Vite plugins: cx-scss-manifest + transform-cx-imports, Vite-based litmus setup

[mstijak]

Summary

Adds two Vite plugins — vite-plugin-cx-scss-manifest and vite-plugin-transform-cx-imports — and converts litmus to optionally run on Vite 8 to prove them out end-to-end.

packages/vite-plugin-cx-scss-manifest

Vite counterpart of cx-scss-manifest-webpack-plugin.

• Scans import statements of the app's own modules with es-module-lexer in the transform hook, validates candidates against cx/manifest.js, and generates the same manifest.scss format as the webpack plugin (files are interchangeable between the two).
• Handles named imports (alias-aware), cross-namespace re-exports (e.g. Repeater from cx/widgets → ui/Repeater), deep imports, and skips import type statements and node_modules.
• Dev: debounced writes; Vite tracks manifest.scss as a sass dependency, so new widget styles hot-reload without a page refresh.
• Build: full-graph scan; warns when the manifest changed during the build (CSS compiled with the previous manifest — rerun to apply).
• Seeds its entry set from the existing file on startup, so an on-demand dev session never shrinks a manifest produced by a full build. Entries are append-only; reset by deleting entries + running a build.

packages/vite-plugin-transform-cx-imports

Vite counterpart of babel-plugin-transform-cx-imports. Rewrites namespace barrel imports into direct file imports using cx/manifest.js:

import { Button, Grid as CxGrid } from "cx/widgets";
// becomes
import { Button } from "cx/widgets/Button.js";
import { Grid as CxGrid } from "cx/widgets/grid/Grid.js";

• Halves litmus's transformed module count (354 → 181) since barrels no longer pull the whole namespace through the pipeline — the main win is dev-server cold start.
• Unknown names stay on the barrel with a one-time warning (instead of the babel plugin's hard error); import type, namespace, default, and dynamic imports are left untouched. Sourcemaps preserved via magic-string.
• Optional scss flag mirrors the babel plugin's sass option (currently dormant — the shipped manifest has no scss entries).
• Perf note: uses the same es-module-lexer Vite itself runs on every module during import-analysis, gated behind node_modules/extension/indexOf("cx/") checks — measured build overhead of both plugins together is ~15ms (within noise).

fix(cx): type-only re-exports

Three type-only names were re-exported as values (AccessorChain in ui/index.ts, JSX in jsx-dev-runtime.ts, GridRowConfig in Grid.tsx). Babel tolerated this, but any isolated-modules transpiler (esbuild/oxc/swc) keeps the import and fails at runtime — this breaks all jsxImportSource: "cx" source-consuming setups, not just litmus. Fixed with export type (verified via tsc --isolatedModules, which now reports no TS1205 errors).

feat(litmus): Vite setup alongside webpack

• yarn start:vite (port 8090) / yarn build:vite; the webpack workflow is untouched.
• Aliases cx/* to packages/cx/src — framework source edits hot-reload directly, no compile step.
• Automatic JSX runtime with jsxImportSource: "cx" (no babel). Legacy .js demos containing JSX go through a small esbuild bridge plugin, since rolldown's built-in transform doesn't allow enabling JSX for .js (its TransformOptions.lang is ignored in the native plugin). The active demo is renamed to .tsx as the migration path — pure oxc handles those.
• Vite 8 production build: ~0.6s.

Testing

• Verified in a real browser (dev + production build): widget styles present, chart/switch/select rendered correctly, HMR loop (new import → manifest update → CSS hot update) works without page reload, direct file imports visible in the dev network log.
• yarn check-types clean; yarn test — 535 passing, 1 pre-existing failure on master (babel-plugin-transform-cx-imports vs. stale dist/manifest.js after the cx/widgets barrel refactor, unrelated to this PR).