fix: OptimismPortal fuzz flakes (#11818)

OptimismPortal fuzz tests were flaking because the base fee would
increase so much that there wouldn't be enough gas to burn for the
user to be able to buy the gas that they want. Introduces an
additional assumption that will prevent the elasticity multiplier
and max change denominator from being such that the maximum
change to the base fee won't cause us to run out of gas.

packages/contracts-bedrock/test/L1/OptimismPortal.t.sol

@@ -1211,19 +1211,31 @@ contract OptimismPortalResourceFuzz_Test is CommonTest {
     {
         // Get the set system gas limit
         uint64 gasLimit = systemConfig.gasLimit();
+
         // Bound resource config
         _maxResourceLimit = uint32(bound(_maxResourceLimit, 21000, MAX_GAS_LIMIT / 8));
         _gasLimit = uint64(bound(_gasLimit, 21000, _maxResourceLimit));
         _prevBaseFee = uint128(bound(_prevBaseFee, 0, 3 gwei));
+        _prevBoughtGas = uint64(bound(_prevBoughtGas, 0, _maxResourceLimit - _gasLimit));
+        _blockDiff = uint8(bound(_blockDiff, 0, 3));
+        _baseFeeMaxChangeDenominator = uint8(bound(_baseFeeMaxChangeDenominator, 2, type(uint8).max));
+        _elasticityMultiplier = uint8(bound(_elasticityMultiplier, 1, type(uint8).max));
+
         // Prevent values that would cause reverts
         vm.assume(gasLimit >= _gasLimit);
         vm.assume(_minimumBaseFee < _maximumBaseFee);
-        vm.assume(_baseFeeMaxChangeDenominator > 1);
         vm.assume(uint256(_maxResourceLimit) + uint256(_systemTxMaxGas) <= gasLimit);
-        vm.assume(_elasticityMultiplier > 0);
         vm.assume(((_maxResourceLimit / _elasticityMultiplier) * _elasticityMultiplier) == _maxResourceLimit);
-        _prevBoughtGas = uint64(bound(_prevBoughtGas, 0, _maxResourceLimit - _gasLimit));
-        _blockDiff = uint8(bound(_blockDiff, 0, 3));
+
+        // Base fee can increase quickly and mean that we can't buy the amount of gas we want.
+        // Here we add a VM assumption to bound the potential increase.
+        // Compute the maximum possible increase in base fee.
+        uint256 maxPercentIncrease = uint256(_elasticityMultiplier - 1) * 100 / uint256(_baseFeeMaxChangeDenominator);
+        // Assume that we have enough gas to burn.
+        // Compute the maximum amount of gas we'd need to burn.
+        // Assume we need 1/5 of our gas to do other stuff.
+        vm.assume(_prevBaseFee * maxPercentIncrease * _gasLimit / 100 < MAX_GAS_LIMIT * 4 / 5);
+
         // Pick a pseudorandom block number
         vm.roll(uint256(keccak256(abi.encode(_blockDiff))) % uint256(type(uint16).max) + uint256(_blockDiff));
 

packages/contracts-bedrock/test/L1/OptimismPortal2.t.sol

@@ -1464,19 +1464,32 @@ contract OptimismPortal2_ResourceFuzz_Test is CommonTest {
     {
         // Get the set system gas limit
         uint64 gasLimit = systemConfig.gasLimit();
+
         // Bound resource config
         _maxResourceLimit = uint32(bound(_maxResourceLimit, 21000, MAX_GAS_LIMIT / 8));
         _gasLimit = uint64(bound(_gasLimit, 21000, _maxResourceLimit));
         _prevBaseFee = uint128(bound(_prevBaseFee, 0, 3 gwei));
+        _prevBoughtGas = uint64(bound(_prevBoughtGas, 0, _maxResourceLimit - _gasLimit));
+        _blockDiff = uint8(bound(_blockDiff, 0, 3));
+        _baseFeeMaxChangeDenominator = uint8(bound(_baseFeeMaxChangeDenominator, 2, type(uint8).max));
+        _elasticityMultiplier = uint8(bound(_elasticityMultiplier, 1, type(uint8).max));
+
         // Prevent values that would cause reverts
         vm.assume(gasLimit >= _gasLimit);
         vm.assume(_minimumBaseFee < _maximumBaseFee);
         vm.assume(_baseFeeMaxChangeDenominator > 1);
         vm.assume(uint256(_maxResourceLimit) + uint256(_systemTxMaxGas) <= gasLimit);
-        vm.assume(_elasticityMultiplier > 0);
         vm.assume(((_maxResourceLimit / _elasticityMultiplier) * _elasticityMultiplier) == _maxResourceLimit);
-        _prevBoughtGas = uint64(bound(_prevBoughtGas, 0, _maxResourceLimit - _gasLimit));
-        _blockDiff = uint8(bound(_blockDiff, 0, 3));
+
+        // Base fee can increase quickly and mean that we can't buy the amount of gas we want.
+        // Here we add a VM assumption to bound the potential increase.
+        // Compute the maximum possible increase in base fee.
+        uint256 maxPercentIncrease = uint256(_elasticityMultiplier - 1) * 100 / uint256(_baseFeeMaxChangeDenominator);
+        // Assume that we have enough gas to burn.
+        // Compute the maximum amount of gas we'd need to burn.
+        // Assume we need 1/5 of our gas to do other stuff.
+        vm.assume(_prevBaseFee * maxPercentIncrease * _gasLimit / 100 < MAX_GAS_LIMIT * 4 / 5);
+
         // Pick a pseudorandom block number
         vm.roll(uint256(keccak256(abi.encode(_blockDiff))) % uint256(type(uint16).max) + uint256(_blockDiff));