cmd/mbf: shallow by default

This is going to be used most of the time, with --deep only useful for fetching bootstrap artifacts.

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

cmd/mbf/cache.go

@@ -28,6 +28,8 @@ type cache struct {
 	idle bool
 	// Unset [pkg.CSuppressInit].
 	verboseInit bool
+	// Unset [pkg.CExternShallow].
+	deep bool
 	// Loaded artifact of [rosa.QEMU].
 	qemu pkg.Artifact
 
@@ -57,6 +59,9 @@ func (cache *cache) open() (err error) {
 	if !cache.verboseInit {
 		flags |= pkg.CSuppressInit
 	}
+	if !cache.deep {
+		flags |= pkg.CExternShallow
+	}
 
 	done := make(chan struct{})
 	defer close(done)