martineoficial/ebanx-challenge-golang ? reverse-engineered prompt

Build me a small Go API for the EBANX challenge, using only the standard library and keeping everything in memory.

I need three endpoints, POST /reset, GET /balance, and POST /event, with support for deposit, withdraw, and transfer. The API should behave exactly like the challenge says, including returning plain text 0 for not found cases, creating accounts automatically on deposit and transfer when needed, and keeping state only while the server is running. Please make it thread safe too, since there are concurrent tests.

I want the code split cleanly between the business rules and the HTTP layer, so the core logic does not depend on net/http or JSON details. Please also include tests that cover the main flows and concurrency behavior, and make sure the app runs on port 8080 with a simple command in cmd/api. If you need to check the latest Go docs or any detail from the challenge suite, look it up online.