{"abstract":"Dns servfail is retryable while nxdomain is terminal.","category":"DNS resolution","checks":4,"contract":"Bounded offline decision model: dns servfail is retryable while nxdomain is terminal. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.","evaluation_group":"xh-dns-servfail-is-retryable-while-nxdomain-is-terminal","failed_approach":"The attempted repair uses `rcode == 2` and still violates a separate fixture.","family":"xh-dns-servfail-is-retryable-while-nxdomain-is-terminal","id":"FA-7416","implementations":{"attempt":{"sha256":"352811ad97e74d7a2d68dea7d60aa52203634859cad4b1d66519ef308dce3005","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(rcode):\n    return rcode == 2\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(2), True)\", \"check('fixture 2', solve(5), True)\", \"check('fixture 3', solve(3), False)\", \"check('fixture 4', solve(0), False)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\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":"6a71c9db791c3fb6767fa05d27a153bec99d71eebc9d3f1fdcce6992920c6485","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(rcode):\n    return rcode != 0\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(2), True)\", \"check('fixture 2', solve(5), True)\", \"check('fixture 3', solve(3), False)\", \"check('fixture 4', solve(0), False)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\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"},"fixed":{"sha256":"a4e6dd6f5ab904aa05e23936875f23a1519fcd5f16998d61461ff2c681c27f04","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(rcode):\n    return rcode in (2,5)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(2), True)\", \"check('fixture 2', solve(5), True)\", \"check('fixture 3', solve(3), False)\", \"check('fixture 4', solve(0), False)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\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":"Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. 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":"xh-dns-servfail-is-retryable-while-nxdomain-is-terminal","generated_at":"2026-09-29T14:38:11.736229+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic dns resolution model isolates the dns-servfail-is-retryable-while-nxdomain-is-terminal policy at a network component boundary.","repair":"Apply the explicit dns-servfail-is-retryable-while-nxdomain-is-terminal contract, including the tested boundary and negative cases.","root_cause":"The faulty implementation uses `rcode != 0` for the dns-servfail-is-retryable-while-nxdomain-is-terminal decision.","sha256":"d20022125b1d94ca1306b60780abc95e3749933a51f234f0e2c526abd08bd3d3","title":"Dns servfail is retryable while nxdomain is terminal · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":42.29,"exit_code":1,"observations":[{"actual":false,"check":"fixture 2","expected":true,"passed":false},{"actual":false,"check":"fixture 3","expected":false,"passed":true},{"actual":false,"check":"fixture 4","expected":false,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":42.345,"exit_code":1,"observations":[{"actual":true,"check":"fixture 2","expected":true,"passed":true},{"actual":true,"check":"fixture 3","expected":false,"passed":false},{"actual":false,"check":"fixture 4","expected":false,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":55.852,"exit_code":0,"observations":[{"actual":true,"check":"fixture 2","expected":true,"passed":true},{"actual":false,"check":"fixture 3","expected":false,"passed":true},{"actual":false,"check":"fixture 4","expected":false,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}