{"abstract":"Block-causal mask lets keys cross supplied block boundaries.","category":"Attention mask construction","checks":6,"contract":"Given nonnegative block lengths, expand owner IDs; visibility is same owner and causal. Zero-length blocks are allowed.","contract_signature":"lengths","evaluation_group":"length_block_causal_v1","failed_approach":"Restricting a block to adjacent token positions removes valid long-range causal keys.","family":"w3-attention-mask-construction-block-causal-lengths","id":"FA-98206","implementations":{"attempt":{"sha256":"f663cfe5b4c8cc9d7e7421a332e0e88bce8c2a41f7e8d0f3fa831af362f76a7f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(lengths):\n    owners=[]\n    for b,size in enumerate(lengths): owners.extend([b]*size)\n    return [[owners[i]==owners[j] and j<=i and i-j<=1 for j in range(len(owners))] for i in range(len(owners))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nl=[N,0,2]\no=[]\nfor b,z in enumerate(l): o.extend([b]*z)\ncheck('zero block boundary',solve(l),[[o[i]==o[j] and j<=i for j in range(len(o))] for i in range(len(o))])\ncheck('two singleton blocks',solve([1,1]),[[True,False],[False,True]])\ncheck('no blocks',solve([]),[])\ncheck('all empty blocks',solve([0,0]),[])\ncheck('one block',solve([3]),[[True,False,False],[True,True,False],[True,True,True]])\ncheck('trailing empty block',solve([2,0]),[[True,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":"f0ae500e23034cc6fff01e7490ff94b2f8487566f7bddd0f4fe01b241ca5260d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(lengths):\n    return [[j<=i for j in range(sum(lengths))] for i in range(sum(lengths))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nl=[N,0,2]\no=[]\nfor b,z in enumerate(l): o.extend([b]*z)\ncheck('zero block boundary',solve(l),[[o[i]==o[j] and j<=i for j in range(len(o))] for i in range(len(o))])\ncheck('two singleton blocks',solve([1,1]),[[True,False],[False,True]])\ncheck('no blocks',solve([]),[])\ncheck('all empty blocks',solve([0,0]),[])\ncheck('one block',solve([3]),[[True,False,False],[True,True,False],[True,True,True]])\ncheck('trailing empty block',solve([2,0]),[[True,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":"These are toy Boolean matrix contracts; they do not define a production model architecture or tensor library behavior. 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-attention-mask-construction-block-causal-lengths","generated_at":"2026-09-30T16:48:10.630126+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small explicit visibility matrix makes sequence-attention boundary behavior reviewable.","root_cause":"The mask compares flattened positions and never derives the owner of each position.","sha256":"a95cf34d474e1728333e2a2a2257a6c96f4249c1b6cc81938b535079db74bc14","title":"Block-causal mask lets keys cross supplied block boundaries · 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":28.499,"exit_code":1,"observations":[{"actual":[[true,false,false],[false,true,false],[false,true,true]],"check":"zero block boundary","expected":[[true,false,false],[false,true,false],[false,true,true]],"passed":true},{"actual":[[true,false],[false,true]],"check":"two singleton blocks","expected":[[true,false],[false,true]],"passed":true},{"actual":[],"check":"no blocks","expected":[],"passed":true},{"actual":[],"check":"all empty blocks","expected":[],"passed":true},{"actual":[[true,false,false],[true,true,false],[false,true,true]],"check":"one block","expected":[[true,false,false],[true,true,false],[true,true,true]],"passed":false},{"actual":[[true,false],[true,true]],"check":"trailing empty block","expected":[[true,false],[true,true]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"zero block boundary\", \"actual\": [[true, false, false], [false, true, false], [false, true, true]], \"expected\": [[true, false, false], [false, true, false], [false, true, true]], \"passed\": true}, {\"check\": \"two singleton blocks\", \"actual\": [[true, false], [false, true]], \"expected\": [[true, false], [false, true]], \"passed\": true}, {\"check\": \"no blocks\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"all empty blocks\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"one block\", \"actual\": [[true, false, false], [true, true, false], [false, true, true]], \"expected\": [[true, false, false], [true, true, false], [true, true, true]], \"passed\": false}, {\"check\": \"trailing empty block\", \"actual\": [[true, false], [true, true]], \"expected\": [[true, false], [true, true]], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":28.872,"exit_code":1,"observations":[{"actual":[[true,false,false],[true,true,false],[true,true,true]],"check":"zero block boundary","expected":[[true,false,false],[false,true,false],[false,true,true]],"passed":false},{"actual":[[true,false],[true,true]],"check":"two singleton blocks","expected":[[true,false],[false,true]],"passed":false},{"actual":[],"check":"no blocks","expected":[],"passed":true},{"actual":[],"check":"all empty blocks","expected":[],"passed":true},{"actual":[[true,false,false],[true,true,false],[true,true,true]],"check":"one block","expected":[[true,false,false],[true,true,false],[true,true,true]],"passed":true},{"actual":[[true,false],[true,true]],"check":"trailing empty block","expected":[[true,false],[true,true]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"zero block boundary\", \"actual\": [[true, false, false], [true, true, false], [true, true, true]], \"expected\": [[true, false, false], [false, true, false], [false, true, true]], \"passed\": false}, {\"check\": \"two singleton blocks\", \"actual\": [[true, false], [true, true]], \"expected\": [[true, false], [false, true]], \"passed\": false}, {\"check\": \"no blocks\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"all empty blocks\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"one block\", \"actual\": [[true, false, false], [true, true, false], [true, true, true]], \"expected\": [[true, false, false], [true, true, false], [true, true, true]], \"passed\": true}, {\"check\": \"trailing empty block\", \"actual\": [[true, false], [true, true]], \"expected\": [[true, false], [true, true]], \"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."}}