Allow risk-based 永期 exits via premium multiple as well as base×k.

Settings UI picks 基数 or 权利金×n; sizing preview and control monitor follow.

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

backend/app/api/settings.py

@@ -524,10 +524,14 @@ async def put_strategy_settings(
         )
     ).strip().lower()
     if sizing_mode == "risk_based":
-        data["exit_mode"] = "fixed_usdt"
+        # 永期以损：允许 exit_mode=fixed_usdt（基数×k）或 premium_multiple（权利金×倍）
+        # 期期仍强制 fixed（目标由预算×盈亏比写入）
+        if hedge_mode == "option_option":
+            data["exit_mode"] = "fixed_usdt"
         data.pop("perp_qty_eth", None)
         data.pop("option_qty_eth", None)
-        data.pop("net_profit_target", None)
+        if str(data.get("exit_mode") or db.get_setting("exit_mode", "") or "").strip().lower() != "premium_multiple":
+            data.pop("net_profit_target", None)
         loss_mode = str(
             data.get(
                 "risk_loss_mode",