{"abstract":"Concurrent readers use positional I/O instead of a shared mutable seek cursor.","category":"HTTP ranges","checks":6,"contract":"requests are [absolute-offset,count]; return independent ASCII slices for each request. The underlying shared handle cursor is irrelevant.","evaluation_group":"s3-http_ranges-stream-transfer","failed_approach":"The partial repair uses cursor=requests[0][0] if requests else 0\nout=[]\nfor start,count in requests:\n    out.append(body[cursor:cursor+count]); cursor+=count\nreturn out, which still violates the stated contract.","family":"s3-http_ranges-stream-shared-handle-cursor","id":"FA-26626","implementations":{"attempt":{"sha256":"8f4c954b9e314ed3a2972c6d6ef464698a0fb840ef517cb9c664e3c04d20c917","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(body, requests):\n    cursor=requests[0][0] if requests else 0\n    out=[]\n    for start,count in requests:\n        out.append(body[cursor:cursor+count]); cursor+=count\n    return out\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('stream-shared-handle-cursor fixture 0', solve(\"abcdef\"*N,[[2,2],[0,2]]), [\"cd\",\"ab\"])\ncheck('stream-shared-handle-cursor fixture 1', solve(\"abcdef\",[[0,1],[3,1]]), [\"a\",\"d\"])\ncheck('stream-shared-handle-cursor fixture 2', solve(\"\",[]), [])\ncheck('stream-shared-handle-cursor fixture 3', solve(\"abc\",[[1,1]]), [\"b\"])\ncheck('stream-shared-handle-cursor fixture 4', solve(\"abc\",[[0,0],[2,1]]), [\"\",\"c\"])\ncheck('stream-shared-handle-cursor fixture 5', solve(\"abcdef\",[[1,2],[1,2]]), [\"bc\",\"bc\"])\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":"7730eaaa86508e24c16d97f86bf33258b4ad58a9e5be076a07138214f0e02049","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(body, requests):\n    cursor=0\n    out=[]\n    for start,count in requests:\n        out.append(body[cursor:cursor+count]); cursor+=count\n    return out\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('stream-shared-handle-cursor fixture 0', solve(\"abcdef\"*N,[[2,2],[0,2]]), [\"cd\",\"ab\"])\ncheck('stream-shared-handle-cursor fixture 1', solve(\"abcdef\",[[0,1],[3,1]]), [\"a\",\"d\"])\ncheck('stream-shared-handle-cursor fixture 2', solve(\"\",[]), [])\ncheck('stream-shared-handle-cursor fixture 3', solve(\"abc\",[[1,1]]), [\"b\"])\ncheck('stream-shared-handle-cursor fixture 4', solve(\"abc\",[[0,0],[2,1]]), [\"\",\"c\"])\ncheck('stream-shared-handle-cursor fixture 5', solve(\"abcdef\",[[1,2],[1,2]]), [\"bc\",\"bc\"])\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":"fd4eb1d2ffed9adb7ed560ee172c857baed00e1ada8866412308e701b2162ecc","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(body, requests):\n    return [body[start:start+count] for start,count in requests]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('stream-shared-handle-cursor fixture 0', solve(\"abcdef\"*N,[[2,2],[0,2]]), [\"cd\",\"ab\"])\ncheck('stream-shared-handle-cursor fixture 1', solve(\"abcdef\",[[0,1],[3,1]]), [\"a\",\"d\"])\ncheck('stream-shared-handle-cursor fixture 2', solve(\"\",[]), [])\ncheck('stream-shared-handle-cursor fixture 3', solve(\"abc\",[[1,1]]), [\"b\"])\ncheck('stream-shared-handle-cursor fixture 4', solve(\"abc\",[[0,0],[2,1]]), [\"\",\"c\"])\ncheck('stream-shared-handle-cursor fixture 5', solve(\"abcdef\",[[1,2],[1,2]]), [\"bc\",\"bc\"])\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":"Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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":"s3-http_ranges-stream-shared-handle-cursor","generated_at":"2026-09-29T14:41:17.662101+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Range responses combine representation identity, conditional requests, framing, and partial-object state.","repair":"Apply the bounded decision exactly: return [body[start:start+count] for start,count in requests]","root_cause":"The stream-shared-handle-cursor decision uses cursor=0\nout=[]\nfor start,count in requests:\n    out.append(body[cursor:cursor+count]); cursor+=count\nreturn out.","sha256":"7cd371d08a8c4ef4147320911487828def6c2be9ba509e0bf70a6bce8d2e3072","title":"Concurrent