Whether unstarted events keep to their own block or sit in one deadline
order with the running ones. Both are right for somebody, so it is the
reader's answer and it survives a reload like the rest of the board's
shape does.
Defaults to the block, which is the board as it was before the choice
existed. Only read while `timelineUpcoming` is on — with nothing
unstarted plotted there is no block to keep apart — but stored either
way, so switching that back on restores what they said rather than a
default.
The Controls test builds a whole `Prefs`, so a new required field lands
there in the same commit or nothing typechecks in between.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
