handle div by zero edge case in maxRedeem

src/PrizeVault.sol

@@ -856,6 +856,7 @@ contract PrizeVault is TwabERC20, Claimable, IERC4626, ILiquidationSource, Ownab
     }
 
     /// @notice Converts assets to shares with the given vault state and rounding direction.
+    /// @dev Returns zero if the vault is in a lossy state AND there are no more assets.
     /// @param _assets The assets to convert
     /// @param _totalAssets The total assets that the vault controls
     /// @param _totalDebt The total debt the vault owes
@@ -873,7 +874,7 @@ contract PrizeVault is TwabERC20, Claimable, IERC4626, ILiquidationSource, Ownab
             // If the vault controls less assets than what has been deposited a share will be worth a
             // proportional amount of the total assets. This can happen due to fees, slippage, or loss
             // of funds in the underlying yield vault.
-            return _assets.mulDiv(_totalDebt, _totalAssets, _rounding);
+            return _totalAssets == 0 ? 0 : _assets.mulDiv(_totalDebt, _totalAssets, _rounding);
         }
     }
 

test/unit/PrizeVault/PrizeVault.t.sol

@@ -405,6 +405,25 @@ contract PrizeVaultTest is UnitBaseSetup {
         assertEq(vault.maxRedeem(alice), 0);
     }
 
+    function testMaxRedeem_ReturnsZeroIfLossyAndNoTotalAssets() public {
+        // deposit some assets
+        underlyingAsset.mint(alice, 1e18);
+        vm.startPrank(alice);
+        underlyingAsset.approve(address(vault), 1e18);
+        vault.deposit(1e18, alice);
+        vm.stopPrank();
+
+        assertGt(vault.maxRedeem(alice), 0);
+
+        // yield vault loses all funds
+        underlyingAsset.burn(address(yieldVault), underlyingAsset.balanceOf(address(yieldVault)));
+        assertEq(underlyingAsset.balanceOf(address(yieldVault)), 0);
+        assertEq(underlyingAsset.balanceOf(address(vault)), 0);
+        assertEq(vault.totalPreciseAssets(), 0);
+
+        assertEq(vault.maxRedeem(alice), 0);
+    }
+
     /* ============ previewWithdraw ============ */
 
     function testPreviewWithdraw() public {