Based on the terse conversation at https://github.com/actions/download-artifact/issues/3, it looks like download-artifact is not a solution to caching across invocations of workflows.
My use case is a project using Go, where I would like to preserve GOCACHE from one Workflow invocation to another. This particular project is taking about 11 minutes to run
go test -race ./.... If it could use the build cache from a previous run, I would expect it to take less than a minute, as many of the test results would be cached and most of the compilation results would be cached too.
Not being able to transfer GOCACHE between runs is a significant hindrance to adopting GitHub Actions.