{"abstract":"Duplicate ack counter resets on forward progress.","category":"Transport flow control","checks":4,"contract":"Bounded offline decision model: duplicate ack counter resets on forward progress. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.","contract_signature":"previous, ack, duplicates","evaluation_group":"xh-duplicate-ack-counter-resets-on-forward-progress","failed_approach":"The attempted repair uses `duplicates if ack == previous else 0` and still violates a separate fixture.","family":"xh-duplicate-ack-counter-resets-on-forward-progress","id":"FA-7241","implementations":{"attempt":{"sha256":"70aa470c2ca3e857b546c2c5e75fdc220abc29f3df8c193750d6c2b94b162ea4","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(previous, ack, duplicates):\n    return duplicates if ack == previous else 0\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(10, 10, 2), 3)\", \"check('fixture 2', solve(10, 11, 2), 0)\", \"check('fixture 3', solve(0, 0, 0), 1)\", \"check('fixture 4', solve(10, 12, 0), 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":"128543c9a71be0ca27998e95222b1be6c3d05202e47f9d046eb32ba8047800a8","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(previous, ack, duplicates):\n    return duplicates+1\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(10, 10, 2), 3)\", \"check('fixture 2', solve(10, 11, 2), 0)\", \"check('fixture 3', solve(0, 0, 0), 1)\", \"check('fixture 4', solve(10, 12, 0), 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-duplicate-ack-counter-resets-on-forward-progress","generated_at":"2026-09-29T14:38:09.823996+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic transport flow control model isolates the duplicate-ack-counter-resets-on-forward-progress policy at a network component boundary.","root_cause":"The faulty implementation uses `duplicates+1` for the duplicate-ack-counter-resets-on-forward-progress decision.","sha256":"33e831cb29f06c19b143bc1f2b1c4e03b89a8f2eddeac05a5dbd847806582fd5","title":"Duplicate ack counter resets on forward progress · 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":50.611,"exit_code":1,"observations":[{"actual":0,"check":"fixture 2","expected":0,"passed":true},{"actual":0,"check":"fixture 3","expected":1,"passed":false},{"actual":0,"check":"fixture 4","expected":0,"passed":true},{"actual":2,"check":"fixture 1","expected":3,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"fixture 3\", \"actual\": 0, \"expected\": 1, \"passed\": false}, {\"check\": \"fixture 4\", \"actual\": 0, \"expected\": 0, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": 2, \"expected\": 3, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":46.859,"exit_code":1,"observations":[{"actual":3,"check":"fixture 2","expected":0,"passed":false},{"actual":1,"check":"fixture 3","expected":1,"passed":true},{"actual":1,"check":"fixture 4","expected":0,"passed":false},{"actual":3,"check":"fixture 1","expected":3,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": 3, \"expected\": 0, \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": 1, \"expected\": 1, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": 1, \"expected\": 0, \"passed\": false}, {\"check\": \"fixture 1\", \"actual\": 3, \"expected\": 3, \"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."}}