Function set_fragment_yield_budget 

pub fn set_fragment_yield_budget(budget: Option<usize>)

Ask digestion to yield at legal fragment seams once budget boxes have accumulated at the current level (None restores eager digestion). Set by the streaming pass-1 driver; the budget is a box COUNT — the driver derives it from the byte ceiling via the measured per-box footprint, the same basis as the box-list guards.