feat: add A2A protocol channel for agent-to-agent communication

packages/a2a/README.md

@@ -0,0 +1,65 @@
+# @flue/a2a — Agent-to-Agent Protocol Channel
+
+A Flue channel adapter that makes any Flue agent speak the [A2A protocol](https://a2a-protocol.org/), enabling agent-to-agent communication and discovery.
+
+## What this does
+
+- **Agent Card**: serves `/.well-known/agent-card.json` for A2A discovery
+- **message/send**: accepts A2A JSON-RPC messages and routes them to the Flue agent
+- **Task lifecycle**: tracks task state (submitted → working → completed)
+- **Skills**: maps Flue skills to A2A skill descriptors
+
+## Quick Start
+
+```typescript
+import { createA2AChannel } from '@flue/a2a';
+
+const channel = createA2AChannel({
+  name: 'My Agent',
+  description: 'A helpful assistant',
+  port: 3000,
+});
+
+// Agent is now discoverable via A2A protocol
+// GET /.well-known/agent-card.json
+// POST / (message/send)
+```
+
+## A2A Protocol
+
+The [Agent-to-Agent (A2A) protocol](https://a2a-protocol.org/latest/specification/) enables interoperability between AI agents. Key concepts:
+
+- **Agent Cards**: JSON metadata describing an agent's capabilities, served at a well-known URL
+- **message/send**: JSON-RPC method for sending messages between agents
+- **Tasks**: Units of work with lifecycle states (submitted, working, completed, failed)
+- **Skills**: Declared capabilities that clients can discover and invoke
+
+## Configuration
+
+| Option | Type | Description |
+|--------|------|-------------|
+| `name` | string | Agent display name |
+| `description` | string | Agent description |
+| `port` | number | HTTP server port (default: 3000) |
+| `skills` | Skill[] | A2A skill descriptors |
+| `version` | string | Agent version |
+| `protocolVersion` | string | A2A protocol version (default: "1.0") |
+
+## Testing
+
+```bash
+# Start the agent
+npm start
+
+# Discover the agent
+curl http://localhost:3000/.well-known/agent-card.json
+
+# Send a message
+curl -X POST http://localhost:3000/ \
+  -H "Content-Type: application/json" \
+  -d '{"jsonrpc":"2.0","method":"message/send","params":{"message":{"messageId":"1","role":"user","parts":[{"kind":"text","text":"Hello"}]}},"id":"1"}'
+```
+
+## License
+
+MIT