Convert FD-based callback functions (close, read, write, fstat, ftruncate, fdatasync, fsync, fchmod, fchown, futimes, readv, writev) from sync handler + process.nextTick to async handlers using the undefined | Promise pattern, matching the approach already used for path-based operations. Add async FD handlers to setup.js that call the async methods on MemoryFileHandle (read, write, stat, truncate, close) instead of their sync counterparts, avoiding event loop blocking for custom VFS providers that do real I/O. Fix vfs.md documentation that was significantly out of date: - Remove false claim that chmod, chown, truncate, utimes, link, fdatasync, fsync have no VFS equivalent (all are implemented) - Add missing intercepted methods to the fs integration section (truncate, link, chmod, chown, lchown, utimes, lutimes, mkdtemp, lchmod, cp, statfs, opendir, readv, writev, ftruncate, fchmod, fchown, futimes, fdatasync, fsync) - Shrink "not intercepted" list to just glob/globSync - Add missing provider.supportsWatch documentation - Update overlay mode operation routing lists