revert: restore auto-hiding overlay scrollbars

packages/ui/src/components/ui/OverlayScrollbar.tsx

@@ -25,12 +25,6 @@ const isSameThumbMetrics = (a: ThumbMetrics, b: ThumbMetrics): boolean => {
   return Math.abs(a.length - b.length) < METRIC_EPSILON && Math.abs(a.offset - b.offset) < METRIC_EPSILON;
 };
 
-// Desktop shells (Electron, VS Code webview) use persistent, not
-// auto-hiding, scrollbars. Reads the same `desktop-runtime` root class that
-// index.css keys off, so JS and CSS never disagree on what counts as desktop.
-const isDesktopScrollbarRuntime = (): boolean =>
-  typeof document !== "undefined" && document.documentElement.classList.contains("desktop-runtime");
-
 const OverlayScrollbarComponent: React.FC<OverlayScrollbarProps> = ({
   containerRef,
   minThumbSize = 32,
@@ -134,15 +128,8 @@ const OverlayScrollbarComponent: React.FC<OverlayScrollbarProps> = ({
     if (isHoveringRef.current) {
       return;
     }
-    // Desktop shells keep the thumb visible once shown instead of
-    // auto-hiding it after a delay. userIntentOnly callers (e.g. chat
-    // auto-follow scroll) opt out of persistence on purpose, so they keep
-    // the existing auto-hide behavior even on desktop.
-    if (isDesktopScrollbarRuntime() && !userIntentOnly) {
-      return;
-    }
     hideTimeoutRef.current = setTimeout(() => setVisible(false), hideDelayMs);
-  }, [hideDelayMs, userIntentOnly]);
+  }, [hideDelayMs]);
 
   const markUserIntent = React.useCallback(() => {
     lastUserIntentAtRef.current = Date.now();
@@ -175,10 +162,7 @@ const OverlayScrollbarComponent: React.FC<OverlayScrollbarProps> = ({
     if (!container) return;
 
     updateMetrics();
-    // On desktop shells, show the thumb immediately if content overflows
+    setVisible(false);
-    // instead of waiting for the first scroll event (persistent affordance,
-    // matching native desktop scrollbar conventions).
-    setVisible(isDesktopScrollbarRuntime() && !userIntentOnly);
 
     const onScroll = () => handleScroll();
     const onKeyDown = (event: KeyboardEvent) => {

packages/ui/src/index.css

@@ -1804,10 +1804,8 @@ input[aria-label="Terminal input"] {
 
 }
 
-/* Settings dialog: hide the overlay scrollbar on mobile/web; wheel/keyboard
+/* Settings dialog: hide the overlay scrollbar; wheel/keyboard scroll still works. */
-   scroll still works. Desktop shells keep the persistent scrollbar so the
+[data-settings-view="true"] .overlay-scrollbar {
-   Settings sub-panels aren't left with no scroll affordance at all. */
-html:not(.desktop-runtime) [data-settings-view="true"] .overlay-scrollbar {
   display: none;
 }