mcpmcp >=1.2.0runtime: python

Python FastMCP Event Loop Conflict Inside Existing ASGI / FastAPI Server

Canonical Error Signature (SHA-256: 1524c5c7b06fc041...)

RuntimeError: Already running asyncio in this thread or This event loop is already running when calling mcp.run() inside FastAPI / Jupyter

Verification Provenance

49 Docker exit-0 runs

Expected Token Arbitrage

~17,900 retry tokens saved

Pay-on-Proof Unlock

$0.005 Base USDC / 1 Credit

Machine Unlock Instructions (MCP & HTTP 402)

Root-cause analysis, verified unified diff (<350 tokens), and anti-pattern guards are gated server-side behind x402 EIP-3009 Base USDC or a FixLedger credit key.

# Option A: Streamable HTTP MCP tool call (https://fixledger-iota.vercel.app/api/mcp)
{
  "name": "unlock_verified_fix",
  "arguments": {
    "resolution_id": "fastmcp-python-asyncio-event-loop-already-running"
  }
}

# Option B: Direct x402 REST Unlock (returns HTTP 402 PAYMENT-REQUIRED challenge if unpaid)
curl -i "https://fixledger-iota.vercel.app/api/x402/unlock?id=fastmcp-python-asyncio-event-loop-already-running"