[PR #37] p1-core: vBNB collateral path broken — redeem returns native BNB, IERC20.balanceOf reads 0

[obchain]

PR: #37 feat(contracts): full Aave + Venus + PancakeSwap liquidation flow
Commit: 54fe2bb
File: contracts/src/CharonLiquidator.sol lines 278-295

Problem: For vBNB collateral, IVToken.redeem(vBal) causes Venus vBNB contract to send raw native BNB via ETH transfer to caller. Code then immediately calls:

uint256 colBal = IERC20(p.collateralToken).balanceOf(address(this));

If p.collateralToken is native BNB sentinel (e.g. address(0) or 0xEeeee…), IERC20.balanceOf reverts or returns 0. Subsequent exactInputSingle receives amountIn = 0 and slippage guard (amountOutMinimum > 0) reverts. Every vBNB-collateral liquidation fails here.

Impact: vBNB collateral path — one of Venus's largest markets — non-functional at deployment. Silently skips profitable liquidation opportunities and reverts on-chain for any vBNB position.

Fix: After redeem(), check if seized collateral is vBNB; wrap received native BNB into WBNB before reading balanceOf:

if (p.collateralToken == WBNB) {
    IWBNB(WBNB).deposit{value: address(this).balance}();
}
uint256 colBal = IERC20(p.collateralToken).balanceOf(address(this));

Add IWBNB interface and WBNB immutable (BSC mainnet: 0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c). Existing receive() payable already accepts native BNB; wrap step must follow.

[obchain]

Fixed on feat/12-charon-liquidator-full in b189447.

• Added contracts/src/interfaces/IWETH.sol (deposit/withdraw) as a local minimal interface; no new external dependency.
• Hard-coded BSC mainnet VBNB = 0xA07c5b74C9B40447a954e1466938b865b6BBea36 and WBNB = 0xbb4CdB9CBd36B01bD1cBaEBF2De08d9173bc095c as internal constants.
• After redeem(vBal) in executeOperation, when p.collateralVToken == VBNB the contract now calls IWETH(WBNB).deposit{ value: address(this).balance }(), then continues through the same IERC20(p.collateralToken).balanceOf → approve → swap path as every other vToken.
• executeLiquidation requires callers that seize vBNB to pass collateralToken == WBNB — the swap leg must route through a real PCS V3 pool, and the post-swap balance check must read the correct token.
• Validated with forge build and forge fmt --check.