fix(unplugin): transform .astro files that arrive already compiled

[wobsoriano]

What changed / motivation ?

I wanted to try StyleX in an Astro app and couldn't get it working. Any style I declared inside a .astro file was ignored, and the build failed with:

Error: Unexpected 'stylex.create' call at runtime.
Styles must be compiled by '@stylexjs/babel-plugin'.

It turned out the plugin picks which files to handle by file extension, and .astro isn't on the list, so those files get skipped entirely.

Supporting them doesn't need anything special. Astro turns .astro files into plain JavaScript before any bundler plugin runs, so by the time this plugin sees them they're ordinary modules. Adding the extension is enough.

Linked PR/Issues

Fixes # (issue)

Additional Context

Two new ones. Both fail on main and pass with this change:

• one checks .astro files are picked up
• one compiles a real .astro module and checks the CSS actually comes out

I also created a sample app with a patched @stylexjs/unplugin package (repo, demo)

NOTE: Even with the fix, an Astro app still needs a little glue to get the stylesheet onto the page. In dev the plugin adds its styles through a hook Astro doesn't use, and in a build it appends its rules to an existing stylesheet, so a site without one ends up with a CSS file nothing links to. Neither fails loudly, you just get an unstyled page.

Happy to follow up with an @stylexjs/unplugin/astro entry, or add an example in the examples folder, or I can just release a community astro-stylex integration (ref)

Pre-flight checklist

• I have read the contributing guidelines
  Contribution Guidelines
• Performed a self-review of my code

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[Copilot]

Pull request overview

This PR fixes @stylexjs/unplugin behavior in Astro projects by ensuring modules with a .astro ID are included in the plugin’s transform pipeline, preventing uncompiled stylex.create calls from reaching runtime.

Changes:

• Add .astro to the set of “transformable” module IDs via a shared isTransformableId() helper.
• Update both transformInclude() and the early-return guard in transform() to use the new helper.
• Add tests to verify .astro inclusion and end-to-end CSS emission from a compiled .astro-identified module.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/@stylexjs/unplugin/src/core.js	Extends transform targeting to include .astro module IDs and centralizes the ID check.
packages/@stylexjs/unplugin/tests/unplugin.test.js	Adds coverage ensuring .astro IDs are included and StyleX compilation produces CSS output.

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