L4D1 survivors don't have a callback to filter what items they're allowed to gift

[alexiscoutinho]

In c6m3, the L4D1 survivors don't have a callback like AllowFallenSurvivorItem to filter what items they are allowed to gift to the survivors. This would be very helpful for mutations that convert first aid kits into something else, for example. The current workaround of killing any forbidden gifts is unsatisfactory because the L4D1 survivors would still do the animation and say the gifting lines only to have their gift vanish right off their hands. Quite rude on their part 😄.

[True-Boredom]

In The Passing, the L4D1 survivors are able to gift players items that are not normally available in the l4d1coop mutation, such as adrenaline. #334