Module build fails when CSS contains a remote @import URL

[domutala]

Description

Building a Runable module fails when one of its CSS entries contains a remote @import URL.

The @tsdown/css plugin appears to resolve the URL as a path relative to the CSS file instead of preserving it as an external CSS import.

Minimal reproduction

Create a Runable module with a CSS entry:

import { defineModule } from "runable";

export default defineModule({
  css: ["./app/css/main.css"],
});

Add a remote import to app/css/main.css:

@import url("https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap");

@import "tailwindcss";

Then run:

pnpm build

Actual behavior

The build fails because the remote URL is interpreted as a local file path:

WARN [@tsdown/css] Failed to resolve import
'https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap'

Error: ENOENT: no such file or directory, open
'/path/to/project/app/css/https:/fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap'

Expected behavior

Remote CSS imports should either:

1. remain unchanged in the generated CSS, or
2. be treated as external resources and not passed to the local filesystem resolver.

Environment

• Runable: 1.1.0
• @runablejs/cli: 1.1.0
• @tsdown/css: 0.22.14
• Node.js: 24.19.0
• Package manager: pnpm
• OS: Linux

Workaround

Removing the remote @import allows the module to build successfully.

Using a locally packaged font would also avoid the issue, but remote CSS imports are valid CSS and should not be resolved as relative filesystem paths.