feat(locker): add drag-drop attachment in grid

- Add attachItemFromGrid server action for drag-drop attachment
- Add attach drop detection in LockerGrid handleDragEnd
- Add attach drop styling with amber highlight on weapon footprint
- Add isAttachDrop prop to GridCell for attach-specific feedback
- Add dragError state with 5s auto-clear for attach failures
- Reuse setItemAttachment/removeItemAttachment semantics
- Handle slot replacement with no-room fallback for old attachments

src/components/frontend/locker/LockerGrid.tsx

@@ -24,22 +24,29 @@ import {
   Monitor,
   MoonStar,
   Package,
+  Palette,
   Shield,
   Shirt,
   Target,
   Wrench,
   Crosshair,
+  Tag,
 } from "lucide-react";
 import type { Asset } from "@/payload-types";
 import {
+  ATTACHMENT_CATEGORIES,
   findLockerMergeTarget,
   getAssetTypeColor,
   getLockerItemFootprint,
   getLockerGridOccupancy,
+  isAttachmentCompatible,
   isLockerPlacementValid,
+  resolveAssetId,
   type LockerGridItem,
+  type LockerItemEquipment,
 } from "@/lib/locker";
 import { GridCell } from "@/components/frontend/storage/GridCell";
+import type { ActionResult } from "@/app/(frontend)/locker/actions";
 import { cn } from "@/lib/utils";
 
 export function getAssetIcon(assetType: Asset["assetType"], className?: string) {
@@ -75,6 +82,8 @@ export function getAssetIcon(assetType: Asset["assetType"], className?: string)
       return <Wrench className={cls} />;
     case "explosive":
       return <Gem className={cls} />;
+    case "skin":
+      return <Palette className={cls} />;
     case "miscellaneous":
       return <Luggage className={cls} />;
     default:
@@ -88,20 +97,31 @@ function assetThumbnailUrl(asset: Asset): string | null {
   return null;
 }
 
+function itemContainsCell(item: LockerGridItem, x: number, y: number): boolean {
+  const fp = getLockerItemFootprint(item.asset, item.rotated);
+  return x >= item.gridX && x < item.gridX + fp.width && y >= item.gridY && y < item.gridY + fp.height;
+}
+
 export function LockerItemFace({
   asset,
   quantity,
   rotated,
   cellSize,
+  equipment,
 }: {
   asset: Asset;
   quantity: number;
   rotated?: boolean;
   cellSize: number;
+  equipment?: LockerItemEquipment;
 }) {
   const fp = getLockerItemFootprint(asset, rotated ?? false);
   const bgColor = getAssetTypeColor(asset.assetType);
   const thumb = assetThumbnailUrl(asset);
+  const displayName = equipment?.customName?.trim() || asset.name;
+  const hasCustomName = !!equipment?.customName?.trim();
+  const hasSkin = equipment?.skin != null;
+  const attachmentCount = equipment?.attachments?.length ?? 0;
 
   return (
     <div
@@ -112,6 +132,29 @@ export function LockerItemFace({
       className="relative rounded-md overflow-hidden flex flex-col items-center justify-center gap-0.5 select-none"
     >
       <div className="absolute inset-0 opacity-20" style={{ backgroundColor: bgColor }} />
+      {(hasSkin || attachmentCount > 0 || hasCustomName) && (
+        <div className="absolute top-0.5 right-0.5 flex flex-col items-end gap-0.5 z-10">
+          {hasCustomName && (
+            <span className="rounded-sm bg-sky-400 p-0.5 text-white shadow" title="Custom name">
+              <Tag className="size-2.5" />
+            </span>
+          )}
+          {hasSkin && (
+            <span className="rounded-sm bg-amber-400 p-0.5 text-white shadow" title="Skin applied">
+              <Palette className="size-2.5" />
+            </span>
+          )}
+          {attachmentCount > 0 && (
+            <span
+              className="flex items-center gap-0.5 rounded-sm bg-primary px-0.5 py-0.5 text-white shadow"
+              title={`${attachmentCount} attachment${attachmentCount === 1 ? "" : "s"}`}
+            >
+              <Crosshair className="size-2.5" />
+              <span className="text-[8px] font-bold leading-none">{attachmentCount}</span>
+            </span>
+          )}
+        </div>
+      )}
       <div className="relative flex flex-col items-center justify-center gap-0.5 p-1 w-full h-full">
         {thumb ? (
           <img src={thumb} alt={asset.name} className="size-6 object-contain opacity-80" />
@@ -119,7 +162,7 @@ export function LockerItemFace({
           <span className="text-muted-foreground/70">{getAssetIcon(asset.assetType, "size-5")}</span>
         )}
         <span className="text-[10px] leading-tight font-medium text-center text-foreground/90 line-clamp-2 px-0.5">
-          {asset.name}
+          {displayName}
         </span>
         {quantity > 1 && (
           <span
@@ -139,11 +182,13 @@ function DraggableLockerItem({
   cellSize,
   onSelect,
   selected,
+  highlight,
 }: {
   item: LockerGridItem;
   cellSize: number;
   onSelect: (item: LockerGridItem) => void;
   selected: boolean;
+  highlight?: boolean;
 }) {
   const didDrag = useRef(false);
   const fp = getLockerItemFootprint(item.asset, item.rotated);
@@ -189,13 +234,20 @@ function DraggableLockerItem({
         "transition-shadow duration-150",
         selected && "ring-2 ring-primary",
         !selected && "hover:ring-1 hover:ring-primary/50",
+        highlight && "locker-search-highlight",
       )}
       {...listeners}
       {...attributes}
       onClick={handleClick}
       suppressHydrationWarning
     >
-      <LockerItemFace asset={item.asset} quantity={item.quantity} rotated={item.rotated} cellSize={cellSize} />
+      <LockerItemFace
+        asset={item.asset}
+        quantity={item.quantity}
+        rotated={item.rotated}
+        cellSize={cellSize}
+        equipment={item.equipment}
+      />
     </div>
   );
 }
@@ -210,6 +262,8 @@ interface LockerGridProps {
   onRemoveItem: (entryId: string) => Promise<void>;
   onSelectItem: (item: LockerGridItem | null) => void;
   selectedItem: LockerGridItem | null;
+  highlightId?: string | null;
+  onAttachItem?: (weaponEntryId: string, attachmentEntryId: string) => Promise<ActionResult>;
 }
 
