While trying to minmax a build for a Bladesinger by way of the new TCoE book I happened upon a curious problem with which I need assistance. The bonus damage from Hexblade's Curse reads
[...] You gain a bonus to damage rolls against the cursed target. The bonus equals your proficiency bonus.
So my question can be summed up as 'What constitutes a separate damage roll?' Are damage rolls separated by source? Perhaps by damage type? Are they separated by when the damage is dealt?
A creature is struck by a Bladesinger/Hexblade using the special Extra Attack feature in Tasha's Cauldron of Everything; once using a standard rapier, and once using Booming Blade. The creature is under the effects of Hexblade's Curse.
How is the damage calculated? Is the Hexblade's curse damage applied to the initial strike, the second strike, and the damage the creature takes when it moves? Or is the curse damage ignored when the creature moves since the source of that damage has already dealt the curse damage?