{"abstract":"An L2 hit fails to populate the faster cache tier.","category":"Caching","checks":4,"contract":"On an L1 miss and L2 hit, copy the L2 value into L1. Existing L1 data wins. Return [new-L1,selected value or None]; this model output does not distinguish a terminal miss from a cached None.","contract_signature":"l1, l2, key","evaluation_group":"xc-multi-tier-promotion","failed_approach":"Truthiness skips zero-valued L2 entries and unconditional L2 assignment overwrites an existing L1 value.","family":"xc-multi-tier-promotion","id":"FA-10526","implementations":{"attempt":{"sha256":"30061591a338f53a3ad9b470c40fa13a6726e872d780468199e930bbf8c78538","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(l1, l2, key):\n    out=dict(l1)\n    if l2.get(key): out[key]=l2[key]\n    return [out,out.get(key)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*({}, {'a': 4}, 'a')), [{'a': 4}, 4])\ncheck('fixture 2', solve(*({}, {'a': 0}, 'a')), [{'a': 0}, 0])\ncheck('fixture 3', solve(*({'a': 'fresh'}, {'a': 'old'}, 'a')), [{'a': 'fresh'}, 'fresh'])\ncheck('fixture 4', solve(*({'b': 2}, {}, 'a')), [{'b': 2}, 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":"19060fc126f66c0c2e4a734adf7e4dbadc5ed17a30fda357405e4bf18d9800a3","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(l1, l2, key):\n    return [dict(l1),l1.get(key,l2.get(key))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('fixture 1', solve(*({}, {'a': 4}, 'a')), [{'a': 4}, 4])\ncheck('fixture 2', solve(*({}, {'a': 0}, 'a')), [{'a': 0}, 0])\ncheck('fixture 3', solve(*({'a': 'fresh'}, {'a': 'old'}, 'a')), [{'a': 'fresh'}, 'fresh'])\ncheck('fixture 4', solve(*({'b': 2}, {}, 'a')), [{'b': 2}, 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-multi-tier-promotion","generated_at":"2026-09-29T14:38:39.863007+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.","root_cause":"Reading the slower tier returns its value without performing promotion.","sha256":"c8905e50d8dc5cd82275464e7f493156f801f06ada66e19dba8b35ab8a9e8d13","title":"An L2 hit fails to populate the faster cache tier · 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":40.619,"exit_code":1,"observations":[{"actual":[{"a":4},4],"check":"fixture 1","expected":[{"a":4},4],"passed":true},{"actual":[{},null],"check":"fixture 2","expected":[{"a":0},0],"passed":false},{"actual":[{"a":"old"},"old"],"check":"fixture 3","expected":[{"a":"fresh"},"fresh"],"passed":false},{"actual":[{"b":2},null],"check":"fixture 4","expected":[{"b":2},null],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": [{\"a\": 4}, 4], \"expected\": [{\"a\": 4}, 4], \"passed\": true}, {\"check\": \"fixture 2\", \"actual\": [{}, null], \"expected\": [{\"a\": 0}, 0], \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": [{\"a\": \"old\"}, \"old\"], \"expected\": [{\"a\": \"fresh\"}, \"fresh\"], \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": [{\"b\": 2}, null], \"expected\": [{\"b\": 2}, null], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.247,"exit_code":1,"observations":[{"actual":[{},4],"check":"fixture 1","expected":[{"a":4},4],"passed":false},{"actual":[{},0],"check":"fixture 2","expected":[{"a":0},0],"passed":false},{"actual":[{"a":"fresh"},"fresh"],"check":"fixture 3","expected":[{"a":"fresh"},"fresh"],"passed":true},{"actual":[{"b":2},null],"check":"fixture 4","expected":[{"b":2},null],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 1\", \"actual\": [{}, 4], \"expected\": [{\"a\": 4}, 4], \"passed\": false}, {\"check\": \"fixture 2\", \"actual\": [{}, 0], \"expected\": [{\"a\": 0}, 0], \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": [{\"a\": \"fresh\"}, \"fresh\"], \"expected\": [{\"a\": \"fresh\"}, \"fresh\"], \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": [{\"b\": 2}, null], \"expected\": [{\"b\": 2}, null], \"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."}}