libtmux::Connection::notification_fd

For a caller who owns their own event loop. Without it, integrating means a thread blocked in wait_for_notifications, a queue of their own, and a self-pipe to wake the loop — which is this descriptor, rebuilt by hand on top of the thread and queue this connection already has.

Do not read from it: readability is the signal and the byte is this connection's to consume. Drain with take_notifications, which clears it. A broken stream makes it readable too, so a poller learns of the failure rather than waiting for an answer that cannot come.

Valid until the connection is destroyed or moved from; -1 if the pipe could not be created.