> I'm sorry, I probably miss too much background information here,
> because I don't really understand what is the issue you are describing
> here.  E.g., why is user intent important, when all you need is to
> keep buffer text synchronized between several sessions?

That’s the baseline for collaborative editing, there’s apparently
solution that satisfies this single property (convergence property)
but are extremely bad — e.g. the effect of some user input takes
no effect, or a trivial program displaying an empty buffer for 
every user. Actually if we only want this property there’s much
simpler way than CRDT/OT, e.g. let the server (or one client)
send the whole buffer periodically.

One example of diff not preserving user intent is:
suppose in the buffer there is
“one two one”
And users agree that this sentence should always end in “one”.
Now user A deleted the first two words “one two “
user B inserted “three” between the first “one” and “two”
However, the diff have no idea about users’ agreement
and what exactly user does (unless we get it from modification
hooks). For user A, the diff just see “one” after and assume
that A delete the suffix “two one”. The CRDT then does it job
correctly and gives final synchronization result “one three”.
Clearly, user intent is violated.