What is the topic of a comment?

Some hypotheses:
1. It’s not contained in the comment itself, it’s something about the comment, in the context of the conversational tree it’s in.
2. There’s not just one topic. For some early embedding experiments, we’re treating it that way, and that’s fine for now, but trust flows through the system by dot products, which means trust flows somewhat highly between a comment whose topics include Chemistry and Movies, and a different comment whose topics include Chemistry and Cooking.