A2A Protocol

Agent-to-Agent protocol adapter for inter-agent communication and sub-agent spawning.

The a2a module provides the Agent-to-Agent (A2A) protocol adapter, enabling Aleph agents to communicate with each other and spawn sub-agents for collaborative task execution.

Overview

A2A is a protocol for inter-agent communication that allows:

Sub-agent spawning — Create child agents for parallel task execution
Agent-to-agent messaging — Send messages between agents in the same system
Task delegation — Delegate sub-tasks to specialized agents
Result aggregation — Collect and merge results from multiple agents

Architecture

A2A Adapter
  ├── Domain — Core A2A types and messages
  ├── Port — Protocol interface definitions
  ├── Service — Business logic for agent coordination
  ├── Adapter — Concrete protocol implementations
  ├── Config — A2A configuration
  └── Sub-agent — Sub-agent lifecycle management

Core Components

Domain

Core types for A2A messaging:

// src/a2a/domain/mod.rs
pub struct AgentMessage {
    pub from: AgentId,
    pub to: AgentId,
    pub payload: MessagePayload,
}

pub enum MessagePayload {
    TaskRequest { task: TaskSpec },
    TaskResponse { result: TaskResult },
    StatusUpdate { state: AgentState },
}

Service

Orchestrates inter-agent communication:

// src/a2a/service/mod.rs
pub struct A2AService {
    adapter: Box<dyn A2AAdapter>,
}

impl A2AService {
    pub async fn spawn_sub_agent(
        &self,
        spec: AgentSpec,
    ) -> Result<AgentId>;
    
    pub async fn send_message(
        &self,
        msg: AgentMessage,
    ) -> Result<()>;
    
    pub async fn collect_results(
        &self,
        task_id: TaskId,
    ) -> Result<Vec<TaskResult>>;
}

Sub-Agent

Manages sub-agent lifecycle:

// src/a2a/sub_agent/mod.rs
pub struct SubAgentManager {
    active: HashMap<AgentId, SubAgentHandle>,
}

impl SubAgentManager {
    pub async fn spawn(
        &mut self,
        spec: AgentSpec,
    ) -> Result<AgentId>;
    
    pub async fn terminate(
        &mut self,
        id: AgentId,
    ) -> Result<()>;
}

Message Flow

Parent Agent                    A2A Service                    Sub-Agent
     │                              │                              │
     │── spawn(spec) ──────────────▶│                              │
     │                              │── create ───────────────────▶│
     │                              │◀─ AgentId ───────────────────│
     │◀─ AgentId ───────────────────│                              │
     │                              │                              │
     │── send(task) ───────────────▶│── forward ──────────────────▶│
     │                              │                              │
     │                              │◀─ result ────────────────────│
     │◀─ TaskResult ────────────────│                              │

Configuration

A2A is configured through config.toml:

[a2a]
enabled = true
max_sub_agents = 10
sub_agent_timeout = 300  # seconds

Code Location

src/a2a/mod.rs — Module entry point
src/a2a/domain/ — Core types and messages
src/a2a/service/ — Business logic
src/a2a/adapter/ — Protocol implementations
src/a2a/sub_agent/ — Sub-agent lifecycle
src/a2a/config.rs — Configuration