diff --git a/app/components/layout/ChatSidebar.module.css b/app/components/layout/ChatSidebar.module.css
index 5007805ec..64fe34c95 100644
--- a/app/components/layout/ChatSidebar.module.css
+++ b/app/components/layout/ChatSidebar.module.css
@@ -2,7 +2,7 @@
 	display: flex;
 	flex-direction: column;
 	height: 100%;
-	max-height: var(--visual-viewport-height);
+	max-height: var(--visual-viewport-height, 100dvh);
 	overflow: hidden;
 }
 
diff --git a/app/components/layout/index.tsx b/app/components/layout/index.tsx
index e340bdda5..0179dec2a 100644
--- a/app/components/layout/index.tsx
+++ b/app/components/layout/index.tsx
@@ -26,6 +26,8 @@ import { useChatContext } from "~/features/chat/useChatContext";
 import { FriendMenu } from "~/features/friends/components/FriendMenu";
 import { useDateTimeFormat } from "~/hooks/intl/useDateTimeFormat";
 import { useHydrated } from "~/hooks/useHydrated";
+import { useLayoutSize } from "~/hooks/useMainContentWidth";
+import { useVisualViewportHeight } from "~/hooks/useVisualViewportHeight";
 import type { RootLoaderData } from "~/root";
 import type { Breadcrumb, SendouRouteHandle } from "~/utils/remix.server";
 import {
@@ -213,9 +215,16 @@ export function Layout({
 	const [sideNavModalOpen, setSideNavModalOpen] = React.useState(false);
 	const [chatSidebarModalOpen, setChatSidebarModalOpen] = React.useState(false);
 
+	const layoutSize = useLayoutSize();
+	useVisualViewportHeight();
 	const chatSidebarOpen = chatContext?.chatOpen ?? false;
 	const setChatSidebarOpen = chatContext?.setChatOpen ?? (() => {});
 
+	const setChatSidebarModalOpenAndSync = (open: boolean) => {
+		setChatSidebarModalOpen(open);
+		setChatSidebarOpen(open);
+	};
+
 	const { t } = useTranslation(["front", "common"]);
 	const { formatRelativeDate } = useRelativeDayFormat();
 	const isHydrated = useHydrated();
@@ -393,7 +402,7 @@ export function Layout({
 						className={styles.chatSidebarModalOverlay}
 						isDismissable
 						isOpen={chatSidebarModalOpen}
-						onOpenChange={setChatSidebarModalOpen}
+						onOpenChange={setChatSidebarModalOpenAndSync}
 					>
 						<Modal className={styles.chatSidebarModal}>
 							<Dialog
@@ -424,7 +433,7 @@ export function Layout({
 						}
 						onChatModalToggle={
 							data?.user
-								? () => setChatSidebarModalOpen((prev) => !prev)
+								? () => setChatSidebarModalOpenAndSync(!chatSidebarModalOpen)
 								: undefined
 						}
 						chatUnreadCount={chatContext?.totalUnreadCount}
@@ -440,7 +449,7 @@ export function Layout({
 				{children}
 				<Footer />
 			</div>
-			{chatSidebarOpen ? (
+			{chatSidebarOpen && layoutSize === "desktop" ? (
 				<div
 					className={clsx(
 						styles.chatSidebar,
diff --git a/app/features/chat/ChatProvider.tsx b/app/features/chat/ChatProvider.tsx
index c11dac5b8..87d96f4fb 100644
--- a/app/features/chat/ChatProvider.tsx
+++ b/app/features/chat/ChatProvider.tsx
@@ -479,13 +479,14 @@ function ChatProviderInner({
 	const setChatOpen = React.useCallback(
 		(open: boolean) => {
 			_setChatOpen(open);
-			if (open && activeRoom) {
-				markAsRead(activeRoom);
-			}
+			if (!open) return;
 
