<div>
    <p>How many idle agents to keep for this label at all times, including while nothing is queued.
    This is what makes them <i>hot</i> spares: they are paid for while idle so that the next build
    for the label starts without waiting for an instance to boot.</p>

    <p>It is also the floor the spare target decays to once the label goes quiet, so it is the
    standing cost of the label.</p>

    <p>0 lets the label scale all the way to nothing when it is idle. The first build after a quiet
    period still has to wait for an instance, but queueing it asks for a whole <i>Hot spare step</i>
    of agents there and then, so it starts on whichever of them comes up first and the builds behind
    it find the rest already waiting.</p>
</div>