Major mail-handling reliability overhaul. Conversations are now true to each folder: a conversation shows only that folder's messages plus your replies, and deleted or restored messages switch conversations for good. Unread badges match the list exactly and update instantly. Deleting and archiving survive network failures and app kills, Empty Trash really empties it, Undo is trustworthy, and multi-account actions always target the right account. Reply bursts collapse into one notification.
