feat(ngos): keep the explorer sort in the URL

src/components/ngos/NgoExplorer.test.tsx

@@ -114,6 +114,34 @@ describe('NgoExplorer', () => {
     expect(screen.getAllByRole('heading', { level: 2 })).toHaveLength(15);
   });
 
+  it('restores the sort from the URL on mount', () => {
+    mockSearchParams = new URLSearchParams('sort=most-active-streams');
+    const ngos = [
+      makeNgo({ id: 'a', name: 'Alpha', stats: { totalCommitted: '0', totalWithdrawn: '0', activeStreamCount: 1, donorCount: 0 } }),
+      makeNgo({ id: 'b', name: 'Beta', stats: { totalCommitted: '0', totalWithdrawn: '0', activeStreamCount: 5, donorCount: 0 } }),
+      makeNgo({ id: 'c', name: 'Gamma', stats: { totalCommitted: '0', totalWithdrawn: '0', activeStreamCount: 3, donorCount: 0 } }),
+    ];
+    render(<NgoExplorer ngos={ngos} />);
+
+    expect(screen.getByRole('combobox')).toHaveValue('most-active-streams');
+
+    const headings = screen.getAllByRole('heading', { level: 2 }).map((h) => h.textContent);
+    expect(headings).toEqual(['Beta', 'Gamma', 'Alpha']);
+  });
+
+  it('writes the sort to the URL when changed (and clears page)', () => {
+    mockSearchParams = new URLSearchParams('q=Water&page=2');
+    const ngos = buildNgos();
+    render(<NgoExplorer ngos={ngos} />);
+
+    fireEvent.change(screen.getByRole('combobox'), { target: { value: 'most-committed' } });
+
+    expect(mockReplace).toHaveBeenLastCalledWith(
+      '/ngos?q=Water&sort=most-committed',
+      { scroll: false },
+    );
+  });
+
   it('shows an empty state when the search matches nothing', () => {
     const ngos = buildNgos();
     render(<NgoExplorer ngos={ngos} />);

src/components/ngos/NgoExplorer.tsx

@@ -32,14 +32,22 @@ function parsePage(value: string | null): number {
   return Number.isInteger(page) && page > 0 ? page : 1;
 }
 
+// Only a non-default sort is carried in the URL; 'newest' is the implicit
+// default and is omitted to keep shared links tidy.
+const SORT_OPTIONS: readonly SortOption[] = ['newest', 'most-active-streams', 'most-committed'];
+
+function parseSort(value: string | null): SortOption {
+  return SORT_OPTIONS.includes(value as SortOption) ? (value as SortOption) : 'newest';
+}
+
 export function NgoExplorer({ ngos }: { ngos: NgoProfile[] }) {
   const router = useRouter();
   const pathname = usePathname();
   const searchParams = useSearchParams();
 
   const [searchQuery, setSearchQuery] = useState(() => searchParams.get('q') ?? '');
   const [page, setPage] = useState(() => parsePage(searchParams.get('page')));
-  const [sortBy, setSortBy] = useState<SortOption>('newest');
+  const [sortBy, setSortBy] = useState<SortOption>(() => parseSort(searchParams.get('sort')));
 
   // Sync incoming URL changes before rendering, while keeping immediate
   // local updates from the handlers below until navigation completes.
@@ -49,14 +57,15 @@ export function NgoExplorer({ ngos }: { ngos: NgoProfile[] }) {
     setPreviousQueryString(queryString);
     setSearchQuery(searchParams.get('q') ?? '');
     setPage(parsePage(searchParams.get('page')));
+    setSortBy(parseSort(searchParams.get('sort')));
   }
 
   const visibleCount = page * PAGE_SIZE;
 
-  // Only q and page are synced (see acceptance criteria) — sort stays
-  // local. Replaced rather than pushed so search-as-you-type doesn't fill
-  // the back-button history with one entry per keystroke.
-  function syncParams(next: { q?: string; page?: number }): void {
+  // q, page and sort are synced to the URL so links/back-forward preserve
+  // the full explorer state. router.replace (not push) so search-as-you-type
+  // doesn't fill history with one entry per keystroke.
+  function syncParams(next: { q?: string; page?: number; sort?: SortOption }): void {
     const params = new URLSearchParams(searchParams.toString());
 
     if (next.q !== undefined) {
@@ -73,6 +82,13 @@ export function NgoExplorer({ ngos }: { ngos: NgoProfile[] }) {
         params.delete('page');
       }
     }
+    if (next.sort !== undefined) {
+      if (next.sort !== 'newest') {
+        params.set('sort', next.sort);
+      } else {
+        params.delete('sort');
+      }
+    }
 
     const query = params.toString();
     router.replace(query ? `${pathname}?${query}` : pathname, { scroll: false });
@@ -98,7 +114,7 @@ export function NgoExplorer({ ngos }: { ngos: NgoProfile[] }) {
   function handleSortChange(value: SortOption): void {
     setSortBy(value);
     setPage(1);
-    syncParams({ page: 1 });
+    syncParams({ sort: value, page: 1 });
   }
 
   function handleLoadMore(): void {