Worked on the envoyproxy/envoy repository to deliver the upstream.locality attribute for the HTTP WebAssembly filter, enabling Wasm filters to access upstream host locality information. This addition allows for the implementation of locality-aware routing policies and enhanced telemetry within distributed systems. The work involved extending the expression context in C++ to support the new attribute, updating YAML-based documentation, and ensuring comprehensive changelog entries. By validating the end-to-end impact, the developer ensured that Wasm filters could leverage locality data for improved routing decisions and observability, demonstrating a focused approach to API development and system programming within a complex codebase.