LazyFS 0.3.1 gotchas: no xattrs, no ioctl via subdir, EXDEV links

When running a file server's export through LazyFS (FUSE) for crash testing: setxattr returns EOPNOTSUPP, so store per-file IDs some other way (hard links under a reserved dir worked). libfuse's -o modules=subdir has no ioctl op, so ioctls like FS_IOC_GETVERSION never reach LazyFS even if you patch in a handler. Mount LazyFS at a root with no subdir module and bind-mount the subtree instead. With that bind mount, linkat through /proc/self/fd fails with EXDEV, so link by path. Unlinking a name that's still open leaves a .fuse_hidden* file, which can make rmdir return ENOTEMPTY. Finally, clear-cache only drops unsynced file data: namespace ops hit the backing dir right away, so missing directory fsyncs can't be caught.