Cross-references resolve in one batch per pass, the index reads every leader gap
before filling one, and a zone's tabs lay out with the other zones' — and only
where a field asks for the page count or the chapter map.
List marker and list style decorations are rebuilt only for a transaction
reaching into a list; the unsaved dot compares documents structurally, and the
autosave serializes when it writes rather than per keystroke.
The columns flow applies every op it can judge in a pass, so a section pages in
one pass. Two long files that took 33 s and 20 s now settle in 9 s and 2 s.