Better code splitting and removed final instances of react-dnd

src-web/lib/dnd.ts

@@ -0,0 +1,23 @@
+import type { DragMoveEvent } from '@dnd-kit/core';
+
+export function computeSideForDragMove(
+  id: string,
+  e: DragMoveEvent,
+): 'above' | 'below' | null {
+  if (e.over == null || e.over.id !== id) {
+    return null;
+  }
+  if (e.active.rect.current.initial == null) return null;
+
+  const overRect = e.over.rect;
+  const activeTop =
+    e.active.rect.current.translated?.top ?? e.active.rect.current.initial.top + e.delta.y;
+  const pointerY = activeTop + e.active.rect.current.initial.height / 2;
+
+  const hoverTop = overRect.top;
+  const hoverBottom = overRect.bottom;
+  const hoverMiddleY = (hoverBottom - hoverTop) / 2;
+  const hoverClientY = pointerY - hoverTop;
+
+  return hoverClientY < hoverMiddleY ? 'above' : 'below';
+}