Function candidates_where 

pub fn candidates_where(
    p: &SpatialProgram,
    target: &SpatialTarget,
    keep: &dyn Fn(&BlockPlan) -> bool,
) -> Vec<Candidate>

Every legal candidate of p on target, scored, where the plans a caller will keep decide whether the grid may outgrow the mesh: items wrap onto sites only when no blocked plan the caller keeps fits the mesh. A caller that restricts the arrangement (a calibration run pinning the packer’s accumulate) gets the best plan of that arrangement, not the streaming fallback of a round the plans it discards had filled.