Function resolve_session_in 

pub fn resolve_session_in(
    explicit: Option<String>,
    provider: &str,
    provider_pid: u32,
    cmdline: impl Fn(u32) -> Vec<String>,
    accounts_base: Option<&Path>,
) -> Option<String>

resolve_session with the node’s saved adoptions: when the provider has exactly one adopted session, an attach with no session of its own is that session (any number of reloads, any time after the adoption, across node restarts). This keeps adopt and attach on one account (attach-<provider>-<session>).