The supply gap is the second half of the floor. Credits only work if there are homes to spend them on; where homes are short, rents rise until the credits are gone. So the bodies that publish the floor measure also publish where floor housing is falling behind, read from one signal: the credit index rising faster than the cost of building.
When a gap opens, a public builder of last resort builds floor-standard homes in that region and rents or sells them at cost. Most floor housing is still built in the ordinary way. No zoning or land rule may block floor housing within reach; a rule that does is manufactured scarcity.
The public builder can borrow cheaply because floor credits give it a rent stream that cannot be seized or stopped.