fix(packing): tell a dragged category by its data type, not by a state flag

A flag set on dragstart could still be unrendered when a quick drag reached
the next card, and the drop was lost. The category now travels in the drag
under its own type, read from the first dragover on and at the drop.

client/src/components/Packing/PackingListPanelCategoryGroup.tsx

@@ -39,16 +39,14 @@ interface KategorieGruppeProps {
   // the reader cannot see.
   reorderable?: boolean
   // Moving the whole category among the others, wired by the list, which sees every
-  // card. `active` is true while any category is being dragged, so a dragged ITEM
-  // passing over a card is left to the item rows.
+  // card. `onDrop` gets the category that was dragged onto this one.
   categoryDrag?: {
-    active: boolean
     isDragging: boolean
     isOver: boolean
     onStart: () => void
     onOver: () => void
     onEnd: () => void
-    onDrop: () => void
+    onDrop: (dragged: string) => void
   }
   // Three-tier sharing (#858) — threaded down to each item's share control.
   currentUserId?: number
@@ -363,16 +361,28 @@ export function KategorieGruppe({ kategorie, items, tripId, allCategories, onRen
 
 type CategoryDrag = NonNullable<KategorieGruppeProps['categoryDrag']>
 
+/** The data type a dragged category carries, its name as the value. */
+const CATEGORY_DRAG_TYPE = 'application/x-trek-packing-category'
+
 /**
  * The card, and while a category is dragged its drop target. Captured, because
  * the item rows stop their own drops from bubbling.
  */
 function CategoryDropFrame({ drag, children }: { drag?: CategoryDrag; children: React.ReactNode }) {
-  const target = drag?.active ? drag : null
+  // Told apart by the drag's own data type, which is there from the first event on:
+  // a flag set in state on dragstart can still be unrendered when a quick drag
+  // arrives, and a dragged item must pass through to its rows untouched.
+  const isCategoryDrag = (e: React.DragEvent) => e.dataTransfer.types.includes(CATEGORY_DRAG_TYPE)
   return (
     <div
-      onDragOverCapture={target ? (e => { e.preventDefault(); e.dataTransfer.dropEffect = 'move'; target.onOver() }) : undefined}
-      onDropCapture={target ? (e => { e.preventDefault(); e.stopPropagation(); target.onDrop() }) : undefined}
+      onDragOverCapture={drag ? (e => {
+        if (!isCategoryDrag(e)) return
+        e.preventDefault(); e.dataTransfer.dropEffect = 'move'; drag.onOver()
+      }) : undefined}
+      onDropCapture={drag ? (e => {
+        if (!isCategoryDrag(e)) return
+        e.preventDefault(); e.stopPropagation(); drag.onDrop(e.dataTransfer.getData(CATEGORY_DRAG_TYPE))
+      }) : undefined}
       style={{
         marginBottom: 6, background: 'var(--bg-card)', borderRadius: 16, border: '1px solid var(--border-secondary)', overflow: 'visible',
         opacity: drag?.isDragging ? 0.4 : 1,
@@ -394,7 +404,12 @@ function CategoryGrip({ drag, kategorie, label }: { drag?: CategoryDrag; kategor
       role="button"
       aria-label={label}
       title={label}
-      onDragStart={e => { e.dataTransfer.effectAllowed = 'move'; e.dataTransfer.setData('text/plain', kategorie); drag.onStart() }}
+      onDragStart={e => {
+        e.dataTransfer.effectAllowed = 'move'
+        e.dataTransfer.setData(CATEGORY_DRAG_TYPE, kategorie)
+        e.dataTransfer.setData('text/plain', kategorie)
+        drag.onStart()
+      }}
       onDragEnd={drag.onEnd}
       style={{ cursor: 'grab', display: 'flex', alignItems: 'center', color: 'var(--text-faint)', flexShrink: 0, marginInlineStart: -6 }}
     >

client/src/components/Packing/PackingListPanelList.tsx

@@ -47,16 +47,12 @@ export function PackingList(S: PackingState) {
               onReorder={(orderedIds) => reorderPackingItems(tripId, orderedIds)}
               reorderable={sort === 'manual'}
               categoryDrag={canEdit ? {
-                active: draggedCategory !== null,
                 isDragging: draggedCategory === kat,
                 isOver: overCategory === kat && draggedCategory !== null && draggedCategory !== kat,
                 onStart: () => { setDraggedCategory(kat); setOverCategory(null) },
                 onOver: () => setOverCategory(kat),
                 onEnd: endCategoryDrag,
-                onDrop: () => {
-                  if (draggedCategory !== null) moveCategory(draggedCategory, kat)
-                  endCategoryDrag()
-                },
+                onDrop: (dragged) => { moveCategory(dragged, kat); endCategoryDrag() },
               } : undefined}
               currentUserId={currentUserId}
               onSetSharing={handleSetSharing}