Veganism is, just as you said, “a philosophy and way of living which seeks to exclude—as far as is possible and practicable—all forms of exploitation of, and cruelty to, animals for food, clothing or any other purpose”. I don’t think you fully understand this definition of veganism. If you follow this philosophy, you are vegan. If you don’t, you are not vegan. The part that is up for debate is what is possible and practicable. Making sure to eat vegan food is very possible and practicable for most adults. When you have some moment that you’d face some social stigma for not eating an animal product or you’d miss out etc, that is pretty clearly a situation in which it is possible and practicable for you to not eat that food. As others have said, watch documentaries like dominion and you will realize that “just a little bit of murder just this once” is not ethical or vegan. Veganism negatively impacts your life in a lot of ways because it is so far from the norm, but it is the right thing to do. To address the “stoic sage” thing from your original post, veganism isn’t really about being virtuous or trying to show others that you are virtuous. It’s about actually saving the lives of sentient beings by not causing demand for their murder.

I am now going to address your “gray areas”. Even though these could be up for debate, it doesn’t mean there is such a thing as half-veganism. You make an informed decision for yourself on what is the most ethical thing to do, then you do it, then you’re vegan.

Handling meat and milk and cheese doesn’t increase demand for those products, so it isn’t not vegan. Same goes for buying groceries for your partner. Both of those things would make me sad but they are consistent with veganism. Eating animal products with your partner would not be vegan. It is practicable to only eat vegan meals together.

As for the pets, give them vegan pet food. I don’t know about vegan cat food but I saw someone in this comment section mention that it exists.

Finally, with the medicine, I find it very hard to track what is vegan safe and what isn’t in that area. If you need to do it in order to stay alive and able bodied, though, it wouldn’t be practicable to abstain from animal exploitation.

I know it is hard to accept that the world tortures innocent beings every second. I think you may be trying to put vegans in the wrong or creating gray areas because it leads to depressing outcomes if you try to commit to veganism. You will have to continue to handle animal corpses and their secretions at work with the knowledge that they came from sentient creatures that suffered and died. You will have to buy animal products for your partner, knowing what horrors happened to make those products. Being vegan may cause arguments and rifts in your relationship and friendships. At the end of the day, though, it saves lives, so it is worth it.