Function item_window 

pub fn item_window(p: &SpatialProgram) -> usize

The item-loop window the event graph unrolls. Work items are rounds of one choreography whose state (FIFO occupancy, semaphore rounds) carries over with a dependence distance bounded by the deepest FIFO; the unrolled graph is periodic beyond that, so a token-free cycle exists in the full unrolling iff it exists within deepest FIFO + 2 consecutive rounds. Every engine of a site (and every member of a multicast group) loops the same count, so the cap keeps producer/consumer pairings consistent.