fix: use emitted CSS in vite_stylesheet_tag for Rolldown CSS entries (close #615)

[breken-ai]

Description 📖

This pull request fixes #615. vite_stylesheet_tag now links the CSS that Vite emitted for a CSS-only entrypoint, including the Vite 8 / Rolldown case where the manifest file for that entry is a JavaScript wrapper.

Background 📜

This was happening because vite_stylesheet_tag used path_for, which always returns the entry's file. For some CSS-only entrypoints Rolldown writes a .js wrapper to file and puts the real stylesheet in css[], like this:

"entrypoints/print.css": {
  "file": "assets/print.4b6e2a1f.js",
  "src": "entrypoints/print.css",
  "isEntry": true,
  "css": ["assets/print.9c0d7e35.css"]
}

So in production the helper rendered <link rel="stylesheet" href="/vite/assets/print.4b6e2a1f.js"> and the page lost its styles. Development is not affected, because the dev server serves the source path directly.

The Fix 🔨

By changing vite_stylesheet_tag to resolve each name with resolve_entries(name, type: :stylesheet), which is the same approach as the workaround in the issue:

• when file is a .css file, it is kept (normal CSS entries render exactly as before);
• the css[] paths are added and deduplicated;
• when there are no css[] paths (always the case while the dev server runs), file is used, so dev paths such as entrypoints/sassy.scss are unchanged.

Tests:

• New test_vite_stylesheet_tag_with_javascript_wrapper_entry in test/helper_test.rb, with a wrapper entry added to the manifest-assets.json fixture. On main it fails with href="/vite-production/assets/print.4b6e2a1f.js"; with this change it renders print.9c0d7e35.css, and the dev-server path stays /vite-dev/entrypoints/print.css.
• bin/rake test (Ruby 4.0.3, Rails 8.1 from the root Gemfile): 121 tests, 0 failures (120 tests, 0 failures on main).
• rubocop on the changed Ruby files: no offenses. git diff --check: clean.
• I did not run the Rails 7.2 / 8.0 gemfiles locally; CI covers those.

An AI coding agent (Claude Code, run by breken-ai) found this bug and wrote this change; I checked the red/green test above before opening the PR.

Screenshots 📷

Not applicable: this changes the generated stylesheet URL and has no visual UI.