In June 2025, contributed to stan-dev/math by performing a Production-Test Boundary Cleanup that removes unnecessary test utility includes from two production headers, preventing production code from depending on testing infrastructure. This targeted refactor improves build separation, reduces coupling between production and test code, and enhances overall stability. The change is tracked under commit 091c734e27fbd4ca0fef324ce006cbe7ef118f27 with the message: "bugfix: removing includes to files in the test directory." Impact: cleaner header boundaries reduce compilation fragility, simplify maintenance, and mitigate risk of production builds pulling in test-only code. Accomplishments include delivering a precise, low-risk code hygiene improvement with measurable positive effects on build reliability. Technologies/skills demonstrated: C++ header management, build-system hygiene, dependency decoupling, and disciplined version control in a large-scale library project.