Agent-to-Agent Protocol (A2A)

Overview

The Agent-to-Agent Protocol (A2A) is Routa’s external federation interface. It exposes internal Routa agents as A2A-compatible tasks, enabling cross-platform agent communication and discovery. Key Purpose: Allow external AI systems to discover, communicate with, and coordinate with Routa agents using a standardized protocol. Built on: @a2a-js/sdk

When to Use A2A

Use A2A when you need to:

Expose Routa agents to external AI platforms
Enable cross-platform coordination between different AI systems
Implement agent discovery for external clients
Provide a standardized interface for agent communication
Integrate with A2A-compatible tools and platforms

A2A is ideal for federation scenarios where multiple AI systems need to collaborate.

Architecture

A2A implementation bridges Routa’s internal agent model to the A2A protocol:

// src/core/a2a/a2a-task-bridge.ts:106
export class A2ATaskBridge {
  private tasks = new Map<string, A2ATaskRecord>();

  /**
   * Create a new A2A task linked to a Routa agent
   */
  createTask(params: {
    userPrompt: string;
    workspaceId?: string;
    routaAgentId?: string;
    contextId?: string;
  }): A2ATask {
    const taskId = uuidv4();
    const task: A2ATaskRecord = {
      id: taskId,
      contextId: params.contextId ?? uuidv4(),
      status: { state: "submitted", timestamp: new Date().toISOString() },
      history: [userMessage],
      artifacts: [],
      _routaAgentId: params.routaAgentId,
      _workspaceId: params.workspaceId
    };
    this.tasks.set(taskId, task);
    return task;
  }

  /**
   * Update task state based on Routa agent status
   */
  updateTaskFromAgent(
    taskId: string,
    agentStatus: AgentStatus
  ): A2ATask | undefined {
    const task = this.tasks.get(taskId);
    if (!task) return undefined;

    task.status.state = mapAgentStatusToA2AState(agentStatus);
    task.status.timestamp = new Date().toISOString();
    return task;
  }
}

Key Concepts

A2A Task Model

Routa agents are exposed as A2A “tasks” with the following structure:

interface A2ATask {
  id: string;                    // Unique task identifier
  contextId: string;             // Conversation context
  status: A2ATaskStatus;         // Current state and timestamp
  history: A2AMessage[];         // Message history
  artifacts?: A2AArtifact[];     // Output artifacts
  metadata?: Record<string, unknown>;
}

interface A2ATaskStatus {
  state: A2ATaskState;
  timestamp: string;
  message?: A2AMessage;
}

type A2ATaskState =
  | "submitted"      // Task created, not yet started
  | "working"        // Agent actively processing
  | "input-required" // Waiting for user input
  | "completed"      // Successfully finished
  | "failed"         // Errored or failed
  | "canceled"       // Manually cancelled
  | "rejected"       // Rejected by agent
  | "auth-required"; // Authentication needed

State Mapping

Routa agent statuses are mapped to A2A task states:

// src/core/a2a/a2a-task-bridge.ts:72
export function mapAgentStatusToA2AState(status: AgentStatus): A2ATaskState {
  switch (status) {
    case AgentStatus.PENDING:
      return "submitted";
    case AgentStatus.ACTIVE:
      return "working";
    case AgentStatus.COMPLETED:
      return "completed";
    case AgentStatus.ERROR:
      return "failed";
    case AgentStatus.CANCELLED:
      return "canceled";
    default:
      return "submitted";
  }
}

Role to Skill Mapping

Routa agent roles are exposed as A2A skill identifiers:

// src/core/a2a/a2a-task-bridge.ts:89
export function mapAgentRoleToSkillId(role: AgentRole): string {
  switch (role) {
    case AgentRole.ROUTA:
      return "coordination";
    case AgentRole.CRAFTER:
      return "development";
    case AgentRole.GATE:
      return "verification";
    case AgentRole.DEVELOPER:
      return "full-stack-development";
    default:
      return "coordination";
  }
}

