fix: preserve package descriptions through snapshot export/import

Add MarshalJSON to PackageSnapshot that outputs rich object format
when descriptions exist, preserving them through export → re-import.
Also show descriptions in runCustomInstall display and fix
UnmarshalJSON to accept rich objects with casks/npm only.

Fixes #14

Author: fullstackjam

internal/installer/installer.go

@@ -115,15 +115,9 @@ func runCustomInstall(cfg *config.Config) error {
 	ui.Info(fmt.Sprintf("Estimated install time: ~%d min for %d packages", minutes, totalPackages))
 	fmt.Println()
 
-	if formulaeCount > 0 {
-		ui.Muted("  CLI tools: " + strings.Join(cfg.RemoteConfig.Packages.Names(), ", "))
-	}
-	if caskCount > 0 {
-		ui.Muted("  Apps:      " + strings.Join(cfg.RemoteConfig.Casks.Names(), ", "))
-	}
-	if npmCount > 0 {
-		ui.Muted("  npm:       " + strings.Join(cfg.RemoteConfig.Npm.Names(), ", "))
-	}
+	printPackageList("CLI tools", cfg.RemoteConfig.Packages)
+	printPackageList("Apps", cfg.RemoteConfig.Casks)
+	printPackageList("npm", cfg.RemoteConfig.Npm)
 	fmt.Println()
 
 	if !cfg.Silent && !cfg.DryRun {
@@ -1114,6 +1108,31 @@ func runUpdate(cfg *config.Config) error {
 	return nil
 }
 
+func printPackageList(label string, pkgs config.PackageEntryList) {
+	if len(pkgs) == 0 {
+		return
+	}
+	hasDesc := false
+	for _, pkg := range pkgs {
+		if pkg.Desc != "" {
+			hasDesc = true
+			break
+		}
+	}
+	if !hasDesc {
+		ui.Muted(fmt.Sprintf("  %s: %s", label, strings.Join(pkgs.Names(), ", ")))
+		return
+	}
+	ui.Muted(fmt.Sprintf("  %s:", label))
+	for _, pkg := range pkgs {
+		if pkg.Desc != "" {
+			ui.Muted(fmt.Sprintf("    %s — %s", pkg.Name, pkg.Desc))
+		} else {
+			ui.Muted(fmt.Sprintf("    %s", pkg.Name))
+		}
+	}
+}
+
 func estimateInstallMinutes(formulaeCount, caskCount, npmCount int) int {
 	totalSeconds := formulaeCount*estimatedSecondsPerFormula +
 		caskCount*estimatedSecondsPerCask +

internal/snapshot/snapshot.go

@@ -67,7 +67,8 @@ func (ps *PackageSnapshot) UnmarshalJSON(data []byte) error {
 			Desc string `json:"desc"`
 		} `json:"npm"`
 	}
-	if err := json.Unmarshal(data, &richObj); err == nil && len(richObj.Formulae) > 0 {
+	if err := json.Unmarshal(data, &richObj); err == nil &&
+		(len(richObj.Formulae) > 0 || len(richObj.Casks) > 0 || len(richObj.Npm) > 0) {
 		ps.Descriptions = make(map[string]string)
 		for _, p := range richObj.Formulae {
 			ps.Formulae = append(ps.Formulae, p.Name)
@@ -127,6 +128,47 @@ func (ps *PackageSnapshot) UnmarshalJSON(data []byte) error {
 	return fmt.Errorf("packages must be an object {formulae,casks,taps,npm} or an array")
 }
 
+// MarshalJSON outputs packages as rich objects when descriptions exist,
+// falling back to plain string arrays for backward compatibility.
+func (ps PackageSnapshot) MarshalJSON() ([]byte, error) {
+	if len(ps.Descriptions) == 0 {
+		type alias PackageSnapshot
+		return json.Marshal(alias(ps))
+	}
+
+	type entry struct {
+		Name string `json:"name"`
+		Desc string `json:"desc,omitempty"`
+	}
+
+	formulae := make([]entry, len(ps.Formulae))
+	for i, name := range ps.Formulae {
+		formulae[i] = entry{Name: name, Desc: ps.Descriptions[name]}
+	}
+
+	casks := make([]entry, len(ps.Casks))
+	for i, name := range ps.Casks {
+		casks[i] = entry{Name: name, Desc: ps.Descriptions[name]}
+	}
+
+	npm := make([]entry, len(ps.Npm))
+	for i, name := range ps.Npm {
+		npm[i] = entry{Name: name, Desc: ps.Descriptions[name]}
+	}
+
+	return json.Marshal(struct {
+		Formulae []entry  `json:"formulae"`
+		Casks    []entry  `json:"casks"`
+		Taps     []string `json:"taps"`
+		Npm      []entry  `json:"npm"`
+	}{
+		Formulae: formulae,
+		Casks:    casks,
+		Taps:     ps.Taps,
+		Npm:      npm,
+	})
+}
+
 type MacOSPref struct {
 	Domain string `json:"domain"`
 	Key    string `json:"key"`

