Function spawn_shm_router_with_stop 

pub fn spawn_shm_router_with_stop<const N: usize>(
    path: PathBuf,
    cfg: RouterLoopConfig,
    options: RouterThreadOptions,
    stop: Arc<AtomicBool>,
) -> Result<RouterThread>

Spawn a router thread using a caller-provided stop flag.

This is the lowest-level thread spawner: callers can share/coordinate stop across multiple threads.