Continuous integration and deployment (CI/CD) is now a widely adopted development model in practice as it reduces the time from ideas to customers. This adoption has also revived the idea of "shifting left" during software development -- a practice intended to find and prevent defects early in the software delivery process. To assist with that, engineering systems integrate developer bots in the development workflow to improve developer productivity and help them identify issues early in the software delivery process.

Today's build systems distribute build tasks across thousands of machines, reusing cached build results whenever possible. But despite the sophisticated nature of modern build tools, the core software architecture of the system under build defines the lower bound for how fast the system can compile. Long, consecutive build chains or slow individual build targets can introduce expensive compilation bottlenecks. Further, the growing complexity of both build systems and software systems under build makes comprehending, debugging, and optimizing build performance a significant challenge faced by many software engineers. We present a design study to describe and help mitigate the cognitive challenges faced by software engineers that use modern, cached, and distributed build systems. We characterize the performance analysis process and identify the main stakeholders involved, key usage scenarios, and elicit important requirements for tool support. We propose an interactiveBuildExplorertool for understanding, optimizing, and debugging cached and distributed build sessions, justifying our design decisions among alternative solutions. Our novel solution is evaluated through usage scenario walkthroughs, iterative deployments of the tool in the field, and a user study.