{"abstract":"The final target mask is dropped with the input slice.","category":"Autoregressive target shifting","checks":6,"contract":"Return booleans for labels[1:] indicating whether each target is supervised.","contract_signature":"labels, ignore","evaluation_group":"w3-ars-loss_mask","failed_approach":"Appending a valid mask unconditionally mishandles a final ignored label.","family":"w3-autoregressive-target-shifting-ignore-label-mask-tail","id":"FA-98276","implementations":{"attempt":{"sha256":"1b4ac31602b185fb1e6cc3461feb67ea586b3a5d9b9c7f76f5ba4b4930538c7d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(labels, ignore):\n    return [True for x in labels[1:]]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('terminal ignored',solve([1,2,-1],-1),[True,False])\ncheck('terminal valid',solve([1,2,3],-1),[True,True])\ncheck('two labels',solve([-1,4],-1),[True])\ncheck('singleton',solve([1],-1),[])\ncheck('empty',solve([],-1),[])\ncheck('internal ignore',solve([9,-1,7,8],-1),[False,True,True])\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":"8659a78cadf3e6a833091f7b26293843ba0637178181eacee721122138ad51d5","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(labels, ignore):\n    return [labels[i]!=ignore for i in range(max(0,len(labels)-2))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('terminal ignored',solve([1,2,-1],-1),[True,False])\ncheck('terminal valid',solve([1,2,3],-1),[True,True])\ncheck('two labels',solve([-1,4],-1),[True])\ncheck('singleton',solve([1],-1),[])\ncheck('empty',solve([],-1),[])\ncheck('internal ignore',solve([9,-1,7,8],-1),[False,True,True])\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-ignore-label-mask-tail","generated_at":"2026-09-30T16:48:11.054684+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":"Mask construction zips against the unshifted input length and loses the last target.","sha256":"cd3cc1ab53a4573899efb500a630527ea8ec01d81c703e8530a48bfa323e9f86","title":"The final target mask is dropped with the input slice · case 01","variant":1,"variant_policy":"The same explicitly authored fixtures repeat across all five numbered records; runtime N is unused. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":25.548,"exit_code":1,"observations":[{"actual":[true,true],"check":"terminal ignored","expected":[true,false],"passed":false},{"actual":[true,true],"check":"terminal valid","expected":[true,true],"passed":true},{"actual":[true],"check":"two labels","expected":[true],"passed":true},{"actual":[],"check":"singleton","expected":[],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[true,true,true],"check":"internal ignore","expected":[false,true,true],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"terminal ignored\", \"actual\": [true, true], \"expected\": [true, false], \"passed\": false}, {\"check\": \"terminal valid\", \"actual\": [true, true], \"expected\": [true, true], \"passed\": true}, {\"check\": \"two labels\", \"actual\": [true], \"expected\": [true], \"passed\": true}, {\"check\": \"singleton\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"internal ignore\", \"actual\": [true, true, true], \"expected\": [false, true, true], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":25.228,"exit_code":1,"observations":[{"actual":[true],"check":"terminal ignored","expected":[true,false],"passed":false},{"actual":[true],"check":"terminal valid","expected":[true,true],"passed":false},{"actual":[],"check":"two labels","expected":[true],"passed":false},{"actual":[],"check":"singleton","expected":[],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[true,false],"check":"internal ignore","expected":[false,true,true],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"terminal ignored\", \"actual\": [true], \"expected\": [true, false], \"passed\": false}, {\"check\": \"terminal valid\", \"actual\": [true], \"expected\": [true, true], \"passed\": false}, {\"check\": \"two labels\", \"actual\": [], \"expected\": [true], \"passed\": false}, {\"check\": \"singleton\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"internal ignore\", \"actual\": [true, false], \"expected\": [false, true, true], \"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."}}