diff --git a/frontend/node-polyfill.cjs b/frontend/node-polyfill.cjs
index 6cd7861..08641af 100644
--- a/frontend/node-polyfill.cjs
+++ b/frontend/node-polyfill.cjs
@@ -1,4 +1,11 @@
-// Polyfill markAsUncloneable on node:worker_threads for Node 20 runtime compatibility (undici/jsdom)
+/**
+ * Polyfill worker_threads.markAsUncloneable untuk Node 20 runtime compatibility (undici/jsdom).
+ *
+ * Catatan:
+ * File CJS ini dimuat via NODE_OPTIONS="--require /app/node-polyfill.cjs" di Docker runner
+ * (require-time sebelum entrypoint Node dievaluasi).
+ * Untuk penggunaan import-time di TypeScript/ESM, lihat src/lib/services/markdown/nodeCompat.ts.
+ */
 try {
 	const wt = require('node:worker_threads');
 	if (wt && typeof wt.markAsUncloneable === 'undefined') {
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index 7d968cc..4d603fc 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -12,9 +12,7 @@
         "@codemirror/lang-markdown": "^6.3.0",
         "@codemirror/lang-python": "^6.1.0",
         "@codemirror/theme-one-dark": "^6.1.0",
-        "@types/dompurify": "^3.0.5",
         "codemirror": "^6.0.1",
-        "dompurify": "^3.4.14",
         "highlight.js": "^11.11.0",
         "isomorphic-dompurify": "^3.23.0",
         "katex": "^0.16.9",
@@ -1575,15 +1573,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/@types/dompurify": {
-      "version": "3.0.5",
-      "resolved": "https://registry.npmjs.org/@types/dompurify/-/dompurify-3.0.5.tgz",
-      "integrity": "sha512-1Wg0g3BtQF7sSb27fJQAKck1HECM6zV1EB66j8JH9i3LCjYabJa0FSdiSgsD5K/RbrsR0SiraKacLB+T8ZVYAg==",
-      "license": "MIT",
-      "dependencies": {
-        "@types/trusted-types": "*"
-      }
-    },
     "node_modules/@types/estree": {
       "version": "1.0.9",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.9.tgz",
@@ -1619,6 +1608,7 @@
       "version": "2.0.7",
       "resolved": "https://registry.npmjs.org/@types/trusted-types/-/trusted-types-2.0.7.tgz",
       "integrity": "sha512-ScaPdn1dQczgbl0QFTeTOmVHFULt394XJgOQNoyVhZ6r2vLnMLJfBPd53SB52T/3G36VI1/g2MZaX0cwDuXsfw==",
+      "devOptional": true,
       "license": "MIT"
     },
     "node_modules/@vitest/expect": {
diff --git a/frontend/package.json b/frontend/package.json
index c5285c5..d6cc09d 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -27,9 +27,7 @@
     "@codemirror/lang-markdown": "^6.3.0",
     "@codemirror/lang-python": "^6.1.0",
     "@codemirror/theme-one-dark": "^6.1.0",
-    "@types/dompurify": "^3.0.5",
     "codemirror": "^6.0.1",
-    "dompurify": "^3.4.14",
     "highlight.js": "^11.11.0",
     "isomorphic-dompurify": "^3.23.0",
     "katex": "^0.16.9",
diff --git a/frontend/src/hooks.server.ts b/frontend/src/hooks.server.ts
index 5eb958f..6321164 100644
--- a/frontend/src/hooks.server.ts
+++ b/frontend/src/hooks.server.ts
@@ -6,16 +6,8 @@
  * elemes-ts network namespace, so the backend lives on localhost.
  */
 
-// Polyfill markAsUncloneable on node:worker_threads for Node 20 runtime compatibility (undici/jsdom)
-try {
-	// eslint-disable-next-line @typescript-eslint/no-require-imports
-	const wt = require('node:worker_threads');
-	if (wt && typeof wt.markAsUncloneable === 'undefined') {
-		wt.markAsUncloneable = () => {};
-	}
-} catch {
-	// ignore
-}
+import { patchWorkerThreadsCompat } from '$lib/services/markdown/nodeCompat';
+patchWorkerThreadsCompat();
 
 import type { Handle } from '@sveltejs/kit';
 
diff --git a/frontend/src/lib/services/markdown/nodeCompat.ts b/frontend/src/lib/services/markdown/nodeCompat.ts
new file mode 100644
index 0000000..a0e3c28
--- /dev/null
+++ b/frontend/src/lib/services/markdown/nodeCompat.ts
@@ -0,0 +1,30 @@
+/**
+ * Polyfill worker_threads.markAsUncloneable untuk kompatibilitas Node 20
+ * dengan isomorphic-dompurify/jsdom/undici.
+ *
+ * Root Cause:
+ * isomorphic-dompurify@3.23.0 -> jsdom@30.0.1 -> undici@8.10.0 memanggil
+ * `markAsUncloneable` dari `node:worker_threads`. Pada Node 20 runtime (v20.20.2),
+ * method ini belum ada (ditambahkan pada Node 22+), menyebabkan
+ * `TypeError: webidl.util.markAsUncloneable is not a function` saat SSR.
+ *
+ * Catatan:
+ * File ini adalah helper TypeScript/ESM (import-time). Terdapat juga salinan CJS di
+ * `frontend/node-polyfill.cjs` yang digunakan khusus untuk `NODE_OPTIONS="--require ..."`
+ * pada Docker container (require-time sebelum entrypoint Node).
+ *
+ * TODO: hapus polyfill ini kalau isomorphic-dompurify/jsdom sudah rilis versi
+ * yang kompatibel penuh dengan Node 20 tanpa markAsUncloneable, atau base image
+ * Docker sudah di-upgrade ke Node 22+.
+ */
+export function patchWorkerThreadsCompat(): void {
+	try {
+		// eslint-disable-next-line @typescript-eslint/no-require-imports
+		const wt = require('node:worker_threads');
+		if (wt && typeof wt.markAsUncloneable === 'undefined') {
+			wt.markAsUncloneable = () => {};
+		}
+	} catch {
+		// ignore - bukan environment Node (misal di browser runtime)
+	}
+}
diff --git a/frontend/src/lib/services/markdown/processEmbeds.ts b/frontend/src/lib/services/markdown/processEmbeds.ts
index f9f979f..39a84f3 100644
--- a/frontend/src/lib/services/markdown/processEmbeds.ts
+++ b/frontend/src/lib/services/markdown/processEmbeds.ts
@@ -1,13 +1,5 @@
-// Polyfill markAsUncloneable on node:worker_threads for Node 20 runtime compatibility (undici/jsdom)
-try {
-	// eslint-disable-next-line @typescript-eslint/no-require-imports
-	const wt = require('node:worker_threads');
-	if (wt && typeof wt.markAsUncloneable === 'undefined') {
-		wt.markAsUncloneable = () => {};
-	}
-} catch {
-	// ignore
-}
+import { patchWorkerThreadsCompat } from './nodeCompat';
+patchWorkerThreadsCompat();
 
 import DOMPurify from 'isomorphic-dompurify';