{"abstract":"A byte-budget truncation returns a partial UTF-8 scalar.","category":"Encodings","checks":4,"contract":"Given scalar text and a nonnegative byte budget, retain the longest UTF-8 prefix ending at a scalar boundary.","contract_signature":"x","evaluation_group":"model-5c93e98ca72f3bcf","failed_approach":"The attempted repair handles the primary example but still violates a separate boundary of the same contract.","family":"xp-utf8-truncate-boundary","id":"FA-3921","implementations":{"attempt":{"sha256":"ddcdf80b223ab339de538ccd5c93ed00188a56e2f9a4eb073a0b3d05dcd41ce3","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[0].encode('utf-8')[:x[1]].decode('utf-8','replace')\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(['éx', 1]), '')\ncheck('boundary 2', solve(['éx', 2]), 'é')\ncheck('boundary 3', solve(['😀a', 4]), '😀')\ncheck('boundary 4', solve(['abc', 2]), 'ab')\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":"436e5ae7e3e83d6b618ef6617f3ada96299e71cbf0a97813c1e3ce1e11e604c3","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[0][: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(['éx', 1]), '')\ncheck('boundary 2', solve(['éx', 2]), 'é')\ncheck('boundary 3', solve(['😀a', 4]), '😀')\ncheck('boundary 4', solve(['abc', 2]), 'ab')\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-truncate-boundary","generated_at":"2026-09-29T14:37:32.825573+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: Given scalar text and a nonnegative byte budget, retain the longest UTF-8 prefix ending at a scalar boundary.","sha256":"029527aeb822131c03265e48abed1c65e466115b8fff43692204d7c580d427f4","title":"A byte-budget truncation returns a partial UTF-8 scalar · 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":51.874,"exit_code":1,"observations":[{"actual":"�","check":"boundary 1","expected":"","passed":false},{"actual":"é","check":"boundary 2","expected":"é","passed":true},{"actual":"😀","check":"boundary 3","expected":"😀","passed":true},{"actual":"ab","check":"boundary 4","expected":"ab","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": \"�\", \"expected\": \"\", \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": \"é\", \"expected\": \"é\", \"passed\": true}, {\"check\": \"boundary 3\", \"actual\": \"😀\", \"expected\": \"😀\", \"passed\": true}, {\"check\": \"boundary 4\", \"actual\": \"ab\", \"expected\": \"ab\", \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":53.689,"exit_code":1,"observations":[{"actual":"é","check":"boundary 1","expected":"","passed":false},{"actual":"éx","check":"boundary 2","expected":"é","passed":false},{"actual":"😀a","check":"boundary 3","expected":"😀","passed":false},{"actual":"ab","check":"boundary 4","expected":"ab","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": \"é\", \"expected\": \"\", \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": \"éx\", \"expected\": \"é\", \"passed\": false}, {\"check\": \"boundary 3\", \"actual\": \"😀a\", \"expected\": \"😀\", \"passed\": false}, {\"check\": \"boundary 4\", \"actual\": \"ab\", \"expected\": \"ab\", \"passed\": true}], \"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."}}