diff --git a/anycode/components/agent/AcpMessage.css b/anycode/components/agent/AcpMessage.css
index 3d20bfa..0e2fcfc 100644
--- a/anycode/components/agent/AcpMessage.css
+++ b/anycode/components/agent/AcpMessage.css
@@ -240,6 +240,37 @@
     color: var(--user-message-fg, var(--theme-accent-foreground, var(--text-color, #ffffff)));
 }
 
+.acp-user-message-body {
+    min-width: 0;
+}
+
+.acp-user-message-body-collapsed {
+    max-height: 180px;
+    overflow: hidden;
+}
+
+.acp-user-message-toggle {
+    display: flex;
+    align-items: center;
+    gap: 5px;
+    margin: 5px auto -2px;
+    padding: 2px 8px;
+    border: 0;
+    border-radius: 999px;
+    background: rgba(0, 0, 0, 0.12);
+    color: inherit;
+    font: inherit;
+    font-size: 0.78em;
+    cursor: pointer;
+    opacity: 0.8;
+}
+
+.acp-user-message-toggle:hover,
+.acp-user-message-toggle:focus-visible {
+    opacity: 1;
+    background: rgba(0, 0, 0, 0.2);
+}
+
 .acp-message-assistant .acp-message-content {
     color: var(--theme-foreground, var(--text-color, #e0e0e0));
 }
diff --git a/anycode/components/agent/AcpMessage.tsx b/anycode/components/agent/AcpMessage.tsx
index 25afac3..70bbe7b 100644
--- a/anycode/components/agent/AcpMessage.tsx
+++ b/anycode/components/agent/AcpMessage.tsx
@@ -27,6 +27,7 @@ interface AcpMessageProps {
   toolUpdates?: AcpToolUpdateMessage[];
   isExpanded?: boolean;
   onToggle?: () => void;
+  onUserMessageToggle?: () => void;
   onUndo?: () => void;
   onOpenFile?: (path: string, line?: number, column?: number) => void;
   onOpenFileDiff?: (path: string, line?: number, column?: number) => void;
@@ -943,65 +944,105 @@ const StreamingMarkdownContent: React.FC<{
 
 const TextMessage: React.FC<{
   message: AcpUserMessage | AcpAssistantMessage;
+  onUserMessageToggle?: () => void;
   onUndo?: () => void;
   onOpenFile?: (path: string, line?: number, column?: number) => void;
   onOpenFileDiff?: (path: string, line?: number, column?: number) => void;
-}> = ({ message, onUndo, onOpenFile, onOpenFileDiff }) => (
-  <div className={`acp-message acp-message-${message.role}`}>
-    <div className="acp-message-content acp-message-content-with-actions">
-      <StreamingMarkdownContent
-        content={message.content}
-        onOpenFile={onOpenFile}
-        onOpenFileDiff={onOpenFileDiff}
-      />
-      {message.role === 'user' && Array.isArray(message.attachments) && message.attachments.length > 0 && (
-        <div className="acp-message-attachments">
-          {message.attachments.map((attachment, index) => {
-            const src = `data:${attachment.mime_type};base64,${attachment.data_base64}`;
-            const isImage = attachment.mime_type.startsWith('image/');
-            const isAudio = attachment.mime_type.startsWith('audio/');
-            if (isImage) {
-              return (
-                <img
-                  key={`${attachment.name}-${index}`}
-                  src={src}
-                  alt={attachment.name}
-                  className="acp-message-attachment-image"
-                />
-              );
-            }
-            if (isAudio) {
+}> = ({ message, onUserMessageToggle, onUndo, onOpenFile, onOpenFileDiff }) => {
+  const [isExpanded, setIsExpanded] = React.useState(false);
+  const [isCollapsible, setIsCollapsible] = React.useState(false);
+  const bodyRef = React.useRef<HTMLDivElement>(null);
+
+  React.useLayoutEffect(() => {
+    const body = bodyRef.current;
+    if (!body || message.role !== 'user') {
+      setIsCollapsible(false);
+      return;
+    }
+
+    setIsExpanded(false);
+    const frame = requestAnimationFrame(() => {
+      setIsCollapsible(body.scrollHeight > body.clientHeight + 1);
+    });
+    return () => cancelAnimationFrame(frame);
+  }, [message.content, message.role]);
+
+  return (
+    <div className={`acp-message acp-message-${message.role}`}>
+      <div className="acp-message-content acp-message-content-with-actions">
+        <div
+          ref={bodyRef}
