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

docs/fenrir.1

@@ -1006,10 +1006,17 @@ self\-voicing also allows an account logged into the active console.
 .PP
 Notifications use the same routing and command authorization as
 self\-voicing.
-A detached notifier with an outdated \f[CR]WINDOWID\f[R] may fail to
-identify a reader.
-Target the intended private socket in that case and check returned
-errors; successful delivery returns an empty reply.
+For GNU Screen callers, Fenrir finds the session\(cqs current attached
+reader instead of relying on the server\(cqs original
+\f[CR]WINDOWID\f[R].
+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+Other detached notifiers with outdated terminal identities may still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.
 .SS Command\-line options
 Fenrir runs as \f[CR]fenrir [options]\f[R].