LangChain — sign every tool-use decision

Drop-in callback handler — no chain code changes.

pnpm add @sbo3l/langchain  # or: pip install sbo3l-langchain

Every tool invocation flows through the SBO3L policy boundary first.

import { Sbo3lCallbackHandler } from "@sbo3l/langchain";

const handler = new Sbo3lCallbackHandler({
  url: "http://localhost:8730",
  agentId: "research-01",
  onDeny: (reason) => console.warn("policy deny:", reason),
});

const result = await chain.invoke({ input }, { callbacks: [handler] });

Each tool call writes a receipt. Pull them all from the chain context.

const receipts = handler.receipts;
console.log(receipts.length, "tool calls,", receipts.filter(r => r.outcome === "deny").length, "denied");