---
title: "engineering · Blog | Once Books"
description: "5 posts tagged “engineering” on the Once Books blog, newest first: Stripe Checkout without webhooks: a pull-based design."
source: "https://www.oncebooks.com/blog/tag/engineering"
---

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Topic

# Engineering

5 posts on this topic.

- [8 October 2026 · 8 min read](https://www.oncebooks.com/blog/stripe-checkout-without-webhooks) — Stripe Checkout without webhooks: a pull-based design How we confirm Stripe Checkout payments with no webhook: session reuse, a unique checkout key, strict verification and a 10-minute reconciliation sweep.
- [7 October 2026 · 7 min read](https://www.oncebooks.com/blog/what-makes-a-maze-hard) — What actually makes a maze hard (we measured it) Size is not difficulty. We graded a maze generator easy to evil, measured every page, and found one of our three difficulty signals ran backwards.
- [1 October 2026 · 8 min read](https://www.oncebooks.com/blog/how-we-guarantee-one-solution-sudoku) — How we make sure every sudoku has one solution How our sudoku generator works: fill a grid, remove clues in pairs, and re-solve after every removal so each board has one answer. Real code and timings.
- [31 August 2026 · 6 min read](https://www.oncebooks.com/blog/the-cast-and-the-sets) — The cast and the sets: the art that holds a book together The hero’s face is the famous consistency problem. The friend, the teacher and every classroom are the harder one. Here’s the reference art behind it.
- [18 August 2026 · 5 min read](https://www.oncebooks.com/blog/how-the-consistency-engine-works) — The four locks behind a consistent AI picture book Character consistency across a whole book isn’t a prompt trick. It takes four specific locks, and here’s what each one does and why it matters.

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