fix(v2): inventory no longer flickers — debounced re-fetch, no loading flash

inventory_delta WS messages were triggering immediate full re-fetch
with setLoading(true), causing content to flash blank. Now:
- Initial load shows loading state (once)
- Subsequent deltas debounced to 2s (batches rapid changes)
- Re-fetch runs silently without clearing existing items

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/windows/InventoryWindow.tsx

@@ -163,19 +163,33 @@ export const InventoryWindow: React.FC<Props> = ({ id, charName, zIndex, invento
   const [activePack, setActivePack] = useState<number | null>(null);
   const [tooltip, setTooltip] = useState<{ item: any; x: number; y: number } | null>(null);
   const [charStats, setCharStats] = useState<any>(null);
-  const [cantripState, setCantripState] = useState<any>(null);
+  const debounceRef = useRef<number>(0);
+  const initialLoadDone = useRef(false);
 
+  // Initial fetch
   useEffect(() => {
     setLoading(true);
     Promise.all([
       apiFetch<any>(`/inventory/${encodeURIComponent(charName)}?limit=1000`).catch(() => ({ items: [] })),
       apiFetch<any>(`/character-stats/${encodeURIComponent(charName)}`).catch(() => null),
     ]).then(([inv, stats]) => {
-      const rawItems = inv.items ?? [];
+      setItems((inv.items ?? []).map(normalizeItem));
-      setItems(rawItems.map(normalizeItem));
       setCharStats(stats);
+      initialLoadDone.current = true;
     }).finally(() => setLoading(false));
-  }, [charName, inventoryVersion]); // re-fetch when inventory_delta arrives
+  }, [charName]);
+
+  // Debounced re-fetch on inventory_delta (no loading flash)
+  useEffect(() => {
+    if (!initialLoadDone.current || !inventoryVersion) return;
+    clearTimeout(debounceRef.current);
+    debounceRef.current = window.setTimeout(() => {
+      apiFetch<any>(`/inventory/${encodeURIComponent(charName)}?limit=1000`)
+        .then(inv => setItems((inv.items ?? []).map(normalizeItem)))
+        .catch(() => {});
+    }, 2000); // 2s debounce — batch rapid deltas
+    return () => clearTimeout(debounceRef.current);
+  }, [charName, inventoryVersion]);
 
   const handleHover = useCallback((item: any | null, e?: React.MouseEvent) => {
     if (item && e) setTooltip({ item, x: e.clientX, y: e.clientY });