Double-submit cookie pattern: login sets bh-csrf-token cookie, proxy.ts validates X-CSRF-Token header on POST/PUT/DELETE to /api/admin/*. New adminFetch() helper in src/lib/csrf.ts auto-includes the header. All admin pages migrated from fetch() to adminFetch(). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>