Use trading account and USDC/USDT market price for sim convert.

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

lib/sim/register.py

@@ -140,12 +140,21 @@ def install_sim_trading(app: Flask, repo_root: str, app_module: Any = None) -> N
             amount = float(body.get("amount") or 0)
         except (TypeError, ValueError):
             return jsonify({"ok": False, "msg": "amount 无效"}), 400
-        result = SimWallets(get_db).convert(
-            from_ccy=str(body.get("from_ccy") or ""),
-            to_ccy=str(body.get("to_ccy") or ""),
-            amount=amount,
-            account=str(body.get("account") or "funding"),
-        )
+        from_ccy = str(body.get("from_ccy") or "USDT").strip().upper()
+        to_ccy = str(body.get("to_ccy") or "USDC").strip().upper()
+        if {from_ccy, to_ccy} != {"USDT", "USDC"}:
+            return jsonify({"ok": False, "msg": "仅支持 USDT↔USDC"}), 400
+        direction = "usdt_to_usdc" if from_ccy == "USDT" else "usdc_to_usdt"
+        account = str(body.get("account") or "trading")
+        ex = getattr(app_module, "exchange", None) or getattr(app_module, "exchange_options", None)
+        if ex is None:
+            return jsonify({"ok": False, "msg": "无公开行情 exchange"}), 500
+        try:
+            result = SimBroker(get_db).convert_usdt_usdc(
+                ex, direction=direction, amount=amount, account=account
+            )
+        except Exception as e:
+            return jsonify({"ok": False, "msg": str(e)}), 400
         if not result.get("ok"):
             return jsonify(result), 400
         return jsonify({**result, **_status_payload()})