P3-1: Scan optimization — only BG↔HL (50+ pair combos → 2)
P3-2: Real-time spread chart — spreadHistory ring buffer +
/api/spread-history endpoint + Chart.js spread chart
P3-3: Live position PnL — positions SSE now includes
estimated current profit/loss + current spread
P3-4: Real-time trade events — trader.OnTradeEvent callback
fires SSE 'trade_open' / 'trade_close' immediately
P3-5: Connection status monitoring — tracks last update time
per exchange, broadcast via stats.connections + /api/connections
Frontend: spread chart card, PnL column in positions,
connection status dots in stats bar,
green/red border flash on trade events
jackyu66git
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