Function task_decompose 

pub async fn task_decompose(
    registry: &Arc<dyn TaskRegistry>,
    agent_id: &str,
    args: Value,
) -> Result<Value, PeError>

Decompose a task into subtasks with optional dependencies.

Args: { task_id, subtasks: [{ title, description?, priority?, depends_on?: [indices] }] } Returns: { parent_id, subtask_ids: [...], dependencies_created }