Ok, I've investigated Confluence some more. Publishing a diagram from Line9 Pro gives you a stable URL that serves a pre-rendered SVG and which updates when you modify the Mermaid. This can easily be displayed in Confluence by inserting an image from a link. Problems I found: 1) you'd need to published with public visibility 2) Confluence appears to cache the image, so updates don't appear in the page. Doing this properly in Confluence will need an app, which I don't have yet.