mmap set offset = 4096 will fail

std::string fileData;
size_t fileSize = sysconf(_SC_PAGESIZE) * 100 + 10;
fileData.reserve(fileSize);
for (size_t i = 0; i < fileSize; i++) {
fileData.push_back(0xff & Random::rand32());
}

File f = File::temporary();
writeStringToFileOrDie(fileData, f.fd());
std::cout << "fileSize" << fileSize << std::endl;
MemoryMapping m(File(f.fd()), 4096, 8193);

Reproduce the provided case using the MemoryMapping entry point with a page offset of 4096 and a length of 8193. Trace where the mapping rejects or mishandles that offset, then verify that the reported case completes successfully without regressing other offset or length behavior.

Written by the indexing model from the issue text.