{"abstract":"Future keys leak through a reversed causal comparison.","category":"Attention mask construction","checks":6,"contract":"For length L, return an LxL lower triangle including diagonal. L may be zero.","contract_signature":"length","evaluation_group":"causal_triangle_v1","failed_approach":"Comparing every key with the final sequence index makes every in-range key visible, including future keys.","family":"w3-attention-mask-construction-causal-inclusive","id":"FA-98141","implementations":{"attempt":{"sha256":"8b9b0e3b80df1e75c2112ec7adf4ed33bc93512b854bdd406c8210c05e29a8c7","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(length):\n    return [[j<=length-1 for j in range(length)] for i in range(length)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle row',solve(N+1),[[j<=i for j in range(N+1)] for i in range(N+1)])\ncheck('singleton',solve(1),[[True]])\ncheck('empty',solve(0),[])\ncheck('last query',solve(3)[2],[True,True,True])\ncheck('first query',solve(3)[0],[True,False,False])\ncheck('rectangular irrelevant',solve(2),[[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":"ef8173dee3b410222dabca2d9de691d6b04f60c652041c5ef2e81f60e08e924b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(length):\n    return [[j>=i for j in range(length)] for i in range(length)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle row',solve(N+1),[[j<=i for j in range(N+1)] for i in range(N+1)])\ncheck('singleton',solve(1),[[True]])\ncheck('empty',solve(0),[])\ncheck('last query',solve(3)[2],[True,True,True])\ncheck('first query',solve(3)[0],[True,False,False])\ncheck('rectangular irrelevant',solve(2),[[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-causal-inclusive","generated_at":"2026-09-30T16:48:09.758160+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 key-query comparison is reversed, admitting future keys and excluding earlier ones.","sha256":"0104e4991e8d3ed7424a975474c8a8cad8d69849aabaab8b97ee0171e3af5900","title":"Future keys leak through a reversed causal comparison · 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":26.778,"exit_code":1,"observations":[{"actual":[[true,true],[true,true]],"check":"middle row","expected":[[true,false],[true,true]],"passed":false},{"actual":[[true]],"check":"singleton","expected":[[true]],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[true,true,true],"check":"last query","expected":[true,true,true],"passed":true},{"actual":[true,true,true],"check":"first query","expected":[true,false,false],"passed":false},{"actual":[[true,true],[true,true]],"check":"rectangular irrelevant","expected":[[true,false],[true,true]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle row\", \"actual\": [[true, true], [true, true]], \"expected\": [[true, false], [true, true]], \"passed\": false}, {\"check\": \"singleton\", \"actual\": [[true]], \"expected\": [[true]], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"last query\", \"actual\": [true, true, true], \"expected\": [true, true, true], \"passed\": true}, {\"check\": \"first query\", \"actual\": [true, true, true], \"expected\": [true, false, false], \"passed\": false}, {\"check\": \"rectangular irrelevant\", \"actual\": [[true, true], [true, true]], \"expected\": [[true, false], [true, true]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":26.66,"exit_code":1,"observations":[{"actual":[[true,true],[false,true]],"check":"middle row","expected":[[true,false],[true,true]],"passed":false},{"actual":[[true]],"check":"singleton","expected":[[true]],"passed":true},{"actual":[],"check":"empty","expected":[],"passed":true},{"actual":[false,false,true],"check":"last query","expected":[true,true,true],"passed":false},{"actual":[true,true,true],"check":"first query","expected":[true,false,false],"passed":false},{"actual":[[true,true],[false,true]],"check":"rectangular irrelevant","expected":[[true,false],[true,true]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle row\", \"actual\": [[true, true], [false, true]], \"expected\": [[true, false], [true, true]], \"passed\": false}, {\"check\": \"singleton\", \"actual\": [[true]], \"expected\": [[true]], \"passed\": true}, {\"check\": \"empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"last query\", \"actual\": [false, false, true], \"expected\": [true, true, true], \"passed\": false}, {\"check\": \"first query\", \"actual\": [true, true, true], \"expected\": [true, false, false], \"passed\": false}, {\"check\": \"rectangular irrelevant\", \"actual\": [[true, true], [false, true]], \"expected\": [[true, 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."}}