Reviving an ancient Google (Asus) Nexus 7 [2012] (WiFi) (“grouper”) tablet

Nexus 7 [2012] running CyanogenMod 12.1 (Android 5.1.1) I’ve had this thing for more than a decade. Stopped using it when it updated from Android 4.x to 5.x and became unusably sluggish. At one point, I evidently unlocked it and installed Linux (LineageOS probably) onto it, but that wasn’t really usable on the 7" screen either, so it sat. I tried a couple of times half-heartedly to restore it using the built-in utilities, but never got anywhere and wasn’t honestly that interested, so it sat in a pile ready to be e-waste recycled. (The Fire tablets I’ve picked up over the years are going that route though, except for the one I’ve used semi-regularly with its “waterproof” housing, as they don’t seem to recharge and won’t turn on. Meh. OTOH they were disposable-cheap. But I digress.) I was stuck waiting to be called via remote court this morning (75 minutes) and, inspired by a Facebook conversation I’d had with a friend who’s also a bit of a geek, I decided to see if I could breath s...