feat(ui): the spell-bar drop ring — retail's authored drag-accept state, and the ring exposed a real drop off-by-one

The green ring is retail's own art: every UIItem cell carries an
authored DragAccept child (catalog 0x21000037, child 0x1000045A), and
the spell bar's drag-over handler (SpellCastSubMenu::OnItemListDragOver
@0x004C5990) flips it to the Accept state (0x10000040 -> surface
0x060011F9) for any spell payload. Ported through a per-slot
SetDragAcceptVisual seam + a catalog DragOverAcceptance hook; other
lists are untouched (null acceptance = neutral). A polarity error in
our older docs (Accept/Reject state ids swapped) was corrected against
three independent sources; the shipped art was always right, only the
labels lied.

The ring shares ONE landing computation with the drop
(FavoriteDropIndex) — and that requirement exposed a genuine #354
off-by-one: the empty-tail path double-applied the -1 adjustment
(retail gates it on the lift's removal @0x004C7157), landing a
reordered spell second-to-last instead of last. Fixed;
discriminator-verified both ways. AP-172 narrowed + its false
empty-tail claim corrected.

Clean-room complete solution: 11,545 passed / 4 skipped / 0 failed.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/AcDream.App/UI/UiCatalogSlot.cs

@@ -36,6 +36,19 @@ public sealed class UiCatalogSlot : UiItemSlot
     public Action<object>? DragEnded { get; init; }
     public Action<object>? Dropped { get; init; }
 
+    /// <summary>
+    /// Per-panel drag-over acceptance — the catalog-cell port of retail's
+    /// per-list drag handler deciding the rollover state
+    /// (<c>UIElement_ItemList::ItemList_DragOver</c> @ 0x004E3400 →
+    /// <c>m_dragHandler->OnItemListDragOver</c>; the spell bar's is
+    /// <c>SpellCastSubMenu::OnItemListDragOver</c> @ 0x004C5990). While a drag
+    /// hovers this cell, the returned acceptance drives the authored
+    /// DragAccept frame (accept 0x060011F9 / reject 0x060011F8). Null (the
+    /// default for every list that never set one) keeps the cell neutral —
+    /// no overlay, exactly the pre-existing presentation.
+    /// </summary>
+    public Func<object, ItemDragAcceptance>? DragOverAcceptance { get; init; }
+
     protected override bool IsShortcutOccupied => EntryId != 0u;
     public override bool IsEmptySlot => EntryId == 0u;
 
@@ -77,9 +90,25 @@ public sealed class UiCatalogSlot : UiItemSlot
                 if (e.Payload is not null) DragBegan?.Invoke(e.Payload);
                 return true;
             case UiEventType.DragEnter:
+                // Pointer entered mid-drag: ask the panel's acceptance seam and show
+                // the authored frame (retail ItemList_DragOver → the list handler's
+                // SetDragAcceptState on the hovered UIItem's 0x1000045A child).
+                SetDragAcceptVisual(e.Payload is { } enterPayload
+                    ? DragOverAcceptance?.Invoke(enterPayload) switch
+                    {
+                        ItemDragAcceptance.Accept => DragAcceptState.Accept,
+                        ItemDragAcceptance.Reject => DragAcceptState.Reject,
+                        _ => DragAcceptState.None,
+                    }
+                    : DragAcceptState.None);
+                return true;
             case UiEventType.DragOver:
+                // UiRoot fires DragOver on LEAVE — retail's dwParam1 == 0 reset to
+                // ItemSlot_DragOver_Normal (0x1000003F) @ 0x004E1438-0x004E1456.
+                SetDragAcceptVisual(DragAcceptState.None);
                 return true;
             case UiEventType.DropReleased:
+                SetDragAcceptVisual(DragAcceptState.None);
                 if (e.Payload is not null) Dropped?.Invoke(e.Payload);
                 return true;
             default:
@@ -141,6 +170,10 @@ public sealed class UiCatalogSlot : UiItemSlot
             if (!string.IsNullOrWhiteSpace(Detail))
                 ctx.DrawString(Detail!, MathF.Max(labelLeft, Width - 48f), 3f, Vector4.One);
         }
+
+        // Drag-rollover frame last — same layering as the physical UIItem draw
+        // (accept/reject above selection; catalog cells have no cooldown layer).
+        DrawDragAcceptOverlay(ctx);
     }
 
     private void DrawSelection(UiRenderContext ctx)