Statics are ignored

I don’t know how to see “inside” the VM, since there is no Dockerfile.

Ah that’s true. This go-example doesn’t have a Dockerfile.
Strangely, there’s another go-example which does have a Dockerfile.
I don’t know which one Fly officially blesses, perhaps you could try the other one?

Anyway, as a general comment, you can use fly ssh · Fly Docs to get into the VM and have a look.

If I understand the [[statics]] concept correctly, these files should be served BEFORE my server receives the traffic.

Yeah that’s right.

But on disk, I have a /public folder with things like robots.txt and site.webmanifest.

You mean your local disk or have you attached a volume to the app?

If the content you want to serve via [[statics]] isn’t a part of the build process / Dockerfile itself, it won’t work.