fix(installer): harden readMarketplaceJsonFromDisk and hoist require

- Add try/catch to readMarketplaceJsonFromDisk so malformed JSON returns
  null instead of throwing an unhandled parse error
- Hoist CustomModuleManager require outside the per-module loop in
  _installOfficialModules

tools/installer/core/installer.js

@@ -569,6 +569,7 @@ class Installer {
    */
   async _installOfficialModules(config, paths, officialModuleIds, addResult, isQuickUpdate, officialModules, ctx) {
     const { message, installedModuleNames } = ctx;
+    const { CustomModuleManager } = require('../modules/custom-module-manager');
 
     for (const moduleName of officialModuleIds) {
       if (installedModuleNames.has(moduleName)) continue;
@@ -598,7 +599,6 @@ class Installer {
 
       // Prefer version from resolution cache (accurate for custom/local modules),
       // fall back to marketplace.json walk-up for official modules
-      const { CustomModuleManager } = require('../modules/custom-module-manager');
       const cachedResolution = CustomModuleManager._resolutionCache.get(moduleName);
       const version = cachedResolution?.version || (sourcePath ? await this._getMarketplaceVersion(sourcePath) : '');
       addResult(displayName, 'ok', '', { moduleCode: moduleName, newVersion: version });

tools/installer/modules/custom-module-manager.js

@@ -148,7 +148,11 @@ class CustomModuleManager {
   async readMarketplaceJsonFromDisk(dirPath) {
     const marketplacePath = path.join(dirPath, '.claude-plugin', 'marketplace.json');
     if (!(await fs.pathExists(marketplacePath))) return null;
-    return JSON.parse(await fs.readFile(marketplacePath, 'utf8'));
+    try {
+      return JSON.parse(await fs.readFile(marketplacePath, 'utf8'));
+    } catch {
+      return null;
+    }
   }
 
   // ─── Discovery ────────────────────────────────────────────────────────────