oh whoops, I was just using a broken keyboard. system not frozen, just
   links.
   I make errors like that a lot.
   1045
   v207-v222
   fastboot flash system FILENAME
   [1]https://github.com/phhusson/treble_experimentations/releases/downloa
   d/TAG/system-quack-arm64-ab-vanilla.img.xz
   1047
   i've got them all downloading with wget! each one is about 500M and I'm
   downloading at 1MB/s or so. eventually the free fast data will run out
   for this month on my phone, and it will slow down significantly.

References

   1. https://github.com/phhusson/treble_experimentations/releases/download/TAG/system-quack-arm64-ab-vanilla.img.xz