More fixes for fenrir's self-voice and notification system. Make sure proper sockets can be accessed.

docs/user.txt

@@ -731,10 +731,15 @@ account; console self-voicing also allows an account logged into the
 active console.
 
 Notifications use the same routing and command authorization as
-self-voicing. A detached notifier with an outdated WINDOWID may fail to
-identify a reader. Target the intended private socket in that case and
-check returned errors; successful delivery returns an empty reply. Do
-not select an arbitrary socket when several readers are running.
+self-voicing. For GNU Screen callers, Fenrir finds the session’s current
+attached reader instead of relying on the server’s original WINDOWID.
+Detached Screen sessions and sessions attached to multiple readers
+return a routing error. This requires the updated Fenrir binary in the
+instance owning the shared socket too. Other detached notifiers with
+outdated terminal identities may still fail to identify a reader. Target
+the intended private socket and check returned errors; successful
+delivery returns an empty reply. Do not select an arbitrary socket when
+several readers are running.
 
 Command-line options