Add ExtensionLoader interface, use that on Config object (#12116)

packages/core/src/utils/extensionLoader.ts

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { EventEmitter } from 'node:events';
+import type { GeminiCLIExtension } from '../config/config.js';
+
+export interface ExtensionLoader {
+  getExtensions(): GeminiCLIExtension[];
+
+  extensionEvents(): EventEmitter<ExtensionEvents>;
+}
+
+export interface ExtensionEvents {
+  extensionEnabled: ExtensionEnableEvent[];
+  extensionDisabled: ExtensionDisableEvent[];
+  extensionLoaded: ExtensionLoadEvent[];
+  extensionUnloaded: ExtensionUnloadEvent[];
+  extensionInstalled: ExtensionInstallEvent[];
+  extensionUninstalled: ExtensionUninstallEvent[];
+  extensionUpdated: ExtensionUpdateEvent[];
+}
+
+interface BaseExtensionEvent {
+  extension: GeminiCLIExtension;
+}
+export type ExtensionDisableEvent = BaseExtensionEvent;
+export type ExtensionEnableEvent = BaseExtensionEvent;
+export type ExtensionInstallEvent = BaseExtensionEvent;
+export type ExtensionLoadEvent = BaseExtensionEvent;
+export type ExtensionUnloadEvent = BaseExtensionEvent;
+export type ExtensionUninstallEvent = BaseExtensionEvent;
+export type ExtensionUpdateEvent = BaseExtensionEvent;
+
+export class SimpleExtensionLoader implements ExtensionLoader {
+  private _eventEmitter = new EventEmitter<ExtensionEvents>();
+  constructor(private readonly extensions: GeminiCLIExtension[]) {}
+
+  extensionEvents(): EventEmitter<ExtensionEvents> {
+    return this._eventEmitter;
+  }
+
+  getExtensions(): GeminiCLIExtension[] {
+    return this.extensions;
+  }
+}