feat: actual exchange fees for entry orders

- BitgetTrade: added GetTradeFee() queries /mix/order/fills
- HyperLiquidTrade: added GetTradeFee() parses MarketOpen response
- trader.placeOrder() now returns (errMsg, actualFeeUSD)
- executeEntry uses actual fee from exchange, falls back to estimate

exchange/hyperliquid_trade.go

@@ -83,6 +83,7 @@ func (h *HyperLiquidTrade) IsConfigured() bool {
 	return h.configured
 }
 
+// PlaceMarketOrder places a market order and returns the raw JSON response.
 func (h *HyperLiquidTrade) PlaceMarketOrder(coin, side, sz string) (string, error) {
 	if !h.configured {
 		return "", fmt.Errorf("HL not configured")
@@ -120,6 +121,33 @@ func (h *HyperLiquidTrade) PlaceMarketOrder(coin, side, sz string) (string, erro
 	return string(respJSON), nil
 }
 
+// GetTradeFee parses the MarketOpen JSON response to extract filled size and
+// estimates the actual fee from the exchange taker rate.
+func (h *HyperLiquidTrade) GetTradeFee(orderResponseJSON string, takerFeePct float64) (feeUSD float64, err error) {
+	var resp struct {
+		Statuses []struct {
+			Filled *struct {
+				TotalSz string `json:"totalSz"`
+				AvgPx   string `json:"avgPx"`
+			} `json:"filled,omitempty"`
+			Error *string `json:"error,omitempty"`
+		} `json:"statuses"`
+	}
+	if err := json.Unmarshal([]byte(orderResponseJSON), &resp); err != nil {
+		return 0, fmt.Errorf("parse order response: %w", err)
+	}
+	for _, st := range resp.Statuses {
+		if st.Filled != nil {
+			sz, _ := strconv.ParseFloat(st.Filled.TotalSz, 64)
+			px, _ := strconv.ParseFloat(st.Filled.AvgPx, 64)
+			if sz > 0 && px > 0 {
+				return sz * px * takerFeePct / 100, nil
+			}
+		}
+	}
+	return 0, fmt.Errorf("no filled status in response")
+}
+
 func (h *HyperLiquidTrade) GetBalance() (float64, error) {
 	if !h.configured {
 		return 0, fmt.Errorf("HL not configured")