+          className={`acp-user-message-body ${message.role === 'user' && !isExpanded ? 'acp-user-message-body-collapsed' : ''}`}
+        >
+          <StreamingMarkdownContent
+            content={message.content}
+            onOpenFile={onOpenFile}
+            onOpenFileDiff={onOpenFileDiff}
+          />
+        </div>
+        {message.role === 'user' && isCollapsible && (
+          <button
+            type="button"
+            className="acp-user-message-toggle"
+            aria-expanded={isExpanded}
+            onClick={() => {
+              onUserMessageToggle?.();
+              setIsExpanded((expanded) => !expanded);
+            }}
+          >
+            <span aria-hidden="true">{isExpanded ? '▲' : '▼'}</span>
+            {isExpanded ? 'Show less' : 'Show more'}
+          </button>
+        )}
+        {message.role === 'user' && Array.isArray(message.attachments) && message.attachments.length > 0 && (
+          <div className="acp-message-attachments">
+            {message.attachments.map((attachment, index) => {
+              const src = `data:${attachment.mime_type};base64,${attachment.data_base64}`;
+              const isImage = attachment.mime_type.startsWith('image/');
+              const isAudio = attachment.mime_type.startsWith('audio/');
+              if (isImage) {
+                return (
+                  <img
+                    key={`${attachment.name}-${index}`}
+                    src={src}
+                    alt={attachment.name}
+                    className="acp-message-attachment-image"
+                  />
+                );
+              }
+              if (isAudio) {
+                return (
+                  <audio
+                    key={`${attachment.name}-${index}`}
+                    controls
+                    src={src}
+                    className="acp-message-attachment-audio"
+                  />
+                );
+              }
               return (
-                <audio
+                <div
                   key={`${attachment.name}-${index}`}
-                  controls
-                  src={src}
-                  className="acp-message-attachment-audio"
-                />
+                  className="acp-message-attachment-file"
+                  title={attachment.mime_type}
+                >
+                  {attachment.name}
+                </div>
               );
-            }
-            return (
-              <div
-                key={`${attachment.name}-${index}`}
-                className="acp-message-attachment-file"
-                title={attachment.mime_type}
-              >
-                {attachment.name}
-              </div>
-            );
-          })}
-        </div>
-      )}
-      {message.role === 'user' && onUndo && (
-        <div className="acp-message-actions">
-          <button className="acp-undo-button" onClick={onUndo} title="Undo">
-            Undo
-          </button>
-        </div>
-      )}
+            })}
+          </div>
+        )}
+        {message.role === 'user' && onUndo && (
+          <div className="acp-message-actions">
+            <button className="acp-undo-button" onClick={onUndo} title="Undo">
+              Undo
+            </button>
+          </div>
+        )}
+      </div>
     </div>
-  </div>
-);
+  );
+};
 
 const MediaMessage: React.FC<{
   message: AcpMediaMessage;
@@ -1089,6 +1130,7 @@ const AcpMessageComponent: React.FC<AcpMessageProps> = ({
   toolUpdates,
   isExpanded = false,
   onToggle,
+  onUserMessageToggle,
   onUndo,
   onOpenFile,
   onOpenFileDiff,
@@ -1128,6 +1170,7 @@ const AcpMessageComponent: React.FC<AcpMessageProps> = ({
       return (
         <TextMessage
           message={message}
+          onUserMessageToggle={onUserMessageToggle}
           onUndo={onUndo}
           onOpenFile={onOpenFile}
           onOpenFileDiff={onOpenFileDiff}
@@ -1170,6 +1213,7 @@ export const AcpMessage = React.memo(AcpMessageComponent, (previous, next) => (
   && previous.toolResult === next.toolResult
