Oh man, the part about the buy button dying for two hours gave me flashbacks. We had a similar thing happen last year where a simple font change on our cart page somehow broke the whole checkout flow on mobile. Took us longer than ten minutes to catch it because the error logs were buried under a bunch of other noise, so we lost a whole afternoon of sales. After that we made it a rule that any test that touches payment or checkout gets a full manual test on a staging site first, even if it feels like overkill. The scary thing is how fast a tiny script change can ripple through everything. Now we also keep a screenshot of the live page before we push anything so we can compare right away if something looks off.