LangGraph: guard files with CAIN

1 Get a key

Give each agent its own key in production (console → Agent keys): decisions, trust history and revocation are then per agent.

2 Install

pip install "cainstudio[langchain] @ https://cainstudio.online/cainstudio-0.4.1-py3-none-any.whl#sha256=1bea5cf49aeeb2775acec58933fc39b008a1c84bfd7c9690c54723ed707af689"
export CAIN_API_KEY=...

cainstudio 0.4.1, pinned by URL and SHA-256 so pip installs exactly the published wheel (the package is not on PyPI yet). Framework dependencies come from PyPI as usual.

3 Put CAIN in front of the tools your graph's nodes call

The same adapter as LangChain, re-exported for LangGraph's tool-calling agents. Guard the tools rather than the nodes: a node may do several things and the decision belongs on the consequential one.

from langchain_core.tools import tool
from langgraph.prebuilt import create_react_agent
from cainstudio.integrations.langgraph import protect

@tool
def write_file(path: str, content: str) -> str:
    """Files: an agent that writes files."""
    ...  # your existing code, unchanged

tools = protect([write_file], agent_id='files-agent')
agent = create_react_agent(model, tools)

On a refusal the agent gets the refusal as the tool's error. The tool body never runs: not on a refusal, not on a hold, not when CAIN cannot be reached.

4 See what CAIN decides for this exact call

This is the request the integration sends when the model calls write_file with these arguments. record: false evaluates it without writing an evidence record. A new agent has no trust history, so expect REQUIRE_APPROVAL at first; destinations outside your egress allowlist are refused by the egress stage.

5 Write the rule, and test it before you save it

Writing SSH keys is refused; writing to the agent's own output folder runs.

The panel sends the draft rule to the rule tester: it says which rule would decide the call and saves nothing. Swap in the safe arguments below to see it pass through. matches is a case-insensitive glob (*, ?), not a regular expression; conditions on one rule must all hold; the first matching rule by priority wins.

Safe arguments: {"path": "/srv/app/out/report.csv", "content": "a,b"}

When it does what you want, save it from the console or with POST /fabric/tool-rules:

curl -sS -X POST https://cainstudio.online/fabric/tool-rules \
  -H "X-API-Key: $CAIN_API_KEY" -H 'Content-Type: application/json' \
  -d '{"name": "files-guard", "effect": "deny", "priority": 10, "match_path": "/tools/write_file", "conditions": [{"field": "path", "op": "matches", "value": "*/.ssh/*"}]}'

6 Handle the calls that wait for a person

A held call is not executed. It appears in the approval queue with its exact arguments; an approval lets that one call run once. Adapters can wait instead of returning: wait_for_approval=120.

7 Check it before you ship

cainstudio redteam --agent files-agent   # dry-runs dangerous calls; exit 2 if any would run
cainstudio decisions                 # what was decided, and why
cainstudio explain <decision_id>

Every recorded decision is signed; Cain().verify(decision) checks its quorum certificate on your machine (Python SDK).