Function drive_plan 

async fn drive_plan(
    plan: Plan,
    client: RobonixSystemExecutorExecuteClient<Channel>,
    events_tx: Sender<ForestEvent>,
    forest_revision: Arc<AtomicU64>,
)

Drive one dispatched plan’s Execute stream to completion, forwarding node states for visualisation and collecting terminal results. Sends exactly one PlanDone when the stream ends. Runs as its own task so the supervisor loop never blocks on a single tree — concurrent trees form the forest.