{"abstract":"End marker is omitted from next-token supervision.","category":"Autoregressive target shifting","checks":6,"contract":"Return [input,target] pairs for each token followed by eos; empty tokens yield no pair.","contract_signature":"tokens, eos","evaluation_group":"w3-ars-eos_target","failed_approach":"Appending EOS but starting at index one drops the first observed-token target pair.","family":"w3-autoregressive-target-shifting-eos-supervision","id":"FA-98261","implementations":{"attempt":{"sha256":"cd7d206ac643a503b3e6f7f7bc666dec01323fb13d69c7c01562f9e443bb1aa3","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(1,len(s)-1)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('last target eos',solve([N,N+1],99),[[N,N+1],[N+1,99]])\ncheck('one token',solve([4],7),[[4,7]])\ncheck('empty',solve([],7),[])\ncheck('eos equals token',solve([3,3],3),[[3,3],[3,3]])\ncheck('unique tail',solve([1,2,8],5),[[1,2],[2,8],[8,5]])\ncheck('negative token',solve([-1,0],4),[[-1,0],[0,4]])\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":"2bd3de120a1fdefb0f4e79d1fa8d191ffa8df461a572f473d92b84c74c523435","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(tokens, eos):\n    return [[tokens[i],tokens[i+1]] for i in range(len(tokens)-1)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('last target eos',solve([N,N+1],99),[[N,N+1],[N+1,99]])\ncheck('one token',solve([4],7),[[4,7]])\ncheck('empty',solve([],7),[])\ncheck('eos equals token',solve([3,3],3),[[3,3],[3,3]])\ncheck('unique tail',solve([1,2,8],5),[[1,2],[2,8],[8,5]])\ncheck('negative token',solve([-1,0],4),[[-1,0],[0,4]])\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-supervision","generated_at":"2026-09-30T16:48:11.053612+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 target stream ends at the final observed token.","sha256":"ec707ea717eec0c76f9bba60c72f816f6d2797f8e02fc4816d190fe8b8fa5bbc","title":"End marker is omitted from next-token supervision · 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":27.051,"exit_code":1,"observations":[{"actual":[[2,99]],"check":"last target eos","expected":[[1,2],[2,99]],"passed":false},{"actual":[],"check":"one token","expected":[[4,7]],"passed":false},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[[3,3]],"check":"eos equals token","expected":[[3,3],[3,3]],"passed":false},{"actual":[[2,8],[8,5]],"check":"unique tail","expected":[[1,2],[2,8],[8,5]],"passed":false},{"actual":[[0,4]],"check":"negative token","expected":[[-1,0],[0,4]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"last target eos\", \"actual\": [[2, 99]], \"expected\": [[1, 2], [2, 99]], \"passed\": false}, {\"check\": \"one token\", \"actual\": [], \"expected\": [[4, 7]], \"passed\": false}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"eos equals token\", \"actual\": [[3, 3]], \"expected\": [[3, 3], [3, 3]], \"passed\": false}, {\"check\": \"unique tail\", \"actual\": [[2, 8], [8, 5]], \"expected\": [[1, 2], [2, 8], [8, 5]], \"passed\": false}, {\"check\": \"negative token\", \"actual\": [[0, 4]], \"expected\": [[-1, 0], [0, 4]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":25.159,"exit_code":1,"observations":[{"actual":[[1,2]],"check":"last target eos","expected":[[1,2],[2,99]],"passed":false},{"actual":[],"check":"one token","expected":[[4,7]],"passed":false},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[[3,3]],"check":"eos equals token","expected":[[3,3],[3,3]],"passed":false},{"actual":[[1,2],[2,8]],"check":"unique tail","expected":[[1,2],[2,8],[8,5]],"passed":false},{"actual":[[-1,0]],"check":"negative token","expected":[[-1,0],[0,4]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"last target eos\", \"actual\": [[1, 2]], \"expected\": [[1, 2], [2, 99]], \"passed\": false}, {\"check\": \"one token\", \"actual\": [], \"expected\": [[4, 7]], \"passed\": false}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"eos equals token\", \"actual\": [[3, 3]], \"expected\": [[3, 3], [3, 3]], \"passed\": false}, {\"check\": \"unique tail\", \"actual\": [[1, 2], [2, 8]], \"expected\": [[1, 2], [2, 8], [8, 5]], \"passed\": false}, {\"check\": \"negative token\", \"actual\": [[-1, 0]], \"expected\": [[-1, 0], [0, 4]], \"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."}}