{"abstract":"After a partial batch failure, resumption skips work that never completed.","category":"Queues","checks":3,"contract":"Persist the first unacknowledged index as the next resume position.","evaluation_group":"model-bea795411b7c52e2","failed_approach":"Rolling back an extra position replays an already acknowledged item.","family":"checkpoint","id":"FA-031","implementations":{"attempt":{"sha256":"83d7aab3319be99157ac3205fc3c7dcc518346e1c053ef281ef6550d17d0c33f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(batch, failed_index):\n    return max(0, failed_index - 1) if failed_index is not None else len(batch)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbatch = list(range(N+3))\ncheck('partial failure', solve(batch, N), N)\ncheck('first item fails', solve(batch, 0), 0)\ncheck('complete batch', solve(batch, None), len(batch))\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":"d9ede88a8d0577ff115ee0f70a43b2ecf292de7d1384e1e00509e3009dc5e289","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(batch, failed_index):\n    return len(batch)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbatch = list(range(N+3))\ncheck('partial failure', solve(batch, N), N)\ncheck('first item fails', solve(batch, 0), 0)\ncheck('complete batch', solve(batch, None), len(batch))\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":"45d32b7705d943f0e4b3909406637ed3f4142e2196a470b1ae45686b3201de7d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(batch, failed_index):\n    return failed_index if failed_index is not None else len(batch)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nbatch = list(range(N+3))\ncheck('partial failure', solve(batch, N), N)\ncheck('first item fails', solve(batch, 0), 0)\ncheck('complete batch', solve(batch, None), len(batch))\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":"checkpoint","generated_at":"2026-09-29T14:36:49.870403+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A compact reasoning and repair task with executable evidence.","repair":"Persist the first unacknowledged index as the next resume position.","root_cause":"The checkpoint records attempted batch length instead of the acknowledged prefix.","sha256":"44398ab763239ec3caeec50546a53c44e613098bcb472e440de543474d9fd16e","title":"A checkpoint advances past an unacknowledged item · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":32.243,"exit_code":1,"observations":[{"actual":0,"check":"partial failure","expected":1,"passed":false},{"actual":0,"check":"first item fails","expected":0,"passed":true},{"actual":4,"check":"complete batch","expected":4,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"partial failure\", \"actual\": 0, \"expected\": 1, \"passed\": false}, {\"check\": \"first item fails\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"complete batch\", \"actual\": 4, \"expected\": 4, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.144,"exit_code":1,"observations":[{"actual":4,"check":"partial failure","expected":1,"passed":false},{"actual":4,"check":"first item fails","expected":0,"passed":false},{"actual":4,"check":"complete batch","expected":4,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"partial failure\", \"actual\": 4, \"expected\": 1, \"passed\": false}, {\"check\": \"first item fails\", \"actual\": 4, \"expected\": 0, \"passed\": false}, {\"check\": \"complete batch\", \"actual\": 4, \"expected\": 4, \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":31.293,"exit_code":0,"observations":[{"actual":1,"check":"partial failure","expected":1,"passed":true},{"actual":0,"check":"first item fails","expected":0,"passed":true},{"actual":4,"check":"complete batch","expected":4,"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"partial failure\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"first item fails\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"complete batch\", \"actual\": 4, \"expected\": 4, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}