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# A2A Protocol Specification v0.1
## Overview
Agent-to-Agent (A2A) is a decentralized message protocol for agent negotiation within newOS4. Agents discover each other via VFS registrations and communicate through a shared message queue. No central broker.
## Message Format
All messages are JSON with this envelope:
```json
{
"a2a_version": "0.1",
"msg_id": "<uuid>",
"type": "request" | "response" | "broadcast" | "lease" | "heartbeat",
"from": "<agent_id>",
"to": "<agent_id>" | "*",
"timestamp": "<ISO 8601>",
"ttl_seconds": 30,
"contract": {
"capabilities": ["list_files", "read_file", "web_search"],
"constraints": {
"max_tool_turns": 8,
"max_duration_seconds": 60
}
},
"payload": { }
}
```
## Transport Layer
Each agent has a VFS mailbox at `/agents/<agent_id>/inbox.json` and publishes to `/agents/<agent_id>/outbox.json`. The orchestrator monitors inboxes via periodic polling (500ms interval).
## Message Types
- **request**: Point-to-point task delegation. From=orchestrator, To=worker.
- **response**: Task result. From=worker, To=orchestrator.
- **broadcast**: Discovery / capability advertisement. To="*".
- **lease**: Time-bound contract granting a worker exclusive task rights.
- **heartbeat**: Alive signal. Every 5 seconds. Missing 3 consecutive = presumed dead.
## Lifecycle
1. Orchestrator broadcasts AGENT_REQUEST
2. Workers respond with capability claim
3. Orchestrator issues LEASE with TTL
4. Worker executes, sends RESPONSE
5. Orchestrator ACKs, LEASE expires
6. Worker returns to available pool
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