{"abstract":"The end marker receives a spurious outgoing prediction.","category":"Autoregressive target shifting","checks":6,"contract":"Return one pair per observed token, with EOS as the final target and never as an input.","contract_signature":"tokens, eos","evaluation_group":"w3-ars-eos_target","failed_approach":"Filtering EOS-valued inputs also drops legitimate content when a token value equals the configured EOS sentinel.","family":"w3-autoregressive-target-shifting-eos-input-leak","id":"FA-98266","implementations":{"attempt":{"sha256":"dae5781ed5a60d366a1931b5a2758a4f191b552a3131c3b8b14d71b80628ace1","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(tokens, eos):\n    s=tokens+[eos]\n    return [[s[i],s[i+1]] for i in range(len(s)-1) if s[i]!=eos]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('no eos input',solve([1,2],9),[[1,2],[2,9]])\ncheck('single token',solve([N],8),[[N,8]])\ncheck('empty',solve([],8),[])\ncheck('eos repeated',solve([3,3],3),[[3,3],[3,3]])\ncheck('several',solve([4,5,6],0),[[4,5],[5,6],[6,0]])\ncheck('eos first token',solve([0,1],0),[[0,1],[1,0]])\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":"b6688ec079063cdbfbd05febbd349a7c1c39cc109f8994f55e8a37862b479164","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(tokens, eos):\n    s=tokens+[eos]\n    return [[s[i],s[i+1]] for i in range(len(s)-1)] + ([[eos,eos]] if tokens else [])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('no eos input',solve([1,2],9),[[1,2],[2,9]])\ncheck('single token',solve([N],8),[[N,8]])\ncheck('empty',solve([],8),[])\ncheck('eos repeated',solve([3,3],3),[[3,3],[3,3]])\ncheck('several',solve([4,5,6],0),[[4,5],[5,6],[6,0]])\ncheck('eos first token',solve([0,1],0),[[0,1],[1,0]])\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":"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-eos-input-leak","generated_at":"2026-09-30T16:48:11.055048+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":"The pair builder adds an artificial EOS-to-EOS transition after the valid terminal target.","sha256":"0248bc5a0a21b4d4e669ad589754812b558be619c54f807a469fea41acccf8df","title":"The end marker receives a spurious outgoing prediction · 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":27.938,"exit_code":1,"observations":[{"actual":[[1,2],[2,9]],"check":"no eos input","expected":[[1,2],[2,9]],"passed":true},{"actual":[[1,8]],"check":"single token","expected":[[1,8]],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[],"check":"eos repeated","expected":[[3,3],[3,3]],"passed":false},{"actual":[[4,5],[5,6],[6,0]],"check":"several","expected":[[4,5],[5,6],[6,0]],"passed":true},{"actual":[[1,0]],"check":"eos first token","expected":[[0,1],[1,0]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"no eos input\", \"actual\": [[1, 2], [2, 9]], \"expected\": [[1, 2], [2, 9]], \"passed\": true}, {\"check\": \"single token\", \"actual\": [[1, 8]], \"expected\": [[1, 8]], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"eos repeated\", \"actual\": [], \"expected\": [[3, 3], [3, 3]], \"passed\": false}, {\"check\": \"several\", \"actual\": [[4, 5], [5, 6], [6, 0]], \"expected\": [[4, 5], [5, 6], [6, 0]], \"passed\": true}, {\"check\": \"eos first token\", \"actual\": [[1, 0]], \"expected\": [[0, 1], [1, 0]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":25.541,"exit_code":1,"observations":[{"actual":[[1,2],[2,9],[9,9]],"check":"no eos input","expected":[[1,2],[2,9]],"passed":false},{"actual":[[1,8],[8,8]],"check":"single token","expected":[[1,8]],"passed":false},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[[3,3],[3,3],[3,3]],"check":"eos repeated","expected":[[3,3],[3,3]],"passed":false},{"actual":[[4,5],[5,6],[6,0],[0,0]],"check":"several","expected":[[4,5],[5,6],[6,0]],"passed":false},{"actual":[[0,1],[1,0],[0,0]],"check":"eos first token","expected":[[0,1],[1,0]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"no eos input\", \"actual\": [[1, 2], [2, 9], [9, 9]], \"expected\": [[1, 2], [2, 9]], \"passed\": false}, {\"check\": \"single token\", \"actual\": [[1, 8], [8, 8]], \"expected\": [[1, 8]], \"passed\": false}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"eos repeated\", \"actual\": [[3, 3], [3, 3], [3, 3]], \"expected\": [[3, 3], [3, 3]], \"passed\": false}, {\"check\": \"several\", \"actual\": [[4, 5], [5, 6], [6, 0], [0, 0]], \"expected\": [[4, 5], [5, 6], [6, 0]], \"passed\": false}, {\"check\": \"eos first token\", \"actual\": [[0, 1], [1, 0], [0, 0]], \"expected\": [[0, 1], [1, 0]], \"passed\": false}], \"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."}}