Function run_relay_bridge 

pub async fn run_relay_bridge(
    cfg: RelayBridgeConfig,
    cancel: CancellationToken,
) -> Result<()>

Run the relay bridge until cancel fires.

When node-id rotation is permitted (auto-mint mode) this is a supervisor: it keeps one live link and, on a scheduled cadence or an on-demand trigger, mints a fresh id, registers it ALONGSIDE the old one for a grace window (the relay binds both ids to the same pubkey, so A10 is preserved and clients mid-session on the old id keep working), waits for the new link to register, persists the new id atomically (so it reaches clients in-band on their next renewal), then retires the old link. With rotation off (or an operator-pinned id) it is just a single link.