(originally posted by @vkhq but taken out of original post in order to mark this as solution)
Immediately after posted this, I tried again, and it started excitedly shouting rainbows!
reflash it again via particle-cli: particle flash --usb tinker
set it up: particle setup
Since we only can mark a separate post as solution for a thread, I took out your edit and reposted it.
If you want you can repost your solution in your own name and I’ll remove this post not to take credit for your own found solution.