{"abstract":"Acknowledged byte count excludes already acknowledged prefix.","category":"Transport flow control","checks":4,"contract":"Given ack, previous, sent, acknowledged byte count excludes already acknowledged prefix. Return the protocol decision or transformed value; fields are validated and fixtures state boundary outcomes.","contract_signature":"ack, previous, sent","evaluation_group":"xh-acknowledged-byte-count-excludes-already-acknowledged-prefix","failed_approach":"The attempted repair uses `max(0,ack-previous)` and still violates a separate fixture.","family":"xh-acknowledged-byte-count-excludes-already-acknowledged-prefix","id":"FA-7211","implementations":{"attempt":{"sha256":"15aec4e6164efa855b27209449d5f31b48e04cd9e82373a27c7be7fa6305ed37","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(ack, previous, sent):\n    return max(0,ack-previous)\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(10, 8, 12), 2)\", \"check('fixture 2', solve(7, 8, 12), 0)\", \"check('fixture 3', solve(13, 8, 12), None)\", \"check('fixture 4', solve(8, 8, 12), 0)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\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":"358c5a5324140fc76e0aef102d8e5842eff776e831b4832d7fbf06ff61edd39c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport ipaddress\nimport re\nfrom urllib.parse import urlsplit, urljoin\nN = 1\nobservations = []\ndef solve(ack, previous, sent):\n    return ack\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(10, 8, 12), 2)\", \"check('fixture 2', solve(7, 8, 12), 0)\", \"check('fixture 3', solve(13, 8, 12), None)\", \"check('fixture 4', solve(8, 8, 12), 0)\"]\nfor _line in _fixtures[N % len(_fixtures):] + _fixtures[:N % len(_fixtures)]:\n    exec(_line)\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":"Bounded deterministic policy model over validated inputs; not a complete protocol stack or an interoperability claim. The five variants rotate the same explicit fixture set. 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":"xh-acknowledged-byte-count-excludes-already-acknowledged-prefix","generated_at":"2026-09-29T14:38:09.412956+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic transport flow control model isolates the acknowledged-byte-count-excludes-already-acknowledged-prefix policy at a network component boundary.","root_cause":"The faulty implementation uses `ack` for the acknowledged-byte-count-excludes-already-acknowledged-prefix decision.","sha256":"30766a393f6fb17fcfbe03b72e40b0f70c0578ad14cc383a5778a20982454a7a","title":"Acknowledged byte count excludes already acknowledged prefix · 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":50.224,"exit_code":1,"observations":[{"actual":0,"check":"fixture 2","expected":0,"passed":true},{"actual":5,"check":"fixture 3","expected":null,"passed":false},{"actual":0,"check":"fixture 4","expected":0,"passed":true},{"actual":2,"check":"fixture 1","expected":2,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": 5, \"expected\": null, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": 2, \"expected\": 2, \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":43.057,"exit_code":1,"observations":[{"actual":7,"check":"fixture 2","expected":0,"passed":false},{"actual":13,"check":"fixture 3","expected":null,"passed":false},{"actual":8,"check":"fixture 4","expected":0,"passed":false},{"actual":10,"check":"fixture 1","expected":2,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": 7, \"expected\": 0, \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": 13, \"expected\": null, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": 8, \"expected\": 0, \"passed\": false}, {\"check\": \"fixture 1\", \"actual\": 10, \"expected\": 2, \"passed\": false}], \"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."}}