Killing sessions by closing the descriptor

The input descriptor gets closed, but until all of them close, the message isn't really sent and it isn't enough to wake up a poll. Closing all of them requires the session to finish, but that doesn't happen until the poll wakes up. There is a way to clean up this flow, either using other signals, or changing the way the descriptors will react under this cases. Will elaborate more...

No file, test, or entry point is named. Start by locating the session cleanup, descriptor-closing, and poll-wakeup flow described in the issue. Done should mean sessions can be terminated without waiting for the poll to wake, with the behavior covered by an appropriate test.

Written by the indexing model from the issue text.