{"abstract":"Character bigram extraction omits the last window.","category":"Text processing","checks":4,"contract":"Return all overlapping two-codepoint substrings, including the final window.","evaluation_group":"model-a627793da60cdce9","failed_approach":"The attempted repair handles the primary example but still violates a separate boundary of the same contract.","family":"xp-bigram-window-tail","id":"FA-3966","implementations":{"attempt":{"sha256":"cc91edc3b19f8c5f124f7bccb8633bc0adee4a8806458787584b24a8d0fa5cc5","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct\nfrom urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit\nfrom email.header import decode_header, make_header\nfrom email.utils import getaddresses\nfrom xml.etree import ElementTree as ET\nimport shlex, string, textwrap\n\nN = 1\nobservations = []\ndef solve(x):\n    try:\n        return [x[i:i+2] for i in range(0,len(x)-1,2)]\n    except Exception as exc:\n        return {\"error\": type(exc).__name__}\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])\ncheck('boundary 2', solve('ab'), ['ab'])\ncheck('boundary 3', solve('a'), [])\ncheck('boundary 4', solve(''), [])\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":"3e02645c606dcc9cce39c0d7c4cca9e2b1496337f153166402ae3caf2339d1bd","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct\nfrom urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit\nfrom email.header import decode_header, make_header\nfrom email.utils import getaddresses\nfrom xml.etree import ElementTree as ET\nimport shlex, string, textwrap\n\nN = 1\nobservations = []\ndef solve(x):\n    try:\n        return [x[i:i+2] for i in range(len(x)-2)]\n    except Exception as exc:\n        return {\"error\": type(exc).__name__}\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])\ncheck('boundary 2', solve('ab'), ['ab'])\ncheck('boundary 3', solve('a'), [])\ncheck('boundary 4', solve(''), [])\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":"eacf9ecac8c94eb9a338d52c1e4fc275bbe46bc77ec13b0b3d31c5e628fb0f69","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct\nfrom urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit\nfrom email.header import decode_header, make_header\nfrom email.utils import getaddresses\nfrom xml.etree import ElementTree as ET\nimport shlex, string, textwrap\n\nN = 1\nobservations = []\ndef solve(x):\n    try:\n        return [x[i:i+2] for i in range(len(x)-1)]\n    except Exception as exc:\n        return {\"error\": type(exc).__name__}\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('boundary 1', solve('abcd'), ['ab', 'bc', 'cd'])\ncheck('boundary 2', solve('ab'), ['ab'])\ncheck('boundary 3', solve('a'), [])\ncheck('boundary 4', solve(''), [])\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":"xp-bigram-window-tail","generated_at":"2026-09-29T14:37:33.572393+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.","repair":"Implement the complete stated contract, including the boundary fixtures: Return all overlapping two-codepoint substrings, including the final window.","root_cause":"The implementation applies an operation whose text or grammar semantics violate this contract: Return all overlapping two-codepoint substrings, including the final window.","sha256":"a841c69de5d6ff35147def0efc1337faaa2eee9d90ff4ed955fe0960db760780","title":"Character bigram extraction omits the last window · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":75.821,"exit_code":1,"observations":[{"actual":["ab","cd"],"check":"boundary 1","expected":["ab","bc","cd"],"passed":false},{"actual":["ab"],"check":"boundary 2","expected":["ab"],"passed":true},{"actual":[],"check":"boundary 3","expected":[],"passed":true},{"actual":[],"check":"boundary 4","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [\"ab\", \"cd\"], \"expected\": [\"ab\", \"bc\", \"cd\"], \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": [\"ab\"], \"expected\": [\"ab\"], \"passed\": true}, {\"check\": \"boundary 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"boundary 4\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":101.448,"exit_code":1,"observations":[{"actual":["ab","bc"],"check":"boundary 1","expected":["ab","bc","cd"],"passed":false},{"actual":[],"check":"boundary 2","expected":["ab"],"passed":false},{"actual":[],"check":"boundary 3","expected":[],"passed":true},{"actual":[],"check":"boundary 4","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [\"ab\", \"bc\"], \"expected\": [\"ab\", \"bc\", \"cd\"], \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": [], \"expected\": [\"ab\"], \"passed\": false}, {\"check\": \"boundary 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"boundary 4\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":57.985,"exit_code":0,"observations":[{"actual":["ab","bc","cd"],"check":"boundary 1","expected":["ab","bc","cd"],"passed":true},{"actual":["ab"],"check":"boundary 2","expected":["ab"],"passed":true},{"actual":[],"check":"boundary 3","expected":[],"passed":true},{"actual":[],"check":"boundary 4","expected":[],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [\"ab\", \"bc\", \"cd\"], \"expected\": [\"ab\", \"bc\", \"cd\"], \"passed\": true}, {\"check\": \"boundary 2\", \"actual\": [\"ab\"], \"expected\": [\"ab\"], \"passed\": true}, {\"check\": \"boundary 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"boundary 4\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}