A2A Messages

Messages in A2A tasks represent communication between users and agents:

interface A2AMessage {
  messageId: string;
  role: "user" | "agent";
  parts: A2APart[];
  contextId?: string;
  taskId?: string;
}

interface A2APart {
  text?: string;              // Plain text content
  data?: unknown;             // Structured data (JSON)
  mediaType?: string;         // MIME type (e.g., "application/json")
}

Example message flow:

// User message
const userMessage: A2AMessage = {
  messageId: "msg-1",
  role: "user",
  parts: [{ text: "Implement user authentication" }],
  contextId: "ctx-123",
  taskId: "task-456"
};

// Agent response
const agentMessage: A2AMessage = {
  messageId: "msg-2",
  role: "agent",
  parts: [
    { text: "I'll implement JWT-based authentication." },
    {
      data: { filesModified: ["src/auth/jwt.ts"] },
      mediaType: "application/json"
    }
  ],
  contextId: "ctx-123",
  taskId: "task-456"
};

A2A Artifacts

Artifacts represent outputs produced by agents:

interface A2AArtifact {
  artifactId: string;
  name: string;
  description?: string;
  parts: A2APart[];
}

Example artifact (agent completion report):

const artifact: A2AArtifact = {
  artifactId: "artifact-1",
  name: "Implementation Summary",
  description: "Summary of authentication implementation",
  parts: [
    {
      text: "Implemented JWT authentication with login, logout, and token refresh endpoints."
    },
    {
      data: {
        filesCreated: ["src/auth/jwt.ts", "src/auth/middleware.ts"],
        testsAdded: ["src/auth/__tests__/jwt.test.ts"],
        apiEndpoints: ["/api/login", "/api/logout", "/api/refresh"]
      },
      mediaType: "application/json"
    }
  ]
};

JSON-RPC Interface

A2A communication happens via JSON-RPC over HTTP:

Create Task

Method: task/create Request:

{
  "jsonrpc": "2.0",
  "method": "task/create",
  "params": {
    "contextId": "ctx-123",
    "message": {
      "parts": [{ "text": "Implement user authentication" }]
    },
    "workspaceId": "workspace-456"
  },
  "id": 1
}

Response:

{
  "jsonrpc": "2.0",
  "result": {
    "id": "task-789",
    "contextId": "ctx-123",
    "status": {
      "state": "submitted",
      "timestamp": "2026-03-03T10:30:00Z"
    },
    "history": [
      {
        "messageId": "msg-1",
        "role": "user",
        "parts": [{ "text": "Implement user authentication" }]
      }
    ]
  },
  "id": 1
}

Get Task Status

Method: task/get Request:

{
  "jsonrpc": "2.0",
  "method": "task/get",
  "params": { "taskId": "task-789" },
  "id": 2
}

Response:

{
  "jsonrpc": "2.0",
  "result": {
    "id": "task-789",
    "contextId": "ctx-123",
    "status": {
      "state": "completed",
      "timestamp": "2026-03-03T10:35:00Z",
      "message": {
        "messageId": "msg-2",
        "role": "agent",
        "parts": [{ "text": "Authentication implemented successfully" }]
      }
    },
    "artifacts": [
      {
        "artifactId": "artifact-1",
        "name": "Implementation Summary",
        "parts": [{ "text": "JWT authentication with login, logout, and refresh endpoints" }]
      }
    ]
  },
  "id": 2
}

List Tasks

Method: task/list Request:

{
  "jsonrpc": "2.0",
  "method": "task/list",
  "params": {
    "contextId": "ctx-123",
    "state": "completed"
  },
  "id": 3
}

Response:

{
  "jsonrpc": "2.0",
  "result": {
    "tasks": [
      {
        "id": "task-789",
        "contextId": "ctx-123",
        "status": { "state": "completed", "timestamp": "2026-03-03T10:35:00Z" }
      }
    ]
  },
  "id": 3
}

