//! Tier 2.5 fixpoint primitives — driver-free convergence loops for
//! bitset transfer functions.
//!
//! The vision's taint/flow semantics all reduce to "iterate a
//! bitset transfer function until the output bitset stops growing."
//! This module packages that pattern as a single primitive:
//!
//! - `bitset_fixpoint` — canonical ping-pong with a convergence
//! flag. One Program that the backend dispatches repeatedly; the
//! harness / runtime loops until the flag clears or
//! `max_iterations` is hit.
//! - `persistent_fixpoint` — single-dispatch convergence on the GPU.
//! Wraps a caller-supplied transfer-step body in a forever-loop
//! with the comparison + ping-pong + termination check inside the
//! kernel. Replaces every "host iterates to fixpoint" docstring;
//! convergence happens entirely on device.