{"abstract":"The operation returns a result or retained state that violates this contract: Update existing keys from the right map while retaining left insertion positions and appending new right keys.","category":"Mapping semantics","checks":4,"contract":"Update existing keys from the right map while retaining left insertion positions and appending new right keys. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-2da7a4cffd0d8d36","failed_approach":"Skipping existing keys prevents required overwrites.","family":"xr-map-update-right-precedence","id":"FA-4396","implementations":{"attempt":{"sha256":"79647244a0cd48e3747d60be48388a6057dc733fa65682dbbed32b7fbeb4991d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [[k,v] for k,v in x.items()]+[[k,v] for k,v in y.items() if k not in x]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('overwrite and insert', solve({'a': 1, 'b': 2}, {'a': 3, 'c': 4}), [['a', 3], ['b', 2], ['c', 4]])\ncheck('empty left', solve({}, {'a': 1}), [['a', 1]])\ncheck('empty right', solve({'a': 1}, {}), [['a', 1]])\ncheck('None overwrite', solve({'a': 1}, {'a': None}), [['a', None]])\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":"b81b36bc4b74f8db334ce779cdcf46e96dc2cc4ac8adc90e62b8769f2e4aeb0f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    a=dict(y); a.update(x); return list(map(list,a.items()))\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('overwrite and insert', solve({'a': 1, 'b': 2}, {'a': 3, 'c': 4}), [['a', 3], ['b', 2], ['c', 4]])\ncheck('empty left', solve({}, {'a': 1}), [['a', 1]])\ncheck('empty right', solve({'a': 1}, {}), [['a', 1]])\ncheck('None overwrite', solve({'a': 1}, {'a': None}), [['a', None]])\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":"xr-map-update-right-precedence","generated_at":"2026-09-29T14:37:38.546669+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","root_cause":"Reversing update operands gives stale left values precedence and changes insertion order.","sha256":"e6bdf77a2d7c9fd23f2aebd27b209f509dd0cb2b53f2669ecf45945a0e87f3bc","title":"Map update right precedence · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":38.253,"exit_code":1,"observations":[{"actual":[["a",1],["b",2],["c",4]],"check":"overwrite and insert","expected":[["a",3],["b",2],["c",4]],"passed":false},{"actual":[["a",1]],"check":"empty left","expected":[["a",1]],"passed":true},{"actual":[["a",1]],"check":"empty right","expected":[["a",1]],"passed":true},{"actual":[["a",1]],"check":"None overwrite","expected":[["a",null]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overwrite and insert\", \"actual\": [[\"a\", 1], [\"b\", 2], [\"c\", 4]], \"expected\": [[\"a\", 3], [\"b\", 2], [\"c\", 4]], \"passed\": false}, {\"check\": \"empty left\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", 1]], \"passed\": true}, {\"check\": \"empty right\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", 1]], \"passed\": true}, {\"check\": \"None overwrite\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", null]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.3,"exit_code":1,"observations":[{"actual":[["a",1],["c",4],["b",2]],"check":"overwrite and insert","expected":[["a",3],["b",2],["c",4]],"passed":false},{"actual":[["a",1]],"check":"empty left","expected":[["a",1]],"passed":true},{"actual":[["a",1]],"check":"empty right","expected":[["a",1]],"passed":true},{"actual":[["a",1]],"check":"None overwrite","expected":[["a",null]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overwrite and insert\", \"actual\": [[\"a\", 1], [\"c\", 4], [\"b\", 2]], \"expected\": [[\"a\", 3], [\"b\", 2], [\"c\", 4]], \"passed\": false}, {\"check\": \"empty left\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", 1]], \"passed\": true}, {\"check\": \"empty right\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", 1]], \"passed\": true}, {\"check\": \"None overwrite\", \"actual\": [[\"a\", 1]], \"expected\": [[\"a\", null]], \"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."}}