John Haitas contributed to the facebook/buck2-prelude repository by implementing Apple SDK version compatibility mapping, specifically adding support for iOS 18.2 to macOS 15.2 within the apple_target_sdk_version.bzl configuration file. He approached the task by updating Starlark-based build system logic to reflect the latest Apple SDK releases, ensuring that Buck2 Prelude users could build against new device targets with minimal friction. His work included validating the mapping against Xcode 18.2 beta, focusing on compatibility and future-proofing. This effort demonstrated skills in build system configuration, domain-specific language (DSL) changes, and careful verification, laying groundwork for ongoing SDK maintenance.