Missing fee-on-transfer accounting in _handleWrap leads to potential under-collateralization of wrapped tokens

In _handleWrap, the bridge mints wrapped tokens based on the nominal transfer amount without verifying how many original tokens were actually received:

IERC20(pair.originalToken).safeTransferFrom(
    wctx.user, address(this), recipient.amount - tokenFee
);
if (tokenFee > 0) {
    IERC20(pair.originalToken).safeTransferFrom(
        wctx.user, feeCollector, tokenFee
    );
}
WrappedToken(pair.wrappedToken).mint(
    wctx.prerotatedKeyHash, recipient.amount - tokenFee
);

If the original token applies a transfer tax (fee-on-transfer), the bridge receives fewer tokens than recipient.amount - tokenFee, but still mints the full nominal amount of wrapped tokens. Over time, this creates a collateral deficit: more wrapped tokens exist than the bridge holds in original tokens.

Token pair registration via registerKeyPairWithTransfer has no token-type validation or whitelist, so nothing prevents a fee-on-transfer token from being registered. This is particularly relevant on BSC, where fee-on-transfer tokens (SafeMoon-style) are prevalent.

If a fee-on-transfer token is registered as an original token, the bridge gradually becomes under-collateralized for that pair. Late unwrappers would find insufficient original tokens in the bridge to redeem their wrapped tokens.

Use balance-before/after accounting to mint only the actually received amount:

uint256 balBefore = IERC20(pair.originalToken)
    .balanceOf(address(this));
IERC20(pair.originalToken).safeTransferFrom(
    wctx.user, address(this), recipient.amount - tokenFee
);
uint256 actualReceived = IERC20(pair.originalToken)
    .balanceOf(address(this)) - balBefore;
WrappedToken(pair.wrappedToken).mint(
    wctx.prerotatedKeyHash, actualReceived
);

YadaCoin, Confirmed.

Zealynx, Fixed.