TIL: You can have a reference to an unreachable commit in a `go.mod` file and get no warnings or errors in the build process. tl;dr: The build will work until that commit gets GC'd at some point in the future.
Cool story, #golang. Yes, package management is hard. But, come on. You should get a warning from `go mod tidy` if you're pointing to a GC eligible commit. Even if you're vendoring, it's important to know you may be incompatible with upstream in a way that's likely _NOT_ documented since the commit was never merged.