{"abstract":"LZ match copying freezes the source before expansion.","category":"Compression format semantics","checks":6,"contract":"For a nonempty seed, valid distance into seed, and nonnegative length, append length symbols by repeatedly reading distance symbols behind the growing output.","contract_signature":"seed, distance, length","evaluation_group":"model-11bf11ac11288166","failed_approach":"Repeating only the last symbol fixes distance one but destroys longer periodic matches.","family":"z-compression-overlapping-match","id":"FA-11591","implementations":{"attempt":{"sha256":"9ebae2c3a688ceceae90be8b715c3c389905c1bf76aba0bc1600945d7541c14b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(seed, distance, length):\n    return seed + seed[-1:] * length\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('overlap',solve('ab',2,2*N+1),'ab'+'ab'*N+'a')\ncheck('distance one',solve('x',1,4),'xxxxx')\ncheck('no match',solve('abc',2,0),'abc')\ncheck('partial period',solve('abc',3,2),'abcab')\ncheck('exact period',solve('abc',3,3),'abcabc')\ncheck('suffix period',solve('zab',2,5),'zabababa')\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":"a1016418e07521cca3fbdaef1e4322151505cc40f3b5a7f17de80a1547ec401d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(seed, distance, length):\n    return seed + seed[-distance:][:length]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('overlap',solve('ab',2,2*N+1),'ab'+'ab'*N+'a')\ncheck('distance one',solve('x',1,4),'xxxxx')\ncheck('no match',solve('abc',2,0),'abc')\ncheck('partial period',solve('abc',3,2),'abcab')\ncheck('exact period',solve('abc',3,3),'abcabc')\ncheck('suffix period',solve('zab',2,5),'zabababa')\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":"Controlled educational model, not a complete implementation of a production compression format. 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":"z-compression-overlapping-match","generated_at":"2026-09-29T14:38:49.289771+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small offline codec model isolates a compression-specific failure without external files or libraries.","root_cause":"A match is read from a snapshot instead of the growing output.","sha256":"e9f01d6e3819b21f2ca7c71fdaa45871af6e3769cde915c476ce55703de0c8b0","title":"LZ match copying freezes the source before expansion · 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":39.048,"exit_code":1,"observations":[{"actual":"abbbb","check":"overlap","expected":"ababa","passed":false},{"actual":"xxxxx","check":"distance one","expected":"xxxxx","passed":true},{"actual":"abc","check":"no match","expected":"abc","passed":true},{"actual":"abccc","check":"partial period","expected":"abcab","passed":false},{"actual":"abcccc","check":"exact period","expected":"abcabc","passed":false},{"actual":"zabbbbbb","check":"suffix period","expected":"zabababa","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overlap\", \"actual\": \"abbbb\", \"expected\": \"ababa\", \"passed\": false}, {\"check\": \"distance one\", \"actual\": \"xxxxx\", \"expected\": \"xxxxx\", \"passed\": true}, {\"check\": \"no match\", \"actual\": \"abc\", \"expected\": \"abc\", \"passed\": true}, {\"check\": \"partial period\", \"actual\": \"abccc\", \"expected\": \"abcab\", \"passed\": false}, {\"check\": \"exact period\", \"actual\": \"abcccc\", \"expected\": \"abcabc\", \"passed\": false}, {\"check\": \"suffix period\", \"actual\": \"zabbbbbb\", \"expected\": \"zabababa\", \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.674,"exit_code":1,"observations":[{"actual":"abab","check":"overlap","expected":"ababa","passed":false},{"actual":"xx","check":"distance one","expected":"xxxxx","passed":false},{"actual":"abc","check":"no match","expected":"abc","passed":true},{"actual":"abcab","check":"partial period","expected":"abcab","passed":true},{"actual":"abcabc","check":"exact period","expected":"abcabc","passed":true},{"actual":"zabab","check":"suffix period","expected":"zabababa","passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overlap\", \"actual\": \"abab\", \"expected\": \"ababa\", \"passed\": false}, {\"check\": \"distance one\", \"actual\": \"xx\", \"expected\": \"xxxxx\", \"passed\": false}, {\"check\": \"no match\", \"actual\": \"abc\", \"expected\": \"abc\", \"passed\": true}, {\"check\": \"partial period\", \"actual\": \"abcab\", \"expected\": \"abcab\", \"passed\": true}, {\"check\": \"exact period\", \"actual\": \"abcabc\", \"expected\": \"abcabc\", \"passed\": true}, {\"check\": \"suffix period\", \"actual\": \"zabab\", \"expected\": \"zabababa\", \"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."}}