#479 Performance: Inefficient last-key access with tuple(dict.keys())[-1]

engine/interpreters/inline_executor.py:690,893 Getting last key via tuple conversion is inefficient: ```python last_task_id = tuple(task_graph.keys())[-1] # Creates intermediate tuple ``` FIX: Use next(reversed(dict.keys())) which is O(1) vs O(n) for tuple creation.