pub fn refused_as_a_diagram(picked: &Path) -> Option<String>Expand description
Why a picked folder is not a diagram, or None where it is one.
The picker cannot filter folders by suffix, so this is where the choice
is judged: a diagram is a .bwx directory (or one someone renamed that
still holds a manifest). A lone .json document is not one and can never
be — it carries neither the revs nor the assets — so a folder full of them
is refused by name rather than opened into a session that would lose half
of itself.