Brownfield Slack alerts: a 6-minute guided MCP run on Stripe + Resend webhooks

A guided MCP session showed how to add Slack alerts for failed payments in a brownfield Next.js/FastAPI repo.

The agent traced existing Stripe checkout, Clerk JWT checks, and Resend receipt webhooks to find the right integration point.

It discovered that failures were mostly being printed, then validated upstream webhook behavior with a payment_intent.payment_failed scenario.

The example shows that real integration work depends on understanding the codebase and failure surfaces, not just writing new code.