- a download button in the header opens the web app's export dialog
(.drawio, .png, .svg, .drawio.svg), which the classic page had and the
shell lacked when it became the default
- the shell asks draw.io for the custom library menu (libraries=1), as
the classic page did; the web app keeps libraries=0
- the newest card no longer shows "Rendering preview" for good: the sync
takes the thumbnail of a diagram the server recovered from its file
(saved without pictures) while the canvas kept it, and of a write whose
picture was skipped because an edit came first, once the canvas shows
the write again
- e2e: the get_selection test covers a shape in a container the user
entered; a download test saves a .drawio file