   && previous.toolUpdates === next.toolUpdates
   && previous.isExpanded === next.isExpanded
+  && previous.onUserMessageToggle === next.onUserMessageToggle
   && previous.onOpenFile === next.onOpenFile
   && previous.onOpenFileDiff === next.onOpenFileDiff
 ));
diff --git a/anycode/components/agent/AcpMessages.tsx b/anycode/components/agent/AcpMessages.tsx
index ada397e..38dc693 100644
--- a/anycode/components/agent/AcpMessages.tsx
+++ b/anycode/components/agent/AcpMessages.tsx
@@ -18,6 +18,7 @@ interface AcpMessagesProps {
   expandedThoughts: Set<number>;
   activeSearchMessageIndex?: number;
   onWorkGroupExpansionChange?: () => void;
+  onUserMessageToggle?: () => void;
   onToggleToolCall: (index: number) => void;
   onToggleToolResult: (index: number) => void;
   onToggleThought: (index: number) => void;
@@ -34,6 +35,7 @@ const AcpMessagesComponent: React.FC<AcpMessagesProps> = ({
   expandedThoughts,
   activeSearchMessageIndex,
   onWorkGroupExpansionChange,
+  onUserMessageToggle,
   onToggleToolCall,
   onToggleToolResult,
   onToggleThought,
@@ -187,6 +189,7 @@ const AcpMessagesComponent: React.FC<AcpMessagesProps> = ({
           toolUpdates={toolUpdates}
           onOpenFile={onOpenFile}
           onOpenFileDiff={onOpenFileDiff}
+          onUserMessageToggle={onUserMessageToggle}
           onUndo={
             message.role === 'user' && onUndoMessage
               ? () => onUndoMessage(message)
diff --git a/anycode/components/agent/AcpSession.tsx b/anycode/components/agent/AcpSession.tsx
index c3b57e6..e78bd8f 100644
--- a/anycode/components/agent/AcpSession.tsx
+++ b/anycode/components/agent/AcpSession.tsx
@@ -689,6 +689,7 @@ const AcpSessionComponent: React.FC<AcpSessionProps> = ({
               expandedThoughts={searchExpandedThoughts}
               activeSearchMessageIndex={activeSearchMessageIndex}
               onWorkGroupExpansionChange={handleWorkGroupExpansionChange}
+              onUserMessageToggle={disableAutoScroll}
               onToggleToolCall={handleToggleToolCall}
               onToggleToolResult={handleToggleToolResult}
               onToggleThought={handleToggleThought}
diff --git a/anycode/tests/demo.spec.ts b/anycode/tests/demo.spec.ts
index 099e200..cf0061a 100644
--- a/anycode/tests/demo.spec.ts
+++ b/anycode/tests/demo.spec.ts
@@ -336,6 +336,26 @@ test.describe('Anycode Live Demo Mode E2E Tests', () => {
         }
     });
 
+    test('should collapse and expand long user messages', async ({ page }) => {
+        const promptInput = page.getByPlaceholder('Ask anything...');
+        if (await promptInput.isVisible({ timeout: 5000 }).catch(() => false)) {
+            const longPrompt = Array.from({ length: 24 }, (_, index) => `Log line ${index + 1}: repeated diagnostic output`).join('\n');
+            await promptInput.fill(longPrompt);
+            await promptInput.press('Enter');
+
+            const userMessage = page.locator('.acp-message-user').filter({ hasText: 'Log line 24' }).last();
+            const toggle = userMessage.getByRole('button', { name: 'Show more' });
+            await expect(toggle).toBeVisible({ timeout: 10000 });
+            await expect(toggle).toHaveAttribute('aria-expanded', 'false');
+            await expect(userMessage.locator('.acp-user-message-body')).toHaveClass(/acp-user-message-body-collapsed/);
+
+            await toggle.click();
+            await expect(userMessage.getByRole('button', { name: 'Show less' })).toHaveAttribute('aria-expanded', 'true');
+            await expect(userMessage.locator('.acp-user-message-body')).not.toHaveClass(/acp-user-message-body-collapsed/);
+            await expect(page.getByRole('button', { name: 'Enable auto-scroll' })).toBeVisible();
+        }
+    });
+
     test('should search ACP text without expanding unrelated work groups', async ({ page }) => {
         const promptInput = page.getByPlaceholder('Ask anything...');
         if (await promptInput.isVisible({ timeout: 5000 }).catch(() => false)) {