F001: CSTP Server Infrastructure

Field	Value
Feature ID	F001
Status	Draft
Priority	P0 (Foundation)
Depends On	None
Blocks	F002, F003, F004
Decision	a42a3514

---

Summary

Create the CSTP HTTP server infrastructure with Agent Card support and JSON-RPC 2.0 endpoint.

Goals

1. FastAPI-based HTTP server
2. Agent Card endpoint at /.well-known/agent.json
3. JSON-RPC 2.0 handler at POST /cstp
4. Bearer token authentication
5. Health check endpoint

Non-Goals

• Method implementations (F002-F004)
• gRPC support
• Push notifications

---

Specification

Directory Structure

cognition-agent-decisions/
└── a2a/
    ├── __init__.py
    ├── server.py           # FastAPI application
    ├── agent_card.py       # Agent Card generation
    ├── jsonrpc.py          # JSON-RPC 2.0 handler
    ├── auth.py             # Bearer token auth
    ├── config.py           # Server configuration
    └── models/
        ├── __init__.py
        ├── requests.py     # JSON-RPC request models
        └── responses.py    # JSON-RPC response models

Agent Card Endpoint

GET /.well-known/agent.json

{
  "name": "cognition-engines",
  "description": "Decision intelligence for AI agents",
  "version": "0.7.0",
  "url": "https://agent.example.com",
  "capabilities": {
    "cstp": {
      "version": "1.0",
      "methods": [
        "cstp.announceIntent",
        "cstp.queryDecisions",
        "cstp.checkGuardrails"
      ]
    }
  },
  "authentication": {
    "schemes": ["bearer"]
  }
}

JSON-RPC Endpoint

POST /cstp

Headers:

• Content-Type: application/json
• Authorization: Bearer <token>

Request format:

{
  "jsonrpc": "2.0",
  "method": "cstp.<method>",
  "id": "request-id",
  "params": { ... }
}

Success response:

{
  "jsonrpc": "2.0",
  "id": "request-id",
  "result": { ... }
}

Error response:

{
  "jsonrpc": "2.0",
  "id": "request-id",
  "error": {
    "code": -32601,
    "message": "Method not found",
    "data": { ... }
  }
}

Authentication

a2a/auth.py

from fastapi import HTTPException, Header

async def verify_token(authorization: str = Header(...)) -> str:
    """Verify Bearer token and return agent ID."""
    if not authorization.startswith("Bearer "):
        raise HTTPException(401, "Invalid authorization header")

    token = authorization[7:]
    agent_id = validate_token(token)  # Check against config

    if not agent_id:
        raise HTTPException(401, "Invalid token")

    return agent_id

Configuration

config/server.yaml

server:
  host: "0.0.0.0"
  port: 8100
  cors_origins: ["*"]

agent:
  name: "cognition-engines"
  version: "0.7.0"
  url: "https://agent.example.com"

auth:
  enabled: true
  tokens:
    - agent: "emerson"
      token: "${CSTP_TOKEN_EMERSON}"
    - agent: "claude-ops"
      token: "${CSTP_TOKEN_CLAUDE}"

Health Check

GET /health

{
  "status": "healthy",
  "version": "0.7.0",
  "uptime_seconds": 3600
}

---

Implementation Tasks

• Create a2a/ directory structure
• Implement server.py with FastAPI
• Implement agent_card.py with Pydantic model
• Implement jsonrpc.py request/response handling
• Implement auth.py Bearer token verification
• Implement config.py with YAML loading
• Add health check endpoint
• Create pyproject.toml optional deps: [a2a]
• Add CLI: uv run a2a/server.py --port 8100
• Write tests for server, auth, jsonrpc

---

Acceptance Criteria

1. GET /.well-known/agent.json returns valid Agent Card
2. POST /cstp with valid JSON-RPC returns 200 (stub response)
3. POST /cstp without Bearer token returns 401
4. GET /health returns healthy status
5. Server starts with uv run a2a/server.py
6. All tests pass

---

Dependencies

# pyproject.toml [project.optional-dependencies]
a2a = [
    "fastapi>=0.109.0",
    "uvicorn>=0.27.0",
    "pydantic>=2.0.0",
    "pyyaml>=6.0",
]