feat: persist marketplace watchlist

src/components/marketplace/SavedListingsRail.tsx

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+'use client';
+
+export interface SavedListing {
+  id: string;
+  title: string;
+  price: string;
+  status?: 'Active' | 'Sold' | 'Cancelled';
+}
+
+export function SavedListingsRail({
+  listings,
+  savedIds,
+  onRemove,
+  onSelect,
+}: {
+  listings: SavedListing[];
+  savedIds: ReadonlySet<string>;
+  onRemove: (id: string) => void;
+  onSelect?: (id: string) => void;
+}) {
+  const saved = listings.filter((listing) => savedIds.has(listing.id));
+  if (saved.length === 0) return null;
+
+  return (
+    <section aria-label="Saved listings" className="mb-6 rounded-xl border border-white/10 p-4">
+      <h2 className="mb-3 text-sm font-semibold text-white">Saved</h2>
+      <ul className="flex gap-3 overflow-x-auto">
+        {saved.map((listing) => (
+          <li key={listing.id} className="min-w-44 rounded-lg bg-white/5 p-3 text-sm text-white">
+            <button type="button" onClick={() => onSelect?.(listing.id)} className="block text-left">
+              <span className="block font-medium">{listing.title}</span>
+              <span className="block text-white/60">{listing.price}</span>
+              {listing.status && listing.status !== 'Active' && (
+                <span className="block text-xs text-amber-300">{listing.status}</span>
+              )}
+            </button>
+            <button
+              type="button"
+              aria-label={`Remove ${listing.title} from saved listings`}
+              onClick={() => onRemove(listing.id)}
+              className="mt-2 text-xs text-cyan-300 underline"
+            >
+              Remove
+            </button>
+          </li>
+        ))}
+      </ul>
+    </section>
+  );
+}

src/hooks/useMarketplaceWatchlist.test.ts

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+/** @vitest-environment happy-dom */
+
+import { describe, expect, it } from 'vitest';
+import { renderHook, act } from '@testing-library/react';
+import {
+  MARKETPLACE_WATCHLIST_KEY,
+  useMarketplaceWatchlist,
+} from './useMarketplaceWatchlist';
+
+describe('useMarketplaceWatchlist', () => {
+  it('restores and persists saved listing ids', () => {
+    localStorage.setItem(MARKETPLACE_WATCHLIST_KEY, JSON.stringify(['listing-1']));
+    const { result } = renderHook(() => useMarketplaceWatchlist());
+
+    expect(result.current.isSaved('listing-1')).toBe(true);
+    act(() => result.current.toggle('listing-2'));
+    expect(JSON.parse(localStorage.getItem(MARKETPLACE_WATCHLIST_KEY) ?? '[]')).toEqual([
+      'listing-1',
+      'listing-2',
+    ]);
+  });
+});

src/hooks/useMarketplaceWatchlist.ts

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+'use client';
+
+import { useCallback, useEffect, useMemo, useState } from 'react';
+
+export const MARKETPLACE_WATCHLIST_KEY = 'commitlabs:marketplace-watchlist';
+
+function readWatchlist(): string[] {
+  try {
+    const value: unknown = JSON.parse(window.localStorage.getItem(MARKETPLACE_WATCHLIST_KEY) ?? '[]');
+    return Array.isArray(value) ? value.filter((id): id is string => typeof id === 'string') : [];
+  } catch {
+    return [];
+  }
+}
+
+export function useMarketplaceWatchlist() {
+  const [savedIds, setSavedIds] = useState<string[]>([]);
+
+  useEffect(() => setSavedIds(readWatchlist()), []);
+
+  useEffect(() => {
+    window.localStorage.setItem(MARKETPLACE_WATCHLIST_KEY, JSON.stringify(savedIds));
+  }, [savedIds]);
+
+  const toggle = useCallback((listingId: string) => {
+    setSavedIds((current) =>
+      current.includes(listingId)
+        ? current.filter((id) => id !== listingId)
+        : [...current, listingId],
+    );
+  }, []);
+
+  const isSaved = useCallback((listingId: string) => savedIds.includes(listingId), [savedIds]);
+  const savedSet = useMemo(() => new Set(savedIds), [savedIds]);
+
+  return { savedIds, savedSet, isSaved, toggle };
+}