okay, so I went back and checked my design notes, and i guess i got things twisted somewhere along the way 😅
originally, War Dice were supposed to be single-use, and you were able to gain +1D6 War Dice when levelling up, not just one. that way, you can either take a trait and get a reusable, specialized buff, or gamble for multiple, universal consumable buffs. some traits give one War Die and a small reusable buff as an in-between option.
somewhere along the way I got the idea that War Dice were reusable and then "balanced" +1D6 War Dice to just +1. thanks for catching this pretty big design error!! I'm going to upload a version with this + a few other fixes, but to definitively answer your question, War Dice are single-use and you can choose to gain 1D6 War Dice when your character advances!