fix: close install gaps aligned with fullstack-cli

- latest version: re-check installed version after API resolves, skip
  download when already up to date
- actionPlugins sync: ensure package.json record is updated even when
  install is skipped (already_installed path)
- peerDependencies: warn about missing peer deps after extraction
  instead of silently ignoring them

shortcuts/apps/plugin_common.go

@@ -506,6 +506,47 @@ func pluginRemoveActionPlugin(pkg map[string]interface{}, key string) {
 	delete(m, key)
 }
 
+// pluginSyncActionPlugins ensures the actionPlugins record in package.json
+// matches the actually installed version, even when install is skipped.
+func pluginSyncActionPlugins(projectPath, key, version string) {
+	pkg, err := pluginReadPackageJSON(projectPath)
+	if err != nil {
+		return
+	}
+	ap := pluginGetActionPlugins(pkg)
+	if ap[key] == version {
+		return
+	}
+	pluginSetActionPlugin(pkg, key, version)
+	_ = pluginWritePackageJSON(projectPath, pkg)
+}
+
+// pluginCheckPeerDeps reads peerDependencies from the installed plugin's
+// package.json and returns the names of any that are missing from node_modules.
+func pluginCheckPeerDeps(projectPath, pluginKey string) []string {
+	pkgPath := filepath.Join(projectPath, "node_modules", pluginKey, "package.json")
+	data, err := os.ReadFile(pkgPath) //nolint:forbidigo // shortcuts cannot import internal/vfs; local package read.
+	if err != nil {
+		return nil
+	}
+	var pkg map[string]interface{}
+	if err := json.Unmarshal(data, &pkg); err != nil {
+		return nil
+	}
+	peerDeps, ok := pkg["peerDependencies"].(map[string]interface{})
+	if !ok || len(peerDeps) == 0 {
+		return nil
+	}
+	var missing []string
+	for dep := range peerDeps {
+		depDir := filepath.Join(projectPath, "node_modules", dep)
+		if !pluginDirExists(depDir) {
+			missing = append(missing, dep)
+		}
+	}
+	return missing
+}
+
 // pluginParseInstallTarget parses "key[@version]" where version is optional.
 // For scoped packages like "@scope/name@1.0.0", the split is at the last "@".
 func pluginParseInstallTarget(s string) (key string, version string) {

shortcuts/apps/plugin_install.go

@@ -77,9 +77,10 @@ func pluginInstallOne(ctx context.Context, rctx *common.RuntimeContext, projectP
 		return appsValidationParamError("--name", "invalid plugin name %q", name)
 	}
 
-	// Check if already installed with same version
+	// Check if already installed with same version (pre-API fast path)
 	if version != "" && version != "latest" {
 		if installed := pluginInstalledVersion(projectPath, key); installed == version {
+			pluginSyncActionPlugins(projectPath, key, version)
 			result := map[string]interface{}{
 				"key": key, "version": version, "status": "already_installed",
 			}
@@ -96,6 +97,18 @@ func pluginInstallOne(ctx context.Context, rctx *common.RuntimeContext, projectP
 		return err
 	}
 
+	// Post-API check: latest may resolve to the already-installed version
+	if installed := pluginInstalledVersion(projectPath, key); installed == resolvedVersion {
+		pluginSyncActionPlugins(projectPath, key, resolvedVersion)
+		result := map[string]interface{}{
+			"key": key, "version": resolvedVersion, "status": "already_installed",
+		}
+		rctx.OutFormat(result, nil, func(w io.Writer) {
+			fmt.Fprintf(w, "✓ %s@%s is already up to date\n", key, resolvedVersion)
+		})
+		return nil
+	}
+
 	// Download tgz
 	tgzData, err := pluginDownloadPackage(ctx, rctx, key, resolvedVersion, downloadURL, approach)
 	if err != nil {
@@ -114,6 +127,9 @@ func pluginInstallOne(ctx context.Context, rctx *common.RuntimeContext, projectP
 		return appsFileIOError(err, "cannot extract plugin package for %s", key)
 	}
 
+	// Check peer dependencies
+	missingPeers := pluginCheckPeerDeps(projectPath, key)
+
 	// Update package.json
 	pkg, err := pluginReadPackageJSON(projectPath)
 	if err != nil {
@@ -127,8 +143,15 @@ func pluginInstallOne(ctx context.Context, rctx *common.RuntimeContext, projectP
 	result := map[string]interface{}{
 		"key": key, "version": resolvedVersion, "status": "installed",
 	}
+	if len(missingPeers) > 0 {
+		result["missing_peer_dependencies"] = missingPeers
+	}
 	rctx.OutFormat(result, nil, func(w io.Writer) {
 		fmt.Fprintf(w, "✓ Installed %s@%s\n", key, resolvedVersion)
+		if len(missingPeers) > 0 {
+			fmt.Fprintf(w, "⚠ Missing peer dependencies: %s\n", strings.Join(missingPeers, ", "))
+			fmt.Fprintln(w, "  Run 'npm install' in the project directory to install them.")
+		}
 	})
 	return nil
 }