gta_merge stacked all N deltas into [N,out,in] plus several full copies,
peaking at ~3.5 GB for a single 21504x3072 FLUX layer (~13x the delta). It now
streams over a list: one accumulator for the elected sign, then numerator/
divisor accumulators, freeing each input delta as consumed. Peak ~1.7 GB/key,
independent of N. Preserves mergekit parity incl. the density<1 sparsified
sign vote (3-state torch.sign so sparsified-out zeros are excluded). gta_merge
now consumes its deltas list (documented); behavior test snapshots first.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
