{"abstract":"Replacement token is inserted after the rejected draft token.","category":"Speculative decoding bookkeeping","checks":7,"contract":"For valid slot index k, replace draft[k] with replacement and preserve every other draft slot, including the suffix after k.","contract_signature":"draft, k, replacement","evaluation_group":"spec-replacement-slot","failed_approach":"Replacing the final list element works only when rejection happens at the tail.","family":"w3-speculative-decoding-bookkeeping-replacement-slot","id":"FA-100656","implementations":{"attempt":{"sha256":"7e69c882980fb38a613827b6e6577cc710caf7348f10cb062b6fe2987eec342c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(draft, k, replacement):\n    return draft[:k]+draft[k+1:]+[replacement]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle replacement', solve([1,2,3],1,9),[1,9,3])\ncheck('first replacement', solve([1,2],0,8),[8,2])\ncheck('last replacement', solve([1,2],1,7),[1,7])\ncheck('singleton', solve([N],0,4),[4])\ncheck('replacement zero', solve([0,1],0,0),[0,1])\ncheck('preserve suffix', solve([1,2,3,4],1,8),[1,8,3,4])\ncheck('vary token', solve([N,N+1],1,N+3),[N,N+3])\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":"3b73c88943512307c57150668b5fa7e18c7a5269897576a32b70cd4e9065f90e","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(draft, k, replacement):\n    return draft[:k+1]+[replacement]+draft[k+1:]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle replacement', solve([1,2,3],1,9),[1,9,3])\ncheck('first replacement', solve([1,2],0,8),[8,2])\ncheck('last replacement', solve([1,2],1,7),[1,7])\ncheck('singleton', solve([N],0,4),[4])\ncheck('replacement zero', solve([0,1],0,0),[0,1])\ncheck('preserve suffix', solve([1,2,3,4],1,8),[1,8,3,4])\ncheck('vary token', solve([N,N+1],1,N+3),[N,N+3])\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 are finite toy sequences with explicit contracts; they make no claim about production decoder behavior or model quality. 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-speculative-decoding-bookkeeping-replacement-slot","generated_at":"2026-09-30T16:48:38.100039+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A self-contained bookkeeping model makes prefix and token-count semantics observable without a model runtime.","root_cause":"Replacement is appended after the rejected draft token.","sha256":"ccd3fb2ee0e7ffe3de6ff0f344e39a016ed6bd78899bfbddc05c2908ed889251","title":"Decoding: Replacement token is inserted after the rejected draft token · 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":29.143,"exit_code":1,"observations":[{"actual":[1,3,9],"check":"middle replacement","expected":[1,9,3],"passed":false},{"actual":[2,8],"check":"first replacement","expected":[8,2],"passed":false},{"actual":[1,7],"check":"last replacement","expected":[1,7],"passed":true},{"actual":[4],"check":"singleton","expected":[4],"passed":true},{"actual":[1,0],"check":"replacement zero","expected":[0,1],"passed":false},{"actual":[1,3,4,8],"check":"preserve suffix","expected":[1,8,3,4],"passed":false},{"actual":[1,4],"check":"vary token","expected":[1,4],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle replacement\", \"actual\": [1, 3, 9], \"expected\": [1, 9, 3], \"passed\": false}, {\"check\": \"first replacement\", \"actual\": [2, 8], \"expected\": [8, 2], \"passed\": false}, {\"check\": \"last replacement\", \"actual\": [1, 7], \"expected\": [1, 7], \"passed\": true}, {\"check\": \"singleton\", \"actual\": [4], \"expected\": [4], \"passed\": true}, {\"check\": \"replacement zero\", \"actual\": [1, 0], \"expected\": [0, 1], \"passed\": false}, {\"check\": \"preserve suffix\", \"actual\": [1, 3, 4, 8], \"expected\": [1, 8, 3, 4], \"passed\": false}, {\"check\": \"vary token\", \"actual\": [1, 4], \"expected\": [1, 4], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":27.412,"exit_code":1,"observations":[{"actual":[1,2,9,3],"check":"middle replacement","expected":[1,9,3],"passed":false},{"actual":[1,8,2],"check":"first replacement","expected":[8,2],"passed":false},{"actual":[1,2,7],"check":"last replacement","expected":[1,7],"passed":false},{"actual":[1,4],"check":"singleton","expected":[4],"passed":false},{"actual":[0,0,1],"check":"replacement zero","expected":[0,1],"passed":false},{"actual":[1,2,8,3,4],"check":"preserve suffix","expected":[1,8,3,4],"passed":false},{"actual":[1,2,4],"check":"vary token","expected":[1,4],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle replacement\", \"actual\": [1, 2, 9, 3], \"expected\": [1, 9, 3], \"passed\": false}, {\"check\": \"first replacement\", \"actual\": [1, 8, 2], \"expected\": [8, 2], \"passed\": false}, {\"check\": \"last replacement\", \"actual\": [1, 2, 7], \"expected\": [1, 7], \"passed\": false}, {\"check\": \"singleton\", \"actual\": [1, 4], \"expected\": [4], \"passed\": false}, {\"check\": \"replacement zero\", \"actual\": [0, 0, 1], \"expected\": [0, 1], \"passed\": false}, {\"check\": \"preserve suffix\", \"actual\": [1, 2, 8, 3, 4], \"expected\": [1, 8, 3, 4], \"passed\": false}, {\"check\": \"vary token\", \"actual\": [1, 2, 4], \"expected\": [1, 4], \"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."}}