Second to last update before the final verdict.
It went well! I drove out there (I finally understand why Californians hate traffic so much) and had my interview. It was with the lead designer and lead programmer of the game I'd be working on. They asked me to talk about some of my old projects, how I handled certain problems, stuff like that. Then just general design questions - "In Hearthstone, one complaint is that there isn't a lot of counterplay for spells that are too powerful. What would you implement to fix that?" "As far as design goes, what makes your projects unique?" They even had me draw up and run them through an example of a board game I developed a while back. Then they had me break out my laptop and show them examples of my code and explain my thought process, and told me they'd probably call me some time this coming week.
Overall, I felt pretty good, but I wonder if I was almost... Too confident. Like, I asked at one point, "Will I be full or part time?" And they responded, "That's a conversation for once we decide whether or not to take you." Like, I almost forgot that it was an interview and that the decision wasn't made. So I've gotta work on that in the future, I think.
All in all, not bad. Thanks for the tips, everyone! I'll include the exciting conclusion to this saga as soon as I know it.