{"abstract":"Multipart delimiters cannot occur at payload line boundaries.","category":"HTTP ranges","checks":6,"contract":"Choose candidate, candidate+x, ... until no part contains a line starting --candidate. Parts are ASCII strings; only start of body or after CRLF is a line boundary.","evaluation_group":"s3-http_ranges-multipart","failed_approach":"The partial repair uses return candidate+\"x\" if any((\"--\"+candidate) in p for p in parts) else candidate, which still violates the stated contract.","family":"s3-http_ranges-multipart-boundary-collision","id":"FA-26441","implementations":{"attempt":{"sha256":"21d94157d62945c211dd76f9f7ee676344fea0224b333045fd520b71b167e87c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(candidate, parts):\n    return candidate+\"x\" if any((\"--\"+candidate) in p for p in parts) else candidate\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('multipart-boundary-collision fixture 0', solve(\"b\"+str(N),[\"--b\"+str(N),\"--b\"+str(N)+\"x\"]), \"b\"+str(N)+\"xx\")\ncheck('multipart-boundary-collision fixture 1', solve(\"b\",[\"abc--b\"]), \"b\")\ncheck('multipart-boundary-collision fixture 2', solve(\"b\",[\"x\\r\\n--b\"]), \"bx\")\ncheck('multipart-boundary-collision fixture 3', solve(\"b\",[]), \"b\")\ncheck('multipart-boundary-collision fixture 4', solve(\"b\",[\"\"]), \"b\")\ncheck('multipart-boundary-collision fixture 5', solve(\"b\",[\"--other\"]), \"b\")\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":"137503b52dd64bcf4b8931b0193bd95c669ae3ac0bc4e341c4c86c5055c5af09","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(candidate, parts):\n    return candidate\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('multipart-boundary-collision fixture 0', solve(\"b\"+str(N),[\"--b\"+str(N),\"--b\"+str(N)+\"x\"]), \"b\"+str(N)+\"xx\")\ncheck('multipart-boundary-collision fixture 1', solve(\"b\",[\"abc--b\"]), \"b\")\ncheck('multipart-boundary-collision fixture 2', solve(\"b\",[\"x\\r\\n--b\"]), \"bx\")\ncheck('multipart-boundary-collision fixture 3', solve(\"b\",[]), \"b\")\ncheck('multipart-boundary-collision fixture 4', solve(\"b\",[\"\"]), \"b\")\ncheck('multipart-boundary-collision fixture 5', solve(\"b\",[\"--other\"]), \"b\")\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"},"fixed":{"sha256":"e7ca246abaad902dfb647ff920debec0292fd162d53da3aa7021ce5e49f5d14f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(candidate, parts):\n    while any(p.startswith(\"--\"+candidate) or (\"\\r\\n--\"+candidate) in p for p in parts):\n        candidate += \"x\"\n    return candidate\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('multipart-boundary-collision fixture 0', solve(\"b\"+str(N),[\"--b\"+str(N),\"--b\"+str(N)+\"x\"]), \"b\"+str(N)+\"xx\")\ncheck('multipart-boundary-collision fixture 1', solve(\"b\",[\"abc--b\"]), \"b\")\ncheck('multipart-boundary-collision fixture 2', solve(\"b\",[\"x\\r\\n--b\"]), \"bx\")\ncheck('multipart-boundary-collision fixture 3', solve(\"b\",[]), \"b\")\ncheck('multipart-boundary-collision fixture 4', solve(\"b\",[\"\"]), \"b\")\ncheck('multipart-boundary-collision fixture 5', solve(\"b\",[\"--other\"]), \"b\")\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":"Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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":"s3-http_ranges-multipart-boundary-collision","generated_at":"2026-09-29T14:41:16.089451+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Range responses combine representation identity, conditional requests, framing, and partial-object state.","repair":"Apply the bounded decision exactly: while any(p.startswith(\"--\"+candidate) or (\"\\r\\n--\"+candidate) in p for p in parts):\n    candidate += \"x\"\nreturn candidate","root_cause":"The multipart-boundary-collision decision uses return candidate.","sha256":"70f8c10f901e5951b8df19390817102b0ab08ba350cb250c0b53c3793191fab4","title":"Multipart delimiters cannot occur at payload line boundaries · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":36.36,"exit_code":1,"observations":[{"actual":"b1x","check":"multipart-boundary-collision fixture 0","expected":"b1xx","passed":false},{"actual":"bx","check":"multipart-boundary-collision fixture 1","expected":"b","passed":false},{"actual":"bx","check":"multipart-boundary-collision fixture 2","expected":"bx","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 3","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 4","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 5","expected":"b","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"multipart-boundary-collision fixture 0\", \"actual\": \"b1x\", \"expected\": \"b1xx\", \"passed\": false}, {\"check\": \"multipart-boundary-collision fixture 1\", \"actual\": \"bx\", \"expected\": \"b\", \"passed\": false}, {\"check\": \"multipart-boundary-collision fixture 2\", \"actual\": \"bx\", \"expected\": \"bx\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 3\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 4\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 5\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":39.229,"exit_code":1,"observations":[{"actual":"b1","check":"multipart-boundary-collision fixture 0","expected":"b1xx","passed":false},{"actual":"b","check":"multipart-boundary-collision fixture 1","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 2","expected":"bx","passed":false},{"actual":"b","check":"multipart-boundary-collision fixture 3","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 4","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 5","expected":"b","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"multipart-boundary-collision fixture 0\", \"actual\": \"b1\", \"expected\": \"b1xx\", \"passed\": false}, {\"check\": \"multipart-boundary-collision fixture 1\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 2\", \"actual\": \"b\", \"expected\": \"bx\", \"passed\": false}, {\"check\": \"multipart-boundary-collision fixture 3\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 4\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 5\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":39.242,"exit_code":0,"observations":[{"actual":"b1xx","check":"multipart-boundary-collision fixture 0","expected":"b1xx","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 1","expected":"b","passed":true},{"actual":"bx","check":"multipart-boundary-collision fixture 2","expected":"bx","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 3","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 4","expected":"b","passed":true},{"actual":"b","check":"multipart-boundary-collision fixture 5","expected":"b","passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"multipart-boundary-collision fixture 0\", \"actual\": \"b1xx\", \"expected\": \"b1xx\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 1\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 2\", \"actual\": \"bx\", \"expected\": \"bx\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 3\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 4\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}, {\"check\": \"multipart-boundary-collision fixture 5\", \"actual\": \"b\", \"expected\": \"b\", \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}