proc_raster_apply_accumulator

Folds one tile's fixed-point accumulator into a layer, clearing the accumulator for the next batch.

proc.raster's Raster:resolveAccumulator(layerName, scratchName, work?) runs this after proc_raster_edge_add has folded in what a neighbour pushed across the seam, then refreshes layerName's apron so the next step reads a consistent neighbourhood.

It reads params (lane 0 holds the tile's stored-cell stride), adds each cell of delta, an atomic<i32> accumulator in units of 1/65536, into the same cell of field, and sets that cell of delta to 0. One thread per stored cell, apron included, in 8x8 workgroups.