Function persistent_fixpoint_program 

pub fn 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.

The generated program runs transfer_body, ping-pongs current and next, and stops when the convergence flag reads zero or max_iterations is reached. Runtime and driver crates call this self-substrate wrapper instead of depending on the primitive catalog directly.

Convergence-flag form

words sizes the widest buffer this wrapper declares, and dispatch_element_count_for_program (vyre-driver/src/program_walks/dispatch_params.rs:19) sizes an atomic-carrying program’s launch from its widest declared buffer, so words is the launch span and it selects the harness:

• words <= PERSISTENT_FIXPOINT_WORKGROUP_SIZE[0]: one workgroup covers the launch, so persistent_fixpoint runs with its single shared changed[0] word and stops when that word reads zero. The word is cleared by a plain store fenced only by a workgroup-scope barrier; with one group the fence is incidentally grid-wide, so the clear cannot race the atomic_or that sets the flag.
• words above that width: persistent_fixpoint_grid, which never clears the flag, gives each iteration its own changed word, and separates waves with MemoryOrdering::GridSync. The single-word form is limited to one workgroup precisely because its clear and its set are unordered across groups: group 0’s clear can erase another group’s set, that group then reads zero and returns early with unconverged state, and the flag the host reads afterwards reports a convergence no group agreed to.

The caller supplies changed, so it must be max_iterations zero-filled words once words exceeds one workgroup width and one word at or below it.

This wrapper can only see the buffers the harness declares. A caller whose transfer_body reads buffers wider than words, or that widens the launch through DispatchConfig, owns that span itself.