A2A Event Flow Architecture - Complete Analysis

Status: 🟢 In-use Category: Architecture & Core Design Date: October 27, 2025

Overview

This document provides a thorough analysis of the Agent-to-Agent (A2A) protocol event flow in the CAIPE platform, from end client through supervisor to sub-agents, documenting actual event types, streaming behavior, and data flow patterns.

Testing Commands

Test Supervisor

curl -X POST http://10.99.255.178:8000 \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream" \
  -d '{"id":"test-1","method":"message/stream","params":{"message":{"role":"user","parts":[{"kind":"text","text":"show argocd version"}],"messageId":"msg-1"}}}'

Test Sub-Agent Direct

curl -X POST http://localhost:8001 \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream" \
  -d '{"id":"test-2","method":"message/stream","params":{"message":{"role":"user","parts":[{"kind":"text","text":"show argocd version"}],"messageId":"msg-2"}}}'

Related

External References

• A2A Protocol Specification - Official Google A2A protocol spec
• Model Context Protocol (MCP) - MCP official documentation
• LangGraph Event Streaming - LangGraph streaming guide

Internal Documentation

• Sub-Agent Tool Message Streaming (Oct 25, 2024) - Historical debugging investigation

  • Documents LangGraph streaming limitations
  • Investigation of sub-agent tool message visibility
  • Architectural discoveries and attempted solutions

• Session Context (Oct 25, 2024) - Earlier investigation session

• Architecture: architecture.md