"This doesn't seem to apply to the tooling. For example, `go get` has a new behavior since the introduction of modules.... Is that hypocritical as an idea because people use the `go` CLI for scripting and the behavior of it changed."
It does not apply to tooling. It is not hypocritical because it was never claimed that it applies to tooling. It has always been a promise about code.
That's not the question. The question is, what was promised, not what can you can you twist their promise into if you choose different definitions than they do. They have only ever promised that code written in Go 1.0 will be forwards-compatible, not that the build systems will all be the same.
When I promise my kid that I'm "taking them to the park" this weekend, they have no grounds to complain when I don't take them to a full-fledged amusement park just because "taking them to the park" would technically cover that too.
It does not apply to tooling. It is not hypocritical because it was never claimed that it applies to tooling. It has always been a promise about code.