Extract shared renderToolbarItems() function to eliminate ~850 lines of
duplicated toolbar code between 'top' and 'below-subject' positions.
Add overflow support to Reply, Reply All, and Forward buttons with
data-overflow-item attributes and corresponding More menu entries.
Fix overflow detection algorithm: temporarily disable flex-shrink on
child groups during measurement so scrollWidth reflects natural widths
instead of flex-compressed values. Add overflow-hidden to toolbar
container to prevent visual overflow during recalculation.
Linus Rath
a886edda6f