refactor: add burnableShares for epm storage

src/contracts/core/DelegationManager.sol

@@ -307,10 +307,9 @@ contract DelegationManager is
             sharesToDecrease: operatorSharesSlashed
         });
 
-        // NOTE: native ETH shares will be burned by a different mechanism in a future release
-        if (strategy != beaconChainETHStrategy) {
-            strategyManager.increaseBurnableShares(strategy, totalDepositSharesToBurn);
-        }
+        IShareManager shareManager = _getShareManager(strategy);
+        // NOTE: for beaconChainETHStrategy, increased burnable shares currently have no mechanism for burning
+        shareManager.increaseBurnableShares(strategy, totalDepositSharesToBurn);
     }
 
     /**

src/contracts/core/StrategyManager.sol

@@ -140,7 +140,7 @@ contract StrategyManager is
         strategy.withdraw(staker, token, shares);
     }
 
-    /// @inheritdoc IStrategyManager
+    /// @inheritdoc IShareManager
     function increaseBurnableShares(IStrategy strategy, uint256 addedSharesToBurn) external onlyDelegationManager {
         burnableShares[strategy] += addedSharesToBurn;
         emit BurnableSharesIncreased(strategy, addedSharesToBurn);

src/contracts/interfaces/IDelegationManager.sol

@@ -351,7 +351,7 @@ interface IDelegationManager is ISignatureUtils, IDelegationManagerErrors, IDele
 
     /**
      * @notice Decreases the operators shares in storage after a slash and increases the burnable shares by calling
-     * into the StrategyManager. Burnable shares for the beaconChainETHStrategy/EigenPodManager are specifically not handled.
+     * into either the StrategyManager or EigenPodManager (if the strategy is beaconChainETH).
      * @param operator The operator to decrease shares for
      * @param strategy The strategy to decrease shares for
      * @param prevMaxMagnitude the previous maxMagnitude of the operator

src/contracts/interfaces/IEigenPodManager.sol

@@ -54,6 +54,9 @@ interface IEigenPodManagerEvents {
     event BeaconChainSlashingFactorDecreased(
         address staker, uint64 prevBeaconChainSlashingFactor, uint64 newBeaconChainSlashingFactor
     );
+
+    /// @notice Emitted when an operator is slashed and shares to be burned are increased
+    event BurnableETHSharesIncreased(uint256 shares);
 }
 
 interface IEigenPodManagerTypes {
@@ -161,4 +164,7 @@ interface IEigenPodManager is
     function beaconChainSlashingFactor(
         address staker
     ) external view returns (uint64);
+
+    /// @notice Returns the accumulated amount of beacon chain ETH Strategy shares
+    function burnableETHShares() external view returns (uint256);
 }

src/contracts/interfaces/IShareManager.sol

@@ -37,4 +37,13 @@ interface IShareManager {
     /// @dev strategy must be beaconChainETH when talking to the EigenPodManager
     /// @dev returns 0 if the user has negative shares
     function stakerDepositShares(address user, IStrategy strategy) external view returns (uint256 depositShares);
+
+    /**
+     * @notice Increase the amount of burnable shares for a given Strategy. This is called by the DelegationManager
+     * when an operator is slashed in EigenLayer.
+     * @param strategy The strategy to burn shares in.
+     * @param addedSharesToBurn The amount of added shares to burn.
+     * @dev This function is only called by the DelegationManager when an operator is slashed.
+     */
+    function increaseBurnableShares(IStrategy strategy, uint256 addedSharesToBurn) external;
 }

src/contracts/interfaces/IStrategyManager.sol

@@ -114,16 +114,6 @@ interface IStrategyManager is IStrategyManagerErrors, IStrategyManagerEvents, IS
         bytes memory signature
     ) external returns (uint256 shares);
 
-    /**
-     * @notice Increases burnable Strategy shares for the given strategy when an operator is slashed.
-     * @notice Increase the amount of burnable shares for a given Strategy. This is called by the DelegationManager
-     * when an operator is slashed in EigenLayer. The shares can be burned in a separate transaction calling `burnShares`.
-     * @param strategy The strategy to burn shares in.
-     * @param addedSharesToBurn The amount of added shares to burn.
-     * @dev This function is only called by the DelegationManager when an operator is slashed.
-     */
-    function increaseBurnableShares(IStrategy strategy, uint256 addedSharesToBurn) external;
-
     /**
      * @notice Burns Strategy shares for the given strategy by calling into the strategy to transfer
      * to the default burn address.

