safe-agentic-workflow / rules

---
description: "Stripe payment integration: webhooks, checkout sessions, subscriptions, idempotency, test mode safety."
globs: "core/**/billing/**,core/**/payments/**,core/**/stripe/**,**/webhook*stripe*"
alwaysApply: false
---

# Stripe Payment Rules

These rules apply when working on Stripe payment integration, webhooks, checkout flows, or subscription management.

## Test Mode Safety (CHECK FIRST)

Before ANY payment work:

- [ ] Verify `STRIPE_SECRET_KEY` starts with `sk_test_`
- [ ] Confirm test webhook secret (`whsec_...` from Stripe CLI)
- [ ] Use test card numbers only (4242 4242 4242 4242)
- [ ] Never use production keys in development

## Webhook Handler Pattern

**ALWAYS** verify webhook signatures and handle idempotency:

```python
import stripe
from fastapi import Request, HTTPException

async def handle_stripe_webhook(request: Request):
    payload = await request.body()
    signature = request.headers.get("stripe-signature")

    try:
        event = stripe.Webhook.construct_event(
            payload, signature, settings.STRIPE_WEBHOOK_SECRET
        )
    except stripe.error.SignatureVerificationError:
        raise HTTPException(status_code=400, detail="Invalid signature")

    # Idempotency: check if event already processed
    existing = await get_webhook_event(event.id)
    if existing:
        return {"status": "already_processed"}

    # Process event and record
    await process_event(event)
    await record_webhook_event(event.id, event.type)
    return {"status": "processed"}
```

## Idempotency Checklist

For ALL webhook handlers:

- [ ] Store event ID before processing
- [ ] Check for duplicate events before processing
- [ ] Use database transactions for atomicity
- [ ] Return 200 OK even on idempotency skip (Stripe retries on non-200)

## Common Webhook Events

```python
SUBSCRIPTION_EVENTS = [
    "customer.subscription.created",
    "customer.subscription.updated",
    "customer.subscription.deleted",
    "invoice.payment_succeeded",
    "invoice.payment_failed",
]
```

## Local Webhook Testing

Use the Stripe CLI to forward events locally:

```bash
# Start webhook forwarding
stripe listen --forward-to localhost:8000/api/v1/webhooks/stripe

# Trigger test events
stripe trigger checkout.session.completed
stripe trigger invoice.payment_succeeded
stripe trigger customer.subscription.deleted
```

## FORBIDDEN

- Hardcoding API keys (use environment variables)
- Skipping webhook signature verification
- Processing webhooks without idempotency checks
- Using production Stripe keys in development or CI
- Ignoring failed payment events (always handle `invoice.payment_failed`)

## Evidence Template for Linear

Attach this after completing payment work:

```markdown
**Payment Testing Evidence**

- [ ] Test mode verified (`sk_test_` key)
- [ ] Webhook signature verification tested
- [ ] Idempotency tested (duplicate event handling)
- [ ] Success flow tested (card 4242...)
- [ ] Failure flow tested (card 4000 0000 0000 0002)
- [ ] Subscription lifecycle tested (create/update/cancel)

**Test Results:**
- Webhook events processed: {count}
- All flows: PASSED
```

## Key References

- **Stripe Docs**: https://stripe.com/docs
- **Webhook best practices**: https://stripe.com/docs/webhooks/best-practices
- **Payment patterns**: `patterns_library/` (search for payment/billing patterns)
- **Full skill docs**: `.claude/skills/stripe-patterns/SKILL.md`