Move copy build step to js script

package.json

@@ -10,9 +10,8 @@
     "url": "https://github.com/jupyter/nbclassic.git"
   },
   "scripts": {
-    "bower:cp-umd": "cp nbclassic/static/components/marked/lib/marked.umd.js nbclassic/static/components/marked/lib/marked.js",
-    "bower:copy-umd": "copy nbclassic/static/components/marked/lib/marked.umd.js nbclassic/static/components/marked/lib/marked.js",
-    "bower": "bower install && (npm run bower:cp-umd || npm run bower:copy-umd)",
+    "bower:copy-marked": "node tools/copy-marked.js",
+    "bower": "bower install && npm run bower:copy-marked",
     "build:webpack": "webpack --mode production",
     "build:notebook": "node tools/build-main.js notebook",
     "build:tree": "node tools/build-main.js tree",

tools/copy-marked.js

@@ -0,0 +1,28 @@
+const fs = require('fs');
+const path = require('path');
+
+const sourceFile = path.join('nbclassic', 'static', 'components', 'marked', 'lib', 'marked.umd.js');
+const destFile = path.join('nbclassic', 'static', 'components', 'marked', 'lib', 'marked.js');
+
+// Check file existence
+const sourceExists = fs.existsSync(sourceFile);
+const destExists = fs.existsSync(destFile);
+
+if (!sourceExists && !destExists) {
+    // Both files missing - critical error
+    console.error(`Error: ${destFile} is required but cannot be created (${sourceFile} not found)`);
+    process.exit(1);
+} else if (!sourceExists) {
+    // Source missing but dest exists - skip copy
+    console.log(`Copy skipped: ${sourceFile} not found (using existing ${destFile})`);
+    process.exit(0);
+}
+
+// Source exists, attempt copy
+try {
+    fs.copyFileSync(sourceFile, destFile);
+    console.log(`Successfully copied ${sourceFile} to ${destFile}`);
+} catch (err) {
+    console.error(`Error copying file: ${err.message}`);
+    process.exit(1);
+}