{"abstract":"The acceptor accept operation is admitted even though the same ballot accepts two different values.","category":"Consensus","checks":9,"contract":"Return a Boolean admission decision for accept a proposal value. The record r must satisfy all of: tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1]); r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]; r['slot_untrimmed'][0] > r['slot_untrimmed'][1]; len(r['value_length'][0]) <= r['value_length'][1]; r['accept_persisted'] is True. Extra tracing fields are ignored; validation does not mutate the record.","contract_signature":"r","evaluation_group":"xd-acceptor-accept","failed_approach":"Adding the ballot value unique check repairs the reported defect, but replacing the adjacent slot untrimmed check loses that independent invariant.","family":"xd-acceptor-accept-ballot_value_unique","id":"FA-506","implementations":{"attempt":{"sha256":"f5c28954fc803e8b27eff530626776fcb154f5c8bece9fa0e791fc13624a95df","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1])) and (r['ballot_value_unique'][0] is None or r['ballot_value_unique'][0] == r['ballot_value_unique'][1]) and (len(r['value_length'][0]) <= r['value_length'][1]) and (r['accept_persisted'] is True)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'ballot_promised': [[6, 1], [5, 2]], 'ballot_value_unique': ['x', 'x'], 'slot_untrimmed': [11, 10], 'value_length': ['abc', 3], 'accept_persisted': True}\ncheck('valid operation', solve(r), True)\ncheck('A value is accepted below the promised ballot', solve(dict(r, **{'ballot_promised': [[5, 1], [5, 2]]})), False)\ncheck('The same ballot accepts two different values', solve(dict(r, **{'ballot_value_unique': ['x', 'y']})), False)\ncheck('A forgotten slot is reopened without its chosen evidence', solve(dict(r, **{'slot_untrimmed': [10, 10]})), False)\ncheck('An accept request bypasses the bounded value envelope', solve(dict(r, **{'value_length': ['abcd', 3]})), False)\ncheck('An accept acknowledgement precedes durable acceptance', solve(dict(r, **{'accept_persisted': False})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'ballot_promised': [[5, 1], [5, 2]], 'ballot_value_unique': ['x', 'y'], 'slot_untrimmed': [10, 10], 'value_length': ['abcd', 3], 'accept_persisted': False}\nkeys = list(invalid)\npair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}\ncheck('two independent violations in variant', solve(dict(r, **pair)), False)\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":"fca08905229152fed36ae3c0cd18bb809976219c1397330d073349cdc6b038ec","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (tuple(r['ballot_promised'][0]) >= tuple(r['ballot_promised'][1])) and (r['slot_untrimmed'][0] > r['slot_untrimmed'][1]) and (len(r['value_length'][0]) <= r['value_length'][1]) and (r['accept_persisted'] is True)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'ballot_promised': [[6, 1], [5, 2]], 'ballot_value_unique': ['x', 'x'], 'slot_untrimmed': [11, 10], 'value_length': ['abc', 3], 'accept_persisted': True}\ncheck('valid operation', solve(r), True)\ncheck('A value is accepted below the promised ballot', solve(dict(r, **{'ballot_promised': [[5, 1], [5, 2]]})), False)\ncheck('The same ballot accepts two different values', solve(dict(r, **{'ballot_value_unique': ['x', 'y']})), False)\ncheck('A forgotten slot is reopened without its chosen evidence', solve(dict(r, **{'slot_untrimmed': [10, 10]})), False)\ncheck('An accept request bypasses the bounded value envelope', solve(dict(r, **{'value_length': ['abcd', 3]})), False)\ncheck('An accept acknowledgement precedes durable acceptance', solve(dict(r, **{'accept_persisted': False})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'ballot_promised': [[5, 1], [5, 2]], 'ballot_value_unique': ['x', 'y'], 'slot_untrimmed': [10, 10], 'value_length': ['abcd', 3], 'accept_persisted': False}\nkeys = list(invalid)\npair = {keys[N % len(keys)]: invalid[keys[N % len(keys)]], keys[(N+1) % len(keys)]: invalid[keys[(N+1) % len(keys)]]}\ncheck('two independent violations in variant', solve(dict(r, **pair)), False)\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":"xd-acceptor-accept-ballot_value_unique","generated_at":"2026-09-29T14:36:53.732672+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic local contract for consensus. Each negative fixture violates exactly one invariant. No transport timing, persistence, cryptographic verification, or full protocol implementation is claimed.","root_cause":"The admission path omits the ballot value unique invariant while validating the other operation preconditions.","sha256":"fc241cd203fc0f11ac4c5d19e30aafe34b15146b84f0873d027941cbada0924c","title":"Accept a proposal value: The same ballot accepts two different values · 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":38.086,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A value is accepted below the promised ballot","expected":false,"passed":true},{"actual":false,"check":"The same ballot accepts two different values","expected":false,"passed":true},{"actual":true,"check":"A forgotten slot is reopened without its chosen evidence","expected":false,"passed":false},{"actual":false,"check":"An accept request bypasses the bounded value envelope","expected":false,"passed":true},{"actual":false,"check":"An accept acknowledgement precedes durable acceptance","expected":false,"passed":true},{"actual":true,"check":"unrelated tracing metadata","expected":true,"passed":true},{"actual":true,"check":"repeat validation is pure","expected":true,"passed":true},{"actual":false,"check":"two independent violations in variant","expected":false,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"valid operation\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"A value is accepted below the promised ballot\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The same ballot accepts two different values\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A forgotten slot is reopened without its chosen evidence\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"An accept request bypasses the bounded value envelope\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"An accept acknowledgement precedes durable acceptance\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"unrelated tracing metadata\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"repeat validation is pure\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"two independent violations in variant\", \"actual\": false, \"expected\": false, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.918,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A value is accepted below the promised ballot","expected":false,"passed":true},{"actual":true,"check":"The same ballot accepts two different values","expected":false,"passed":false},{"actual":false,"check":"A forgotten slot is reopened without its chosen evidence","expected":false,"passed":true},{"actual":false,"check":"An accept request bypasses the bounded value envelope","expected":false,"passed":true},{"actual":false,"check":"An accept acknowledgement precedes durable acceptance","expected":false,"passed":true},{"actual":true,"check":"unrelated tracing metadata","expected":true,"passed":true},{"actual":true,"check":"repeat validation is pure","expected":true,"passed":true},{"actual":false,"check":"two independent violations in variant","expected":false,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"valid operation\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"A value is accepted below the promised ballot\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The same ballot accepts two different values\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"A forgotten slot is reopened without its chosen evidence\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"An accept request bypasses the bounded value envelope\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"An accept acknowledgement precedes durable acceptance\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"unrelated tracing metadata\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"repeat validation is pure\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"two independent violations in variant\", \"actual\": false, \"expected\": false, \"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."}}