 export function LockerGrid({
@@ -222,10 +276,14 @@ export function LockerGrid({
   onRemoveItem,
   onSelectItem,
   selectedItem,
+  highlightId,
+  onAttachItem,
 }: LockerGridProps) {
   const [activeItem, setActiveItem] = useState<LockerGridItem | null>(null);
   const [hoverPosition, setHoverPosition] = useState<{ x: number; y: number } | null>(null);
   const [pendingRotated, setPendingRotated] = useState(false);
+  const [dragError, setDragError] = useState<string | null>(null);
+  const dragErrorTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
   const [cellSize, setCellSize] = useState(48);
   const gridRef = useRef<HTMLDivElement>(null);
   const containerRef = useRef<HTMLDivElement>(null);
@@ -280,15 +338,56 @@ export function LockerGrid({
   const hoverInfo = useMemo(() => {
     if (!hoverPosition || !activeItem) return null;
     const fp = getLockerItemFootprint(activeItem.asset, pendingRotated);
+    const isAttachment = ATTACHMENT_CATEGORIES.some(
+      (c) => c.assetType === activeItem.asset.assetType,
+    );
+
+    const targetItem =
+      items.find(
+        (it) => it.id !== activeItem.id && itemContainsCell(it, hoverPosition.x, hoverPosition.y),
+      ) ?? null;
+    const mergeTarget = findLockerMergeTarget(
+      items,
+      activeItem,
+      hoverPosition.x,
+      hoverPosition.y,
+      pendingRotated,
+    );
+
+    let mode: "move" | "merge" | "attach" = "move";
+    if (mergeTarget) {
+      mode = "merge";
+    } else if (
+      isAttachment &&
+      targetItem?.asset.assetType === "weapon" &&
+      isAttachmentCompatible(targetItem.asset, activeItem.asset)
+    ) {
+      const alreadyInstalled = (targetItem.equipment?.attachments ?? []).some(
+        (a) => resolveAssetId(a.asset) === activeItem.assetId,
+      );
+      if (!alreadyInstalled) {
+        mode = "attach";
+      }
+    }
+
     const cells = new Set<string>();
+    if (mode === "attach" && targetItem) {
+      const tFp = getLockerItemFootprint(targetItem.asset, targetItem.rotated);
+      for (let dx = 0; dx < tFp.width; dx++) {
+        for (let dy = 0; dy < tFp.height; dy++) {
+          cells.add(`${targetItem.gridX + dx},${targetItem.gridY + dy}`);
+        }
+      }
+    } else {
       for (let dx = 0; dx < fp.width; dx++) {
         for (let dy = 0; dy < fp.height; dy++) {
           cells.add(`${hoverPosition.x + dx},${hoverPosition.y + dy}`);
         }
       }
-    const mergeTarget = findLockerMergeTarget(items, activeItem, hoverPosition.x, hoverPosition.y, pendingRotated);
+    }
+
     const valid =
-      mergeTarget !== null ||
+      mode !== "move" ||
       isLockerPlacementValid(
         items,
         activeItem.id,
@@ -299,7 +398,8 @@ export function LockerGrid({
         gridWidth,
         gridHeight,
       );
-    return { cells, valid };
+
+    return { cells, valid, isAttachDrop: mode === "attach" };
   }, [hoverPosition, activeItem, items, gridWidth, gridHeight, pendingRotated]);
 
