letsping 0.2.0

Behavioral Firewall and Cryo-Sleep State Parking for AI Agents

LetsPing Python SDK

The official state management infrastructure for Human-in-the-Loop (HITL) AI agents.

LetsPing is a behavioral firewall and governance layer. It provides mathematically secure state-parking (Cryo-Sleep) and execution governance for autonomous agents built on frameworks like LangGraph, CrewAI, and custom architectures.

Features

• The Behavioral Shield: Silently profiles your agent's execution paths via Markov Chains. Automatically intercepts 0-probability reasoning anomalies (hallucinations/prompt injections).
• Cryo-Sleep State Parking: Pauses execution and securely uploads massive agent states directly to storage using Signed URLs, entirely bypassing serverless timeouts and webhook payload limits.
• Smart-Accept Drift Adaptation: Approval decisions mathematically alter the baseline. Old unused reasoning paths decay automatically via Exponential Moving Average (EMA).

Installation

pip install letsping

# Or with LangGraph support
pip install "letsping[langgraph]"

Configuration

Set your API key as an environment variable (recommended) or pass it directly.

export LETSPING_API_KEY="lp_live_..."

Usage

1. The "Ask" Primitive (Blocking)

Use this when you want to pause a script until a human approves.

from letsping import LetsPing

client = LetsPing()

# Pauses here for up to 24 hours (default)
decision = client.ask(
    service="payments-agent",
    action="transfer_funds",
    payload={
        "amount": 5000,
        "currency": "USD",
        "recipient": "acct_99"
    },
    priority="critical"
)

# Execution resumes only after approval
print(f"Transfer approved by {decision['metadata']['actor_id']}")

Quick 2-Minute Demo

You can feel the LetsPing loop (intercept → approve → resume) with a tiny script:

# demo.py
import os
from letsping import LetsPing

def main() -> None:
    api_key = os.getenv("LETSPING_API_KEY")
    if not api_key:
        raise SystemExit("Missing LETSPING_API_KEY env var.")

    client = LetsPing(api_key=api_key)

    print("Sending demo approval request to LetsPing…")
    decision = client.ask(
        service="demo-agent",
        action="transfer_funds",
        payload={"amount": 500, "currency": "USD", "recipient": "acct_demo_123"},
        priority="high",
    )

    status = decision["status"]
    if status == "REJECTED":
        print("Demo request REJECTED by human. No action taken.")
    elif status == "APPROVED_WITH_MODIFICATIONS":
        print("APPROVED WITH MODIFICATIONS:")
        print(decision.get("diff_summary"))
    else:
        print("APPROVED with original payload.")

if __name__ == "__main__":
    main()

Run:

export LETSPING_API_KEY="lp_live_..."
python demo.py

Then open the LetsPing dashboard for your project, approve/reject the demo-agent / transfer_funds request, and watch the script resume.

2. Async / Non-Blocking (FastAPI/LangGraph)

For high-concurrency environments or event loops.

import asyncio
from letsping import LetsPing

async def main():
    client = LetsPing()

    # Non-blocking wait, with massive state snapshot.
    # The state is AES-GCM encrypted and uploaded via signed URL (Cryo-Sleep).
    decision = await client.aask(
        service="github-agent",
        action="merge_pr",
        payload={"pr_id": 42},
        timeout=3600,  # 1 hour timeout
        state_snapshot=graph.get_state()
    )

asyncio.run(main())

3. LangChain / Agent Integration

LetsPing provides a compliant tool interface that can be injected directly into LLM agent toolkits (LangChain, CrewAI, etc). This allows the LLM to decide when to ask for help.

from letsping import LetsPing

client = LetsPing()

tools = [
    # ... your other tools (search, calculator) ...
    
    # Inject the human as a tool
    client.tool(
        service="research-agent",
        action="review_draft",
        priority="high"
    )
]

4. LangGraph Integration (Persisted State)

LetsPing provides a LetsPingCheckpointer for LangGraph under letsping.integrations.langgraph.

