One Click, Two Bookings

Retry semantics / idempotency · intermediate · MERN stack

A workshop booking sometimes appears twice after a brief connection interruption. The attendee clicked once and saw one confirmation. Normal bookings work, and refreshing the bookings list confirms that both entries were saved.

The bug report

You get the whole project — a React front end, an Express API, and Mongoose models — opened in a browser editor. Reproduce the symptom by reading the code, change what’s wrong, and run the hidden tests to prove it.

What the fix must prove

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