{"abstract":"Rollback removes only the final draft token.","category":"Speculative decoding bookkeeping","checks":7,"contract":"Keep the first k draft tokens and discard the rejected token plus all later draft tokens.","contract_signature":"draft, k","evaluation_group":"s3-http_ranges-resume-client","failed_approach":"Removing the last token loses a valid suffix whenever rejection is earlier.","family":"w3-speculative-decoding-bookkeeping-discarded-suffix","id":"FA-100661","implementations":{"attempt":{"sha256":"7372ece63bd513fa54f4592c52e837406613655367dbddf729fb5d6dff3fc19f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(draft, k):\n    return draft[:k+1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle rollback', solve([1,2,3,4],2),[1,2])\ncheck('reject first', solve([1,2],0),[])\ncheck('accept all', solve([1,2],2),[1,2])\ncheck('empty draft', solve([],0),[])\ncheck('singleton rejected', solve([N],0),[])\ncheck('keep one', solve([1,2,3],1),[1])\ncheck('drop long suffix', solve([0,1,2,3,4],1),[0])\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":"00c49cd26c5f7eee165f7e68883fa6e6b6a9c9fee102c9946f9755aa53250c4a","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(draft, k):\n    return draft[:-1]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('middle rollback', solve([1,2,3,4],2),[1,2])\ncheck('reject first', solve([1,2],0),[])\ncheck('accept all', solve([1,2],2),[1,2])\ncheck('empty draft', solve([],0),[])\ncheck('singleton rejected', solve([N],0),[])\ncheck('keep one', solve([1,2,3],1),[1])\ncheck('drop long suffix', solve([0,1,2,3,4],1),[0])\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-discarded-suffix","generated_at":"2026-09-30T16:48:38.098905+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":"Rollback removes only the single rejected token.","sha256":"cbd606ba3f38f736d8208bb7af23a6a0f6ab4a29e81a0268b07cfd24d0f74710","title":"Decoding: Rollback removes only the final 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":30.499,"exit_code":1,"observations":[{"actual":[1,2,3],"check":"middle rollback","expected":[1,2],"passed":false},{"actual":[1],"check":"reject first","expected":[],"passed":false},{"actual":[1,2],"check":"accept all","expected":[1,2],"passed":true},{"actual":[],"check":"empty draft","expected":[],"passed":true},{"actual":[1],"check":"singleton rejected","expected":[],"passed":false},{"actual":[1,2],"check":"keep one","expected":[1],"passed":false},{"actual":[0,1],"check":"drop long suffix","expected":[0],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle rollback\", \"actual\": [1, 2, 3], \"expected\": [1, 2], \"passed\": false}, {\"check\": \"reject first\", \"actual\": [1], \"expected\": [], \"passed\": false}, {\"check\": \"accept all\", \"actual\": [1, 2], \"expected\": [1, 2], \"passed\": true}, {\"check\": \"empty draft\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton rejected\", \"actual\": [1], \"expected\": [], \"passed\": false}, {\"check\": \"keep one\", \"actual\": [1, 2], \"expected\": [1], \"passed\": false}, {\"check\": \"drop long suffix\", \"actual\": [0, 1], \"expected\": [0], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":26.73,"exit_code":1,"observations":[{"actual":[1,2,3],"check":"middle rollback","expected":[1,2],"passed":false},{"actual":[1],"check":"reject first","expected":[],"passed":false},{"actual":[1],"check":"accept all","expected":[1,2],"passed":false},{"actual":[],"check":"empty draft","expected":[],"passed":true},{"actual":[],"check":"singleton rejected","expected":[],"passed":true},{"actual":[1,2],"check":"keep one","expected":[1],"passed":false},{"actual":[0,1,2,3],"check":"drop long suffix","expected":[0],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"middle rollback\", \"actual\": [1, 2, 3], \"expected\": [1, 2], \"passed\": false}, {\"check\": \"reject first\", \"actual\": [1], \"expected\": [], \"passed\": false}, {\"check\": \"accept all\", \"actual\": [1], \"expected\": [1, 2], \"passed\": false}, {\"check\": \"empty draft\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"singleton rejected\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"keep one\", \"actual\": [1, 2], \"expected\": [1], \"passed\": false}, {\"check\": \"drop long suffix\", \"actual\": [0, 1, 2, 3], \"expected\": [0], \"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."}}