Add check-update cmd, update README

- New check-update cmd queries GitHub API for latest release
- Add Linux install instructions
- Add Updating section
- Fix plugins exclusion docs (plugins/cache + plugins/marketplaces)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: FelixIsaac

README.md

@@ -46,8 +46,28 @@ scoop install claude-code-sync
 go install github.com/felixisaac/claude-code-sync@latest
 ```
 
+**Linux (manual):**
+```bash
+# Download latest release (adjust arch: amd64 or arm64)
+curl -sL https://github.com/felixisaac/claude-code-sync/releases/latest/download/claude-code-sync_linux_amd64.tar.gz | tar xz
+sudo mv claude-code-sync /usr/local/bin/
+```
+
 **Manual:** Download the latest binary from [GitHub Releases](https://github.com/felixisaac/claude-code-sync/releases).
 
+### Updating
+
+```bash
+# Check for updates
+claude-code-sync check-update
+
+# Update via package manager
+brew upgrade claude-code-sync    # macOS
+scoop update claude-code-sync    # Windows
+
+# Or download latest from GitHub Releases
+```
+
 ### First Time Setup
 
 ```bash
@@ -95,6 +115,7 @@ claude-code-sync pull
 | `reset [--keep-key]` | Delete all sync data |
 | `unlink` | Disconnect from remote repo (keep local data) |
 | `version` | Show version |
+| `check-update` | Check for newer version |
 | `help` | Show help |
 
 ## What Gets Synced
@@ -124,7 +145,8 @@ claude-code-sync pull
 - `debug/` - Debug logs
 - `file-history/` - File history cache
 - `ide/` - IDE integration cache
-- `plugins/` - Plugin cache
+- `plugins/cache/` - Plugin cache
+- `plugins/marketplaces/` - Marketplace cache (installed_plugins.json and known_marketplaces.json ARE synced)
 - `shell-snapshots/` - Shell state snapshots
 - `telemetry/` - Telemetry data
 - `stats-cache.json` - Statistics cache

internal/cmd/root.go

@@ -37,6 +37,7 @@ func init() {
 	rootCmd.AddCommand(resetCmd)
 	rootCmd.AddCommand(unlinkCmd)
 	rootCmd.AddCommand(doctorCmd)
+	rootCmd.AddCommand(checkUpdateCmd)
 }
 
 // UI helpers

internal/cmd/update.go

@@ -0,0 +1,134 @@
+package cmd
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"runtime"
+	"strings"
+	"time"
+
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+)
+
+const (
+	repoOwner = "felixisaac"
+	repoName  = "claude-code-sync"
+)
+
+type githubRelease struct {
+	TagName string `json:"tag_name"`
+	HTMLURL string `json:"html_url"`
+	Assets  []struct {
+		Name               string `json:"name"`
+		BrowserDownloadURL string `json:"browser_download_url"`
+	} `json:"assets"`
+}
+
+var checkUpdateCmd = &cobra.Command{
+	Use:   "check-update",
+	Short: "Check for newer version",
+	RunE:  runCheckUpdate,
+}
+
+func runCheckUpdate(cmd *cobra.Command, args []string) error {
+	logInfo("Checking for updates...")
+
+	latest, err := getLatestRelease()
+	if err != nil {
+		return fmt.Errorf("failed to check for updates: %w", err)
+	}
+
+	latestVer := strings.TrimPrefix(latest.TagName, "v")
+	currentVer := version
+
+	if latestVer == currentVer {
+		logSuccess(fmt.Sprintf("You're on the latest version (v%s)", currentVer))
+		return nil
+	}
+
+	// Simple version comparison (works for semver)
+	if compareVersions(latestVer, currentVer) > 0 {
+		fmt.Println()
+		color.Yellow("Update available: v%s → v%s", currentVer, latestVer)
+		fmt.Println()
+		fmt.Println("Download:")
+		fmt.Printf("  %s\n", latest.HTMLURL)
+		fmt.Println()
+
+		// Show direct download link for current platform
+		assetName := getAssetName()
+		for _, asset := range latest.Assets {
+			if asset.Name == assetName {
+				fmt.Println("Direct download for your platform:")
+				fmt.Printf("  %s\n", asset.BrowserDownloadURL)
+				break
+			}
+		}
+		fmt.Println()
+		logInfo("To update: download and replace your current binary")
+	} else {
+		logSuccess(fmt.Sprintf("You're on the latest version (v%s)", currentVer))
+	}
+
+	return nil
+}
+
+func getLatestRelease() (*githubRelease, error) {
+	url := fmt.Sprintf("https://api.github.com/repos/%s/%s/releases/latest", repoOwner, repoName)
+
+	client := &http.Client{Timeout: 10 * time.Second}
+	resp, err := client.Get(url)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode == 404 {
+		return nil, fmt.Errorf("no releases found")
+	}
+	if resp.StatusCode != 200 {
+		return nil, fmt.Errorf("GitHub API returned %d", resp.StatusCode)
+	}
+
+	var release githubRelease
+	if err := json.NewDecoder(resp.Body).Decode(&release); err != nil {
+		return nil, err
+	}
+
+	return &release, nil
+}
+
+func getAssetName() string {
+	os := runtime.GOOS
+	arch := runtime.GOARCH
+
+	ext := ".tar.gz"
+	if os == "windows" {
+		ext = ".zip"
+	}
+
+	return fmt.Sprintf("claude-code-sync_%s_%s%s", os, arch, ext)
+}
+
+// compareVersions returns >0 if a > b, <0 if a < b, 0 if equal
+func compareVersions(a, b string) int {
+	aParts := strings.Split(a, ".")
+	bParts := strings.Split(b, ".")
+
+	for i := 0; i < len(aParts) && i < len(bParts); i++ {
+		var aNum, bNum int
+		fmt.Sscanf(aParts[i], "%d", &aNum)
+		fmt.Sscanf(bParts[i], "%d", &bNum)
+
+		if aNum > bNum {
+			return 1
+		}
+		if aNum < bNum {
+			return -1
+		}
+	}
+
+	return len(aParts) - len(bParts)
+}