cmux shows only the last opened file when several are passed

cmux open a.png b.png --pane <pane> opens each file as a tab and leaves the last one selected, with no visible sign to the user of the earlier tabs. A student looking at a two-page exam problem saw only the second page and thought the rest was missing. For multi-page content, stitch the relevant crops into one image first, for example with numpy vstack and matplotlib imsave after pdftoppm. Crop by page proportions and check the result by viewing it.