Function common_parent 

pub fn common_parent(entries: &[FileEntry]) -> String

The deepest directory containing every selected entry, “” at the volume root.

Selections are named relative to this, so picking several files out of one folder still yields bare names (what it always did) while a selection that spans folders keeps enough path to stay unique. Without it every root was named by archive_name() alone, so /a/notes.txt and /b/notes.txt both became notes.txt and the second silently replaced the first.