{"abstract":"A longer target prefix repeats the final context in extra pairs.","category":"Autoregressive target shifting","checks":6,"contract":"Return zipped context and target pairs; unmatched suffix on either side is ignored.","contract_signature":"context, target","evaluation_group":"w3-ars-target_prefix","failed_approach":"Allowing one extra lookahead pair still duplicates the final available context when targets extend further.","family":"w3-autoregressive-target-shifting-target-prefix-length","id":"FA-98296","implementations":{"attempt":{"sha256":"baf63ba2a28ec0b100fa85fdb51fb9d9cdd6bcd1782c01b1d078133af59747f1","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(context, target):\n    return [[context[min(i,len(context)-1)],target[i]] for i in range(min(len(target),len(context)+1))] if context else []\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('target longer',solve([1],[4,5]),[[1,4]])\ncheck('context longer',solve([1,2],[4]),[[1,4]])\ncheck('equal',solve([N,N+1],[7,8]),[[N,7],[N+1,8]])\ncheck('empty target',solve([1],[]),[])\ncheck('empty context',solve([],[2]),[])\ncheck('both empty',solve([],[]),[])\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":"19e540689ba2a791c8d21a837a9bb073a1cf2c6887e4be423a604b693ff3c960","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(context, target):\n    return [[context[min(i,len(context)-1)],target[i]] for i in range(len(target)) if context]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('target longer',solve([1],[4,5]),[[1,4]])\ncheck('context longer',solve([1,2],[4]),[[1,4]])\ncheck('equal',solve([N,N+1],[7,8]),[[N,7],[N+1,8]])\ncheck('empty target',solve([1],[]),[])\ncheck('empty context',solve([],[2]),[])\ncheck('both empty',solve([],[]),[])\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":"Inputs are toy integer token sequences; this contract says nothing about model quality, batching, sampling, or production training frameworks. 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":"w3-autoregressive-target-shifting-target-prefix-length","generated_at":"2026-09-30T16:48:11.499090+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small deterministic token-stream contract makes next-token alignment errors inspectable.","root_cause":"Pair generation repeats the last context when target positions outnumber context positions.","sha256":"c72d968eafa40039232c372917f9c770fdc31fd8e076781fe585cd85ed7d6cd1","title":"A longer target prefix repeats the final context in extra pairs · case 01","variant":1,"variant_policy":"The fixture code references N, supplied as 1 through 5. Fixed boundary checks may repeat. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":28.703,"exit_code":1,"observations":[{"actual":[[1,4],[1,5]],"check":"target longer","expected":[[1,4]],"passed":false},{"actual":[[1,4]],"check":"context longer","expected":[[1,4]],"passed":true},{"actual":[[1,7],[2,8]],"check":"equal","expected":[[1,7],[2,8]],"passed":true},{"actual":[],"check":"empty target","expected":[],"passed":true},{"actual":[],"check":"empty context","expected":[],"passed":true},{"actual":[],"check":"both empty","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"target longer\", \"actual\": [[1, 4], [1, 5]], \"expected\": [[1, 4]], \"passed\": false}, {\"check\": \"context longer\", \"actual\": [[1, 4]], \"expected\": [[1, 4]], \"passed\": true}, {\"check\": \"equal\", \"actual\": [[1, 7], [2, 8]], \"expected\": [[1, 7], [2, 8]], \"passed\": true}, {\"check\": \"empty target\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty context\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":27.796,"exit_code":1,"observations":[{"actual":[[1,4],[1,5]],"check":"target longer","expected":[[1,4]],"passed":false},{"actual":[[1,4]],"check":"context longer","expected":[[1,4]],"passed":true},{"actual":[[1,7],[2,8]],"check":"equal","expected":[[1,7],[2,8]],"passed":true},{"actual":[],"check":"empty target","expected":[],"passed":true},{"actual":[],"check":"empty context","expected":[],"passed":true},{"actual":[],"check":"both empty","expected":[],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"target longer\", \"actual\": [[1, 4], [1, 5]], \"expected\": [[1, 4]], \"passed\": false}, {\"check\": \"context longer\", \"actual\": [[1, 4]], \"expected\": [[1, 4]], \"passed\": true}, {\"check\": \"equal\", \"actual\": [[1, 7], [2, 8]], \"expected\": [[1, 7], [2, 8]], \"passed\": true}, {\"check\": \"empty target\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty context\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"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."}}