The column pass and the add/clip of idct4/idct8 work on whole rows so they
vectorise (same integer steps in the spec's row-then-column order; checked
against the per-column formulation on random blocks). Docs: draft decoding in
architecture.md and perf.stats fields in control-protocol.md.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>