Consider the following situation: user uploads a large file via a share extension (extension writes upload details into shared DB and initiates background transfer), then quickly realizes that's a wrong file, so he switches to containing app, opens up a list of uploads and hits "Cancel". Question is, how containing app is supposed to reliably cancel such transfer, given that only one process can access same NSURLSession at the time, a session is not disconnected until all tasks are complete (or connected process is terminated) and extension may not be terminated yet?