Subtitle: Googling inevitably reveals that my problem is caused by a known bug triggered by doing [the exact combination of things I want to do]. I can fix it, or wait a few years until I don't want that combination of things anymore, using the kitchen timer until then.
https://healthchecks.io
I use the hosted version because the point of monitoring is that it alerts me when the rest of my stuff is down. You can self host it though.