Watch mode doesn't pick up on CSS changes in imported partials #1037

Reproduction link or steps

I'm using tsdown with @tsdown/css. In watch mode, changes to CSS partials imported via @import don't seem to trigger a rebuild.

Example:

index.js:

import './styles.css';

styles.css:

@import './partial.css';

partial.css:

body {
  background: red;
}

When I run tsdown in watch mode, and I make changes to partial.css, it doesn't trigger a rebuild. When I make changes to styles.css a rebuild is triggered as expected.

I also made a repro that uses a slightly different method for compiling CSS with tsdown (adding a separate entry instead of importing it in JS): https://github.com/TimonVS/tsdown-css-repro

What is expected?

Changes to partial.css (or any CSS file imported via @import) should trigger a rebuild, just like changes to the root CSS file.

What is actually happening?

Changes to partial.css don't trigger a rebuild in watch mode.

Any additional comments?

No response