Every SSE snapshot re-render rebuilt the expanded panel's HTML back to 'loading…' and re-fetched — panels flickered per tick and never looked settled. Rendered panels now cache per symbol: re-renders repaint from cache instantly, background refresh at most once/min, single-flight guard against fetch races. Watch panel and trigger panel share the cache; toggleCriteria's duplicate direct fetch removed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>