Reproduction link or steps

https://stackblitz.com/edit/github-gdzm6nl4?file=setup.js,tsdown.config.ts

Run the following commands on Node 20.x

1. pnpm i
2. node setup.js
3. pnpm build

What is expected?

The build suceeds.

What is actually happening?

The following error happens:

Error: [unrun] Import failed (code length: 222): Cannot find package 'a' imported from /home/projects/github-gdzm6nl4/node_modules/.unrun/tsdown.config.ts.fae6e71f66e86bf1ce5b6898e2a68745.mjs

Any additional comments?

I encountered this in vitejs/vite#21095.
https://github.com/vitejs/vite/actions/runs/19219473498/job/54934596955?pr=21095#step:10:20

I guess this is a bug in unrun. FYI Vite handles this case by rewriting all imports to absolute paths. cc @Gugustinette