{"abstract":"Left padding marks padded prefix tokens as valid.","category":"Sequence batch packing","checks":6,"contract":"Left-pad tokens with zero to width and return paired binary validity mask, where only original token slots are one.","contract_signature":"tokens, width","evaluation_group":"w3-seqpack-left-pad-mask-v1","failed_approach":"An off-by-one suffix includes a padding slot or exceeds the requested width.","family":"w3-sequence-batch-packing-left-padding-mask","id":"FA-98056","implementations":{"attempt":{"sha256":"bbb44dad81bb2ab8dec2fac90c049e717977068883d832411d19bad54462e9d5","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(tokens, width):\n    pad=width-len(tokens); return [0]*pad+tokens, [0]*pad+([1]*(len(tokens)+1))[:width]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('short prefix', solve([N],N+2), ([0]*(N+1)+[N],[0]*(N+1)+[1]))\ncheck('full width', solve([1]*N,N), ([1]*N,[1]*N))\ncheck('empty row', solve([],N), ([0]*N,[0]*N))\ncheck('one slot', solve([N],1), ([N],[1]))\ncheck('mixed row', solve([2,3],4), ([0,0,2,3],[0,0,1,1]))\ncheck('zero width', solve([],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":"4dd63d8df494b3c015db4df63f7cc5cf75b1a3813b9fa81cf98643988c60ecdf","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(tokens, width):\n    pad=width-len(tokens); return [0]*pad+tokens, [1]*width\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('short prefix', solve([N],N+2), ([0]*(N+1)+[N],[0]*(N+1)+[1]))\ncheck('full width', solve([1]*N,N), ([1]*N,[1]*N))\ncheck('empty row', solve([],N), ([0]*N,[0]*N))\ncheck('one slot', solve([N],1), ([N],[1]))\ncheck('mixed row', solve([2,3],4), ([0,0,2,3],[0,0,1,1]))\ncheck('zero width', solve([],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 short integer-token lists under the stated toy contract; results do not claim compatibility with a specific training framework. 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-sequence-batch-packing-left-padding-mask","generated_at":"2026-09-30T16:48:08.895672+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic toy packing rule models a common boundary in preparing bounded training sequences.","root_cause":"The validity mask is initialized as all valid, including left-padding slots.","sha256":"73682cf99c5325414fef7b5dfd8226ee1bf6be7d9043333355d7332ce8cf02ce","title":"Left padding marks padded prefix tokens as valid · 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":29.784,"exit_code":1,"observations":[{"actual":[[0,0,1],[0,0,1,1]],"check":"short prefix","expected":[[0,0,1],[0,0,1]],"passed":false},{"actual":[[1],[1]],"check":"full width","expected":[[1],[1]],"passed":true},{"actual":[[0],[0,1]],"check":"empty row","expected":[[0],[0]],"passed":false},{"actual":[[1],[1]],"check":"one slot","expected":[[1],[1]],"passed":true},{"actual":[[0,0,2,3],[0,0,1,1,1]],"check":"mixed row","expected":[[0,0,2,3],[0,0,1,1]],"passed":false},{"actual":[[],[]],"check":"zero width","expected":[[],[]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"short prefix\", \"actual\": [[0, 0, 1], [0, 0, 1, 1]], \"expected\": [[0, 0, 1], [0, 0, 1]], \"passed\": false}, {\"check\": \"full width\", \"actual\": [[1], [1]], \"expected\": [[1], [1]], \"passed\": true}, {\"check\": \"empty row\", \"actual\": [[0], [0, 1]], \"expected\": [[0], [0]], \"passed\": false}, {\"check\": \"one slot\", \"actual\": [[1], [1]], \"expected\": [[1], [1]], \"passed\": true}, {\"check\": \"mixed row\", \"actual\": [[0, 0, 2, 3], [0, 0, 1, 1, 1]], \"expected\": [[0, 0, 2, 3], [0, 0, 1, 1]], \"passed\": false}, {\"check\": \"zero width\", \"actual\": [[], []], \"expected\": [[], []], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":30.183,"exit_code":1,"observations":[{"actual":[[0,0,1],[1,1,1]],"check":"short prefix","expected":[[0,0,1],[0,0,1]],"passed":false},{"actual":[[1],[1]],"check":"full width","expected":[[1],[1]],"passed":true},{"actual":[[0],[1]],"check":"empty row","expected":[[0],[0]],"passed":false},{"actual":[[1],[1]],"check":"one slot","expected":[[1],[1]],"passed":true},{"actual":[[0,0,2,3],[1,1,1,1]],"check":"mixed row","expected":[[0,0,2,3],[0,0,1,1]],"passed":false},{"actual":[[],[]],"check":"zero width","expected":[[],[]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"short prefix\", \"actual\": [[0, 0, 1], [1, 1, 1]], \"expected\": [[0, 0, 1], [0, 0, 1]], \"passed\": false}, {\"check\": \"full width\", \"actual\": [[1], [1]], \"expected\": [[1], [1]], \"passed\": true}, {\"check\": \"empty row\", \"actual\": [[0], [1]], \"expected\": [[0], [0]], \"passed\": false}, {\"check\": \"one slot\", \"actual\": [[1], [1]], \"expected\": [[1], [1]], \"passed\": true}, {\"check\": \"mixed row\", \"actual\": [[0, 0, 2, 3], [1, 1, 1, 1]], \"expected\": [[0, 0, 2, 3], [0, 0, 1, 1]], \"passed\": false}, {\"check\": \"zero width\", \"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."}}