Operating the gateway: logs, traces, health, and degraded mode

The first eight chapters of this series have been about building an Auth Gateway. This one is about living with one. A gateway in front of every authenticated request is a force multiplier — for both your platform and any oncall page. If something is broken, it's broken everywhere at once. So observability isn't a Chapter 9 thing. It's a Chapter 0 thing. We just describe it last because there's enough mechanism to talk about that you need the rest of the series first. This chapter covers the fou