Monthly summary for 2025-05: Delivered major feature enhancements, safety improvements, and quality-focused refactors across chap-core and UI, enabling more powerful backtesting, safer job lifecycle management, and easier integration for downstream consumers. Highlights include backtest API enhancements with data-backed creation, update with validation, batch deletion, and rigorous input handling; enhanced job management with robust filtering, protection against deleting running jobs, and a new cancellation workflow; backend code quality improvements and refactors to simplify interfaces, improve dataset handling, and boost maintainability; and UI enhancements adding external state control to the SplitButton with accompanying docs and type definitions. Overall, these changes reduce risk, accelerate development, and deliver measurable business value through reliable analytics workflows and a better developer/partner experience.