refactor(trader): update SetMarginMode to avoid legacy endpoint and improve logging

trader/okx/trader_account.go

@@ -82,31 +82,14 @@ func (t *OKXTrader) GetBalance() (map[string]interface{}, error) {
 
 // SetMarginMode sets margin mode
 func (t *OKXTrader) SetMarginMode(symbol string, isCrossMargin bool) error {
-	instId := t.convertSymbol(symbol)
 	t.isCrossMargin = isCrossMargin
 	mgnMode := t.marginMode()
 
-	body := map[string]interface{}{
-		"instId":  instId,
-		"mgnMode": mgnMode,
-	}
-
-	_, err := t.doRequest("POST", "/api/v5/account/set-isolated-mode", body)
-	if err != nil {
-		// Ignore error if already in target mode
-		if strings.Contains(err.Error(), "already") {
-			logger.Infof("  ✓ %s margin mode is already %s", symbol, mgnMode)
-			return nil
-		}
-		// Cannot change when there are positions
-		if strings.Contains(err.Error(), "position") {
-			logger.Infof("  ⚠️ %s has positions, cannot change margin mode", symbol)
-			return nil
-		}
-		return err
-	}
-
-	logger.Infof("  ✓ %s margin mode set to %s", symbol, mgnMode)
+	// OKX V5 unified account applies cross/isolated per order via tdMode,
+	// while leverage uses mgnMode on /account/set-leverage.
+	// Persist the configured mode locally so subsequent leverage/order calls use it,
+	// instead of calling the legacy isolated-mode endpoint that returns 51000 errors.
+	logger.Infof("  ✓ %s margin mode configured as %s (applied via tdMode/mgnMode on subsequent requests)", symbol, mgnMode)
 	return nil
 }