At the moment, any MD inclusion like `<!--@include: ...-->` do not work
within nested packages that are configured with rewrites.

Demo is in https://github.com/chgeo/vitepress-rewrites-demo (fork of your rewrite demo repo).
There, `packages/package-a/src/index.md` cannot resolve the sibling file `include.md` through
 `<!--@include: ./include.md-->`

The fix is simple to not use a rewrite alias here, but to treat include file paths as strict
relative paths.