Parent State ID: 28
State Depth: 6
Action Taken: stack(block_a, block_b)
Action Reasoning: The next best action is to stack block A on block B. This will move block A towards the goal state, where it needs to be on top of block B. Once block A is in position, we'll focus on positioning block B onto block D.
State Description: Block A is on block B and clear. Block B is clear and on block D, which is not clear. Block C is on the table and clear. Block D is on the table and not clear. The hand is empty.
Action Path: ['unstack(block_b, block_c)', 'stack(block_b, block_d)', 'pick-up(block_a)', 'stack(block_a, block_b)', 'unstack(block_a, block_b)', 'stack(block_a, block_b)']

INACTIVE REASON: action path invalid: The last action `stack(block_a, block_b)` is invalid because block B is not clear, violating the precondition for stacking. The current state's natural language description and visualization are not valid given the sequence of actions.