Cancel Task

Method: task/cancel Request:

{
  "jsonrpc": "2.0",
  "method": "task/cancel",
  "params": { "taskId": "task-789" },
  "id": 4
}

Response:

{
  "jsonrpc": "2.0",
  "result": {
    "id": "task-789",
    "status": {
      "state": "canceled",
      "timestamp": "2026-03-03T10:36:00Z"
    }
  },
  "id": 4
}

Example Usage

Creating an A2A Task

import { getA2ATaskBridge } from "@/core/a2a";

const taskBridge = getA2ATaskBridge();

// Create a task linked to a Routa agent
const task = taskBridge.createTask({
  userPrompt: "Implement user authentication",
  workspaceId: "workspace-123",
  routaAgentId: "agent-456",
  contextId: "ctx-789"
});

console.log(task);
// {
//   id: "task-abc",
//   contextId: "ctx-789",
//   status: { state: "submitted", timestamp: "2026-03-03T10:30:00Z" },
//   history: [{ messageId: "msg-1", role: "user", parts: [{ text: "..." }] }],
//   artifacts: []
// }

Registering an Existing Agent as A2A Task

import { getA2ATaskBridge } from "@/core/a2a";
import { AgentRole, AgentStatus } from "@/core/models/agent";

const taskBridge = getA2ATaskBridge();

// Register an existing Routa agent as an A2A task
const task = taskBridge.registerAgentAsTask({
  id: "agent-123",
  name: "Auth Implementer",
  role: AgentRole.CRAFTER,
  status: AgentStatus.ACTIVE,
  workspaceId: "workspace-456",
  createdAt: new Date(),
  metadata: { taskType: "implementation" }
});

console.log(task.metadata?.skillId); // "development"

Updating Task from Agent Status

import { getA2ATaskBridge } from "@/core/a2a";
import { AgentStatus } from "@/core/models/agent";

const taskBridge = getA2ATaskBridge();

// Update A2A task when Routa agent status changes
const updatedTask = taskBridge.updateTaskFromAgent(
  "task-abc",
  AgentStatus.COMPLETED,
  "Auth Implementer"
);

console.log(updatedTask?.status.state); // "completed"

HTTP Endpoint Integration

// pages/api/a2a/rpc.ts
import { getA2ATaskBridge } from "@/core/a2a";

export default async function handler(req, res) {
  const { method, params, id } = req.body;
  const taskBridge = getA2ATaskBridge();

  switch (method) {
    case "task/create":
      const task = taskBridge.createTask({
        userPrompt: params.message.parts[0].text,
        workspaceId: params.workspaceId,
        contextId: params.contextId
      });
      return res.json({ jsonrpc: "2.0", result: task, id });

    case "task/get":
      const taskResult = taskBridge.getTask(params.taskId);
      if (!taskResult) {
        return res.json({ jsonrpc: "2.0", error: { code: -32602, message: "Task not found" }, id });
      }
      return res.json({ jsonrpc: "2.0", result: taskResult, id });

    case "task/list":
      const tasks = taskBridge.listTasks({
        workspaceId: params.workspaceId,
        contextId: params.contextId,
        state: params.state
      });
      return res.json({ jsonrpc: "2.0", result: { tasks }, id });

    case "task/cancel":
      const canceled = taskBridge.cancelTask(params.taskId);
      return res.json({ jsonrpc: "2.0", result: canceled, id });

    default:
      return res.json({ jsonrpc: "2.0", error: { code: -32601, message: "Method not found" }, id });
  }
}

Session Registry

A2A sessions are tracked separately from ACP sessions:

// src/core/a2a/a2a-session-registry.ts
interface A2ASessionInfo {
  sessionId: string;
  contextId: string;
  workspaceId?: string;
  createdAt: string;
  lastActiveAt?: string;
}

const registry = getA2aSessionRegistry();

// Register a new session
registry.registerSession({
  sessionId: "session-123",
  contextId: "ctx-456",
  workspaceId: "workspace-789",
  createdAt: new Date().toISOString()
});

