{"abstract":"The queue dead letter operation is admitted even though dead-letter forwarding revisits a queue in its own route.","category":"Queues","checks":9,"contract":"Return a Boolean admission decision for move a poison message to a dead-letter queue. The record r must satisfy all of: r['attempt_threshold'][0] >= r['attempt_threshold'][1]; r['destination_exists'] is True; r['transfer_persisted'] is True; r['cycle_detection'][0] not in r['cycle_detection'][1]; r['original_identity'][0] == r['original_identity'][1]. Extra tracing fields are ignored; validation does not mutate the record.","contract_signature":"r","evaluation_group":"xd-queue-dead-letter","failed_approach":"Adding the cycle detection check repairs the reported defect, but replacing the adjacent original identity check loses that independent invariant.","family":"xd-queue-dead-letter-cycle_detection","id":"FA-816","implementations":{"attempt":{"sha256":"f735dba7b855ee017ce09714ade76604df2b927e7a6e8f4a0fd9519ccf162694","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['attempt_threshold'][0] >= r['attempt_threshold'][1]) and (r['destination_exists'] is True) and (r['transfer_persisted'] is True) and (r['cycle_detection'][0] not in r['cycle_detection'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'attempt_threshold': [5, 5], 'destination_exists': True, 'transfer_persisted': True, 'cycle_detection': ['q3', ['q1', 'q2']], 'original_identity': ['m1', 'm1']}\ncheck('valid operation', solve(r), True)\ncheck('A transient first failure is dead-lettered prematurely', solve(dict(r, **{'attempt_threshold': [4, 5]})), False)\ncheck('The source is deleted without a dead-letter destination', solve(dict(r, **{'destination_exists': False})), False)\ncheck('The source is removed before the target copy is durable', solve(dict(r, **{'transfer_persisted': False})), False)\ncheck('Dead-letter forwarding revisits a queue in its own route', solve(dict(r, **{'cycle_detection': ['q1', ['q1', 'q2']]})), False)\ncheck('Dead-letter transfer loses the original message identity', solve(dict(r, **{'original_identity': ['m2', 'm1']})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'attempt_threshold': [4, 5], 'destination_exists': False, 'transfer_persisted': False, 'cycle_detection': ['q1', ['q1', 'q2']], 'original_identity': ['m2', 'm1']}\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":"3f2fcf0cb6cf0370aed956e1599d82f3371fb9c42578cea08ed8b311bbebae39","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(r):\n    return (r['attempt_threshold'][0] >= r['attempt_threshold'][1]) and (r['destination_exists'] is True) and (r['transfer_persisted'] is True) and (r['original_identity'][0] == r['original_identity'][1])\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nr = {'attempt_threshold': [5, 5], 'destination_exists': True, 'transfer_persisted': True, 'cycle_detection': ['q3', ['q1', 'q2']], 'original_identity': ['m1', 'm1']}\ncheck('valid operation', solve(r), True)\ncheck('A transient first failure is dead-lettered prematurely', solve(dict(r, **{'attempt_threshold': [4, 5]})), False)\ncheck('The source is deleted without a dead-letter destination', solve(dict(r, **{'destination_exists': False})), False)\ncheck('The source is removed before the target copy is durable', solve(dict(r, **{'transfer_persisted': False})), False)\ncheck('Dead-letter forwarding revisits a queue in its own route', solve(dict(r, **{'cycle_detection': ['q1', ['q1', 'q2']]})), False)\ncheck('Dead-letter transfer loses the original message identity', solve(dict(r, **{'original_identity': ['m2', 'm1']})), False)\ncheck('unrelated tracing metadata', solve(dict(r, trace='run-'+str(N))), True)\ncheck('repeat validation is pure', solve(r), True)\ninvalid = {'attempt_threshold': [4, 5], 'destination_exists': False, 'transfer_persisted': False, 'cycle_detection': ['q1', ['q1', 'q2']], 'original_identity': ['m2', 'm1']}\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-queue-dead-letter-cycle_detection","generated_at":"2026-09-29T14:36:56.107705+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A deterministic local contract for queues. 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 cycle detection invariant while validating the other operation preconditions.","sha256":"2d47e271f2508d6ad16feb483393e8a00133d7926fd92af045dc3e0dbcae49f6","title":"Move a poison message to a dead-letter queue: Dead-letter forwarding revisits a queue in its own route · 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":33.429,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A transient first failure is dead-lettered prematurely","expected":false,"passed":true},{"actual":false,"check":"The source is deleted without a dead-letter destination","expected":false,"passed":true},{"actual":false,"check":"The source is removed before the target copy is durable","expected":false,"passed":true},{"actual":false,"check":"Dead-letter forwarding revisits a queue in its own route","expected":false,"passed":true},{"actual":true,"check":"Dead-letter transfer loses the original message identity","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\": \"A transient first failure is dead-lettered prematurely\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The source is deleted without a dead-letter destination\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The source is removed before the target copy is durable\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Dead-letter forwarding revisits a queue in its own route\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Dead-letter transfer loses the original message identity\", \"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"},"broken":{"elapsed_ms":34.07,"exit_code":1,"observations":[{"actual":true,"check":"valid operation","expected":true,"passed":true},{"actual":false,"check":"A transient first failure is dead-lettered prematurely","expected":false,"passed":true},{"actual":false,"check":"The source is deleted without a dead-letter destination","expected":false,"passed":true},{"actual":false,"check":"The source is removed before the target copy is durable","expected":false,"passed":true},{"actual":true,"check":"Dead-letter forwarding revisits a queue in its own route","expected":false,"passed":false},{"actual":false,"check":"Dead-letter transfer loses the original message identity","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 transient first failure is dead-lettered prematurely\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The source is deleted without a dead-letter destination\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"The source is removed before the target copy is durable\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"Dead-letter forwarding revisits a queue in its own route\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"Dead-letter transfer loses the original message identity\", \"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."}}