{"abstract":"Front-coded strings ignore the previous decoded prefix.","category":"Binary formats","checks":4,"contract":"Decode [prefix_length,suffix] records against the previous decoded string, starting with empty text; invalid prefix lengths return None.","contract_signature":"x","evaluation_group":"model-678d4f3bfa4ede6e","failed_approach":"The attempted repair handles the primary example but still violates a separate boundary of the same contract.","family":"xp-front-coded-prefix-reference","id":"FA-4071","implementations":{"attempt":{"sha256":"efc34c3cd49ad9084287d46c68beeac446f512f5db8a4018e18677d49c5c09a2","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        out=[]\n        previous=''\n        for count,suffix in x:\n            previous=previous[:count]+suffix\n            out.append(previous)\n        return out\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([[0, 'car'], [3, 't'], [2, 't']]), ['car', 'cart', 'cat'])\ncheck('boundary 2', solve([[1, 'x']]), None)\ncheck('boundary 3', solve([[0, 'x'], [-1, 'y']]), None)\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":"8df5600e66c16a33cfa8f417a8dbab0e8b6ffe3ca204696a1c12dfc129de864a","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 [suffix for count,suffix in x]\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([[0, 'car'], [3, 't'], [2, 't']]), ['car', 'cart', 'cat'])\ncheck('boundary 2', solve([[1, 'x']]), None)\ncheck('boundary 3', solve([[0, 'x'], [-1, 'y']]), None)\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-front-coded-prefix-reference","generated_at":"2026-09-29T14:37:35.406228+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: Decode [prefix_length,suffix] records against the previous decoded string, starting with empty text; invalid prefix lengths return None.","sha256":"216362e24c906a0103a6c8fc55a4b82a16a9fa6eb349d0022816dc5f55fdd821","title":"Front-coded strings ignore the previous decoded prefix · 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":150.497,"exit_code":1,"observations":[{"actual":["car","cart","cat"],"check":"boundary 1","expected":["car","cart","cat"],"passed":true},{"actual":["x"],"check":"boundary 2","expected":null,"passed":false},{"actual":["x","y"],"check":"boundary 3","expected":null,"passed":false},{"actual":[],"check":"boundary 4","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [\"car\", \"cart\", \"cat\"], \"expected\": [\"car\", \"cart\", \"cat\"], \"passed\": true}, {\"check\": \"boundary 2\", \"actual\": [\"x\"], \"expected\": null, \"passed\": false}, {\"check\": \"boundary 3\", \"actual\": [\"x\", \"y\"], \"expected\": null, \"passed\": false}, {\"check\": \"boundary 4\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":59.277,"exit_code":1,"observations":[{"actual":["car","t","t"],"check":"boundary 1","expected":["car","cart","cat"],"passed":false},{"actual":["x"],"check":"boundary 2","expected":null,"passed":false},{"actual":["x","y"],"check":"boundary 3","expected":null,"passed":false},{"actual":[],"check":"boundary 4","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"boundary 1\", \"actual\": [\"car\", \"t\", \"t\"], \"expected\": [\"car\", \"cart\", \"cat\"], \"passed\": false}, {\"check\": \"boundary 2\", \"actual\": [\"x\"], \"expected\": null, \"passed\": false}, {\"check\": \"boundary 3\", \"actual\": [\"x\", \"y\"], \"expected\": null, \"passed\": false}, {\"check\": \"boundary 4\", \"actual\": [], \"expected\": [], \"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."}}