fix(build): correct writeFileSync usage; harden is-client env check; cleanup map→forEach

src/scripts/build-content-tree.mjs

@@ -41,15 +41,16 @@ function buildContentTree(source, output) {
     dir: source,
   });
 
-  fs.writeFileSync(
-    path.resolve(output),
-    JSON.stringify(content, null, 2),
-    (error) => {
-      if (error) {
-        console.log('scripts/build-content-tree', error);
-      } else {
-        console.log('Successfully built content tree file at ' + output);
-      }
-    }
-  );
+  // fs.writeFileSync does not accept a callback; wrap with try/catch and
+  // log a clear success or error instead.
+  try {
+    fs.writeFileSync(
+      path.resolve(output),
+      JSON.stringify(content, null, 2)
+    );
+    console.log('Successfully built content tree file at ' + output);
+  } catch (error) {
+    console.error('scripts/build-content-tree', error);
+    process.exitCode = 1;
+  }
 }

src/utilities/flatten-content-tree.mjs

@@ -7,11 +7,13 @@ export default (tree) => {
     }
 
     if ('children' in node) {
-      node.children.map(crawl);
+      node.children.forEach(crawl);
     }
   };
 
-  tree.children.map(crawl);
+  if (Array.isArray(tree.children)) {
+    tree.children.forEach(crawl);
+  }
 
   return paths;
 };

src/utilities/is-client.js

@@ -1,3 +1,6 @@
-const isClient = window !== undefined && window.document !== undefined;
+// Guard against ReferenceError in non-browser/SSR environments
+// and use a consistent ESM default export.
+const isClient =
+  typeof window !== 'undefined' && typeof window.document !== 'undefined';
 
-module.exports = isClient;
+export default isClient;