An undeclared COPY --from is refused; an undeclared FROM is said, not yet refused

The mesh's own images start FROM a public base — the control plane's, the builder's,
the tool runtime's — and refusing those refuses genesis. They declare their bases
next; until then the base is named every build, with the remedy.

internal/builder/standing_on_test.go

@@ -120,12 +120,16 @@ FROM scratch
 COPY --from=vendor/tool:latest /tool /tool
 FROM golang:1.25-alpine AS go
 `
-	got := undeclaredFetches(recipe, map[string]bool{"RUNTIME_BASE": true})
-	want := []string{"${MC_BASE} (a build argument the manifest does not declare)", "vendor/tool:latest", "golang:1.25-alpine"}
-	if strings.Join(got, "|") != strings.Join(want, "|") {
-		t.Fatalf("got %v, want %v", got, want)
+	bases, copies := undeclaredFetches(recipe, map[string]bool{"RUNTIME_BASE": true})
+	if strings.Join(copies, "|") != "${MC_BASE} (a build argument the manifest does not declare)|vendor/tool:latest" {
+		t.Fatalf("copies out of undeclared images: %v", copies)
 	}
-	if got := undeclaredFetches(recipe, map[string]bool{"RUNTIME_BASE": true, "MC_BASE": true}); len(got) != 2 {
-		t.Fatalf("declared arguments are not fetches: %v", got)
+	// A base fetched on its own is named apart: the mesh's own images still start FROM one, so
+	// it is said rather than refused until they declare theirs.
+	if strings.Join(bases, "|") != "golang:1.25-alpine" {
+		t.Fatalf("undeclared bases: %v", bases)
+	}
+	if _, copies := undeclaredFetches(recipe, map[string]bool{"RUNTIME_BASE": true, "MC_BASE": true}); len(copies) != 1 {
+		t.Fatalf("declared arguments are not fetches: %v", copies)
 	}
 }