Align hedge-plan perp contract precision with exchange and show TP/SL USDT PnL.

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

lib/hedge_plan/hedge_plan_calc_lib.py

@@ -69,6 +69,23 @@ def suggest_contracts_from_notional(
     return float(notional) / (float(entry) * float(contract_size))
 
 
+def floor_contracts_to_precision(contracts: float, decimals: int) -> float:
+    """按交易所张数精度向下取整,避免建议张数超过可用保证金."""
+    import math
+
+    raw = float(contracts or 0.0)
+    if raw <= 0:
+        return 0.0
+    try:
+        d = int(decimals)
+    except (TypeError, ValueError):
+        d = 0
+    if d <= 0:
+        return float(math.floor(raw + 1e-12))
+    scale = 10**d
+    return math.floor(raw * scale + 1e-12) / scale
+
+
 def build_perp_options_preview(
     *,
     direction: str,