feat(config): load embedded defaults and merge optional overlay

internal/config/config_test.go

@@ -0,0 +1,60 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadDefaultsWhenNoOverlay(t *testing.T) {
+	dir := t.TempDir()
+	cfg, err := Load(filepath.Join(dir, "missing.yaml"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cfg.Version != 1 {
+		t.Errorf("version = %d", cfg.Version)
+	}
+	if len(cfg.ExtraPackages) != 0 {
+		t.Errorf("extra_packages = %v", cfg.ExtraPackages)
+	}
+}
+
+func TestLoadMergesOverlay(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overlay.yaml")
+	content := []byte(`
+version: 1
+extra_packages: [htop, ncdu]
+disabled_modules: [renode]
+theme_overrides:
+  starship: /tmp/mine.toml
+`)
+	if err := os.WriteFile(path, content, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	cfg, err := Load(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := cfg.ExtraPackages; len(got) != 2 || got[0] != "htop" || got[1] != "ncdu" {
+		t.Errorf("extra_packages = %v", got)
+	}
+	if len(cfg.DisabledModules) != 1 || cfg.DisabledModules[0] != "renode" {
+		t.Errorf("disabled_modules = %v", cfg.DisabledModules)
+	}
+	if cfg.ThemeOverrides["starship"] != "/tmp/mine.toml" {
+		t.Errorf("theme_overrides = %v", cfg.ThemeOverrides)
+	}
+}
+
+func TestLoadRejectsUnknownVersion(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "overlay.yaml")
+	if err := os.WriteFile(path, []byte("version: 99\n"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := Load(path); err == nil {
+		t.Fatal("expected version error")
+	}
+}