I can tell my Google Assistant on my Android phone something like "Play the trailer for Their Darkest Hour on my Chromecast", and the Chromecast will start playing a trailer, apparently from YouTube. (It's not my phone's YouTube app that is casting, because I can be simultaneously playing another video locally.) As soon as the trailer finishes, I get a 5-ish-second countdown on the TV screen, and I am instructed to say "OK Google, Stop" to my phone if I don't want to watch another trailer for the same movie, or some other movie-related video. Then the Chromecast launches into some other video. I want it to just stop.

It looks like the Chromecast wants to autoplay its way through all the YouTube search results for whatever I asked for. My phone YouTube app's autoplay is off, and I keep autoplay off on the YouTube web interface as well, but autoplay on the Chromecast seems to be on, and I can't find where I would turn it off.

How do I turn off autoplay on the Chromecast for videos started by the Google Assistant?