{"abstract":"A day-thirty target is not every calendar month end.","category":"Calendar arithmetic","checks":4,"contract":"Valid ISO Gregorian dates in years 1 through 9999; generated dates must remain in that range. Month is 1 through 12 and zero-based weekday is Monday 0 through Sunday 6 unless the output convention says otherwise. Month end date. Exact operational definition: date(date.fromisoformat(text).year,date.fromisoformat(text).month,calendar.monthrange(date.fromisoformat(text).year,date.fromisoformat(text).month)[1]).isoformat()","contract_signature":"text","evaluation_group":"model-c823c5353f9d1d0f","failed_approach":"A universal day twenty-eight avoids invalidity while truncating valid month ends.","family":"xn-month-end-date","id":"FA-6521","implementations":{"attempt":{"sha256":"7787a05ae78c24db99e6198d8444197e0953e3737be7afdaeb24c476f2fb710c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nimport calendar\nimport statistics\nimport itertools\nfrom fractions import Fraction\nfrom datetime import date, datetime, timedelta, timezone\nfrom decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR\n\nN = 1\nobservations = []\ndef solve(text):\n    return date(date.fromisoformat(text).year,date.fromisoformat(text).month,28).isoformat()\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck(\"fixture 1: ('2024-02-10',)\", solve(*('2024-02-10',)), '2024-02-29')\ncheck(\"fixture 2: ('2023-02-10',)\", solve(*('2023-02-10',)), '2023-02-28')\ncheck(\"fixture 3: ('2024-04-02',)\", solve(*('2024-04-02',)), '2024-04-30')\ncheck(\"fixture 4: ('2024-07-31',)\", solve(*('2024-07-31',)), '2024-07-31')\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":"ab203218d4064af2fe1eded05e7ab245b4696804c6b31a915b0b3e8fa68aefee","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport math\nimport calendar\nimport statistics\nimport itertools\nfrom fractions import Fraction\nfrom datetime import date, datetime, timedelta, timezone\nfrom decimal import Decimal, ROUND_HALF_UP, ROUND_DOWN, ROUND_CEILING, ROUND_FLOOR\n\nN = 1\nobservations = []\ndef solve(text):\n    return (date.fromisoformat(text)+timedelta(days=30-date.fromisoformat(text).day)).isoformat()\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck(\"fixture 1: ('2024-02-10',)\", solve(*('2024-02-10',)), '2024-02-29')\ncheck(\"fixture 2: ('2023-02-10',)\", solve(*('2023-02-10',)), '2023-02-28')\ncheck(\"fixture 3: ('2024-04-02',)\", solve(*('2024-04-02',)), '2024-04-30')\ncheck(\"fixture 4: ('2024-07-31',)\", solve(*('2024-07-31',)), '2024-07-31')\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":" 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":"xn-month-end-date","generated_at":"2026-09-29T14:38:02.849707+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Calendar conventions results depend on the stated convention.","root_cause":"A day-thirty target is not every calendar month end.","sha256":"1c3a1d823b31d7cdd29dc1552dd5b0a0b50359f42ebaa03f305d53319f49d45a","title":"Month end date · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":43.52,"exit_code":1,"observations":[{"actual":"2024-02-28","check":"fixture 1: ('2024-02-10',)","expected":"2024-02-29","passed":false},{"actual":"2023-02-28","check":"fixture 2: ('2023-02-10',)","expected":"2023-02-28","passed":true},{"actual":"2024-04-28","check":"fixture 3: ('2024-04-02',)","expected":"2024-04-30","passed":false},{"actual":"2024-07-28","check":"fixture 4: ('2024-07-31',)","expected":"2024-07-31","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1: ('2024-02-10',)\", \"actual\": \"2024-02-28\", \"expected\": \"2024-02-29\", \"passed\": false}, {\"check\": \"fixture 2: ('2023-02-10',)\", \"actual\": \"2023-02-28\", \"expected\": \"2023-02-28\", \"passed\": true}, {\"check\": \"fixture 3: ('2024-04-02',)\", \"actual\": \"2024-04-28\", \"expected\": \"2024-04-30\", \"passed\": false}, {\"check\": \"fixture 4: ('2024-07-31',)\", \"actual\": \"2024-07-28\", \"expected\": \"2024-07-31\", \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":42.25,"exit_code":1,"observations":[{"actual":"2024-03-01","check":"fixture 1: ('2024-02-10',)","expected":"2024-02-29","passed":false},{"actual":"2023-03-02","check":"fixture 2: ('2023-02-10',)","expected":"2023-02-28","passed":false},{"actual":"2024-04-30","check":"fixture 3: ('2024-04-02',)","expected":"2024-04-30","passed":true},{"actual":"2024-07-30","check":"fixture 4: ('2024-07-31',)","expected":"2024-07-31","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1: ('2024-02-10',)\", \"actual\": \"2024-03-01\", \"expected\": \"2024-02-29\", \"passed\": false}, {\"check\": \"fixture 2: ('2023-02-10',)\", \"actual\": \"2023-03-02\", \"expected\": \"2023-02-28\", \"passed\": false}, {\"check\": \"fixture 3: ('2024-04-02',)\", \"actual\": \"2024-04-30\", \"expected\": \"2024-04-30\", \"passed\": true}, {\"check\": \"fixture 4: ('2024-07-31',)\", \"actual\": \"2024-07-30\", \"expected\": \"2024-07-31\", \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}