Best way to get webhook data for when topic is moved from one category to another?

I’d like to do some external automations when a topic is moved from category A to category B. Specifically, I want to remove all comments from the topic when that happens. To achieve this, it seems I need to catch a webhook when the topic is moved, and do it then.

I see there is a webhook event header of topic_edited. The issue I see is that it seems to offer no relevant data about the category it was moved from.

Any suggestions on the best way to achieve this?