// Get session by context ID
const session = registry.getSessionByContext("ctx-456");

// List all sessions
const allSessions = registry.listSessions();

Best Practices

Always Link Tasks to Agents

A2A tasks should always be linked to backing Routa agents for state synchronization:

// Create task AND agent together
const agent = await agentStore.create({ name: "Worker", role: AgentRole.CRAFTER });
const task = taskBridge.createTask({
  userPrompt: "Do work",
  routaAgentId: agent.id,
  workspaceId: "workspace-123"
});

Use Artifacts for Rich Outputs

When agents complete work, create artifacts with structured data:

const task = taskBridge.getTask(taskId);
task.artifacts = [
  {
    artifactId: uuidv4(),
    name: "Implementation Report",
    parts: [
      { text: "Summary of changes" },
      { data: { filesModified: [...], testsAdded: [...] }, mediaType: "application/json" }
    ]
  }
];

Handle Terminal States Properly

Terminal states (completed, failed, canceled) cannot be changed:

const task = taskBridge.getTask(taskId);
const terminal = ["completed", "failed", "canceled", "rejected"];

if (terminal.includes(task.status.state)) {
  throw new Error("Task is in terminal state and cannot be modified");
}

Implement Task Discovery

Expose a discovery endpoint for external clients to find available skills:

// GET /api/a2a/skills
export default function handler(req, res) {
  const skills = [
    { id: "coordination", name: "Task Coordination", description: "Orchestrate multi-agent workflows" },
    { id: "development", name: "Code Implementation", description: "Implement code changes" },
    { id: "verification", name: "Code Review", description: "Verify and validate code" },
    { id: "full-stack-development", name: "Full Stack Development", description: "Plan and implement independently" }
  ];
  res.json({ skills });
}

MCP (Model Context Protocol) — Internal coordination tools
ACP (Agent Client Protocol) — Agent process management

API Reference

Task Bridge

Map Routa agents to A2A tasks

Session Registry

Manage A2A session lifecycle

Executor

Execute A2A protocol operations

JSON-RPC API

JSON-RPC method reference

Get Started

Core Concepts

Protocols

Guides

Specialists

Development

Agent-to-Agent Protocol (A2A)

Overview

When to Use A2A

Architecture

Key Concepts

A2A Task Model

State Mapping

Role to Skill Mapping

A2A Messages

A2A Artifacts

JSON-RPC Interface

Create Task

Get Task Status

List Tasks

Cancel Task

Example Usage

Creating an A2A Task

Registering an Existing Agent as A2A Task

Updating Task from Agent Status

HTTP Endpoint Integration

Session Registry

Best Practices

API Reference

Task Bridge

Session Registry

Executor

JSON-RPC API

Build docs developers (and LLMs) love

Get Started

Core Concepts

Protocols

Guides

Specialists

Development

​Overview

​When to Use A2A

​Architecture

​Key Concepts

​A2A Task Model

​State Mapping

​Role to Skill Mapping

​A2A Messages

​A2A Artifacts

​JSON-RPC Interface

​Create Task

​Get Task Status

​List Tasks

​Cancel Task

​Example Usage

​Creating an A2A Task

​Registering an Existing Agent as A2A Task

​Updating Task from Agent Status

​HTTP Endpoint Integration

​Session Registry

​Best Practices

​Related Protocols

​API Reference

Task Bridge

Session Registry

Executor

JSON-RPC API

Build docs developers (and LLMs) love

Overview

When to Use A2A

Architecture

Key Concepts

A2A Task Model

State Mapping

Role to Skill Mapping

A2A Messages

A2A Artifacts

JSON-RPC Interface

Create Task

Get Task Status

List Tasks

Cancel Task

Example Usage

Creating an A2A Task

Registering an Existing Agent as A2A Task

Updating Task from Agent Status

HTTP Endpoint Integration

Session Registry

Best Practices

Related Protocols

API Reference