Worked on the facebook/pyrefly repository to address a targeted initialization issue affecting dataclasses and Pydantic BaseModels. Focused on backend development and data modeling, the work involved renaming the instance parameter to '__dataclass_self__' to prevent the 'self' field from being incorrectly flagged as a duplicate parameter during model construction. This change aligned the behavior with CPython semantics and eliminated invalid initialization errors. The solution was validated by adding regression tests for both dataclasses and BaseModels, which were incorporated into the Rust-based PyO3 test suite. Utilized Python and Rust to improve reliability and reduce false-positive errors in model initialization.