Function lowerCssImports

Lowers a CSS import into a shared, deduped constructable stylesheet so every component instance — and every module — shares one parse instead of an inline <style>:

import styles from './styles.css';              // #9: bare CSS import
import sheet from './styles.css' with { type: 'css' };  // #10: CSS Module Script syntax
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become, in the emitted module:

const __baniraAdoptStyles = (css) => { … cache on globalThis … };
const styles = __baniraAdoptStyles("…css…");
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The binding is module-level (all instances that adoptedStyleSheets = [styles] share the one sheet), and the helper's cache lives on globalThis keyed by the CSS text, so two different modules importing the same stylesheet adopt the same CSSStyleSheet — the documented adoptedStyleSheets dedupe win. adoptedStyleSheets is Baseline widely available; the CSS Module Script with { type: 'css' } syntax is not (Safari), which is why even the standard form is shimmed here.

Imports with no default binding, or whose CSS file can't be read, are left as-is.