Order doesn't matter when users are completely downloading
mboxrds onto the FS and then opening them with an MUA. The
MUA is expected to sort the results in the user's preferred
order.
However, lei can start streaming the results to its destination
Maildir (or eventually IMAP/JMAP mailbox) with an MUA already
open. This will let users see recent results sooner in their
MUA, as those tend to have a higher docid. This matches the
behavior of the HTML results, as well.
As a bonus, this is around ~5% faster in a one-off, informal
test case with 66k results. I expect this to hold true in all
all cases since git has always optimized storage to favor recent
objects.