The distinct, non-empty owner tokens of the currently-connected listeners.
Each value is a session whose GET stream can receive a session-scoped
server->client request (e.g. ping), so a caller can probe every live
session in turn rather than blindly forwarding an empty token that matches no
session-scoped listener. The empty (unscoped / stateless / shared) token is
excluded, since that path is reached via the no-token ping/requestOnSession.
The distinct, non-empty owner tokens of the currently-connected listeners. Each value is a session whose GET stream can receive a session-scoped server->client request (e.g. ping), so a caller can probe every live session in turn rather than blindly forwarding an empty token that matches no session-scoped listener. The empty (unscoped / stateless / shared) token is excluded, since that path is reached via the no-token ping/requestOnSession.