If anyone is interested - I "vibe-coded" a version of Pathom3 for Jank. I've been testing for some simple cases and it works (I had to also vibe-code a port of Promesa too).
I tried to keep the same namespaces/function names so as soon as Jank supports some stuff that Pathom depends on (for example, spec and guardrails) we can upstream the changes.
The code is here: https://github.com/mauricioszabo/Yakusoku, it's kind of a monorepo (I started by porting promesa, that's why the repo's name means "Promise" in Japanese). All the Pathom things are under pathim namespace