fix: accept flat array format for packages in snapshot push

PackageSnapshot.UnmarshalJSON now handles both the structured object
format {"formulae":[],"casks":[],...} and a plain string array
["pkg1","pkg2"] where all items are treated as formulae.

Fixes #12

Author: fullstackjam

internal/snapshot/snapshot.go

@@ -1,6 +1,10 @@
 package snapshot
 
-import "time"
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
 
 type CaptureHealth struct {
 	FailedSteps []string `json:"failed_steps"`
@@ -33,6 +37,26 @@ type PackageSnapshot struct {
 	Npm      []string `json:"npm"`
 }
 
+// UnmarshalJSON accepts both the structured object format
+// {"formulae":[],"casks":[],...} and a flat string array ["pkg1","pkg2"]
+// where all items are treated as formulae.
+func (ps *PackageSnapshot) UnmarshalJSON(data []byte) error {
+	type alias PackageSnapshot
+	var obj alias
+	if err := json.Unmarshal(data, &obj); err == nil {
+		*ps = PackageSnapshot(obj)
+		return nil
+	}
+
+	var arr []string
+	if err := json.Unmarshal(data, &arr); err == nil {
+		ps.Formulae = arr
+		return nil
+	}
+
+	return fmt.Errorf("packages must be an object {formulae,casks,taps,npm} or a string array")
+}
+
 type MacOSPref struct {
 	Domain string `json:"domain"`
 	Key    string `json:"key"`

internal/snapshot/snapshot_test.go

@@ -1,10 +1,12 @@
 package snapshot
 
 import (
+	"encoding/json"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 // TestSnapshot_Creation tests basic snapshot creation and field initialization.
@@ -37,6 +39,51 @@ func TestPackageSnapshot_Empty(t *testing.T) {
 	assert.Empty(t, ps.Taps)
 }
 
+func TestPackageSnapshot_UnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected PackageSnapshot
+		wantErr  bool
+	}{
+		{
+			name:  "object format",
+			input: `{"formulae":["git","go"],"casks":["docker"],"taps":["homebrew/core"],"npm":["typescript"]}`,
+			expected: PackageSnapshot{
+				Formulae: []string{"git", "go"},
+				Casks:    []string{"docker"},
+				Taps:     []string{"homebrew/core"},
+				Npm:      []string{"typescript"},
+			},
+		},
+		{
+			name:  "flat array treated as formulae",
+			input: `["git","curl","jq"]`,
+			expected: PackageSnapshot{
+				Formulae: []string{"git", "curl", "jq"},
+			},
+		},
+		{
+			name:    "invalid type",
+			input:   `123`,
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var ps PackageSnapshot
+			err := json.Unmarshal([]byte(tt.input), &ps)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tt.expected, ps)
+		})
+	}
+}
+
 // TestMacOSPref_Creation tests MacOS preference creation.
 func TestMacOSPref_Creation(t *testing.T) {
 	pref := MacOSPref{