{"abstract":"The health eviction operation is admitted even though old failure samples evict a recovered backend.","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.","contract_signature":"r","evaluation_group":"xd-health-eviction","failed_approach":"Adding the sample freshness check repairs the reported defect, but replacing the adjacent ejection limit check loses that independent invariant.","family":"xd-health-eviction-sample_freshness","id":"FA-1036","implementations":{"attempt":{"sha256":"13547e3ad97bc8fdf0a4b501e81b907c88ce55a07010379e21fdceb71db53360","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['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":"1fb114e29027bb672e902fd68da0940c1d3ebcb354d429c977ddc3629d97cc69","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['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-sample_freshness","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.","root_cause":"The admission path omits the sample freshness invariant while validating the other operation preconditions.","sha256":"d19e8a0a8256a9d16c1ff740c80010588b97ae65755535c2a426e5f519f00414","title":"Evict an unhealthy backend: Old failure samples evict a recovered backend · 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":31.804,"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":true,"check":"Correlated failures evict more than the allowed pool fraction","expected":false,"passed":false},{"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\": 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\": true, \"expected\": false, \"passed\": false}, {\"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":32.353,"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":true,"check":"Old failure samples evict a recovered backend","expected":false,"passed":false},{"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\": 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\": true, \"expected\": false, \"passed\": false}, {\"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"}},"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."}}