would working on https://github.com/pantsbuild/pants/pull/6891 today (rust/cargo ruleset) be at all useful for this?

Probably not directly 🙂 definitely an interesting background thing, but I don’t think it would directly address these problems

thanks! i'm thinking it would be helpful to canonicalize and robustify the result of the current caching discussion when we have arrived on a solution -- but after we've done that

Sounds good 🙂