{"abstract":"Creation mode subtraction borrows across permission bits.","category":"Filesystem semantics","checks":6,"contract":"Deterministic in-memory filesystem model. Return permission bits for a new file from requested and mask integers in 0..511, using requested AND NOT mask.","contract_signature":"requested, mask","evaluation_group":"model-10baab75d362ce6b","failed_approach":"Clamping subtraction to zero hides negative modes but still changes unrelated permission bits.","family":"z-filesystems-creation-umask","id":"FA-11556","implementations":{"attempt":{"sha256":"e131b80561c5b729c6756bbbed2feb0a72f75ff759d0044efe5d594a3a5a6dd6","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(requested, mask):\n    return max(0,requested-mask)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('absent write bit cannot borrow',solve(0o444,0o022),0o444)\ncheck('normal create',solve(0o666,0o022),0o644)\ncheck('full mask',solve(N,0o777),0)\ncheck('no mask',solve(N,0),N)\ncheck('zero requested',solve(0,N),0)\ncheck('execute only survives write mask',solve(0o111,0o222),0o111)\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":"b03cbe97f18b51a03d005535cfd80e067549584a1198590947d512fcdb9d3988","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(requested, mask):\n    return requested-mask\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('absent write bit cannot borrow',solve(0o444,0o022),0o444)\ncheck('normal create',solve(0o666,0o022),0o644)\ncheck('full mask',solve(N,0o777),0)\ncheck('no mask',solve(N,0),N)\ncheck('zero requested',solve(0,N),0)\ncheck('execute only survives write mask',solve(0o111,0o222),0o111)\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":" 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":"z-filesystems-creation-umask","generated_at":"2026-09-29T14:38:49.008799+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"An offline semantic experiment for file API clients; it models only the stated operations, not a complete operating system.","root_cause":"The creation mask is subtracted as an integer rather than clearing selected permission bits.","sha256":"4f99d026e9e546cbfa954e3c4e4152ba830ac150e7acc97efb2fb7560a77daee","title":"Creation mode subtraction borrows across permission bits · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":39.33,"exit_code":1,"observations":[{"actual":274,"check":"absent write bit cannot borrow","expected":292,"passed":false},{"actual":420,"check":"normal create","expected":420,"passed":true},{"actual":0,"check":"full mask","expected":0,"passed":true},{"actual":1,"check":"no mask","expected":1,"passed":true},{"actual":0,"check":"zero requested","expected":0,"passed":true},{"actual":0,"check":"execute only survives write mask","expected":73,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"absent write bit cannot borrow\", \"actual\": 274, \"expected\": 292, \"passed\": false}, {\"check\": \"normal create\", \"actual\": 420, \"expected\": 420, \"passed\": true}, {\"check\": \"full mask\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"no mask\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"zero requested\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"execute only survives write mask\", \"actual\": 0, \"expected\": 73, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":38.689,"exit_code":1,"observations":[{"actual":274,"check":"absent write bit cannot borrow","expected":292,"passed":false},{"actual":420,"check":"normal create","expected":420,"passed":true},{"actual":-510,"check":"full mask","expected":0,"passed":false},{"actual":1,"check":"no mask","expected":1,"passed":true},{"actual":-1,"check":"zero requested","expected":0,"passed":false},{"actual":-73,"check":"execute only survives write mask","expected":73,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"absent write bit cannot borrow\", \"actual\": 274, \"expected\": 292, \"passed\": false}, {\"check\": \"normal create\", \"actual\": 420, \"expected\": 420, \"passed\": true}, {\"check\": \"full mask\", \"actual\": -510, \"expected\": 0, \"passed\": false}, {\"check\": \"no mask\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"zero requested\", \"actual\": -1, \"expected\": 0, \"passed\": false}, {\"check\": \"execute only survives write mask\", \"actual\": -73, \"expected\": 73, \"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."}}