Function build_user_graph 

pub(crate) fn build_user_graph(
    detail: &DiagnosticsRoomDetail,
    requested_user_id: &str,
) -> Option<Value>

Build the Grafana node graph payload for one user’s media paths in a room.

The graph shows the selected user’s outbound publications through their source media worker to every receiver, and their inbound subscriptions from the producer user through the producer and receiver workers. It is a diagnostics projection of the current routing snapshot, not a transport control API.