{"abstract":"A skipped position is silently written as if it followed the cache tail.","category":"KV cache position mapping","checks":6,"contract":"Given cached logical positions and a candidate position, return whether the append is contiguous. Empty cache accepts any nonnegative position.","contract_signature":"positions, candidate","evaluation_group":"w3-kv-map-append-gap-validation","failed_approach":"Strictly requiring position zero prevents valid continuation from a trimmed prefix.","family":"w3-kv-cache-position-mapping-append-gap-validation","id":"FA-98571","implementations":{"attempt":{"sha256":"b0ed4d849407ae3e121de05080ff15f2d5f4267ea5bd5633c180b746725a5170","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(positions, candidate):\n    return candidate==(positions[-1]+1 if positions else 0)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('contiguous',solve([N,N+1],N+2),True)\ncheck('gap',solve([N,N+1],N+3),False)\ncheck('duplicate tail',solve([N,N+1],N+1),False)\ncheck('empty starts at offset',solve([],N),True)\ncheck('negative empty start',solve([],-1),False)\ncheck('first position zero',solve([],0),True)\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":"6e4324b8f35fe3f81f76f812a99c975e7e4b0ae5f47c78d86cdd33c2508cd32d","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(positions, candidate):\n    return not positions or candidate>positions[-1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('contiguous',solve([N,N+1],N+2),True)\ncheck('gap',solve([N,N+1],N+3),False)\ncheck('duplicate tail',solve([N,N+1],N+1),False)\ncheck('empty starts at offset',solve([],N),True)\ncheck('negative empty start',solve([],-1),False)\ncheck('first position zero',solve([],0),True)\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":"These toy integer maps omit tensor layout, concurrency, device memory, and model-specific cache formats. 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":"w3-kv-cache-position-mapping-append-gap-validation","generated_at":"2026-09-30T16:48:14.544523+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A small in-memory model makes the cache address contract explicit for a serving component.","root_cause":"The append path checks only that a position is larger than the last one.","sha256":"59a08fd67272666bb433b855137407f2452a7fdf0951274a48af5c83db123425","title":"Append rejects a discontinuous logical position · case 01","variant":1,"variant_policy":"The fixture code references N, supplied as 1 through 5. Fixed boundary checks may repeat. These records share one mechanism and must remain together in evaluation splits.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":27.594,"exit_code":1,"observations":[{"actual":true,"check":"contiguous","expected":true,"passed":true},{"actual":false,"check":"gap","expected":false,"passed":true},{"actual":false,"check":"duplicate tail","expected":false,"passed":true},{"actual":false,"check":"empty starts at offset","expected":true,"passed":false},{"actual":false,"check":"negative empty start","expected":false,"passed":true},{"actual":true,"check":"first position zero","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"contiguous\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"gap\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"duplicate tail\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"empty starts at offset\", \"actual\": false, \"expected\": true, \"passed\": false}, {\"check\": \"negative empty start\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"first position zero\", \"actual\": true, \"expected\": true, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":26.989,"exit_code":1,"observations":[{"actual":true,"check":"contiguous","expected":true,"passed":true},{"actual":true,"check":"gap","expected":false,"passed":false},{"actual":false,"check":"duplicate tail","expected":false,"passed":true},{"actual":true,"check":"empty starts at offset","expected":true,"passed":true},{"actual":true,"check":"negative empty start","expected":false,"passed":false},{"actual":true,"check":"first position zero","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"contiguous\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"gap\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"duplicate tail\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"empty starts at offset\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"negative empty start\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"first position zero\", \"actual\": true, \"expected\": true, \"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."}}