resuming did last + 1 on the last stored key and taking did taken + 1, so a corrupted or hand-edited db with a key near u64::MAX panicked on open in debug and wrapped in release, handing out positions that sort below every stored row. relay seqs and time_us are also sent as i64. a stored position without room after it now fails the open, and a commit that would take a position past i64::MAX fails instead of wrapping.