readers use positional I/O instead of a shared mutable seek cursor · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":42.359,"exit_code":1,"observations":[{"actual":["cd","ef"],"check":"stream-shared-handle-cursor fixture 0","expected":["cd","ab"],"passed":false},{"actual":["a","b"],"check":"stream-shared-handle-cursor fixture 1","expected":["a","d"],"passed":false},{"actual":[],"check":"stream-shared-handle-cursor fixture 2","expected":[],"passed":true},{"actual":["b"],"check":"stream-shared-handle-cursor fixture 3","expected":["b"],"passed":true},{"actual":["","a"],"check":"stream-shared-handle-cursor fixture 4","expected":["","c"],"passed":false},{"actual":["bc","de"],"check":"stream-shared-handle-cursor fixture 5","expected":["bc","bc"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"stream-shared-handle-cursor fixture 0\", \"actual\": [\"cd\", \"ef\"], \"expected\": [\"cd\", \"ab\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 1\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"d\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 2\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 3\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 4\", \"actual\": [\"\", \"a\"], \"expected\": [\"\", \"c\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 5\", \"actual\": [\"bc\", \"de\"], \"expected\": [\"bc\", \"bc\"], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":41.213,"exit_code":1,"observations":[{"actual":["ab","cd"],"check":"stream-shared-handle-cursor fixture 0","expected":["cd","ab"],"passed":false},{"actual":["a","b"],"check":"stream-shared-handle-cursor fixture 1","expected":["a","d"],"passed":false},{"actual":[],"check":"stream-shared-handle-cursor fixture 2","expected":[],"passed":true},{"actual":["a"],"check":"stream-shared-handle-cursor fixture 3","expected":["b"],"passed":false},{"actual":["","a"],"check":"stream-shared-handle-cursor fixture 4","expected":["","c"],"passed":false},{"actual":["ab","cd"],"check":"stream-shared-handle-cursor fixture 5","expected":["bc","bc"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"stream-shared-handle-cursor fixture 0\", \"actual\": [\"ab\", \"cd\"], \"expected\": [\"cd\", \"ab\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 1\", \"actual\": [\"a\", \"b\"], \"expected\": [\"a\", \"d\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 2\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 3\", \"actual\": [\"a\"], \"expected\": [\"b\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 4\", \"actual\": [\"\", \"a\"], \"expected\": [\"\", \"c\"], \"passed\": false}, {\"check\": \"stream-shared-handle-cursor fixture 5\", \"actual\": [\"ab\", \"cd\"], \"expected\": [\"bc\", \"bc\"], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":43.294,"exit_code":0,"observations":[{"actual":["cd","ab"],"check":"stream-shared-handle-cursor fixture 0","expected":["cd","ab"],"passed":true},{"actual":["a","d"],"check":"stream-shared-handle-cursor fixture 1","expected":["a","d"],"passed":true},{"actual":[],"check":"stream-shared-handle-cursor fixture 2","expected":[],"passed":true},{"actual":["b"],"check":"stream-shared-handle-cursor fixture 3","expected":["b"],"passed":true},{"actual":["","c"],"check":"stream-shared-handle-cursor fixture 4","expected":["","c"],"passed":true},{"actual":["bc","bc"],"check":"stream-shared-handle-cursor fixture 5","expected":["bc","bc"],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"stream-shared-handle-cursor fixture 0\", \"actual\": [\"cd\", \"ab\"], \"expected\": [\"cd\", \"ab\"], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 1\", \"actual\": [\"a\", \"d\"], \"expected\": [\"a\", \"d\"], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 2\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 3\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 4\", \"actual\": [\"\", \"c\"], \"expected\": [\"\", \"c\"], \"passed\": true}, {\"check\": \"stream-shared-handle-cursor fixture 5\", \"actual\": [\"bc\", \"bc\"], \"expected\": [\"bc\", \"bc\"], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}