{"abstract":"The read index operation is admitted even though a leader reads before committing an entry in its term.","category":"Consensus","checks":9,"contract":"Return a Boolean admission decision for serve a linearizable read at a confirmed index. The record r must satisfy all of: r['current_term_commit'][0] == r['current_term_commit'][1]; len(set(r['quorum_confirmation'][0])) * 2 > r['quorum_confirmation'][1]; r['applied_floor'][0] >= r['applied_floor'][1]; r['context_binding'][0] == r['context_binding'][1]; r['term_stability'][0] == r['term_stability'][1]. Extra tracing fields are ignored; validation does not mutate the record.","evaluation_group":"xd-read-index","failed_approach":"Adding the current term commit check repairs the reported defect, but replacing the adjacent quorum confirmation check loses that independent invariant.","family":"xd-read-index-current_term_commit","id":"FA-451","implementations":{"attempt":{"sha256":"1193f1f7ebf330625052aeddd663d875fa75a92419973c500a17d629fce4c0af","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['current_term_commit'][0] == r['current_term_commit'][1]) and (r['applied_floor'][0] >= r['applied_floor'][1]) and (r['context_binding'][0] == r['context_binding'][1]) and (r['term_stability'][0] == r['term_stability'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'current_term_commit': [5, 5], 'quorum_confirmation': [[1, 2], 3], 'applied_floor': [9, 9], 'context_binding': ['r2', 'r2'], 'term_stability': [5, 5]}\ncheck('valid operation', solve(r), True)\ncheck('A leader reads before committing an entry in its term', solve(dict(r, **{'current_term_commit': [4, 5]})), False)\ncheck('A read uses a response set lacking a voting majority', solve(dict(r, **{'quorum_confirmation': [[1], 3]})), False)\ncheck('The state machine has not applied the confirmed read index', solve(dict(r, **{'applied_floor': [8, 9]})), False)\ncheck('A delayed response confirms another read request', solve(dict(r, **{'context_binding': ['r1', 'r2']})), False)\ncheck('A read completes after the leader observed a higher term', solve(dict(r, **{'term_stability': [5, 6]})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'current_term_commit': [4, 5], 'quorum_confirmation': [[1], 3], 'applied_floor': [8, 9], 'context_binding': ['r1', 'r2'], 'term_stability': [5, 6]}\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":"620a55b6ec6138d32735fef43268c1d6da5cdd733b98cc6269fcdd01fdaff807","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (len(set(r['quorum_confirmation'][0])) * 2 > r['quorum_confirmation'][1]) and (r['applied_floor'][0] >= r['applied_floor'][1]) and (r['context_binding'][0] == r['context_binding'][1]) and (r['term_stability'][0] == r['term_stability'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'current_term_commit': [5, 5], 'quorum_confirmation': [[1, 2], 3], 'applied_floor': [9, 9], 'context_binding': ['r2', 'r2'], 'term_stability': [5, 5]}\ncheck('valid operation', solve(r), True)\ncheck('A leader reads before committing an entry in its term', solve(dict(r, **{'current_term_commit': [4, 5]})), False)\ncheck('A read uses a response set lacking a voting majority', solve(dict(r, **{'quorum_confirmation': [[1], 3]})), False)\ncheck('The state machine has not applied the confirmed read index', solve(dict(r, **{'applied_floor': [8, 9]})), False)\ncheck('A delayed response confirms another read request', solve(dict(r, **{'context_binding': ['r1', 'r2']})), False)\ncheck('A read completes after the leader observed a higher term', solve(dict(r, **{'term_stability': [5, 6]})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'current_term_commit': [4, 5], 'quorum_confirmation': [[1], 3], 'applied_floor': [8, 9], 'context_binding': ['r1', 'r2'], 'term_stability': [5, 6]}\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"},"fixed":{"sha256":"3ba0ad3cc61c4a29fa15605b0116a26627bdcc2f1c54c1bb7e0968a75e3a0290","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['current_term_commit'][0] == r['current_term_commit'][1]) and (len(set(r['quorum_confirmation'][0])) * 2 > r['quorum_confirmation'][1]) and (r['applied_floor'][0] >= r['applied_floor'][1]) and (r['context_binding'][0] == r['context_binding'][1]) and (r['term_stability'][0] == r['term_stability'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'current_term_commit': [5, 5], 'quorum_confirmation': [[1, 2], 3], 'applied_floor': [9, 9], 'context_binding': ['r2', 'r2'], 'term_stability': [5, 5]}\ncheck('valid operation', solve(r), True)\ncheck('A leader reads before committing an entry in its term', solve(dict(r, **{'current_term_commit': [4, 5]})), False)\ncheck('A read uses a response set lacking a voting majority', solve(dict(r, **{'quorum_confirmation': [[1], 3]})), False)\ncheck('The state machine has not applied the confirmed read index', solve(dict(r, **{'applied_floor': [8, 