{"abstract":"The operation returns a result or retained state that violates this contract: Extend by the iterable elements, without recursively flattening nested elements.","category":"Container mutation","checks":4,"contract":"Extend by the iterable elements, without recursively flattening nested elements. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-b8efe79624d877b4","failed_approach":"Recursive flattening destroys nested elements below the requested level.","family":"xr-list-extend-expands-one-level","id":"FA-4371","implementations":{"attempt":{"sha256":"0454d543326d85b03ae49819e002873977810b0f6ee9b2835043c3e47a8ec126","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return list(x)+[z for v in y for z in (v if isinstance(v,list) else [v])]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('flat extension', solve(['a'], ['b', 'c']), ['a', 'b', 'c'])\ncheck('nested stays nested', solve([], [['a'], 'b']), [['a'], 'b'])\ncheck('empty extension', solve(['a'], []), ['a'])\ncheck('string iteration', solve([], 'ab'), ['a', 'b'])\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":"c2ea590cc9bb5384dae1b61b8e7cdd3558252e47881d31340adeafae5bfd7cbb","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return list(x)+[y]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('flat extension', solve(['a'], ['b', 'c']), ['a', 'b', 'c'])\ncheck('nested stays nested', solve([], [['a'], 'b']), [['a'], 'b'])\ncheck('empty extension', solve(['a'], []), ['a'])\ncheck('string iteration', solve([], 'ab'), ['a', 'b'])\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":"5051166d6f7b402769b2a001aeb1ca39fa39b57fd6bd5187210fe43702cb8010","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return list(x)+list(y)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('flat extension', solve(['a'], ['b', 'c']), ['a', 'b', 'c'])\ncheck('nested stays nested', solve([], [['a'], 'b']), [['a'], 'b'])\ncheck('empty extension', solve(['a'], []), ['a'])\ncheck('string iteration', solve([], 'ab'), ['a', 'b'])\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":"xr-list-extend-expands-one-level","generated_at":"2026-09-29T14:37:38.470273+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","repair":"Extend by the iterable elements, without recursively flattening nested elements.","root_cause":"Appending keeps the iterable container as a single element.","sha256":"5259e57c92bb59fea69c37d050f4c9f5002b19602f9922b00fddb22836cbc302","title":"List extend expands one level · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verification":{"attempt":{"elapsed_ms":37.488,"exit_code":1,"observations":[{"actual":["a","b","c"],"check":"flat extension","expected":["a","b","c"],"passed":true},{"actual":["a","b"],"check":"nested stays nested","expected":[["a"],"b"],"passed":false},{"actual":["a"],"check":"empty extension","expected":["a"],"passed":true},{"actual":["a","b"],"check":"string iteration","expected":["a","b"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"flat extension\", \"actual\": [\"a\", \"b\", \"c\"], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": true}, {\"check\": \"nested stays nested\", \"actual\": [\"a\", \"b\"], \"expected\": [[\"a\"], \"b\"], \"passed\": false}, {\"check\": \"empty extension\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"string iteration\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":37.069,"exit_code":1,"observations":[{"actual":["a",["b","c"]],"check":"flat extension","expected":["a","b","c"],"passed":false},{"actual":[[["a"],"b"]],"check":"nested stays nested","expected":[["a"],"b"],"passed":false},{"actual":["a",[]],"check":"empty extension","expected":["a"],"passed":false},{"actual":["ab"],"check":"string iteration","expected":["a","b"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"flat extension\", \"actual\": [\"a\", [\"b\", \"c\"]], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": false}, {\"check\": \"nested stays nested\", \"actual\": [[[\"a\"], \"b\"]], \"expected\": [[\"a\"], \"b\"], \"passed\": false}, {\"check\": \"empty extension\", \"actual\": [\"a\", []], \"expected\": [\"a\"], \"passed\": false}, {\"check\": \"string iteration\", \"actual\": [\"ab\"], \"expected\": [\"a\", \"b\"], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":38.451,"exit_code":0,"observations":[{"actual":["a","b","c"],"check":"flat extension","expected":["a","b","c"],"passed":true},{"actual":[["a"],"b"],"check":"nested stays nested","expected":[["a"],"b"],"passed":true},{"actual":["a"],"check":"empty extension","expected":["a"],"passed":true},{"actual":["a","b"],"check":"string iteration","expected":["a","b"],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"flat extension\", \"actual\": [\"a\", \"b\", \"c\"], \"expected\": [\"a\", \"b\", \"c\"], \"passed\": true}, {\"check\": \"nested stays nested\", \"actual\": [[\"a\"], \"b\"], \"expected\": [[\"a\"], \"b\"], \"passed\": true}, {\"check\": \"empty extension\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"string iteration\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}