It's really the other way around: we joined Fastly because we knew it's a place where we could do this kind of work in the open.

None of the code involved here existed a year ago, and none of it was somehow forced to be open source. (Also, the code in these two repositories is in many ways the most boring part of this solution. See this blog post for an excellent overview of the more interesting parts: https://bytecodealliance.org/articles/making-javascript-run-...)