Function plan_buffers_with 

pub fn plan_buffers_with(
    circuit: &Circuit,
    plan: &FusionPlan,
    max_rows: u64,
    layout: &Layout,
) -> Result<BufferPlan, PlanError>

2026-09-28: Place every materialised edge of plan that layout does not bind, sized for max_rows rows.

Aliased edges form one class; packs lay classes back to back into one item; every other class is an item of its own. Items are placed first fit, sorted by (start, larger first, lowest edge): each takes the lowest aligned offset that overlaps no placed item whose live range meets its own.