fix(html): snapshot responsive variants

Co-Authored-By: Virgil <virgil@lethean.io>

responsive.go

@@ -189,6 +189,9 @@ func (r *Responsive) Variant(name string, layout *Layout) *Responsive {
 	if r == nil {
 		return nil
 	}
+	if layout != nil {
+		layout = layout.Clone()
+	}
 	r.variants = append(r.variants, responsiveVariant{name: name, layout: layout})
 	return r
 }

responsive_test.go

@@ -84,6 +84,22 @@ func TestResponsive_CloneReturnsIndependentCopy(t *testing.T) {
 	}
 }
 
+func TestResponsive_VariantClonesLayoutInput(t *testing.T) {
+	layout := NewLayout("C").C(Raw("original"))
+	responsive := NewResponsive().Variant("desktop", layout)
+
+	layout.C(Raw("mutated"))
+
+	got := responsive.Render(NewContext())
+
+	if !strings.Contains(got, "original") {
+		t.Fatalf("Variant should snapshot the layout at insertion time, got:\n%s", got)
+	}
+	if strings.Contains(got, "mutated") {
+		t.Fatalf("Variant should not share later layout mutations, got:\n%s", got)
+	}
+}
+
 func TestResponsive_NestedPaths(t *testing.T) {
 	ctx := NewContext()
 	inner := NewLayout("HCF").H(Raw("ih")).C(Raw("ic")).F(Raw("if"))