Function build_persistent_fixpoint_program 

pub fn build_persistent_fixpoint_program(
    transfer_body: Vec<Node>,
    current: &str,
    next: &str,
    changed: &str,
    words: u32,
    max_iterations: u32,
) -> Program

Build a persistent-fixpoint Program around a caller-supplied transfer body. Replaces a host-side loop { dispatch(); check } pattern with a single GPU-side dispatch that ping-pongs current ↔ next until changed[0] == 0 or max_iterations.

P-DRIVER-9: every host fixpoint loop should migrate to this substrate Program. Caller supplies transfer_body that reads current and writes next; the wrapper handles the convergence flag and ping-pong copy.