The test stage ran go mod download in its own layer, and go test left
Go's build cache in another. Exporting them took about 20 seconds of
every make test, and nothing reads either one afterwards.
Removing the build cache alone saved almost nothing, because the module
cache is the larger layer. So the download now runs in the same RUN as
go test, and go clean removes both caches once the tests pass. A failing
run still reruns with -v and exits 1.
Model: opus-5-5
sneak