internal/snapshot/snapshot_test.go

@@ -461,3 +461,108 @@ func TestSnapshot_CatalogMatchWithLowRate(t *testing.T) {
 	assert.Equal(t, 4, len(snap.CatalogMatch.Unmatched))
 	assert.InDelta(t, 0.2, snap.CatalogMatch.MatchRate, 0.01)
 }
+
+func TestPackageSnapshot_MarshalJSON_NoDescriptions(t *testing.T) {
+	ps := PackageSnapshot{
+		Formulae: []string{"git", "curl"},
+		Casks:    []string{"docker"},
+		Taps:     []string{"homebrew/core"},
+		Npm:      []string{"typescript"},
+	}
+
+	data, err := json.Marshal(ps)
+	require.NoError(t, err)
+
+	// Should output plain string arrays (backward compat)
+	var raw map[string]json.RawMessage
+	require.NoError(t, json.Unmarshal(data, &raw))
+
+	var formulae []string
+	require.NoError(t, json.Unmarshal(raw["formulae"], &formulae))
+	assert.Equal(t, []string{"git", "curl"}, formulae)
+}
+
+func TestPackageSnapshot_MarshalJSON_WithDescriptions(t *testing.T) {
+	ps := PackageSnapshot{
+		Formulae:     []string{"git", "curl"},
+		Casks:        []string{"docker"},
+		Taps:         []string{"homebrew/core"},
+		Npm:          []string{"typescript"},
+		Descriptions: map[string]string{
+			"git":        "Version control system",
+			"curl":       "Transfer data with URLs",
+			"docker":     "Container platform",
+			"typescript": "Typed JavaScript",
+		},
+	}
+
+	data, err := json.Marshal(ps)
+	require.NoError(t, err)
+
+	// Should output rich objects with desc
+	type entry struct {
+		Name string `json:"name"`
+		Desc string `json:"desc"`
+	}
+	var raw struct {
+		Formulae []entry  `json:"formulae"`
+		Casks    []entry  `json:"casks"`
+		Taps     []string `json:"taps"`
+		Npm      []entry  `json:"npm"`
+	}
+	require.NoError(t, json.Unmarshal(data, &raw))
+
+	assert.Equal(t, "git", raw.Formulae[0].Name)
+	assert.Equal(t, "Version control system", raw.Formulae[0].Desc)
+	assert.Equal(t, "curl", raw.Formulae[1].Name)
+	assert.Equal(t, "Transfer data with URLs", raw.Formulae[1].Desc)
+	assert.Equal(t, "docker", raw.Casks[0].Name)
+	assert.Equal(t, "Container platform", raw.Casks[0].Desc)
+	assert.Equal(t, []string{"homebrew/core"}, raw.Taps)
+}
+
+func TestPackageSnapshot_MarshalJSON_RoundTrip(t *testing.T) {
+	original := PackageSnapshot{
+		Formulae:     []string{"git", "curl"},
+		Casks:        []string{"docker"},
+		Taps:         []string{"homebrew/core"},
+		Npm:          []string{"typescript"},
+		Descriptions: map[string]string{
+			"git":        "Version control system",
+			"curl":       "Transfer data with URLs",
+			"docker":     "Container platform",
+			"typescript": "Typed JavaScript",
+		},
+	}
+
+	data, err := json.Marshal(original)
+	require.NoError(t, err)
+
+	var restored PackageSnapshot
+	require.NoError(t, json.Unmarshal(data, &restored))
+
+	assert.Equal(t, original.Formulae, restored.Formulae)
+	assert.Equal(t, original.Casks, restored.Casks)
+	assert.Equal(t, original.Taps, restored.Taps)
+	assert.Equal(t, original.Npm, restored.Npm)
+	assert.Equal(t, original.Descriptions, restored.Descriptions)
+}
+
+func TestPackageSnapshot_MarshalJSON_RoundTrip_CaskOnly(t *testing.T) {
+	original := PackageSnapshot{
+		Casks: []string{"docker", "slack"},
+		Descriptions: map[string]string{
+			"docker": "Container platform",
+			"slack":  "Team communication",
+		},
+	}
+
+	data, err := json.Marshal(original)
+	require.NoError(t, err)
+
+	var restored PackageSnapshot
+	require.NoError(t, json.Unmarshal(data, &restored))
+
+	assert.Equal(t, original.Casks, restored.Casks)
+	assert.Equal(t, original.Descriptions, restored.Descriptions)
+}