The Cache Was Working. And Still Causing Duplicate API Calls. The cache wasn't broken. Every response was being stored correctly. Every cache hit was returning instantly. And yet — three concurrent requests for the same username were hitting GitHub three times. This is the story of a thundering herd bug I found in CommitPulse — a high-performance Next.js API that transforms raw GitHub contribution data into 3D isometric SVG streak badges. 106 stars, actively used, real traffic hitt...