[0] About 100%
[1] 54 hours spanning Monday through Wednesday.
[2] ^H absolutely most certainly did
[3] Turns out part of the car's A/C UI dynamically fetches JavaScript on startup and our outage stopped serving JS, so A/C module failed to load. The worker thread that spawns the rest of the car's functionality freezes if the A/C module fails to respond. I guess we never tested that, I mean our internal network is pretty reliable, you know?
[4] We moved the JavaScript to a CDN so that means 100% availability. Presumably eventually we'll rewrite the entire client stack anyway thus implicitly killing this horrible dependency.