feat(dnd): highlight playlist drop target; show drag count badge; refine drag payload and lifecycle

packages/frontend/src/components/PaginatedSongList.tsx

@@ -49,7 +49,7 @@ const SongItem = memo<{
   onToggleSelection: (songId: string) => void;
   showCheckbox: boolean;
   onPlaySong?: (song: Song) => void;
-  onDragStart: (songIds: string[]) => void;
+  onDragStart: (e: React.DragEvent, songIdsFallback: string[]) => void;
 }>(({ song, isSelected, isHighlighted, onSelect, onToggleSelection, showCheckbox, onPlaySong, onDragStart }) => {
   // Memoize the formatted duration to prevent recalculation
   const formattedDuration = useMemo(() => formatDuration(song.totalTime || ''), [song.totalTime]);
@@ -86,10 +86,7 @@ const SongItem = memo<{
       transition="background-color 0.2s"
       draggable
       onDragStart={(e) => {
-        // Mark this item as part of the drag selection using a custom type
+        onDragStart(e, [song.id]);
-        onDragStart([song.id]);
-        e.dataTransfer.setData('application/json', JSON.stringify({ type: 'songs', songIds: [song.id] }));
-        e.dataTransfer.effectAllowed = 'copyMove';
       }}
     >
       {showCheckbox && (
@@ -155,6 +152,7 @@ export const PaginatedSongList: React.FC<PaginatedSongListProps> = memo(({
 }) => {
   const [selectedSongs, setSelectedSongs] = useState<Set<string>>(new Set());
   const dragSelectionRef = useRef<string[] | null>(null);
+  const [isDragging, setIsDragging] = useState(false);
   const [localSearchQuery, setLocalSearchQuery] = useState(searchQuery);
   const { isOpen: isPlaylistModalOpen, onOpen: onPlaylistModalOpen, onClose: onPlaylistModalClose } = useDisclosure();
   const observerRef = useRef<IntersectionObserver | null>(null);
@@ -237,11 +235,20 @@ export const PaginatedSongList: React.FC<PaginatedSongListProps> = memo(({
   // Search handled inline via localSearchQuery effect
 
   // Provide drag payload: if multiple selected, drag all; else drag the single item
-  const handleDragStart = useCallback((songIdsFallback: string[]) => {
+  const handleDragStart = useCallback((e: React.DragEvent, songIdsFallback: string[]) => {
     const ids = selectedSongs.size > 0 ? Array.from(selectedSongs) : songIdsFallback;
     dragSelectionRef.current = ids;
+    setIsDragging(true);
+    const payload = { type: 'songs', songIds: ids, count: ids.length };
+    e.dataTransfer.setData('application/json', JSON.stringify(payload));
+    e.dataTransfer.effectAllowed = 'copyMove';
   }, [selectedSongs]);
 
+  const handleDragEnd = useCallback(() => {
+    setIsDragging(false);
+    dragSelectionRef.current = null;
+  }, []);
+
   // Memoized song items to prevent unnecessary re-renders
   const songItems = useMemo(() => {
     return songs.map(song => (
@@ -325,6 +332,12 @@ export const PaginatedSongList: React.FC<PaginatedSongListProps> = memo(({
 
   return (
     <Flex direction="column" height="100%">
+      {/* Global drag badge for selected count */}
+      {isDragging && (
+        <Box position="fixed" top={3} right={3} zIndex={2000} bg="blue.600" color="white" px={3} py={1} borderRadius="md" boxShadow="lg">
+          Dragging {dragSelectionRef.current?.length || 0} song{(dragSelectionRef.current?.length || 0) === 1 ? '' : 's'}
+        </Box>
+      )}
       {/* Sticky Header */}
       <Box
         position="sticky"
@@ -426,7 +439,7 @@ export const PaginatedSongList: React.FC<PaginatedSongListProps> = memo(({
         id="song-list-container"
       >
         <Flex direction="column" gap={2}>
-          {songItems}
+          <Box onDragEnd={handleDragEnd}>{songItems}</Box>
           
           {/* Loading indicator for infinite scroll or playlist switching */}
           {(loading || isSwitchingPlaylist) && (

packages/frontend/src/components/PlaylistManager.tsx

@@ -106,6 +106,7 @@ const PlaylistItem: React.FC<PlaylistItemProps> = React.memo(({
   onDropSongs,
 }) => {
   const [isOpen, setIsOpen] = useState(false);
+  const [isDragOver, setIsDragOver] = useState(false);
   
   // Memoize click handlers to prevent recreation
   const handlePlaylistClick = useCallback(() => {
@@ -140,7 +141,11 @@ const PlaylistItem: React.FC<PlaylistItemProps> = React.memo(({
                 />
               </Box>
             }
-            onDragOver={(e) => e.preventDefault()}
+            onDragOver={(e) => {
+              e.preventDefault();
+              setIsDragOver(true);
+            }}
+            onDragLeave={() => setIsDragOver(false)}
             onDrop={(e) => {
               try {
                 const data = e.dataTransfer.getData('application/json');
@@ -149,7 +154,10 @@ const PlaylistItem: React.FC<PlaylistItemProps> = React.memo(({
                   onDropSongs(node.name, parsed.songIds);
                 }
               } catch {}
+              setIsDragOver(false);
             }}
+            borderColor={isDragOver ? 'blue.400' : undefined}
+            borderWidth={isDragOver ? '1px' : undefined}
           >
             {level > 0 && (
               <Box
@@ -209,7 +217,8 @@ const PlaylistItem: React.FC<PlaylistItemProps> = React.memo(({
         borderRight="1px solid"
         borderRightColor="whiteAlpha.200"
         position="relative"
-        onDragOver={(e) => e.preventDefault()}
+        onDragOver={(e) => { e.preventDefault(); setIsDragOver(true); }}
+        onDragLeave={() => setIsDragOver(false)}
         onDrop={(e) => {
           try {
             const data = e.dataTransfer.getData('application/json');
@@ -218,7 +227,10 @@ const PlaylistItem: React.FC<PlaylistItemProps> = React.memo(({
               onDropSongs(node.name, parsed.songIds);
             }
           } catch {}
+          setIsDragOver(false);
         }}
+        borderColor={isDragOver ? 'blue.400' : undefined}
+        borderWidth={isDragOver ? '1px' : undefined}
       >
         {level > 0 && (
           <Box