Long story short -- I was dumb and attempted to install armbian to the emmc on my s905 box because reading is hard.
So now I have a box that won't boot. I have the original firmware image, which will restore the boot partition (from what I understand, this is the problem with s905s now, though I distinctly remember running debian on this via the emmc in the past, but that's a tangent that doesn't matter if I can't get it to boot anything).
I have it connected via usb/ttl uart and can send commands. But what commands do I send? The amlogic usb burning tool doesn't see this box via usb, but if I run `usb start` it finds one usb device (presumably my pc).
This is what the box reports during boot: https://pastebin.com/DPXdSeLz