Currently EOF is sent to the pty even when read-only mode is requested. This can cause trouble in attached tmux sessions, for example. Since the EOF typically used in shells as a shortcut exit, this can result in undesired disconnects.
When a rune stands over the buffer boundary, invalid UTF-8 bytes were
sent to the client. Now the logic checks if the tail of the buffer can
be decoded as a valid rune. When it's an invalid byte sequence, the logic
keeps it in the buffer and send it in the next loop with the following byte sequence.
