Per-frame slice size, in Uint32 indices (4 MB per slice). Purely a
PACING knob now — no longer a single-shot threshold, because there is
no single-shot path: every ordering streams into the inactive buffer
and flips when complete, and an ordering that fits one slice simply
finishes on its first pump. The baseline showed sort-adjacent tail
spikes already at 5M (20 MB) in one shot, so the slice sits well below
that — 4 MB @ 1M is the spec §6 exit-criterion size that held target
FPS on the Phase-3 perf gate.
Per-frame slice size, in Uint32 indices (4 MB per slice). Purely a PACING knob now — no longer a single-shot threshold, because there is no single-shot path: every ordering streams into the inactive buffer and flips when complete, and an ordering that fits one slice simply finishes on its first pump. The baseline showed sort-adjacent tail spikes already at 5M (20 MB) in one shot, so the slice sits well below that — 4 MB @ 1M is the spec §6 exit-criterion size that held target FPS on the Phase-3 perf gate.