fix: 限制单笔报单最大50手，防止以损定仓计算出超大委托

Co-authored-by: Cursor <cursoragent@cursor.com>

install_trading.py

@@ -13,6 +13,7 @@ from kline_stream import sse_format
 from position_sizing import (
     MODE_FIXED,
     MODE_RISK,
+    DEFAULT_MAX_ORDER_LOTS,
     calc_lots_by_risk,
     calc_order_tick_metrics,
     normalize_sizing_mode,
@@ -540,11 +541,19 @@ def install_trading(app, *, login_required, require_nav, get_db, get_setting, se
             if sl <= 0:
                 conn.close()
                 return jsonify({"ok": False, "error": "以损定仓模式须填写止损价"}), 400
-            lots_calc, err = calc_lots_by_risk(price, sl, direction, _capital(conn), get_risk_percent(get_setting), sym)
+            lots_calc, err = calc_lots_by_risk(
+                price, sl, direction, _capital(conn), get_risk_percent(get_setting), sym,
+            )
             if err:
                 conn.close()
                 return jsonify({"ok": False, "error": err}), 400
             lots = lots_calc or lots
+        if lots > DEFAULT_MAX_ORDER_LOTS:
+            conn.close()
+            return jsonify({
+                "ok": False,
+                "error": f"单笔手数 {lots} 超过上限 {DEFAULT_MAX_ORDER_LOTS}，请加大止损距离或改固定手数",
+            }), 400
         try:
             result = execute_order(
                 conn,