Immanuel Peter contributed to the facebook/pyrefly repository by delivering a feature focused on codebase naming consistency. He refactored the Rust backend to standardize American English spelling, renaming functions and modules from 'summarise' to 'summarize' throughout the codebase. This change involved updates to core files such as pyrefly/lib/commands/check.rs and pyrefly/lib/error/mod.rs, as well as renaming the module file itself. By aligning naming conventions, Immanuel improved code readability and maintainability, reducing potential confusion for future contributors. His work, tracked through a dedicated pull request and commit, demonstrated attention to detail and a methodical approach to backend development in Rust.