In reply to Nick.

That’s how I’d expected it to work, actually, but for whatever reason, the KEPUB export option didn’t appear until I’d manually installed the plugin I’d linked to. The plugin warns that the format isn’t completely documented and hasn’t been fully reverse-engineered, so maybe it was removed from a standard Calibre install?

There were included Kobo-related plugins that were already installed for me, which I suspect are responsible for the niceties like chapter updates and better text handling, but I still needed to take the extra step to have KEPUB export as an option.