✨ Install Go latest + full toolchain at image build time ✨

Go is now downloaded from go.dev/dl at build time (always latest stable,
never pinned). All tools are baked into /usr/local/bin so they are on
PATH out of the box. Module cache and build cache live in the volumed
GOPATH (/usr/local/share/go) so they persist across container restarts
without re-downloading.
- Dockerfile: add /usr/local/go/bin to PATH in both build and final stage
- rootfs/root/docker/setup/05-custom.sh: full Go install + tool install
- detects arch (amd64/arm64/armv6l/386) via uname -m
- fetches latest stable version from go.dev/dl?mode=json via jq
- extracts to /usr/local/go; symlinks go+gofmt to /usr/local/bin
- installs with GOBIN=/usr/local/bin (baked into image, not in volume):
gopls, goimports, gofumpt, stringer, golangci-lint, staticcheck,
govulncheck, gotestsum, dlv, air, goreleaser, wire, mockgen (uber),
ko, protoc-gen-go, protoc-gen-go-grpc
- cleans modcache and build cache after install to keep layer lean
- rootfs/etc/profile.d/go.sh: add /usr/local/go/bin prepend so
interactive shells always find the Go distribution binaries first
Volume strategy:
/usr/local/share/go → GOPATH (module cache + build cache + user bins)
Mount a named volume or bind-mount here to avoid re-downloading modules:
docker run -v go-cache:/usr/local/share/go casjaysdevdocker/go

Dockerfile
rootfs/etc/profile.d/go.sh
rootfs/root/docker/setup/05-custom.sh

rootfs/etc/profile.d/go.sh

@@ -5,12 +5,20 @@
 # /data/go are symlinks to that location, so any of them can be used
 # interchangeably and the data persists across container rebuilds when
 # the volume is named.
+#
+# The Go distribution itself lives at /usr/local/go (baked into the image,
+# not volumed). Tools installed at build time land in /usr/local/bin.
 
 export GOPATH="${GOPATH:-/usr/local/share/go}"
 export GOCACHE="${GOCACHE:-${GOPATH}/cache}"
 export CGO_ENABLED="${CGO_ENABLED:-0}"
 export GOTOOLCHAIN="${GOTOOLCHAIN:-auto}"
 
+case ":${PATH}:" in
+  *":/usr/local/go/bin:"*) ;;
+  *) export PATH="/usr/local/go/bin:${PATH}" ;;
+esac
+
 case ":${PATH}:" in
   *":${GOPATH}/bin:"*) ;;
   *) export PATH="${GOPATH}/bin:${PATH}" ;;