That's what I find confusing in Astro's self-presentation: they talk a lot about MPA vs SPA and how nicely they blend, making it abundantly clear that by MPA, they mean server-rendered. But then there's all the talk about static file hosting and I think the project even started as a static site generator ("dev-machine rendered")? It would be super awesome if they tackled what might be called "three level partial hydration" (build time, server side, client side).

Might even sneak in a fourth level, "server side, but cached until marked dirty". For when you are set up for static rendering, but want to reduce backend load for rarely changing stuff. I'd expect that it would be quite powerful to have that capability inside the engine that handles rendering, on component level if necessary,and not just on some internal microservice boundary (where I think it's quite common?).