In v0.2 this checkpointer persists checkpoints remotely via the LetsPing control plane — encrypted and stored next to your existing Cryo‑Sleep state in Supabase Storage. Threads can survive worker restarts without you plumbing your own database.

from langgraph.graph import StateGraph
from letsping import LetsPing
from letsping.integrations.langgraph import LetsPingCheckpointer

client = LetsPing()
checkpointer = LetsPingCheckpointer(client)

# Initialize the graph with the LetsPing checkpointer
builder = StateGraph(...)
graph = builder.compile(checkpointer=checkpointer)

# Now, every 'thread_id' state is checkpointed remotely and can be resumed across workers.

#### Auto‑resuming a thread after approval (webhook + checkpointer)

Because checkpoints are stored via the LetsPing control plane, you can resume a LangGraph thread from any worker once a human clicks Approve. A minimal FastAPI webhook + auto‑resume flow looks like:

```python
from fastapi import FastAPI, Request, HTTPException
from letsping import LetsPing
from letsping.integrations.langgraph import LetsPingCheckpointer
from langgraph.graph import StateGraph

from .graph import build_graph  # your app's graph definition

lp = LetsPing()
checkpointer = LetsPingCheckpointer(lp)
graph: StateGraph = build_graph(checkpointer=checkpointer)

app = FastAPI()
WEBHOOK_SECRET = "lp_whk_..."  # store securely

@app.post("/letsping/langgraph-webhook")
async def letsping_langgraph_webhook(request: Request):
    raw_body = await request.body()
    signature = request.headers.get("x-letsping-signature", "")

    try:
        event = lp.webhook_handler(
            payload_str=raw_body.decode("utf-8"),
            signature_header=signature,
            webhook_secret=WEBHOOK_SECRET,
        )
    except Exception as e:
        raise HTTPException(status_code=400, detail=str(e))

    data = event["data"]
    state_snapshot = event.get("state_snapshot") or {}

    # You decide how to encode the thread id into your snapshot.
    thread_id = state_snapshot.get("thread_id")
    if not thread_id:
        raise HTTPException(status_code=400, detail="missing thread_id in state_snapshot")

    # Resume the graph from the latest remote checkpoint for this thread.
    await graph.ainvoke(state_snapshot.get("input", {}), config={"configurable": {"thread_id": thread_id}})

    return {"ok": True}

In your LangGraph nodes, you include thread_id and pass a state_snapshot when you call LetsPing. The remote checkpointer + webhook keep the thread resumable even if the worker restarts.

### 5. FastAPI Webhook Rehydration (Cryo-Sleep)

When you pass `state_snapshot` to `ask` / `aask` or `defer` / `adefer`, the client:

- Encrypts the snapshot with either `LETSPING_ENCRYPTION_KEY` or a one‑time key.
- Uploads it to storage using a signed URL.
- Includes a `state_download_url` (and DEK) in the webhook payload.

You can use `webhook_handler` to validate and hydrate webhooks in FastAPI:

```python
from fastapi import FastAPI, Request, HTTPException
from letsping import LetsPing

app = FastAPI()
client = LetsPing()
WEBHOOK_SECRET = "lp_whk_..."  # store securely

@app.post("/letsping/webhook")
async def letsping_webhook(request: Request):
    raw_body = await request.body()
    signature = request.headers.get("x-letsping-signature", "")

    try:
        event = client.webhook_handler(
            payload_str=raw_body.decode("utf-8"),
            signature_header=signature,
            webhook_secret=WEBHOOK_SECRET,
        )
    except Exception as e:
        raise HTTPException(status_code=400, detail=str(e))

    # event = {"id", "event", "data", "state_snapshot"}
    await handle_decision(event)
    return {"ok": True}

async def handle_decision(event: dict):
    # Use event["data"] (decision payload) and event["state_snapshot"]
    # to resume your workflow / LangGraph thread.
    ...

For async frameworks you can also use awebhook_handler with the same pattern.

Error Handling

The SDK uses typed exceptions for control flow.

• ApprovalRejectedError: Raised when the human explicitly clicks "Reject".
• TimeoutError: Raised when the duration (default 24h) expires without a decision.
• LetsPingError: Base class for API or network failures.