{"abstract":"Fast retransmit fires on threshold crossing once.","category":"Transport flow control","checks":4,"contract":"Bounded offline decision model: fast retransmit fires on threshold crossing once. Inputs are already validated protocol fields; the explicit fixtures define the supported policy, not a complete protocol implementation.","contract_signature":"old, new, threshold","evaluation_group":"xh-fast-retransmit-fires-on-threshold-crossing-once","failed_approach":"The attempted repair uses `new > threshold` and still violates a separate fixture.","family":"xh-fast-retransmit-fires-on-threshold-crossing-once","id":"FA-7246","implementations":{"attempt":{"sha256":"e22f4b7881aa8e7845afa9773613a1d98291af3cb32c3290c30994f666fb0eaf","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(old, new, threshold):\n    return new > threshold\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(2, 3, 3), True)\", \"check('fixture 2', solve(3, 4, 3), False)\", \"check('fixture 3', solve(0, 2, 3), False)\", \"check('fixture 4', solve(1, 4, 3), True)\"]\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":"74df6f9d438f31449cb7fd561e4f215c314c1bf95a918292baff5750d0bcf6a7","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(old, new, threshold):\n    return new >= threshold\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\n_fixtures = [\"check('fixture 1', solve(2, 3, 3), True)\", \"check('fixture 2', solve(3, 4, 3), False)\", \"check('fixture 3', solve(0, 2, 3), False)\", \"check('fixture 4', solve(1, 4, 3), True)\"]\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-fast-retransmit-fires-on-threshold-crossing-once","generated_at":"2026-09-29T14:38:09.831510+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"This deterministic transport flow control model isolates the fast-retransmit-fires-on-threshold-crossing-once policy at a network component boundary.","root_cause":"The faulty implementation uses `new >= threshold` for the fast-retransmit-fires-on-threshold-crossing-once decision.","sha256":"112fad23129af826f8a9123fb19f347638f8a232e1f0287412fd798fd49108ce","title":"Fast retransmit fires on threshold crossing once · 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":50.81,"exit_code":1,"observations":[{"actual":true,"check":"fixture 2","expected":false,"passed":false},{"actual":false,"check":"fixture 3","expected":false,"passed":true},{"actual":true,"check":"fixture 4","expected":true,"passed":true},{"actual":false,"check":"fixture 1","expected":true,"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": false, \"expected\": true, \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":46.688,"exit_code":1,"observations":[{"actual":true,"check":"fixture 2","expected":false,"passed":false},{"actual":false,"check":"fixture 3","expected":false,"passed":true},{"actual":true,"check":"fixture 4","expected":true,"passed":true},{"actual":true,"check":"fixture 1","expected":true,"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"fixture 2\", \"actual\": true, \"expected\": false, \"passed\": false}, {\"check\": \"fixture 3\", \"actual\": false, \"expected\": false, \"passed\": true}, {\"check\": \"fixture 4\", \"actual\": true, \"expected\": true, \"passed\": true}, {\"check\": \"fixture 1\", \"actual\": true, \"expected\": true, \"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."}}