@fadroma/ops/Build, @fadroma/scrt/ScrtBuild: Test that the correct source is being build

(Somehow...!)

Thanks to @Wiz1991 (after 3 weeks of me failing to see the issue, because of artifact/upload caching) I finally identified why non-HEAD builds were building from HEAD instead. (Shame on me for scripting the internal build logic in Bash, and for letting something so tiny but at the same time completely outside of my mental model of the situation elude me for so long in spite of repeated reports from downstream. :man_facepalming:)

How to prevent this in the future without putting a whole E2E build in CI? Maybe rewrite the build logic in TS where at least I know how to test it... Maybe (x2), this would involve embedding Node and Fadroma in the build container so that the build logic is shared between RawBuilder and DockerizedBuilder. :thinking: :thought_balloon:

Or maybe something with source checksums...