fix: preserve board scroll position when navigating back from a card (#431)

apps/web/src/hooks/useScrollRestore.ts

@@ -0,0 +1,44 @@
+import type { RefObject } from "react";
+import type { NextRouter } from "next/router";
+import { useEffect, useRef } from "react";
+
+const scrollPositions = new Map<string, number>();
+
+export function useScrollRestore(
+  boardId: string | null | undefined,
+  scrollRef: RefObject<HTMLElement | null>,
+  router: NextRouter,
+  isReady: boolean,
+) {
+  const restored = useRef(false);
+
+  useEffect(() => {
+    if (!boardId) return;
+
+    restored.current = false;
+
+    const saveScrollPosition = () => {
+      if (scrollRef.current) {
+        scrollPositions.set(boardId, scrollRef.current.scrollLeft);
+      }
+    };
+
+    router.events.on("routeChangeStart", saveScrollPosition);
+    return () => router.events.off("routeChangeStart", saveScrollPosition);
+  }, [boardId, router.events, scrollRef]);
+
+  useEffect(() => {
+    if (restored.current || !isReady || !boardId) return;
+    restored.current = true;
+
+    const saved = scrollPositions.get(boardId);
+    if (saved === undefined) return;
+
+    // StrictModeDroppable delays rendering by one requestAnimationFrame
+    requestAnimationFrame(() => {
+      requestAnimationFrame(() => {
+        if (scrollRef.current) scrollRef.current.scrollLeft = saved;
+      });
+    });
+  }, [isReady, scrollRef, boardId]);
+}

apps/web/src/views/board/index.tsx

@@ -26,6 +26,7 @@ import { StrictModeDroppable as Droppable } from "~/components/StrictModeDroppab
 import { Tooltip } from "~/components/Tooltip";
 import { EditYouTubeModal } from "~/components/YouTubeEmbed/EditYouTubeModal";
 import { useDragToScroll } from "~/hooks/useDragToScroll";
+import { useScrollRestore } from "~/hooks/useScrollRestore";
 import { usePermissions } from "~/hooks/usePermissions";
 import { useKeyboardShortcut } from "~/providers/keyboard-shortcuts";
 import { useModal } from "~/providers/modal";
@@ -141,6 +142,8 @@ export default function BoardPage({ isTemplate }: { isTemplate?: boolean }) {
 
   const isLoading = isInitialLoading || isQueryLoading;
 
+  useScrollRestore(boardId, scrollRef, router, !isLoading && (boardData?.lists.length ?? 0) > 0);
+
   const updateListMutation = api.list.update.useMutation({
     onMutate: async (args) => {
       await utils.board.byId.cancel();