Worked on hardening the Sandbox API within the gristlabs/grist-core repository, focusing on improving type safety and long-term maintainability. Addressed type-safety issues in the ISandbox interface by updating the shutdown method to return a precise Promise type, ensuring safer asynchronous operations. Refactored sorting logic to eliminate unsafe unary operations and reduce ESLint warnings, aligning the API with related implementations to remove inconsistencies. Resolved outstanding TODO and FIXME items in core TypeScript files, which improved lint stability and runtime reliability. The work emphasized code refactoring and type safety, leveraging TypeScript to enhance the stability and maintainability of critical core components.