feat(cli): add /agents slash command to list available agents (#16182)

packages/cli/src/ui/commands/agentsCommand.ts

@@ -0,0 +1,51 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type { SlashCommand, CommandContext } from './types.js';
+import { CommandKind } from './types.js';
+import { MessageType, type HistoryItemAgentsList } from '../types.js';
+
+export const agentsCommand: SlashCommand = {
+  name: 'agents',
+  description: 'List available local and remote agents',
+  kind: CommandKind.BUILT_IN,
+  autoExecute: true,
+  action: async (context: CommandContext) => {
+    const { config } = context.services;
+    if (!config) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: 'Config not loaded.',
+      };
+    }
+
+    const agentRegistry = config.getAgentRegistry();
+    if (!agentRegistry) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: 'Agent registry not found.',
+      };
+    }
+
+    const agents = agentRegistry.getAllDefinitions().map((def) => ({
+      name: def.name,
+      displayName: def.displayName,
+      description: def.description,
+      kind: def.kind,
+    }));
+
+    const agentsListItem: HistoryItemAgentsList = {
+      type: MessageType.AGENTS_LIST,
+      agents,
+    };
+
+    context.ui.addItem(agentsListItem, Date.now());
+
+    return;
+  },
+};