<style src="./relative-path.css"> causes ENOENT when using with rolldown (tsdown)

[pont1s]

Describe the bug

Using an external stylesheet via <style src="./Button.css" /> in a Vue SFC fails with ENOENT when bundling with tsdown. The same setup works correctly with Vite.

Steps for reproduction:

1. pnpm i
2. pnpm build

Error

  [plugin unplugin-vue]
  Error: ENOENT: no such file or directory, open './Button.css'
      at Object.readFileSync (node:fs:440:20)
      at LoadPluginContextImpl.load (unplugin-vue/dist/core-1z6RfQNO.mjs:898:30)

Reproduction

https://github.com/pont1s/unplugin-vue-rolldown-style-src-reproduction/

System Info

System:
    OS: macOS 26.3.1
    CPU: (8) arm64 Apple M1
    Memory: 72.16 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 24.11.1
    pnpm: 10.33.0

Used Package Manager

pnpm

Validations

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• The provided reproduction is a minimal reproducible of the bug.