{"abstract":"The health eviction operation is admitted even though a failed probe evicts a replacement process at the same address.","category":"Reliability","checks":9,"contract":"Return a Boolean admission decision for evict an unhealthy backend. The record r must satisfy all of: r['consecutive_failures'][0] >= r['consecutive_failures'][1]; r['minimum_survivors'][0]-1 >= r['minimum_survivors'][1]; r['sample_freshness'][0]-r['sample_freshness'][1] <= r['sample_freshness'][2]; (r['ejection_limit'][0]+1)*100 <= r['ejection_limit'][1]*r['ejection_limit'][2]; r['backend_incarnation'][0] == r['backend_incarnation'][1]. Extra tracing fields are ignored; validation does not mutate the record.","evaluation_group":"xd-health-eviction","failed_approach":"Adding the backend incarnation check repairs the reported defect, but replacing the adjacent consecutive failures check loses that independent invariant.","family":"xd-health-eviction-backend_incarnation","id":"FA-1046","implementations":{"attempt":{"sha256":"57ba192a7f54b84baa563adf33bbedb02f05309472e1ead24130abfdd2bcfdc4","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['minimum_survivors'][0]-1 >= r['minimum_survivors'][1]) and (r['sample_freshness'][0]-r['sample_freshness'][1] <= r['sample_freshness'][2]) and ((r['ejection_limit'][0]+1)*100 <= r['ejection_limit'][1]*r['ejection_limit'][2]) and (r['backend_incarnation'][0] == r['backend_incarnation'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'consecutive_failures': [3, 3], 'minimum_survivors': [3, 2], 'sample_freshness': [10, 8, 2], 'ejection_limit': [1, 10, 20], 'backend_incarnation': ['p2', 'p2']}\ncheck('valid operation', solve(r), True)\ncheck('One intermittent failure causes premature eviction', solve(dict(r, **{'consecutive_failures': [2, 3]})), False)\ncheck('Eviction removes the last required healthy capacity', solve(dict(r, **{'minimum_survivors': [2, 2]})), False)\ncheck('Old failure samples evict a recovered backend', solve(dict(r, **{'sample_freshness': [10, 7, 2]})), False)\ncheck('Correlated failures evict more than the allowed pool fraction', solve(dict(r, **{'ejection_limit': [2, 10, 20]})), False)\ncheck('A failed probe evicts a replacement process at the same address', solve(dict(r, **{'backend_incarnation': ['p1', 'p2']})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'consecutive_failures': [2, 3], 'minimum_survivors': [2, 2], 'sample_freshness': [10, 7, 2], 'ejection_limit': [2, 10, 20], 'backend_incarnation': ['p1', 'p2']}\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":"870fcf855fc1051c5df11ba52ca24a8015558e27a7a1c62443a870ba34a74149","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['consecutive_failures'][0] >= r['consecutive_failures'][1]) and (r['minimum_survivors'][0]-1 >= r['minimum_survivors'][1]) and (r['sample_freshness'][0]-r['sample_freshness'][1] <= r['sample_freshness'][2]) and ((r['ejection_limit'][0]+1)*100 <= r['ejection_limit'][1]*r['ejection_limit'][2])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'consecutive_failures': [3, 3], 'minimum_survivors': [3, 2], 'sample_freshness': [10, 8, 2], 'ejection_limit': [1, 10, 20], 'backend_incarnation': ['p2', 'p2']}\ncheck('valid operation', solve(r), True)\ncheck('One intermittent failure causes premature eviction', solve(dict(r, **{'consecutive_failures': [2, 3]})), False)\ncheck('Eviction removes the last required healthy capacity', solve(dict(r, **{'minimum_survivors': [2, 2]})), False)\ncheck('Old failure samples evict a recovered backend', solve(dict(r, **{'sample_freshness': [10, 7, 2]})), False)\ncheck('Correlated failures evict more than the allowed pool fraction', solve(dict(r, **{'ejection_limit': [2, 10, 20]})), False)\ncheck('A failed probe evicts a replacement process at the same address', solve(dict(r, **{'backend_incarnation': ['p1', 'p2']})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'consecutive_failures': [2, 3], 'minimum_survivors': [2, 2], 'sample_freshness': [10, 7, 2], 'ejection_limit': [2, 10, 20], 'backend_incarnation': ['p1', 'p2']}\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":"b813b1b21004f3eb81a31aa1aa4a7d17977a8d643f38828702f6d0233b41534e","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['consecutive_failures'][0] >= r['consecutive_failures'][1]) and (r['minimum_survivors'][0]-1 >= r['minimum_survivors'][1]) and (r['sample_freshness'][0]-r['sample_freshness'][1] <= r['sample_freshness'][2]) and ((r['ejection_limit'][0]+1)*100 <= r['ejection_limit'][1]*r['ejection_limit'][2]) and (r['backend_incarnation'][0] == r['backend_incarnation'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'consecutive_failures': [3, 3], 'minimum_survivors': [3, 2], 'sample_freshness': [10, 8, 2], 'ejection_limit': [1, 10, 20], 'backend_incarnation': ['p2', 'p2']}\ncheck('valid operation', solve(r), True)\ncheck('One intermittent failure causes premature eviction', solve(dict(r, **{'consecutive_failures': [2, 3]})), False)\ncheck('Eviction removes the last required healthy capacity', solve(dict(r, **{'minimum_survivors': [2, 2]})), False)\ncheck('Old failure samples