Function spawn 

pub fn spawn(
    data_dir: PathBuf,
    dir_hash: String,
) -> Result<Receiver<TrayAction>, String>

ksni’s blocking API drives its own current-thread Tokio runtime (RUNTIME.block_on), which panics if entered from inside another runtime — and both our callers are (run_unix for spawn, the notify task for updates). So the tray lives entirely on its own std thread; everyone else only sends it Updates.