9]})), False)\ncheck('A delayed response confirms another read request', solve(dict(r, **{'context_binding': ['r1', 'r2']})), False)\ncheck('A read completes after the leader observed a higher term', solve(dict(r, **{'term_stability': [5, 6]})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'current_term_commit': [4, 5], 'quorum_confirmation': [[1], 3], 'applied_floor': [8, 9], 'context_binding': ['r1', 'r2'], 'term_stability': [5, 6]}\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-read-index-current_term_commit","generated_at":"2026-09-29T14:36:53.115548+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.","repair":"Require r['current_term_commit'][0] == r['current_term_commit'][1] together with every other stated precondition before accepting the operation.","root_cause":"The admission path omits the current term commit invariant while validating the other operation preconditions.","sha256":"4d0bfe6091e44e1903b3039f727b4b1892a4b415896c51e41d05e84a947ad355","title":"Serve a linearizable read at a confirmed index: A leader reads before committing an entry in its term · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":35.099,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A leader reads before committing an entry in its term","expected":false,"passed":true},{"actual":true,"check":"A read uses a response set lacking a voting majority","expected":false,"passed":false},{"actual":false,"check":"The state machine has not applied the confirmed read index","expected":false,"passed":true},{"actual":false,"check":"A delayed response confirms another read request","expected":false,"passed":true},{"actual":false,"check":"A read completes after the leader observed a higher term","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 leader reads before committing an entry in its term\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A read uses a response set lacking a voting majority\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"The state machine has not applied the confirmed read index\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A delayed response confirms another read request\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A read completes after the leader observed a higher term\", \"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":34.741,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":true,"check":"A leader reads before committing an entry in its term","expected":false,"passed":false},{"actual":false,"check":"A read uses a response set lacking a voting majority","expected":false,"passed":true},{"actual":false,"check":"The state machine has not applied the confirmed read index","expected":false,"passed":true},{"actual":false,"check":"A delayed response confirms another read request","expected":false,"passed":true},{"actual":false,"check":"A read completes after the leader observed a higher term","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 leader reads before committing an entry in its term\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"A read uses a response set lacking a voting majority\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The state machine has not applied the confirmed read index\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A delayed response confirms another read request\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A read completes after the leader observed a higher term\", \"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"},"fixed":{"elapsed_ms":34.47,"exit_code":0,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A leader reads before committing an entry in its term","expected":false,"passed":true},{"actual":false,"check":"A read uses a response set lacking a voting majority","expected":false,"passed":true},{"actual":false,"check":"The state machine has not applied the confirmed read index","expected":false,"passed":true},{"actual":false,"check":"A delayed response confirms another read request","expected":false,"passed":true},{"actual":false,"check":"A read completes after the leader observed a higher term","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":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"valid operation\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"A leader reads before committing an entry in its term\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A read uses a response set lacking a voting majority\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The state machine has not applied the confirmed read index\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A delayed response confirms another read request\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A read completes after the leader observed a higher term\", \"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\": true}\n"}},"verified":true,"visibility":"public"}