Recent fill stream for a Hyperliquid perp coin. POST {coin, n}. Returns the last N fills (direction, side, price, size, notional, fee, trader address) plus an aggregate summary (buy/sell notional split, whale_fill_count for fills ≥ $10k, avg price). Distinct from hl-screen (top traders by lifetime volume) — this is recent trade events as they happen, for whale-watching + flow-following bots.