Add /background commands (when background agent is configured) (#4407)

Co-authored-by: Bryan Morgan <bryanmorgan@google.com>

packages/core/src/background/backgroundAgent.ts

@@ -0,0 +1,126 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { MCPServerConfig } from '../config/config.js';
+import { connectToMcpServer, discoverTools } from '../tools/mcp-client.js';
+import { DiscoveredMCPTool } from '../tools/mcp-tool.js';
+import {
+  BackgroundAgentTasksResponseSchema,
+  BackgroundAgentTaskResponseSchema,
+  BackgroundAgentTask,
+} from './types.js';
+
+export async function loadBackgroundAgent(
+  name: string,
+  config: MCPServerConfig,
+  debugMode: boolean,
+): Promise<BackgroundAgent> {
+  const server = await connectToMcpServer(name, config, debugMode);
+  try {
+    const tools = await discoverTools(name, config, server);
+    return new BackgroundAgent(name, tools);
+  } catch (error) {
+    await server.close();
+    throw error;
+  }
+}
+
+export class BackgroundAgent {
+  readonly startTaskTool: DiscoveredMCPTool;
+  readonly getTaskTool: DiscoveredMCPTool;
+  readonly listTasksTool: DiscoveredMCPTool;
+  readonly messageTaskTool: DiscoveredMCPTool;
+  readonly deleteTaskTool: DiscoveredMCPTool;
+  readonly cancelTaskTool: DiscoveredMCPTool;
+
+  constructor(
+    readonly serverName: string,
+    tools: DiscoveredMCPTool[],
+  ) {
+    const getToolOrFail = (name: string): DiscoveredMCPTool => {
+      for (const tool of tools) {
+        if (tool.serverToolName === name) {
+          return tool;
+        }
+      }
+      throw new Error(`missing expected tool: ${name}`);
+    };
+
+    this.startTaskTool = getToolOrFail('startTask');
+    this.getTaskTool = getToolOrFail('getTask');
+    this.listTasksTool = getToolOrFail('listTasks');
+    this.messageTaskTool = getToolOrFail('messageTask');
+    this.deleteTaskTool = getToolOrFail('deleteTask');
+    this.cancelTaskTool = getToolOrFail('cancelTask');
+  }
+
+  async startTask(prompt: string): Promise<BackgroundAgentTask> {
+    const resp = await this.callTool(this.startTaskTool, {
+      prompt: {
+        role: 'user',
+        parts: [{ text: prompt }],
+      },
+    });
+    const taskResp = await BackgroundAgentTaskResponseSchema.parseAsync(resp);
+    return taskResp.structuredContent;
+  }
+
+  async getTask(
+    id: string,
+    historyLength?: number,
+  ): Promise<BackgroundAgentTask> {
+    const resp = await this.callTool(this.getTaskTool, {
+      id,
+      historyLength,
+    });
+    const taskResp = await BackgroundAgentTaskResponseSchema.parseAsync(resp);
+    return taskResp.structuredContent;
+  }
+
+  async listTasks(): Promise<BackgroundAgentTask[]> {
+    const resp = await this.callTool(this.listTasksTool, {});
+    const tasksResp = await BackgroundAgentTasksResponseSchema.parseAsync(resp);
+    return tasksResp.structuredContent;
+  }
+
+  async messageTask(id: string, message: string) {
+    await this.callTool(this.messageTaskTool, {
+      id,
+      message: {
+        role: 'user',
+        parts: [{ text: message }],
+      },
+    });
+  }
+
+  async deleteTask(id: string) {
+    await this.callTool(this.deleteTaskTool, { id });
+  }
+
+  async cancelTask(id: string) {
+    await this.callTool(this.cancelTaskTool, { id });
+  }
+
+  private async callTool(
+    tool: DiscoveredMCPTool,
+    params: Record<string, unknown>,
+  ): Promise<Record<string, unknown>> {
+    const { llmContent: parts } = await tool.execute(params);
+    if (
+      !Array.isArray(parts) ||
+      parts.length !== 1 ||
+      typeof parts[0] !== 'object' ||
+      parts[0]?.functionResponse?.response === undefined
+    ) {
+      throw new Error('Expected exactly one part with a functionResponse');
+    }
+    const resp = parts[0].functionResponse.response;
+    if ('isError' in resp && resp.isError) {
+      throw new Error(`Error calling ${tool.displayName}: ${resp}`);
+    }
+    return resp;
+  }
+}