src/contracts/pods/EigenPodManager.sol

@@ -219,6 +219,12 @@ contract EigenPodManager is
         }
     }
 
+    /// @inheritdoc IShareManager
+    function increaseBurnableShares(IStrategy, uint256 addedSharesToBurn) external onlyDelegationManager {
+        burnableETHShares += addedSharesToBurn;
+        emit BurnableETHSharesIncreased(addedSharesToBurn);
+    }
+
     // INTERNAL FUNCTIONS
 
     function _deployPod() internal returns (IEigenPod) {

src/contracts/pods/EigenPodManagerStorage.sol

@@ -78,6 +78,9 @@ abstract contract EigenPodManagerStorage is IEigenPodManager {
     /// Note: this is specifically updated when the staker's beacon chain balance decreases
     mapping(address staker => BeaconChainSlashingFactor) internal _beaconChainSlashingFactor;
 
+    /// @notice Returns the amount of `shares` that have been slashed on EigenLayer but not burned yet.
+    uint256 public burnableETHShares;
+
     constructor(IETHPOSDeposit _ethPOS, IBeacon _eigenPodBeacon, IDelegationManager _delegationManager) {
         ethPOS = _ethPOS;
         eigenPodBeacon = _eigenPodBeacon;
@@ -89,5 +92,5 @@ abstract contract EigenPodManagerStorage is IEigenPodManager {
      * variables without shifting down storage in the inheritance chain.
      * See https://docs.openzeppelin.com/contracts/4.x/upgradeable#storage_gaps
      */
-    uint256[43] private __gap;
+    uint256[42] private __gap;
 }

src/test/unit/EigenPodManagerUnit.t.sol

@@ -521,4 +521,48 @@ contract EigenPodManagerUnitTests_BeaconChainETHBalanceUpdateTests is EigenPodMa
         assertEq(eigenPodManager.podOwnerDepositShares(defaultStaker), int(sharesBefore), "Shares should not be adjusted");
         assertTrue(eigenPodManager.beaconChainSlashingFactor(defaultStaker) <= prevSlashingFactor, "bcsf should always decrease");
     }
-}
+}
+
+contract EigenPodManagerUnitTests_increaseBurnableShares is EigenPodManagerUnitTests {
+    function testFuzz_onlyDelegationManager(address invalidCaller) public filterFuzzedAddressInputs(invalidCaller) {
+        cheats.assume(invalidCaller != address(delegationManagerMock));
+        cheats.prank(invalidCaller);
+        cheats.expectRevert(IEigenPodManagerErrors.OnlyDelegationManager.selector);
+        eigenPodManager.increaseBurnableShares(beaconChainETHStrategy, 1 ether);
+    }
+
+    function testFuzz_singleDeposit(uint256 increasedBurnableShares) public {
+        cheats.expectEmit(true, true, true, true, address(eigenPodManager));
+        emit BurnableETHSharesIncreased(increasedBurnableShares);
+
+        cheats.prank(address(delegationManagerMock));
+        eigenPodManager.increaseBurnableShares(beaconChainETHStrategy, increasedBurnableShares);
+
+        assertEq(eigenPodManager.burnableETHShares(), increasedBurnableShares, "Burnable shares not updated correctly");
+    }
+
+    function testFuzz_existingDeposit(
+        uint256 existingBurnableShares,
+        uint256 increasedBurnableShares
+    ) public {
+        // prevent overflow
+        cheats.assume(existingBurnableShares < type(uint256).max - increasedBurnableShares);
+
+        cheats.expectEmit(true, true, true, true, address(eigenPodManager));
+        emit BurnableETHSharesIncreased(existingBurnableShares);
+        cheats.prank(address(delegationManagerMock));
+        eigenPodManager.increaseBurnableShares(beaconChainETHStrategy, existingBurnableShares);
+
+        assertEq(eigenPodManager.burnableETHShares(), existingBurnableShares, "Burnable shares not setup correctly");
+
+        cheats.expectEmit(true, true, true, true, address(eigenPodManager));
+        emit BurnableETHSharesIncreased(increasedBurnableShares);
+        cheats.prank(address(delegationManagerMock));
+        eigenPodManager.increaseBurnableShares(beaconChainETHStrategy, increasedBurnableShares);
+
+        assertEq(
+            eigenPodManager.burnableETHShares(),
+            existingBurnableShares + increasedBurnableShares, "Burnable shares not updated correctly"
+        );
+    }
+}