internal/rosa: use self-hosted stage0

This removes the bootstrap dependency on Gentoo stage3 tarball.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/stage0.go

@@ -1,6 +1,11 @@
 package rosa
 
-import "hakurei.app/internal/pkg"
+import (
+	"runtime"
+	"sync"
+
+	"hakurei.app/internal/pkg"
+)
 
 func (t Toolchain) newStage0() pkg.Artifact {
 	musl, compilerRT, runtimes, clang := t.NewLLVM()
@@ -37,3 +42,32 @@ tar \
 `)
 }
 func init() { artifactsF[Stage0] = Toolchain.newStage0 }
+
+var (
+	// stage0 stores the tarball unpack artifact.
+	stage0 pkg.Artifact
+	// stage0Once is for lazy initialisation of stage0.
+	stage0Once sync.Once
+)
+
+// NewStage0 returns a stage0 distribution created from curing [Stage0].
+func NewStage0() pkg.Artifact {
+	stage0Once.Do(func() {
+		var seed string
+		switch runtime.GOARCH {
+		case "amd64":
+			seed = "tqM1Li15BJ-uFG8zU-XjgFxoN_kuzh1VxrSDVUVa0vGmo-NeWapSftH739sY8EAg"
+
+		default:
+			panic("unsupported target " + runtime.GOARCH)
+		}
+
+		stage0 = pkg.NewHTTPGetTar(
+			nil, "https://hakurei.app/seed/20260210/"+
+				"stage0-"+triplet()+".tar.bz2",
+			mustDecode(seed),
+			pkg.TarBzip2,
+		)
+	})
+	return stage0
+}