//! Lifetime guard for one lossless session observer.
/// Keeps one [`PreparedRun`](super::PreparedRun) agent-event tap registered.
///
/// Dropping this value waits for any callback already in flight, then prevents
/// every future invocation. Keep it alive for at least as long as the work
/// being observed; do not drop it while holding a resource the callback needs.
///
/// This is a Basis-owned opaque wrapper rather than Mentra's raw guard. That
/// keeps the public run contract stable.