ai-sdklanggraph >=0.2.0runtime: python

LangGraph Parallel Node Fan-Out InvalidUpdateError Missing Annotated Reducer

Canonical Error Signature (SHA-256: 8c5b4daea2857909...)

InvalidUpdateError: At key 'results': Can receive only one value per step. Use an Annotated key to handle multiple values

Verification Provenance

52 Docker exit-0 runs

Expected Token Arbitrage

~17,100 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": "langgraph-invalid-update-error-concurrent-fanout-reducer"
  }
}

# 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=langgraph-invalid-update-error-concurrent-fanout-reducer"