diff --git a/internal/builder/mirror.go b/internal/builder/mirror.go
index 3a5b4db..83307fe 100644
--- a/internal/builder/mirror.go
+++ b/internal/builder/mirror.go
@@ -180,6 +180,20 @@ func (r Registry) MirrorImage(ctx context.Context, from, repository string) (str
 	if err != nil {
 		return "", err
 	}
+	// **Already held is already mirrored.** A base is named by digest, and a digest this registry
+	// holds under the module's repository is the same bytes whatever upstream would say — so
+	// upstream is not asked. Asked every build, the public hub's anonymous pull limit was reached
+	// on the first merge that rebuilt a whole catalogue (2026-09-28), and every module whose base
+	// lives there failed on a copy it did not need.
+	if strings.HasPrefix(where.reference, "sha256:") {
+		held, err := r.has(ctx, "http://"+r.Address+"/v2/"+repository+"/manifests/"+where.reference)
+		if err != nil {
+			return "", fmt.Errorf("asking %s whether it holds %s: %w", r.Address, from, err)
+		}
+		if held {
+			return r.Address + "/" + repository + "@" + where.reference, nil
+		}
+	}
 	src := &source{client: r.client()}
 	digest, err := r.copyManifest(ctx, src, where, where.reference, repository)
 	if err != nil {
diff --git a/internal/builder/mirror_test.go b/internal/builder/mirror_test.go
index 6a2749c..7f8adbd 100644
--- a/internal/builder/mirror_test.go
+++ b/internal/builder/mirror_test.go
@@ -103,6 +103,12 @@ func (m *theMeshsRegistry) handler() http.Handler {
 		m.mu.Lock()
 		defer m.mu.Unlock()
 		switch {
+		case r.Method == http.MethodHead && strings.Contains(r.URL.Path, "/manifests/"):
+			if _, ok := m.manifests[r.URL.Path[strings.LastIndex(r.URL.Path, "/")+1:]]; ok {
+				w.WriteHeader(http.StatusOK)
+			} else {
+				w.WriteHeader(http.StatusNotFound)
+			}
 		case r.Method == http.MethodHead && strings.Contains(r.URL.Path, "/blobs/"):
 			if _, ok := m.blobs[r.URL.Path[strings.LastIndex(r.URL.Path, "/")+1:]]; ok {
 				w.WriteHeader(http.StatusOK)
@@ -219,3 +225,27 @@ func TestATagBeforeTheDigestIsNotPartOfTheRepository(t *testing.T) {
 		t.Fatalf("got %+v", got)
 	}
 }
+
+// A base this registry already holds by digest is not asked of upstream at all: the public hub
+// limits anonymous pulls, and a catalogue rebuilt on one merge asked it once per module.
+func TestABaseAlreadyHeldIsNotAskedOfUpstream(t *testing.T) {
+	src, indexDigest, _ := anUpstreamRegistry(t)
+	dst := &theMeshsRegistry{blobs: map[string][]byte{}, manifests: map[string][]byte{}}
+	dstServer := httptest.NewServer(dst.handler())
+	defer dstServer.Close()
+	address := strings.TrimPrefix(dstServer.URL, "http://")
+	r := Registry{Address: address, HTTP: src.Client()}
+	host := strings.TrimPrefix(src.URL, "http://")
+	if _, err := r.MirrorImage(context.Background(), host+"/library/thing:latest", "hello-web/server"); err != nil {
+		t.Fatal(err)
+	}
+	// Upstream gone: the pinned base is answered from what the mesh holds.
+	src.Close()
+	reference, err := r.MirrorImage(context.Background(), host+"/library/thing@"+indexDigest, "hello-web/server")
+	if err != nil {
+		t.Fatalf("a base the registry holds was asked of an upstream that is gone: %v", err)
+	}
+	if reference != address+"/hello-web/server@"+indexDigest {
+		t.Fatalf("pinned as %q", reference)
+	}
+}