Use the LangChain middleware

pip install ctrlrun-langchain

schema: ctrlrun.policy/v2
actions:
  lookup_order:
    decision: allow
  issue_refund:
    effect: "refund:{payment_id}"
    rules:
      - when: { amount_gte: 0, amount_lte: 5000 }   # up to €50.00, autonomous
        decision: allow
      - when: { amount_gte: 0, amount_lte: 500000 } # up to €5,000.00, ask a human
        decision: approve
      - decision: deny

from langchain.agents import create_agent
from ctrlrun import Control
from ctrlrun_langchain import CTRLRunMiddleware

control = Control.from_file("ctrlrun.yaml")

agent = create_agent(
    model="gpt-5.5",
    tools=[lookup_order, issue_refund],
    middleware=[CTRLRunMiddleware(control)],
)

import ctrlrun

with ctrlrun.context(agent="support-agent"):
    result = agent.invoke({"messages": [{"role": "user", "content": "refund order 4471"}]})

issue_refund  amount=900000    CTRLRun refused this call: rule[2]. The tool did not run.
rm_rf                          CTRLRun refused this call: unknown_action. The tool did not run.
issue_refund  amount=1000      (the tool runs)
issue_refund  amount=1000      CTRLRun refused this call: this effect is already committed

CTRLRun is holding this call for a human. Approve it with 'ctrlrun approve apr_...',
then ask again. The tool did not run.