{"abstract":"Representation identity ignores one of the selected request headers.","category":"Caching","checks":4,"contract":"Header names are already normalized lowercase and values are strings. Return sorted unique requested Vary names paired with value or None for missing fields; ignore unselected headers.","evaluation_group":"xc-vary-field-values","failed_approach":"Keying on every request header fragments entries on unrelated tracing metadata.","family":"xc-vary-field-values","id":"FA-10476","implementations":{"attempt":{"sha256":"09207463d2e86b7318329ffb02073419163f2396a378a57e25facba639ce7903","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(vary, headers):\n    return [[name,headers.get(name)] for name in sorted(headers)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*(['accept', 'lang'], {'accept': 'json', 'lang': 'fr', 'trace': 'x'})), [['accept', 'json'], ['lang', 'fr']])\ncheck('fixture 2', solve(*(['lang'], {'lang': 'en', 'trace': 'y'})), [['lang', 'en']])\ncheck('fixture 3', solve(*([], {'trace': 'x'})), [])\ncheck('fixture 4', solve(*(['lang', 'lang'], {})), [['lang', 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":"2642f1fa52920c871369c42739ddb5189959113c453d93a2c14856592f69c781","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(vary, headers):\n    return [[name,headers.get(name)] for name in vary[:1]]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*(['accept', 'lang'], {'accept': 'json', 'lang': 'fr', 'trace': 'x'})), [['accept', 'json'], ['lang', 'fr']])\ncheck('fixture 2', solve(*(['lang'], {'lang': 'en', 'trace': 'y'})), [['lang', 'en']])\ncheck('fixture 3', solve(*([], {'trace': 'x'})), [])\ncheck('fixture 4', solve(*(['lang', 'lang'], {})), [['lang', 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"},"fixed":{"sha256":"25adf4e19484d84e6e7abbb37b64f15595158a614392254bb70631eaa3fa2fa1","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(vary, headers):\n    return [[name,headers.get(name)] for name in sorted(set(vary))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*(['accept', 'lang'], {'accept': 'json', 'lang': 'fr', 'trace': 'x'})), [['accept', 'json'], ['lang', 'fr']])\ncheck('fixture 2', solve(*(['lang'], {'lang': 'en', 'trace': 'y'})), [['lang', 'en']])\ncheck('fixture 3', solve(*([], {'trace': 'x'})), [])\ncheck('fixture 4', solve(*(['lang', 'lang'], {})), [['lang', 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":"xc-vary-field-values","generated_at":"2026-09-29T14:38:39.315665+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic cache state transformation. Inputs are copied or treated as immutable; no remote storage, real clock, or concurrent interleaving is simulated.","repair":"Preserve the cache-state invariant: Header names are already normalized lowercase and values are strings. Return sorted unique requested Vary names paired with value or None for missing fields; ignore unselected headers.","root_cause":"A multi-header variant key keeps only the first selected dimension.","sha256":"284df38a0d678ee2d94a041a9f6f9c310ac6a9b80817fba5549b94931d108a4a","title":"Representation identity ignores one of the selected request headers · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":41.813,"exit_code":1,"observations":[{"actual":[["accept","json"],["lang","fr"],["trace","x"]],"check":"fixture 1","expected":[["accept","json"],["lang","fr"]],"passed":false},{"actual":[["lang","en"],["trace","y"]],"check":"fixture 2","expected":[["lang","en"]],"passed":false},{"actual":[["trace","x"]],"check":"fixture 3","expected":[],"passed":false},{"actual":[],"check":"fixture 4","expected":[["lang",null]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": [[\"accept\", \"json\"], [\"lang\", \"fr\"], [\"trace\", \"x\"]], \"expected\": [[\"accept\", \"json\"], [\"lang\", \"fr\"]], \"passed\": false}, {\"check\": \"fixture 2\", \"actual\": [[\"lang\", \"en\"], [\"trace\", \"y\"]], \"expected\": [[\"lang\", \"en\"]], \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": [[\"trace\", \"x\"]], \"expected\": [], \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": [], \"expected\": [[\"lang\", null]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":43.493,"exit_code":1,"observations":[{"actual":[["accept","json"]],"check":"fixture 1","expected":[["accept","json"],["lang","fr"]],"passed":false},{"actual":[["lang","en"]],"check":"fixture 2","expected":[["lang","en"]],"passed":true},{"actual":[],"check":"fixture 3","expected":[],"passed":true},{"actual":[["lang",null]],"check":"fixture 4","expected":[["lang",null]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": [[\"accept\", \"json\"]], \"expected\": [[\"accept\", \"json\"], [\"lang\", \"fr\"]], \"passed\": false}, {\"check\": \"fixture 2\", \"actual\": [[\"lang\", \"en\"]], \"expected\": [[\"lang\", \"en\"]], \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [[\"lang\", null]], \"expected\": [[\"lang\", null]], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":41.362,"exit_code":0,"observations":[{"actual":[["accept","json"],["lang","fr"]],"check":"fixture 1","expected":[["accept","json"],["lang","fr"]],"passed":true},{"actual":[["lang","en"]],"check":"fixture 2","expected":[["lang","en"]],"passed":true},{"actual":[],"check":"fixture 3","expected":[],"passed":true},{"actual":[["lang",null]],"check":"fixture 4","expected":[["lang",null]],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": [[\"accept\", \"json\"], [\"lang\", \"fr\"]], \"expected\": [[\"accept\", \"json\"], [\"lang\", \"fr\"]], \"passed\": true}, {\"check\": \"fixture 2\", \"actual\": [[\"lang\", \"en\"]], \"expected\": [[\"lang\", \"en\"]], \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [[\"lang\", null]], \"expected\": [[\"lang\", null]], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}