Adds listCommands endpoint to a2a server (#12604)

Co-authored-by: Juanda <jdgarrido@google.com>
Co-authored-by: Shreya Keshive <shreyakeshive@google.com>

packages/a2a-server/src/http/app.ts

@@ -21,6 +21,14 @@ import { loadSettings } from '../config/settings.js';
 import { loadExtensions } from '../config/extension.js';
 import { commandRegistry } from '../commands/command-registry.js';
 import { SimpleExtensionLoader } from '@google/gemini-cli-core';
+import type { Command, CommandArgument } from '../commands/types.js';
+
+type CommandResponse = {
+  name: string;
+  description: string;
+  arguments: CommandArgument[];
+  subCommands: CommandResponse[];
+};
 
 const coderAgentCard: AgentCard = {
   name: 'Gemini SDLC Agent',
@@ -167,6 +175,48 @@ export async function createApp() {
       }
     });
 
+    expressApp.get('/listCommands', (req, res) => {
+      try {
+        const transformCommand = (
+          command: Command,
+          visited: string[],
+        ): CommandResponse | undefined => {
+          const commandName = command.name;
+          if (visited.includes(commandName)) {
+            console.warn(
+              `Command ${commandName} already inserted in the response, skipping`,
+            );
+            return undefined;
+          }
+
+          return {
+            name: command.name,
+            description: command.description,
+            arguments: command.arguments ?? [],
+            subCommands: (command.subCommands ?? [])
+              .map((subCommand) =>
+                transformCommand(subCommand, visited.concat(commandName)),
+              )
+              .filter(
+                (subCommand): subCommand is CommandResponse => !!subCommand,
+              ),
+          };
+        };
+
+        const commands = commandRegistry
+          .getAllCommands()
+          .filter((command) => command.topLevel)
+          .map((command) => transformCommand(command, []));
+
+        return res.status(200).json({ commands });
+      } catch (e) {
+        logger.error('Error executing /listCommands:', e);
+        const errorMessage =
+          e instanceof Error ? e.message : 'Unknown error listing commands';
+        return res.status(500).json({ error: errorMessage });
+      }
+    });
+
     expressApp.get('/tasks/metadata', async (req, res) => {
       // This endpoint is only meaningful if the task store is in-memory.
       if (!(taskStoreForExecutor instanceof InMemoryTaskStore)) {