Function ifds_gpu 

pub fn ifds_gpu(
    _exploded_adj: &str,
    frontier_in: &str,
    frontier_out: &str,
) -> Result<Program, String>

Backwards-compatible three-string shim over ifds_gpu_step. The _exploded_adj argument is the ProgramGraph’s pg_edge_targets buffer; it is ignored here because the step kernel binds pg_edge_* at the canonical names. Kept so older call sites compile unchanged.