Function put_text_diffed 

pub fn put_text_diffed<P>(
    doc: &mut AutoCommit,
    obj: &ExId,
    key: P,
    new: &str,
) -> TextEdit
where
    P: Into<Prop>,

Creates the Text object on first use (inserting the whole value); subsequent calls splice only the diff.

put_object only fails here if obj was concurrently deleted (or retyped) by another collaborator between the read and the write; there is no longer a place to put the text, so this reports the no-op edit rather than panicking.