if edit the file like project.clj, will it process the whole buffer?

Yes, it will process the whole buffer, but it will only make the minimal set of diffs to the buffer required.

I’ve been thinking about a change to only process individual top-level forms, but I haven’t done that yet.

There’s also the potential to only process as far as required to ensure that all changes have been taken into account, now that we know where the changes happen, but I haven’t looked into that either.