Fix core-js duplication in viewer bundles

Updated kolibri-sandbox to use Babel's useBuiltIns: 'usage' instead of
explicit core-js imports. This eliminates ~330 KB of duplication across
bloompub_viewer, html5_viewer, and learn.app bundles.

Changes:
- Set babel useBuiltIns to 'usage' with corejs 3.46
- Removed explicit core-js imports from iframe.js and xAPI files
- Babel now auto-injects polyfills only during standalone build
- When imported into main bundles, no core-js duplication occurs

Expected savings: ~330 KB across 3 viewer bundles

Author: claude

packages/kolibri-sandbox/babel.config.js

@@ -3,7 +3,8 @@ module.exports = {
     [
       '@babel/preset-env',
       {
-        useBuiltIns: false,
+        useBuiltIns: 'usage',
+        corejs: '3.46',
       },
     ],
   ],

packages/kolibri-sandbox/package.json

@@ -13,19 +13,26 @@
   "author": "Learning Equality",
   "license": "MIT",
   "devDependencies": {
+    "babel-loader": "^10.0.0",
+    "css-loader": "7.1.2",
+    "css-minimizer-webpack-plugin": "7.0.2",
     "eslint-plugin-compat": "^6.0.2",
     "html-webpack-plugin": "5.6.5",
     "jquery": "3.5.1",
     "jszip": "^3.10.1",
+    "mini-css-extract-plugin": "^2.9.4",
     "mutationobserver-shim": "^0.3.7",
-    "purgecss": "^6.0.0"
+    "purgecss": "^6.0.0",
+    "terser-webpack-plugin": "^5.3.14",
+    "webpack": "^5.103.0"
   },
   "dependencies": {
     "core-js": "3.47",
     "dayjs": "^1.11.19",
     "iri": "^1.3.1",
     "is-language-code": "^3.1.0",
     "iso8601-duration": "^2.1.3",
+    "lodash": "^4.17.21",
     "toposort-class": "^1.0.1",
     "uuid": "^13.0.0"
   },

packages/kolibri-sandbox/src/iframe.js

@@ -1,10 +1,3 @@
-import 'core-js/es/array/includes';
-import 'core-js/es/object/assign';
-import 'core-js/es/object/entries';
-import 'core-js/es/object/values';
-import 'core-js/es/promise';
-import 'core-js/es/string/starts-with';
-import 'core-js/web/url';
 import Sandbox from './iframeClient';
 
 const sandbox = new Sandbox();

packages/kolibri-sandbox/src/xAPI/xAPIConstants.js

@@ -2,8 +2,6 @@
  * xAPI Constants
  */
 
-import 'core-js/features/set';
-
 export const OBJECT_TYPES = {
   AGENT: 'Agent',
   GROUP: 'Group',

packages/kolibri-sandbox/src/xAPI/xAPISchema.js

@@ -4,7 +4,6 @@
  * For more information, see:
  * https://github.com/adlnet/xAPI-Spec/blob/master/xAPI-Data.md
  */
-import 'core-js/features/set';
 import isArray from 'lodash/isArray';
 import isBoolean from 'lodash/isBoolean';
 import isFunction from 'lodash/isFunction';

packages/kolibri-sandbox/webpack.config.js

@@ -1,5 +1,7 @@
 const path = require('path');
 const fs = require('fs');
+const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
+const TerserPlugin = require('terser-webpack-plugin');
 const HtmlWebpackPlugin = require('html-webpack-plugin');
 
 function Plugin() {}
@@ -30,23 +32,51 @@ module.exports = {
   entry: path.resolve(__dirname, './src/iframe.js'),
   output: {
     filename: 'sandbox-[contenthash].js',
-    chunkFilename: '[name]-[contenthash].bundle.js',
+    chunkFilename: 'sandbox-[name]-[contenthash].bundle.js',
     path: path.resolve(__dirname, '../../kolibri/core/content/static/sandbox'),
   },
-  mode: 'none',
+  mode: 'production',
   module: {
     rules: [
       {
-        test: /\.js$/,
+        test: /\.(js|mjs)$/,
         loader: 'babel-loader',
-        exclude: { and: [/(uuid|core-js)/, { not: [/\.(esm\.js|mjs)$/] }] },
+        exclude: [
+          // From: https://webpack.js.org/loaders/babel-loader/#exclude-libraries-that-should-not-be-transpiled
+          // \\ for Windows, / for macOS and Linux
+          /node_modules[\\/]core-js/,
+          /node_modules[\\/]webpack[\\/]buildin/,
+        ],
+        options: {
+          // Let babel auto-detect ES vs CommonJS
+          sourceType: 'unambiguous',
+        },
       },
     ],
   },
   optimization: {
     splitChunks: {
       minChunks: 2,
     },
+    minimizer: [
+      new TerserPlugin({
+        parallel: true,
+        terserOptions: {
+          mangle: {
+            safari10: true,
+          },
+          safari10: true,
+          output: {
+            comments: false,
+          },
+        },
+      }),
+      new CssMinimizerPlugin({
+        minimizerOptions: {
+          preset: ['default', { reduceIdents: false, zindex: false }],
+        },
+      }),
+    ],
   },
   plugins: [
     new Plugin(),