fix(ui): chat background covers full screen regardless of glassmorphism

Previously the background was applied directly to <Page> (room view
only) when glassmorphism was off, and to document.body only when
glassmorphism was on. This caused two bugs:
- Without glassmorphism: background only visible in the chat panel,
  not behind the sidebar
- With glassmorphism: Page reverted to its opaque theme surface color,
  so the body background only showed through the glass sidebar

Fix: SidebarNav now always applies the active background to
document.body (regardless of glassmorphism). RoomView's <Page> is
made transparent whenever a background is active so the body
background shows through both the sidebar and the chat area.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/features/room/RoomView.tsx

@@ -17,8 +17,6 @@ import { RoomViewFollowing, RoomViewFollowingPlaceholder } from './RoomViewFollo
 import { Page } from '../../components/page';
 import { useSetting } from '../../state/hooks/settings';
 import { settingsAtom } from '../../state/settings';
-import { useTheme, ThemeKind } from '../../hooks/useTheme';
-import { getChatBg } from '../lotus/chatBackground';
 import { useKeyDown } from '../../hooks/useKeyDown';
 import { editableActiveElement } from '../../utils/dom';
 import { useRoomPermissions } from '../../hooks/useRoomPermissions';
@@ -61,10 +59,7 @@ export function RoomView({ eventId }: { eventId?: string }) {
   const roomViewRef = useRef<HTMLDivElement>(null) as React.RefObject<HTMLDivElement>;
   const [chatBackground] = useSetting(settingsAtom, 'chatBackground');
   const [lotusTerminal] = useSetting(settingsAtom, 'lotusTerminal');
-  const [pauseAnimations] = useSetting(settingsAtom, 'pauseAnimations');
   const [glassmorphismSidebar] = useSetting(settingsAtom, 'glassmorphismSidebar');
-  const theme = useTheme();
-  const isDark = theme.kind === ThemeKind.Dark;
 
   const [hideActivity] = useSetting(settingsAtom, 'hideActivity');
 
@@ -98,20 +93,13 @@ export function RoomView({ eventId }: { eventId?: string }) {
     ),
   );
 
-  // When glassmorphism is active, document.body already carries the background so the
-  // sidebar blur has something to work through. Skip applying it here to avoid running
-  // the same CSS animation twice (one per layer = double GPU work).
-  const chatBgStyle = useMemo(
-    () =>
-      glassmorphismSidebar
-        ? {}
-        : getChatBg(
-            lotusTerminal && chatBackground === 'none' ? 'tactical' : chatBackground,
-            isDark,
-            pauseAnimations,
-          ),
-    [chatBackground, lotusTerminal, isDark, pauseAnimations, glassmorphismSidebar],
-  );
+  // document.body always carries the active background (set by SidebarNav).
+  // Make Page transparent so the body background shows through the chat area.
+  // When no background is active, Page keeps its default theme surface color.
+  const chatBgStyle = useMemo(() => {
+    const hasBg = chatBackground !== 'none' || glassmorphismSidebar || lotusTerminal;
+    return hasBg ? ({ background: 'transparent' } as React.CSSProperties) : {};
+  }, [chatBackground, glassmorphismSidebar, lotusTerminal]);
 
   return (
     <Page ref={roomViewRef} style={chatBgStyle}>

src/app/pages/client/SidebarNav.tsx

@@ -40,7 +40,9 @@ export function SidebarNav() {
   // Fix: mirror the active chat background onto document.body so the sidebar blurs through it.
   useEffect(() => {
     const { style } = document.body;
-    if (!glassmorphismSidebar) {
+    const hasBg = chatBackground !== 'none' || glassmorphismSidebar || lotusTerminal;
+
+    if (!hasBg) {
       style.removeProperty('background-image');
       style.removeProperty('background-color');
       style.removeProperty('background-size');
@@ -48,13 +50,15 @@ export function SidebarNav() {
       style.removeProperty('animation');
       return;
     }
-    const effectiveBg = chatBackground === 'none' ? 'tactical' : chatBackground;
+
+    const effectiveBg = chatBackground !== 'none' ? chatBackground : 'tactical';
     const bgStyle = getChatBg(effectiveBg, isDark, pauseAnimations);
     style.backgroundImage = (bgStyle.backgroundImage as string | undefined) ?? '';
     style.backgroundColor = (bgStyle.backgroundColor as string | undefined) ?? '';
     style.backgroundSize = (bgStyle.backgroundSize as string | undefined) ?? '';
     style.backgroundPosition = (bgStyle.backgroundPosition as string | undefined) ?? '';
     style.animation = (bgStyle.animation as string | undefined) ?? '';
+
     return () => {
       style.removeProperty('background-image');
       style.removeProperty('background-color');