My job requires me to shuck oysters
The Buddhist teachings do not exist for you to create suffering for yourself. Oysters are extremely primitive life forms. While they breathe oxygen, they are very close to plants. Oysters have a nervous system but not a brain. We practise non-killing as Buddhists so we cultivate a respect for life and cease to be violent people. If killing oysters (that don't suffer or don't have relatives or loved one's who suffer about them) is against your moral principles then find a new job. However, if you think deeply about what or who you have harmed, I don't think much will be found. Don't worry about it. Let it go. An oyster does not have a  brother, sister, mother or father somewhere in the universe grieving about their lost relative oyster. The Buddha appeared to infer in SN 12.63 that lifeforms consuming other lifeforms is part of the cycle of life. As a "vegan", I imagine your views about food are more extreme than the average Buddhist. For example, the Buddha did not preach vegetarianism. The above said, personally, I would not like to kill oysters for a living.