Function close_pane 

async fn close_pane(
    state: &AppState,
    req: &UiRunCommandRequest,
    own_block_id: &str,
) -> Response

RunCommand pane:close: the pane named by target, closed the way ClosePane closes it (app_api::pane::close_pane_as). A pane the agent is in closes at once; another agent’s pane waits 15 s for its user to keep it, and the answer says so. The key itself closes the focused pane at once, with no undo, so the page never runs it for MuxAPI.