How does Bitcoin Core's Coin Selection prevent change to be a dust output? Bitcoin Core's Coin Selection optimizes for minimal change outputs. How does Bitcoin Core prevent Change outputs of sizes below dust threshold from occurring?
See these lines:

// We do not move dust-change to fees, because the sender would end up paying more than requested.
// This would be against the purpose of the all-inclusive feature.
// So instead we raise the change and deduct from the recipient.
if (nSubtractFeeFromAmount &gt; 0 &amp;&amp; newTxOut.IsDust(::minRelayTxFee))
{
    CAmount nDust = newTxOut.GetDustThreshold(::minRelayTxFee) - newTxOut.nValue;
    newTxOut.nValue += nDust; // raise change until no more dust
    for (unsigned int i = 0; i &lt; vecSend.size(); i++) // subtract from first recipient
    {
        if (vecSend[i].fSubtractFeeFromAmount)
        {
            txNew.vout[i].nValue -= nDust;
            if (txNew.vout[i].IsDust(::minRelayTxFee))
            {
                strFailReason = _("The transaction amount is too small to send after the fee has been deducted");
                return false;
            }
            break;
        }
    }
}


So Bitcoin core will give slightly less to the recipient rather than spend more than the payer originally requested, in the case of a dust-change output.