federatedPlayer
The player role of the federatedCore placement — the seating a federated player passes to gameNodeRoom.
A federated player is never one of the core voters and owns no attachment directory: it rides as a learner behind its one server and always forwards to that server, so the (player) -> server attachment lookup a server uses to pick a core hop is never consulted on a player. This is exactly federatedCore(core) { null } — a named constructor so a player never has to spell (or accidentally omit) the always-null lookup, and the { null } footgun stays off the player-facing surface. A server still bootstraps with federatedCore, which requires the live lookup.
Parameters
The NodeIds of the server core — every one of them votes in this game. The player is never in it. Must be non-empty.