Demo background agent (#4409)

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

package-lock.json

@@ -916,6 +916,10 @@
       "resolved": "packages/core",
       "link": true
     },
+    "node_modules/@google/gemini-cli-examples": {
+      "resolved": "packages/examples",
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@@ -5657,6 +5661,19 @@
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+      "license": "MIT",
+      "dependencies": {
+        "resolve-pkg-maps": "^1.0.0"
+      },
+      "funding": {
+        "url": "https://github.com/privatenumber/get-tsconfig?sponsor=1"
+      }
+    },
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@@ -9190,6 +9207,16 @@
         "node": ">=4"
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+    "node_modules/resolve-pkg-maps": {
+      "version": "1.0.0",
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+      "dev": true,
+      "license": "MIT",
+      "funding": {
+        "url": "https://github.com/privatenumber/resolve-pkg-maps?sponsor=1"
+      }
+    },
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@@ -10490,6 +10517,26 @@
       "dev": true,
       "license": "0BSD"
     },
+    "node_modules/tsx": {
+      "version": "4.20.3",
+      "resolved": "https://registry.npmjs.org/tsx/-/tsx-4.20.3.tgz",
+      "integrity": "sha512-qjbnuR9Tr+FJOMBqJCW5ehvIo/buZq7vH7qD7JziU98h6l3qGy0a/yPFjwO+y0/T7GFpNgNAvEcPPVfyT8rrPQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "esbuild": "~0.25.0",
+        "get-tsconfig": "^4.7.5"
+      },
+      "bin": {
+        "tsx": "dist/cli.mjs"
+      },
+      "engines": {
+        "node": ">=18.0.0"
+      },
+      "optionalDependencies": {
+        "fsevents": "~2.3.3"
+      }
+    },
     "node_modules/type-check": {
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@@ -11860,6 +11907,17 @@
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       "license": "MIT"
     },
+    "packages/examples": {
+      "name": "@google/gemini-cli-examples",
+      "version": "0.1.0",
+      "dependencies": {
+        "@modelcontextprotocol/sdk": "1.15.1",
+        "zod": "^3.23.8"
+      },
+      "devDependencies": {
+        "tsx": "^4.16.2"
+      }
+    },
     "packages/vscode-ide-companion": {
       "name": "gemini-cli-vscode-ide-companion",
       "version": "0.0.1",

packages/examples/background_agent/README.md

@@ -0,0 +1,16 @@
+# Demo Background Agent
+
+A pretend background agent that does not actually process tasks in the background. Configure in your settings.json with:
+
+```javascript
+ "backgroundAgents": {
+    "demo-background-agent": {
+      "command": "npm",
+      "args": [
+        "run",
+        "start:demo-background-agent",
+        "--workspace=@google/gemini-cli-examples"
+      ]
+    }
+  },
+```

packages/examples/background_agent/demo-background-agent.ts

@@ -0,0 +1,217 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { StdioServerTransport } from '@modelcontextprotocol/sdk/server/stdio.js';
+import { z } from 'zod';
+
+const BackgroundAgentMessageSchema = z.object({
+  role: z.enum(['user', 'agent']),
+  parts: z.array(z.any()),
+});
+
+const BackgroundAgentTaskStatusSchema = z.object({
+  state: z.enum([
+    'submitted',
+    'working',
+    'input-required',
+    'completed',
+    'canceled',
+    'failed',
+  ]),
+  message: BackgroundAgentMessageSchema.optional(),
+});
+
+const BackgroundAgentTaskSchema = z.object({
+  id: z.string(),
+  status: BackgroundAgentTaskStatusSchema,
+  history: z.array(BackgroundAgentMessageSchema).optional(),
+});
+type BackgroundAgentTask = z.infer<typeof BackgroundAgentTaskSchema>;
+
+const server = new McpServer({
+  name: 'demo-background-agent',
+  version: '1.0.0',
+});
+
+const idToTask = new Map<string, BackgroundAgentTask>();
+
+server.registerTool(
+  'startTask',
+  {
+    title: 'Start a new task',
+    description: 'Launches a new task asynchronously.',
+    inputSchema: { prompt: BackgroundAgentMessageSchema },
+    outputSchema: BackgroundAgentTaskSchema.shape,
+  },
+  ({ prompt }) => {
+    const task: BackgroundAgentTask = {
+      id: crypto.randomUUID(),
+      status: {
+        state: 'submitted',
+        message: prompt,
+      },
+      history: [],
+    };
+
+    idToTask.set(task.id, task);
+
+    return {
+      content: [],
+      structuredContent: task,
+    };
+  },
+);
+
+server.registerTool(
+  'getTask',
+  {
+    title: 'Get a task',
+    inputSchema: { id: z.string() },
+    outputSchema: BackgroundAgentTaskSchema.shape,
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+
+    return {
+      content: [],
+      structuredContent: task,
+    };
+  },
+);
+
+server.registerTool(
+  'listTasks',
+  {
+    title: 'Lists tasks',
+    outputSchema: {
+      tasks: z.array(BackgroundAgentTaskSchema),
+    },
+  },
+  () => {
+    const out = {
+      tasks: Array.from(idToTask.values()),
+    };
+    return {
+      content: [],
+      structuredContent: out,
+    };
+  },
+);
+
+server.registerTool(
+  'messageTask',
+  {
+    title: 'Send a message to a task',
+    inputSchema: {
+      id: z.string(),
+      message: BackgroundAgentMessageSchema,
+    },
+  },
+  ({ id, message }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+
+    task.history?.push(message);
+    task.status.message = message;
+
+    const statuses = BackgroundAgentTaskStatusSchema.shape.state.options;
+    const randomStatus = statuses[Math.floor(Math.random() * statuses.length)];
+    task.status.state = randomStatus;
+
+    return {
+      content: [],
+    };
+  },
+);
+
+server.registerTool(
+  'deleteTask',
+  {
+    title: 'Delete a task',
+    inputSchema: { id: z.string() },
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+    idToTask.delete(id);
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'Task deleted',
+        },
+      ],
+    };
+  },
+);
+
+server.registerTool(
+  'cancelTask',
+  {
+    title: 'Cancels a task',
+    inputSchema: { id: z.string() },
+  },
+  ({ id }) => {
+    const task = idToTask.get(id);
+    if (!task) {
+      return {
+        isError: true,
+        content: [
+          {
+            type: 'text',
+            text: 'No such task',
+          },
+        ],
+      };
+    }
+    task.status.state = 'canceled';
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: 'Task cancelled',
+        },
+      ],
+    };
+  },
+);
+
+const transport = new StdioServerTransport();
+await server.connect(transport);

packages/examples/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "@google/gemini-cli-examples",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "start:demo-background-agent": "tsx background_agent/demo-background-agent.ts",
+    "build": "echo 'nothing to build'"
+  },
+  "dependencies": {
+    "@modelcontextprotocol/sdk": "1.15.1",
+    "zod": "^3.23.8"
+  },
+  "devDependencies": {
+    "tsx": "^4.16.2"
+  }
+}