feat(components): add InputNumberExperimental primitive on Base UI

packages/components/rollup.config.mjs

@@ -15,14 +15,25 @@ const createMultiInput =
   typeof multiInput === "function" ? multiInput : multiInput.default;
 
 /**
- * When PREBUILD_CSS is supplied, only build the main index.ts file.
+ * When PREBUILD_CSS is supplied, only build the main barrels.
  * This ensures postcss maintains consistent ordering of styles across builds.
  *
  * Using multiInput (input with globs) produces inconsistent ordering within styles.css
  * because files are loaded in a non-deterministic order, and postcss bundles them in
  * that order.
+ *
+ * The primitives barrel is included in addition to the main barrel so that styled
+ * primitives (under `src/primitives/`) contribute their CSS module hashes to the
+ * extracted styles.css. Without this, primitives' class hashes appear in the JS
+ * bundle but not in the stylesheet, so consumers see no styles applied.
  */
 const PREBUILD_CSS = process.env.PREBUILD_CSS === "true";
+// Object form gives each entry a unique `[name]` for output filenames; both
+// inputs share the basename `index.ts`, so the array form would collide.
+const PREBUILD_CSS_INPUTS = {
+  index: "src/index.ts",
+  "primitives/index": "src/primitives/index.ts",
+};
 
 /**
  * PostCSS plugin to remove @charset declarations.
@@ -52,7 +63,7 @@ export default {
 
     warn(warning);
   },
-  input: PREBUILD_CSS ? "src/index.ts" : `src/**/index.{ts,tsx}`,
+  input: PREBUILD_CSS ? PREBUILD_CSS_INPUTS : `src/**/index.{ts,tsx}`,
   plugins: [
     nodePolyfills(),
     nodeResolve(),