 Solution

Inside the supplied MainFrame, after both buttons and the label are defined, add:The invariant is that clickCount equals the total number of handled click events from the two buttons. It starts at zero; each matching event increments it exactly once and refreshes the label. The buttons' existing self-listeners can still change their own text independently. Listening to both publishers is necessary: their listenTo(this) calls subscribe each button to itself, not the frame to both buttons. Updating the label is not another button click, so it does not recursively increment the counter. An arbitrary-precision integer keeps the count exact without a lifetime overflow bound.^[ref]

The supplied layout already contains the label, so no additional component is needed. Before any click it retains its initial zero-click message; afterwards it displays the cumulative count across both buttons.