Attach a stage output to data's origin entry. Returns whether it was
admitted (false: no origin, entry gone/replaced, or no spare budget).
opts.scan: the caller is inside dimension playback (see
SliceCache.setStage for why a scan admits into free budget only).
Attach a stage output to
data's origin entry. Returns whether it was admitted (false: no origin, entry gone/replaced, or no spare budget).opts.scan: the caller is inside dimension playback (seeSliceCache.setStagefor why a scan admits into free budget only).