Demo: injecting latency and packet loss with Toxiproxy

Step by step

1. Run Toxiproxy with Docker Compose; create a proxy in front of the payment provider stub.
2. Point Shop's payment URL at the proxy and place an order normally.
3. Add a latency toxic of 3 s with a 2 s client timeout; watch the order status.
4. Add a toxic that drops the response (for example limit_data or reset_peer on the downstream); check whether Payments recorded the charge.
5. Planned mistake: retry blindly on timeout and show a double charge in the stub's records. Fix with an idempotency key (preview of MID-029).
6. Write the list of inconsistencies observed.