provision

Pushes the key to a backend as soon as a player lands on it.

Why the proxy pushes instead of answering a request: a backend can only speak to the proxy by sending a clientbound plugin message through a player, and Velocity refuses to forward — or raise an event for — any non- minecraft: channel the player's client has not itself registered (canForwardPluginMessage consults the client's known channels on 1.13+). A vanilla client never registers this channel, so a backend request is dropped before any plugin sees it. Verified empirically: a catch-all handler logging every plugin message on every channel never fired once.

The proxy→backend direction has no such gate: it writes straight to the backend connection. That connection already exists in every topology, including the normal case where proxy and backends are on different machines, so nothing new is exposed on the wire.