{"abstract":"Drops the first variadic argument after binding and changes the required Python-language result.","category":"Call argument binding","checks":6,"contract":"Call f(a, *tail, flag=False), returning [a,list(tail),flag]. flag must be named; arbitrary extra positions belong to tail. Inputs use the finite Python types shown in the fixtures. An error string denotes the specified caught exception, not an unhandled process failure.","contract_signature":"args, kwargs","evaluation_group":"xl-variadic-positional-binding","failed_approach":"The alternative still fails because it copies a named flag into the positional tail.","family":"xl-variadic-positional-binding-tail-first-lost","id":"FA-4896","implementations":{"attempt":{"sha256":"2c35d383c290f5eb2d51e6880fcb0c06f1881f78f523096577f1430bb0bdd66c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(args, kwargs):\n    def f(a, *tail, flag=False):\n        return [a,list(tail)+([flag] if flag is not False else []),flag]\n    try:\n        return f(*args, **kwargs)\n    except TypeError:\n        return \"TypeError\"\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('only required', solve([1], {}), [1, [], False])\ncheck('several extras', solve([1, 2, 3], {}), [1, [2, 3], False])\ncheck('named flag', solve([1, 2], {'flag': True}), [1, [2], True])\ncheck('nested tail preserved', solve([1, [2, 3]], {}), [1, [[2, 3]], False])\ncheck('unknown keyword', solve([1], {'other': 2}), 'TypeError')\ncheck('missing required', solve([], {}), 'TypeError')\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":"b041e88f271e3abecd95ef47062035f7c8e9bef889719f080a710165b2983432","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(args, kwargs):\n    def f(a, *tail, flag=False):\n        return [a,list(tail[1:]),flag]\n    try:\n        return f(*args, **kwargs)\n    except TypeError:\n        return \"TypeError\"\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('only required', solve([1], {}), [1, [], False])\ncheck('several extras', solve([1, 2, 3], {}), [1, [2, 3], False])\ncheck('named flag', solve([1, 2], {'flag': True}), [1, [2], True])\ncheck('nested tail preserved', solve([1, [2, 3]], {}), [1, [[2, 3]], False])\ncheck('unknown keyword', solve([1], {'other': 2}), 'TypeError')\ncheck('missing required', solve([], {}), 'TypeError')\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":"xl-variadic-positional-binding-tail-first-lost","generated_at":"2026-09-29T14:37:44.082047+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Runs Python standard-library language operations in a deterministic local reproducer. Literal expected answers are authored independently. Related defects share an evaluation group to avoid benchmark split leakage.","root_cause":"Drops the first variadic argument after binding. The executable reproducer isolates this operation from the rest of the contract.","sha256":"98dfe0a0a2a285f2b7ecf35c42f456070bc733e1646b84ef85269d47066d05e3","title":"Variadic positional binding: Drops the first variadic argument after binding · case 01","variant":1,"variant_policy":"The five numbered cases rerun the same authored boundary fixtures; they are reproducibility runs, not independent input variants.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":38.974,"exit_code":1,"observations":[{"actual":[1,[],false],"check":"only required","expected":[1,[],false],"passed":true},{"actual":[1,[2,3],false],"check":"several extras","expected":[1,[2,3],false],"passed":true},{"actual":[1,[2,true],true],"check":"named flag","expected":[1,[2],true],"passed":false},{"actual":[1,[[2,3]],false],"check":"nested tail preserved","expected":[1,[[2,3]],false],"passed":true},{"actual":"TypeError","check":"unknown keyword","expected":"TypeError","passed":true},{"actual":"TypeError","check":"missing required","expected":"TypeError","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"only required\", \"actual\": [1, [], false], \"expected\": [1, [], false], \"passed\": true}, {\"check\": \"several extras\", \"actual\": [1, [2, 3], false], \"expected\": [1, [2, 3], false], \"passed\": true}, {\"check\": \"named flag\", \"actual\": [1, [2, true], true], \"expected\": [1, [2], true], \"passed\": false}, {\"check\": \"nested tail preserved\", \"actual\": [1, [[2, 3]], false], \"expected\": [1, [[2, 3]], false], \"passed\": true}, {\"check\": \"unknown keyword\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}, {\"check\": \"missing required\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.335,"exit_code":1,"observations":[{"actual":[1,[],false],"check":"only required","expected":[1,[],false],"passed":true},{"actual":[1,[3],false],"check":"several extras","expected":[1,[2,3],false],"passed":false},{"actual":[1,[],true],"check":"named flag","expected":[1,[2],true],"passed":false},{"actual":[1,[],false],"check":"nested tail preserved","expected":[1,[[2,3]],false],"passed":false},{"actual":"TypeError","check":"unknown keyword","expected":"TypeError","passed":true},{"actual":"TypeError","check":"missing required","expected":"TypeError","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"only required\", \"actual\": [1, [], false], \"expected\": [1, [], false], \"passed\": true}, {\"check\": \"several extras\", \"actual\": [1, [3], false], \"expected\": [1, [2, 3], false], \"passed\": false}, {\"check\": \"named flag\", \"actual\": [1, [], true], \"expected\": [1, [2], true], \"passed\": false}, {\"check\": \"nested tail preserved\", \"actual\": [1, [], false], \"expected\": [1, [[2, 3]], false], \"passed\": false}, {\"check\": \"unknown keyword\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}, {\"check\": \"missing required\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"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."}}