Have you considered replacing the three chair legs with a separate ladder object when they’re assembled? That is, in the action handler where the legs are assembled, swap out the three legs for a ladder object. Something like this:
action() {
"You snap the final leg into place, creating a makeshift ladder. ";
ladder.moveInto(brokenLegs.location);
brokenLegs.moveInto(nil);
}
Then, you can give ladder the appropriate vocabulary, description, action handlers, etc.