decouple display from trading: snapMu + RefreshSnapshot/ReadSnapshot

- Add snapMu RWMutex + positionsSnapshot to Trader
- RefreshSnapshot() called from main loop after Tick() — acquires
  t.mu briefly, stores deep copy under snapMu
- ReadSnapshot() returns snapshot copy under snapMu.RLock — never
  touches t.mu, zero contention with trading path
- Dashboard + handleStatus + hourly summary + status log all
  use ReadSnapshot() instead of GetPositionsCopy()
- Trading path (Tick/TryEntry/executeEntry/checkExit/checkScaleIn)
  never blocked by display reads
- Snapshot is at most 1 tick behind live state — acceptable delay

dashboard.go

@@ -290,8 +290,8 @@ func (d *Dashboard) broadcastLoop() {
 		}
 		d.hub.Broadcast("prices", prices)
 
-		// 2. Open positions with live PnL (P3-3) — use safe copy for concurrent read
-		positions := d.trader.GetPositionsCopy()
+		// 2. Open positions with live PnL (P3-3) — read from decoupled snapshot, never blocks trader
+		positions := d.trader.ReadSnapshot()
 		posList := make([]map[string]interface{}, 0, len(positions))
 		for _, pos := range positions {
 			posEntry := map[string]interface{}{
@@ -428,7 +428,7 @@ func (d *Dashboard) handleIndex(w http.ResponseWriter, r *http.Request) {
 
 func (d *Dashboard) handleStatus(w http.ResponseWriter, r *http.Request) {
 	snap := d.store.GetAll()
-	positions := d.trader.GetPositionsCopy()
+	positions := d.trader.ReadSnapshot()
 	converged, diverged, flat, total := d.trader.GetClosedStats()
 
 	resp := map[string]interface{}{

main.go

@@ -147,8 +147,8 @@ func main() {
 			}
 			log.Printf("[Status] %d prices / %d coins connected", count, len(snap))
 
-			// Show open positions
-			if positions := trader.GetOpenPositions(); len(positions) > 0 {
+			// Show open positions (read from decoupled snapshot)
+			if positions := trader.ReadSnapshot(); len(positions) > 0 {
 				for _, pos := range positions {
 					log.Printf("  [Position] %s %s open %d scales $%.0f since %s",
 						pos.Coin, pos.Direction, pos.ScaleLevels, pos.AmountUSD,
@@ -162,6 +162,7 @@ func main() {
 
 			// Tick the trader (monitor open positions for exit)
 			trader.Tick(store, notifier)
+			trader.RefreshSnapshot() // decoupled snapshot for display
 			t1 := time.Now()
 
 			// Scan for arbitrage entries using maker fees (limit orders)
@@ -190,7 +191,7 @@ func main() {
 			// Hourly trade summary — use hour-based tracking (wider window than second-granularity)
 			hour := now.Hour()
 			if hour != lastHour && now.Minute() < 1 {
-				positions := trader.GetPositionsCopy()
+				positions := trader.ReadSnapshot()
 				notifier.SendTradeSummary(positions, now.Format("2006-01-02 15:04"))
 				lastHour = hour
 			}

trader.go

@@ -89,6 +89,26 @@ func (t *Trader) GetPositionsCopy() []ArbPosition {
 	return r
 }
 
+// RefreshSnapshot takes a trading-lock snapshot of open positions for display use.
+// Call this after each Tick() from the main loop — never during a trading operation.
+// The display reads from this snapshot without blocking trading.
+func (t *Trader) RefreshSnapshot() {
+	copy := t.GetPositionsCopy() // acquires t.mu briefly (not held during Tick call)
+	t.snapMu.Lock()
+	t.positionsSnapshot = copy
+	t.snapMu.Unlock()
+}
+
+// ReadSnapshot returns a copy of the last display snapshot — never locks t.mu.
+// Safe to call from any goroutine without impacting trading latency.
+func (t *Trader) ReadSnapshot() []ArbPosition {
+	t.snapMu.RLock()
+	defer t.snapMu.RUnlock()
+	r := make([]ArbPosition, len(t.positionsSnapshot))
+	copy(r, t.positionsSnapshot)
+	return r
+}
+
 // Trader handles scalable arbitrage between Bitget and HyperLiquid.
 type Trader struct {
 	cfg         *Config
@@ -102,6 +122,10 @@ type Trader struct {
 	closedTrades  []TradeRecord // history of closed trades
 
 	OnTradeEvent func(event string, data interface{}) // P3-4: real-time SSE push
+
+	// Decoupled snapshot for display — snapMu never contended by trading path
+	snapMu            sync.RWMutex
+	positionsSnapshot []ArbPosition
 }
 
 // TradeRecord stores a finalized trade for stats tracking.