Constant SLAB_BUDGET_BYTES 

pub const SLAB_BUDGET_BYTES: usize = _; // 268_435_456usize

Bytes of (u64, u64, f32) triplets a streaming-write slab may hold, and the padded size of one such triplet. One definition, because the two streaming pipelines (the subset trait method and the handlers’ column-selection writer) each carried their own copy and two memory ceilings drift apart.