{"abstract":"Dns server retry excludes already failed servers.","category":"DNS resolution","checks":4,"contract":"Given servers, failures, transport, dns server retry excludes already failed servers. Return the protocol decision or transformed value; fields are validated and fixtures state boundary outcomes.","contract_signature":"servers, failures, transport","evaluation_group":"xh-dns-server-retry-excludes-already-failed-servers","failed_approach":"The attempted repair uses `[s for s in servers if not any(f[0] == s for f in failures)]` and still violates a separate fixture.","family":"xh-dns-server-retry-excludes-already-failed-servers","id":"FA-7421","implementations":{"attempt":{"sha256":"5ad2c4af502534b6e66a1be73ed89fa5db6356ad1cfe6fdc3463a298da4d68f9","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(servers, failures, transport):\n    return [s for s in servers if not any(f[0] == s for f in failures)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(['a', 'b'], [('a', 'udp')], 'udp'), ['b'])\", \"check('fixture 2', solve(['a'], [('a', 'udp')], 'tcp'), ['a'])\", \"check('fixture 3', solve([], [], 'udp'), [])\", \"check('fixture 4', solve(['a'], [], 'udp'), ['a'])\"]\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":"aad6913a3a28384fba164de656dcdf83f072063ceb6866bb122b38e18ab2bb07","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(servers, failures, transport):\n    return servers\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(['a', 'b'], [('a', 'udp')], 'udp'), ['b'])\", \"check('fixture 2', solve(['a'], [('a', 'udp')], 'tcp'), ['a'])\", \"check('fixture 3', solve([], [], 'udp'), [])\", \"check('fixture 4', solve(['a'], [], 'udp'), ['a'])\"]\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-server-retry-excludes-already-failed-servers","generated_at":"2026-09-29T14:38:11.774495+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic dns resolution model isolates the dns-server-retry-excludes-already-failed-servers policy at a network component boundary.","root_cause":"The faulty implementation uses `servers` for the dns-server-retry-excludes-already-failed-servers decision.","sha256":"db34cd57c6ccf681287b23be03700b2f0ea989cdb69c19a788e829119e3770a8","title":"Dns server retry excludes already failed servers · 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":48.11,"exit_code":1,"observations":[{"actual":[],"check":"fixture 2","expected":["a"],"passed":false},{"actual":[],"check":"fixture 3","expected":[],"passed":true},{"actual":["a"],"check":"fixture 4","expected":["a"],"passed":true},{"actual":["b"],"check":"fixture 1","expected":["b"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": [], \"expected\": [\"a\"], \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": [\"b\"], \"expected\": [\"b\"], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":45.056,"exit_code":1,"observations":[{"actual":["a"],"check":"fixture 2","expected":["a"],"passed":true},{"actual":[],"check":"fixture 3","expected":[],"passed":true},{"actual":["a"],"check":"fixture 4","expected":["a"],"passed":true},{"actual":["a","b"],"check":"fixture 1","expected":["b"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [\"a\"], \"expected\": [\"a\"], \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": [\"a\", \"b\"], \"expected\": [\"b\"], \"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."}}