Fixed bug in score computation with price improvement fees

Solves #6

Author: tamir-cow

circuit_breaker_validator/models.py

@@ -311,12 +311,13 @@ def reverse_protocol_fee(self, trade: OnchainTrade) -> OnchainTrade:
         """Reverse the price improvement-based protocol fee to get the pre-fee trade.
 
         This method calculates what the trade would have been before improvement fee was applied:
-        1. Calculate the price improvement compared to the reference quote
-        2. Calculate the price improvement fee based on price_improvement_factor
-        3. Calculate a maximum volume-based fee using price_improvement_max_volume_factor
-        4. Take the minimum of these two fees to determine the actual fee
-        5. For sell orders: Increase buy_amount by adding back the fee
-        6. For buy orders: Decrease sell_amount by removing the fee
+        1. Calculate the price improvement compared to the reference quote and limit price
+        2. Use the better of quote or limit price for fee calculation
+        3. Calculate the price improvement fee based on price_improvement_factor
+        4. Calculate a maximum volume-based fee using price_improvement_max_volume_factor
+        5. Take the minimum of these two fees to determine the actual fee
+        6. For sell orders: Increase buy_amount by adding back the fee
+        7. For buy orders: Decrease sell_amount by removing the fee
 
         The fee calculations use:
         - price_improvement_fee = price_improvement * price_improvement_factor /
@@ -328,7 +329,16 @@ def reverse_protocol_fee(self, trade: OnchainTrade) -> OnchainTrade:
         Returns a new trade object with the fee reversed.
         """
         new_trade = deepcopy(trade)
-        price_improvement = trade.price_improvement(self.quote)
+        
+        # Calculate price improvement compared to quote
+        quote_price_improvement = trade.price_improvement(self.quote)
+        
+        # Calculate price improvement compared to limit price (surplus)
+        limit_price_improvement = trade.surplus()
+        
+        # Use the better of quote or limit price for fee calculation
+        # "Better" means smaller improvement, as that results in a smaller fee
+        price_improvement = min(quote_price_improvement, limit_price_improvement)
         volume = trade.volume()
         price_improvement_fee = max(
             0,