Sergei Moryahin, QA Lead @ JetBrains: Join Sergei, QA Lead at JetBrains, as he shares how his team supported a complete refactoring of the Kotlin plugin for IntelliJ IDEA over three years without disrupting millions of users. This talk covers the testing strategy behind a live rewrite of compiler and IDE integration, how QA collaborated with development, managed risks across JetBrains IDEs and third-party plugins, and defined quality gates that enabled a silent, staged rollout. A real-world case study in testing under continuous change, invisible deployments, and maintaining trust through QA engineering.