d1d532eaaef4","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(history, width, distance):\n    return history[-distance] if 1 <= distance <= min(width,len(history)) else None\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('expired',solve('a'*(N+3),N,N+1),None)\ncheck('oldest valid',solve('abcdef',3,3),'d')\ncheck('nearest',solve('abc',2,1),'c')\ncheck('before stream',solve('a',5,2),None)\ncheck('zero',solve('abc',2,0),None)\ncheck('empty history',solve('',4,1),None)\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":"Controlled educational model, not a complete implementation of a production compression format. 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"z-compression-window-expiration","generated_at":"2026-09-29T14:38:49.290517+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small offline codec model isolates a compression-specific failure without external files or libraries.","repair":"Check distance inclusively against both available history and the configured window before dereferencing.","root_cause":"The decoder checks against all past output rather than the retained window.","sha256":"f774f7c36ff48c6588c80c24f3e338d77c11f71a7ed1077d77a317dfddb657f8","title":"LZ history keeps references beyond its window · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":38.23,"exit_code":1,"observations":[{"actual":null,"check":"expired","expected":null,"passed":true},{"actual":null,"check":"oldest valid","expected":"d","passed":false},{"actual":"c","check":"nearest","expected":"c","passed":true},{"actual":null,"check":"before stream","expected":null,"passed":true},{"actual":null,"check":"zero","expected":null,"passed":true},{"actual":null,"check":"empty history","expected":null,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"expired\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oldest valid\", \"actual\": null, \"expected\": \"d\", \"passed\": false}, {\"check\": \"nearest\", \"actual\": \"c\", \"expected\": \"c\", \"passed\": true}, {\"check\": \"before stream\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"zero\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"empty history\", \"actual\": null, \"expected\": null, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.42,"exit_code":1,"observations":[{"actual":"a","check":"expired","expected":null,"passed":false},{"actual":"d","check":"oldest valid","expected":"d","passed":true},{"actual":"c","check":"nearest","expected":"c","passed":true},{"actual":null,"check":"before stream","expected":null,"passed":true},{"actual":null,"check":"zero","expected":null,"passed":true},{"actual":null,"check":"empty history","expected":null,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"expired\", \"actual\": \"a\", \"expected\": null, \"passed\": false}, {\"check\": \"oldest valid\", \"actual\": \"d\", \"expected\": \"d\", \"passed\": true}, {\"check\": \"nearest\", \"actual\": \"c\", \"expected\": \"c\", \"passed\": true}, {\"check\": \"before stream\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"zero\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"empty history\", \"actual\": null, \"expected\": null, \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":41.298,"exit_code":0,"observations":[{"actual":null,"check":"expired","expected":null,"passed":true},{"actual":"d","check":"oldest valid","expected":"d","passed":true},{"actual":"c","check":"nearest","expected":"c","passed":true},{"actual":null,"check":"before stream","expected":null,"passed":true},{"actual":null,"check":"zero","expected":null,"passed":true},{"actual":null,"check":"empty history","expected":null,"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"expired\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"oldest valid\", \"actual\": \"d\", \"expected\": \"d\", \"passed\": true}, {\"check\": \"nearest\", \"actual\": \"c\", \"expected\": \"c\", \"passed\": true}, {\"check\": \"before stream\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"zero\", \"actual\": null, \"expected\": null, \"passed\": true}, {\"check\": \"empty history\", \"actual\": null, \"expected\": null, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}