The virtual filesystem root at `${os.devNull}/vfs` was previously inaccessible through fs calls, causing attempts to list mounted virtual filesystems to fail because calls fell through to the real filesystem.

The reserved root directory for virtual filesystems was not implemented as a readable directory, so fs operations could not enumerate or access mount points, leading to incorrect behavior and inability to view mounted filesystems.

Implemented a read-only virtual directory at the reserved root that lists all mount points by their last path segment, supports recursive directory listings, and prohibits modifications by returning appropriate errors. Added a helper function vfs.vfsBase() to expose the root path programmatically. Adjusted readdir and realpath behaviors for consistency and correctness.

Virtual filesystem roots should explicitly handle directory read operations to expose mount points, and filesystem APIs must carefully manage path representations and error codes to reflect the virtual filesystem's semantics accurately.