   const handleDragStart = useCallback((event: DragStartEvent) => {
@@ -310,6 +410,7 @@ export function LockerGrid({
       setPendingRotated(item.rotated ?? false);
     }
     setHoverPosition(null);
+    setDragError(null);
   }, []);
 
   const handleDragMove = useCallback(
@@ -365,6 +466,32 @@ export function LockerGrid({
         return;
       }
 
+      if (onAttachItem) {
+        const isAttachment = ATTACHMENT_CATEGORIES.some((c) => c.assetType === item.asset.assetType);
+        const targetItem =
+          items.find(
+            (it) => it.id !== item.id && itemContainsCell(it, targetX, targetY),
+          ) ?? null;
+        if (
+          isAttachment &&
+          targetItem?.asset.assetType === "weapon" &&
+          isAttachmentCompatible(targetItem.asset, item.asset)
+        ) {
+          const alreadyInstalled = (targetItem.equipment?.attachments ?? []).some(
+            (a) => resolveAssetId(a.asset) === item.assetId,
+          );
+          if (!alreadyInstalled) {
+            const result = await onAttachItem(targetItem.id, item.id);
+            if (!result.success && result.error) {
+              setDragError(result.error);
+              if (dragErrorTimer.current) clearTimeout(dragErrorTimer.current);
+              dragErrorTimer.current = setTimeout(() => setDragError(null), 5000);
+            }
+            return;
+          }
+        }
+      }
+
       const fp = getLockerItemFootprint(item.asset, pendingRotated);
       const valid = isLockerPlacementValid(
         items,
@@ -381,7 +508,7 @@ export function LockerGrid({
         await onMoveItem(item.id, targetX, targetY, pendingRotated);
       }
     },
-    [items, gridWidth, gridHeight, onMoveItem, onMergeStacks, cellSize, pendingRotated],
+    [items, gridWidth, gridHeight, onMoveItem, onMergeStacks, onAttachItem, cellSize, pendingRotated],
   );
 
   const handleBackgroundClick = useCallback(() => {
@@ -414,6 +541,7 @@ export function LockerGrid({
                     isDropTarget={!!activeItem}
                     isHovered={hoverInfo !== null && hoverInfo.cells.has(key)}
                     isInvalidDrop={hoverInfo !== null && !hoverInfo.valid}
+                    isAttachDrop={hoverInfo?.isAttachDrop ?? false}
                   />
                 );
               }),
@@ -426,6 +554,7 @@ export function LockerGrid({
                 cellSize={cellSize}
                 onSelect={onSelectItem}
                 selected={selectedItem?.id === item.id}
+                highlight={highlightId === item.id}
               />
             ))}
           </div>
@@ -439,6 +568,7 @@ export function LockerGrid({
             {gridWidth} x {gridHeight}
           </span>
         </div>
+        {dragError && <p className="text-xs text-red-400">{dragError}</p>}
       </div>
 
       <DragOverlay dropAnimation={null}>

src/components/frontend/storage/GridCell.tsx

@@ -11,6 +11,7 @@ interface GridCellProps {
   isDropTarget: boolean;
   isHovered: boolean;
   isInvalidDrop: boolean;
+  isAttachDrop?: boolean;
 }
 
 export function GridCell({
@@ -21,6 +22,7 @@ export function GridCell({
   isDropTarget,
   isHovered,
   isInvalidDrop,
+  isAttachDrop = false,
 }: GridCellProps) {
   const { setNodeRef } = useDroppable({
     id: `cell-${x}-${y}`,
@@ -32,8 +34,9 @@ export function GridCell({
       ref={setNodeRef}
       className={cn(
         "border border-border/60 transition-colors duration-75",
-        isHovered && !isInvalidDrop && "bg-green-500/25 border-green-500/50",
+        isHovered && isAttachDrop && "bg-amber-400/30 border-amber-400/60",
-        isHovered && isInvalidDrop && "bg-red-500/25 border-red-500/50",
+        isHovered && !isAttachDrop && !isInvalidDrop && "bg-green-500/25 border-green-500/50",
+        isHovered && !isAttachDrop && isInvalidDrop && "bg-red-500/25 border-red-500/50",
         !isHovered && isDropTarget && "bg-primary/5 border-primary/20",
       )}
       style={{ width: cellSize, height: cellSize }}