EPBDS-16211 fix watch-lib: same config as the published build

CLAUDE.md

@@ -13,7 +13,7 @@ The modernization roadmap (React 17/18 upgrade, `semantic-ui-react` exit, projec
 - `npm start` — Run demo app in dev mode (webpack-dev-server)
 - `npm run build` — Build the demo app for GitHub Pages deployment
 - `npm run build-lib` — Build the publishable library to `dist/` (webpack + tsc)
-- `npm run watch-lib` — Watch mode for library build
+- `npm run watch-lib` — Watch mode for the library build. Uses the SAME webpack config as `build-lib`, deliberately: it had its own parallel config until 2026-09-15, and it had drifted into emitting the stylesheet under a different name and producing no type declarations
 - `npm run yalc-publish` — Build lib and publish locally via yalc (for testing in consuming apps)
 - `npm run yalc-watch` — Auto-rebuild and yalc-publish on src changes
 - `npm run deploy` — Deploy demo to GitHub Pages (run `build` first)

package.json

@@ -31,7 +31,7 @@
     "start": "webpack serve --mode development --config webpack.demo.config.mjs",
     "build": "webpack --mode production --config webpack.demo.config.mjs && cp build/index.html build/404.html",
     "build-lib": "webpack --mode production --config webpack.library.config.mjs && npm run gen-ts",
-    "watch-lib": "webpack --watch --mode production --config webpack.watch.config.mjs",
+    "watch-lib": "npm run gen-ts && webpack --watch --mode production --config webpack.library.config.mjs",
     "yalc-publish": "npm run build-lib && yalc publish --push",
     "yalc-watch": "nodemon --watch src --ext js,jsx,ts,tsx --exec 'npm run yalc-publish'",
     "gen-ts": "tsc --project tsconfig.build.json",

src/style/__tests__/css.pipeline.parity.test.js

@@ -348,15 +348,33 @@ describe('CSS pipeline parity — final CSS, post-PostCSS (§9.5)', () => {
  * Selector granularity only: the published file is minified, and cssnano may merge or split declaration
  * blocks without changing scoping.
  */
-const hasPublishedCss = fs.existsSync(PUBLISHED_CSS);
-const describeIfBuilt = hasPublishedCss ? describe : describe.skip;
+/**
+ * READ AT MODULE LOAD, NOT IN `beforeAll`, and the difference is a real failure this suite produced
+ * repeatedly before it was understood.
+ *
+ * It used to test `existsSync` here and `readFileSync` in a `beforeAll`. Something in a full-suite
+ * run EMPTIES the root `static/` directory between those two moments, so the describe was not
+ * skipped — the file existed when the decision was made — and then three tests died on ENOENT.
+ * Intermittent, invisible in an isolated run, and it reads like a broken assertion rather than a
+ * missing file.
+ *
+ * What is established about the cause, and what is not: the emptying is reliably triggered by the
+ * LESS render in `css.semantic-parity.test.js` (bisected suite by suite, then by disabling that
+ * suite's compile — with it off the directory survives, with it on the directory is emptied every
+ * time). It is NOT done through `fs` in the jest process: probes wrapping `rmSync`, `unlinkSync`,
+ * `rmdirSync`, `renameSync` and their async and `fs.promises` forms, installed both in `setupFiles`
+ * and at the top of the suite itself, never fire. No stray watcher process is running. The
+ * mechanism is unexplained, and is written down here rather than guessed at.
+ *
+ * Reading once, at load, makes this suite correct regardless: it either has the bytes it checked
+ * for, or it skips. CI is unaffected either way — it runs jest before `build-lib`, so these three
+ * always skip there, which is what the describe name says.
+ */
+const publishedCssAtLoad = fs.existsSync(PUBLISHED_CSS) ? fs.readFileSync(PUBLISHED_CSS, 'utf8') : null;
+const describeIfBuilt = publishedCssAtLoad !== null ? describe : describe.skip;
 
 describeIfBuilt('published static/all.css (needs `npm run build-lib` — skipped when absent)', () => {
-    let publishedCss;
-
-    beforeAll(() => {
-        publishedCss = fs.readFileSync(PUBLISHED_CSS, 'utf8');
-    });
+    const publishedCss = publishedCssAtLoad;
 
     it('leaks the same global selectors as the in-process webpack pipeline', () => {
         expect(occurrenceCounts(globalRuleInventory(publishedCss))).toEqual(H8_LEAK_OCCURRENCES);

webpack.library.config.mjs

@@ -36,7 +36,12 @@ export default {
             export: 'default',
         },
         globalObject: 'this',
-        clean: true,
+        // `keep` rather than a bare `true`, and it is what makes `watch-lib` usable: webpack owns
+        // `dist/index.js`, but `dist/*.d.ts` come from `tsc` in a separate step. A plain clean
+        // wipes them on every rebuild, and in watch mode nothing regenerates them — measured, a
+        // watch session left `dist` with ZERO declaration files after `build-lib` had produced two.
+        // For `build-lib` this changes nothing: `gen-ts` runs immediately after and rewrites them.
+        clean: { keep: /\.d\.ts$/ },
     },
     externals:{
         moment: 'moment',