internal/pkg: make checksum available to cure

This enables deduplication by value as implemented in execArtifact.

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

internal/pkg/testdata/main.go

@@ -21,7 +21,7 @@ func main() {
 	log.SetFlags(0)
 	log.SetPrefix("testtool: ")
 
-	var hostNet, layers bool
+	var hostNet, layers, promote bool
 	if len(os.Args) == 2 && os.Args[0] == "testtool" {
 		switch os.Args[1] {
 		case "net":
@@ -34,6 +34,10 @@ func main() {
 			log.SetPrefix("testtool(layers): ")
 			break
 
+		case "promote":
+			promote = true
+			log.SetPrefix("testtool(promote): ")
+
 		default:
 			log.Fatalf("Args: %q", os.Args)
 			return
@@ -46,7 +50,7 @@ func main() {
 	wantEnv := []string{"HAKUREI_TEST=1"}
 	if len(os.Environ()) == 2 {
 		overlayRoot = true
-		if !layers {
+		if !layers && !promote {
 			log.SetPrefix("testtool(overlay root): ")
 		}
 		wantEnv = []string{"HAKUREI_TEST=1", "HAKUREI_ROOT=1"}
@@ -208,6 +212,10 @@ func main() {
 		}
 	}
 
+	if promote {
+		ident = "O-6VjlIUxc4PYLf5v35uhIeL8kkYCbHYklqlmDjFPXe0m4j6GkUDg5qwTzBRESnf"
+	}
+
 	next() // testtool artifact
 
 	next()