staking for increase collateral

[gupadhyaya]

currently, the vaults have to bare the collateral themselves for securing the BTC Bridge for the amount of BTC that they facilitate the transfer for. in an over-collateralized system like BTC Bridge, this can be a huge burden on the vault providers. this feature will allow ONE holders to stake their ONE to any vault which can be utilized for increasing the collateral of the vault and hence allow bridging of more BTC. the delegators receive the ONE reward incentives that vaults currently receive after the deduction of 1-2% (subjected to discussion in the forum with vault runners) for vault fee.

[hashmesan]

Design:

Based on my understand, these are the core entry functions into the vault add/remove collateral

Vault Registry:
    function lockAdditionalCollateral() public payable
    function withdrawCollateral(uint256 amount) external

Keep existing functions for backward compatibility, and introduce two new functions:

    function lockAdditionalCollateralForVault(vaultId) public payable
    function withdrawCollateralFromVault(vaultId, uint256 amount) external

These would account for vaultId -> msg.sender (the staker) -> for the msg.value locked.

We'll keep track the vaultId -> msg.sender (stakers) with:

    // vault -> stakers -> amount
    mapping(address => mapping(address => uint256)) private vaultStakers;

The structure similar to ERC20 allowances

Likely to keep ICollateral intact to keep track of the entire total amount in vault.

Upgradability

Please advise on upgradability of contract. This impacts on how to think about how to store the data.

[apptreeso]

@hashmesan Good design.

I'd like to write it in detail.
The vault stakers will share the vault rewards and it will work in a way similar to the MasterChef.
The data structure for the vault staker will be like this.

struct VaultStaker {
   uint256 balance;   // staked amount
   uint256 accClaimableRewards;   // pending reward
   uint256 rewardDebt;   // reward debt
}

The relation between the vault and its stakers will be defined like this.

// Vault -> User -> VaultStaker
mapping(address => mapping(address => VaultStaker)) public vaultStakers;