fix: cache useSyncExternalStore snapshot to prevent infinite re-render

getSnapshot() was calling JSON.parse() on every invocation, returning
a new array reference each time. useSyncExternalStore uses Object.is
comparison, so it saw a "new" value on every render and triggered
an infinite update loop. Fix by caching the parsed result and only
re-parsing when the raw localStorage value changes.

apps/web/src/hooks/use-recent-tools.ts

@@ -2,17 +2,28 @@ import { useSyncExternalStore } from "react";
 
 const STORAGE_KEY = "snapotter-recent-tools";
 const MAX_RECENT = 5;
+const EMPTY: string[] = [];
 
 let listeners: Array<() => void> = [];
+let cachedRaw: string | null = null;
+let cachedParsed: string[] = EMPTY;
 
 function getSnapshot(): string[] {
-  try {
   const raw = localStorage.getItem(STORAGE_KEY);
-    return raw ? JSON.parse(raw) : [];
+  if (raw !== cachedRaw) {
+    cachedRaw = raw;
+    try {
+      cachedParsed = raw ? JSON.parse(raw) : EMPTY;
     } catch {
-    return [];
+      cachedParsed = EMPTY;
     }
   }
+  return cachedParsed;
+}
+
+function getServerSnapshot(): string[] {
+  return EMPTY;
+}
 
 function subscribe(listener: () => void) {
   listeners.push(listener);
@@ -25,9 +36,10 @@ export function recordRecentTool(toolId: string) {
   const current = getSnapshot();
   const updated = [toolId, ...current.filter((id) => id !== toolId)].slice(0, MAX_RECENT);
   localStorage.setItem(STORAGE_KEY, JSON.stringify(updated));
+  cachedRaw = null;
   listeners.forEach((l) => l());
 }
 
 export function useRecentTools(): string[] {
-  return useSyncExternalStore(subscribe, getSnapshot, () => []);
+  return useSyncExternalStore(subscribe, getSnapshot, getServerSnapshot);
 }