Crypto ETF Sentinel — Activity feed of recent notable SEC filings + comment letters for US spot crypto ETFs (Bitcoin, Ethereum, Solana, XRP and more; last 60 days by default). Tracks S-1, 424B, 8-A12B, CERT, EFFECT and review correspondence. Stage-filtered to drop trading-stage housekeeping noise — a 'what's happening in crypto ETF regulation' heartbeat for monitoring agents.