render.settings.set saves validated named render setups (camera, output size, exposure, environment) as one undo step, and render.settings.get reads them back without applying a camera. When validated render settings are the only change, the engine keeps the evaluated model instead of rebuilding it. Setups are saved under design format 21; format-20 designs read as having none. Fixes #658; refs #620. Contributed by @0xlillith. Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>