Watch a decision get made without a search

The link row says production cannot exceed the big-M constant times the setup switch. Demand pushes production up from below. Somewhere in between, the switch stops being a decision.

Try this. Put demand at zero and the switch is free. Raise it by one unit and the fraction lifts off the floor, rounding takes it to 1, and the search never gets asked. Then push demand past the big-M constant and watch the model become impossible.

The fainter line is the bound before rounding, the solid one after. Rounding a bound on a whole-number variable is the cheapest reasoning in the whole solver, and on this row it settles the variable outright.