Fix dist-to-breakeven as strike-to-equilibrium spread.

Chain and order panel now show expiry_be minus strike instead of index distance.

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

lib/options/options_pricing_lib.py

@@ -519,12 +519,19 @@ def close_breakeven_idx(
 
 
 def idx_distance_to_be(idx_px: float | None, be_px: float | None) -> float | None:
-    """指数距平衡点(正=指数需上涨才到平衡点)."""
+    """指数距平衡点(正=指数需上涨才到平衡点).用于平掉回本等随盘变化场景."""
     if idx_px is None or be_px is None:
         return None
     return round(float(be_px) - float(idx_px), 2)
 
 
+def strike_distance_to_be(strike: float | None, be_px: float | None) -> float | None:
+    """行权价与到期平衡的价差(平衡价 - 行权价).链上「距平衡」列用此值."""
+    if strike is None or be_px is None:
+        return None
+    return round(float(be_px) - float(strike), 2)
+
+
 def format_options_breakeven_line(
     *,
     expiry_be_px: float | None,