I didn't manage to get code errors on save, only after running the build task manually.
The errors I got were along the lines of
2026-02-18T21:40:09.231 [warning] first.d:384:visit Could not locate object.d or object.di
2026-02-18T21:40:09.235 [warning] first.d:481:visit Could not resolve location of module 'std/stdio'
It also seems to be broken for a friend who's been using Windows.
Building serve-d from source and configuring d.servedPath seems to fix the issue.