512 MB was chosen as enough-for-now on the day the feature landed, and it applies
to every account equally. The owner asked for it per user before the code was an
hour old.
Notes the adjacent question while it is in view: a size limit bounds one send, and
nothing bounds what a sender accumulates in somebody's tree over a month.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
