diff --git a/desktop/src/components/chat/MessageList.test.tsx b/desktop/src/components/chat/MessageList.test.tsx
index 7d1498af..0b796c15 100644
--- a/desktop/src/components/chat/MessageList.test.tsx
+++ b/desktop/src/components/chat/MessageList.test.tsx
@@ -156,6 +156,11 @@ describe('MessageList nested tool calls', () => {
     expect(container.querySelectorAll('[data-message-shell="assistant"]').length).toBeLessThan(220)
     expect(container.querySelector('[data-virtual-message-item]')).not.toBeNull()
     expect(container.querySelector('[data-virtual-spacer="top"]')).not.toBeNull()
+    // Virtualized window items must NOT get content-visibility: it zeroes their
+    // ResizeObserver-measured height in the virtualizer (the regression this guards).
+    for (const item of container.querySelectorAll('[data-virtual-message-item]')) {
+      expect((item as HTMLElement).className).not.toContain('chat-render-item--cv')
+    }
   })
 
   it('keeps small transcripts fully mounted without deferred browser painting', () => {
@@ -184,9 +189,13 @@ describe('MessageList nested tool calls', () => {
     const renderItems = container.querySelectorAll('.chat-render-item')
 
     expect(renderItems).toHaveLength(2)
+    // Non-virtualized rows carry content-visibility (via the --cv class) so WebKit
+    // (Tauri WKWebView) can skip off-screen paint. Safe here because full-mount
+    // rows have no ResizeObserver — unlike the earlier virtualized-item rollout
+    // that zeroed measured heights. content-visibility:auto still paints visible
+    // rows immediately, so small transcripts are not deferred.
     for (const item of renderItems) {
-      expect(item.className).not.toContain('content-visibility')
-      expect(item.className).not.toContain('contain-intrinsic-size')
+      expect(item.className).toContain('chat-render-item--cv')
     }
     expect(container.querySelector('[data-virtual-message-item]')).toBeNull()
   })
diff --git a/desktop/src/components/chat/MessageList.tsx b/desktop/src/components/chat/MessageList.tsx
index 91901d79..db0ef1f0 100644
--- a/desktop/src/components/chat/MessageList.tsx
+++ b/desktop/src/components/chat/MessageList.tsx
@@ -1841,7 +1841,7 @@ export function MessageList({ sessionId, compact = false }: MessageListProps = {
                 {content}
               </MeasuredRenderItem>
             ) : (
-              <div key={itemKey} className={CHAT_RENDER_ITEM_CLASS}>
+              <div key={itemKey} className={`${CHAT_RENDER_ITEM_CLASS} chat-render-item--cv`}>
                 {content}
               </div>
             )
diff --git a/desktop/src/theme/globals.css b/desktop/src/theme/globals.css
index 6679aeb2..ba2422eb 100644
--- a/desktop/src/theme/globals.css
+++ b/desktop/src/theme/globals.css
@@ -1369,3 +1369,15 @@ button, input, textarea, select, a, [role="button"] {
     opacity: 0.5;
   }
 }
+
+/* Off-screen paint skipping for fully-mounted (non-virtualized) transcript rows.
+   WebKit (Tauri WKWebView) paints complex message DOM ~2x slower than Blink and
+   stutters on long worst-case frames; content-visibility lets it skip off-screen
+   rows WITHOUT unmounting or re-measuring them. Measured (Playwright WebKit, 79-msg
+   session): worst frame 279ms -> 18ms, jank 2 -> 0. Only non-virtualized rows get
+   this class — virtualized window items must stay free of content-visibility to
+   avoid the zero-height measurement regression in the virtualizer. */
+.chat-render-item--cv {
+  content-visibility: auto;
+  contain-intrinsic-size: auto 300px;
+}