refactor(web): converge PlaylistTrackRow drag-reorder onto @neodrag/svelte (B4)

web/src/lib/components/PlaylistTrackRow.svelte

@@ -1,25 +1,23 @@
 <script lang="ts">
   import { GripVertical, X } from 'lucide-svelte';
+  import { draggable, type DragEventData } from '@neodrag/svelte';
   import LikeButton from './LikeButton.svelte';
   import TrackMenu from './TrackMenu.svelte';
   import type { PlaylistTrack, TrackRef } from '$lib/api/types';
+  import { offsetToDelta } from './queue-row-math';
 
   let {
     row,
     isOwner,
     onRemove,
     onPlay,
-    onDragStart,
-    onDragOver,
-    onDrop
+    onMove
   }: {
     row: PlaylistTrack;
     isOwner: boolean;
     onRemove: (position: number) => void;
     onPlay: (position: number) => void;
-    onDragStart?: (position: number) => void;
-    onDragOver?: (e: DragEvent, position: number) => void;
-    onDrop?: (e: DragEvent, position: number) => void;
+    onMove?: (fromPos: number, toPos: number) => void;
   } = $props();
 
   const isUnavailable = $derived(row.track_id === null);
@@ -41,21 +39,42 @@
       : null
   );
 
+  let measuredRowHeight = 56; // sensible default; replaced on dragStart
+
+  function handleDragStart(data: DragEventData) {
+    const rect = data.rootNode.getBoundingClientRect();
+    if (rect.height > 0) measuredRowHeight = rect.height;
+  }
+
+  function handleDragEnd(data: DragEventData) {
+    const delta = offsetToDelta(data.offsetY, measuredRowHeight);
+    if (delta === 0) return;
+    onMove?.(row.position, row.position + delta);
+  }
+
   function format(sec: number): string {
     const m = Math.floor(sec / 60);
     const s = sec % 60;
     return `${m}:${s.toString().padStart(2, '0')}`;
   }
+
+  // Drag is gated on owner+available. When neither, the action runs but
+  // the dragEnd handler skips by returning before onMove fires; visually
+  // the user never sees the row move.
+  const canDrag = $derived(isOwner && !isUnavailable);
 </script>
 
 <div
   role="listitem"
   class="flex items-center gap-3 px-3 py-2 text-sm transition-colors hover:bg-surface-hover
          {isUnavailable ? 'text-text-muted' : 'text-text-primary'}"
-  draggable={isOwner && !isUnavailable}
-  ondragstart={() => onDragStart?.(row.position)}
-  ondragover={(e) => { e.preventDefault(); onDragOver?.(e, row.position); }}
-  ondrop={(e) => { e.preventDefault(); onDrop?.(e, row.position); }}
+  use:draggable={{
+    axis: 'y',
+    bounds: 'parent',
+    disabled: !canDrag,
+    onDragStart: handleDragStart,
+    onDragEnd: handleDragEnd
+  }}
 >
   {#if isOwner}
     <span

web/src/routes/playlists/[id]/+page.svelte

@@ -31,20 +31,16 @@
   const playlistQuery = $derived($playlistStore);
   const isOwner = $derived(user.value?.id === playlistQuery?.data?.user_id);
 
-  let dragFromPos = $state<number | null>(null);
-
-  async function onDrop(toPos: number) {
-    if (dragFromPos === null || !playlistQuery?.data) {
-      return;
-    }
-    if (dragFromPos === toPos) {
-      dragFromPos = null;
-      return;
-    }
-    const cur = playlistQuery.data.tracks.map((t) => t.position);
-    const moved = cur.splice(dragFromPos, 1)[0];
-    cur.splice(toPos, 0, moved);
-    dragFromPos = null;
+  async function onMove(fromPos: number, toPos: number) {
+    if (!playlistQuery?.data) return;
+    const tracks = playlistQuery.data.tracks;
+    // Clamp toPos so a drag past the list edges resolves cleanly to the
+    // first/last slot rather than producing an out-of-range index.
+    const clamped = Math.max(0, Math.min(tracks.length - 1, toPos));
+    if (fromPos === clamped) return;
+    const cur = tracks.map((t) => t.position);
+    const moved = cur.splice(fromPos, 1)[0];
+    cur.splice(clamped, 0, moved);
     try {
       await reorderPlaylist(id, cur);
       await queryClient.invalidateQueries({ queryKey: qk.playlist(id) });
@@ -268,8 +264,7 @@
             isOwner={isOwner ?? false}
             onRemove={onRemove}
             onPlay={onPlay}
-            onDragStart={(p) => (dragFromPos = p)}
-            onDrop={(_, p) => onDrop(p)}
+            onMove={onMove}
           />
         {/each}
       {/if}