A block sweeps across the screen. Tap to drop it. Misalign and overhang shears off — keep too-narrow stacks from collapsing. Stack as high as you can.
COLLAPSED
Foundation lost.
CONTROLS
Click / tap / Space — drop block.
Each placement keeps only the overlap with the floor below. Perfect alignment (within 5px) keeps the full width and stacks a combo bonus. Run ends if a block has nothing to land on.