evict a recovered backend', solve(dict(r, **{'sample_freshness': [10, 7, 2]})), False)\ncheck('Correlated failures evict more than the allowed pool fraction', solve(dict(r, **{'ejection_limit': [2, 10, 20]})), False)\ncheck('A failed probe evicts a replacement process at the same address', solve(dict(r, **{'backend_incarnation': ['p1', 'p2']})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'consecutive_failures': [2, 3], 'minimum_survivors': [2, 2], 'sample_freshness': [10, 7, 2], 'ejection_limit': [2, 10, 20], 'backend_incarnation': ['p1', 'p2']}\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-health-eviction-backend_incarnation","generated_at":"2026-09-29T14:36:58.023833+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic local contract for reliability. Each negative fixture violates exactly one invariant. No transport timing, persistence, cryptographic verification, or full protocol implementation is claimed.","repair":"Require r['backend_incarnation'][0] == r['backend_incarnation'][1] together with every other stated precondition before accepting the operation.","root_cause":"The admission path omits the backend incarnation invariant while validating the other operation preconditions.","sha256":"c036b0ad7b8aac79ee229bd81f1e4b6be4c67ab6d2567abe8093ad70a4f93516","title":"Evict an unhealthy backend: A failed probe evicts a replacement process at the same address · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":35.429,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":true,"check":"One intermittent failure causes premature eviction","expected":false,"passed":false},{"actual":false,"check":"Eviction removes the last required healthy capacity","expected":false,"passed":true},{"actual":false,"check":"Old failure samples evict a recovered backend","expected":false,"passed":true},{"actual":false,"check":"Correlated failures evict more than the allowed pool fraction","expected":false,"passed":true},{"actual":false,"check":"A failed probe evicts a replacement process at the same address","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\": \"One intermittent failure causes premature eviction\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"Eviction removes the last required healthy capacity\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Old failure samples evict a recovered backend\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Correlated failures evict more than the allowed pool fraction\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A failed probe evicts a replacement process at the same address\", \"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":33.134,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"One intermittent failure causes premature eviction","expected":false,"passed":true},{"actual":false,"check":"Eviction removes the last required healthy capacity","expected":false,"passed":true},{"actual":false,"check":"Old failure samples evict a recovered backend","expected":false,"passed":true},{"actual":false,"check":"Correlated failures evict more than the allowed pool fraction","expected":false,"passed":true},{"actual":true,"check":"A failed probe evicts a replacement process at the same address","expected":false,"passed":false},{"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\": \"One intermittent failure causes premature eviction\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Eviction removes the last required healthy capacity\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Old failure samples evict a recovered backend\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Correlated failures evict more than the allowed pool fraction\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A failed probe evicts a replacement process at the same address\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"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":28.61,"exit_code":0,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"One intermittent failure causes premature eviction","expected":false,"passed":true},{"actual":false,"check":"Eviction removes the last required healthy capacity","expected":false,"passed":true},{"actual":false,"check":"Old failure samples evict a recovered backend","expected":false,"passed":true},{"actual":false,"check":"Correlated failures evict more than the allowed pool fraction","expected":false,"passed":true},{"actual":false,"check":"A failed probe evicts a replacement process at the same address","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\": \"One intermittent failure causes premature eviction\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Eviction removes the last required healthy capacity\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Old failure samples evict a recovered backend\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Correlated failures evict more than the allowed pool fraction\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"A failed probe evicts a replacement process at the same address\", \"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"}