diff --git a/frontend/pluto_duck_frontend/app/globals.css b/frontend/pluto_duck_frontend/app/globals.css
index 7bbb49f..476c4a1 100644
--- a/frontend/pluto_duck_frontend/app/globals.css
+++ b/frontend/pluto_duck_frontend/app/globals.css
@@ -241,6 +241,21 @@
   }
 }
 
+@keyframes stepIn {
+  from {
+    opacity: 0;
+    transform: translateY(6px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+.animate-step-in {
+  animation: stepIn 0.4s cubic-bezier(0.23, 1, 0.32, 1) forwards;
+}
+
 .animate-text-glow {
   animation: textGlow 2.2s ease-in-out infinite;
 }
diff --git a/frontend/pluto_duck_frontend/components/ai-elements/code-block.tsx b/frontend/pluto_duck_frontend/components/ai-elements/code-block.tsx
index 90cf7c3..a44ef9f 100644
--- a/frontend/pluto_duck_frontend/components/ai-elements/code-block.tsx
+++ b/frontend/pluto_duck_frontend/components/ai-elements/code-block.tsx
@@ -10,7 +10,6 @@ import {
   type HTMLAttributes,
   useContext,
   useEffect,
-  useRef,
   useState,
 } from "react";
 import { type BundledLanguage, codeToHtml, type ShikiTransformer } from "shiki";
@@ -50,6 +49,19 @@ const lineNumberTransformer: ShikiTransformer = {
   },
 };
 
+function escapeHtml(raw: string): string {
+  return raw
+    .replaceAll("&", "&")
+    .replaceAll("<", "&lt;")
+    .replaceAll(">", "&gt;")
+    .replaceAll('"', "&quot;")
+    .replaceAll("'", "&#39;");
+}
+
+function createPlainCodeHtml(code: string): string {
+  return `<pre class="shiki"><code>${escapeHtml(code)}</code></pre>`;
+}
+
 export async function highlightCode(
   code: string,
   language: BundledLanguage,
@@ -59,18 +71,25 @@ export async function highlightCode(
     ? [lineNumberTransformer]
     : [];
 
-  return await Promise.all([
-    codeToHtml(code, {
-      lang: language,
-      theme: "one-light",
-      transformers,
-    }),
-    codeToHtml(code, {
-      lang: language,
-      theme: "one-dark-pro",
-      transformers,
-    }),
-  ]);
+  try {
+    return await Promise.all([
+      codeToHtml(code, {
+        lang: language,
+        theme: "one-light",
+        transformers,
+      }),
+      codeToHtml(code, {
+        lang: language,
+        theme: "one-dark-pro",
+        transformers,
+      }),
+    ]);
+  } catch (error) {
+    // Keep chat rendering resilient when Shiki theme chunks fail to load in runtime.
+    console.error("Failed to highlight code block with Shiki:", error);
+    const fallbackHtml = createPlainCodeHtml(code);
+    return [fallbackHtml, fallbackHtml];
+  }
 }
 
 export const CodeBlock = ({
@@ -83,19 +102,19 @@ export const CodeBlock = ({
 }: CodeBlockProps) => {
   const [html, setHtml] = useState<string>("");
   const [darkHtml, setDarkHtml] = useState<string>("");
-  const mounted = useRef(false);
 
   useEffect(() => {
+    let cancelled = false;
+
     highlightCode(code, language, showLineNumbers).then(([light, dark]) => {
-      if (!mounted.current) {
+      if (!cancelled) {
         setHtml(light);
         setDarkHtml(dark);
-        mounted.current = true;
       }
     });
 
     return () => {
-      mounted.current = false;
+      cancelled = true;
     };
   }, [code, language, showLineNumbers]);
 
diff --git a/frontend/pluto_duck_frontend/components/chat/ChatPanel.tsx b/frontend/pluto_duck_frontend/components/chat/ChatPanel.tsx
index a625945..1da533f 100644
--- a/frontend/pluto_duck_frontend/components/chat/ChatPanel.tsx
+++ b/frontend/pluto_duck_frontend/components/chat/ChatPanel.tsx
@@ -19,7 +19,7 @@ import {
   PromptInputModelSelectItem,
   type PromptInputMessage,
 } from '../ai-elements/prompt-input';
-import { ActivityLoader } from '../ai-elements/activity-loader';
+import { LoadingDots } from '../ai-elements/loading-dots';
 import { MentionMenu } from './MentionMenu';
 import { ChatOnboarding } from './ChatOnboarding';
 import { RenderItem, type FeedbackType } from './renderers';
@@ -282,8 +282,9 @@ const ConversationMessages = memo(function ConversationMessages({
       })}
 
       {chatLoadingMode === 'agent-streaming-fallback' && (
-        <div className="px-2.5 py-2.5">
-          <ActivityLoader />
+        <div aria-live="polite" aria-atomic="true">
+          <span className="sr-only">에이전트가 응답을 생성하고 있습니다</span>
+          <LoadingDots className="animate-step-in" />
         </div>
       )}
     </>