{"abstract":"An Allow response includes HEAD when GET is available.","category":"HTTP semantics","checks":4,"contract":"An Allow response includes HEAD when GET is available: return the result specified by the explicit input/output boundary fixtures.","contract_signature":"methods","evaluation_group":"xh-allow-header","failed_approach":"The attempted repair uses `sorted(set(methods) | {'HEAD'})` and still violates a separate fixture.","family":"xh-allow-header","id":"FA-6606","implementations":{"attempt":{"sha256":"8da925dcb610b2e10a7f7f6e70d2c8b80522e2991f9d8854618207bb02823b66","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(methods):\n    return sorted(set(methods) | {'HEAD'})\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(['GET']), ['GET', 'HEAD'])\", \"check('fixture 2', solve(['POST']), ['POST'])\", \"check('fixture 3', solve([]), [])\", \"check('fixture 4', solve(['HEAD', 'GET', 'GET']), ['GET', 'HEAD'])\"]\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":"20d03718125cc86b029e3cd24729ca9e57f83d495ed7bf79909cdfea0c927c68","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(methods):\n    return sorted(set(methods))\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(['GET']), ['GET', 'HEAD'])\", \"check('fixture 2', solve(['POST']), ['POST'])\", \"check('fixture 3', solve([]), [])\", \"check('fixture 4', solve(['HEAD', 'GET', 'GET']), ['GET', 'HEAD'])\"]\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-allow-header","generated_at":"2026-09-29T14:38:03.701565+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic http semantics model isolates the allow-header policy at a network component boundary.","root_cause":"The faulty implementation uses `sorted(set(methods))` for the allow-header decision.","sha256":"9a527213692e8d4be02748c3b15fe816479d515288ff2aef4b42951404c2544d","title":"An Allow response includes HEAD when GET is available · 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":39.177,"exit_code":1,"observations":[{"actual":["HEAD","POST"],"check":"fixture 2","expected":["POST"],"passed":false},{"actual":["HEAD"],"check":"fixture 3","expected":[],"passed":false},{"actual":["GET","HEAD"],"check":"fixture 4","expected":["GET","HEAD"],"passed":true},{"actual":["GET","HEAD"],"check":"fixture 1","expected":["GET","HEAD"],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": [\"HEAD\", \"POST\"], \"expected\": [\"POST\"], \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": [\"HEAD\"], \"expected\": [], \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": [\"GET\", \"HEAD\"], \"expected\": [\"GET\", \"HEAD\"], \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": [\"GET\", \"HEAD\"], \"expected\": [\"GET\", \"HEAD\"], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":36.133,"exit_code":1,"observations":[{"actual":["POST"],"check":"fixture 2","expected":["POST"],"passed":true},{"actual":[],"check":"fixture 3","expected":[],"passed":true},{"actual":["GET","HEAD"],"check":"fixture 4","expected":["GET","HEAD"],"passed":true},{"actual":["GET"],"check":"fixture 1","expected":["GET","HEAD"],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": [\"POST\"], \"expected\": [\"POST\"], \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [\"GET\", \"HEAD\"], \"expected\": [\"GET\", \"HEAD\"], \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": [\"GET\"], \"expected\": [\"GET\", \"HEAD\"], \"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."}}