[lmm]

> You have two poison pills (`import "server-only"` and `import "client-only"`) that cause a build error when transitively imported from the wrong environment.

Sure, but even though it's "build time" it feels more like runtime (indeed I think the only reason it works that way is your code is being run at build time). I should be able to look at a given piece of code and know locally whether it's client-side, server-side, or polymorphic, rather than having to trace through all its transitive imports.