feat(theming): apply updates overlay theme_overrides.__active

internal/theming/theming_test.go

@@ -79,3 +79,41 @@ func TestApplyUnknownThemeErrors(t *testing.T) {
 		t.Fatal("want error on unknown theme")
 	}
 }
+
+func TestApplyUpdatesOverlayActive(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	if err := Apply(config.Config{}, "gruvbox"); err != nil {
+		t.Fatal(err)
+	}
+	data, err := os.ReadFile(filepath.Join(home, ".config", "archduino", "overlay.yaml"))
+	if err != nil {
+		t.Fatalf("overlay missing: %v", err)
+	}
+	if !strings.Contains(string(data), "__active: gruvbox") {
+		t.Fatalf("overlay missing active theme: %s", data)
+	}
+}
+
+func TestApplyPreservesOtherOverlayKeys(t *testing.T) {
+	home := t.TempDir()
+	t.Setenv("HOME", home)
+	op := filepath.Join(home, ".config", "archduino", "overlay.yaml")
+	if err := os.MkdirAll(filepath.Dir(op), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(op, []byte("version: 1\nextra_packages:\n  - foo\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := Apply(config.Config{}, "gruvbox"); err != nil {
+		t.Fatal(err)
+	}
+	data, _ := os.ReadFile(op)
+	if !strings.Contains(string(data), "- foo") {
+		t.Fatalf("extra_packages lost: %s", data)
+	}
+	if !strings.Contains(string(data), "__active: gruvbox") {
+		t.Fatalf("active theme missing after preserve: %s", data)
+	}
+}