Fix batchHandleWithdrawals underflow

mainnet-contracts/src/PufferProtocol.sol

@@ -323,13 +323,19 @@ contract PufferProtocol is IPufferProtocol, AccessManagedUpgradeable, UUPSUpgrad
             // Get the burnAmount for the withdrawal at the current exchange rate
             uint256 burnAmount =
                 _getBondBurnAmount({ validatorInfo: validatorInfos[i], validatorBondAmount: bondAmount });
+            // Failsafe in extreme rare case validator balance falls under (32-bondAmount) ETH
+            if (burnAmount > bondAmount) {
+                burnAmount = bondAmount; // residual loss socialized to pufETH holders
+            }
+
             uint256 vtBurnAmount = _getVTBurnAmount($, bondWithdrawals[i].node, validatorInfos[i]);
 
             // Update the burnAmounts
             burnAmounts.pufETH += burnAmount;
             burnAmounts.vt += vtBurnAmount;
 
             // Store the withdrawal amount for that node operator
+            // Underflow is not possible because of the checks in the `_getBondBurnAmount` function and the fact that we are capping the burn amount to the bond amount
             // nosemgrep basic-arithmetic-underflow
             bondWithdrawals[i].pufETHAmount = (bondAmount - burnAmount);
 

mainnet-contracts/test/unit/PufferProtocol.t.sol

@@ -1250,6 +1250,35 @@ contract PufferProtocolTest is UnitTestHelper {
         assertApproxEqAbs(_getUnderlyingETHAmount(address(bob)), 1 ether, 1, "bob got back the bond");
     }
 
+    function test_batch_claim_underflow() public {
+        _registerAndProvisionNode(bytes32("alice"), PUFFER_MODULE_0, alice);
+
+        StoppedValidatorInfo memory aliceInfo = StoppedValidatorInfo({
+            module: NoRestakingModule,
+            moduleName: PUFFER_MODULE_0,
+            pufferModuleIndex: 0,
+            withdrawalAmount: 29 ether, // Withdrawal amount is less than 32 ETH - bond, but still shouldn't revert due to fix
+            startEpoch: 100,
+            endEpoch: _getEpochNumber(28 days, 100),
+            wasSlashed: false
+        });
+
+        StoppedValidatorInfo[] memory stopInfos = new StoppedValidatorInfo[](1);
+        stopInfos[0] = aliceInfo;
+
+        uint256 burnedAmount = pufferVault.convertToShares(1 ether); // 1 ETH to pufETH. This is the bond, the max that can be burned
+
+        vm.expectEmit(true, true, true, true);
+        emit IPufferProtocol.ValidatorExited(
+            _getPubKey(bytes32("alice")),
+            0,
+            PUFFER_MODULE_0,
+            burnedAmount,
+            _getVTBurnAmount(100, _getEpochNumber(28 days, 100))
+        );
+        pufferProtocol.batchHandleWithdrawals(stopInfos, _getHandleBatchWithdrawalMessage(stopInfos));
+    }
+
     // Batch claim of different amounts
     function test_different_amounts_batch_claim() public {
         // Buy and approve VT

mainnet-contracts/test/unit/Timelock.t.sol

@@ -18,6 +18,8 @@ contract TimelockTest is Test {
     stETHMock public stETH;
     Timelock public timelock;
 
+    address public constant BROADCASTER = 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266;
+
     function setUp() public {
         PufferDeployment memory deployment = new DeployPufETH().run();
 
@@ -33,6 +35,7 @@ contract TimelockTest is Test {
         vm.assume(caller != timelock.OPERATIONS_MULTISIG());
         vm.assume(caller != address(timelock));
         vm.assume(caller != address(accessManager));
+        vm.assume(caller != BROADCASTER);
 
         // Upgrades are forbidden
         (bool canCall, uint32 delay) =
@@ -236,10 +239,11 @@ contract TimelockTest is Test {
         assertTrue(!canCall, "should not be able to call");
     }
 
-    function test_pause_depositor_slectors(address caller) public {
+    function test_pause_depositor_selectors(address caller) public {
         vm.startPrank(timelock.pauserMultisig());
         vm.assume(caller != address(timelock));
         vm.assume(caller != address(accessManager));
+        vm.assume(caller != BROADCASTER);
 
         address[] memory targets = new address[](1);
         targets[0] = address(pufferDepositor);