libtmux::Session::select_next_window

Named for what they do rather than for what they return: next_window() would read as a question, and these change which window is active.

Relative navigation is tmux's to perform, not a caller's to compute. Next and previous wrap around the window list, and "last" means the previously selected window — state only the server holds, which a caller listing windows has no way to reconstruct.

Each fails when there is nowhere to go, as tmux does: a session with one window refuses all three rather than selecting the window already active.