{"abstract":"Download checkpoints advance only after durable writes.","category":"HTTP ranges","checks":6,"contract":"Return durable checkpoint: synced writes advance to written; unsynced writes retain prior checkpoint. written>=checkpoint.","evaluation_group":"s3-http_ranges-resume-client","failed_approach":"The partial repair uses return checkpoint, which still violates the stated contract.","family":"s3-http_ranges-resume-checkpoint-after-fsync","id":"FA-26766","implementations":{"attempt":{"sha256":"bf8412c87a2fba291dae872cd546f45c432b9a4e4167c431b34cfb9c1c97cf0a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(checkpoint, written, synced):\n    return checkpoint\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)\ncheck('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)\ncheck('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)\ncheck('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)\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":"c2c9d5785e8dc5e6ee25267cc3b2c33d500b35407addd85106854387a30e7600","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(checkpoint, written, synced):\n    return written\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)\ncheck('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)\ncheck('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)\ncheck('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)\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":"75955d7f2881ed1b0d8d1b4311ae5831c9b00b4a9169a57da9b9c2f87f972cf7","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(checkpoint, written, synced):\n    return written if synced else checkpoint\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('resume-checkpoint-after-fsync fixture 0', solve(N,2*N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 1', solve(N,2*N,True), 2*N)\ncheck('resume-checkpoint-after-fsync fixture 2', solve(0,0,False), 0)\ncheck('resume-checkpoint-after-fsync fixture 3', solve(0,N,True), N)\ncheck('resume-checkpoint-after-fsync fixture 4', solve(N,N,False), N)\ncheck('resume-checkpoint-after-fsync fixture 5', solve(0,N,False), 0)\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-resume-checkpoint-after-fsync","generated_at":"2026-09-29T14:41:18.874548+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 written if synced else checkpoint","root_cause":"The resume-checkpoint-after-fsync decision uses return written.","sha256":"44b2ec7b5150fadd274b950db0880c94ab6995b1c7e82e6c4ae370b589f50a3b","title":"Download checkpoints advance only after durable writes · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":40.866,"exit_code":1,"observations":[{"actual":1,"check":"resume-checkpoint-after-fsync fixture 0","expected":1,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 1","expected":2,"passed":false},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 2","expected":0,"passed":true},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 3","expected":1,"passed":false},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 4","expected":1,"passed":true},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 5","expected":0,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"resume-checkpoint-after-fsync fixture 0\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 1\", \"actual\": 1, \"expected\": 2, \"passed\": false}, {\"check\": \"resume-checkpoint-after-fsync fixture 2\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 3\", \"actual\": 0, \"expected\": 1, \"passed\": false}, {\"check\": \"resume-checkpoint-after-fsync fixture 4\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 5\", \"actual\": 0, \"expected\": 0, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.114,"exit_code":1,"observations":[{"actual":2,"check":"resume-checkpoint-after-fsync fixture 0","expected":1,"passed":false},{"actual":2,"check":"resume-checkpoint-after-fsync fixture 1","expected":2,"passed":true},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 2","expected":0,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 3","expected":1,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 4","expected":1,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 5","expected":0,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"resume-checkpoint-after-fsync fixture 0\", \"actual\": 2, \"expected\": 1, \"passed\": false}, {\"check\": \"resume-checkpoint-after-fsync fixture 1\", \"actual\": 2, \"expected\": 2, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 2\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 3\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 4\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 5\", \"actual\": 1, \"expected\": 0, \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":39.125,"exit_code":0,"observations":[{"actual":1,"check":"resume-checkpoint-after-fsync fixture 0","expected":1,"passed":true},{"actual":2,"check":"resume-checkpoint-after-fsync fixture 1","expected":2,"passed":true},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 2","expected":0,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 3","expected":1,"passed":true},{"actual":1,"check":"resume-checkpoint-after-fsync fixture 4","expected":1,"passed":true},{"actual":0,"check":"resume-checkpoint-after-fsync fixture 5","expected":0,"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"resume-checkpoint-after-fsync fixture 0\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 1\", \"actual\": 2, \"expected\": 2, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 2\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 3\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 4\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"resume-checkpoint-after-fsync fixture 5\", \"actual\": 0, \"expected\": 0, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}