-			if (open && rooms.length === 1 && !activeRoom) {
+			if (activeRoom) {
+				markAsRead(activeRoom);
+			} else if (rooms.length === 1) {
 				requestHistory(rooms[0].chatCode);
 				setActiveRoom(rooms[0].chatCode);
+				markAsRead(rooms[0].chatCode);
 			}
 		},
 		[activeRoom, markAsRead, requestHistory, rooms.length, rooms[0]?.chatCode],
@@ -501,9 +502,11 @@ function ChatProviderInner({
 		rooms,
 		userId,
 		isLoading,
+		readyState,
 		activeRoom,
 		setActiveRoom,
 		setChatOpen,
+		markAsRead,
 		subscribe,
 		unsubscribe,
 		setRooms,
@@ -568,9 +571,11 @@ function useChatRouteSync({
 	rooms,
 	userId,
 	isLoading,
+	readyState,
 	activeRoom,
 	setActiveRoom,
 	setChatOpen,
+	markAsRead,
 	subscribe,
 	unsubscribe,
 	setRooms,
@@ -581,9 +586,11 @@ function useChatRouteSync({
 	rooms: RoomInfo[];
 	userId: number;
 	isLoading: boolean;
+	readyState: "CONNECTING" | "CONNECTED" | "CLOSED";
 	activeRoom: string | null;
 	setActiveRoom: (chatCode: string | null) => void;
 	setChatOpen: (open: boolean) => void;
+	markAsRead: (chatCode: string) => void;
 	subscribe: (chatCode: string) => void;
 	unsubscribe: (chatCode: string) => void;
 	setRooms: React.Dispatch<React.SetStateAction<RoomInfo[]>>;
@@ -604,6 +611,31 @@ function useChatRouteSync({
 	const subscribedRoomRef = React.useRef<string[]>([]);
 	const previousRouteChatCodeRef = React.useRef<string[]>([]);
 	const previousPathnameRef = React.useRef<string | null>(null);
+	const hasConnectedRef = React.useRef(false);
+
+	// On reconnect the server sends a fresh initial rooms payload that drops
+	// rooms we joined via SUBSCRIBE as a non-participant, and the previous
+	// socket's subscriptions died with it. Clear the subscription tracking so
+	// the route sync effect below re-subscribes once the new payload arrives,
+	// and refresh history for the open room to fill any gap from the downtime.
+	const onReconnect = React.useEffectEvent(() => {
+		logger.debug("WS reconnected, re-acquiring room subscriptions and history");
+		subscribedRoomRef.current = [];
+		if (activeRoom) {
+			requestHistory(activeRoom);
+		}
+	});
+
+	React.useEffect(() => {
+		if (readyState !== "CONNECTED") return;
+
+		if (!hasConnectedRef.current) {
+			hasConnectedRef.current = true;
+			return;
+		}
+
+		onReconnect();
+	}, [readyState]);
 
 	React.useEffect(() => {
 		if (isLoading) return;
@@ -657,6 +689,7 @@ function useChatRouteSync({
 				}
 				if (layoutSize === "desktop") {
 					setChatOpen(true);
+					markAsRead(chatCodes[0]);
 				}
 			}
 		} else {
@@ -677,6 +710,7 @@ function useChatRouteSync({
 					}
 					if (layoutSize === "desktop") {
 						setChatOpen(true);
+						markAsRead(matchedRoom.chatCode);
 					}
 				}
 			}
@@ -690,6 +724,7 @@ function useChatRouteSync({
 		activeRoom,
 		setActiveRoom,
 		setChatOpen,
+		markAsRead,
 		layoutSize,
 		subscribe,
 		unsubscribe,
diff --git a/app/hooks/useVisualViewportHeight.ts b/app/hooks/useVisualViewportHeight.ts
new file mode 100644
index 000000000..558fb4982
--- /dev/null
+++ b/app/hooks/useVisualViewportHeight.ts
@@ -0,0 +1,35 @@
+import { useIsomorphicLayoutEffect } from "./useIsomorphicLayoutEffect";
+
+const CSS_VARIABLE = "--visual-viewport-height";
+
+/**
+ * Keeps the `--visual-viewport-height` CSS variable in sync with the visual
+ * viewport height on the document root. CSS has no native way to read the
+ * visual (as opposed to layout) viewport, so elements that must stay above the
+ * mobile on-screen keyboard rely on this variable to clamp their height as the
+ * keyboard opens and closes.
+ */
+export function useVisualViewportHeight() {
+	useIsomorphicLayoutEffect(() => {
+		const viewport = window.visualViewport;
+		if (!viewport) return;
+
+		const update = () => {
+			document.documentElement.style.setProperty(
+				CSS_VARIABLE,
+				`${viewport.height}px`,
+			);
+		};
+
+		update();
+
+		viewport.addEventListener("resize", update);
+		viewport.addEventListener("scroll", update);
+
+		return () => {
+			viewport.removeEventListener("resize", update);
+			viewport.removeEventListener("scroll", update);
+			document.documentElement.style.removeProperty(CSS_VARIABLE);
+		};
+	}, []);
+}