Function xdg_runtime_dir 

pub fn xdg_runtime_dir() -> PathBuf

Get XDG runtime directory.

Returns $XDG_RUNTIME_DIR or falls back to system temp directory.

Embedders use this to compose their own runtime paths:

use kaish_kernel::paths::xdg_runtime_dir;

let myapp_sockets = xdg_runtime_dir().join("myapp");