Those are excellent questions, answers to which are indeed missing from my summary of spec changes!
In my opinion, the client should send a PUT with the intended Content-Length and what the server would assume to be the entire file. Then, if for whatever reason the server doesn’t receive that amount of bytes (and the reason can be that the client just doesn’t want to send it at once), it needs to wait for the client to finish the upload until the file is considered complete and thus appears in directory listings and such.
As the same version of a file should never be uploaded by two different clients at the same time, only the uploading client has to know about the partial file’s existence. Which it does, because it needs to keep track of what it sent successfully, until the upload is complete.
Expiring the partially uploaded file is actually specified in the Tus Expiration extension. So the question is if we want to allow one or more extensions from the start or not.