Function earliest_cert2_height 

async fn earliest_cert2_height<State>(state: &State, height: u64) -> Option<u64>
where
    State: VersionedDataSource,
    for<'a> State::ReadOnly<'a>: NodeStorage<SeqTypes>,

The earliest stored cert2 height at or after height. Errors are treated as no cert2: this only chooses between proof strategies, and the chosen path will surface any persistent error.