Worked on improving quantity handling in the oasisprotocol/oasis-sdk repository by addressing a bug related to BigInt value conversion in TypeScript. Implemented a guard within ts-web/core to reject negative BigInt values when converting to quantities, ensuring that only non-negative values are processed. This approach throws a RangeError for invalid input, preventing downstream errors and invalid quantity representations during transaction processing. Enhanced input validation and test coverage were introduced to further strengthen reliability. The work focused on robust error handling and BigInt manipulation using TypeScript, resulting in improved stability and clearer error signaling for both developers and users of the SDK.