You have an existing Azure Pipelines build and want to support incremental builds without cleaning or purging the build environment between runs. What should you use?

A self-hosted agent is the correct choice because it allows you to maintain the build environment between runs. Unlike Microsoft-hosted agents, which provide a fresh, clean virtual machine for each job, a self-hosted agent's working directory and tools persist. This persistence enables incremental builds, as the agent can reuse previously downloaded dependencies and compiled artifacts, significantly speeding up subsequent builds. Microsoft-hosted parallel jobs are a scaling mechanism, not a solution for maintaining build state. A File Transform task is used for modifying configuration files during deployment, not for managing the build environment's persistence.