Struct DriveSession 

pub struct DriveSession { /* private fields */ }

A live Drive OAuth2 session: holds the refresh token and the current in-memory access token, refreshing on demand.

Uses tokio::sync::Mutex (not std::sync::Mutex) held across the refresh network call — mirrors crate::gmail::auth::GmailSession’s explicit single-flight-refresh design (issue #1465’s “concurrent callers don’t stampede” requirement): a second concurrent caller blocks on this mutex and, once unblocked, observes the already-refreshed token instead of issuing a second POST.