{"abstract":"An optional BOM is appended instead of prepended.","category":"Encodings","checks":4,"contract":"Encode text as UTF-8 with exactly one generated leading BOM; preserve any BOM in the input text.","contract_signature":"x","evaluation_group":"model-c1271ad1dd2dc52c","failed_approach":"The attempted repair handles the primary example but still violates a separate boundary of the same contract.","family":"xp-utf8-signature-encoding","id":"FA-3931","implementations":{"attempt":{"sha256":"b767ce18b008b6b5bf0a09e1dddb3e59a8cd98ef06b1e266c0441ac8aa101a7a","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 list(x.encode('utf-8')+bytes.fromhex('efbbbf'))\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('a'), [239, 187, 191, 97])\ncheck('boundary 2', solve(''), [239, 187, 191])\ncheck('boundary 3', solve('\\ufeff'), [239, 187, 191, 239, 187, 191])\ncheck('boundary 4', solve('é'), [239, 187, 191, 195, 169])\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":"91e25cb7b5d77bdb7dbb22c02959bcb1439f6274633a865b9291953f9d994441","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 list(x.encode('utf-8'))\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('a'), [239, 187, 191, 97])\ncheck('boundary 2', solve(''), [239, 187, 191])\ncheck('boundary 3', solve('\\ufeff'), [239, 187, 191, 239, 187, 191])\ncheck('boundary 4', solve('é'), [239, 187, 191, 195, 169])\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-utf8-signature-encoding","generated_at":"2026-09-29T14:37:33.216376+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.","root_cause":"The implementation applies an operation whose text or grammar semantics violate this contract: Encode text as UTF-8 with exactly one generated leading BOM; preserve any BOM in the input text.","sha256":"6e6717124a4ea967bae766050694ebac3961cb40c4c82d773383023d205d29b8","title":"An optional BOM is appended instead of prepended · 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":68.74,"exit_code":1,"observations":[{"actual":[97,239,187,191],"check":"boundary 1","expected":[239,187,191,97],"passed":false},{"actual":[239,187,191],"check":"boundary 2","expected":[239,187,191],"passed":true},{"actual":[239,187,191,239,187,191],"check":"boundary 3","expected":[239,187,191,239,187,191],"passed":true},{"actual":[195,169,239,187,191],"check":"boundary 4","expected":[239,187,191,195,169],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [97, 239, 187, 191], \"expected\": [239, 187, 191, 97], \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": [239, 187, 191], \"expected\": [239, 187, 191], \"passed\": true}, {\"check\": \"boundary 3\", \"actual\": [239, 187, 191, 239, 187, 191], \"expected\": [239, 187, 191, 239, 187, 191], \"passed\": true}, {\"check\": \"boundary 4\", \"actual\": [195, 169, 239, 187, 191], \"expected\": [239, 187, 191, 195, 169], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":122.793,"exit_code":1,"observations":[{"actual":[97],"check":"boundary 1","expected":[239,187,191,97],"passed":false},{"actual":[],"check":"boundary 2","expected":[239,187,191],"passed":false},{"actual":[239,187,191],"check":"boundary 3","expected":[239,187,191,239,187,191],"passed":false},{"actual":[195,169],"check":"boundary 4","expected":[239,187,191,195,169],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [97], \"expected\": [239, 187, 191, 97], \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": [], \"expected\": [239, 187, 191], \"passed\": false}, {\"check\": \"boundary 3\", \"actual\": [239, 187, 191], \"expected\": [239, 187, 191, 239, 187, 191], \"passed\": false}, {\"check\": \"boundary 4\", \"actual\": [195, 169], \"expected\": [239, 187, 191, 195, 169], \"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."}}