This paper presents EconCSLib, a Lean 4 library and workflow for formalizing research papers in Economics and Computation with language-model assistance. The central design principle is a human-AI-Lean workflow: an LLM writes Lean code, Lean checks formal statements and proofs, and humans (assisted by an LLM) verify the translation boundary from paper claims to formal statements. EconCSLib is organized around research papers, preserving their formal statements and following their proof structure to the extent possible; reusable mathematical statements are elevated into shared EconCS infrastructure. The workflow is designed to be author-facing: researchers can formalize their own papers, inspect the Lean code's translations of paper-facing statements, and contribute reusable components back to the library; this is supported by post-formalization validation reports, paper result dependency graphs, and a review dashboard. The current public repository contains 11 formalized papers and 3 partially formalized papers, along with initial libraries for probability, auctions, matching markets, and graph tools. The library and workflow are available at https://github.com/nikhgarg/EconCSLib, with corresponding project webpage at https://gargnikhil.com/EconCSLib/. To our knowledge, we are also among the first applied math researchers to systematically pursue Lean formalization of one's own publications in the process of building such a community library. We welcome users and contributors to the project.