immeas - emissions for null epochs are lost

[sherlock-admin]

immeas

high

emissions for null epochs are lost

Summary

Emissions are sent to the vaults upon epoch creation. If no one stakes in the vault during the epoch the emissions in that vault will be lost.

Vulnerability Detail

When creating an epoch for Carousel the owner has the choice to add emissions for that epoch, that are distributed to stakers:
https://github.com/sherlock-audit/2023-03-Y2K/blob/main/Earthquake/src/v2/Carousel/CarouselFactory.sol#L148-L152

These emissions are then locked to that epoch:
https://github.com/sherlock-audit/2023-03-Y2K/blob/main/Earthquake/src/v2/Carousel/Carousel.sol#L591-L597

If no one stakes in the vault during this epoch (null epoch) these emission tokens will be lost in the contract forever as there are no shares to split them with:
https://github.com/sherlock-audit/2023-03-Y2K/blob/main/Earthquake/src/v2/Carousel/Carousel.sol#L630-L636

Impact

All emission tokens for an epoch will be effectively burnt if there are no stakers during that epoch (null epoch).

Code Snippet

See above

Tool used

Manual Review

Recommendation

If finalTVL is 0 for an epoch (no stakers). Return all emissions for that epoch to treasury:
Add to Carousel.sol:

    function resolveEpoch(uint256 _id)
        external
        override(VaultV2)
    {
        super.resolveEpoch(_id);

        // null epoch, no stakers, hand back emissions
        if(finalTVL[_id] == 0) {
            emissionsToken.safeTransfer(treasury,emissions[_id]);
        }
    }

Duplicate of #122