Run Tailscale on a Heroku dyno.
This is intended to be run as a second/third/whatever buildpack for an app. At least, that's how I intend to use it - but I'm new to Heroku, and I favor an experimental approach to learning. so anything could happen.
Looks to be based on https://tailscale.com/kb/1107/heroku/.
Much appeciation to @kongmadai, and anyone else who wrote boilerplate so I don't have to. Also Tailscale is one of the most impressive projects out there right now, amd not just for what it does. A constant stream of updates and new features, really high quality code, thorough documentation, solid relationship between devs and community, a generous free tier...the list goes on. The people on that project are kind of making the rest of us look bad.