Which, btw, proved to not be where the bottleneck in Astro builds really is, contrary to prior beliefs. It only matters if you have >4k pages being rendered from the same .astro file using Content Collections. For the vast majority of people the bottleneck of Astro builds is Rollup

Won't be first party, but an integration. The three mages have gathered. This is another of their creations, after fully incremental builds.

Coming Soon™ to a package registry near you.
Any language that can compile to WASM or has an interpreter in WASM will be usable on the frontmatter.