{"abstract":"The operation returns a result or retained state that violates this contract: Append to a bounded deque, evicting from the left when capacity is exceeded; zero capacity retains nothing.","category":"Bounded deques","checks":4,"contract":"Append to a bounded deque, evicting from the left when capacity is exceeded; zero capacity retains nothing. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-8ef041ad65fa3a2f","failed_approach":"A negative-zero slice retains everything at zero capacity.","family":"xr-bounded-deque-append-evicts-oldest-left","id":"FA-4761","implementations":{"attempt":{"sha256":"8c9c4e075686521fab96a656747aef95e855318b88d2a27dc055b30605010ced","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nfrom collections import Counter, ChainMap, deque\nimport heapq\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return (list(x)+[y[1]])[-y[0]:]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('full evicts oldest', solve(['a', 'b'], [2, 'c']), ['b', 'c'])\ncheck('zero capacity', solve([], [0, 'a']), [])\ncheck('room remains', solve(['a'], [3, 'b']), ['a', 'b'])\ncheck('empty accepts', solve([], [2, 'a']), ['a'])\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":"b8d2e22206e2112aeea7d8892b288e163ab34741be7b84f8873ecddff017d12d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nfrom collections import Counter, ChainMap, deque\nimport heapq\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return (list(x)+[y[1]])[:y[0]]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('full evicts oldest', solve(['a', 'b'], [2, 'c']), ['b', 'c'])\ncheck('zero capacity', solve([], [0, 'a']), [])\ncheck('room remains', solve(['a'], [3, 'b']), ['a', 'b'])\ncheck('empty accepts', solve([], [2, 'a']), ['a'])\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-bounded-deque-append-evicts-oldest-left","generated_at":"2026-09-29T14:37:42.572552+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.","root_cause":"Keeping the oldest prefix discards the new value instead of evicting the oldest.","sha256":"83fb7ce475366898f5863c3289a8954dbdc125002d79f37292c452e85ff1ff56","title":"Bounded deque append evicts oldest left · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":37.382,"exit_code":1,"observations":[{"actual":["b","c"],"check":"full evicts oldest","expected":["b","c"],"passed":true},{"actual":["a"],"check":"zero capacity","expected":[],"passed":false},{"actual":["a","b"],"check":"room remains","expected":["a","b"],"passed":true},{"actual":["a"],"check":"empty accepts","expected":["a"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"full evicts oldest\", \"actual\": [\"b\", \"c\"], \"expected\": [\"b\", \"c\"], \"passed\": true}, {\"check\": \"zero capacity\", \"actual\": [\"a\"], \"expected\": [], \"passed\": false}, {\"check\": \"room remains\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}, {\"check\": \"empty accepts\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.431,"exit_code":1,"observations":[{"actual":["a","b"],"check":"full evicts oldest","expected":["b","c"],"passed":false},{"actual":[],"check":"zero capacity","expected":[],"passed":true},{"actual":["a","b"],"check":"room remains","expected":["a","b"],"passed":true},{"actual":["a"],"check":"empty accepts","expected":["a"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"full evicts oldest\", \"actual\": [\"a\", \"b\"], \"expected\": [\"b\", \"c\"], \"passed\": false}, {\"check\": \"zero capacity\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"room remains\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"b\"], \"passed\": true}, {\"check\": \"empty accepts\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"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."}}