feat: limit EVM max gas refund to 150% of used gas

- Encourages more accurate gas estimation
- Previously, 100% of unused gas was refunded

core/state_transition.go

@@ -471,31 +471,39 @@ func (st *StateTransition) TransitionDb() (*ExecutionResult, error) {
 }
 
 func (st *StateTransition) refundGas(refundQuotient uint64) uint64 {
-	// Apply refund counter, capped to a refund quotient
-	refund := st.gasUsed() / refundQuotient
-	if refund > st.state.GetRefund() {
-		refund = st.state.GetRefund()
+	// Calculate state change refund
+	stateRefund := st.gasUsed() / refundQuotient
+	if stateRefund > st.state.GetRefund() {
+		stateRefund = st.state.GetRefund()
 	}
 
-	if st.evm.Config.Tracer != nil && st.evm.Config.Tracer.OnGasChange != nil && refund > 0 {
-		st.evm.Config.Tracer.OnGasChange(st.gasRemaining, st.gasRemaining+refund, tracing.GasChangeTxRefunds)
+	// Calculate the total refund (unused gas + state refund)
+	totalRefund := st.gasRemaining + stateRefund
+
+	// Calculate the maximum refund allowed (150% of gas used)
+	maxRefund := st.gasUsed()/2 + st.gasUsed()
+
+	// Ensure the refund does not exceed the maximum allowed
+	if totalRefund > maxRefund {
+		totalRefund = maxRefund
 	}
 
-	st.gasRemaining += refund
+	// Update gasRemaining
+	st.gasRemaining += stateRefund
 
-	// Return ETH for remaining gas, exchanged at the original rate.
-	remaining := new(big.Int).Mul(new(big.Int).SetUint64(st.gasRemaining), st.msg.GasPrice)
-	st.state.AddBalance(st.msg.From, remaining, tracing.BalanceIncreaseGasReturn)
+	// Return ETH for total refund, exchanged at the original rate.
+	totalRefundValue := new(big.Int).Mul(new(big.Int).SetUint64(totalRefund), st.msg.GasPrice)
+	st.state.AddBalance(st.msg.From, totalRefundValue, tracing.BalanceIncreaseGasReturn)
 
+	// Notify the tracer about the gas change
 	if st.evm.Config.Tracer != nil && st.evm.Config.Tracer.OnGasChange != nil && st.gasRemaining > 0 {
 		st.evm.Config.Tracer.OnGasChange(st.gasRemaining, 0, tracing.GasChangeTxLeftOverReturned)
 	}
 
-	// Also return remaining gas to the block gas counter so it is
-	// available for the next transaction.
+	// Update gas pool
 	st.gp.AddGas(st.gasRemaining)
 
-	return refund
+	return stateRefund
 }
 
 // gasUsed returns the amount of gas used up by the state transition.