Draw Walls: Click to start, click to continue chaining. Right-click to stop.  |  Door / Window: Click to set start, click to set end on the same wall. Right-click to cancel.  |  Place Tool: Select from dropdown, then click canvas to place. Right-click to cancel.  |  Options: Hover a door to see controls. Triangle cycles swing, lock toggles lock.  |  Draw Duct: Click to start a duct run; each subsequent click adds a segment. Right-click ends the run. Scroll wheel on a placed duct segment changes diameter (4", 6", 8"). Click a Y-branch marker to toggle a branch direction.  |  Erase: Click a wall segment to remove it.  |  Remove: Click a door, window, or duct to remove it.  |  Right-click cancels the current action in any mode.