diff --git a/packages/cli/src/config/extension-manager.ts b/packages/cli/src/config/extension-manager.ts
index 45ca5a0d8a1..f9264cd0312 100644
--- a/packages/cli/src/config/extension-manager.ts
+++ b/packages/cli/src/config/extension-manager.ts
@@ -465,9 +465,6 @@ Would you like to attempt to install via "git clone" instead?`,
     );
   }
 
-  /**
-   * Loads all installed extensions, should only be called once.
-   */
   async loadExtensions(): Promise<GeminiCLIExtension[]> {
     if (this.loadedExtensions) {
       throw new Error('Extensions already loaded, only load extensions once.');
@@ -480,24 +477,66 @@ Would you like to attempt to install via "git clone" instead?`,
 
     const extensionsDir = ExtensionStorage.getUserExtensionsDir();
     this.loadedExtensions = [];
-    if (!fs.existsSync(extensionsDir)) {
+
+    let subdirs: string[];
+    try {
+      subdirs = await fs.promises.readdir(extensionsDir);
+    } catch {
+      // Directory doesn't exist or can't be read
       return this.loadedExtensions;
     }
-    for (const subdir of fs.readdirSync(extensionsDir)) {
+
+    const loadPromises = subdirs.map((subdir) => {
       const extensionDir = path.join(extensionsDir, subdir);
-      await this.loadExtension(extensionDir);
+      return this.loadExtension(extensionDir);
+    });
+
+    const results = await Promise.all(loadPromises);
+
+    // Validate and collect successfully loaded extensions
+    const names = new Set<string>();
+    const extensions: GeminiCLIExtension[] = [];
+
+    for (const result of results) {
+      if (result === null) continue;
+
+      if (names.has(result.name)) {
+        debugLogger.error(`Duplicate extension name detected: ${result.name}`);
+        continue;
+      }
+      names.add(result.name);
+      extensions.push(result);
+    }
+
+    // Single atomic update to shared state
+    this.loadedExtensions = extensions;
+
+    // Start extensions sequentially to preserve ordering guarantees
+    for (const extension of this.loadedExtensions) {
+      await this.maybeStartExtension(extension);
     }
+
     return this.loadedExtensions;
   }
 
   /**
-   * Adds `extension` to the list of extensions and starts it if appropriate.
+   * Loads an extension configuration from the given directory.
+   *
+   * Note: The caller is responsible for:
+   * - Adding the returned extension to the `this.loadedExtensions` array.
+   * - Calling `this.maybeStartExtension(extension)` to activate it.
    */
   private async loadExtension(
     extensionDir: string,
   ): Promise<GeminiCLIExtension | null> {
     this.loadedExtensions ??= [];
-    if (!fs.statSync(extensionDir).isDirectory()) {
+
+    try {
+      const stats = await fs.promises.stat(extensionDir);
+      if (!stats.isDirectory()) {
+        return null;
+      }
+    } catch {
       return null;
     }
 
@@ -652,9 +691,7 @@ Would you like to attempt to install via "git clone" instead?`,
         skills,
         agents: agentLoadResult.agents,
       };
-      this.loadedExtensions = [...this.loadedExtensions, extension];
 
-      await this.maybeStartExtension(extension);
       return extension;
     } catch (e) {
       debugLogger.error(
@@ -736,7 +773,6 @@ Would you like to attempt to install via "git clone" instead?`,
         return undefined;
       }
 
-      // Hydrate variables in the hooks configuration
       const hydratedHooks = recursivelyHydrateStrings(
         rawHooks.hooks as unknown as JsonObject,
         {