{"abstract":"The operation returns a result or retained state that violates this contract: Split into nonoverlapping pairs and preserve a final singleton.","category":"Sequence semantics","checks":4,"contract":"Split into nonoverlapping pairs and preserve a final singleton. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-32df32e846bb25ec","failed_approach":"Restricting output to complete pairs discards a final singleton.","family":"xr-nonoverlapping-pairs-keep-tail","id":"FA-4176","implementations":{"attempt":{"sha256":"f440cea22ec7fd95d2fec5a5bdee173f7c38c8080bd887a10fe118fdc3ab4104","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [x[i:i+2] for i in range(0,len(x)-1,2)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), [])\ncheck('singleton collection', solve(['a']), [['a']])\ncheck('two distinct elements', solve(['a', 'b']), [['a', 'b']])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [['b', 'a'], ['b', 'c']])\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":"bac05dca933df6174c5f9a19bdb87dbd5b4729ae1136e5c45d87ecb66376cc87","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [[x[i],x[i+1]] for i in range(len(x)-1)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('empty collection', solve([]), [])\ncheck('singleton collection', solve(['a']), [['a']])\ncheck('two distinct elements', solve(['a', 'b']), [['a', 'b']])\ncheck('nonadjacent duplicate and unsorted order', solve(['b', 'a', 'b', 'c']), [['b', 'a'], ['b', 'c']])\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":"xr-nonoverlapping-pairs-keep-tail","generated_at":"2026-09-29T14:37:36.493789+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","root_cause":"Sliding windows duplicate positions that belong to separate chunks.","sha256":"60dddd5d19728b84fc2995e38bfc8b0d47457405dc5b2257e6750a31ed4d03cb","title":"Nonoverlapping pairs keep tail · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":35.98,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[["a"]],"passed":false},{"actual":[["a","b"]],"check":"two distinct elements","expected":[["a","b"]],"passed":true},{"actual":[["b","a"],["b","c"]],"check":"nonadjacent duplicate and unsorted order","expected":[["b","a"],["b","c"]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [], \"expected\": [[\"a\"]], \"passed\": false}, {\"check\": \"two distinct elements\", \"actual\": [[\"a\", \"b\"]], \"expected\": [[\"a\", \"b\"]], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [[\"b\", \"a\"], [\"b\", \"c\"]], \"expected\": [[\"b\", \"a\"], [\"b\", \"c\"]], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":120.578,"exit_code":1,"observations":[{"actual":[],"check":"empty collection","expected":[],"passed":true},{"actual":[],"check":"singleton collection","expected":[["a"]],"passed":false},{"actual":[["a","b"]],"check":"two distinct elements","expected":[["a","b"]],"passed":true},{"actual":[["b","a"],["a","b"],["b","c"]],"check":"nonadjacent duplicate and unsorted order","expected":[["b","a"],["b","c"]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"empty collection\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton collection\", \"actual\": [], \"expected\": [[\"a\"]], \"passed\": false}, {\"check\": \"two distinct elements\", \"actual\": [[\"a\", \"b\"]], \"expected\": [[\"a\", \"b\"]], \"passed\": true}, {\"check\": \"nonadjacent duplicate and unsorted order\", \"actual\": [[\"b\", \"a\"], [\"a\", \"b\"], [\"b\", \"c\"]], \"expected\": [[\"b\", \"a\"], [\"b\", \"c\"]], \"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."}}